Although we have estimated that the average price for solar photovoltaic components in the previous article as USD4.00 per watt, that is the price for a single home installation. If we form a community and create a larger project, we can have even bigger savings. Solar photovoltaic panels are much cheaper when you purchase in bulk than you do personal purchase. In fact if we could grab the government incentives, we could have much cheaper price per kWh than the electricity from coal.
We just recently launch the ecogreen4us Community as one part of this website. One of the main purposes is for all readers to form local communities or local projects. It is a free service and for instance you could form a community for local solar project.
Share the idea and gain more knowledge from other members. Some members might already have an experience and they can help you on the topic. In this way, hopefully any green project could be developed without big mistakes. Let’s us check how to estimate the solar photovoltaic system for our home.
Step 1 – Monthly Usage of Your Electricity Bill
You have to check your monthly usage of electricity from your previous bills. There are few methods how to calculate this. The first and the most recommended method is to take the average in kWh of your monthly electricity bill.
For instance, if you keep your bill for one year or 12 months. You could simply sum all bills and then divided it by 12. Then you can get the average amount of power usage for 1 month. Please do not take the average of how much you pay for the bill rather than the average of electric power in kWh that you use.
This is a sample of an electric bill for one user. The user consumes electricity of 765 kWh for that particular month. If you have more bills for longer period, you also could use them because summing up for much longer period makes the accuracy even better.
Another method is to find the best month that your area has the highest solar potential energy. You simply pick that month and refer it with your previous electricity bill. That will be your reference for solar energy systems installation.
The highest solar energy potential from January till December could be referred from the NREL website. This information is for the United States. For other countries we could not find any available free sources from internet. Readers could check with local government websites or offices to find those numbers.
On the NREL page you could check maps under titles PV Solar Radiation (10 km)—Static Maps and PV Solar Radiation (40km)—Static Maps as reference.
Nevertheless, most people agreed that using the monthly average of electricity bill as the easiest method. It is very difficult to estimate by picking up the best month with the best solar sun hours. After you have the number then write it down. Now you have already the average monthly usage of electricity for your home.
Step 2 – Sun Hours or Solar Photovoltaic (PV) Resource
Please do not confuse with so many units and numbers. Another common or regular term for sun hours is insolation. Insolation is regularly calculated in MJ/m2, megajoules per square meter or J/cm2, joules per square centimeter.
This unit is recommended by World Meteorological Organization. Joule is unit of energy and insolation is a measure of solar radiation on a surface area and recorded during a given time.
Power (Watt) = Energy (Joule)/time
From this map you could estimate sun hours for your home. This map is produced by NREL and could be obtained from the same page that we mentioned earlier. Once you get approximately the value of sun hours in kWh/m2 per day then write it down.
We tried to find similar measurements for other countries which are freely available on internet. The nearest information that we could find is from solargis.info. Readers could check their website to find the information for sun hours. Try to adjust the measurements to be in unit of kWh/m2 per day.
Calculation of Solar Photovoltaic System
From step 1 your monthly electricity usage is = 765 kWh
Thus your daily usage is approximately = 765/30 = 25.5 kWh (divided by 30 days in a month)
Approximately 25% inefficiency shall occur in the solar energy system such as DC to AC conversion, battery etc. For that reason we need to add 25% more to tolerate with the inefficiencies.
Thus the number would be 25.5 X 125% = 31.88 kWh
Note: 125% after adding more 25% becoming 125%
For instance from the step 2, you obtained the sun hours measurement for your area is 6 kWh/m2 per day.
Thus if you would like to cover 100% of your home with solar energy system, you need solar energy system producing: 100% X 31.88/6 = 5.31 DC kW
If you would like only 50% of the electricity usage to be with solar energy then, you need solar energy system producing: 50% X 31.88/6 = 2.66 DC kW
1 DC kWh eliminates approximately 18,600 lbs. of carbon dioxide or CO2 per year. Planting a tree approximately eliminates 690 lbs. of carbon dioxide or CO2 per year. Hence if we use solar photovoltaic to generate electricity with 2.66 DC kW, we eliminate approximately 49,476 lbs. of CO2 per year and equivalent to planting 72 trees. Thanks for reading.