they deliver; a CHP system will work best only when delivering a particular
mix; this inflexibility leads to inefficiencies at times when, for example,
excess heat is produced; in a typical house, much of the electricity demand
comes in relatively brief spikes, bearing little relation to heating demand.
A final problem with some micro-CHP systems is that when they have excess
electricity to share, they may do a poor job of delivering power to the

Finally we add in heat pumps, which use electricity from the grid to
pump ambient heat into buildings.

The steep green lines show the combinations of electricity and heat
that you can obtain assuming that heat pumps have a coefficient of per-