Solar water heat: I've had a few lukewarm showers

Our passive solar water heating system was installed on 23 April 2007 ...almost 2 months ago. If the weather stays sunny, the system works great. Morning showers are as hot as one would like. But now that the storm season is upon us, we are finding that if we have a full day of overcast weather, then the water doesn't get up as hot as we'd like.

On the morning after a sunny day, I have to have the shower faucet set to about half hot and half cold -- any more than that and it would be too hot. On the morning after a full day of clouds, even with the faucet turned all the way to hot, the shower is only warm.

Well, this was not unexpected. We had hoped that we could get by with just the passive system, no tank in the garage, and zero energy consumption aside from what the sun delivers for free. Now it's on to Plan B. Our plan all along was that if we discovered that we sometimes needed more hot water, then we would install a gas-fired, tankless water heater as a backup. So we'll start shopping for something like this Bosch unit. The cost is about $750 ...so even if have someone else install it (still deciding), after the federal tax credit, our net would be a cost of about $700 or less. We'll see. And the periodic lukewarm shower isn't really that bad anyway :)