Stage #2: Solar Water Boiler
Why use natural gas or oil to heat your home's water supply when the sun can do it for free? The big boiler in the sky lays down 100 watts of power across a single square foot. The simple solar-powered hot-water system that I've built from scratch will put these free watts to work on the rooftop of my new eco-conscious home. Once I get it installed, it will generate about 450 gallons of hot water a day, plenty for my family of four, while consuming half the amount of energy of a conventional hot-water system. Plus, it will fuel my home's radiant heating system, a series of polyethylene pipes built into the floor that use hot water to warm the house.
The first step is to build two 150-square-foot solar collectors—tidy sandwiches of glass, copper tubes, aluminum sheets and foam insulation held together by a pair of aluminum frames. I'll position the panels at 65 degrees to the plane of the roof, facing south, like my house, to catch as much sun as possible to heat up the fluid (the antifreeze glycol) flowing through the copper tubes.
Next I'll install a pair of insulated 158-gallon storage tanks in the basement to hold my supply of municipal water. To heat it up, a pump will circulate hot glycol from the collectors through a heat exchanger inside each tank. When sensors in the roof-mounted panels calculate that the panels are warmer than the tanks, a controller automatically turns a valve to start circulating the glycol. One tank distributes water for showers and dishes while the other services the radiant floors.
What happens during the winter when the sun's intensity wanes? That's where heat from my newly drilled geothermal well comes in. More on that project next month.
- Repurposed aluminum window frame: The corners are cut at 45 degrees. Screws and right-angle brackets join each corner.
- Glass: Five 3-by-10-foot panels of tempered glass.
- Copper Tubing: Cut the copper piping (375 feet per panel) down to size, and fit it together so that it lies flat.
- Foam Insulating: A one-inch layer keeps in the heat.
- Aluminum Sheet: This layer lines the bottom of the panel for weatherproofing.
- Black Paint(not shown): Black paint covers the copper manifold and aluminum backboard to encourage heat absorption.
Sold on Solar?
Four Other Ways to Bring Home the Sun
Bury a low-voltage wire around the perimeter of your yard, and the electric Automower mows for you, undocking from its charging station on a programmed schedule to trim the lawn. Unlike other robotic mowers, this hybrid model draws power from a dorsal-mounted photovoltaic array to double its runtime. $3,000; automower.us
2. Backup Power
The solar-powered PowerCube 600 generator wraps photovoltaic panels, batteries and a power-management system into one 6-by-3.5-foot box. Just open the lid to expose the cells, and plug in. The base model delivers 3,500 volt-amps of continuous charge, enough to power a small home. $25,000; powercubeenergy.com
3. Heated Floors
Most radiant-heat systems require very hot water to heat effectively. Warmboard uses an aluminum surface bonded to plywood that spreads heat throughout each floor panel more evenly and efficiently, allowing it to use 90° to 110°F solar or geothermally heated water. It also prevents hotspots and won't warp wood floors. $15/square ft. (installed); warmboard.com
4. Battery Booster
This brick-size solar panel produces only about 2.25 watts of power, but that's enough to keep a car battery charged. Just suction-cup it to a window or the dashboard, and plug it into a power outlet. Or connect it directly to the battery terminals on your weekend-use-only ATV to avoid early-Saturday-morning jump-starts. $50; sunsei.com —Chuck Cage
Additional : I'm using a tank loading system to "warm up" the water in both the domestic and the radiant tanks. If the solar panels are warm enough I'll run the glycol thru the heat exchangers in each tank based on need. If for example the domestic water tank is at full temp the full solar panel array will be dedicated to the radiant floor load in the winter. When I can't produce enough from the solar panel for domestic and radiant demands I'll use my geothermal system to "charge" up the water in both tanks- via a second heat exchanger located in each tank...
Popular Science Magazine
I built a smaller one of these for research purposes at school. We used a propane torch on the underside to apply some solder to the small gaps left between the metal plate on the bottom and the pipe, to aid in conduction. It wasn't a good bond between the two, so it won't hold the pipe in, but it is better than air.
The text says 375 feet of copper tubing per collector. It would be nice if the layout was shown or described.
Why is the schematic for the tanks, pump, valves, controls, etc. not given? This is the hard part for me.
I noticed you used black paint in the project. A competitive magazine published over 20 years ago found that a dark (leaf) green color efficiently absorbed more heat than black. A paint used for automotive exhaust manifolds would be good if you could locate a suitable color. In that same article tubing was also silver-soldered to sheets of copper flashing. I believe you could use any absorbent metal, creating a "hat-shaped" section, over the copper tubing using a thin coat of (electronic) heat sink compound to improve the thermal bond between adjacent metal surfaces.
In my (Southern US) climate all solder joints may need to be silver-soldered to prevent future leaks, and it might help to use 6 inches of fiberglass insulation underneath the absorbent surfaces. The effects of solar heat may well melt some of the more critical solder joints if you use regular plumbing solder. Silver solder is usually available from suppliers of heating and air-conditioning parts.
The specification of 375 feet per pannel 3 x 10 does not make sense (75 feet x 5 pannels) look more probable. Can you please confirm this and also what size piping is used 1/2" or 3/4". Thanks
Very superficial article.
How much is the estimated cost?
How many joules of heat do you expect to capture?
You do a disservice to those who are interested in making real changes with a poorly researched "comic book" article such as this. Don't talk down to us. We are big boys - lets have some science in the article.
Nature is in the intensive care ward, and we are ripping out the IVs.
Could someone post a link that will provide more detail of the components of the collector, how they are assembled, more detail on the plumbing layout, etc. Thanks
It seems like a bad idea to use so many soldered joints of copper pipe, as it increases the chances of leaks later on. Will the solder hold up to longterm extreme heat conditions that may occur on top of the roof in the summertime? Does all the air have to be bled out of the glycol circulation system like it does in a car's pressurized cooling system? The system sounds like it could be riddled with unforseen problems so it might be a good idea to design it to be highly serviceable.
When reading through the other 'Green Dream' posts, I can't help but notice that this one, that clearly pertains to the topic, has been conveniently left out of the posts. John Carnett's name also does not link to this article. PopSci, please tell me that you aren't trying to hide an article from us because people are being critical of the article's merits. The benefit of user comments is obvious, but what is the point of letting users comment if you are going to squelch their input by hiding articles like this? Now, can we please put this article where it belongs on the site.
Now this is a good system, though, I do favor the concept of underground heating. I am informed that you can recycle the water and given it is underground there is little temp variation and water loss through vaporization is minimal.