Conference unifix::sailing

re .0:

Given present technology, I don't think solar-generatred electrical 
power is a practical source of power for propelling boats.

At cruising speed (about 5.7 knots), the diesel engine in my 32' cutter 
is making about 8 hp. 1 electrical horsepower is 746 watts, so 8 hp is 
5968 watts. Assume I use Arco 42 watt (peak power) solar panels. I will 
need 142 panels to get 8 hp. The unit discount price of these panels is
$370 or so. 142 panels would cost $52540 (before quantity discounts) and
cover an area of 544 sq ft (at a guess, the deck area of my boat is
perhaps half that). 

Even with a ten-fold increase in panel efficiency (wildly improbable 
anytime soon), finding 54 sq of deck space would be difficult. And don't 
forget that the average power output is rather less than peak power. 

    
    
    re -.1
       Gee Alan, what's 52 grand??? I mean you would save changing the oil
    and filter twice a year at 10 bucks a shot, You only need 2600 years
    to get your dough back. If you could dodge the Mass tax scams for 
    gas powered vessels, you could probably pay for it in 10 years.
    
       The best part of such a beast would not be knowing you are saving
    resouces. No, the best part would be the way-cool stereo you could 
    run out there once you shut the engine off. The way I figure it,
    half the panels (windward side) would be exposed with the sails up.
    That leaves almost 3000 watts of power. Why I bet you could deaden
    the sound of almost any jet-ski with such a set-up. 
    
       the real trick is where to put those batteries. Most storms I have
    been in ussally bring BIG DARK clouds with them. The time I need power the
    most, I have the least.
    
       Who needs a motor anyways. I mean Chris Columbus didn't discover
    the new world with a Pen-Yan on board right ??
    
        Tongue-in-cheek 
    
          john 

    Little known history of Arco Solar, years ago 10 or more a start up
    company on Rt 128 in Waltham by the name of Tyco Solar announced a
    major breakthrough in the fabrication of "cost effective solar panels"
    Seems Tyco had broken the code on how to do a continues extraction
    process in the fabrication of Solar Panels. Before that they were all
    essentially made one at a time by hand. Tyco announced that the process
    would allow for the 100X increase in the price performance of any Solar
    devices to date. Well time went by and the next thing you know go old
    Atlantic Richfield buys out tiny little Tyco. Draw your oun
    conclusions, but how do you think this kind of technology would have
    affected world petroleum prices if left to develop ? I think that their 
    internal cost to produce a Boat US Catalog $100.00 Arco Solar panel
    may be 1/10 it's list or less. They were after all talking about
    hitting their goal of $1.00 to $.50 /watt. what happened?

    My boating friend came up with this reply:
    
    "I think the response is off the wall a little. Petro engines and
    electric engines measure horse power different. A quarter horse power
    electric (I don't have the equations -- just a guesstimate) is roughly
    equivalent to the 8 "brake" horsepower of petro driven engine."
    
    Look at the electric motors you can buy these days. They can drive a
    fair dinghy for hours from a small marine battery. I don't know the
    figures yet, but it seems to me that a 3hp electric motor produces as
    much thrust as a 20hp gas engine, looking at the Sears models being
    sold. Does anyone know the difference here?????
    
    Ray
    
    

Excuse me, but horsepower is horsepower, and one horsepower = 746 watts 
(international standard). There is an enormous difference between
propelling a small dinghy with a small electric motor and propelling a
large, heavy boat. Have you ever tried to row a 12000 lb, 32' boat? A
human can easily row a small dinghy at maybe 4 knots, which implies that
a human can produce a fraction of a horsepower for a limited time. Ain't
no way on the gods' blue ocean that you're going to row a large boat at
more than a very small fraction of a knot. And by the way, the European
specification of internal combustion engine output these days is in
kilowatts, and a small engine makes many, many kilowatts. 

    
    
    I. for one don't want to be anywhere near a dinghy propelled by a 20 hp
    outboard.
    
     Horspower is horsepower- the reson that gasoline and electric engines
    powering the same device (like an air compressor) is that the electric
    motor is much more effiecient and can run continuosly at max output.
    
     Running an internal combusdtion engine at max HP oputput tends
    drastically shorten it's life(high rpm and high torque.)
    
    .
    
    

Sailboats are already "solar powered". They use an ingenious solar-to-wind
conversion scheme called "weather". Because of the imperfections in this
process the scheme is not 100% reliable. Sometimes the supply of propulsion
can even be excessive and hard to control :-) 

--RS

    Both of you guys are missing the main point...powering a large sailboat
    with the sun.  Also, you are both trying to put the solar panels
    on deck. Alternatively, what you need is a large triangular
    vertical area that would hold the solar panels.  The obvious 
    answer is flexible panels that can be impregnated into the 
    mylar on your main. So get out your abacuses and figure that
    out and we can all stop playing around with notes files and go
    enjoy the sun!
    
    Beau 

re .8:

Slight problem with using the sails: They cannot always directly face 
the sun, and solar cell efficiency falls off fairly quickly with 
increasing angle of incidence for the sunlight. Plus, to go back to my 
calculations in .1, the solar panel area needed for my boat exceeds my
normal working sail area -- main and jib. The durability of of a solar 
cell in a sail would be very short due to thermal and mechanical 
stresses and the need for completely effective waterproofing. Again, a 
vast improvement in technology is needed before solar electrical power 
is practical for propelling boats. 

    Re: previous notes.
    
    All right, you clever dicks.
    
    Comparing electric and petro horsepower (HP) is the same as comparing
    apples and oranges. Electric HP is measured in watts or torque. Petro
    engines are measured by brake HP.
    
    It takes a large petro (gas or diesel) engine to accelerate a car from
    a stop (particularly at low revs) because of very low torque horsepower
    (one reason why gears are so important -- else the engine stalls and
    dies). A petro engine's HP is measured by revving an engine to full
    speed, then engaging the clutch. The brake force required to stop the
    engine is the measure of "brake" horsepower.
    
    A friend considered buying a two passanger hatchback electric car
    sold in Denver. It could go 40 MPH with a range of 50 miles on 6 small
    car batteries. The electic motor in the car was no more than one HP
    (probably a half HP)... About the size of a starter motor in an old 454
    cin. engine. He was going to put solar cells on the roof to charge it
    while parking. But then ended up transfering to Massachsetts where
    there isn't much sun and typical commute is several time longer.
    
    And electric car technology is getting better. Read about the recent GM
    developments. And here's something else. The batteries are working out
    at a total of LESS THAN THE WEIGHT OF THE EQUIVALENT ENGINE AND FUEL.
    And here's another thing. If you have sails, you only want to use the
    battery power for short periods of time. Or when becalmed, as I
    originally stated before you applied the heaps of scorn. And I'd far
    rather have ten hours propulsion from batteries charged by solar energy
    than be drifting, out of gas.
    
    So there.
    
    My guess (I don't have the equations around anymore) is that a quarter
    HP electric engine can easily have the torque and RPM of around an 8
    or 10 brake HP diesel engine. Perhaps it is this mistaken assumption of
    equivalence in horsepower rating that has resulted in the absence of
    electric motors in boats? A relatively small bank of modern solar cells
    can power a quarter HP (high efficiency) electric motor on a partly
    clouded day. 
    
