# Can solar panels be safely short-circuited?

Discussion in 'Electronic Basics' started by Pimpom, Dec 19, 2012.

1. ### PimpomGuest

Can solar panels be safely short-circuited while they are fully
illuminated? I've looked at the specs and I understand the
concept of MPP, conversion efficiency, etc. I have no particular
design or application in mind where short-circuiting the output
plays a role - just that it might be useful to know.

2. ### PimpomGuest

I mean safe for the panel. Please disregard consideration of
external circuits.

3. ### Tom BiasiGuest

Usually not a problem. Most panels run close to their short circuit
current capability.

4. ### George HeroldGuest

I use photodiodes 'short circuited' (into a TIA opamp circuit). It
doesn't seem like short circuiting a solar panel could hurt it. (But
I've never used one!) It might be useful as the short circuit current
would be some measure of the total intensity. Are the panels all just
single 'diode drops' or do they sometimes put a few in series?

George H.

Thanks.

6. ### PimpomGuest

I didn't get that right away but let's see (basic college
thermodynamics is >40 years in the past). The panel receives
solar radiation, much (most?) of which is thermal and the black
panel is efficient at absorbing it. So the panel gets heated up
quite a bit. But some of the radiant energy is converted to an
electrical potential. If that electrical potential is
short-circuited, there's no change in the power expended in the
cells, and therefore no additional heat produced. Is that the
logic?

But then not all the radiation is thermal and the non-thermal
part is also converted to electricity. Wouldn't that produce

7. ### PimpomGuest

I have one panel as a sample and it has 39 cells in series.
Judging from the size, I'd guess the power rating as somewhere
around 50W. Its open circuit voltage in bright sunlight is about
23V. I haven't tested it yet to plot its characteristics under
different levels of load and sunlight. No datasheet, and the
company has only a rudimentary website.

Someone gave me the sample to play with and see if I could turn
it into something useful. It seems they have truckloads of the
things but they don't know what to do with them. I didn't bother
asking why they bought them in the first place. Probably with
some vague idea of using them as backup power.

8. ### Jasen BettsGuest

If you short circuit them they will heat up, there will be the
same amount of heating as if you leave them open circuit and
unloaded, just via a slightly different mechanism.

9. ### George HeroldGuest

That seems right. The energy has to go somewhere.
But when the cell is open circuited there's no energy 'lost' from the
cell either. The photo-generated e-h pairs recombind in the silicon.
So the cell runs at it's coolist when you are pulling just the right
amount of energy out of it.

George H.

- Hide quoted text -

10. ### George HeroldGuest

Right!... sorry I should have read to the end of the thread before
posting.

(Can you see the temperature rise 'in practice', as opposed to 'in
theory'?)

George H.

11. ### Jasen BettsGuest

It was an issue for the builders of the sunshark
http://en.wikipedia.org/wiki/Sunshark_Solar_Car_Team
I had a chat with them around 1991 some time.

In their design the silicon wafers are beneith a layer
of fibreglass abd the overheating was causing delamination.

12. ### Bret CahillGuest

Can solar panels be safely short-circuited while they are fully
Not as much hotter as they would get cooler in the shade w/o a short.

Bret Cahill