P2H should become a participant

[ChaelKruip]

Part of quintel/etmodel#1868

This is a conversion technology with volume (kWh) and capacity (kW) depending on the number of units of the households_flexibility_p2h_electricity node.

It converts excess electricity into heat according to the 'storage order' described in quintel/etmodel#1965 and stores the heat in a buffer. The efficiency of households_flexibility_p2h_electricity needs to be taken into account here. The heat is extracted from the buffer according to a demand profile for hot water (also see https://github.com/quintel/merit/issues/131).

The rules are:

• If there is excess left in this time step (after possibly higher ranked technologies have been used), convert as much electricity into heat as capacity and volume allow
• Extract an amount of heat from the buffer according to the hot water demand profile (limited by capacity and amount of heat stored)

[jorisberkhout]

This has been implemented and works like a charm! Closing.