Trying to understand electricity in a solar application?

Question

Ok, I'm trying to set up a solar lighting system, so i need to understand what I need in terms of power. That is, how much solar panel output I need to charge a battery in the course of a day of a given capacity to burn a given number of high-output LEDs at night. problem for me is the lights & the panels are rated in watts and the batteries in amp-hours. Lets just say I want to burn 50 LEDs at 1.6 watts (140mA) and 6 volts apiece for 10 hours, what capacity battery (in amp-hrs) would that need, and what solar panel output (in watts at 12v) would it take to charge that battery to full in a 10 hour day?

Answer 1

A 12 volt battery produces 12 Watt hours per Ampere hour.

So a 100 ampere hour 12 volt battery stores 1200 watt hours.

As the battery approaches end of its life, or if the water level is low, the battery will store less than rated amp-hours.

Most LED will operate 3 in series on a 12 volt battery to get maximum use.  But if your units require 6 volts you would put them 2 in series on 12 volt battery, and still get 0.14 amps of 12 volt power.

25 such groupings will  draw 25 * 0.14 amps close to 4 amps, which will run 25 hours on a 100 amp hour battery.

You will likely want to run other things too, so I suggest you go for a 100 amp hour battery.

Now to fully charge that, if a solar panel is putting out 2 watt hours a day for each watt of rated capacity, you need to provide 600 watts of rated capacity.  (100 amps hours  times 12 volts is 1200 watts. But the original task was to provide only about 500 watt hours, so you could get along with about  250 watts of solar panels.  

Those numbers are pessimistic, based on never switching off any lights, leaving them all on all the time. But it is also based on my yield in winter, which may be different from yours.

You would confirm what your local winter output would be per watt of rated capacity.  (likely between 1.5 and 5 watt-hours per watt of rated capacity.

One would provide excess capacity in the battery to allow you to store extra power if it happens. Excess capacity in panels is expensive.

Answer 2

Are you living off the grid, or where there's no power available?

If you are currently hooked up to the grid- stay that way-using the grid as back up power, and assuranse of continuos flow of electricity. That way, you don't have to mess with batteries, just using a direct current to alternating current, converter. However this chinese guy at MIT ( yet ming chang,I believe), is developing a waayyy more powerful lithium ion battery that will make the current ones in use obsolete, as well as unsafe. There's also a lady making batteries from electrically charged nanobacteriological film, similar to the way the surface on an aboloney shell is made. There is so much exciting stuff going on at the eco-tech front right now. And the conservatives can't stop us all. The most conservative thing about them , I seem to notice, is their usage of brain cells, not to mention conservation of initiative. Very negative, indeed!! Too bad. They belong in the past, with the rest of the conservative minds of history. Keep up the good work. There is no way we can go wrong, AND we can only get better, the more we do it.