Unlike passive solar panels (which generate heat to warm water or the living space), I have photovoltaic solar panels (which directly generate electricity from sunlight).
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0. Are you generating heat or electricity?
Unlike passive solar panels (which generate heat to warm water or the living space), I have photovoltaic solar panels (which directly generate electricity from sunlight).
1. How long is the payoff period?
It depends on how efficient the panels remain and how much electricity is worth in 20+ years, but I estimate 20-25 years. The panels will continue to operate for decades after that, but they will slowly become less efficient. Their useful life will end when their efficiency becomes so low that it would be more economical to install brand new panels with whatever new technology is available, probably in 40-50 years. So after the 20-25 year payoff period, the amount of money I save on my electricity bills will equal the amount of money it cost me to install the system, and all electricity generated after that is income.
2. How much does a solar system like this cost?
I had the main system on the house roof professionally installed. The installers generally charge a flat rate of $7-$10 per watt (which will include all parts, labor, fees, etc). For a system the size of mine, this is like buying a new car, except instead of continually paying for gas and maintenance, this system will pay me on every month's utility bill.
To help offset the costs, Wisconsin residents can apply for a cash rebate from Focus on Energy of 20%-25% of the installation cost. (Other states may have similar programs. Check DSIRE for a list of currently active incentive programs in your state and at the federal level.)
Also, the federal government's Energy Policy Act of 2005 (which was extended through 12/31/08 by Tax Relief and Health Care Act of 2006 and again extended through 12/31/2016 by Emergency Economic Stabilization Act of 2008) will provide a tax credit of 30% of the installation costs (after subtracting state or local incentives such as Focus on Energy). For systems installed in 2008 or earlier, this tax credit was capped at $2,000, but the Emergency Economic Stabilization Act of 2008 lifted the cap for systems installed in 2009 or later.
The small system on the garage was installed by me. I already had the inverter and batteries, so I only had to buy a solar panel (it retails for about $700, but my installer gave me a discount, because I was buying so many for the house), a charge controller (about $90), and some miscellaneous electrical components (less than $100 of junction boxes, fuses, connectors, etc.).
3. How much do you earn?
We Energies has approved my installation for their
Solar Buy-Back Rate, guaranteeing me $0.225 for every kWh generated for the first 10 years. After that my payback will fluctuate at the market rate for electricity (currently about $0.14/kWh, according to my recent utility bills). (Note: This buy-back rate is no longer available to new solar installations as of October 10, 2008, because the program reached its capacity.)
The Milwaukee area historically receives the equivalent annual average of about 1665 hours of full sun at 37° tilt (calculated with PVWATTS). Assuming some typical losses (including shading) of 20%, my array could generate an average of 1665*3.72*0.8 = 4957 kWh per year. So, I could earn about $1115 per year for the first 10 years, and (if the current market rate remains constant forever), $694 per year thereafter. Of course, solar panel efficiency will decline over time, and electricity market rates will rise, so these are just estimates.
Ignoring the first partial year of operation (which was affected by the "flat-top" problem described in the "Daily Performance" section of the Performance page), my array actually generated 4043 kWh during the first full calendar year of operation. Assuming the amount of sunlight received was equal to the historical average, this represents losses of 35%. This extrapolates to $910 per year for the first ten years, and $566 per year thereafter.
4. Why does We Energies pay you more than it's worth?
Utility companies are under pressure to include more renewable energy in the mix of their power sources. (For example, Wisconsin has mandated that its utility companies must generate at least 10% of their power from renewables by 2015.) Solar energy is particular appealing, because its peak generation is on sunny summer days, when the utility load is highest (mostly from all the air conditioners). However, the payoff period is so long that it is hard for a utility company to justify it, from a business perspective. So, We Energies gives private individuals an incentive (reducing our payoff period), which encourages us to take on the risk of the long-term investment, so We Energies can buy our renewable energy and claim it as part of their mix.
5. How much do you use?
During the first twelve months the system was in operation, my home used a total of 4779 kWh, and this system provided 85% of my electricity needs. I expect that could increase to as much as 90% in the next year or two. Seasonally, I use a lot more than I generate during the summer (when my air conditioner is running) and winter (when snow cover and low sun angle reduce generation), but I am a net generator in the spring and fall.
6. What's your annual carbon savings?
According to the most recent EPA eGrid2006 data (compiled in 2006 from data submitted by utilities in 2004), utility companies serving my subregion create 1.556 lb of CO2 for every kWh of electricity generated, mostly by burning coal.
In the first three years of operation, my system generated 12075 kWh, so I saved the equivalent of 18789 lb of CO2. More accurately, this amount of energy I generated onto the utility grid meant We Energies didn't have to burn coal to make that energy, so I prevented We Energies from liberating an additional 18789 lb of CO2 into the atmosphere during these year.
