I am fascinated by the solar power monitor. As soon as the sun comes up, the solar panels start to make electricity. As the sun moves through the sky, the amount of electricity goes up. As clouds pass between the panels and the sun, you can see the watts go down and then back up. Our sky is partly cloudy right now, so the watts are going up and down as the sun peeks out and then goes behind the clouds. (If you look closely at the pictures on the right, you can see the batteries charged to 29.9 volts, sunrise at 07:03, and 2.9 kWH generated.)
I have not seen the watts go to zero when the sun is up and the clouds are thick. At a sunny 10:00 a.m, there are about 400 watts generated. If a hazy cloud goes by, the watts drop to 250 (see kW in second pirture). With a thicker cloud, the watts dip to 100 or so. At noon the system makes about 1000 watts if there are no clouds.
The solar panels made by REC are rated at 210 watts. With six panels, we theoretically should get up to 1260 watts. The installers told me the overall wattage could be as high as 1700. I’m not sure why there is a difference between the rating and the actual, but so far our system has gone as high as 1630 watts (see firs picture).
As you learned earlier, the refrigerator and freezer, according to the specifications, should be using 3 KWh each day. To measure what they are using, I found (with the help of a friend) this really cool gadget called a Kill a Watt. It is about the size of a wall plug and costs about $29. When you plug it into an outlet and then plug something into it, the Kill a Watt tells you how much electricity the device is using. After plugging both appliances into the Kill a Watt, I learned that they use 4 watts when the motors aren’t running, about 120 watts when one motor is running, and about 240 watts when both appliances are chugging away. In a 24 hour period, they together use about 3.5 kilowatt hours. I’m wondering if the ratings are inaccurate, or if the appliances have to work harder in a warm garage. Perhaps they will use less energy in the winter in a cold garage.
Overall the monitor reports that the system generates 5-6 KWh each day. I think that suggests the batteries need about 2 KWh per day to stay fully charged. Usually by noon or so, the system has already generated enough electricity to have to start discarding electricity. By 1:00 p.m. the system is making only 700 watts even though it could make 1200 watts. The system gets to 1500 only if the morning is very cloudy, and then the maximum wattage occurs about 2:00 p.m. Normally by 3:00 p.m. the system is keeping only 200 watts, even though there is plenty of solar potential.
If we spent a few thousand dollars more to hook the solar system into the power company, we could make use of all the energy generated in the panels. We could sell the extra KWh to the power company for 2 cents each. Like many things solar, it is just not worth it. I am hoping we can find other ways to use more of the energy without spending more money.