using solar pannels to recharge batteries

[bowman316]

how many square ft of solar panel would I need to recharge a deep cycle battery in a reasonable amount of time. Basically I would need to charge the batteries enough in the day, so that I have enough juice for lights at night.

I might switch off one battery, and charge that one, while I use the other one.

you a 2 square ft pannel charge up the battey enough in a day?

 

[diesel5599]

Re: using solar pannels to recharge batteries

I'm not going to claim to be a solar expert, although the field definitely interests me, but below is where I went when I was doing calculations similar to yours:

http://tlc.howstuffworks.com/home/question418.htm

Basically I highly doubt you will find a solar setup that will recharge your battery in a single day. Even my deep cycle wall battery charger takes about 3 days to completely charge a drained deep cycle battery and that's with 120v input.

Batteries don't just charge faster the more input current they have, the input current has to be modulated and cannot exceed a current amperage threshold to keep the battery from overheating. Also, to prevent battery 'memory' most chargers also condition the battery while charging.

I think solar is great for keeping a charged battery topped off, but it would probably be cheaper for you to get a deep cycle charger if you are trying to recharge completely dead marine batteries.

I researched this once just to power a motion sensor light at night for a shed that is too far from the house for house power, and I think I was nearing the $800 mark just for a decent solar array and a few deep cycle batteries, the inverter, and charge controller.

 

[Silvertip]

Re: using solar pannels to recharge batteries

You would need a panel the size of your boat and bright sunlight for a couple days straight to charge a single battery. Most panels in the 2 square foot range are 5 Watt output. Note I said 5 Watt -- not 5 Amps. That equals 0.4 amps which is hardly enough power to light a small auto dash light bulb. A 90 AHr battery at 1/2 amp would take roughly 180 hours to charge that battery (if you were lucky enough to have bright sunlight for 24 hours each day). Solar is not the answer for battery charging unless you have one the size of the roof on your house.

 

[H20Rat]

Re: using solar pannels to recharge batteries

lets say a decent size deep cycle at 150 amp hour. (1900 watt/hour) So if you want to charge that battery in 8 hours, you need something capable of 244 watts at an absolute minimum.

currently HF has a 80 watt panel ($599) that is roughly 2x4 feet, so you would need at least 4 of those, not counting the charge controller (you will lose a decent chunk of your raw energy due to the controller/clouds/etc... You would be talking almost $3000 for a system of that capacity ready to go. You would also have almost an extra hundred pounds just in solar panels and controller.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=66369
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94790

you could also get by substantially cheaper by going to older tech solar panels, 15 watts, 1 foot by 3 feet, for $70. That would bring the total for a little over $1100 in panels, but you would also have to find room for 17 (51 sq feet) of them!

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96418

 

[trendsetter240]

Re: using solar pannels to recharge batteries

I think everyone is getting a bit off topic here. He said he wanted to recharge during the day to run lights at night. That is very feasible.

IF your lights are a low current draw i.e LED lights then sure you will do fine with about 30 watts of solar panels. Two 15 watt panels will take up about 4ft x 3 ft space. I have such a setup and they fold in two for storage which takes up half that space.

If you start out with a fuly charged battery set and use them only for LED lights at night you will be absolutely fine. However if you drain the batteries using something else i.e. a trolling motor you are out of luck. A deeply drained battery will take weeks to recharge.

 

[jimsheila1996]

Re: using solar pannels to recharge batteries

A lot of us at our club use battery powered winches on our boat lifts. Most charged with a 5 watt solar panel. They will keep up with raising and lowering the lift a couple of times a day indefinitly with normal light (not necc. full sun either). They will NOT though recharge a battery from dead. I think that the O.P. could run his lights for a couple of hours in the evening and expect trhat the battery would recharge from that the following day. Just depends on how much he uses.

 

[PhilfromOhio]

Re: using solar pannels to recharge batteries

If all your doing is running the lights at night, then a cheap pannel from harborfreight is perfect. Get to the fishing spot during the day or whatever, put the pannel out and your good. or just leave the pannel out during the day to charge and then go out at night? I use one and it seems to work.
Granted I have a separate battery for the trolling motor, and I put that one on a regular charger when finished, Solar pannels wont cut the mustard for that one. Tried it once....NOT...

 

[bowman316]

Re: using solar pannels to recharge batteries

maybe i could put a mindmill at the top of my mast too.

i am trying to live on this boat, without shore power.

 

[trendsetter240]

Re: using solar pannels to recharge batteries

maybe i could put a mindmill at the top of my mast too.

i am trying to live on this boat, without shore power.

Yep, great idea.

http://www.e-marine-inc.com/products/wind_generators/airxmarine.html

 

[tschmidty]

Re: using solar pannels to recharge batteries

A wind generator will get you a lot more power than solar, most cruisers use both. The calculations are not htat hard and you really can't get away form doing them.

It's going to come down to you having to have shore power for a live aboard, there is almost no way around it.

Think about this: How are you going to power that AC unit that will be a dang necessity on a boat in the middle of maryland summers? If you are sailing/cruising places you can get away a little more roughing it, but even then those guys 1) recharge their batteries during the day motoring from place to place (even on sailboats) and 2) run generators otherwise.

 

[bowman316]

Re: using solar pannels to recharge batteries

i have a generator, but it is pretty big, and i don't have much outside deck space to store it.
i don't want to run the generator inside due to the carbon monixide.

this is not a marine generator

 

[trendsetter240]

Re: using solar pannels to recharge batteries

I think everyone is getting a bit off topic here. He said he wanted to recharge during the day to run lights at night. That is very feasible.

IF your lights are a low current draw i.e LED lights then sure you will do fine with about 30 watts of solar panels. Two 15 watt panels will take up about 4ft x 3 ft space. I have such a setup and they fold in two for storage which takes up half that space.

If you start out with a fuly charged battery set and use them only for LED lights at night you will be absolutely fine. However if you drain the batteries using something else i.e. a trolling motor you are out of luck. A deeply drained battery will take weeks to recharge.

Just wanted to update this as I measured my panels and the two together are actually 3ft by 2ft. So even smaller than I initially stated.

 

[roostonu]

Re: using solar pannels to recharge batteries

i have a generator, but it is pretty big, and i don't have much outside deck space to store it.
i don't want to run the generator inside due to the carbon monixide.

this is not a marine generator

I have a 55w panel and digital charge controller that will charge at 5 amps in full sun on my travel trailer. The panel is something like 2' x 4'. That will charge my 2 group 41 AGM batteries (by 3:00-4:00 pm) to the point that the charger is cycling on and off after an evening of 12v light use as well as heater blower, refrigerator circuitry, ipod charging and portable DVD usage.