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DayCreek Journal

June 15 , 2004

Harvesting The Sun's Energy

The digital electric meter has been installed, the contract has been signed and finally the sun is shining. To know that clean, renewable energy is powering our house and the surplus is going out on the wire to help power our neighbor's homes is quite liberating. This moment has been a long time coming and I have certainly learned a lot along the way. I've learned about procedures, politics, state laws, utilities, lawyers, utility commissions, big rocks, pry bars, head gashes, inverters, PV's, NEC chapter 690, proper grounding techniques, opto-isolators and edge-of-cloud effect. It's been quite an experience— A very enlightening experience.

So now that the system is up and running it will be interesting to see how well it performs vs. statistics for the area. According to our climate and latitude, the system should produce somewhere in the neighborhood of 460kW-hours for the month of June. As of today, it looks like we'll fall short of that number based on abnormally cloudy weather, but we should be able to generate at least 400kW-hours if trends continue.

So far, since the system has been in operation there has not been a completely sunny day, but on a mostly sunny day the system was able to crank out almost 22kW-hours of power. Partly sunny days have produced somewhere in the neighborhood of 17kW-hours, while completely cloudy, rainy days have produced as little as 3.5kW-hours.

Here's a chart showing the solar output from about 6:30 in the morning until 7:30 in the evening. The bumps in the line early in the morning are caused by the sun rising over the bluff behind the house. At about 9:30AM, the panels are in full sunlight for the remainder of the day. If it was a perfectly sunny day, a bell curve would be seen without any spikes.

One interesting note is the edge-of-cloud effect. Just as the cloud begins to cover the sun or when the sun is emerging from behind a cloud, there is a sudden burst of energy that produces more power than normal. This is caused by light refraction. On a day with bright blue skies and fair weather cumulus (cumulus fractus) clouds, the effect is quite noticeable as seen in the chart above. The spikes are caused by this phenomena.

That's about it for now. Don't forget this weekend is the Midwest Renewable Energy Fair and I will be discussing the "Evolution of our Double-Wall Cordwood House" on Friday afternoon at 4PM. Be there or be square!

If you would like to view up-to-the-hour statistics of the solar electric system, you can do so now by clicking on the snapshot image above.