Monday, January 11, 2010

Bragging Rights: Past Students Current projects: Solar Integration

Shelter Institute students are some of the most talented, exciting, thoughtful and determined people in the world. And we love to keep in touch and hear what our graduates are doing. Check out this recent note from James and Kim who took the Small Housebuilding Class of 2008.

The evolution of our back porch from an 1850’s-era summer shade piece to the backbone of a solar generating plant happened over seven years. We first designed and installed a 10-panel electrical system, wiring the house for both 12-volts DC and 120 volts AC, constructing a sixteen-piece battery bank, and hooking up everything to run through a panel with a smart charger and house-sized inverters. Our original intention was to start with wind as our power source, but fortunately we took a chance with sun first. Now that we have both wind and sun systems generating electricity for us, the sun has turned out to be much more reliable a power source, although the wind provides excellent supplemental power and provides charging on windy nights and stormy days, when the sun isn’t an option.

A year ago, we finished the design for a solar water heating system using a re-circulating antifreeze loop and a 3 watt DC pump controlled by a Maine-designed electrical solar thermostat. We had difficulty finding plumbers in our area who were familiar with this technology, though we hired one company that had little experience with our type of design. In the end, we ended up reworking many of the lines, flow-meters, and check valves the plumbers installed to get our system to work. Our experience has been that many contractors try to sell themselves as “green” contractors and as having experience with alternative energy systems, but we have not found many that live up to their claims.

Disappointingly, Maine winter sun is insufficient to heat our small 40 gallon hot water tank to bathing temperature, so we designed and built a second parallel antifreeze loop to run off our wood stove. The heat exchanger is a fabricated deep water-filled copper pan in which our closed antifreeze loop is immersed. The antifreeze is re-‘circulated through our hot water tank using a second 3 watt DC pump and electrical controller. Since we heat our home with wood in the winter, this system provides sufficient hot water for our winter domestic use.


  1. Thanks for a great write up. One comment though: you wrote, "disappointingly, Maine winter sun in insufficent to heat our small 40 G hot water tank to bathing temperatures, so..."

    From the photos, I suspect that this has less to do with the Maine sun and the collectors, and everything to do with installation angle. That solar hot water collector appears to be installed at about a 25 degree pitch which means that in the winter when the sun is low in the sky(just 21 degrees above the horizon on the winter solstice) the collectors are producing less than 50% of what they could be if they were optimally oriented. With 30 evacuated tubes and a 40 G tank, you could almost certainly heat that little tank just fine through most of the winter.

    best of luck.

  2. Fortunat:

    Thanks for the note and kind words. You're correct about the roof pitch. We'll probably try angling it up another year. Flush mounting has great advantages for durability, but a bit of an angle adjustment probably would give us noticeably more hot water.

    We've found that hot water evacuated tube designs are hindered by the fragility of the glass. Two have already broken, partly because the fit into the manufacturer's mounting platform was too snug. The installer didn't know what to do when they wouldn't just pop in.

    Happily, however, the wood stove heat exchanger provides us with plenty of hot water in the winter.