Our electricity bill for the year was about $8, about double that of last year.
5 inches of rain. Big storm, strong, gusty winds. Wet, wet, wet. That is the prediction over the coming weekend.
I have been meaning to write a follow on to my hooked on solar entry, but have been stymied by the writer’s block, most likely brought on by Shanthala’s return to a punishing, unrelenting schedule. I wanted to put up an entry that showed how the solar panel performed over the course of a year. How close was the actual production to the specifications ? What factors affected the performance ? How did the performance vary through the day ? Through the year ?
A quick recap of the story. In the first year after the installation of the panels, our electricity bill for the entire year was $4.68, not including the monthly minimums (about $2 or so per month). The solar panels are 13 panels of Evergreen’s ES-A 205 panels with a Fronius IG 3000 Inverter. The solar panels were installed by Solarcity. As part of their service, they provide monitoring service with all sorts of relevant information captured and made accessible over the web. The information is captured by a device and sent every 15 minutes to the monitoring location. Via a web portal, I can access either graphs that summarize the relevant information or get the raw collected data. The following charts were taken from the web portal back in November, when I planned the followup to my original article on installing solar panels, so they’re a little dated, but since they tell the story across a year, their current age shouldn’t alter the story by much.
The Year’s Story
Here is a graph that shows the production over the past year. The peak production for the year occurred, naturally, in the summer months of June (490 kWh), July (496 kWh) and August (465 kWh). The worst production has been in the winter months of January (177 kWh) and February (225 kWh). So, the best months produced about double the energy of the worst months.
A look at the month’s data (the best and the worst) reveals:
During January, there is barely 10 hours of daylight and the cloud cover is an average of 51% (which hides the data that had some days of 100% cloud cover and a couple of days of sunshine) while in July, daylight hours average about 14.5 hours with an average cloud cover of only 23%. Only cloud cover during the daylight hours are taken into account in this statistic. So, you have days in January that barely show up in the chart while most days in July have energy production consistently upwards of 15 kWh.
However, if you look at two cloudy days, with the same amount of cloudiness (85%), one in the pitch of autumn and one in almost summer, the production is still quite significantly different as the following two charts show. The hours of sunlight and that the sun is higher in the sky during early summer probably explain the entire difference.
Other similarly cloudy days in May got far better performance as this graph shows:
If you compare a single bright sunny day’s energy production during a summer and a winter month, you get the graph below.
Sunrise was at 7.22 am on the winter day and sunset was at 5.02 pm. The corresponding numbers for the summer day were 5.55 am and 8.14 pm. Energy production peaked around noon on both days. Both the rise and fall in production are quite precipitous. The yellow line shows the production on a day when the cloud cover was 100%. The line barely manages to lift itself off the ground.
So, the lesson from this is that even though the total panel rating is 2.665 kWh, this number is produced around a very narrow spectrum of hours in a day (about 5.5 sun hours, according to this document). Further, the conversion from DC to AC (this is measured at the inverter) cuts the peak power from 2.665 to around 2.25 kWh, about a loss of 15%. According to this document on solar panel performance produced by USREA, system wiring and inverter losses by about 11%. System wiring losses include reduction due to varying performance of the individual panels. If a panel is rated as being 205W +/- 5W, then the production of that panel can be 200W or 210W. Eventually, the total production drops to that of the lowest performing panel according to this document. Evergreen panels state this problem specifically and say that is why they endeavor to keep their panel performance with only a possible upside, never a downside to the production i.e. our panels can produce 205-210 W per panel, but never lower than the rated 205W.
Actual Vs Predicted Performance
There are various tools out on the web that provide some measure of predicted performance based on some installation specific information and solar radiation data gathered over 30 years (1960-90) by NOAA. One such site is US government’s NREL(National Renewable Energy Lab)’s site on solar with its calculator called PVWatts. The detailed installation information provided by SolarCity enabled me to enter all the requested information to obtain the predicted performance data. Here is a chart that shows the predicted vs actual production (not including December) using San Francisco’s data (the closest point to Sunnyvale in the charts):
Like everything else that uses past data, the tool warns that it uses averages of the data and that the performance of any particular year can vary from the predicted performance by as much as 30% (+/-) on a monthly basis and +/-10% on a yearly basis. Still, like an investor looking at a single year’s return of his funds feels thrilled that they have performed well compared to the market indices, I felt somewhat gratified that the panel’s performance over the year has been a little better than the predicted performance. However, Sunnyvale is sunnier than San Francisco with a lot less fog. Oh! Well. The tool provides equivalent data if you stay in some other part of the country, say the Northeast or the Midwest.
