On a simple network, the extra energy is "absorbed" by the remaining hardware components (think: wired getting hotter, etc.), eventually resulting in failure du

On a simple network, the extra energy is "absorbed" by the remaining hardware components (think: wired getting hotter, etc.), eventually resulting in failure due to operating at higher voltages or currents than designed for. Most electricity networks have a "system operator" whose job is to keep electricity generated track electricity consumed very closely. (An organization, with many automated systems, not a single person). In practice, on a large network, the most noticeable side effect would be AC frequency fluctuations. In a severe case of imbalance, sensors/switches on the network would disconnect part of the network to protect the underlying equipment (probably causing blackouts, if not cascading blackouts). The operator predicts demand and tells each of the many electricity generators how much electricity to generate. Some types of generation are easier to ramp-up o or throttle-down: for example, hydro and natural gas are very easy, while nuclear is not. Residential roof-based solar makes things complicated because it is now a new part of the system that is no longer under the operators control. Some networks also have access to sinks of energy, the most common being pumped storage (usually in connection to a hydro facility), or even, industrial consumers who are willing to "ramp up" on demand. On top of all this is usually a market layer (depending if the electricity generation is privatized or not). For example, in Ontario, the IESO (independent electricity system operator) asks for bids every 5 minutes from all the providers, and based on a modified dutch-auction, selects which providers are allowed to produce and sends them the corresponding instructions. Of course, taking into account various other technical requirements to decide who gets to power or not. In this kind of market, nuclear power, because it cannot throttle up or down, typically bids 0 or negative (because the actual price set is based on the last most expensive bid to get in). During some hours of the year, the market price of electricity is sometimes negative, because nuclear is the only bidder. In Ontario, the government phased out all coal production (yay, no more smog!), but... had to build a lot of new natural gas plants to be able to do the fast ramp-up/throttling the network requires on some days of the year. Most of the year, these plants sit idle.