If the solar system generates more energy than is needed by the house, the excess energy is put into the grid, and Rocky Mountain Power (RMP) gives a credit for that energy. That is, RMP "buys" the excess energy at the rate charged the consumer for power consumed from the grid. RMP doesn't actually pay cash for the excess energy, but it does allow people to use that credit later on for energy. However, RMP zeros out the credit once a year in March, and all solar energy not used at that time is lost. Based on my reading of the RMP website, I think the credit for unused solar energy is zeroed right after the bill for March is calculated, but I'm not sure about this. If I'm correct, the -64 kwh (shown below) will be removed by RMP.
01/9/2016 The RMP bill now gives the amount of credit obtained due to solar power, and it states that excess power is to be used until the bill comes for 03/2016. This confirms that the excess power is zero'd after the 03/2016 bill. The 01/2016 bill stated 330 kwh are available, and that figure is the same as my calculated figure given below.
The figures shown in this post are the monthly difference between the energy taken from the grid and the solar energy given to the grid, and they come from the monthly bill received from RMP. These figures are negative when there is solar energy that has not been used and positive when all of the solar energy has been used but there is additional energy taken from the grid. As can be seen, the first bill to have excess energy was the March bill. That bill included approximately the last three weeks of February and the first week in March. However, starting with the last three weeks of June and the first week of July, the A/C used energy that wasn't provided by the solar system. Also shown in this page is the total credit for excess energy. This figure is the cumulative sum of the monthly credits.
Note: I've had my solar energy for over one year, and I have a pretty good idea how my installation works. Thus, I'm not updating this page.
Credit for
Month Excess Energy (Kwh)
December 2014 0
January 2015 0
February 2015 0
March 2015 -64 Zero'd by RMP
April 2015 -520
May 2015 -1182
June 2015 -1650
July 2015 -1621 A/C used during most of the month
August 2015 -583 A/C used during most of the month
September 2015 -1489 A/C used during most of the month
October 2015 -1593 A/C off most of the month. Dehydrator on.
November 2015 -1674 Starting to use our electric space heater
December 2015 -1266 Used our electric space heater a lot
January 2016 -330 Most of the month of December was snow & cold, space heater used
February 2016 80 Most of January and first week of February was cloudy and cold
March 2016 -80 A coincidence for "80" between Feb and Mar. Excess zero'd by RMP
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