Panel effiency vs. panel cost

I have noticed "great deals" with panels of lower efficiencies with a similar same wattage as more costly and more efficient panels.

Does it boil down to price per watt or where does the efficiency factor become an issue? Low light/clouds etc.

Please advise.


  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Panel effiency vs. panel cost

    There's three basic types of panels: amorphous (least efficient), polycrystaline, and monocrystaline (most efficient). Within those types efficiency varies only a little from one to another. (false as only the poly and mono are somewhat close as amorphous is about 1/2 efficient as the other 2. niel) The Standard Test Condition ratings gives an analogous side-by-side comparison for Watts with which you can compare one to another based on price per Watt. After that the only issue is whether or not you can fit the physical size in the space available: the same Watts output will take up less space in for a monocrystaline panel than a polycrystaline one, with the amorphous units trailing far behind (about half as efficient as a poly panel).

    Otherwise there's no performance differences. Amorphous panels can have some quirks such as starting out with higher output and then degrading a bit to what should be their rating and some issues with longevity. As a rule they aren't very desirable. Between the poly- and mono- units it's pretty much just $ per Watt.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Panel effiency vs. panel cost

    Efficiency has to do with panel size. The more efficient the panel is, the smaller it is for the same output. So panel efficiency matters when the space you have to locate the panels is tight, or costly. The space that the panels occupy can also increase the costs of the install, because you need more mounting hardware and longer cables for a big space, than you do for a small space.
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Panel effiency vs. panel cost

    The cells that the panels are made of may have various degrees of impurities. The more impurities, the worse the performance. Mono panels are made of single crystal and therefore have less impurities and are more efficient. Poly panels are made of many crystals molten together and have more impurities and are less efficient. Although "bad" mono panel may be less efficient than "good" poly panel.

    The efficiency difference is small. For example, for 60 cell panels, the rating will range from 220 to 270. 270 panel will have less impurites than 220.

    If space is not a concern, there's no difference. Although some people think that panel deterioration is much more pronounced around impurities. If that's true, 270 panel has a chance to last longer than 220 panel, and capacity degradation will be slower in 270 panel too. I don't know if that's true or not, but I decided to go with higher efficiency mono panels just in case.
  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    Re: Panel effiency vs. panel cost

    Unless you have constricted roof space, what do you care about efficiency? What counts for most money constrained people is DOLLARS PER WATT. The high efficiency makers try to connect high efficiency with high quality. Its a bogus argument. The mainsteam makers all have great quality. However, do be careful about the specs given by some makers for their power output. Some of them play games (you can bet if its spec'd +/-3% that the actual output is close to -3%). Pick a maker that is most likely to still be here in 25 years, then get the best deal in terms of dollars/watt and forget about efficiency.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,468 admin
    Re: Panel effiency vs. panel cost

    Remember to include the mounts/wiring in the costs too--2x the surface area (amorphous panels vs crystalline), can add significantly to your costs (some folks used to use $1 per watt of panel for mounting costs--getting close to where the mounts are 1/3 to 1/2 the cost of installation).

    Regarding companies around in 25 years--I my panels were made by an oil company going big in solar... Now, not so much. :roll: Company still in business, solar unit is not (don't know what it will do for my warranty).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset