What happens to excess energy fed into the power grid?

The closest question to this is Linear useage of excess power generation.

I'm no engineer so I may not be able to phrase this correctly and would appreciate an answer which assumes minimal background knowledge (I have only a basic understanding of voltage, transformers, etc). The question arises from all this talk of the variable wind and power potentially disrupting the grid.

For example see the 2012 Electrical Connection article Rapid increase in solar installations potentially overloading the grid which discusses the potential for "reverse power flow" and also talks about some sort of "network protector" device. Also there is a or similar article about Hawaii The Interconnection Nightmare in Hawaii and Why It Matters to the US Residential PV Industry , which says the only "concrete concern identified by the Hawaii experience is the potential for transient overvoltage on the feeder – essentially a short duration voltage spike".

I'm curious about what happens here both with regard to a large grid and in a micro environment. For example, let's say I have a fully charged battery and I keep flowing electricity into it. What happens? Are there devices which will divert or dissipate the electricity as heat without damaging anything? I found a few similar questions online but the answers weren't too clear.

Answer

The most simple and direct answers to the main question depend on how "excessive" it is. Since most equipment is designed to operate within +/- 5% of nominal, the "extra energy" usually gets dissipated as heat, in the device itself. In the case of a light bulb (for example), it produces more light and heat. If the excess energy goes beyond the tolerance of the devices, they will overheat and/or burn (cause damage). These results will be obtained regardless of what causes the "excess energy" on the grid (lightning, solar installations, wind power, etc.).

For the last two questions, if you are charging a 12v battery with a 13v source, the extra 1v will keep the battery "warm" after it is charged to 12v. If you are charging it with an 24v unregulated supply, the battery will overheat, burn up, and possibly explode. If you charge it with an over-voltage and current-limited supply, the battery will be charged to 12v and the extra energy will be dissipated as heat in the supply regulators. One way you can make "efficient" use of any "extra energy," would be to use a bank of batteries and a "smart" charger, which would switch the charging to another battery when one is charged, and shut off (disconnect) when all the batteries in the bank are charged. If there is no interest in saving the extra energy, it can be "dumped" into an appropriate load and converted to heat.