PV Output

So, what happens when a PV cell is left disconnected <rhetorical question>? All that happens is that a voltage appears at its terminals and n current flows.

So, what's the problem?

So no matter the power produced the energy produced is dissipated through the panels again ? Or no energy is produced since there is no connection to let the electrons flow? which is sensible?

As power produced is terminal volts multiplied by amps produced, and amps produced is zero, power produced is zero.

The panel keeps warm, though!

So no matter the power produced the energy produced is dissipated through the panels again ?

No.

Or no energy is produced since there is no connection to let the electrons flow? which is sensible?

This one.

If you have a use for the energy that could be produced, then it is wise to use the panels for that use: selling power to the power company, heating water, etc. These things help to amortize the cost of the panels.

Well, this is going to sound dumb, but will the solar cells have extra heat to dissipate when there is no current flowing? Or, does somehow their reflectivity increase with no power flowing, so the heat doesn't continue to build up?

Phrasing it another way, I wonder if there is a difference in the thermal equilibrium temperature reached between when zero current is flowing and full current is flowing? Maybe the difference is so small it doesn't matter.

(To state what I'm thinking (and presumably some others are thinking), you get a certain amount of (heat) energy input from the sun on each solar cell. When electricity is flowing, some of that heat energy is converted to electrical energy and leaving the solar cell. When current is not flowing, no heat energy is converted to electrical energy to leave the solar cell, so the solar cell must deal with all the heat energy from the sun.

A PV does not convert any heat into electricity. Heat, in fact, induces resistance in the panel and reduces its efficiency. PVs put out more power (operate more efficiently) the colder they are.

Ok, let me rephrase my question:

you get a certain amount of energy input from the sun on each solar cell. When electricity is flowing, some of that energy is converted to electrical energy and leaves the solar cell.

The remainder of the energy from the sun on the solar cell is, I think, either reflected away or absorbed and converted to heat.

When current is not flowing, all of the energy input from the sun must be either reflected away or absorbed and converted to heat.

So, when current is not flowing, does the temperature of a solar cell increase due to absorption of extra solar energy converted to heat?

As I understand it, the only sunlight converted into electricity is the wavelengths which can be absorbed by the film. When this happens it excites the electrons in the atomic structure. If there is a circuit for the electrons to flow, it does so, if not (open circuit) the atom just stays in an excited state and any further input from light is reflected. So, I think, there is a nominal temperature gain with a panel in an open circuit state, but the temperature gain is minimal above what the panel would heat up otherwise. Take into account that a panel represents only 10-20 watts/ square foot. Not much power to produce a whole lot of heat compared to, say, a 1000 watt toaster.

Thanks!

I guess I'm thinking that (like you suggest) extra photons that don't cause electrons to flow get reflected--I mean, that makes sense.

I would mention that the incident sunlight on a square foot can be somewhere around 100 watts (of energy/power), so if an extra 10 or 20 watts has to be dissipated because current is not flowing, that could represent 10 to 20% extra energy.

Anyway, I guess I won't worry about the PV cells burning out at open circuit conditions. :-)

In the UK most PV units are connected to the mains via an inverter. So any excess is exported to the utility company.

(BATTERIES NOT INCLUDED (or required))

PV's can open circuit without danger. Although it is a good opportunity to use that "extra" energy to do work. Sell back to the grid, pump water, heat water, something...

There's always some kind of load impedance. in this case the load's impedance is infinite or as we call it "open circuit impedance"