    Ray
    

re .14:
    
>>>    Comparing electric and petro horsepower (HP) is the same as comparing
>>>    apples and oranges. Electric HP is measured in watts or torque. Petro
>>>    engines are measured by brake HP.

True in the past and mostly true today. But horsepower is power -- 
torque (force) multiplied by time. It really doesn't matter what units 
you use -- horsepower or watts. Torque is not power, it is force. And 
one horsepower is one horsepower whether it comes from an electric motor 
or an internal combustion engine or a steam engine. As was mentioned in 
an earlier reply, internal combustion engines are seldom if ever 
operated at maximum power for any length of time to maximize their life. 
The exception to this is heavy duty industrial and marine engines (whose
cost you wouldn't believe). 
    
>>>    It takes a large petro (gas or diesel) engine to accelerate a car from
>>>    a stop (particularly at low revs) because of very low torque horsepower
>>>   (one reason why gears are so important -- else the engine stalls and
>>>   dies). 

Powerful internal combustion engines are used in automobiles because 
drivers want to accelerate quickly, not because of the low torque. And 
many engines, especially industrial and truck diesels have well over 500 
ft-lbs of torque. My 1957 VW Beetle had a 36 hp engine and, on a cool 
day with a strong tail wind, could accelerate to 60 mph in 30 seconds. 
Not the kind of sparkling performance that sells cars today (or even 
then -- I was given the car). 

>>> A petro engine's HP is measured by revving an engine to full
>>> speed, then engaging the clutch. The brake force required to stop the
>>> engine is the measure of "brake" horsepower.
    
Not quite. An engine brake or dynamometer measures the power and torque 
produced by the engine at a constant engine speed. Normally this is done 
at full throttle. This is not a brake in the sense of stopping something 
moving.

>>>    A friend considered buying a two passanger hatchback electric car
>>>    sold in Denver. It could go 40 MPH with a range of 50 miles on 6 small
>>>    car batteries. The electic motor in the car was no more than one HP
>>>    (probably a half HP)... 

Here you're the one comparing apples and oranges. The rolling resistance 
of a small, light car is rather small and the mass to accelerate is 
rather small. The resistance to be overcome (rolling and air) is small 
at low speeds -- air resistance is proportional to the square of speed 
and isn't probably a significant factor below around 40 mph. Beyond that 
air/wind resistance increases quickly. The resistance to moving a boat 
is much higher due to the greater density of water and the much greater 
area and mass of a boat.

>>>    And here's another thing. If you have sails, you only want to use the
>>>    battery power for short periods of time. Or when becalmed, as I
>>>    originally stated before you applied the heaps of scorn. 

Oh, now you're adding batteries. Well, since you mentioned a 40' 
motorsailer .... that's probably a large, heavy boat with substantial 
wetted surface and a good bit of drag (certainly far more than a car 
would have). Assume a 2 hp electrical motor would do (I think that more 
power would be needed ....) 2 hp is 118 amps at 12.6 volts. You want 10
hours, so that is 1180 amp-hrs. A good 100 amp-hr battery weighs about 65
pounds, and you can get about 80% of the capacity and usually much less. 
So you need at least 1480 amp-hrs of battery capacity. That's about 15
batteries weighing about 975 pounds. 15 good batteries would be about
$1500. Recharging these 15 batteries in any reasonable time would be
another interesting engineering problem. 
    
So there yourself. I'll keep my little diesel, thank you very much.
    
>>>    My guess (I don't have the equations around anymore) is that a quarter
>>>    HP electric engine can easily have the torque and RPM of around an 8
>>>    or 10 brake HP diesel engine. Perhaps it is this mistaken assumption of
>>>    equivalence in horsepower rating that has resulted in the absence of
>>>    electric motors in boats? A relatively small bank of modern solar cells
>>>    can power a quarter HP (high efficiency) electric motor on a partly
>>>    clouded day. 
    
My guess is that you're wrong. At any given speed, a quarter hp electic 
motor will have the same torque as an internal combustion engine 
developing a quarter hp. Remember that the power developed by an 
internal combustion engine varies with engine speed and throttle
setting, and the power ratings are given for a specific engine speed.
Normally, propellers are chosen so that at cruising speed the engine is 
running nearish to the speed at which maximum power is developed. Also 
normally, you are running at part throttle and so the engine is not 
developing maximum power. My diesel is rated at 20 hp continuous and 
only about 8 hp is actually needed at cruising speed in calm water. A 
8 hp electric motor would be needed to achieve the same cruising speed. 

Alan (who in a past life was a physicist)    

RE:.3 by TUNER::SILVA

> Well time went by and the next thing you know go old Atlantic Richfield 
> buys out tiny little Tyco. 

Arco solar is for sale.  The last I heard,  a Japanese company was expected to
buy it.

Solar cells have gotten a lot cheaper over the past decade.  They might be used
for large scale peaking power in another decade if price trends continue.  

RE:.0,.1

The motors used on boats overstate the power needed,  as the motor must drive
alternators,  oil and water pumps,  and assorted mechanical losses,  none of
which goes to driving the boat,  but is included in the rated horsepower.  It 
would be better to get the real driving power needs and calculate the needed 
power from that.  It's not (quite) as bad as Alan's calculation,  but it's not 
practical either.  Also,  remember that the speed rises slowly with increasing
power.  Half power doesn't mean half speed.

A "New York 32",  which is a 45.5 foot LOA,  25500 pound full keeled heavy 
displacement boat,  needs about 15 lbs to propel it to 2 knots,  60 lbs to 
4 knots or about 175 lbs to 6 knots.  Assume 50% prop and motor losses.
(Sailing theory and practice, by Marchaj Fig 155)

2 Knot speed means 100 ft-lbs or .18 hp or 137 W.  40 watts for $340 panel for
a total of $1360.  No problem.  A human in reasonable shape could put out this
power all day as well.

4 Knot speed means 1200 ft-lb/s or 2.2 hp or 1600 W.  $14K?

6 Knot speed means 3500 ft-lb/s or 13 hp or 9.6 KW.  Hmm only 240 of the $340
each panels?  That's $81K?!  Ignoring quantity discount.


Phil

re .10:
    
>>>    My guess (I don't have the equations around anymore) is that a quarter
>>>    HP electric engine can easily have the torque and RPM of around an 8
>>>    or 10 brake HP diesel engine. 
    
If your guess is correct, how do you explain the following practical 
experiences?

1. My diesel, which I think is developing about 8 hp, drives an 
alternator that produces up to 40A at 14 volts (560 watts or 0.75 hp) 
while pushing the boat along at 5.7 knots.

2. I made a battery charger by coupling (with a V-belt) an automotive 
alternator to a 1/4 hp 120vac electric motor. The alternator output is 
varied by changing the resistance in the field input. The electric motor 
begins to slow noticeably when the alternator is producing 15A to 18A at 
14V (252 watts or 0.34 hp). The motor also overheats quickly. Maximum 
sustained alternator output without overheating the electric motor is 
10A to 12A (168 watts or 0.23 hp). 

