In a thread during the week about solar panels fitted with mirrors for sale on ebay I promised to do a
test this weekend. Here are the results.
The Myth:
Adding a mirror to a solar system increases the power available.
My Setup:
A Solarex SX50U Panel (poly crystalline)
P.max 50W
V.oc 21.0
I.sc 3.23
2 x 35AH Gell Cell batteries wired in parallel at about 80% SOC.
The weather was warm and
bright with passing high level cloud (shadows still slightly visible).
The panel was wired directly to batteries without a regulator. I put a clamp ammeter over the positive lead and a multimeter set up across the battery terminals.
The area between outer boundaries of the cells on the solar panel measured 400 square cm. The only mirror I could pinch (from my wife’s dressing table) was 221 square cm.
The panel was set up normal to the incoming sunlight and everything left out for an hour to heat up (panel disconnected from the batteries!). The mirror was adjusted to throw its full reflection onto the panel. The panel surface temp at the start of the testing was 38.2 C measured with an infrared thermometer:
Image Could Not Be Found
To make the transition from mirror OFF to mirror ON I used a tarp I could flick off the mirror quickly while photographing the meters:
Image Could Not Be Found
The Results.
Under light cloud:
No Mirror:
Image Could Not Be Found
With Mirror:
Image Could Not Be Found
Full Sun:
No Mirror:
Image Could Not Be Found
Mirror:
Image Could Not Be Found
So in summary the results were:
No mirror under light cloud: 40.0W (14.09V x 2.84A etc)
With mirror under full cloud:48.0W
Improvement 19.9%
No mirror in full sun: 52.97W
With mirror in full sun: 58.2W
Improvement 9.9%
I repeated this several times both under cloud and full sun with similar results.
While I have some doubts about the absolute power reading in full sun (52.97W from an unassisted 50W panel albeit in ideal conditions) the deltas are interesting. Given my mirror was only 55% of the panel size and hence only added illumination to just over half the cells the increase in power is significant – especially under light cloud.
So:
Myth Plausible.
As you would expect.
I assume a bigger mirror matched to the panel size would give a better result. That reflective mylar sheet could be a good starting point for a light weight reflector.
For me this is all academic as I already have a 160W folding monocrystaline panel that keeps my Waeco and other electrical stuff ticking over quite nicely with my 70AH of gell cells. And yes I do normally use a regulator.
Buit it is interesting.
OK, helmet on, sandbags up, flak vest on, prepared for incoming fire.
Cheers
Pete