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).
The simple answer to "where would the overproduced electricity go" is that the generator will not produce excess electricity and that causes a reduction in the fuel that feeds the driver of the generator. It is more complex than that. Some types and sizes of generating equipment are easier to "throttle back" than others. Suppliers or groups of suppliers have a range of generating equipment. In general, small and inefficient generators are easy to throttle back and large, more efficient ones can not be efficiently throttled back very much without being shut down completely. Once they are shut down completely, the larger generators tend to require more time and effort (cost) to restart.

Suppliers that are interconnected can negotiate over how much energy will be produced by each supplier so that the most efficient mix of equipment is always in operation. A distribution system that does not have a good assortment of supply equipment may be forced, either economically or technically, to discontinue service to some customers in order to shut down some equipment that does not have sufficient customer demand. With interconnected suppliers, situations occasionally arise where one supplier pays another supplier to take "excess energy" for a short time to avoid shutting down equipment that will be difficult tor restart etc.

Suppliers will offer to sell energy at the lowest price to customers who accurately predict their demand. To get such a price, the customer may need to agree to compensate the supplier if the actual energy used deviates too much from the prediction. Large customers will have a contract that covers a range of possibilities.