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Ask Renee: Calculating your solar power needs


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Hey Renee,

My girlfriend and I recently bought a home and we're trying to make it as energy efficient as possible. 

We're building a barn in the back yard, just something simple to put some gym equipment in. We plan on having some energy-efficient lights and a small space heater in there and we were wondering if it would be possible to run the building — at least partially — on rooftop solar panels and what steps we would take to get those setup on the structure.

Any info you have on setting up a solar powered operation at home would be a huge help! Also, would this give us tax breaks along the way?


Hey, Cavan!

On Tuesday, I shared a few thoughts on which type of system you might need to power your barn gym. Today, I’ll shed a little light on calculating the size of system to install.

First, find the wattage on the label for your space heater, lights and any other electronics you plan to use. The wattage will be listed as “W” and is the maximum power used by that device. I’ll guess that your space heater is 1,500W and you’ll use four lamps with 100W equivalent LED bulbs (actual 15W per lamp).

1,500 + (4 x 15)

That’s a 1,560W load.

Now, divide that by 1,000 to get the kW.


That’s 1.56kW.

Finally, multiply the kW by the number of hours per day you plan to use your heater and lights. Let’s say you’re an overachiever and spend two hours a day in your gym.

2 x 1.56

You’ll use 3.12kWh per day.

Rectify Solar* gave the ratio of 4-5 kWh per day requires a 1kW system. Based on this, I’d say you need about a .7kWh (700W) system.

Piece out,

*I manage a program for Hoosier Environmental Council called HEC Green Business and am very proud to promote these businesses who are good stewards of the environment and support the mission of HEC.


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