Solar Myth Busters - Revisited
We had another highly successful show in Miami this year, with a lot of interest in our solar offerings, but we still find it necessary to spend considerable time with interested parties having to explain the what’s what of solar power for boats. Evidently there is still a lot of misinformation out there on the subject, so this seems like a good time to re-hash one of our most popular blogs from many moons ago. Here follows a list of ten myths and busts in an effort to set the record straight.
MYTH 1 - Glass solar panels with aluminum frames are the most efficient.
BUST - No, no, no! The type of cell determines how efficient a solar panel is, not how it is constructed. Coastal Climate Control offers three types of panels:
- aluminum-framed glass panels,
- razor-thin walk-on panels, and
- flexible panels, primarily for installation in canvas areas like biminis, dodgers, etc.
All three types are available with the same high efficiency cells, now with around 25% efficiency, and so they are comparable in efficiency as complete panels. Glass panels are the more common and least expensive, but not necessarily the most efficient.
MYTH 2 - You can’t walk on solar panels.
BUST - In theory you can walk on any type of solar panel, but either you or the panel, or both, might not be very happy with the outcome! You definitely don’t want to walk on aluminum-framed glass panels, but other types are designed specifically to be walked on, like Solara’s Standard and Power M series. These are specifically designed and constructed to mount directly onto a deck and be walked on (no high heels please!). Some other manufacturers say that you may “step on” their panels occasionally, but exactly what that allows is open to interpretation.
MYTH 3 - The wattage rating of the panel indicates how many watts it will produce when it is in sunlight.
BUST - Oh, if only! No, the wattage rating of a solar panel is what it theoretically might just possibly produce in the highly unlikely event that absolutely perfect conditions exist. The Standard Test Conditions, known as STC, are a defined amount and quality of sunlight, plus a specified cell temperature, and these conditions are replicated in a testing machine where panels get tested. STC conditions are akin to being on the equator at midday on the equinox with the temperature at zero degrees.
MYTH 4 - So, to estimate the daily yield of a panel you take, say, 80% of the watts rating times 6 (hours sunlight) right?
BUST - There are just too many variables to come up with a definitive formula to estimate daily yield, and different cells work differently in low light, low sun angle, and high heat conditions. Having worked the numbers many different ways, we came up with the following general guidelines, which so far have proved to be quite accurate.
- For panels with genuine, high grade SunPower® cells, divide panel wattage by three for daily 12v amp/hour yield.
- For panels with standard monocrystalline cells divide wattage by four, and
- For panels with polycrystalline cells divide wattage by five.
Those numbers assume a “good” solar day with a full-time load. Remember; no load - no solar output!
MYTH 5 - Those totally unrealistic wattage ratings are used as an intentionally misleading sales gimmick.
BUST - Actually, solar panels are rated that way so that if a number of them are connected together in an array, the wiring, fusing, and other components can be sized accordingly for the theoretical highest possible output. It’s a safety issue. Boring, I know, but it makes sense.
MYTH 6 - Whatever wattage a solar panel is advertised to be, then that is what it produced when tested.
BUST - Ha! No way! No two cells or solar panels are identical. The watt rating is a nominal rating for that batch or design of panel, and will vary within the manufacturers’ published Power Tolerance. If a 120 watt panel has a negative Power Tolerance of -10%, it might be capable of only producing 108 watts at STC conditions. Most of the marine panels that Coastal Climate Control offers have negative Power Tolerances of -5% or even 0%. Positive Power Tolerances are not really relevant unless you really want to believe that your pet panel might produce 10% or more than its rating!
MYTH 7 - There will be much better, more efficient and less expensive cells and panels available soon.
BUST - There has been very little progress in silicon solar cell efficiency over the past 25 years, and nothing will be happening any time soon. There are some exciting new developments in other solar technologies, like thin-film, but they are still lower efficiency than what we have now, and are still in the research phase and so a long way from being available on the general market. Cost seems to be the driving factor, as once the efficiencies of the new boys in town approach the sort of numbers we have now, the focus shifts to lowering production costs. It’s a very, very competitive market, with a lot at stake. Remember Solyndra?
MYTH 8 - Any shading will shut down the output of a solar panel.
BUST - It’s all proportional. Gentle shading will reduce a panel’s output a little, while heavy shading will reduce the output to greater degree. Shading on one portion of a cell will not reduce output as much as shading an entire cell. Unless a cell or group of cells is completely covered (totally shaded) by an opaque object like canvas, a towel, bathing suit, Albatross poop, etc., there will still be some output from the panel, and the amount produced will be proportional to the amount of shading.
MYTH 9 - By-Pass Diodes prevent loss of power from shading.
BUST - Another popular misconception. No, By-Pass Diodes are a safety device to prevent cell and panel damage from the effects of a cell or group of cells being total shaded. Silicon solar cells will actually consume power when shaded, and if there is enough power produced by the other cells in the panel that are feeding the shaded one(s), the result can be a burnt cell, panel, and/or boat. By-Pass Diodes shunt power around the section of panel that is shaded, lowering the panel’s output voltage, but preventing hot-spot damage and a possible conflagration. The marine panels that Coastal Climate Control offers feature two integral or external By-Pass Diodes, each protecting one half of the panel. Many of the lower-cost panels on the market have only one By-Pass Diode protecting the whole of the panel, and that lack of adequate protection has been seen to have resulted in some serious cell-burning.
MYTH 10 - Solar is a bit of a joke on boats as it can’t do much except to give the captain some feel-good greenie vibes.
BUST - Rubbish! Use the best panels with the highest output and you could very well cover all your daily power needs. Buy select, true, marine panels with worthwhile marine-specific warranties (all marine panels offered by Coastal Climate Control have a 5 year marine warranty), and you won’t be looking to replace them after a couple of years of salt-water douches and similar grueling treatment. It was due to the fact that we hear far too many sad tales of woe concerning low-cost panels that we formulated our mantra: Do it once- Do it right.