    I must first admit that the theory here is way above my head, however
    I shall add the "wisdom" of a Newfoundland Fisherman.  I was moored
    in  a fishing community and, as often happens, the fisherman came
    along the wharf for a chat.  After exhausting the ususal topics
    of weather etc. we got to talking engines - I noted that I could
    not understand that a small outboard on the back of his skiff had
    the same horsepower rating as the big hunk of diesel under my cockpit.
    He looked at each, scratched his ear and said "My son they're just
    different horses !"

    re .12:
    
    Assume much better efficiency on the part of the electric engine, then
    recalculate. Let's try to investigate the physical feasibility of this,
    then revisit the cost, with the likely assumption that battery
    technology and solar cells are going to improve for same unit cost.
    
    It looks like getting 2 knots with a reasonable size sailboat, with
    battery and solar power, is certainly feasible, even now. We havn't yet
    looked at reliability, and I've never been particularly pleased with
    the reliability of my batteries...
    
    Ray

    Further, I'm thinking that this could be a great solution for a large
    Catamaran. Think about it......massive uncluttered deck space for solar
    cells and much reduced water resistance, for greater speed at same
    propulsion power.
    
    Are things getting morefeasible, yet (even at today's prices!)
    
    Ray

    Here we go with some calculations:
    
    Assume a 45' Catamaran, with non-propulsion power needs for 24 hours
    satisfied by batteries recharged during daylight hours at a rate of
    1KW. It will make 6 knots (conservative estimate) at 1.6KW from
    electric motor propulsion which has 50% propellor and motor losses
    (very conservative estimate for electric motor).
    
    Assume you can get a rugged electric motor at $500, weighing about
    60lbs.
    
    Assume 42 watt Arco panels at 4 sq feet each, running at 60% efficiency
    on average during the day. We will assume that propulsion only operates
    during daylight hours, at this stage.
    
    We have a total power requirement of 2.6KW
    
    # solar panels needed is 2600/25.2 =103 panels
    
    Surface area needed is 103 x 4 = 412 square feet = about 21 x 21 feet
    
    Batteries are only needed as a buffer, but let's assume that when under
    wind power (most of the time, hopefully!), we keep a full day's worth
    of propulsion energy stored), so we need about:
    
    1.6KW x 10hours = approx. 120 Amps x 10, say 15 batteries at about
    $1500 and weighing about 1,000 lbs. With motor, 1,050lbs, I would guess
    about the same as a tank with 200 gallons of gas in it; the
    electric/battery combination is probably on average about 500 lbs
    lighter. Interesting point!!
    
    Solar panels at todays prices would work out at 103 x 340 = $35,000.
    With discounts for quantity, probably closer to $15,000.
    
    Total price for power and propulsion system roughly $17K, the
    greatest portion being in solar panels
    
    Now, let's put some reality into this.
    
    Questions that need answering:
    
    How much $$$$ gas or diesel do large boat owners use per year?
    How much does a motor commensurate to 6 knots cost?
    How much does it weigh?
    
    How about this as a goal
    ************************
    
    Unlimited free propulsion with one full daylight day's propulsion
    energy storage.
    
    Total solar panel, battery and motor cost of $4000.
    
    All we need to make this goal, with today's solar panel technology, is
    for the price of those panels to come down to $19 each. The rest is
    practical!! Worth looking again 5-10 years out.......maybe we can
    eventually eliminate the need for sails altogether, during the day
    (oops, I'll have to move this to the Powerboat Notesfile!).
    
    Ray

re .17:

>>>    How much $$$$ gas or diesel do large boat owners use per year?
>>>    How much does a motor commensurate to 6 knots cost?
>>>    How much does it weigh?
    
A 25 hp diesel (which will give about 6 knots) is about $6000 and weighs 
unders 400 lbs. 40 gallons of diesel fuel (our tankage) weighs about 250 
lbs and provides (our boat and propeller) a range under power in excess 
of 400 miles. We use less than 50 gallons of fuel per year. The life of 
a semi-well-maintained diesel is over ten years, the life of 
semi-well-maintained batteries is maybe five years. 

re .11

>  True in the past and mostly true today. But horsepower is power -- 
>  torque (force) multiplied by time. It really doesn't matter what units 


Sorry ...  Energy is Force mutiplied by Distance. 
           Power is Energy per unit Time.
      or   Power is Force (torque) multiplied by Velocity (RPM, Rad/sec, etc.)


Force multiplied by Time is an Impulse and is related to Momentum for 
instantaneous events. Like hitting a baseball. 

    
> Not quite. An engine brake or dynamometer measures the power and torque 
> produced by the engine at a constant engine speed. Normally this is done 
> at full throttle. This is not a brake in the sense of stopping something 
> moving.


This is real picky. A Dynamometer only *measures* torque. Power is
*calulated* by multiplying the torque by the rotational velocity.

A brake is a device which slows or stops motion. So yes, a dynamometer
does use a brake. The motor is supported on rotary bearings by its 
driveshaft. An arm is fixed to the body of the motor and a force is 
applied at this arm to prevent the motor from rotating under varying 
velocity and load. The arm length mutiplied by the force is the torque.
So in a strict sense, even torque is calculated.  

Paul   (who in a current life is a mechanical engineer)

re .19:

It was a long ago former life. I should have known better.

re the dynamometer:

I think that there are various types. Are you saying that, say, a big
industrial diesel is supported by its driveshaft when on a dynamometer?
This doesn't sound reasonable. 

At least a thought experiment: What if the engine was supported on its 
normal mounts and connected to a huge alternator (with known frictional 
and other losses) and the output of the alternator was in turn connected 
to a huge variable resistor. Now run the engine and measure the 
electrical power output of the alternator when the alternator fully 
loads the engine. Sounds like a power measurement from which torque 
could be calculated. 

(Hey, it get boring talking about just sailing!)

    More approximations:
    
    The typical use I've seen the Sailboat engine power has been for getting
    in and out of the harbour and for a couple of hours at a time (borne
    out by Alan's estimate of 60 gallons of deisel per year).
    
    Let's assume a peak loading on battery power of four hours at a time,
    underway at 6 knots, a reasonable speed.
    
    What do we need?
    
    Batteries
    *********
    
    1.6KW for 4 hours = about 5 100a/h batteries
    
    Solar panels
    ************
    
    To fully charge in 8 hours sunlight, say, we only need about 12' x 12'
    of solar panels, or 15 panels, at $5K.
    
    Engine
    ******
    
    Simple and reliable, say $500?
    
    Total
    *****
    
    About $6000, zero cost for fuel, guarantee of lots of on-line power for
    ship's systems, no more worries about running out of battery power,
    unbelievably reliable motor, battery replacements at, say, $600 every 5
    years, almost no maintenance cost if done right the first time, etc.
    etc. etc.
    
    When I buy my first big Cat, it's going to have electric propulsion!
    
