system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why can't a power plant "dump" extra unused electricity?

Some countries produce too much electricity at a certain period of the year, and have to pay another country to get rid of their extra own unconsumed electricity. Why can't a power plant produce more electricity than consumed, what's the physical obstacle to do so? 

Also, what will the receiving country do if this surplus of electricity is again not consumed entirely?
gpt
The energy has to go somewhere. Power grids can deal with small mismatches in supply and load by allowing the frequency to deviate. A drop in frequency has the effect of reducing the load due to non-ELI5 effects like inductive reactance.

For large mismatches in supply and demand, simply pushing more energy into the grid will increase frequencies until the grid becomes unstable. The only way to “dump” the energy is to attach more load to dump it into. This could be in the form of batteries, pumped storage, hydrogen generators or anything else. The limiting factor is often the cost of installing new transmission lines. The cost of transmission is often much higher than the cost of generation for renewables.

Some thermal power plants are able to dump the excess energy into their cooling system without it ever being turned into electrical power but really it’s best to switch off or throttle down in most cases as it’s just a huge waste of resources unless there is some kind of combined heat and power system.