PV Gap

Olga Said:

How do you figure the amount needed watts of solar panel and the number of 12 volt batteries you need ?

We Answered:

Add up all your electrical loads in watts. For example, say 100 watts.

Calculate how many hours of direct sun you will get per day, on average, worse case. For example 8.

Decide on how many hours the batteries need to supply power if the sun is not out, eg, on cloudy days, or several cloudy days. For example 24 hours.



Since you only have sun 1/3 of the day, you need 100 watts x3 or 300 watts of solar power.

But you need more to charge the batteries for cloudy days, so double that to 600 watts.

A large lead acid battery will store 1kW-hr of energy, or enough for 100 watts for 10 hours. Since our example has stored power for 24 hours, that is 2.4 batteries, say 3 batteries.


so bottom line, you need
1. a 600 watt solar panel ($4000)
2. 3 marine lead acid batteries, each 100 amp-hour, about $900
3. A charge controller $400
4. An inverter to convert 12 volts DC to 120/240 volts 1000w $300


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Veronica Said:

Can a 18W solar panel charge two car batteries? I am planning going solar, thanks?

We Answered:

In short you need to read ratings and ask manufactures. There are lots of ways to figure power using current, voltage and resistance. The voltage has to be around 14 to 15 volts to charge a 12 volt battery and if you only have, say, less than one amp available, it could take days/weeks/more to charge the batteries. On the surface without knowing details, it doesn't sound feasible and if it is, functionality should be considered, if the battery will be discharged in four hours and it takes two days to charge it, is that really something you want. You need to seriously investigate the system you are planning to build/use.

MT C

Brandy Said:

What type of batteries do i get for a solar panel?

We Answered:

You really should get deep cycle batteries. They are available flooded or sealed. Flooded cost less than sealed, but require you check the water and acid on a regular basis. A well maintained flooded battery should lat longer than a sealed battery that doesn't need much maintenance, but if you don't maintain it, it will die early. You can see both types here, http://www.altestore.com/store/Deep-Cycl… .

Be careful about putting too many together in parallel, general rule of thumb is not to do more than 3 in parallel. You can put as many as you need in series to get to the right voltage, but putting more than 3 in parallel can cause uneven charging and discharging and shorten their life.

Marion Said:

Solar panel batteries.?

We Answered:

they should be ok the excess charge only lasts till the batteries cool down you do need to put a charge limiter on the charger to prevent overchargeing the could blow up. the limiter detects the full charge and stops putting more in. it should be built into your charger if not get one or build one. your life will be easier.

Cindy Said:

4 batteries (dry) 48 v is charging by a solar panel,can it be charged at the same time by an electrect charge?

We Answered:

If you want to charge the batteries via a solar panel(s) plus via a battery charger, the two sources need to be isolated via rectifier diodes to prevent current from the panels flowing into the charger when it is turned off, and current from the charger flowing into the panels when there is no sun.

Two rectifier diodes rated at the max current that each source can deliver will do. Note that either or both may already have diodes internally as part of their design.

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Harry Said:

How to make charge controller for solar panel to batteries?

We Answered:

I don't think you'll get a straight answer here ... If you do, beware. It's much to complicated of a topic to address in a forum like this. It depends on the battery type, the voltage and current of your panel, etc. There are may schemes that can be used depending on whether you are charging lead acid, NiMH, Lithium (can be dangerous if done wrong). If your panel has a lower voltage than your battery, you need a boost converter. If the panel has a high voltage, you need a buck converter. These types of supplies/chargers are tricky to design and build correctly even for experienced engineers.

Having said all that, if your panel has a voltage slightly higher than 12V (like 14V) and your battery is a 12V lead acid type, you might be able to just get by with a direct hookup using a reverse blocking diode so the battery does not back feed the solar cells when shaded.