Note: The information contained in this periodical weblog may be outdated. This was my personal weblog published before January 1, 2015. Since then I have been the co-owner and Principal Solar Designer at Florida Solar Design Group.

Solar Rabbit vs. Solar Tortoise

My father-in-law who is a Professional Engineer made a very astute comment to me one day. He said that it is impossible to manage something without an accounting system. As a guy with a degree in Finance, I agreed wholeheartedly . But, he was actually applying this concept to energy. How can you manage your energy use if you don’t know what appliances and devices are consuming?!

In a previous entry I promised to discuss the power and energy needs of a hairdryer vs. a 60 watt light bulb. If you need a primer on the difference between power and energy, please read this post first…

A hairdryer is like the rabbit, using a lot of power for a short period of time. The light bulb is the tortoise, using a relatively small amount of power for a long period of time. For just about every appliance in your home, you can check the nameplate to see how many watts it consumes. Watts is a measure of power. Sometimes the nameplate will give you just volts and amps. To calculate watts, simply multiply volts x amps.


My wonderful wife has a hairdryer that is 120V and 10A. That means is consumes up to 1,200 watts when running. We already know that the light bulb consumes 60W. That means the hairdryer uses 20 times the power of the 60W light bulb! (20 x 60W = 1200W)

Another way of looking at it is that operating a hairdryer for 1 minute uses the same energy as a light bulb for 20 minutes!

The same concepts apply to solar electric energy production. In either case, light bulb or hairdryer, we need to produce the equivalent energy of 1,200W for one minute to cover the energy use. If your solar electric system is producing 4,800 watts of power, it would have to run for 15 seconds to produce enough energy for either the hairdryer for one minute or the 60W light bulb for 20 minutes.

Of course, these comparisons don’t work for everything in your home. Some appliances like ovens and fans use variable amounts of power. And others like refrigerators, water heaters, and pumps only consume power when running at intervals not readily or directly controlled. Nonetheless, it is important to understand how much relative power and energy appliances and devices in your home use to better understand your solar needs and establish an energy conservation plan. We need to account for energy use before we can manage it!

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