Solar cell output - Page 1
Forum section: electronics / beginners

author: MikeK
author_rank: Super Contributor
timestamp: July 17, 2012, 01:12:01 am
content: I picked up a small solar panel (80mm x 125mm) from Radio Shack and can't get it near the expected current output. It's quoted as 250mA, but the best I can do in full sun is 150mA.I noticed that the cell has 24 "sections", so I did some measurements this evening, under a desk lamp. I found that at least 4 of the sections have almost no effect on the current output and a couple more have not much effect.Is this normal, about what I can expect from a Chinese solar cell from Radio Shack?

author: IanB
author_rank: Super Contributor
timestamp: July 17, 2012, 01:18:45 am
content: I don't know--but what's the part number? Radio Shack has many small solar panels.

author: MikeK
author_rank: Super Contributor
timestamp: July 17, 2012, 01:39:35 am
content: It's this one:http://www.radioshack.com/product/index.jsp?productId=12628239

author: amspire
author_rank: Super Contributor
timestamp: July 17, 2012, 02:01:49 am
content: Quote from: MikeK on July 17, 2012, 01:12:01 amWhat part of the US are you in? Unless you are somewhere near the Mexican border, you never get a full strength Sun. More energy gets absorbed by the atmosphere before it reaches you. If you were living in New York, 150mA peak may be all you could expect from a 250mA panel.

author: MikeK
author_rank: Super Contributor
timestamp: July 17, 2012, 02:09:44 am
content: About 40 degrees N latitude. I hadn't considered it, but that makes sense. Thanks.

author: IanB
author_rank: Super Contributor
timestamp: July 17, 2012, 02:24:19 am
content: That panel has an area of about 17 sq in and a claimed maximum output of 1.5 W.A typical solar panel has an output between 50 and 90 mW/sq in, with most being around 70 mW/sq in.To get 1500 mW from a 17 sq in panel would require 1500/17 = 88 mW/sq in.It's probable that panel is optimistically rated. Maybe the peak output is only achieved under direct overhead sun at the equator on a clear day.

author: KTP
author_rank: Frequent Contributor
timestamp: July 17, 2012, 03:18:12 am
content: As other have suggested, your insolation (this is the correct term) is probably not optimal to get the 250mA but those near dead cells worry me. They could be actually stealing power.On a side note...does anyone find it sad that RS condensed the entire electronics section to just 3 sliide out drawers?

author: digsys
author_rank: Unknown
timestamp: July 17, 2012, 03:31:46 am
content: QuoteNope, that doesn't sound good. Can you work out if ALL the cells are in series or - parallel strings of series?Can you see if they use any protection diodes - these are used to short out any series cell(s) that have failed.You're right, they should ALL behave the same, some tolerance expected.

author: Jeff1946
author_rank: Regular Contributor
timestamp: July 18, 2012, 10:08:02 pm
content: As long as the sun is reasonibly high in the sky, the output should be the same if you angle the panel 90 degrees to the sunlight. After all the sun is about the same distance away (actually a little closer in the northern hemisphere in the winter). For solar panel wavelengths there is little clear sky attentuation.

author: amspire
author_rank: Super Contributor
timestamp: July 19, 2012, 04:27:49 am
content: Quote from: Jeff1946 on July 18, 2012, 10:08:02 pmIf you are north of the tropic of Cancer or south of the Tropic of Capricorn, the sunlight always has to pass through a longer path through the atmosphere then the peak sunlight that you get between the two Tropic latitudes. The peak sunlight energy is less.

author: Valen
author_rank: Newbie
timestamp: July 19, 2012, 02:58:23 pm
content: How exactly do you have the cell connected to your measurement device? The current it provides is also based on voltage, or the resistance of the load. Aside from the amount of light that hits it. You really ought to use 2 multimeters to measure current AND voltage together to be able to tell how much power it provides. And test it with different load resistances to figure out the I-V-curve. The shunt resistor in the multimeter you used might not get it at the optimal power generation point.http://en.wikipedia.org/wiki/Current–voltage_characteristic#In_solar_cellsandhttp://en.wikipedia.org/wiki/Maximum_power_point_tracking

author: MikeK
author_rank: Super Contributor
timestamp: July 25, 2012, 02:21:24 am
content: Am I going to lose anything if I get a piece of glass to cover it to protect against the elements? The panel is epoxy coated which would likely scratch easily.

author: digsys
author_rank: Unknown
timestamp: July 25, 2012, 02:50:41 am
content: Quote from: MikeK on July 25, 2012, 02:21:24 amUnfortunately, even though most solar panels are bonded to glass, there can be many % loss due to refraction andabsorption in the glass. App 1-3% at high inclination and up to 8% at high angle. ie the "rays" bounce off.They decided to use thick glass to protect from possible hail damage.Now depending on the construction of the silicon, scratches may be NO ISSUE at all. Try this test -Put the panel in the sun, connect to a load and measure the current (and voltage). Place your finger or a pencilalong ONE cell, then across TWO cells. If there is NO appreciable drop, then the cells are in a multi- series / parallelarrangement and all you'll lose is the AREA of the scratch !! So no big deal.IF you lose the entire cell, and possibly others in the series chain, then report back and we can rethink.We pay up to $100,000 to have our Solar car laminated and micro-grooved for MAX collection.Our panels are wafer thin and flexible.

author: erupter
author_rank: Contributor
timestamp: July 27, 2012, 02:52:25 pm
content: http://aom.giss.nasa.gov/srlocat.htmlThis could help defining the correct output to expect, although I had a more specific link (tailored to solar panels installations) but can't find it at the moment.Also thishttp://www.wunderground.com/calculators/solar.htmland thishttp://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/atlas/