Fortunately, we got "lucky". The end of a very long drought had weakened the pinion trees on our property and the bark beetles eventually killed about 80% of the trees. Left with a hillside of dead trees and a heating bill higher then the Himalayas, we installed a wood-burning stove and used the free source of fuel to heat the house. This has worked for the last 4 years, but the wood is getting increasingly hard to get and the pain of gathering, splitting and burning wood had taken its toll. This solution is clearly not sustainable. There had to be a better way.
Given the sunny climate of northern New Mexico, a properly constructed house can be heated passively. My girlfriend and I decided to take a long weekend and stay in a Taos earthship over the winter. This was an eye-opening experience! It was well below freezing with two feet of snow on the ground. When our host opened the door of the house, a waft of 90 degree air blew all around us. We had to open vents to cool the place down, and the house stayed above 70 F all night long. No wood, propane, or electricity. No external fuel or power of any kind. Just 100% passive solar gain combined with a large thermal mass. That's the way houses should be built! The interested reader is encouraged to see the documentary "Garbage Warrior". It really highlights how government regulation and a housing industry primed for profit and throughput has resulted in almost zero innovation in housing. Its a sad state of affairs really.
So here is my problem, and I suspect its a problem that is shared by many in the southwest. The sun can provide the energy for all my heat, but my house was not built to take advantage of it. I need to retrofit my house to be solar. I could use solar thermal panels to heat the fluid that circulates through my radiant heating system. The concrete floor should provide a good thermal mass. So simple...until you look into it
Typical solar thermal panels runs over $1,000 for a 4X8 ft panel. I went to a local distributor and was quoted an unbelievable $3,000 per panel, uninstalled and not including shipping or crating. There sale pitch was that I could get a 30% rebate. Of course, that does not help if the price is 300% more then it should be. Based on some simple back-of-the-envelope calculations, heating my house will take at about 10 panels. That's $10,000-$30,000 of upfront cost in just panels, not to mention shipping and installation, which is not trivial. The panels are really big and really heavy and have to be lifted to the roof. To save cost I need to install them myself. Installing over a thousand pounds of solar panels on the top of my roof sounds like a real pain or really expensive. There is all manner of things that could go wrong, the least of which is me going bankrupt.
I did not have that sort of money in the bank, and even if I did, I don't think I could bring myself to spend it on metal pipe painted black. Its not like generating heat from the sun is a technological miracle. Why are the panels so expensive? How can I build an affordable solar panel?
I thought about the problem of an affordable solar panel for a few years off and on. The solution I came up with was not entirely obvious at first, which is an indication to me I am on the right track. I think that solar thermal panels need to built out of plastic rather then glass and metal. Glass and metal are both expensive and heavy. The heavier it is, the harder and more expensive it is to ship and to install. The problem is that plastic cannot take extreme heat like metal and glass, and that could well be the nail in the coffin for plastic solar panels. The reason for this is that solar thermal panels require insulation to reduce heat loss in the winter, and this insulation virtually guarantees that the panels will over-heat if the heat is not removed. Just think of the panel sitting there in the summer, mid afternoon, getting hotter and hotter.
So the problem, put simply, is that plastic solar thermal panels, if built like traditional solar thermal panels, cannot turn themselves off if they start to overheat. You cant just paint a plastic panel black, slap some glazing on it and call it a solar thermal panel. Well actually you can, like this guy did, but its only good for hot water in the summer and is functionally no different then modern swimming pool heater. If you stop removing the heat from the panel, and the panel is built from plastic, it will melt eventually. The problem, as I understand it, is figuring out how to make a solar panel turn off. If you can figure this one out, then the panel could be built of plastic and the cost reduced to a point where it is affordable to everybody.
With this problem in mind, these are some of the ideas I had at first:
1) Circulate a black fluid through transparent panels. A drain-back system is then used so that the fluid is removed from the panels if the fluid gets too hot. As I looked into it, this idea has been around for awhile. The first problem is finding a stable black solution, which turns out not to be that easy. The second problem is insuring that this black fluid does not muck-up the inside of the panels. If it does, the over-heating problem come back again. The third problem is that you have a large vat of "ink" circulating in your system. What happens if a leak occurs? The LAST thing I would want is 50 gallons of black fluid spilling all over my house and utility room.