This means my annual carbon savings (averaged over the first three years) due to the solar panels is 3.1 tons.
7. That's a lot of money and a long payoff period. Isn't it a drastic step?
Yes. Before considering a solar electric system, you should do everything you can to reduce your consumption. (I have installed many Energy Star appliances, replaced most of my light bulbs with compact fluorescents, added a lot of insulation to the house, and replaced most of the windows.) You should also consider a solar thermal system or a wind electric system, both of which are cheaper to install and have shorter payoff periods. (These aren't effective solutions for my site.)
8. What does "grid-tied" mean?
Solar panels can only make electricity some of the time, so you need to be able to store the excess energy generated during sunny days for use during cloudy days or at night. One way to do this is with batteries: a "stand-alone" or "off-grid" system. However, batteries are expensive, require maintenance, and need to be replaced every 5-7 years, so this really only makes sense for rural systems that are far from a utility grid.
Instead, most urban systems are connected to the local utility's power grid: a "grid-tied" system. These systems sell surplus energy to the grid during sunny days, and buy energy from the grid when needed, essentially using the grid as a giant, free battery.
9. Then why do you have a stand-alone system on your garage?
The garage system is mostly for fun, to see if I could put together a small solar system by myself, and to put some old batteries to a good use. It also makes sense to use it for recharging cordless tools, whose "wall-wart" transformers are constantly plugged in, parasitically drawing power continuously to keep the tool ready at all times, even though I only use the tool a few times a month.
10. What does "parallel generation" mean?
Grid-tied systems can be connected to the utility company through one meter ("net generation") or two ("parallel generation"). When there is only one meter, it runs forward on cloudy days and at night (when buying energy from the grid) and backwards on sunny days (when pushing surplus energy out to the grid). Therefore, you're always buying energy at the same price as you're selling it to the grid.
However, We Energies' Solar Buy-Back Rate purchases my energy for a higher price than the price they are selling it back to me. In order to price the energy differently, it needs to be measured independently, so you need two meters. One meter always runs forward, measuring how much energy I'm using, night or day. The other meter always runs backward, measuring how much energy I'm generating, regardless of consumption. My bill will show both numbers. If I use more than I generate, I pay the difference. If I generate more than I use (and if that amount ever accumulates to more than $100), I get a check for the difference.
11. Do your panels track the sun?
No, although trackers increase the array's output by as much as 30%, they increase the installation cost by at least 25% and require regular maintenance for their moving parts. My house roof's pitch of 37° up from horizontal is nearly ideal, so I decided to go with a simpler, fixed, flush-mounted system.
Note: the theoretical ideal pitch of a fixed system is equal to your latitude (about 43° here), but Wisconsin skies tend to be less cloudy in the summer, so it is better to be pitched a little less than your latitude to take better advantage of the sunnier months.
12. So, you'll still have power if a storm knocks out the grid, right?
Not really. The house's inverter is designed for grid connection. It seeks to match its output voltage and phase to the grid's power signature, so the grid must always be present. If the grid goes down, the inverter immediately stops generating power and goes offline. This is a safety feature; otherwise, it would be energizing the lines that the utility company's linemen will be shortly trying to repair. Part of the utility company's final approval involved testing this feature to make sure the inverter's output went dead as soon as the AC disconnect was tripped.
However, the stand-alone system on the garage will provide a small amount of power in case the utility grid goes down. It won't power my whole house, but it will run small loads (such as my Energy Star refrigerator) for a short time.
13. What if you need to re-shingle your roof?
The panels and rails would need to be removed first, and then re-installed after the roofing job is done. However, I had my house roof re-shingled in 2004 and my garage roof in 2005, so the roof should outlast the solar system.
14. Will you have to shovel snow off the panels?
Not really. Snow is translucent, so enough light gets through to start making electricity. This causes the PV cells to warm up, melting the bottom layer of snow, and then whatever remains just slides off. In general, this happens around noon on the first sunny day after the snowfall. However, there have been a few exceptions. One nasty storm in late November 2008 included dense snow and freezing rain, resulting in a hard cap of ice and snow that couldn't slide and took over 10 days to melt. Another time in January 2009 we had a light snowfall but extremely cold temperatures (the daily high temperatures were 0°F), so the heat generated by the panels wasn't enough to melt the snow, until it finally warmed up to 20°F a few days later.
15. Will you have to wash the panels?
Supposedly not. It's a problem for an array with little or no tilt, but at my tilt angle the force of the rainwater is supposed to be enough to rinse off any accumulated dust.
16. How much of your roof is covered with panels?
As much as physically possible. Each of the big panels is 15.2 square feet, and each of the small panels is 10.0 square feet, so the total amount of roof space covered with panels is 283 square feet. According to my measurements, the roof has a total of 428 square feet of flat, south-facing surface (i.e. after subtracting the footprint of the dormer), so 66% of the available space is covered with panels.