The current billing period beginning on March 2, has been extremely productive. As you can see in the chart from my utility, the gray bars that dip below the 0 axis are the days my solar panels generated more than I used in my home. The statistics for the period are revealing. The overall average was 108 percent, which included a low of 41 percent and a high of 152 percent. 19 of the 28 days, the system generated over 100 percent of the energy used.
My electricity bill for the last 12 months is $540.70. That averages out to $45.07 a month. If I assume that my monthly bill used to average around $250 a month, that is an annual savings of $2,459.30 a year. My solar panels have been operational for 11 years. That means I have saved a total of $27,052.30 over the period. Add in the $17,600 incentive received from the state on installation 11 years ago and my solar panels have generated $44,652.30 over the past 11 years.
Here’s an update on the performance of my solar panels this year. My new mini-split A/C is paying dividends by allowing me to cool my bedroom at night to a comfortable level while keeping the rest of the house at a higher temperature. The days are getting longer and I am optimistic about the next three months, normally the most productive ones of the year.
People often ask how my solar panels affect my electric bills. My total cost of electricity for 2017 was $521.37. Here’s a chart from my utility that illustrates my monthly electric utility bills. Note that my average monthly bill is $45.
If one assumes that the average monthly bill for a south Florida home is around $200, then I have saved $18,600 in electricity bills over the ten years my solar panels have been in operation. If one assumes that the average home’s bill is $250 a month, then I have saved $23,600 in ten years. Projecting my system’s operational life out to 50 years shows a saving of nearly $100,000.
I’ve been running my house using my new air conditioning procedure. I turn off the central air for most of the day. I run the Mitsubishi, high efficiency, mini-split in my bedroom at night. In the morning I run the central air for about half an hour to take the humidity out of the house. It’s proving to be very efficient to operate this way. Yesterday, the solar panels on my roof generated 94.26% percent of the electricity needed to run my home. The days are the shortest of the year and many of them have been cloudy.
My new SEER30+ mini-split air conditioner has been operational for a few days now. I’ve been running it at night with my central air conditioner off. It’s difficult to say how much impact that has had in increased efficiency, but there is no doubt it has to have contributed greatly. Other factors to be considered are cooler temperatures and cloudless days. Looking at the percentage of electricity from my solar panels over the last ten days, and considering that these are the shortest days of the year, I can only conclude that it seems to be a big step in efficiency for my house.
Ten years ago, when we conceptualized our photovoltaic system as an emergency power source when the grid was not available. The plan included a mini-split air conditioner for the master bedroom. The idea was that during an extended grid outage, such as occurs after a hurricane, we would be able to power our house and have an air conditioned refuge powered by solar panels and battery backup.
Recently, Hurricane Irma caused a six day power outage and the system functioned wonderfully, powering the house day and night. However, the refuge room concept had not been implemented, even though planned for. Those hot sweaty days and nights motivated me to implement this final component in the system.
On Wednesday, November 14, 2017, JWair and Urban Solar installed a Mitsubishi, inverter based, SEER 30+, 9,000 btu mini-split air conditioner in my master bedroom running on a 240 volt dedicated circuit pulled from my two inverters.
In the weeks and months to come, I will be testing the system by running it on solar panels and battery backup. I will collect and publish data on its performance here. The unit will provide increases in efficiency by allowing me to turn off the central air at night and sleep with only the master bedroom cooled by the Mitsubishi. In extended outages it will provide air conditioning powered by solar and battery backup.
Milder daytime temperatures since the hurricane have reduced consumption from air conditioning, along with a lot of cloudless days have resulted in higher percentages of energy being produced from my solar panels. The chart on the right shows that over the last ten days, percentages generated from solar have been near seventy percent on average.