Improved electricity to x metrics for additional compute modules

[brtietz]

Is your feature request related to a problem? Please describe.

The battery compute modules provide useful metrics like "Electricity to load from system" which are not available when a battery is not present.

Describe the solution you'd like

Utilize the powerflow shared code in a stand alone compute module that can run with any behind the meter system. This can also lead to annual/lifetime metrics such as "percent of load energy met by the system."

Additional considerations: need to test that the powerflow code is robust to a zero battery size, otherwise we'll need to consider alternatives.