Thursday, May 26, 2011


Well, after 11 months, our system remodel has drawn to a fitful conclusion. The contractor spent the last month going through the "punch list" of items like cracks along tile/wall joins that needed fixing. In the end, I simply left a couple of small items involving paint finishing because it was time to call it done. They still need to send the final bill with my contingency returned. Now comes the interesting part, measuring how well the improvements we made work.

I have one data point already. Usually for the month of April our electricity bill showed something like minus 6 to plus 12 kwh usage, depending on the amount of sun. This year, we had a whopping  minus 500+ kwh, the impact of our new, more-than-twice-as-large solar PV system. Since we don't yet have our Nissan Leaf, the power is simply going back into the grid. We've just about eliminated the big bill from Feb. when we had to turn the electric floor heating on in the sunroom and upstairs bathroom over a weekend to reduce the amount of moisture from wet drywall mud and we had no solar panels. Unfortunately, the Leaf won't show up until July so we will have a couple more months of large surpluses before we start balancing out.

Naturally, the solar thermal hot water system is cranking too. I turned the temperature down on the tank to 130F to avoid damage to the Stiebel-Eltron electric on demand hot water heater. The company claims it is rated up to 131F. I am wondering if I can instead simply turn the electric hot water heater off for the summer and keep the solar thermal tank at 180F, or if that temperature will damage the electric heater when it is off, but I probably won't try it because the Stiebel-Eltron was expensive. Not that it matters for the water we use. The mixing value brings the temperature down to 120F anyway, but keeping the tank extra hot reduces the overheating strain on the heat transfer fluid, and reduces the probability that a couple days of cloudy weather will reduce the tank temperature below 120F where the electric on-demand heater will cut in. I still need to reinsulate the tank, since the plumber destroyed the fiberglass batt blanket I had installed. I am planning on using aerogel insulation. Should be interesting, aerogel is a new material with some promise, but still pretty expensive. Fortunately, I don't need much for the tank.

In a few weeks, I want to write a retrospective about the job, and also do a piece about reinsulating the solar tank with some pictures I'll probably also have something to say when our Leaf arrives. However, inevitably, the frequency of my postings will be reduced now that I don't have much to blog about. Thanx to all my loyal readers who have pushed my page views up from single digits to low double digits.


  1. Congratulations. You know, there's no reason to stop posting just because the job is done.

  2. You might qualify for a new solar rebate program.
    Find out if you are qualified now!