Other interesting data provided by the SolarCity include the amount of CO2 offset by the solar panels (I presume this is based on assuming the saving had the equivalent energy been produced by conventional fossil fuels by the electric company) and the dollar amount of energy produced since the time of installation. As of today, these data are that the panels have offset 5,805 lbs of CO2 since installation and produced $816 worth of electricity. Incidentally, 5,805 lbs of CO2 is the equivalent of what 2.8 mature trees would offset over the same duration. Wow! All the CO2 that is offset by all this money (the cost of installing the panels) is matched by just 3 mature trees ?
That was our electricity bill for the whole year.
The story of this electricity bill began incongruously enough. Ever since we purchased this house, we wanted to get rid of the pool. We wanted a more usable backyard. When the previous owner of the house heard about our ideas for the pool, he called us up. He told us how the pool had been a labor of love for him, how he had constructed the pool with the best materials and equipment. He suggested some alternatives to get ourselves a bigger backyard such as extending our fence all the way to the sidewalk.
We were very new to the whole house owning experience and were warned of the dangers of getting poor quality on the pool removal. A bad job could, for example, result in the covered ground rising up like some ghostly swimming pool out for revenge when the rains began. Perturbed by the images that our imagination conjured up and daunted by another rather large expense after the most expensive purchase of our lives, we decided to keep the pool.
But the pool ended up nickel-and-diming us to death. It required some minimal maintenance to look clean and a little more than that to be usable. Based on a friend’s advice, we installed Polaris, a robotic pool cleaner. But that still required emptying the robot’s bag every other day or so, especially in the fall, when the trees stripped themselves bare. The robotic cleaner also didn’t get rid of the dust and grime that accumulated on the steps, which required that I scrub the steps with a brush. Scrubbing around the time the cleaner was on ensured that the dust didn’t just settle down again. Besides cleaning, I had to keep a constant supply of chemicals to keep the pool’s pH level appropriate. Mess up the pH and green algae would take hold, giving the pool a dirty, untended look, a real eyesore. Leave the algae a little longer and they’d become black algae which was even more painful to get rid of. The cleaning chores didn’t end there. The pool filter had to be cleaned, the skimmer had to periodically emptied, and the jacuzzi had to be cleaned separately because it was too small for the robotic cleaner to do an effective job.
In summer, the water evaporated and we had to constantly refill the pool with fresh water. I once forgot to securely shut the water and the water overflowed, out of the pool and into the backyard. Luckily, we caught it before it did any serious damage. And when the rains came, if it rained too hard and too long, the pool would overflow. So, we had to keep a pump handy to drain the water out of the pool if the pool’s water level got too high. The pool required that we filter the entire water at least once a day, which meant running a motor for about 8 hours every day to circulate all the water through the pool’s filters. Shanthala and I disliked the additional burden on water supply and electricity the pool created.
All this trouble would’ve been somewhat bearable if we used the pool regularly. We abhorred wasting electricity to heat the pool which meant the pool was usable only in the summer. The pool itself was not long enough to provide a decent lap distance. And since I was a bit tardy in maintaining the pool, when I wanted to swim, I had to first rid the pool of any detritus that had gathered since the Polaris had done its job, check that the chemical levels were appropriate and then start swimming. The net result was that I used the pool only a few times in the past decade. It got more use when our neighbors stopped by on hot summer days to cool themselves and their kids in the pool.
When Maya was born, the danger the pool posed to her finally tipped the scales in favor of closing the pool once and for all. Shanthala wanted to be able to roam the backyard, do her gardening and have Maya be part of the scene without worrying about the dangers of the pool.
A neighbor was redoing her pool and when we learned what a thorough job she had done in picking the guy for the job, we decided to hire her contractor to help us cover up the pool. It cost us half the amount we had originally thought that it might cost us and a month shy of Maya’s first birthday, the pool was gone.
