Energy Consumption Assessment

Here are the simple steps to perform an energy assessment for your project. An energy assessment is simply an evaluation of how much energy you use today and a calculation of how much solar power generation is required to meet the needs of your household or business. You can figure this out for yourself by answering three basic questions.

How Much Energy Do I Use?

Start with your monthly electric utility bill. Find the kilowatt hours or kWh used. Most utility bills will show the current month, the last 12 months and the daily average kilowatt hours used in the home or business.

For the upcoming calculation, you want to know the annual kWh used for the most recent 12 months. Make a note of this. It is also good to look at the monthly variance to understand your high and low consumption throughout the year. Also make note of the billing amount for each month to calculate payback and ROI later.

How Much Solar Energy Do I Need?

For most utility grid-connected homes, the amount of solar energy needed is between 80% to 120% of the annual kWh used. The difference really depends on the available space and your budget. More on these later.

For grid-tied systems, the solar panels will typically generate more power than is needed in the home during the daytime. Don't worry, your electric meter will spin backwards as the extra power is sent to the utility company. Known as NET-METERING, the utility will give you credit for the extra power. Then at night, when the solar panels are not working, the power comes from the utility, going against the credits built up during the day.

The solar panels will degrade about 20% over 25 years. You may want to oversize your solar array to allow for module degradation. Most utilities will allow 120% of the previous 12 months kWh consumption.

For off-grid systems, a more detailed calculation is needed to determine the energy load in AC kWh that will need to be supplied. This requires information about every device that demands energy - how much power it draws, how long and how frequently it is turned on. Start with a SOLAR DESIGN for help with an off-grid load estimate. 

How Many Watts of Solar Power Do I Need?

Using the the AC kWh from the electric bill or off-grid load estimate, go to the ONLINE SOLAR ENERGY CALCULATOR to determine how many DC watts of solar power are needed to generate the kWh. Once you know the amount of watts, then the number of solar panels can be determined. For example, if you need 1,000 watts or 1 kW of power, and you select 250 watt PV modules, then you would need four (4) solar panels.

Remember, you decide how much solar to get based on the need, available space and budget. There is no rule that you have to offset 100% of current energy use. Sometimes it makes better dollars and sense to start small and add-on later as prices are expected to decline. If you are a high volume utility user, you may be paying a higher rate for the larger consumption. Installing a smaller system to offset just 25% of your energy use may reduce the monthly power bill by 50%.