The two most popular are SunPower and Sharp. Then, there’s a big drop off to Kyocera and Suntech. You won’t see BP’s number get any higher as the company has decided to shut down it’s solar division.

So, now that we know which solar panel brands are being installed the most, let’s see how difficult it can be to compare solar panels.

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.

2.  Area efficiency (aka Density) measures how much usable energy a module produces in a given area. It’s Watts per square foot, so the more Watts, the more energy you’ll get from a specific area (or available space on your roof). So if a module spits out 210 Watts in 15 square feet, it’s density is… c’mon, it’s Watts per square feet (and I made it an easy number). Okay, it’s 14 W/sqft (= 210 W / 15 sqft). If you have limited roof space, get the panel with the highest density.

3. Cell efficiency is measured the same way as module efficiency, but only with a single cell. This is the number news media and blogs love to tout in their headlines as ‘record breaking’ and ‘highest efficiency achieved’. This number is generally not useful for the average consumer. If you work in a solar cell lab, don’t give up on increasing this number.

So that’s the basics of solar efficiency. Now, let’s make it even simpler by dividing solar panels into 5 Efficiency Tiers (or levels).

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).

You no longer have to worry about the 4-digit efficiency value and wonder what it means. Is 13.81% efficiency good, bad, or average? Now, you can simply consider the Tier ranking of the solar module. A 13.81% efficiency is Tier 3, so it’s average efficiency! That simply means it’s in the middle 20% of efficiency (40 -59%) compared to all eligible modules.

Tier 1 Efficiency modules are in the top 20% of efficiency of over 7,300 modules eligible for California solar incentives. They are more efficient than 80% of the other solar modules. Basically, the smart ones in the efficiency class.

Tier 2 modules are more efficient than 60% of all other modules, while Tier 3 have basically average efficiency. Tier 4 is below average and Tier 5 modules are in the bottom 20% in terms of module efficiency.

How efficient are your solar panels?

“Below average, but I got a good deal on them.”

“The most efficient, because my roof space is limited.”

“My panels have average efficiency and my installer did a great job!”

There are three points I want to make.

1. Use the solar panel’s warranty to compare output loss over time because that is the only output you are guaranteed.
2. Realistically expect less than a 3% decrease in output the first year, and about .5% decrease per year after that for most panels.
3. One solar panel from 1979 was tested in 2010 (after 30 years) and its output was better than the original factory specs.

First, the industry standard for solar output warranties is 90% output in year 10, and 80% output in year 25. This is the 2011 warranty for companies such as JA Solar, First Solar, Yingli Solar, Canadian Solar, Sanyo, and Sharp. Right now there is not enough data to know reliable degradation rates after 20-25 years, so you must rely on manufacturer warranties in order to compare expected solar output losses over time.

Now, most solar panels won’t degrade this much. This is just want the manufacturers will guarantee. So, some manufacturers are starting to update their warranties to set themselves apart from the competition. Here is a list of the best warranties available from major solar panel manufacturers.

1. SolarWorld and Trina Solar both offer linear performance guarantees which basically means that they are guaranteeing only the small decrease for each year up to 25 years. Technically, it protects you a little more. Check both of their websites to see how they explain it.
2. Suntech protects you at year 5, 12, 18, and 25, which gives you more protection than the standard.
3. Sunpower warranties 90% to year 12, which is 2 years longer than the standard.
4. Every other solar company is the standard – 90% at year 10, and 80% at 25.

Here is a chart comparing the solar output warranties of 10 major companies. Click to enlarge.

Lastly, solar panels will last for more than 30 years. They were originally designed to withstand the conditions in space and to be used in remote places without electricity access. There are no moving parts in a solar panel. The cells are encased in metal and glass frames designed to withstand hurricane winds, rain, hail and other extreme weather conditions.

Martin Holladay bought a panel back in 1980 that was manufactured in 1979. In 2010, he tested the output of his solar panel for the 30 year anniversary. It performed better than expected, returning 97% of the original voltage and more amps than the spec sheet said it should output originally. You can read more here.

Solar will last a long time. Expect a 2% decrease when you install them, and then a reasonable 0.5% per year after that. Let’s hope this article helps improve the 2011 industry standard warranties.

Solar Manufacturer Warranty Documents

Notes: 1. Trina Solar has two different warranties for Mono and Poly modules.
2. Manufacturers were chosen based on 2010 market share and name recognition.

1. Suntech - 2011 and 2010
2. JA Solar
3. First Solar
4. Yingli Solar
5. Trina Solar
6. Sharp
7. Canadian Solar
8. Sanyo Electric – HIT Series
9. Sunpower Solar
10. SolarWorld

Related Articles:

1. Solar Efficiency Losses Over Time - Chart comparing solar manufacturer warranties and explanation of how much you can expect solar output to decrease over time.

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.

