The hybrid solar home, part 2
My thoughts have turned lately to the challenge of heating and powering residential homes in the Pacific Northwest with renewable energy. My goal was not to just find a way to reduce fossil fuel use, but to eliminate it. When I started this exercise I wasn’t at all sure it could be done (in an affordable manner). Here in the Seattle area we average a little more than two clear days a month for six months of the year!
Back in January, I mulled over the concept of an affordable, solar-powered, carbon-neutral home designed for this latitude and longitude that would have no gas, electric, or hot water bills. The key to affordability was small size. You traded the status garnered from cavernous space for the status of being the first on your block with solar technology. That article was based on rough back-of-the-envelope estimates. At the time I was considering hydrogen storage and parabolic collectors. I received a lot of feedback on that first article, which I have incorporated into this latest iteration. People wanted south-facing windows. A lot of people were also skeptical about living in a 1,200 square foot home.
I just completed a fairly rigorous analysis (with simulation and testing) and have some good news to report. The latest design has 2,800 square feet of heated living space, the equivalent of fourteen 4′ x 4′ windows, and is three stories tall. It could be bigger or it could be smaller. All you have to do is keep the panel area, mass storage, heated volume, and insulated envelope ratios about the same. It took weeks and several iterations to come up with a design that worked. Forget hydrogen. Not only would it be complex and expensive, it would have to be stored in gaseous form and would take up a comically large tank farm. Forget parabolic collectors. Also expensive and complex, they require clear cloudless skies and failure prone tracking devices. Their mirror finishes also degrade fairly rapidly.
As part of this analysis I also built a solar panel test rig and used it to test two types of panels (which I also designed and built). The rig was necessary to fill in some blanks and give me a measure of confidence in my calculations. Yes, those are my daughter’s chickens in the foreground and no, I didn’t water my lawn this summer.
Almost without exception, when you read about a solar-powered home you are reading about a solar-assisted home. Typically these homes will achieve modest to respectable reductions in the cost of space heating, hot water, or electricity, but claim to drastically reduce or eliminate all three. There is usually something like a wood or propane heater not mentioned in the article making up the difference. It just costs too much to try to take it all the way. An analogy would be to try to make a Hummer get the same mileage as a Prius by bolting a hybrid drive onto it and filling the trunk with batteries. As with the Prius, to get the desired results you have to start from scratch. You can’t go fossil-fuel-free by retrofitting an existing house, at least not in Seattle.
Regulations allowing, this latest home design could sell energy to its neighbors. Engineering being the art of compromise, there are any number of cost variables that I could have traded off. As designed, this home should cost roughly 10 to 20 percent more than an equal sized, multi-story fossil-fueled home. I’m going to keep how that is possible, along with most other details, under my hat for now.
I wanted this design to have a large margin of error and to be simple enough to be reliable. For example, I didn’t assume the owners would turn the thermostat down to 65 degrees at night, or turn off the fresh air heat exchanger when they leave for work, or make any effort at all to reduce electricity or hot water use. It would consume the average amount of hot water. I assumed the electric load would be the same as that of my four-person family (washer, dryer, dishwasher, and all the attendant electronic devices and phantom loads you can imagine, using natural gas for cooking, heating, and hot water).
Just for the hell of it I’m going to put together several floor plans and options for things like decks, double decks, skylights, emergency power storage, and even an option to capture 90 percent of the rain that falls on your house during the long dark winter. You can mirror the house floor plans East to West but not North to South (or upside down or inside out).
This thought exercise yielded some epiphanies:
- Conventional hot water solar panels consume prodigious amounts of copper because it is such a good conductor (and much cheaper than silver). But thanks to China, the price of copper has risen over 400 percent in the past few years. I wanted this solar home design to be scalable. I’m not sure there is enough copper on this planet to build everyone conventional hot water solar panels, which is why I don’t use any copper in this design.
- Locally produced solar power cannot be used to power dense housing because the ratio of solar panel area to insulated envelope would be far too low. You could supplement hot water to some degree but that will be the limit of it. Even so, apartments and condos will still be more efficient per person than even a hybrid solar home. Locally produced solar power requires a lot of space and no shadows. But if you want to raise a family in a house, this is the kind you should do it in.
- Even though this house would generate all of its own electricity, it would not reduce CO2 emissions from the local coal-fired power plant by a single pound. That’s because the load is too small to detect. They would not throw one less chunk of coal on the fire. The only hope for a home like this to reduce coal use would be for the design to catch on and spread rapidly. A few thousand of these homes in a given grid area would be noticed and the utility would have to find a way to burn less coal or go bankrupt. The tail would be wagging the dog. Utilities will be forced to come up with a way to handle massive amounts of home-generated solar power.
- It struck me as absurd that we go to such extremes to pamper ourselves inside artificial climates. The surface of the planet is covered with a thin film of housing with microclimates inside. Our cars are an extension of that climate. Nobody hangs out and naps in the shade when it gets hot or snuggles by the fire under a blanket with hot tea and a book when it gets cold. Our homes are like flour sieves. If you hold a candle under a sieve and measure the air temperature in the space, it will rise as the wire mesh impedes the loss of heat. That’s essentially what our walls and windows do. And everybody wants lots and lots of windows.
- In all seriousness, somebody should bother to create a line of heated clothing using the latest technology of fast charging batteries and microprocessors. We could stay warm and cozy in a 55 degree home if suited up with electrically heated socks, vests and fingerless gloves. When you think about it, this idea of heating the air in an entire house to 70 degrees 365 days a year when you could just put on some heated underclothes is kind of ridiculous.
- Why do people move to places that can get very cold or very hot, or both? I suspect that subtle instincts motivate us to spread out like water on a table. The same thing that causes lemmings to migrate. That’s why there were Inuit and Eskimos living in the Arctic. They traded conflict and competition with neighbors for survival in an extreme climate.
In conclusion, the scalable technology to affordably eliminate fossil fuel use in single family residences exists, which begs the question: Where are these homes? I believe this is a case where house designers in this neck of the woods have not realized it can be done, yet. But the cat is out of the bag now. There also hasn’t been a demand for this kind of house. Most consumers are still under the mistaken impression that, as with SUVs, bigger is better. That’s going to change also.
Like a Prius, the solution isn’t one piece of technology but a dozen technologies strung together in the name of efficiency. And if it can be done here, it can be done anywhere for much less, except maybe in Alaska. If you live in Alaska, your best bet is still long underwear.