    Ray

reprinted without permission from IEEE Spectrum June 90:

A catamaran motorboat powered by 14 solar-cell modules on its roof made its
gentle debut at the International Garden and Greenery Exposition in Osaka,
Japan, on April 1. The 5-meter, 450-kilogram boat moves at 4 kilometers per
hour, and after its battery has been fully charged can travel 13 km.

The solar-cell modules, which together weigh 28 kg and generate 220 watts, were
developed by Sanyo Electric Co., Osaka. The boat's motor was built by Yamaha
Motor Co., Osaka.

Used in the solar cells is amorphous siicon, a type of thin-film photovoltaics
technology. Though the efficiency for each module is 7 percent, which lags
behind the 13.3 percent record for amorphous silicon set by Energy Conversion
Devices Inc., Troy, Mich., the modules are flexible enough to fit the curved
surface of the boat's roof because they have a plastic and aluminum base
rather than the glass base commonly found in flat solar modules.

Sanyo hopes to improve the efficiency of its cells so that they can be used
for high-voltage applications, such as panels for homes and electric generation
instead of just calculators and watches. The company has no plans at present
to develop the boat for commercialization. The Expo ends Sept. 30.

    re:  .20
    
    I've experimented with BIG electric motors on Dynamometers using the
    shaft support method. We pumped water with them and varied the load 
    by closing a downstream valve. I've also seen small automotive test 
    engines (4 cylinder) and steam turbines (about the size of a desk) 
    supported this way. 
    
    As I'm sure you're aware, control of measurement errors is important
    while experimenting. That's the beauty of simple shaft support, it's
    very direct. Measuring the power output of an alternater introduces
    many new variables. But I'd bet that GE (deisel electric locomotives)
    does it as part of their tests.
    
    Does GM or Ford have some kind of exotic engine support method?
    Probably.
    
    Paul  
    

re .21:

>>>  The typical use I've seen the Sailboat engine power has been for getting
>>>  in and out of the harbour and for a couple of hours at a time (borne
>>>  out by Alan's estimate of 60 gallons of deisel per year).
    
Typical only when daysailing on days with wind. When cruising or 
passagemaking, the engine is often run continuously a day or more at a 
time (I have motored the entire passage between Maine to Marblehead 
more than once).In real life, I doubt anyone would accept an engine 
installation not capable of several days of continuous operation. 

For getting in and out of harbor when daysailing, I could just as well 
replace my $6000, 25 hp inboard diesel with a 5 hp outboard ($800 and 
less than 100 lbs including a full gas tank) and have lots more stowage 
space. Why bother with the much higher cost and space of a solar system?

Besides, I think you're on the wrong track in talking about solar. The 
efficiency improvements and cost reductions you need are simply not 
reasonable to expect. Try another idea: Most sailboats have heavy lead 
keels. Why not develop a small, self-contained, fail-safe nuclear power 
system that is contained in and shielded by the lead keel? Now you have 
the possibility of round-the-world range under power without worrying 
about refueling or cloudy weather. Sounds like a much more practical 
idea to me.

RE:.24 by MSCSSE::BERENS "Alan Berens"

> For getting in and out of harbor when daysailing, I could just as well 
> replace my $6000, 25 hp inboard diesel with a 5 hp outboard ($800 and 
> less than 100 lbs including a full gas tank) and have lots more stowage 
> space. Why bother with the much higher cost and space of a solar system?

Or a human powered system,  as 2 knots is enough to get into and out of a
slip.  Perhaps a stationary bicycle and propeller,  as it would be much more 
efficient than oars...


> Besides, I think you're on the wrong track in talking about solar. The 
> efficiency improvements and cost reductions you need are simply not 
> reasonable to expect. 

Solar cells may reduce in cost to where this is practical,  but I wouldn't
count on it.  Try again in a decade.

> Why not develop a small, self-contained, fail-safe nuclear power system 
> that is contained in and shielded by the lead keel? 

Or replace some of that lead with palladium and have a "cold fusion powered
boat"?  :-)


Phil

    Did anyone else read about the sailboat (going back about 15 years)
    that had a giant rubber band to drive the propeller? I wonder how well
    it worked out.
    
    We used to build rubber band powered planes as kids and compete in
    gymnasiums for max time aloft. You can get alot of winds on a well
    lubed rubber band. Great for silent trips in and out of harbor. Then
    you can rewind with a small solar powered electric motor while the
    boat sits all week on the mooring.
    
    Paul 

	Somewhere I learned that horsepower is a  "rate of doing work",
or a capacity for doing work.  Seems the units were ft. lbs per second
(or per minute ?)  and the quantity was 550 (or 33,000 ?).  Anyways, 
watts have the same dimensions, 

		i.e.    f x d/t

		force  times  distance   per unit of time.


	R

    It isn't just the batteries that wear out.  I think that solar cells
    themselves age with exposure to sunlight and drop off in efficiency
    over the years.  So you have to figure in that cost as well.
    
    There are other technolgies than chemical batteries for storing
    electrical power.  An long-past issue of Scientific American (December,
    probably around 1973-76) describes very-high-speed fiberglass flywheels
    spinning in a vaccuum supported by magnetic levitation.  See, power
    stored is proportional to flywheel mass but goes up with the square of
    rotational velocity, so they proposed very high speeds (10K RPM) and
    relatively low weight.  Had the advantage (at least in cars) of
    collecting energy during braking.
    
    Another way to recharge, especially at anchor, and on bad-weather days,
    is a small windmill.  At least if you hang around one spot long
    enough...
    
    There is one thing going for electric propulsion - when we run out of
    petroleum to the extent that we can't afford to burn it any more to
    move our cars and boats around, but only use it for medicines and
    powering aircraft (which need high emergy-density fuels), solar is
    still available.  Non-polluting too.  Better check into what it takes
    to manufacture the solar cells though.  Did you know that the energy
    it takes to refine the aluminum in FOUR soft-drink cans could power
    your TV-set for an hour?
    
    Ahh, we are in too much of a hurry.  As William Buckley put it in one
    of his sailing books, having in the first place chosen to go by
    sailboat, to worry about how fast we get there is, well, perverse.

    
    As long as we're talking about exotic propulsion mechanisms, I read
    about a fellow in Japan who was trying to use superconducting magnets
    for propulsion.  Not sure how it worked, or IF it worked.  Doubtful
    that anyone wants to carry around tanks of liquid nitrogen anyway!! ;)

    
    
    
    	Having a good time, guys ?
    
    
    
    
    	Why not have the propulsion coming from a light weight gas turbine
    	which is fueled by methane gas you get from liquid manure in the 
    	(ex-)diesel tank ? 
    
    	(Filling stations downwind, please)
    
    	Lots of 8^D !!

RE:.17 by SDEVAX::THACKERAY

> Assume a 45' Catamaran, with non-propulsion power needs for 24 hours
> satisfied by batteries recharged during daylight hours at a rate of
> 1KW. It will make 6 knots (conservative estimate) at 1.6KW 

I don't think this is a conservative estimate of speed.  Catamarans tend to
have somewhat higher driving power requirement at low speeds than similar 
monohulls.  Cats will have more wetted area,  which is the main source of
drag at low speeds.


