Question: I have been reading lately about electricity markets and I have stumbled upon the term ["volume risk"](https://en.wikipedia.org/wiki/Electricity_market#Risk_management). 

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> Volume risk is often used to denote the phenomenon whereby electricity market participants have uncertain volumes or quantities of consumption or production. For example, a retailer is unable to accurately predict consumer demand for any particular hour more than a few days into the future and a producer is unable to predict the precise time that they will have plant outage or shortages of fuel. 
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Basically, a fault in the prediction of both the buyer and seller may occur and either the electricity that has been purchased, may not end up being delivered or vice versa, the buyer may have ended up purchasing more electricity than needed.

However, I haven't found a clear explanation, what is done in these two cases. Who would cover the electricity difference if the generator does not end up producing the quantity stated in the trade or where would the overproduced electricity go, if the consumer has estimated his consumption poorly?

Answer: 
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> where would the overproduced electricity go, if the consumer has
>  estimated his consumption poorly?
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It doesn't go anywhere - if the consumer under-consumes compared to the original prediction then, that under-consumption is physically less-current being taken and less-power being supplied by the generator. 

Electricity isn't like a delivery van setting off to deliver bread or cakes - it's much more instant than that and if a load takes less current or power then it's pretty much instantly reflected in the generator producing less power and the oil/coal/energy being used by the turbine and generator being less.

There is a financial deficit only and that gets resolved by credit arrangements (my guess).
There are different kinds of generators. Some do supply constant electricity with monthly schedules like nuclear and thermal power plant, these can't dynamically change the production. 

The variable part of the demand is supplied by power plants that can quickly turn on and off, these are gas turbine, hydroelectric plant, diesel. In case of increased demand, these power plants are turned on.

In case of unplanned decreased demand, and if all small power plants are off, they will try: fill the basins full for reversible power plants (generator/motor), to sell the electricity for small money (or even to pay for) to foreign country, contact steel forgeries to increase production, turn on street lights even in daylight,...whatever to gain time until the demand is repristinated.