The Sun. A Product?
The Sun may not be a product you can buy, but it deserves consideration in every house, in every climate, because it can save you money - or cost you. While it can be a free source of winter space heating, a source of free hot water year round, or a source for “free” electricity (with photovoltaic (PV) panels), it can also cause a house to overheat, bleach colors, and deteriorate ultra-violet (UV) light sensitive materials. Whether or not you use it to your advantage, you need to consider the Sun.
I’ve heard our house referred to as a “solar house.” I don’t believe it is. I’ve simply considered the Sun and will use it to our advantage. Our house will face “solar south”. This keeps sunlight on the front of the house. The south facing windows will be clear glass (not low-e) so that radiant heat from the sun is allowed to enter the house. The overhangs are designed to shade these windows from the high summer sun (when we don’t want heat) and allow the low in the sky winter sun to enter (when we want the heat). The glass will be coated to block harmful UV light.
I found this overhand design tool quite useful: http://www.susdesign.com/overhang/
The orientation of the house gives us over 1,200 square feet of south facing roof, ideal for both PV panels and solar thermal (hot water) panels.
I haven’t found the right solar hot water system yet, but I have hopes of finding one that can be installed on day 1. I’ve been using http://www.solar-rating.org/ for non-biased performance ratings of various systems. I just need to get a quote that makes economic sense.
I intend to install an on-demand hot water heater (brand?) that will satisfy our hot water needs immediately, and work nicely as a “finishing” unit if the solar hot water system is unable to completely meet our hot water needs. I still haven’t decided if propane or electric will fuel the on-demand system. Propane is a less expensive fuel at this time (natural gas is not available in our area), but electricity can come from 100% renewable sources. I am leaning towards electricity based on principle.
PV is another story… I love the idea of being able to generate my own electricity. However, there are two things stopping me from installing a PV system on day 1.
1 – The current cost of electricity from a PV system is not competitive with commercial power generated by renewable sources - even with the substantial subsidies available to home owners. To date, I have not found a PV system that is able to produce enough electricity to offset the increase in my mortgage payment. Wonderful idea, poor economics.
2 – There are PV products in the pipeline that will dramatically change the economics of PV systems. One of the most notable that I am aware of is Nanosolar (www.nanosolar.com). Nanosolar’s PV product promises to be in the range of $1 per watt installed (perhaps higher based on the rules of supply and demand) versus $5-$10 per watt for systems available today. Assuming Nanosolar starts shipping product to consumers in the next few years, any previously installed PV system will be rendered obsolete and devalued immediately.
As I mentioned before, every major product I purchase for this house must pay for itself in one way or another. PV systems available today, while “green,” just don’t make economic sense. Perhaps next year things will be different.
Solar and storage
Nanosolar is shipping and Aleo Solar (Germany) is supposed to start soon with another new low cost PV technology. I'd hold back for a year or few until prices drop, just enable easy installation with wire chases, room for integration with grid power, etc.
We are building a greenhouse in SE MN and taking a shot at using seasonal thermal energy storage. A fairly modest solar thermal collector array storing energy spring, summer and fall and to a lesser extent in the winter, should be able to heat a house with only modest energy inputs for ventilation air and heat transfer fluid circulation. The storage area must be isolated from ambient to prevent energy losses to winter cold and to the percolation flow of rainfall. We put about 325 55 gal HDPE sealed drums of water into the earth behind the greenhouse and have about 2600 feet of thin 4" PVC pipe running over and under the barrels for heat transfer. I can send you more detail if you are interested. The idea is to have a near passive gain system without the tendency to overheat. It is an experiment we will live with....
Also, a German company just announced its intent to market a product for seasonal thermal energy storage. Info at: http://www.worldofrenewables.com/index.php?do=viewarticle&artid=1323&title=new-building-material
More info about energy storage at www.earthshelters.com
We also plan to build a house this year, perhaps earth sheltered if the finances work. Otherwise it will be superinsulated convential with thermal energy storage and will probably put in a new wood cookstove for backup heat and cooking.
Thats a lot o' barrels!
If I have the decimal point in the right place, you're getting just shy of 1.5 therms per degree F rise in storage temperatures. Assuming you can get it up to 120F by the beginning of the heating season, and that you have a hydronic heat delivery system that can still provide peak heating load at 90F, that's about 45 therms of storage capacity (that's assuming lossless storage and delivery- call it 40therms w/losses accounted for.) I'm not sure how hot you can go with HDPE before it degrades(?) and insulating & plumbing 325 drums sufficiently sounds like quite a project all by itself!
Seasonal storage tanks I've previously read about were fabbed from large septic tanks with R25+ of spray-applied 2lb. polyurethane on the outside (which also has a degradation temp- gotta design it right), then buried below the structure. It takes multiple 1500gallon septic tanks to get there too, but seems more managable than 325 barrels. (None of that plumbing will ever leak or need to be repaired, right? :-( )
Hopefully 40 therms the right order of magnitude for storage (You don't say how much greenhouse or how well insulated it is, or whether this is for frost-control vs. maintaining some other minimum temp.) Peak loads will likely occur in January/February while the water is still pretty warm, and by March the daily input from the thermal array + passive greenhouse gains start picking up big time (and was never zero, even in December/January). It may want a smaller higher-temp tank to utilize for late winter/early spring short term peaks but if there's back up it might not be cost-effective. Hope you've done the math right though, on the actual peak loads & delivery systems as well as the total seasonal load. Assuming the greenhouses are insulated and multiply-glazed a wood stove for backup can do wonders to help keep up when the daily highs only reach -5F, even if the hydronic systems are tapped out.
dana
I Wish You Luck
Really... I wish you luck. At one time I considered using evacuated tube solar collectors to keep a large storage tank in the basement full of hot water. The water could then be used as a pre-heat for domestic hot water use, and to feed a ground source heat pump (in a standing column well configuration) for concentration and distribution throughout the house.
The idea seemed pretty strait forward to me, but I wasn't able to find anyone willing to engineer the system. In this area of the country, many people still believe GSHPs are experimental - let alone using solar panels to add heat to the system. With 80-90 F entering water temperature, the efficiency of a GSHP soars - think 600-700% efficient!
Here are a few of the issues I know about:
There is one more thing... very few banks are willing to finance experimental homes.
If you are interested in reporting on the progress of you house on this site, let me know and we can work something out.
Ed
Mr. Green Dreams
NanoSolar spigot has cracked open!
They've opened the valve, let the photovoltaic floods begin:
http://www.nanosolar.com/blog3/2007/12/18/nanosolar-ships-first-panels/
Don't hold your breath on getting panel-product at $0.99/peak-watt, but CIGS technology may drive some silicon vendors out of the biz if they can't develop their own low cost/high efficiency PV technology. Raw materila costs for a silicon cell are more expensive than the anticipated retail price of a CIGS cells, watt-for-watt. Interesting times!
dana