LED Home Lighting Experimentation Part 1.

The best way to understand the intricacies of a simple home lighting using solar is to make one.
Let's start with "Solar Constant" Solar constant is a misnomer for it is not really a constant. The value varies between 1350 to 1370 W/sq. meter. Solar radiation received at any given moment is solar constant times the earth's cross sectional area. Since only half the spherical area is exposed to the sun, the area is Pi * Diameter Squared / 4. Where Diameter is earth's diameter. Average solar power per unit area is 1/4 of the solar constant.
So 1350/4 =340W/m^2. Out of this amount 30% is reflected back to the space and 24%-25% is absorbed by the atmosphere, only 45% reaches the Earth.

340 * 0.45 = 153 watts/m² or 153/3.28²  =14W/Sq. Foot.

Now consider the solar panel efficiency of 15%. One square foot of solar panel will have an output of 14 * 0.15 = 2.1W. This may be close to the peak power output say for example at 12PM, Clean crystaline panels and bright sunlight.

Now for LED lighting, the solar energy has to be stored and this media would be lead acid battery. 12V, 6AH battery at the charge rate of say 1/10 the capacity, would need 14.4V @ 600mA, which would mean one would need 8.64 Watts or approximately 2 * 2 =4 Sq. foot of Solar panel. This panel with the help of series parallel combination of PV cells and a switched mode Lead Acid battery charger would help charge the battery in approximately10 hours. I will consider the charger efficiency as part of the design in part 2.
10W worth of LED lights, from 72 VAH battery would give us 7 hours of light. LED lights being bright, we can even split the lights into three, three watt lights.
Panels retail today for about Rs. 100/watt. So one is looking at Rs. 800-1000/- in panels and may be another Rs. 500/- for the chargers. We will have to make our own LED lighting.

This is the first part that figures out the size of the panels required for a 10W LED project. In the next few days, I will write about both the battery charger and the LED driver.