Solar Panels-Part II

We will talk about some basics in this blog before we begin to put together our own solar panel system. A good article that explains the working of a solar cell can be read here. The solar energy absorbed by our solar cells then requires a storage, i.e. a rechargeable battery. Finally, we would need an inverter to convert direct current (DC) supplied by the battery to alternating current (AC) for majority of our household appliances.

I have started with building a stand-alone system for two reasons: Affordability and portability. We can move a stand-alone system from room to room as per our necessity, keep it in our vehicles, or take it with us while camping, boating, etc. It is also easier to understand the workings/components of a stand-alone system.

Let us take a couple of example and see how we can save some money:

How much does it cost to make our dinner? The menu includes slow roasted chicken and some fried greens. Suppose the chicken is roasted for an hour and the greens are fried for 15 minutes. The oven and the hot plate operates continuously at 1500-watt and 1200-watt respectively.
Power, P, (watts) = Current, I (Ampere) x Voltage, V (Volt)
Energy, E = Power, P x Time, t = 1.5 kW x 1 hr + 1.2 kW x 15/60 hr = 1.8 kWh
Suppose your electricity company charges you 10 cents/kWh
Therefore, the cost of making dinner = $0.1/kWh x 1.8 kWh = $ 0.18
Suppose you do the same for a year, therefore, the cost of making the same dinner for a year would be = $ 0.18 x 365 days = $65.70

So, if you use your battery and inverter to make dinner and then charge your battery through the solar panel, that'll save you $65.70 per year of electricity cost.

Think about how much you can save with a high capacity battery, inverter and solar panel. Of course, professionally built solar panels don't come cheap and that is the reason why one should sit down and make a reasonable estimation of their electricity consumption and evaluate how much time it may take to break even the investment in a solar panel system. It is also advisable to optimize the electricity usage with proper insulation, use of "energy star" appliances, and temperature regulation.

Now, let us calculate (roughly) the area of solar panels required for a house in Harrisburg, PA that consumes 1200 kWh per month or 40 kWh/day. We'll neglect the tilt requirement in this case. The cost of electricity is assumed to be 10 cents/kWh. Assume one solar cell in your panel has a peak power of 2 watts and is 0.125 square feet in area. Therefore, power per unit area = 16 watts/ft^2 or 172 watts/m^2 or 0.172 kW/m^2.
Assume that the average sun hours per day is 4 hours, therefore
Energy/day = 0.172 kW/m^2 x 4 hrs/day = 0.688 kWh/m^2/day

Required energy per day = 40 kWh/day

We'll multiply this by a factor of 1.2 to compensate for losses in energy in the battery and wires.

Therefore, required energy per day = 40 kWh/day x 1.2 = 48 kWh/day

Hence, the area of solar panel required (for the specified solar cells) = (48 kWh/day)/(0.688 kWh/m^2/day) = 69.8 m^2 or 751.3 ft^2.

Based on our example, we can infer that it requires a pretty huge panel or number of panels to go off the grid completely and a lot of us cannot afford to invest so heavily despite of tax breaks. What a lot of us can do though is to go off the grid partially and that's exactly why I am writing this blog so as to enable all of you to be able to build a stand-alone solar power system.

I would appreciate everybody's inputs. Please do correct me where I may have erred. We'll learn some basics of electrical circuits and battery capacity before starting to build a panel. Till then, have a nice day absorbing all this information. You can also visit some of the following websites for further reading...

http://www.eia.doe.gov/kids/energyfacts/sources/renewable/solar.html

http://www.nrel.gov/solar/

http://www.pvwatts.org/