Microgrids Explained

Microgrids are self-sufficient energy systems serving a concentrated geographic area, like a neighborhood, or in Rossmoor, one or two entries. Typically a microgrid will combine all the components shown in the diagram:
1. Solar panels — mounted on home roofs, or in open space;
2. Batteries — located separately from the homes in a small, discreet structure;
3. Diesel or natural gas-powered standby generator — for long outages (optional);
4. Microgrid controller — the brains of the system;
5. Transfer switch — enables the microgrid to be isolated from the PG&E grid;
6. Distribution transformer — connects the microgrid to the high-voltage public utility grid;
7. PG&E grid — the transmission lines and large-scale generators operated by the publicly regulated utility company.

How the microgrid works when PG&E is operating normally

During the sunny part of the day, the solar panels provide all the power the homes need.  The excess power is channeled into the batteries.  When the batteries are full, the microgrid controller directs the excess solar power to the PG&E grid and the homeowners receive a credit.

During cloudy periods and nights the batteries supply the power needed by the homes.  If there is insufficient power left in the batteries, power is drawn from the PG&E grid, and the homeowners are charged.  The microgrid controller keeps the right amount of electricity in the batteries to ride out any expected PG&E outage.

How the microgrid works when PG&E has an outage

As soon as the microgrid controller detects a PG&E outage, it flips the transfer switch, isolating the microgrid from the PG&E grid. If the outage is during the day, the homes are powered by the solar panels and excess power is stored in the batteries. At night the homes are powered by the batteries. If the batteries run out, then the microgrid controller fires up the standby generator to power the homes.

Microgrid economics

Residential microgrids are usually set up so that — over the course of a year — the solar panels produce as much power as the homes need.  This means that the homeowners only pay for their share of the microgrid’s depreciation and maintenance — which is generally about the same as or less than the cost of PG&E power.  So the microgrid costs the homeowners no more than they are already paying for electricity, but provides them with “better” — more sustainable and more resilient — electricity