Tuesday, November 25, 2008

Tardy Response

In response to a not-so-recent post entitled A Good Day I received some questions. Here are my tardy responses.

1. Do you have back-up power sources or do you depend on the grid during low wind periods?

The grid stops about ten miles from my house so I have to provide all of my electricity. I guess 90% of my electricity comes from solar and 10% from wind. I have a gas generator that I use occasionally. I probably run the generator an average of two hours per month. I'll not need it for three months or so and then need it a day or two to fully charge the batteries. I run the generator more in the summer during the monsoon season than I do in the remaining nine months of the year.

Solar array and wind generator.
Solar array and wind generator. The rest of the equipment (batteries, inverter, etc) is installed in the building. The gasoline generator is not in the building but is installed in an addition behind the solar array. (Larger version)

2. Do you ever get cloudy but windy stretches when the solar panels are weak but the turbine is spinning steadily?

Short answer: yes. There is some wind almost every day. There are periods when it's extremely windy with frequent gusts over 30 mph. There aren't many cloudy days. We get about 300 days of sunshine per year or close to 90% of all possible sunshine. On cloudy days and at nights the small wind turbine adds some power. Even if it's sunny the wind generator assists the solar panels until the batteries are almost full. Then the turbine will brake since it's set at a slightly lower voltage than the solar charger. If the refrigerator compressor engages then the wind turbine will begin charging until the refrigerator turns off. One of the ways I monitor my system is by watching the turbine. When I get home after work and drive up to the house I check to see if the blades are turning. If there's enough wind but the turbine is in brake mode then I know the batteries are full.

Solar array tilt adjustment.
Solar array tilt adjustment. Every two or three months I adjust the array to keep the panels aligned with the angle of the sun. (Larger version)

3. What's the wattage of your solar panels?

I have a one kilowatt array consisting of eight panels of 125 watts. I have them wired in four strings of 24 volts and installed on a pole mount. I've installed the limit for the mount and the charge controller. If I needed more electricity then I'd replace the charge controller rather than adding more panels. It's possible to rewire the panels for 96 volts and use a controller than can put more power in the batteries. It's a matter of newer and more expensive technology.

4. How much battery capacity do you have?

I have 900 amps. I installed sixteen batteries rated at 6 volts and 225 amps. Since it's a 24 volt system I have four parallel strings of four batteries wired in series. Thus, 4 times 225 yields 900 amps. Normally the batteries never drop below 80% capacity so I draw out about 180 amps after the sun sets. I've never let the batteries get below 65% capacity. When I'm down to about 70% I prepare to start the generator. The batteries are a little over four years old and aren't showing signs of decline. I hope to get eight years of usage before replacing them. Their lifespan depends on the care if give them.

A final note: If the power grid were extended to my house I wouldn't connect. I like living with wind and solar. Julie knows how to live with the system, monitor the batteries and use the gasoline generator. She's never equalized the batteries nor added distilled water. Those are my jobs. I spend perhaps one hour per month maintaining the system so it's neither difficult nor time consuming.


Anonymous Anonymous said...

I would like to know what appliances you are running if any.
Thanks for these posts - very helpful to know what folks are doing that works for them.

11/25/2008 03:45:00 PM  
Blogger Alex Pendragon said...

I'm just gonna go nuclear. I'm sure I can get North Korea to sell me a cute little reactor, just to piss off the neo-cons.

11/25/2008 06:55:00 PM  

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