Adding Underwater Solar Light

Re: Adding Underwater Solar Light

The 500 watt fixture at 120 volts is over 4 amps... So the 0.5 amp of the LED lamps should be OK... If you put a bunch in parallel--you will have to look at the voltage drop... 3 volt drop at 120 volts is much different than 3 volt drop at 12 volt.

Regarding the solar panel--sounds like a 3-4 volt panel... Unless you use some boost type electronic power supply to get 14-15 volts at the battery (which is not usually done)--that panel will not work for you.

You need a panel rated for charging a 12 volt battery (typically around 17 volts Vmp (max power)).

And, usually, you will need a solar charge controller between the solar panel and the battery. Also, it would be nice to have an automatic controller to turn the lights off when you don't need them any more.

Morning Star has some nice solar lighting controllers made exactly for this function. Morning Star also has a very nice new model MPPT type controller (better power production for up to 200 watts of solar panels).

In the end, the size of the solar panel and the battery depend on how much light/power you need, where you live, what season(s) you want to run the lights, and how much sun you have.

As a real rough guide--Say you want to run 4 of your solar lights for 3 hours per night.

4 lights * 0.5 amps * 3 hours = 6amp*hours per night...

Roughly, you get about 2 hours worth of sun from a solar panel 6+ months of the year. So, to run this, you would need a solar panel rated at:

6amp*hours / 2 hours of "sun" per day = 3 amp rated panel.

A 3 amp panel in watts is:

3 amp * 17.5 volts = 52.5 watt rated panel...

The lead acid storage battery would typically be sized to support 3 days of no sun and 50% maximum discharge (for best battery life)

6 amp*hour * 3 days * 1/50% = 36 amp*hour deep cycle storage battery

None of the above is written in stone--but gives you a good idea of the basics of estimating a system's performance and cost.

For a more exact match to your area see this link (and you can look at the month by month--or even day by day) power consumption. You can take the defaults--but use a derating factor of ~0.52 for a battery powered system. You will have to use 1kW of solar panels then divide down to your 100 watt (or whatever) panel (1kW is the minimum that this program will take).

-Bill