Prosumer customer models not supported

[jecollins]

This is because a single tariff cannot handle both consumption and production, and because customers cannot simultaneously subscribe to multiple tariffs.

[jecollins]

Seems like there are three possible approaches:

1. Add a new PowerType (or more than one) that includes both consumption and production. The problem with this is that there are lots of places where PowerType is tested, and especially where the distinction between production and consumption types is important.
2. Support tariffs with multiple PowerType entries. This seems likely to be worse than the first option.
3. Support coupling of a production tariff with a consumption tariff, and a Rate type that refers to the coupled tariff. So a production tariff could be coupled with a consumption tariff in a way that simulates net metering -- the production pays out as much as the consumption charges, up to the point where production zeros out consumption. A second Rate would then cover excess production. The problem with this is that a typical net-metering tariff does the net accounting over months or even years. We would have to use shorter accounting periods to be useful in the simulation, but anything short of a day would not make a lot of sense, at least for solar producers.