Wednesday, June 24, 2015

Household Cogeneration

The news that net metering may be going away at our utility a lot sooner than we hoped had me think about how we could make solar work without net metering.

The obvious answer is something like the Tesla Powerwall - adding battery storage to our solar panels. That would solve the problem of time-shifting the energy from when it's generated during the day to when we consume it in the evening. However, it does nothing to help us time-shift the energy from the sunny summer months to the dark winter months.

Winter has other energy requirements: namely heating.

In the power generation industry, there is a technique called cogeneration (I had to study it in college). Basically, you burn a fuel in some sort of generator to produce electricity, then take what would normally be waste heat and use it for something productive, like heating the powerplant facilities.

It turns out Honda and a couple other companies are selling household cogeneration units. They replace your central furnace and dump power into your electrical system - sometimes using net metering with the electric utility, just like solar power generation.

So, if money was no object, we could theoretically go off-grid (electrically) using solar panels and batteries in the summer, and a cogeneration unit and batteries in the winter.

Money is an object, of course.

The quotes we got for solar panels indicate we would have to pay roughly $26,000 (before subsidies) for 6kW of solar panels, installation, and the necessary electrical work. Tesla's Powerwall batteries have just about the best kWh per dollar price, but won't even be available til next year, at the earliest. Even then, we would probably need about $15-20,000 in batteries. I haven't found a price for a cogeneration unit, but equivalent-sized generators run about $5-6,000.


Anyway, I like the thought of going off-grid. Can't afford it at our current electric consumption, though.


  1. So have you thought of wind energy for the cloudy winter days. Here it is usually windy when it is winter and we could harness that too. Just thinking.

    1. Haha, I've thought of putting a turbine on our local beaver dam!

      There's no way we could get a wind turbine past our HOA. I'm not really sure where we would put one even if we could - we have quite a few tall trees around us.

    2. Too bad. Usually an HOA doesn't allow for a mast higher than 15 feet above your roof line. For us, that would be enough, but if you have trees much for that idea.