My Experiences with Solar Electric and Solar Hot Water Systems
An energy management consultant since 1974, Andrew Rudin shares his personal accounts, the good and the bad, with using solar panels to generate electricity and to heat water.
I have been an energy management consultant since 1974. Before suggesting that someone buy an energy-saving gadget, I evaluate that gadget myself. In this article, I describe some of my personal energy-saving gadget experiences.
My Solar-PV System
In 1998, I got interested in solar PV. Earlier that year, our local combined electric and gas utility (PECO Energy) changed its electric rate to allow net metering for solar-electric systems. Net metering eliminates the need for batteries, which increase system maintenance, generate combustible hydrogen, and decrease system electric production. Electrons move into the grid or into our home/office, depending on the amount of available sunlight and our need for electricity. My 2.7kW system started operating in July 1998. It was pictured on the cover of Home Energy magazine's Sept/Oct '02 issue.
The system cost $26,180 -- about the same as a new car. I received two turnkey bids from contractors, but I thought the prices were too high. I hired a solar system designer -- Ron Celentano—and ordered the system components from California suppliers. Hundreds, if not thousands, of PV systems had been installed in California. I hired a roofing contractor to install the panels and a commercial electrician to wire them. At that time, there were no rebates. I took advantage of the federal 10% tax credit. Since the system is installed on a home/office, it also qualifies for accelerated depreciation, but my accountant at the time didn't know that. So I lost my first (and greatest) tax advantage that first year. I replaced that accountant with one who brought in a check from the IRS for $3,645, for accelerated depreciation in the second year. That, plus a couple more years of accelerated depreciation, reduced the initial cost to about $19,000. The only maintenance cost on the system so far has been $100 to find and replace a blown fuse, which is amazingly low for such an expensive investment over a dozen years.
The electric metering is complicated. In late February 2002, the utility replaced a single net meter (one with a disk that moves one way or the other, depending on how much the sun is shining and what my electric loads are) with two electronic meters, with digital displays on the rear outside wall of my house. The In meter measures the electricity that comes into the home/office, and the Out meter measures the electricity that goes out. Since the Out meter is wired in reverse, both meters display positive values as the power passes through either one or the other. Since I am interested in net metering, I installed an additional conventional disk-spinning meter, so I could observe which way the power was flowing (the disk spins backward or forward). To visitors who may not understand solar-generated electricity, the backward spin of the disk inside this meter is the most visible (and often remarkable) evidence of what the system does.
From the beginning, I have had a fourth electric meter that measures all of the kWh produced by the PV system. This fourth electric meter is the solar meter. In June 2001, I replaced the standard kWh solar meter with one that also reads maximum kW power production. In the basement, I also have a standard electric meter that measures all the electricity that the home/office uses, regardless of whether it comesfrom the grid or from the solar-PV system. I read these five meters every day; on the 15th and last day of each month, I record the data on a spreadsheet. I record the solar peak kW by resetting the solar meter and subtracting the reading, estimated to 0.01 kW (10 watts), from the reading that I took the last time I reset the meter. When I am away on vacation, I read the meters when I return and prorate the kWh for each day. The peak kW would be the peak for all of the vacation time.
On the roof, there are 36 75W British Petroleum (BP) panels. When the sun hits them, they generate direct current (DC) electricity that is collected by wires that travel through the roof to an inverter in the attic. The inverter does three things. First, it collects all the DC electricity and converts it to the alternating current (AC) that the home/office uses. Second, it receives the frequency of the AC power input from the utility and synchronizes its AC output to correspond. And third, it increases the voltage of the solar-generated electricity by a few volts above the utility voltage, which is enough to move electrons back into the grid, if the electric load is satisfied in the home/office. When sunlight is barely sufficient the inverter makes a quiet thumping sound, which stops when the sun is either too dim or sufficiently bright for the inverter to generate alternating current. Unless I am hearing that sound, or watching the electric meters, I can't tell that the system is working.
Because I receive solar renewable energy credits (SRECs) from my utility, I make about 13¢ for each kWh that my system generates, whether I use it in the home/office or not. Since May 2005, I have sold my SRECs to the Energy Cooperative of Pennsylvania for about $2,400. (In 2009, for example, our net cost of electricity and gas was $385 for the year.) As part of the deal, I buy 100% renewable energy from the cooperative.
