Russell's Blog

New. Improved. Stays crunchy in milk.

One year with solar

Posted by Russell on July 12, 2009 at 3:34 a.m.
A little more than a year ago, my mother installed 14 SunPower 230 watt panels on her roof. After a year of production, my mom's solar array has produced 5.3 megawatt-hours of electricity. That's about $1500 worth of electricity production.

Her actual use was about 3 mwh, yielding a surplus of about 2 mwh over the year. Rock on! Pasadena Water & Power won't actually write a check for the balance, but are carrying it forward indefinitely. Eventually, I suppose, they will figure out a way for her to cash in. I figure that someday she will be able to buy an electric car, and the extra production (plus the surplus stashed away in her utility bill) will go toward charging it.

Before installing the panels, she had whittled her electricity usage from about 32 kwh a day down to about 13. I thought it would be interesting to see the how things look now.

I decided to invert the Y-axis to represent net energy balance from the homeowner's point of view. Negative numbers represent net consumption, positive numbers are net production. The green region indicates the interval since the panels were installed. PWD bills on a bi-monthly basis, so unfortunately there are not very many data points.

The panels were installed in the middle of a billing period, so the first data point lifts away from the prior trend, and settles on a new trend. The third point in the green region -- the one that dips back into the negative -- is the middle of winter. Production was lowest, and my mom was running a space heater at her desk to keep her feet warm.

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