2) Create a mechanical mechanism to shade the panel. This could work. Think of a venetian blind that rolls up or down, or slats that open and close, powered by some motor in the panels. The "off" state would have to be the minimum energy state so that if the power went off the panel would shade itself. My problems with the idea simply have to do with reliability. The panels need to be cheap but reliable. Nobody wants a cheap solar panel that is going to break in a year. Putting little electric motors and gears in a plastic panel, exposing it to freezing temperatures, and then expecting them to work reliably for years is a stretch of the imagination.
3) Create an external mechanism to rotate the panels. When the panels get too hot, all the panels just flip over. This idea is feasible and potentially inexpensive if all panels are hooked to the same control mechanism. The problems with this idea is installation. Finding a place to install such a rotation device would be difficult if all the panels must share the same axle. Another problem is wind, as the panels are basically sails. A great deal of stress would be placed on the axle, leading to problems. In short, this is possible, but not really, because the mounting mechanisms become so much more complicated and expensive.
4) Use a central "power tower" and a bunch of mirrors to focus the light to a central spot. The problems here are safety, cost and efficiency. High-temperatures equate to low efficiencies. A bunch of sun-tracking helostats are expensive and prone to failure. A central high-temperate location is very dangerous. I love the concept, but I would never install something like that anywhere near my house.
These ideas and simple variations also pop into others minds. From discussing this with people, and asking them how they would solve the problem, all of the above ideas are usually mentioned, the various problems revealed, and then the discussion devolves into a hodge-podge of wacky and unrealistic ideas or the subject is changed. It turns out the problem is hard, and in my mind this is why we are currently stuck with expensive solar thermal panels.
My solution came to me quickly when I was able to generate the problem statement. My previous work, completely unrelated to solar thermal systems, provided the seed of inspiration. Over the last eight years I have been working on a concept I call "Knowm", which basically amounts to building artificial synapses on microelectronic chips that could enable "brain-based" microelectronics. I currently consult for the government on programs along these lines. To make a very long story short, my original idea amounts to having a bath of nanoparticles in a colloidal suspension above a CMOS chip. High electric density between electrodes (which are powered by electronic "neurons") causes the particles to be attracted to the gap, forming a connection and hence a "plastic" synapse. The idea is hard for people to understand and totally out of left field, so just understand that I think about particles in a solution much more than the average person. And that is my solution: Particles.
A panel is oriented mostly vertical so that it is perpendicular to the sun, which is low on the horizon in the winter for all latitudes that actually need the energy. Liquid flows up through the panel. Small black particles in the fluid are pushed up by the liquid flow, but are also pulled down by gravity. When the liquid is flowing at a rate that matches the speed that the particles sink, the particles should distribute themselves through the panel and act as an absorber of light, passing the energy into the liquid which flows into the house. When the flow stops, the particles sink back down below a shaded region. A mirrored surface behind the panel then reflects the light away and the panel stays cool.
As I looked into the idea of a particle-flow system built with plastic I found all sorts of great and interesting things. First, polycarbonate and acrylic plastic, which is used in greenhouses and warranted for 10 years of sun exposure, is inexpensive (~$40-$100 per 4' x 8' panel). Second, its very light and durable. Third, it does not react with Glycol, a primary thermal transfer fluid. Fourth, it turns out that it comes pre-formed into channels, which is exactly what I needed. The result? I can build my solar panels with off-the-shelf components for 20% of the cost of buying traditional panels.
To test the concept I built a prototype. It took awhile to find the materials and improve the technique to the point where a functional panel was created. I have by no means created the first "production-ready" panel, but I have demonstrated the basic concept and have learned some things. I am very busy with my real job and have no experience with plastics, so there is steep and long road ahead of me. The prospects of eliminating the heating bills of millions of people, starting with mine, is definitely worth the toil.