Solar Apples Metaphor

At the supermarket, there are two types of apples for sale. They taste EXACTLY the same. There is no quality difference – only a size difference. One type of apple is big and the other is small.

• -You can get 3 big apples for $6. The amount of apple you get is 600 grams (200 grams/big apple).

• -You can get 4 smaller apples for $5.50 and the amount of apple is 640 grams (160 grams/small apple).

Yes, the bigger apples are more efficient – there’s more to eat per apple. But the farmer needed to spend a little more effort to get the apples bigger, so they cost a little more. The smaller apples are easier for the farmer to harvest, so they cost a little less than the big ones.

If the apples taste exactly the same, came from neighboring farms in the same delicious apple-growing region, and you only wanted to get the most apple for your buck, then the smaller, cheaper apples are better a deal.

I believe the same holds true for solar panels that are equally warrantied by their respective manufacturers.

Less Efficient Solar Can Be Better

Efficiency only matters when space is limited. If you want to get the most output of a limited space, then you’ll want the most efficient solar panels. However, if the area available for solar isn’t limited, then you can fit a few more ‘less efficient’ panels on the roof and possibly add up to more total output than the ‘more efficient’ panels.

For example, you could have 22 ‘less efficient’ panels that produce 7,100 kWh and cost $35,000. Or 20 ‘more efficient’ panels producing 6,800 kWh per year costing $40,000.

Or you could have 28 of each, but the ‘less efficient’ panels actually take up more space, but end up producing more than the ‘more efficient’ panels. They are ‘more efficient’ because they produce more in the same (or less) area, not necessarily more overall. Look at the ‘Area’ row in the chart below.

It’s just like the apples. Don’t let the salesman try to convince you that you should buy the big apples because there’s more per apple. Just buy a few more smaller apples and get more apple for a better price.

Now, you might be thinking that the ‘more efficient’ panels will produce ‘better’ energy. It all comes from the Sun, so there’s NO difference in quality of energy produced.

But maybe the ‘more efficient’ panels will produce more over time because they will degrade less. Ask your solar installer the details of the warranties for the panels. She’ll probably say both the ‘less efficient’ and ‘more efficient’ panels are warrantied for 90% output for 10 years, and 80% for 25 years. Until they guarantee more output overtime, that’s the same taste.

Less efficient can be a better deal.

Related posts:

1. Solar Comparison Table
2. Top 40 Most Efficient Solar Panels
3. Most Efficient Solar Panels

Yes, I recommend signing up with them, even if you don’t go solar with them.

Original link

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.

The good news is that Pacific Gas and Electric (PG&E) and San Diego Gas and Electric (SDG&E) have received enough California Solar Initiative (CSI) applications to install solar that they have reached the maximum amount for Step 6 in the incentive scale. Current and future applications to install solar for customers of these two utilities will be eligible for the Step 7 incentive rate of $0.65/watt DC.

Pacific Gas and Electric serves most of the residents living in the upper two-thirds of California, while San Diego Gas and Electric supplies electricity to approximately 3 million people living in and around San Diego County. Combined, this represents about half of California’s current electricity customers.

The bad news is that for those customer in these areas who decided to wait to install solar after April 2, 2010 will receive 40% less of a rebate.

For example, a customer who decided to install a 6 kW solar system before April 2 may have received a rebate of about $5,346. However, the next door neighbor who waited until after to install the same 6 kW system will only receive a $3,159 rebate. That’s a difference of more than $2,000 in solar rebate money for waiting only a few days.

The CSI incentives were designed to “step” down over time as more solar systems were installed in a utility’s area. As the cost to install has dropped, so have the incentive rebates from the utilities.

There is still money to be had as there are 215 MW available at Step 7, but if you wait too long, the next step will drop your rebate down to $0.35/watt. To see how much it might cost to install solar, check out the Solar Calculators at SRoeCo Solar.

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.

Then, divide the total cost of the system ($21,000, or $14,000) by the amount of energy produced. This will tell you how much money per kwh you’ll be paying. If money matters (which to most people it does), then choose the solar system with the best VALUE!

Another visitor asked:

Should I be looking for the panel that has the highest efficiency or for the panel that produces electricity at the lowest rate?

If space is a concern, meaning that you have very limited space and want to produce as much energy as possible, then look for the highest efficiency on the Top 40 Most Efficient Solar Panels chart. However, most people will consider price as an important factor. Therefore, for most people, I recommend choosing the panel that produces the most electricity (kwh) at the lowest cost.

It depends what is most important to you. If saving space is important (rarely the case), then choose the panels that have a smaller area. If saving money, while maximizing output (energy production) is important (usually the case), then choose the solar pv system with the best value.

Related Articles:

• Five Questions You Should Ask Before Installing Solar
• Five Financial Reasons to Go Solar Now
• Solar Panel Comparison Article
  

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