Phil

    This note is starting to sound like one currently runnng in
    SILK::ENGINEERING_IN_MINATURE. That one invloves building a steam power
    plant for home use.
    
    How about a solar collector up the mast, generating steam to run an
    engine? The mast could be a curved reflector, focusing the sun on teh
    pipe.
    
    

    According to an earlier note, Marchaj has it that a 25500lb, 45.5' LOA
    full keeled boat can be pushed at 4 knots with 60 lb thrust.
    
    OK, so then I went to examine electric motors and found one that
    produces 28lb thrust, at 12 amps (or 144 watts) consumption. So, let's
    assume two of these motors (which include prop, mount etc.), which
    produce 56lb thrust, so this boat is going to go a little under 4
    knots. Fair enough.
    
    That means we get 8 hours of thrust from two 105 a/h batteries, or two
    full day's thrust from eight 105 a/h batteries, at approx $800 for the
    batteries and $600 for the motors, a total of $1400. Not bad, eh?
    
    Now to get a full charge again, by solar means. I went to Boat/US on
    Friday and found a solar panel which produces 42 watts, or about 3
    charging amps. Assume we buy three of these at about $1000, for, say 9
    charging amps on a reasonably sunny day.
    
    To bring the batteries up to full charge, it would take about 4 days,
    which would INCLUDE the motoring time.
    
    So, for a total outlay of $2400, we have almost four knot capability on
    a big boat for two days out of every six non-stop, complete
    independence from fuel costs, incredibly reliable electric motors that
    should have many years lifetime and even if we assume that we replace
    the batteries every 6 years, a maintenance cost of about $160 per year,
    averaged over that time, with the added bonus of having all that
    battery power available, trickled up to full charge, at any time (a
    usual headache avoided!). Even if we include complete replacement of
    the solar cells every five years, this averages about $360 per year.
    Still a lot less than the gas or diesel engine options, I bet.
    
    And we haven't even considered the issue of augmentation to the
    charging capability by the cheap addition of a wind generator.
    
    Finally, there are trade-offs to be had. Someone could start off a lot
    cheaper, with less solar panels and batteries, to suit their usual
    cruising profile. Not many people need a full non-stop two day
    relience on their motors, so one could conceivably start really cheaply
    with just 8-hours, or entry price of about $1000, with plenty of spare
    battery power, and augment solar charging with dockside charging. The
    options are limitless, and don't need large initial outlays.
    
    Or one could go the full tilt and set up solar powered direct
    propulsion, which would almost guarantee full-day electric motor power,
    at at total of about $13K, still well within the prices of diesel
    options.
    
    There are certainly bugs to be worked out of this, but with these basic
    facts I don't see how people can justify scoffing the idea. It merits
    experimentation, at least.
    
    Ray
    
    

    
    re: wind generator
    
        somewhere I saw an idea for a wind propeller connected to a gear
        assembly which drove a water propeller.  Conceivably this could
        be attached like an outboard to power you directly into the wind.
    
        /Jim
    

    
    
    Ray, ow many sunny hours are you planning on per day?  When I made a quick
    trip through your numbers it looks as though you are planning to have
    nearly 100% of available sunshine for the solar cells.
    
    I've used solar collectors for my domestic hot water here in New
    England for a number of years.  They're effective enough-most of the
    time.  They are oriented towards the Sun, when it's available.  I have
    the back-up system from my oil burner which I used quite a bit during
    the last month.  
    
    May in Boston usually averages about 60% of available sunshine.  Of
    course this year we didn't quite that well.  At times when I need my
    auxiliary propulsion, I want to be sure it's there.  Last year I used
    almost nine gallons of diesel fuel, but was really glad to have it
    available a couple of times.
    
    The idea has merit, but I guess I'm just not an early adopter for
    technology. 
    
    djc
     

    Re: -.1
    
    Remember, I'm assuming 2 full days of battery power. With
    that set-up, you are going to have power when you need it. There are
    many trade-offs. In the Bahamas, you'll get plenty of sunshine; in the
    summer months of Boston, maybe half of that. Note I only assumbed 8
    hours of daylight and left room for conservative estimates.
    
    Re: -.2
    
    But a more reliable idea might be to have an electrical wind generator
    and use it to either feed the motor or keep the batteries charged.

    Ray, I did not see you deduct anything from your power budget for
         power transmission or conversion losses; If you get at all
    serious, plan on maybe 50% of what you have calculated to date.
    
    J

    I wasn't being rigorous in the assumption statements, but I've made
    rule-of-thumb efficiency allowances all over the place.
    Ray

RE:.34 by SDEVAX::THACKERAY

> OK, so then I went to examine electric motors and found one that
> produces 28lb thrust, at 12 amps (or 144 watts) consumption. 

I think you have the wrong spec on the motor,  as 28lbs thrust at 4 knots
requires a lot more power than 144 watts.  See .12.  At least 400 W.


Phil

    The spec came from the manufacturer's package. Will note details next
    time I peruse the same shop.
    
    BTW, wattages and thrust are easily confused.
    
    Ray

re .34:

Two motors will use 24 amps. The usual amp-hour rating of a battery 
is determined by using the load that discharges the battery in 20 
hours. For a 105 amp-hr battery, this load would be about 5 amps. 
The amp-hr capacity of a battery is considerably less at higher 
load currents. You will not get 105 amp-hrs from a 105 amp-hr 
battery with a load of 24 amps. You will get much less. That this is 
true is shown by simple experience. After only a few minutes of 
engine cranking, a battery will no longer turn the starter motor. 
The average starter motor draws maybe 300 amps. Ten minutes of 
cranking (often enough so that the starter motor will no longer 
turn) uses only 30 amp-hr. The usual starting battery is 85 amp-hr 
or more. At a guess you'll need at least three batteries for eight 
hours of powering, perhaps even four batteries. Plus, battery life
is greatly shortened by very deep discharges (a life of even a year 
would be unlikely). The usual optimum operating discharge for optimum
life is about 50% of total capacity. This implies even more batteries
for eight hours of powering -- six to eight. (Your eight hours of
powering will require 192 amp-hrs.) 

Battery recharging is not 100% efficient. You need to return perhaps 
1.2 amp-hrs for each amp-hr used. Moreover, solar panels rarely put 
out their peak power -- which is, I think, in full, direct sunlight. 
I'd guess that the average power output is about 50% of maximum when 
the hours of daylight is, say, two hours less than the time between 
sunrise and sunset. After all, solar panel efficiency falls off 
considerably when the sunlight hits at an angle other than vertical.
With these assumptions you will need about 46 hours (at least 4 days) of
sunlight to recharge a usage of 192 amp-hrs (this assumes no electrical
usage during this time and using only three 42 watt panels). This is
long, long way from two days of powering in six that you calculate.

I think your calculations are extremely optimistic and greatly 
overestimate the practicality of solar-electrical propulsion and greatly 
underestimate costs. The amount of diesel fuel used by the average
sailor is so small that even if the price were over $10 per gallon, a
diesel engine would be more practical and cost effective than
solar-electric. For reasons of convenience, to say nothing of safety, I
would not accept a system incapable of several days of continuous
operation, especially when that system cost several times what a diesel 
engine would cost.

