I believe these are the most efficient PV panels on the market.
http://us.sunpowercorp.com/residential/products-services/products/panels.php
I've been looking at the 315s for my modified Duffy launch. They are 41x63 inches and put out 315W at peak.
Jim
(If anyone is curious, I've got an old Duffy 18 double-ender with an Electric Yacht system and an oversized prop. According to the numbers, 3 of those panels will allow me to do over 4kt on pure solar. There's also room for 12 Trojan T-125s in the battery hold, which would give me a range of around 50 miles at 4.5 to 5 kt. I haven't installed the big battery bank or solar panels yet, but based on preliminary testing of amps-vs-kts the numbers should be pretty close.)
--- In electricboats@yahoogroups.com, "Bill Gow" <billgow@...> wrote:
>
>
> From: David Goldsmith
>
> Off the cuff it sounds to me like you're dreaming.
>
> 8 of those PVL-68s is only a 544 watt array.
>
> - I've been agonizing over this electric power option for almost a month
> now and I finally figured I had to discuss this with people with more
> experience than I have. Thanks for the quick and straightforward response!
>
> From: Eric
>
> There is no way that you can beat the power to weight ratio, economy, or
> simplicity of regular outboards with any type of electric propulsion.
>
> BTW, using lead acid batteries, 1000 pounds will get you 22.5 Kwh total,
> 13.5Kwh usable. With LiFePO4, 800 pounds can get you 32Kwh total, or 24 Kwh
> usable for almost three times the cost. As somebody else mentioned, 8 PV68
> panels will only provide 544w under optimum conditions, usually less than
> 400w, which won't drive you at 2.5 knots, or would take 4 sunny days to
> charge 12Kwh at anchor.
>
> - Thanks, Eric! Hey, I sailed my first catamarans out of Marina del Rey! A
> Sol Cat and later a Nacra. I sailed the Tuesday night races for a while. I
> remember many nights sitting becalmed just outside of that breakwall... ;)
> I also have a very funny story about blowing down the channel at the public
> boat launch in Santa Anna conditions and pitch polling right out in the main
> channel in front of about a gazillion spectators... Lots of memories!
>
> - I've read a little about the Lithium Iron Phosphate batteries. I think
> they'll become a viable alternative once the auto manufacturers are using
> them.
>
> - I need lightweight solar. Is there something better than the PVL-68
> laminates? I've searched around and these look like my best bet.
>
> - I have a couple other methods of recharging batteries. My electric motors
> can regenerate electricity and at anchor, I'll set up a wind generator.
>
> - Besides propulsion, I'll be using a lot of electricity for refrigeration,
> navigation electronics, water maker, pumps (bilge, baitwells and tuna
> tubes), and lights, etc..
>
> - Would it make better sense to go diesel electric and wait for the battery
> technology to mature a little more?
>
> - I'm not put off by the initial cost of the batteries. I know, over time,
> they more than pay for themselves. Even more important, I'll always have
> power. Something I may not have available while at sea for long periods of
> time otherwise. I think the best thing about the LiFePO4 technology is
> flexibility in shape. Instead of dedicating a large square battery
> compartment, I can stash them in more convenient places where space allows.
>
> - Thanks for all the advice!
>
