Calculating Your Home’s Solar Power Needs
by: Jakob Jelling
Now that you know your total annual electric needs, you need to match them with a solar panel of an appropriate size. Note that solar panels have a peak rated output and an average rated output, and you will need to find out your panel’s average yearly output.
To make it simple: a 10 kW solar array will have a 12,000 kW/h estimated yearly output; if this panel is installed in a place like Philadelphia (this area has an average of 7 daily hours of sunshine).
So, a 10 kW panel can run a home that uses 12,000 kWh of electric annually in the Philadelphia area. What would the dimensions of a 10 kW system be? Its total area would be around 700-1,000 Sq ft. The array could consist of 48 smaller solar panels by 210 watts each.
Two important notes:
1. Estimated output of a panel largely varies depending on the geographical location of the home, as well as on the orientation of the installed panels.
2. Solar panel retailers often estimate the average output of a panel for the sunniest areas in the world, such as the Mojave Desert in California. They may estimate a10 kW panel output to be as much as 30,000 kW/h annually, which exceeds the normal value by 3 times (the 30,000 kW/h value would be correct for those who live in the Mojave Desert, and incorrect for those who live in a moderate climate area like Philadelphia).
Financial Aspects – Costs and Savings
How much money could a 10 kW panel save you annually, in terms of electric? An average standard grid electric rate in the US is $0.12/kWh. If we multiply 12,000 kWh by $0.12, we will get a total of $1,440 annually.
A commercial system of this size could cost around $30,000 (after all the rebates and tax credits, such as the 30% US Tax Credit). The system would pay for itself in around 20 years, and then start generating free electric. Building this system on your own could save you many thousands of dollars, allowing your system to pay for itself much-much faster.