RE:.41 by SDEVAX::THACKERAY

> BTW, wattages and thrust are easily confused.

Thrust is force,  wattage is power which is force times speed.  The reason 
why I claim you are in error as to wattage (or thrust or speed) is that the
thrust times speed is greater than the wattage you give.

Perhaps the motor will put out that much force,  but not at the speed required.


Phil

    I saw on the news that some Japanese company has developed a new kind
    of battery that has a much longer discharge time (something like 20x)
    and a much shorter charge time than lead-acid.  It was in a discussion
    about electric cars.  I can't remember the company.  No mention of what
    these things cost, or how they work.
    
    (Like, I know a liquid sodium battery stores more power per pound than
    a lead acid battery, but imagine what would happen if the battery
    leaked...  at sea.)

     My problem with this concept is 4 knots. 
     The idea is great and I'd love to see it work, but so far the costs 
calculated are more than I spent on my boat. My boat is relatively small,
would not have the space for the batteries and has no free space for solar 
panels. I wouldn't mind having solar power to recharge my single battery,
but I have other things to spend money on first. Also I'd add that I probably
wouldn't feel comfortable with the system unless I had a back-up generator
and that's defeating the purpose. 
     My problem with 4 knots of speed comes from my experience in Woods Hole
over Memorial Day Weekend. I'm new to having a boat large enough to travel
on so there was a lot of things I learned on this trip. I don't want to run
my motor if there is any hint of headway with wind and I held fast to this 
(il)logic as I crossed Buzzard's Bay. I reached Woods Hole only about an 
hour after the current had turned against me. I figured it wouldn't be to 
bad and I could still sail through. Sailing into the hole was bad enough with 
lots of traffic to avoid and restricted area for tacking. Fortunately the 
center channel, "The Strait", was at an angle such that I could reach right
through it. I got into The Strait and was sailing just over 4.2 knots, but I 
was doing so in 4.2 knots of current. I had to change course, jibe and find
a calm spot to start my motor. At 5.6 knots I made it through with much less
trouble.
     4 knots isn't enough! The current in Vinyard sound runs at 3.2 knots,
in Woods Hole it'll do more than 4 an hour into the Ebb or Flood. I think the
Cape Cod Canal run as high as 6, but I might have that confused with it's 
length. 
     Solar power is a wonderful concept, do it if you can. But you need 
better than 4 knots if you're going to sail around the cape. Maybe the rest
of the worlds oceans aren't going to have this kind of current, but I don't
believe that nor would I take the risk. 

     But I've only been sailing on salt water for a month and a half, what 
do I know?

     Geoff

    Re:.45
    Geoff:
    I think you would find the Cape Cod Canal running mostly in the
    4 knots speed range, just reaching 5.0 three days in May, June & July
    this year.
    

    OK ... OK!  Maybe for a 40 footer an electrical iron jib is not doable.
    
    How about a 25 footer???  Weighing 2.5 ton or less, max (under power)
    cruising time of 6-8 hr (I mostly use my motor for not more than 1/2
    hour)?  Then would electrical power plant be doable????
    
    Cheers,
    
    Tom
    
    

    Tom,
    
    You can buy a Minn Kota, with 28lbs thrust, for three hundred bucks.
    One fully charged 105 amp'hour battery will run it for 8 hours.
    
    If 28lbs thrust will suit you, it's doable. According to calculations
    I've seen, I don't see why you shouldn't get 4-5 knots.
    
    But this is all theoretical at this stage!!
    
    I'm right on the borderline of buying one for my 25' boat and using it
    as a back-up/trolling motor. As I always have four fully-charged 105
    a/h batteries, I reckon that gives me a good 24 hours at trolling
    speed!
    
    Cheers,
    
    Ray

    Further recent information:
    
    I just got a brochure (can't remember the company name, will post it
    sometime if anyone's interested) on wind generators and solar panels.
    
    Prices are REALLY coming down! There is one panel which produces 60
    watts at 17 volts (with blocking diode, that's a charging current of
    about 3.7 amps) and the price is only $340! That means for $1300, you
    can get about 14 amps at a good voltage, enough to power quite a
    reasonably powerful electric motor during the day.
    
    With all the tradeoffs in mind, an ideal application would be on a
    reasonable size boat (say 40') in the Carribean, for most days the
    ability, when becalmed, to be able to cruise all day on direct solar
    power through a cheap electric motor, and when not cruising, keep a
    small bank of 105 amp/hour batteries charged, with TONS of power for
    refrigerators, lights, electronics, etc.....
    
    Total cost including motor, say, about $1800 with extremely low
    maintenance and no need ever to go into dock looking for fuel!!
    
    Let's face it, for the average cruising profile, this is enough for
    almost anyone except those really serious people who demand to be able
    to run on motor power for four or five days, around the clock. How many
    of you guys out there have EVER had to do that??
    
    Couple of more years and I bet we're getting to the stage where we can
    keep a bank of batteries fully solar charged for 24-hour operation,
    price for full system, say, $2000. You may not want it in Boston, but
    off Jamaica? Yeah mon!
    
    Ray

    Say I was to buy an electric trolling motor, disassemble and fiberglass
    the lower unit (electrical motor) to the bottom of my boat.  I now
    have an inboard engine (kinda of) and can do away with the 7.5 hanging
    off the stern.  This will fix the problem of poor stearage at low
    speed do to no prop wash across rudder.  All seem doable given today 
    technology divided by my utilization rate.
    
    Question,  is the lower unit of a trolling motor sealed well enough to
    handle being under water for a prolong period of time (6 months)?
     
    Is there any other question I should be thinking of????
    
    
    Cheers,
    
    Tom
    
    

re .50:
     
>>>    Is there any other question I should be thinking of????
    
Resale value of your boat. This modification will (IMHO) certainly 
reduce it.    
    

    re .50
    
    Maintainability.  Will you be able to remove the guts for repair or
    replacement?  Can you do it without a haulout?

    Re  .51  Do you think it will reduce the value by a lot?  My guess would
    be that it would not reduce the value by more than 5%.
    
    Re: .52 Maintainability should not be that big a problem as the boat is 
    trailerable and I have the trailer, however that's not to say it's not
    a pain the the %%% to pull out. 
    
    Durability is as I see it the biggest problem, can an "off the shelf unit"
    take being under water for 5 month per year.  If it can not and it
    leaks you've lost 50% of your investment (and if it quits when you need
    it most (natural law number 7)!!!).  
    
    So, how do folk feel about these motor handling being under water for 
    5 months?????
    
    
    Tom
    
     

re .last:

As should be evident, I am extremely skeptical of the practicality of 
electric propulsion for boats. In spite of Mr. Thackeray's enthusiasm, I 
think electric propulsion is quite impractical and nowhere near cost
effective any time soon if ever. If you add an electric motor to your
25' boat, my guess is that you might well make the boat unsellable.
Battery charging will be a really major problem that will, I think,
deter potential buyers, to say nothing of the performance penalty (drag)
imposed by the electric motor and shaft. If you make this modification,
be prepared to completely undo it when you decide to sell the boat. 

signed,

just one man's opinion

    
    
    re.53
    
          When trailering, do you have to post those Corrosive signs on 
    the boat?
    
