Photo-Voltaic solar panels are very expensive. Most of a home's energy needs are for heating water, heating and air-conditioning. All of these can be met with thermal solar collectors which are much less expensive. The thermal solar panels would heat water stored in a hot water tank which then can be used as hot water, to heat the home, or as the heat source to a Lithium Bromide Absorption chiller to air-condition a home. With the base line needs met without expensive panels and without inefficient energy conversions, only a small Photo-Voltaic array would be needed for the remaining power needs and since those needs are variable, there would still be power to sell to the grid.
Just read some of the other posts and I am surprised at the answers. Solar thermal systems typically have a payback of less than seven years on residential system without the tax break. A complete system can be installed for about 5k or less. Compare that to 20k or more for PV with a fifteen to twenty year pay off. Each home and area is different so a site evaluation must be done for exact figures and pay offs. I am going off my own experience in my above statements Flat panel collectors work well in most areas for DHW. Evacuated tubes often run too hot which works well for some applications or high usage. Heating water is the single greatest energy usage other than space heating and cooling. It often surpasses the two above systems based on its widespread usage(every houshold in USA has one) and its the amount it is used(24/7@365) The amount of energy spent to heat water is by order of magnitude the greatest number out there. Having a solar thermal system providing hot water for a average American household is equivalent to taking 40,000 miles off the freeway in a car every year. The BTU's required to heat the water is huge. So why is this more developed cheaper and more efficient technology behind PV in awareness? Natural Gas the number one choice for heating water is cheap. It's by product is invisible and misunderstood. What I find fascinating is if you look at the increase in Natural Gas vs Electricity you will be surprised by how much it has jumped in the last seven years. It is not talked about nearly as much as electricity It does not get the same level of press that PV does. So in short the answer is cheap Natural Gas prices and public perception of this product have kept it off the list of many that are turning toward the green trend. It is less sexy than watching your meter spin backwards. It is the best improvement at the best cost except for conservation which is and was the most cost effective energy saving that can be employed
Solar thermal systems aren't really that much cheaper. You have to have complex systems to pump the water, heat exchangers, regulate the temperature in the panels so it doesn't get too hot, regularly inspect it for leaks, have a system to maintain a constant output temperature, etc. The return on investment of such systems are usually very long, on the order of several decades, even for very large buildings. If they were cost competitive with traditional heaters then they would already be much more widely used I think. Plus with solar thermal you have the unfortunate reality that technologically they aren't going to get much more advanced. That's probably not the case for PV panels. So the only way I can really see solar thermal being used on a larger scale would be some kind of subsidy. PV on the other hand may have a breakthrough tomorrow that drastically reduces its cost. I'd be curious to find out how well those solar AC units actually work though, I can see how they might have potential.
That sounds good to me. I'm all for any kind of new energy as long as it's renewable and doesn't pollute the environment. I'm even a fan of solar water heating.
you completely nailed it!! speaking about large buildings, it would benefit one to do a little more research. my company just installed a 640 collecter system on a million sq foot building. it consists of a absorption chiller (which uses no coolant, just water a silica gel beds, runs of the power of its controller, thats it) 27,000 gallon tank. chiller feeds 2 rotation units and 2 large office spaces for heat and cool. payback expected at less than 5 years. we will expand this system another 200 collectors. residential installs, if tax credits used, achieve 5-7 year payback pending domestic hot water only or dhw and space heating. thermal collectors actually produce more energy than pv panels do, therefore more bang for your buck, also as i hope you all know, pv has around 25% eff, thermal has 95%. also to say the tech part is gone, we use flowmeters that calculate carbon offsets, energy saved, money saved etc...all located in a wireless monitor for the consumer to enjoy.
I agree with you John and for the same reason already put forth as a negative. Solar thermal is a more mature technology. This is the reason why I spent so much of the last winter studying it. I can be reasonably sure that what I learn will not be obsolete tomorrow with a new technological breakthrough. I built a solar addition/greenhouse to personally study the effects. So solar thermal panels are not the only way to go. With respect to electrical production. I have seen parabolic reflectors coupled to stirling engines and solar thermal trough heaters used to supplement steam generation for alternatively gas fired steam / electrical generation plants. On a trip to China over 4 years ago I noticed solar hot water vacuum tube collectors being sold in their local hardware and big box style stores. These were gravity fed package units intended to have the tank on the roof with a supplemental electric backup. The vacuum tube collectors seem to be one of the latest innovations in this technology. Using phase change materials temperatures in these panels can be produced in excess of 400 deg F. and they are useful in colder temps and on cloudy days. While they are still costly for many applications, I have been discussing the use of vacuum tube collectors with the owner of a laundrymat. Solar thermal will not pay back as well as conservation in many cases of older construction, but it currently seems better than photovoltaic panels. Solar thermal requires more understanding of systems and relative efficiencies. In one way solar thermal is more like the electric car while the internal combusion engine is like photovoltaic. The idea of producing electricity from the sun is a sexier idea. It is also more in line with our paridigm of: just producing lots of energy and to H with any conservation efforts. For that reason it seems to get more press.
