PV Gap

Eugene Said:

What size marine battery/s would I need to run 4 100 watt bulbs for 12 hours? ?

We Answered:

400 watts for 12 hours is 4.8 kWH. Due to the inefficiencies of the inverter and charger, you'll need to harvest about 6 kWH each day. In most of the country, that's 1.5 kW DC of solar panels, which will cost you about $8,000 US.

To avoid discharging the batteries more that 50% even on a cloudy day, you'll need about 15-20 kWH of batteries. 20 kWH of batteries is 8 L16 floor scrubber batteries, which will cost you about $2,000.

If you use CFL's, that will cut your use by 75%, and you'd use only 1.2 kWH/day. That's only about 300 watts of panels which would cost you about $1,500. You could get by with 2 L16 batteries.

DK

Edna Said:

I bought a 1991 Jayco pop up with inverter. Can I use a marine deep cycle and just plug the camper into it?

We Answered:

A marine deep cycle battery is exactly what you need. Do not get a marine starting battery, be sure to get the deep cycle. You can wire the inverter directly to the battery.

As for the solar panel, It may not fully charge the battery in one day. It just depends on how much power you use from the battery. You may want to consider a second battery and/or a small generator with a battery charger which would recharge the battery in about 2 hrs if it is fully drained.

Brett Said:

Can I use a 36 volt DC Motor to charge a 12 volt marine battery?

We Answered:

You have accidentally hit upon the core of the windmill issue. You can use the higher voltage motor in a windmill application because the voltage will not reach 36 at the lower rpm. Install a voltage regulator to ensure you don't exceed 13.2 VDC or so in the event of high winds etc. for a better explanation you can check out this link: http://tinyurl.com/6gmsgk4 Which in my experience is the best ebook dealing with the use of electric motors as generators and windmills in particular.

Leslie Said:

What size batteries should I purchase to operate a 24v, 65# thrust transom mount motor?

We Answered:

Minimum of two group 29's, wired in series.

Gloria Said:

If I have an 80W solar panel charging a deep cycle battery how long will the lights stay on for?

We Answered:

A 50 Amp Hour battery can provide 1 amp for 50 hours or 2 amps for 25 hours or X amps for 50/X hours. So how many amps does a 12 volt battery have to provide to be providing 26 watts (2*13)?

Watts = Volts * Amps.

26 watts = 12 Volts * X amps
26/12 = 2.167 amps

and

50/2.167 = 23 hours.

Now most CFLs are 120 volts AC and not 12 volts DC like the battery, so I assume you have an inverter to make 120V AC power from the battery. The inverter will not be 100% efficient so the lights will last a little less than the full 23 hours. But certainly all night if the battery starts fully charged.


How long to charge the battery? Most solar panels are 12 volt so use the same equation to find out how many amps the panel makes.

80W = 12V * X Amps

80/12 = 6.67 amps

A 50 Amp Hour battery takes 50 hours to charge at 1 amp, 25 hours to charge at 2 amps, and 50/X hours to charge at X amps, just like the discharge calculation above.

50/6.67=7.5 hours.

However, the 80 W panel only makes the full 80 watts when it faces directly at the Sun on a clear day. It can only do that if it is mounted on a motorized stand that turns it slowly during the day to face the Sun like a sunflower. If it is mounted on a roof or fixed stand, it will only make 80 watts at (probably) noon when the Sun is directly in front of it. It will make much less in the morning and evening.

Also, batteries are not completely efficient. It takes more than 50 hours to charge a 50 Amp Hour battery with a 1 Amp current. So how much will all these inefficiencies reduce your power? It is really hard to say, but I bet at least 50%. Especially the part about not turning the solar panel to face the Sun directly. That alone if a giant loss of efficiency that most people just put up with because it is clumsy and expensive to make a motorized mount to track the Sun.