Determining the Renewable Energy Source for You

Sizing a Solar Electric System to Fit Your Needs

In reality, the process for determining the size of your solar electric system is the opposite order of what we just went through in the previous example. First, you determine how much energy you need on a daily basis in kilowatt-hours (kWh). This data can be found on your electric bill on a monthly basis if you have one for your location. Otherwise you will need to go through the process of estimating your energy consumption. We offer a "load" calculator in our How To section, or alternatively you can print out and use our load calculator that's located here in our How To section. To estimate the energy usage on a daily basis, take your monthly estimate and divide by 30.

Second, you need to determine the solar insolation value for your site. If you're going to be totally disconnected from the electric grid/utility company then you will need to use the minimum (worst case) solar insolation value for your location. If you're going to be feeding your electricity into the electric grid then use the average solar insolation value.

Lastly, you need to divide your estimated daily energy usage (kilowatt-hours) by the solar insolation value and multiply by an system inefficiency factor:

Total Watts of Solar Electric Panels Needed = [(Daily Kilowatt-hours)/(solar insolation)] x Inefficiency Factor

The ineffiicency factor for systems that are disconnected from the electric grid (off-grid) is 1.3. For systems that are connected to the grid (also called on-grid, grid tied, grid intertied or grid connected) that value is usually assumed to be 1.2. The reason that it is higher for off-grid systems is that these systems have to store the energy in battery banks which are not perfectly efficient. Most on-grid systems either don't use batteries at all or use them in such a way that their inefficiencies are minimized.

Choosing the Solar Electric Panels Right for You

Now that you know the total wattage of the solar electric panel array you need, it's up to you select the specific solar panels that will make up this total wattage. For example, if determined that for your home you needed a total of 2000 watts of solar panels and you decided you liked Kyocera 130 watt solar electric panel then you would need 16 of them (2000 watts divided by 130 watts = approximately 16 panels, rounding up to the next whole number).

People make selections of solar panels based upon many different factors. Some people prefer only larger solar panels (150 watts or above) because it means they have to do less wiring in interconnecting the panels. Others choose moderate size panels (80 to 120 watts) because they're easier to lift and manuver. Other people will choose panels based upon color, electric properties, whether or not the manufacturer is a petroleum company, which country the panels are manufactured in, whether the panels are immediately availablity and, of course, price per watt plays a big role for most people. Review the many solar panels we offer and speak with one of our sales people to help you refine the solar panel that best suits your needs.

• For more free educational information on solar electric power, see our How To section on solar electric systems, by clicking here.