Sunday, August 14, 2005


Dump load versus grid tie

A couple of readers have asked me why I'm worried about dump loads when I should be able to sell my excess power to the local utility (DTE Energy). This was my reply:

Michigan didn't pass a net-metering bill until a couple of months ago, after I had ordered my equipment. I don't know how it will be implemented by DTE, or when, and the inverter I have is not designed to sell to the grid. If the law had been in place when I started, I might have gone with a different inverter (Outback actually now makes a battery/grid-tie inverter similar to mine). But I don't think there will be too many times when I have so much extra power that I can't benefit from it--make the basement a little drier in the summer, the house a little warmer in the winter.

For now I'm using the grid as backup to my solar. After I've operated the system for a year or so, I may find that I can make it without the grid at all--in which case I can save the basic monthly connection fee.

The most cost-effective solar electric installations are the grid-tie ones without batteries. Basically all you need are panels and a grid-tie inverter. But you get no blackout protection, since the utilities require that your system shut down when the power is out (to protect line workers, I think).

I based a lot of my decisions based on what I really wanted, not on the economics. The most cost-effective thing to do would have been to take the simple conservation measures (insulation, compact fluorescent bulbs, Energy Star appliances, switching off phantom loads) and staying with the grid. However, if the energy crisis kicks in in earnest in the next couple of years, I may still come out ahead, having bought my solar equipment at what may in retrospect look like low prices, and not paying sky-high electric bills. If not, I've still got a cool blackout-proof self-powered house for about the cost of a new car.

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