Hi All,
I'm a newbie to the forum but thought I'd share and collect some ideas for a project I'm working on.
I'm piecing together a solar thermal collection system to offset the cost of water heating in my home. The system is intended to suppliment hot water only and not be tied to heating of my home.
I started by putting together a small 1' x 10' copper tube/plate collector. Roughly sixty feet of 1/2" rigid copper tubing spot soldered to a 1' x 10' copper sheeting in a 2x4 frame. It's insulated with 1" foam board below and covered with a scrap sheet of aclar film stapled and taped around it's edges. There is also a temperature sensor clamped to one of the pipes via a hose clamp.
http://home.comcast.net/~rossfree/solar/solar10.jpg
http://home.comcast.net/~rossfree/solar/solar9.jpg
http://home.comcast.net/~rossfree/solar/solar12.jpg
My heat storage was a 30 gallon ice chest. I drilled a couple of holes in it's side and plumbed it to the collector. There is a small pond pump in the ice chest and when turned on it simply circulates the water from the ice chest through the collector and back into the ice chest. A second temperature sensor was placed in the ice chest.
http://home.comcast.net/~rossfree/solar/solar11.jpg
Control was by way of a PIC processor and minimal circuitry. With a simple program, the pump was turned on whenever the collector was 10 degrees F above the storage temperature and turned off when the collector was only 5 degrees F above. It also kept track of how long the pump was running during the day.
http://home.comcast.net/~rossfree/solar/solar6.jpg
I live in southern New Hampshire and put this together back in early April. The daytime temps were running in the low 60's but with sunshine I could raise the water temperature 20 - 25 degrees in a given day. With three days of sun I got the storage temperature up to 153 degrees F. Not too shabby. And at that temperature I would loose at least 10 degrees at night from cooling through the icechest. The ice chest only has about an inch of insulation around it. If I took the time to improve the insulation around the ice chest, I'm sure I could have hit 180 degrees... no problem. At that temperature, I would have started worrying about the plastic softening.
At one point, I came home and the display read that the temperature of the ice chest was 79 degrees and the collector was 210 degrees. I could hear the pump running and knew it couldn't be right. I figured the electronics got fowled, being uncovered and exposed to the elements. I reached down to feel the copper pipe protruding from the collector and got a surprise. It burned me good! It didn't dawn on me how it could have gotten so hot with the pump running until I opened the ice chest. The pump had popped off of the tubing and was not circulating water through the collector. Sitting in the sun with no circulation, the collector had hit over 200 degrees! HELLO! So I reconnected the pump to the collector and turned it back on. While it circulated water, I put my hand underwater in the ice chest to feel the water entering from the collector and... duh! ...burned myself again! Ha!
I can be not to brite sometimes.
When the pump comes on, it only runs for about 30 seconds. In that amount of time, cooler water has replaced the warmer water in the collector and brought the temperature below the 5 degree cut-off temperature. Average run-time during a sunny day was less than 45 minutes. That equates to about 1/2 penny cost per day based on $.12 / kilowatt hour.
I'm happy to report a very sucessful small scale test.
Enough for now. I'll share the beginnings of my larger 330 gallon system soon.
http://home.comcast.net/~rossfree/solar/solar1.jpg
http://home.comcast.net/~rossfree/solar/solar2.jpg
http://home.comcast.net/~rossfree/solar/solar3.jpg
Ross