I found a similar question here on this site, but my question is slightly different. If a solar panel is exposed to sunlight but is not plugged in to anything–dc load, inverter, etc–where does that electricity go? In this example, I'm assuming the solar exposure is still freeing electrons, but where do they go?
[Physics] Where does electricity go from a solar panel that is not plugged in to anything
electric-circuitsrenewable energysolar-cells
Related Solutions
There are several ways to design the circuit.
If it's a Smart system, then when there's surplus power, additional devices will get turned on, to use it: dishwashers, washing machines, or immersion heaters in hot-water storage tanks. If there's still surplus after that, then it's as below.
If it's grid-connected, with an inverter, then it's usually designed to export surplus power to the grid. There's typically either an export meter, or the property's main electricity meter runs backwards during those times, to ensure that payment is made for the exports.
If it's designed as standalone, then it might have a battery where surplus power is initially sent. When the battery's full, then it's as below.
In the absence of other uses of the surplus, there's a resistance heater and heat sink where the generated power is dumped.
And in general, the economics tends to ensure that enormous amounts of energy are not wasted. If there's going to be a large surplus, that will be enough to justify expenditure on one or more of: a Smart system, a grid export connection, local storage.
When the sun is near the horizon, the sun rays have to travel through more air to get to you than when it's directly overhead. This phenomenon is known as atmospheric extinction, and this page has a nice cartoon diagram to illustrate it:
This effect can be quite large. This page has a graph of the approximate effect as a function of zenith angle, which is the angle from directly overhead; a zenith angle of 90° is therefore an object on the horizon.
This graph is logarithmic; every unit on the vertical axis corresponds to a factor of about 2.5 times less energy getting to the ground. We can see that anything closer than about 15° to the horizon will have its light diminished substantially, certainly enough that you would notice on a power meter.
In addition, sunlight near the horizon is reddened substantially; blue light is more likely to be scattered by molecules in the air, while red light is more likely to travel straight through the atmosphere to your solar panel. (This is why sunsets are red & orange compared to the light you see during the day.) Roughly speaking, your solar panels take particles of light (photons) and turn them into electrical energy. But because of the properties of solar cells, there is a minimum energy that a photon must have (called the band gap) to excite any electricity at all. Redder photons have less energy than bluer photons, so the red photons that are prevalent in sunlight from near the horizon may not be able to generate any electricity.* In other words, there's a double whammy: less photons are getting to your solar panel, and the ones that do get to your solar panel have less energy on average and can't generate electricity.
*I say "may not" because solar panel engineers are clever folks, and there are some more modern types of solar panel that are better at converting sunlight into electricity over a wide range of photon energies. Look up "multi-junction cells" for more information.
Best Answer
The photons from the sun have energy and momentum, but not "electricity".
Essentially, a photon (solar or otherwise) striking the solar panel can create an electron-hole pair (EHP) and, if the EHP is within or near the depletion zone, the pair will be separated by the built-in electric field.
This results in a separation of charge and with that, a voltage across the panel. If there is an external circuit connected, there will be an electric current through the circuit.
But, if there is no external circuit through which an electric current can circulate, the electric field due to the separated charge opposes further separation of charge; the generated electron-hole pairs simply recombine rather than separate.
Electric power is the product of voltage and current. If there is no external circuit, there can be no current and thus no electric power can be delivered by the panel, i.e., the "electricity" is never developed and thus, there is no need to consider "where it goes".