In your research trying to understand solar power, you feel like solar panel efficiency is something you should be able to easily grasp. Efficiency should be easy to understand, right? Except the deeper you dig, the more confused you get. What’s the difference between solar cell efficiency and solar panel efficiency? Who can you trust when it comes to solar efficiency?
I got an email from someone purchasing solar panels from a supplier asking the difference between these two efficiencies. Helping people understand questions about solar is the whole point of this website, so after I answer a question via email – it often ends up here so that more people can learn.
Here’s the question:
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 14.93%. What is the difference between panel and cell efficiency and which should be my guide?
Are you looking for the most efficient solar panel available in 2014 to put on your roof? Here are the top 20 most efficient solar panels actually available for sale (on the market) – not just tested in a lab. All of these modules (solar panels) are eligible for incentives in California, which means they’ve been tested and have a minimum 10 year warranty against defects and undue degradation.
Of the top 26 most efficient solar inverters 20 are SMA inverters. Only 26 individual solar inverters are rated at either 98 or 98.5% efficiency (which is the highest efficiency for inverters). SMA has been around since 1981 and seems to be the clear leader in manufacturing top-of-the-line inverters for solar applications.
So, the Sun shines on Earth and in that sunshine there is energy. Plants convert that energy into mass because energy is mass. E = mc2. Energy equals Mass times a constant (which is not important here). We eat the plants for energy, or we eat animals that eat the plants. That’s how we survive.
Well, solar panels are humans’ attempt at making “plants” that convert the Sun’s energy into energy we use – to heat, chill, or light our homes, to power our TV’s, fridges, computers, etc. Well, it’s not easy converting that sunshine into energy we can use. And as it turns out, most solar panels convert 12-15% of the Sun’s energy that falls on the panel. The Sun dumps ~1,000 W/m2 at sea level on a clear day (source: wikipedia).
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.
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).
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.
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.
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).