The next step was covering the space with something. We liked seeing the green of a lawn, but loathed the criminal use of water that was the price of that sight. Shanthala investigated the pros and cons of artificial turf. After ensuring that the one we finally picked was free of any dangerous chemicals (we took the samples of the turf to a HAZMAT lab for analysis), we installed an Astroturf and got ourselves an eye-pleasing green backyard with enough room for Maya to run around and have fun.
Observing our green choices, the contractor asked us if we were interested in installing solar panels. He said that since the coming of Obama, the incentives for installing solar in residences had gone up. He was just getting his license to install solar panels and offered to do the job completely free of labor charges to gain the experience and show a reference to future customers.
Contrary to what many people think, I don’t view solar energy as solving the world’s energy problems. I suspect it will set off a whole different set of problems w.r.t. resource usage. Consider for example what it takes to make a solar panel. What materials are used in making it, what is the environmental impact of its manufacture, how long does it take before the panels produce more power than what it took to manufacture them. How long did the panels last and what was their warranty like ?
My investigations led me to Evergreen panels that were offered by a few solar installation companies. They were manufactured completely in the US and were therefore subject to far more stringent environmental laws than most of the world. Their manufacturing process had the lowest environmental impact compared to the other solar panels. Finally, in 13 months, they overtook the amount of energy it took to manufacture them by producing the equivalent energy; from then on it was a net gain. Fortunately, we live in a part of the world that enjoys gorgeous, sunny weather for most of the year.
Most panels come with two or three kinds of warranties. One covers the period that is labor free support (usually 5 years), one covers the period up to which the panels will produce up to 90% of their rating (usually 10 years) and a final one that covers the period up to which the panels will produce up to 80% of their rating (usually 25 years).
Our contractor meanwhile had teething trouble with his new venture and had to withdraw. But, we were already well down the solar road. We interviewed a few solar installation companies and settled on SolarCity. They were extremely efficient, doing most of the work on the telephone, dispensing with the sales pitch and glossy brochures. Using Google Maps they were even able to ask all relevant questions w.r.t the positioning of the panels on the rooftop and sent us a picture of what the final result would look like. Thanks to Obama, the feds offered a tax credit that was 30% of the total installation price (tax credit meant that we could deduct the amount from the total tax we owed independent of any cutoffs). Further, the local utility company offered us another 10-15% off the purchase price as part of California’s solar incentive program. So, even with the contractor withdrawing his offer of free labor, the difference in price between what he was charging and what we ended up paying was only about $1000 (though he was providing us with a higher wattage setup).
We found an experienced outfitter in SolarCity, one who was fully immersed in the modern world. For example, their initial inspection involved almost an entire day of determining how the cables would get laid out, how they would flow through the attic etc. All this work was photographed and made accessible to us via a password protected website. They also offered a monitoring service which again we could access to see all kinds of interesting statistics about the energy production.
Even before installing solar, our electricity bill was quite low. Despite living in a large 5 bedroom house, our average electricity bill was about $60 per month. Shanthala and I rarely turn on the air conditioner, we air dry our clothes (so almost zero use of the dryer), we never heated our pool and don’t possess many gadgets including any kind of TV. Based on our usage patterns for the past year, SolarCity estimated that we would need to install solar panels capable of producing 2.6kW.
Finally, at the beginning of November last year, the solar panels came on. According to state law, we would get credit for the excess energy that we produced, the credits accumulating up to a year. So, from November 2009 to October 2010, the credits would accumulate and in October, we would get a final bill that told us if we owed the local utility company any money or if we were net producers of energy. If we were net producers, we didn’t get any money back for the excess production. Starting January 2011, the local utility companies will also pay us for the excess production.
Is it financially a sound return on investment ? If you’re talking strictly about how many years is it before the installation cost pays off in savings over the electricity bill, we’re looking at a fairly long period, about 15 or so years, assuming that we made no changes to our lifestyle and that the electricity costs don’t change. This seems a long time for many, even those who are financially well off. But the very same people never question what is the payoff for something like installing granite or marble imported from some distant part of the world, or purchasing expensive furniture. Why is it that we ask a different set of questions about one kind of purchase versus another ? What aspects of our world view does this reflect ? For Shanthala and me, doing what little we can to reduce our carbon footprint so that our children may benefit from a more ecologically sound world (which includes their safety, BTW, because of the dangers of conflict due to resource crunches and effects of global warming) seems a sufficiently satisfactory return for our investment.