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Solar Panel Comparison

Power (PTC)

The solar module`s DC power output under PVUSA Test Conditions:

  • Solar irradiance of 1,000 W/m²
  • Air temperature at 25° C
  • Wind speed of 1 m/s, 10 m above ground level
PTC is generally regarded as a better measure of solar panel performance because PVUSA Test Conditions are more realistic.

Power (STC)

The solar module`s DC power output under Standard Test Conditions:

  • Solar irradiance of 1,000 W/m²
  • Cell temperature at 25° C
  • AM of 1.5 (air mass)
  • ASTM G173-03 standard spectrum


A measure of how much of the solar energy that hits the solar module is converted into electricity under Standard Test Conditions (STC):

Module Efficiency (%) = Power (STC) (W) / [Area (m²) x Irradiance (1,000 W/m²)]

Note that the efficiency of any given solar panel is dependent on many different variables including, but not limited to, temperature, irradiance angle and wind speed. Performance is therefore not constant and will vary throughout the day and between seasons.

The efficiency of an individual solar cell is typically higher than the efficiency of an entire solar module.

Power Density

Power density under Standard Test Conditions (STC) is calculated using the following formula:

Power Density (W/m²) = Power (STC) (W) / Area (m²)

A high power density, which is typically what you will find in mono- and polycrystalline solar modules indicate high area-efficiency. These are the types of solar panels someone with a limited roof should choose. Thin-film solar panels have low power density.

Cell Type

Cell type refers to what photovoltaic technology and materials the solar module is based own:

  • Mono (Monocrystalline silicon)
  • Poly (Polycrystalline silicon)
  • CdTe (Cadmium telluride)
  • a-Si (Amorphous silicon)
  • a-Si + micro-c (Amorphous and microcrystalline silicon)
  • CIS/CIGS (Copper indium gallium selenide)
  • Ribbon (String ribbon – a type of polycrystalline)

String ribbon solar panels are no longer in production. The remaining types belongs to the category of thin-film solar cells, which typically aren`t good choices in residential situations.

The majority of homeowners either go with mono- or polycrystalline silicon solar panels.

Read more about the various solar cell types and their benefits in Which Solar Panel Type is Best? Mono- vs. Polycrystalline vs. Thin Film.

CSI Approved

Whether or not a solar module is compliant with California Solar Initiative`s SB1 Guidelines. Only CSI-compliant solar modules are eligible for incentives in California.

Manufacturer and Module ID

The manufacturer and ID of the particular solar module you are looking at. Module IDs typically include rated power in standard testing conditions (STC).

Length, Width, Area and Weight

These terms are all self-explanatory, but keep in mind that the values are based on the international system of units. Length and width are measured in millimeters (mm), area in square meters (m²) and weight in kilograms (kg).

Temperature Coefficient

The temperature coefficient of a solar module is a measure of output loss or gain per degree Celsius (%/°C) starting at STC (25°C). Solar panels based on monocrystalline silicon are slightly more heat resistant compared to polycrystalline silicon. Thin-film solar panels tolerate heat well.

Comments - 11

Alwyn John

Please correct the chart entitled “Cell Type Summary”, your have more titles than you do data.



January 14, 2013 5:53 pm Reply


What do you mean AJ? Please take a screenshot of what you`re seeing and link us to it.

January 14, 2013 10:46 pm Reply


Hi mathias,
AJ is right…

Monocrystaline is put on the wrong place.

M, thanks for the info. Great content!

January 16, 2013 4:38 pm Reply


Looks like this…
The Monocrystalline category doesn’t have any data.
Thanks so much for the helpful explanation.

January 19, 2013 7:05 pm Reply


Thank you Josh.

The content has been fixed and moved to this page: Which Solar Panel Type is Best?

March 31, 2013 8:26 pm Reply


There are a lot of errors in this ranking when you sort by Panel Efficiency. 315 to 310Wp Poly panels which use Qty 72 156mm cells do not produce panel efficiencies above 16% efficiency. Several are noted in the 17.5% range and above.

September 5, 2013 4:52 pm Reply


Should have added output voltage to that last request also.

September 17, 2013 6:39 pm Reply


Looking for solar panels 120 watt range, must have 5 yr min workmanship and materials warranty as well as power warranty at 10 and 25. Would prefer US made.


November 1, 2013 12:02 pm Reply

Ron Winton

Efficiency is almost meaningless when it comes to real world performance. A 300 watt high efficiency solar module puts out pretty much the same 300 watts as a 300 watt low efficiency solar module. If the 300 watt solar module did put out more power, it would be labeled at a higher wattage. The only real difference between the two, is the physical size of each solar module. The higher the efficiency, the smaller the footprint. What really matters, according to the California Energy Commission, is the solar module’s PTC rating. And Hyper X solar modules offer a higher PTC to STC ratio than over 100 of Sunpower’s modules. Hyper X also offers a better temperature coefficient rating than SunPower for better performance in hot climates.

November 14, 2013 1:35 am Reply


Finding the content herein pretty meaningless. Efficiency (as others have pointed out) is purely a product of STC/m2. Only real world comparison such as Photon Lab’s Outdoor Module Test is a truely comparative (useful) measure between panels.

July 25, 2014 3:23 pm Reply


There’s other useful data you could add if you want to go to the trouble. Great site thanks.
1) Bypass Diodes / panel
2) Pmax temperature deration
3) Wholesale $/W
4) links to datasheets


August 18, 2014 6:09 am Reply

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