Monday, August 27, 2007

Solar PV Array: One Year Update

The question I most frequently get is "How are those solar panels working for you?" My response is usually "Just as advertised." With the panels being up and running for a year, it is worthwhile to look back and see how things have gone.

The expected amount of power to be generated monthly by the 2.5 KW system was included with the proposed installation. The calculation included corrections for the observed shading and average expected sunshine, but, of course, it couldn't put in the actual amount of clouds. Some differences are to be expected.

How has it done so far? In the figure below, the actual and predicted amount of energy is shown from June, 2006 through July, 2007. (Click to enlarge.)

The system was installed in May, 2006, so this month will be taken out of the following numbers. In the year 6/2006-5/2007, a total of 2471 KWh were generated with 2423 KWh expected. The worst month was Apr-07, down by 20% from average. This was also a record-breaking month in terms of the amount of rain.

In early May, 2007, we removed another one of our trees that was partially shading the solar panels in the morning hours. So far, the tree removal appears to have increased our output by 10-15%. The trend of enhanced power over epectation should continue going forward.

In terms of dollar amounts, we have saved $563.46 over the 6/2006-5/2007 period from the power costs (now $.17/KWh here in Fairfield County, CT!). This includes a 6 cents per KWh green-tag credit paid to us by MassEnergy. Return on investment appears to be over 5%.

The one difference from the proposal is that the power is less as a percentage of our usage as was guestimated in early 2006. We were still in renovation mode, and the amount of power we would use wasn't clear. Our use is significanly more than we were expecting, but that is mainly because of the geothermal heating and cooling. More on that in a later post.

One other interesting comment is that the spring/summer generation is about double that of the winter generation. That is a big swing. For most of the nation, peak power consumption is in the summer. Our peak power usage, however, has shifted to the winter season, again due to the geothermal heating.

In summary, then, the panels are indeed working as advertised.