Table 1 shows our annual kWh use and PV production for the years 1999 through 2010. The average of the kW readings is the average of the bimonthly peaks for the year, with a few less than 24 bimonthly meter readings to account for summer vacations. The average peak numbers show that the base kW is not that different from the average kW. I found this interesting because it shows the peak production for the year is not that different from the average of the bimonthly readings for the whole year. The peak for the year is the maximum of the readings. Table 1 does not give figures for 1998, because that was a partial year. There were no kW recordings until I installed the demand meter in June 2000. The ups and downs in production are likely due to changes in solar irradiation, atmospheric clarity, and cloud cover. The overall trend since I installed the system, however, has been a 33% reduction in generated electricity and a 17% reduction in peak generated kW.
The columns on the right are the number of days each year that the panels did not generate 1 kWh and the percent change from the previous year. Note that this number increased by more than 550% as the panels aged.
The electricity we use in our home/office has been consistently low. The average home in PECO Energy's service territory uses about 7,200 kWh per year, so at 2,289 kWh, we use less than 1/3 of the average. Not bad for two adults, five computers, a home entertainment center, and all the usual appliances. We use natural gas for space heating, cooking, clothes drying, and heating domestic hot water (DHW).
Not So Simple Payback
I look at payback in several ways. Simple system costs payback is a very weak reward for me, given the extensive publicity the systems have provided—publicity that, I hope, has furthered the cause of renewable energy. I installed the solar systems as part of an effort to improve my lifestyle. I gave away my car at about the same time as I installed the systems, saving me about $6,000 per year. All this happened after I talked with some Amish farmers in Lancaster, Pennsylvania. As you probably know, they refuse to be connected to a utility grid, or to own or drive a car. They do this, not because they are looking for payback, but because they believe that to live simply improves the quality of life for their families and communities.
Since the utility installed its two new unidirectional meters in February 2002, they have measured 14,144 kWh coming into the home/office and 12,466 kWh going out, over about nine years. So let's assume that the home/office requires about 190 kWh per year more than the solar-electric system produces. The current price of electricity, based on my October 2010 electric bill, is $0.216/kWh. This includes electric distribution, transmission, and transition, and the premium renewable-energy supply. Essentially, I have a feed-in tariff agreement, since I pay my renewable-energy supplier for all of my electric usage. Each year, then, I pay about $41 per year at current prices.
The Energy Cooperative of Pennsylvania has paid me about $2,400 since June 2002 (6 1/2 years) for about 17,500 generated kWh (the SREC I get from PECO). At 13¢/kWh, my generation pays about $350 per year. Subtracting the $41 I pay PECO, my net annual gain is about $310 per year. So my simple payback is $19,000 divided by $310, or 61 years. I am not sure what the life of the array will be. BP has backed off its warranty, so I doubt it would replace a bad module even today. It is possible that the system could keep working for many, many years—just at much lower production than I was getting to begin with (see "Not So Simple Payback").
In addition to lowering electric costs, the system also paid off in other ways. About three years after the PV system went on line, the Philadelphia Inquirer asked me for an interview. They were doing a story about three independent power generators, and I was one of them. The other two, however, didn't want to be included in the article. So the front page of Philadelphia's main newspaper (circulation about 380,000 copies at the time) on Wednesday, May 9, 2001, had a picture of me, with the PV panels in the background, and a very flattering article.
I was a local hero. A few days later, I received a call from NBC's Nightly News with Tom Brokaw. After two days of videotaping, I was featured in a 41-second segment about my system on May 17, 2001, just after a segment in which George W. Bush announced his national energy plan. At the time, a 30-second ad on this program would have cost about $55,000, according to a local ad agency. So my segment was worth about $75,000, if I had bought the airtime, never mind the production costs. The impact of that segment on my reputation was huge. I was now a national hero.
Around 2000, Pennsylvania began a solar-PV grant program with funds originating from a rate case settlement from PECO Energy. Although it had little to do with my PV system, they hired Ron Celentano, the guy who designed my system, to run the program, and he hired me to help, working part-time. From April 2004 through January 2009, I earned just over $20,000 in consulting fees. Without a doubt, my system paid for itself -- and not only with money saved on electricity.
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