Solar panel efficiency is simple, but there a few things you need to understand.
There are 3 main types of solar efficiency.
1. Module Efficiency
2. Area Efficiency (Density)
3. Cell Efficiency
1. Module efficiency measures how well a solar module (aka panel) converts the Sun’s energy into usable energy. If the Sun dumps 100 Watts of energy onto the module and the module spits out 15 Watts, the the module is said to have 15% module efficiency (15 W / 100 W = 0.15 = 15%). If you want to brag to your friends that you have a top tier efficiency panel, care about this. Read the rest of this entry »
To simplify solar efficiency further, we have divided all modules into 5 tiers based on their efficiency compared to all other solar panels. Now installers and consumers can easily communicate about module efficiency.
Are the solar panels in the most efficient tier (Tier 1) or do they have average efficiency (Tier 3)? If modules are in the least efficient tier (Tier 5), let’s hope they’re cheaper than the modules in the above-average tier (Tier 2).
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How much do solar panels decrease over time? The solar industry standard is a conservative estimate of 3% in the first year, and less than 1% per year after that. However, solar panel manufacturers are starting to realize that this is too conservative, and they are beginning to warranty their panels to more realistic degradation rates.
There are three points I want to make.
- Use the solar panel’s warranty to compare output loss over time because that is the only output you are guaranteed.
- Realistically expect less than a 3% decrease in output the first year, and about .5% decrease per year after that for most panels.
- One solar panel from 1979 was tested in 2010 (after 30 years) and its output was better than the original factory specs.
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Brad had a very good question that I thought needed to be explained in a post of it’s own.
I’m confused as to how a less efficient system (measured under PTC) could output more.
The simple answer is – if there are more of the ‘less efficient’ panels.
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My prospective supplier states that the Schuco 210 watt SMAU-1 panel has a cell efficiency of 16.8%, whereas your table gives a panel efficiency of 12.43%. What is the difference between panel and cell efficiency and which should be my guide?
Great question.
Confusing chart of solar cell efficiencies
Cell efficiency is measured as the percentage output of energy to the theoretical amount of energy supplied by the Sun (hitting the cell). So if 100 Watts hits the cell (under Standard Testing Conditions, STC, which is laboratory conditions), and it spits out 16.8 Watts, then the cell efficiency is 16.8%.
My table gives panel efficiency of how much output of energy (as measured by PTC, which is the realistic test conditions of a panel on a roof) to the amount of space that panel takes up in squarefoot area.
Your supplier is right, but if you want a point of comparison, ask him to give you the “cell efficiency” of all the competitor’s panels. What my table allows you to do, is compare all the panels (eligible for rebates in CA, which is more than 1,700) by the panel efficiency. Though our efficiency measurements are slightly different, mine are standardized across all panels using the data that CSI (California Solar Initiative) uses to pay rebates. So, you can easily see how Schuco 210′s compare to any other 210 panels (or 200, or 220, etc…)
Hope that answers your question. He’s not lying. I’m just giving you more information.
Occasionally, people ask me how to choose the best solar pv system, or the best panels. Choosing the best solar system depends mainly on your energy needs, roof space, and budget. Most people really want to know how to choose the best solar value. For example, I was asked the following question on my “Help me help you” survey:
I got bid from 2 different installers. One was SunPower panels; the other Canadian Solar. The SunPower bid (for a 5.2 kw DC system) was $21,000 and the Canadian Solar bid was $14,000 – why so far apart?
Great question. There could be many explanations why there is such a gap in the price. Generally, SunPower’s superior efficiency allows for it/ necessitates that it price its solar panels higher. (They have to pay for the best engineers to get the best efficiency, right?) Each installer may be giving you the best deal he can with both brands of panels. What you should check on both proposals is not the DC system size (in this case 5.2 kw DC), but the kilowatt-hours output. Ask your installer(s) how much energy (in kwh) each system expects to produce in the first year. Read the rest of this entry »
*UPDATE – Check out SRoeCo’s sortable, searchable Solar Panel Comparison Table.
This is a chart of the “Top 40 Most Efficient Solar Panels” available on the market today (11/01/09). All 40 most-efficient solar panels are from 2 companies: SunPower and Sanyo Electric. If you have limited space on your roof and budget is not a concern – these are the best solar panels on the market giving you the highest efficiency (greatest output) per area.
All of these solar modules are Monocrystalline clearly proving that this type of solar panel is the most efficient – more efficient than Polycrystalline and Thin Film. The panels listed at 290 kW and above all take up more than 17.5 square feet per panel. The solar panels rated at 230 kW and below take up less than 13.5 square feet. Read the rest of this entry »
Yes, some panels are more efficient than others, but that doesn’t mean that they are worth the additional cost.
Many people ask, “Which solar panel should I choose? Which panels are the best?” Though any salesman is going to tell you his panels are the best, the truth is that it is not easy to compare solar power panels and to firmly state that one brand stands out among the rest as the best.
The solar panel comparison chart I created below shows how difficult it can be to compare panels and brands. Listed are common panels between 190 and 230 watts of 5 common solar panel manufacturers (Canadian Solar, Kyocera, Sharp, SunPower, and Suntech).
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Two great questions many people ask about solar panels are: “Which panels have the highest efficiency?” and, “Which solar PV panels are the best?”
This solar power panel comparison chart below compares the density and module efficiency (huh?) of the most popular 200 W solar panels. All of the modules on this chart are label rated at 200 Watts, which means in strict laboratory conditions, they produce the same output. However, I have compared them based on their PTC ratings which is the rating given under realistic test conditions. Sanyo, SunPower, Canadian Solar, Suntech, Trina, Kyocera, Schuco, BP, Yingli and Sharp are common solar panel manufacturers used by installers in the US.
(Updated 12.11.2011)
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