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DayCreek Journal

January 10, 2005

Where's the sun when you need it?

Geesh! It sure has been cloudy here in southeast Minnesota. Something you normally wouldn't expect in January. Solar hours for the first half of the month is next to nil. At this rate, January will be cloudier than December's weather. But, it does appear that we might get a few good solar days this weekend albeit under the influence of an arctic high pressure system—it will be cold, but at least sunny. (So we hope.) One thing is for sure, the wood stove has been getting a workout.

With the new year now in full swing, I thought I would go through the predicted solar statistics for our solar electric system and see how things are going after the first 7 months of generating solar power. So far, the statistics are unbelievably close to the PVWatts predicted numbers—only 20 kilowatts difference between the predicted and actual numbers!

Here's the stats from June of '04 to December '04:

Month Forecasted (kWhrs) * Actual (kWhrs) Difference (kWhrs)
June 462 452 -10
July 506 491 -15
August 454 442 -12
September 384 496 +112
October 395 279 -116
November 249 266 +17
December 220 224 +4
Total 2,670 2,650 -20
* Based on PVWatts forecasted energy production.

Speaking of solar...
The solar hydronic heating system works quite well whenever the sun is out for periods of 2 to 3 days. This is not the case this year. Weeks have gone by without any solar heating worth mentioning and the solar heated sand bed has lost its juice. This is the first winter since the sand bed has been in operation that such a long stretch of cloudy weather has caused this to occur.

How often will this occur? Were the previous winters sunnier than normal or is this year below average? I think it's a combination of both. The bottom line is that it will take 2 to 3 days of mostly sunny weather to recharge the sand bed to a point in which meaningful heat will begin to flow through the floor.

Because of this, I have been considering marrying both the solar heated sand bed system with the electric boiler radiant floor heating system. (The sand bed is heated by solar heat, while the radiant tubing in the floor slab is heated by an electric boiler.) If the two were combined, I could channel the solar heat directly to the floor slab first for a quick charge and then channel the somewhat cooled but still warm fluid to the sand bed. Of course, I would install valves to break the systems apart when this scenario would not be required.

This might be useful during winter periods when in a given week there is only one good solar day. By channeling the heat directly into the floor, it would give a quick charge to the floor and for that matter, the high-mass walls. Could the house overheat during the day? Possibly, but the walls will probably soak up quite a bit of the Btu's. Right now, this idea is in the thinking stages and if I were to do this, it wouldn't be until sometime this spring or summer for next winter's testing.

Well, I better get back to writing my CoCoCo papers or Richard Flatau might get his ruler out and wrap it across my fingers. Please remember that if you are planning on doing an article for the Continental Cordwood Conference, papers are due this month!

A Red-bellied Woodpecker feasts on suet.