Sunday, October 21, 2007

Demo Solar Panel Performance

We had a freakishly warm and sunny weekend (for late October) here in Chicago, which allowed me to put my solar panels (snap shots here) out in the sun.

Each solar panel is rated to produce approximately 36W (according to my supplier) and each panel has 36 cells, which means each 5" x 2.38" cell must produce roughly 1W.

The maximum theoretical power increase from my design is 40%. Since my acrylic mirrors only reflect 87.5% of the light that falls on them, the panel I'm testing will at most produce a ~31.3% power increase over a standard panel with the same number of cells (assuming everything else is ideal).

One additional note is that the the panels were wired slightly differently, in the standard panel the voltages from each strip of cells add up, in my panel the currents add up. This means that you really need to multiply the voltage x the current to get the power produced to compare the output from the two panels. (My solar panel supplier says this wiring difference was a mistake.)

The bottom line is my demo panel produced between 12%-27% more power than the standard design depending on orientation to the sun.

The first two tests I ran with the panels placed on a small step forming ~5-10 degree angle with the ground.

Standard design
Voltage = 19.4V
Current = 1.75A
Power = 34W

My design
Voltage = 5.0V
Current = 8.0A
Power = 40W

17.6% increase

Standard design
Voltage = 19.3V
Current = 1.99A
Power = 38.4W

My design
Voltage = 5.07V
Current = 8.47A
Power = 42.9W

11.7% increase

The good news is that my panels are clearly producing more power than the standard design, but I was somewhat disappointed that the increase was on average ~1/2 what I was hoping for.

I realised that I basically had the panels pointing straight up at the sky when the sun was clearly down in the sky. So I decided to run one more test with the panels pointed more directly at the sun.

Standard panel (at ~45 degree angle)
Voltage = 20.0V
Current = 2.3A
Power = 46W

My design (at ~50 degree angle)
Voltage = 5.13V
Current = 11-11.4A*
Power = 56.4 - 58.5W

22.6 - 27.1% power increase

*I clearly read values between 11.4-11.5A (w/ some slight fluctuation) but after a big gust of wind nearly knocked my panel over, I found my readings only reached 11A. I didn't think of it the time but following the gust the panel may not have been realigned properly, in any event I'm reporting both numbers. In both cases, it is clear that my design registers greater out performance when pointed directly at the sun.

Some people express concern that concentrating sunlight onto a solar panel may "overheat" the panel and impair performance. I added a thermo-chromic temperature strip to each panel which measures temperate in 5 deg.C steps between 25-100 deg C (77-212F). The temperature showed the panels at about 40C (104F) most of the time I looked at them(after several minutes of warm up time in the sun) . If the air became very still for several minutes I sometimes saw my design creep up to 45C (113F). The ambient temperature was in the 70s both days (the weather service predicted about 5 degF higher on Sunday than Saturday) although Sunday was much windier. A modest increase in cell operating temperature may occur using my design, especially if there is no wind.


At 5:41 PM, Anonymous Jonathan Cole said...

Hi Daniel,

reflecting light on the panel with a mirror has been done before. My understanding is that you can put up to 1.5 suns on a panel without long-term degradation effects. That is half what you are doing with your setup. Other important issues are that light which does not hit the panel at a 90 angle to the surface has proportionally less energy. Another is that solar panels can last for 40 years, but not many mirrors can. Certainly no plastic mirrors. Also, your system would have to have the whole rig track the sun, which is difficult to achieve, because a tracking device that would last for 40 years would also be very expensive. It is probably cheaper and less headache to have a fixed flat panel and just spen the money you save not buying a tracker, to get additional panels to make up for the lower energy capture.

Jonathan Cole

At 2:00 PM, Blogger danielisimon said...

Hi Jonathan, thanks for your comment.

I'm very interested to hear that up to 1.5 suns is ok with degradation. This design puts up to 1.4x sun on the cells (on average maybe 1.3x).

I'm afraid that I do not understand the comment about light angle and energy. Do you mean that solar cells are not able to convert non-normal light as well, or are you simply saying a surface at 45 degrees to a source intercepts 1/3 less light?

This panel does not need to track the sun if installed with the long mirror-cell axis running east west. (Because the sun goes through 180 degrees of sky that way everyday.) The seasonal variation, ~45 degrees, is captured by installing the solar panel so the cells face the sun directly at the winter solstice (i.e. the panel is normal to the sun at the summer solstice).

Since my proof of concept panel does not have a cover, it may not be clear from the picture but both the cells and the mirror have a cover to protect them from the elements. I see no reason why an enclosed mirror would not last for many decades.

I have no doubt that people have used mirrors to reflect light onto panels before, my idea is new (& patent worth) because it incorporates the mirrors within the panel as described.

At 2:02 PM, Blogger danielisimon said...

"1.5 suns is ok with degradation"

should read *without* degradation


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