Solar panels, batteries, and the grid

Last weekend I attended a training exercise of the emergency communications hub at Neighborhood House in West Seattle. During an emergency, like a huge earthquake that knocks out landlines and cell phones, volunteers will jump into action, creating a communications network across the city using ham radios. These hubs will provide information to citizens (e.g. where to find food, shelter, medical care) and back to city officials (e.g. what is needed, status of roads and bridges, status of gas and electricity).

The drill was supposed to mimic the situation six days after an earthquake. One thing they didn’t cover was how they will they keep all the batteries charged? They had a generator, but will they have enough fuel?

The irony of that question is that Neighborhood House has a large set of solar panels on their roof that don’t work if the grid is down. This might surprise you, but it’s an important safety measure. Here’s how a grid-connect solar panels usually works:

  • Each panel generates DC power at a low voltage
  • The DC power from 1-20 panels is fed into an inverter, which converts the DC power to AC power synchronized with the local grid
  • If the inverter doesn’t see AC power, it cuts off the solar power

This is done to protect line workers. If they are fixing a down line, they don’t want it to be energized by your solar system. So, in a power outage solar panels are useless. Even though you can manually disconnect your panels from the grid, you can’t power your home with them because you can’t feed the inverters the AC signal they need to work. Even if you just want DC power to recharge a battery, you can’t get the power off your roof without AC power.

But there is a solution: batteries. If you install a system like the Tesla Powerwall (which has its own inverter which can turn DC to AC) you can disconnect your system from the grid and turn a building like Neighborhood House into a microgrid. The battery system provides the AC power the solar inverters need to work. A well-designed system could power communications and medical equipment, as well as other basic usage. It can even charge the batteries for use at night.

But wait, that’s not all

One of the complexities of the electrical grid is that the power in (from solar panels, dams, nuclear plants, wind farms, and natural gas turbines) needs to exactly equal the power out at every moment. When you start your microwave, if nothing else changes, some generator needs to produce a little more power. As we remove baseload generators like coal plants (those that work 24/7) with renewables like wind and solar (whose output changes with the weather) managing the grid becomes more complicated.  Batteries can be a great tool to balance the supply and demand of power on the grid. Traditionally grid operators only control the supply side (i.e. natural gas “peakers” going up and down to meet the demand in that moment). With batteries the grid operators can increase demand (i.e. charge the batteries) or supply (i.e. drain the batteries) as needed. As we move to 100% renewables and electric cars, batteries controlled by the utility will be a critical tool to maintain grid reliability.

These batteries can be anywhere, so why not put them in public buildings (e.g., schools, community centers, fire stations) with solar power where they can also create islands of power during an emergency. Having islands of power in an extended emergency could easily be the difference between life and death for people injured or made homeless in an extended crisis.

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