          With all that acid on board, do you have to obey hazardous
    material transport regulations ??
    
    
       ;>)

        Ray,
        
        Check out last Friday's Wall Street Journal(29-June). Front page
        of the Market Place Section, page B1. 
        
        Under Lab Notes titled "BATTERIES SO SKINNY THEY COME IN SHEETS".
        
        Summary: Paper-thin (0.015 inch) rechargeable lithium batteries
        are the hope of the Hopes. (father/son team) 220 watts per
        kilogram capacity is at least four times the power density of
        conventional lead acid auto batteries! Since one possibility
        noted was auto battery that would be part of the car's body,
        perhaps the next woud be the ability to mold them into the boat's
        keel producing a postitive effect on the CG.
        
        

    Alan,
    
    I know you're a complete sceptic on the idea of using
    solar/battery/electric propulsion capability, but I think you are
    reacting to the promises that have been made over the years that this
    possibility is "just around the corner", and never made it.
    
    But that's no reason to believe it will never come. There are now many
    indications that the whole concept is on the borderline of becoming a
    practical and economical proposition, worth investigation. Automatic
    rebuffal of the approach is now becoming anachronistic with the more
    recent advances in energy storage and generation.
    
    It is definitely now possible, for the same cost as a deisel system, to
    provide multiple-day continuous, reliable propulsion by electric motor,
    including an effective solar recharging system.
    
    It is even now possible to be able to provide direct power for electric
    propulsion through solar and wind-generation means.
    
    Look at the possible advantages of reaching for this ideal:
    
    	We all know how much more reliable electric motors are. I for one
    	am sick and tired of never-ending problems with fuel systems,
    	ignition systems and mechnical failures, overheatings, seizures etc.
    	associated with internal combustion engines.
    
    	Never having to buy gas or deisel again.
    
    	Never again needing to pullute the earth (or myself!) with oil, gas, 
     	carbon monoxide, fumes, etc. 
    
    	No risk, any more, of fuel explosions.
    
    	Probably MUCH cheaper/longer maintenance schedules.
    
    	Never having to worry ever again about having enough power to run
    	the refrigerator, running lights, internal lights, etc....
    
    Don't write it off, Alan, or pooh-pooh the idea. When its time has
    come, I for one am going to be there.
    
    Ray
    
    	
    

RE:.57 by KEEPER::THACKERAY

> But that's no reason to believe it will never come. There are now many
> indications that the whole concept is on the borderline of becoming a
> practical and economical proposition, worth investigation. 

But it isn't yet and may never be practical or economic.  The biggest question
isn't the solar cells.  It's the batteries.  They are expensive,  short lived,
contain toxic and caustic substances.....


> It is definitely now possible, for the same cost as a deisel system, to
> provide multiple-day continuous, reliable propulsion by electric motor,
> including an effective solar recharging system.

No way.  Batteries have much higher costs of operation.  Even if solar cells
were free,  it would cost more to build and run an electric system.


Phil

    re .57
    
    Ok, Ray,  You sold me on the idea - sound great.
    
    Look forward to seeing your demo.   ;-)
    
    Argument over??
    
    Ron

    Lithium batteries are not rechargeable.

re .57:

Let's just agree to disagree. When you can provide me with a 
fixed-price bid for a solar-electic propulsion system meeting 
my needs, I'll buy it. Until then, I will consider solar-electric 
propulsion impractical for my boat.

Specifications:

   Cost not to exceed $6000 (the approximate cost of replacing my diesel) 

   Weight not to exceed 600 lbs (the approximate weight of my diesel 
   engine and 40 gallons of fuel)

   Speed under power of at 5.7 knots (speed with my present diesel)

   At least 80 hours of non-stop operation (my current capability) at 
   5.7 knots

   The deck area occupied by the solar panels should not exceed 20 sq ft
   (that's all the space I have)

   Less than two days required to fully recharge 75% discharged batteries 
   regardless of weather conditions.   

Imagine a long voyage
Becalmed
Sails slatting, damn slatting
Hot sun beating down, baking the crew
Would it be so awful to drop a trolling style outboard over the stern
   and hum along at two knots?
A few solar panels, a few batteries......
If the batteries died half way through the night, no worse off than 
  sitting in the same spot all day.
Yes, the motor might need a long shank and a bigger prop
If it worked, I would be happy
The light breeze, the gentle motion taking me where I want to go
A few tens of miles in the right direction
That would be enough for me.
    
		Rich

Here are the results of an approximate quantitative analysis of the
total power that can be obtained from a solar panel. The results are
interesting. 

On page 6-2 of the Elecro-Optics Handbook, RCA Corporation, 1968, there
is a graph of the spectral energy distribution of the sunlight
vertically incident on a horizontal surface at sea level. This graph
plots the incident energy (in watts per square meter per Angstrom) as a
function of the wavelength of the light. The light below the visible
(the infrared) is ineffective in producing electricity using solar
panels. A rough numerical integration of the energy distribution in the
visible and ultraviolet regions of the spectrum provides an estimate of
the power (sunlight) available for conversion to electricity by a solar
panel. This estimate is:

     508  watts per square meter
     47.2 watts per square foot

(Note: Though I used three significant figures in my calculations, I 
doubt the numbers are accurate to much better than 10 to 20%. The amount 
of sunlight reaching the earth varies some plus/minus 3.5% from the mean 
depending on the distance between the earth and sun.)

This is an estimate of the practical MAXIMUM power that can be obtained
from a solar panel since it is for: 

     the sun vertically overhead (ie, minimum path length through the 
     atmosphere)

     a 'standard' clear day 

Smog, haze, clouds, and fog can reduce the intensity of the sunlight by
a factor of 10 or more (absorption and scattering is an exponential
function). A 'standard clear day' means a day with visibility > 14.6
miles. An 'exceptionally clear day' is one with visibility > 37.3 miles.
Such days are all too rare (which is why they're exceptional). On an
exceptionally clear day the incident power is very approximately 50% 
greater than on a standard clear day. 

Every day life indicates (and scientific research confirms) that 
sunlight is less intense when the sun is not directly overhead. From 
Figure 6-2 in the Electro-Optics Handbook the following data can be 
derived: 

     altitude of sun   relative solar energy on 
         (deg)         a horizontal surface

           0                  0.6%
          10                  8.8%
          20                 22.2%
          30                 37.9%
          40                 53.8%
          50                 68.5%
          60                 82.3%
          70                 91.1%
          80                 96.8%
          90                100.0%

(This data is for only the visible spectrum, but it is convenient to use 
the data for visible and near ultraviolet light.)

From this data, it is obvious that output of a solar panel will vary 
significantly with time of day, so the question is: how much?

