This report on our first year’s production of electricity by our roof-top solar panels could simply read: Each Watt of installed capacity produced 1000 Watt hours of electricity. Our 6000 Watt (6kW) system actually produced a little over 6,000,000 Watt hours (6MWh) of electricity. It really works great!
To go into more detail, as well as demystifying and simplifying solar photo-voltaics, read on. There are two types of “solar” electric systems: solar-thermal and solar photo-voltaic. Solar-thermal makes heat to create steam which produces the mechanical energy that spins a turbine generator which in turns creates electricity. Traditional power plants spin their generators with a flow of water (hydro-dams) or by steam produced by heating water by “burning stuff” (fossil fuels: primarily coal or natural gas) or by nuclear fission. Solar photo-voltaics immediately produce electricity directly from electromagnetic waves in the visible-light portion of the electromagnetic wave spectrum.
When we say “immediately produced”, consider this: although the sun is 93 million miles away from us, it’s light reaches us in 8.3 minutes (at the speed of light). That is 11 million miles a minute ,a speed fast enough to circle the globe 440 times per minute. Electricity travels at a speed relative to the field it is in, but we can safely say that it travels at least at half the speed of light (could circle the earth some 200 times per minute). So, as opposed to a traditional plant which obtains coal from Montana or Wyoming , brings it in by train, heats water to create steam, etc,etc,sends the electricity out into the grid; solar panels produce electricity practically immediately as soon as they are exposed to light.
The light: As we currently understand it, there is a wide spectrum of electromagnetic waves emanating from our sun. Large and slow waves at one end (radio waves) and fast, short waves at the other (gamma rays). As luck would have it, the visible-light rays near the middle of the spectrum possess packets of energy (photons) which are able to excite electrons of certain elements in such a way that they are freed from their atoms. Once directed in a “flow”, we have our electricity. It is worth noting that the visible light wave length and frequency making all of this possible is in a range somewhat around 500nm long (500 billionths of a meter , or 1/200th the diameter of a hair) and 500THz(500 trillion Hertz,which are wave intervals of 500 trillion per minute).
Our Sun's rays strike our planet with the capacity to produce 1380 W/square meter. The insolation of these rays is reduced by the atmosphere so that potential production is actually about 1000 W/m2 on the surface. If a standard solar panel is roughly 1 by 1 2/3 meter (3' x 5'), then it "could" produce 1666 W (1.666 x 1000). Since the normal PV panel is only 15% efficient, however, it typically can produce around 250 W (.15 x 1666).
Barlow's Mill has 24 panels for a total capacity of 6000 Watts (24 x 250W). Solar Edge DC power optimizers and an inverter manage the power and change the DC current produced by the sun to AC for transportation to the house.
Theoretically, if the sun “stood still” directly over a perfectly angled solar array of 6kW for an hour, we could produce 6kWhours of electricity. At our house near the 42nd. latitude in Fredonia, NY we get sunlight at various angles, various intensities depending on clarity of sky and for various lengths of time depending on the seasons. So, to make an easy to use average, let’s say we get an average of 3 peak hours of sunlight per day. 3hrs. X 6 kW system=18 kWh of electricity in a day. 18kWh per day X 365 days in a year = 6570 kWh/year. Our 6kW system underperformed by about 500kWh due to the extraordinarily long snow cover of last Winter and the cloudy, rainy month of June 2015.
The cost: systems priced in 2013 were in the $3.65 per Watt ballpark. The cost after New York and Federal incentives was around $1.30 per Watt installed (a savings of 64%). The New York average annual residential usage is 7000 kWh @ .18 per kWh. Do the math. It’s easy to see why 40% of all new electric generating capacity brought on line in the first half of 2015 was solar. Currently at 22.7 GW of capacity nationally, we have been installing over 1GW per quarter over the last couple of years!