Friday, November 03, 2006
Passive Solar in the Northern Tier
Passive solar homes seem to be getting some interest again. But the examples are always in the sunny-winter parts of the country.. not cloudy-winter parts of the country. That gets my ire up. Also, the general public think - "ahh, passive solar how cool, I will use it to heat my home" (with no other heat source). Up goes my ire again.
So after our raucous discussion here is what we came up with. First, passive solar will only met about 20% to 30% of a home's space heating needs. Second, a passive solar house needs to be "super insulated." (Yes, it is time to use that 7-'s phrase again.) But this time that super insulated home needs to have (third) a mechanical ducted fresh air ventilation system (with a air to air heat exchanger).
Oh yeah, and for passive to work, your need either really good, high R-value windows or really good window shades that are used religiously. And the windows need to have a high solar heat gain coefficient
And to quote one discussion group member:
"Thermotech, a Canadian window, is the only one I know that uses Libby Owens Ford Energy Advantage II hard coat low-e, U-0.3, SHGC 0.49 (whole window). So, with 100sf of south glazing here, a house would have a net gain of 4 MMBtu/yr."
"5-9% of floor area in south facing glass is an inexpensive way to get 20-25% of heat energy needs. On a 2,500sf house, that's 175sf, an ordinary looking amount of window."
The Germans have basically figured this out. They call it the "Passive House" they dropped the "Solar" (we should too). Google them; they are online.
Their passive house is built with whatever thermal shell that is needed to reduce the building's heating load to 10-watts/square meter. A house built to this standard in Northern Minnesota has R-70 walls and a R-100 ceiling with German made triple pane windows.
The German's passive house ends up meeting it space heating needs with 1/3 passive solar, 1/3 internal heat gain (people, appliances, cooking etc.), and 1/3 some heating source (they seem to dig pellet stoves). But the heating load is a small fraction of the average home - thanks to all the insulation.
So what we need now are decent high R-value and reasonably priced windows that allow the sun's warmth to enter a building. Time for some market transformation.
Recent Solar Electric Developments
1) SunPower - this firm is the cutting edge on crystalline modules. A few reasons include:
- The SunPower SPR 315, 315 watt module with 19.3% efficiency. The high module efficiency results in an area requirement of 55 ft2 per kW of modules. It also means lower installation costs - as fewer modules, less racking, and fewer connections are needed per kW. (The Kyocera D-blue panels require about 85 ft2 per kW of modules.)
- While increasing cell efficiency, they are also making the silicon wafers thinner and thinnner, from 325 micons (industry norm) in 2002 to 200 micorns today. The net result of improving efficincy and reducing cell thickness is that instead of using 15 grams of silicon per watt, they now use 7.5 grams per watt of cell. (Note thin film producer, UniSolar, uses about 6 grams silicon per watt)
- The SunPower CEO stated that there remains vast potential to improve cell efficiency, reduce silicon use and reduce cost. Forecasts of wafer thickness projects 120 micron cells by 2012.
- SunPower is using new cell designs to boost module efficiency (I saw a diagram of their cells somewhere on the web but was unable to find it). For example, by putting the electron pickup wires on the back of the cells and interweaving n and p type silicon on the back of the module. Wires ont he back reduces shading (and, yes, improving efficiency) while making them better looking.
2) Applied Materials (AMAT) enters the solar cell manufacturing business. They make the machines that make large flat screen TV's - where evey pixel has to work. AMAT is a huge company with a capitalization of over $25 billion. I believe that they will be in the thick of the world wide revolution of the solar cell manufacturing process. That revolution will dramatically reduce the cost per watt of cells. AMAT's enterance into the marker helps assure that we see radical new cell designs sooner rather than later.
3) Sanyo Bifacial solar module. As far as I know they are the first to combine crystalline and thinfilm photovoltaic materials in one cell. This trend, of layering different photovoltaic materials that respond to different wavelenghts of radiation (or materials with different bandgaps) is the path to higer efficiency cells.
The Sanyo bifacial panels produce power from both sides and thus have two "front" sides. As a result its efficiency is dependent on the incident light on both sides.
Summary: I am convinced that we will see solar prices per watt fall more rapidly than we have historically (Historically, the market saw about a 20% cost reduction will every doubling of cell production). With these new developments (and the cost of other energy resources increase) we will see solar electric systems take over the world's rooftops.
Forecasts: Solar will be cost effective in much of the world in the next seven years. Both demand and production will increase very rapidly. When demand outpaces production by too much, prices will increase, technical innovation will be pushed even harder, and the market will continue to grow. This is a boom market and will be so for decades.
The Big Question: Will solar electric beat out nuclear? The answer will depend on developments in electricity storage.
Stock pick: At the moment my favorite is SunPower - they seem to be constantly innovating - and now define cutting edge. But can they keep it up? What has Evergreen, UniSolar or the others really done in the last year or so. The companies that constantly innovate will win this race.