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The kW and kWhr of Your Home Solar System Explained

When getting a quote for a home solar system in New Jersey, solar companies will start using terms like kW and kWhrs.  

Most people will understand that these are units of energy, but what is the difference between kW and kWh, and how does that compare to appliances and items you use in your home everyday?

As far as the proposal from your solar company, the kW is the “nameplated” value representing solar system size.  This number is easy to determine. For round numbers sake, (20) 300 kW solar modules, will be a 6 kW home solar system.  This is simply the number of panels (20), multiplied by the panels wattage (300). A kW is also a unit of measuring power at one time.  One kW is 1,000 watts. Hypothetically, that 6kW solar system would be able to produce 6 kW of solar power in a given moment, assuming optimal solar exposure.  

The kWh number the solar company puts on your home solar system is a little different than the kW rating of the solar system.  

A kWh measures how much energy is being used or produced during a period of time. The 6 kW home solar system in NJ for example, may produce 7,200 kWh of solar power per year.  This is how much solar energy production would come out of the system over the course of 12 months. Generally, a home solar system in NJ will have 1.2x production factor, meaning the kWh number will be 1.2x the kW nameplate value of the system.  The production factor varies based on where in the world the solar array is located and the sun exposure, azimuth, and tilt of the solar array. In Florida, for example, that production factor may be closer to 1.5x. It makes more sense when you understand how your electronics use energy over a period of time.

For example, a 100 watt light bulb, on for 10 hours, will use 1 kWh of energy.  

We simply use the wattage of the electronics, in this case a light bulb, and multiply it by the time that it was on.  The 6kW solar system that produces 7,200 kWh annually, will be able to offset the energy used by the that light bulb for 7,200 hours in one year.  Of course, most of our energy will come from things other than light bulbs, so how does that compare? An electric oven for example may use 2.3 kWh per hour.  If the utility cost of electricity is .10 cents per kWh, then having that oven on for an hour cost the homeowner .23 cents. Green Power Energy uses a load calculator that was created by PSE&G to help determine what the kWh needs of a home may be during a given year.  This is great for a customer who just moved into a new home and doesn’t have any historical power data. We can count all the lights, account for the sq. footage of the home, count the appliances, and determine what the estimated kWh usage will be in the home and what size home solar system you would need to offset that amount.  The utility companies in NJ will approve the system to be installed based on this information, but will often wait until the household energy usage starts to be on pace with the assumption before given the formal approval to operate.

When analyzing the quote the solar company gave for your home solar system, remember that system size is different than system production.  Be sure to check with your utility company and ask for your “12 month kWh” usage. Make sure that this number is close or the same as the kWh production number shown by your solar company on their proposal, and have peace of mind knowing how that number relates to your energy consumption.

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