Using standard celestial sight reduction equations and data from the 
Nautical Almanac, the altitude of the sun can be easily determined as a 
function of time-of-day. 

     hours before/after             altitude of sun (deg) 
     local noon        @ 42 deg 30 min latitude    latitude =
                         solstice     equinox      declination @ solstice

       0.0                 70.9         47.5         90.0
       1.0                 67.2         45.4         76.2
       2.0                 58.7         39.7         62.5
       3.0                 48.3         31.4         48.8
       4.0                 37.4         21.6         35.4
       5.0                 26.3         11.0         22.1
       6.0                 15.6          0.0          9.1
       7.0                  5.4                      -3.4
       8.0                 -4.0

Most of my sailing (cruising) is done in June, July, August, and 
September between Marblehead (42 deg 30 min north latitude) and Maine. 
So the sun altitudes at 42 deg 30 min N latitude on the solstice and
equinox provide an approximate maximum and minimum for my sailing. When
the observer's latitude is the same as the latitude of the sun -- the
sun's declination -- the sun will be directly overhead at local noon.
The third column gives the data for latitude 23 deg on the solstice. 

The data from the two tables above can be combined to estimate the solar 
light intensity as a function of time-of-day:

     hours before/after   percent of maximum sun intensity
     local noon        @ 42 deg 30 min latitude    latitude = 
                         solstice     equinox      declination @ solstice

       0.0                 91.7         64.9         100
       1.0                 88.9         61.8          94.9
       2.0                 80.6         53.3          84.7
       3.0                 66.0         40.2          66.9
       4.0                 49.7         24.4          46.6
       5.0                 31.8         10.0          25.2
       6.0                 15.8          0.6           7.9
       7.0                  4.2                      

The area under these curves is proportional to the total watt-hours of 
solar energy available.

     solstice     360 watt-hrs per square foot per day
     equinox      206 watt-hrs per square foot per day
     zenith       352 watt-hrs per square foot per day

(Since these calculations are rather tedious, I haven't done any others.)

It is interesting to note that, to some extent, the longer days in the 
higher latitudes compensate for the reduced intensity of sunlight.

Unfortunately, solar panels are not 100% efficient. An Arco 42 watt
solar panel has an area of 3.84 square feet. This implies a light to
electricity conversion efficiency of 23%. (This higher than I would have
guessed -- perhaps Arco's ratings are conservative). 

For a 42 watt Arco panel (23% conversion efficiency) charging a battery
at 12.6 volts the number of amp-hrs per day from the solar panel will
be: 

     solstice       25
     equinox        14
     zenith         25

Assuming I've done all the number crunching correctly on my HP
calculator, these results are not partcularly cheerful for anyone hoping
to supply much of his/her electrical needs from solar panels. Unless, of
course, one is very frugal with electrical consumption and a profligate
spender of money for panels. These results assume, again, a standard
clear day. Here in New England, really clear days are not as frequent as
one might like. Solar panels on a boat on a mooring cannot be kept aimed
at the sun. About the best one can do is place them flat on the deck
with minimal shade. 

Note that the gain in panel output by facing the panel directly at the
sun isn't as great as you might expect. As the sun's altitude decreases,
the path length of the sunlight through the atmosphere increases. On an
exceptionally clear day, the atmospheric transmittance for the sun at an
altitude of 30 degrees is about 60% of the transmittance with the sun
directly overhead. Since the intensity reduction is an exponential
function of path length and attenuation coefficient, intensity decreases 
rapidly with decreasing visibility and with decreasing sun altitude. 

From this data you can estimate the probable amount of battery charging 
you can expect from one or more solar panels. It certainly appears the 
the cost per amp-hr of charging capacity is quite substantially higher 
for solar panels than other other means (at today's prices). For 
example, an Arco 42 watt solar panel (25 amp-hr per day) is about $350. 
A 400 watt portable Honda generator with a 110 vac battery charger 
(around $500 new) will supply over 600 amp-hr per day. 

RE:.63 by MSCSSE::BERENS "Alan Berens"

> It certainly appears the cost per amp-hr of charging capacity is quite 
> substantially higher for solar panels than other other means (at today's 
> prices). For example, an Arco 42 watt solar panel (25 amp-hr per day) is 
> about $350.  A 400 watt portable Honda generator with a 110 vac battery 
> charger (around $500 new) will supply over 600 amp-hr per day.


You are discussion only initial investment,  not cost.  Cost depends on 
factors not discussed.  The cost of gas and oil for the Honda isn't zero,  
and what is the useful lifetime of solar cells vs Honda generators?  

Capital cost = F(initial investment,interest rate, lifetime)

Operating costs = Gas + maintainance + supervisory time + risks


I agree that solar cells have higher capital costs.  The generator will have
higher operating costs.  If you can live within the limits of a 25 Amp-hr
power budget,  your lowest cost might well be a solar panel.  The larger the 
amount of needed power,  the better the generator will look,  as there is 
good economy of scale in motor-generators,  a 750 Watt generator (West Marine 
$475) is less than twice as much as a 2400 Watt generator (West Marine $835) 
and uses more gas (.29 gal per KWH for the 2400 W vs .31 gal per KWH for the 
750 W).  It will cost about as much to maintain the larger generator as the 
smaller.  And it will take as much of your time to fill the gas tank every n 
hours.  There isn't much economy of scale with solar panels.  Twice the power
costs just about twice as much.


Phil

    Alan,
    
    Thank you for the authoritive data.
    
    However, I cannot agree with your conclusion. It may be the right one
    for YOU, but other people have differing priorities and trade-offs to
    make, which you did not spell out as a part of your recommendation. The
    other variables include:
    
    	Pollution: why use gas engines when you can aviod it?
    
    	Cost of fuel and inconvenience of carrying it.
    
    	Most people are weekend sailors. For them, it is quite practical
    	to charge the batteries over the rest of the week by solar energy.
    	That invalidates the argument that you can't get enough watts
    	in a short enough time.
    
    	Attendance. You have to stand over that gas generator all day until
    	your batteries are charged. You just leave the solar cells all
    	week, or month, or year, no problem.
    
    	Weight. Do you really want that extra 100 pounds generator (or 
    	50 lbs, whatever) and carry it about with you?
    	
    	Maintenance. That damned genny is just like every other internal
    	combustion engine, it has to be serviced. Costs money each time.
    	And some are not so good in marine conditions.
    
    	Battery lifetime. A small charge, keeping those marine batteries
    	at full charge all the time, will increase the life of the
    	batteries, although obviously you need an overvoltage controller.
    	That's not so easy or convenient with a generator, because you
    	have to go the the boat, start it up, watch over it, etc.....
    	This especially goes for winter time, if you are one of those
    	people who tend to be lazy and leave the batteries on board.
    
    Alan, I'm sure you have made the right decision for your typical cruise
    profile. But your recommendation completely missed the alternatives and
    tradeoffs people have to make before buying.
    
    Regards,
    
    Ray
    
    	
    	

Reply .63 is intended to be an approximately quantitative analysis of 
the amount of power you can reasonably expect from a solar panel 
(something I've yet to see published in any yachting publication). It is 
not intended to advocate one means of battery charging over another. It 
is not intended to be an exhaustive cost analysis comparing one charging 
means versus another. Use the data I've presented however you see fit 
and make your own decision as to how you prefer to recharge your 
batteries. 

Alan