Shortage of Solar Hot Water Collectors
21 Aug 08 | General Business, Solar Hot WaterThis was almost inevitable. It seems that there is a growing shortage of solar hot water collectors. One manufacture that I spoke to is having difficulty getting glass for its larger sized collectors. Others are struggling with higher product demand and fixed manufacturing assets. Solar thermal manufactures may be leery of making large investments in facilities because congress still has not approved the renewable energy tax incentives past December 31, 2008 (which is fast approaching).
On the surface, this would seem to be a good thing. The solar business is growing, more and more people are aware of solar, not just Photovoltaics, but solar hot water too. More and more people want these systems installed on their homes and businesses to off set energy use and save money. Those are the positive aspects.
However for a solar installer, it is difficult to get business if you cannot give the potential customer an installation schedule. I am right now, waiting on several collectors to show up so I can finish two jobs. I am also leary of Congress and the lack of progress on the renewable energy tax credits. As I have said before, unless they pass, a great majority of home owners will not be able to afford solar thermal systems. I do not want to take on a large inventory of flat plate collectors that I will not be able to sell in six months.
And so we wait.
I curse incentives and subsides. Too much tinkering around with the market forces if you ask me.
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Tags: Solar Hot Water, solar thermal
Do solar panels increase global warming?
01 Aug 08 | EnvironmentI have had several people tell me that solar panels, both photovoltaic and thermal, increase climate change, aka global warming due to the local “Heat Islanding” effect.
Others have said the cost (in CO2) of manufacturing and shipping solar panels is more than there subsequent use would eliminate.
Solar panel Heat Islanding
There is some validity to the first concern. If you take an area that was normally light reflective and put a solar panel in it, less light is being reflected and thus more heat is being generated. However, in the case of a solar thermal panel, most of that heat is then conducted away by Heat Transfer Fluid (HTF) for use or storage. A typical solar thermal panel is 65-70% efficient at converting and removing the energy striking it. The remaining 30-35% of the energy is either reflected off of the glazing or the absorber plate or it is lost due to heat transfer inefficiencies, insulation losses, etc. In short, a solar thermal panel is very efficient at collecting energy and removing it. Having a solar thermal panel on the roof of your house would reduce the solar gain because most of the heat energy is being removed to another location and the panel shades the roof it is attached to.
Photovoltaics however, are not as efficient as solar thermal. The average PV panel in use today is around 15% efficient. Some of the energy passes through the panel and some of it is reflected. Therefore, about 80% the energy striking the panel is converted to heat. The average insolation on earth at mean sea level is 1,000 watts per square meter per hour.
A 4.3 KW grid tied solar system has 24 Sanyo HIP190BA3 PV modules. Each Module is 1.16 M2. The total area is 26.78 M2. Therefore the total energy striking this array is 26.78 KW/hr. The total heat being generated by this array on a sunny day is about 22 KW/hr or about 75,000 BTU/hr. In the mean time, it is producing 4.3 KW of electricity. The average peak sun hours in the Hudson Valley is 4.5 per day so this system can be expected to produce an average of 19.35 kWh per day or 7063 kWh per year. Electricity production in the United States is about 32% efficient. Therefore, that 19.35 kWh if purchased from the power company, would have produced 13.16 KW of waste heat and 32.9 pounds of CO2 vs 99 KW of waste heat and zero pounds of CO2. This system will save 12,000 pounds of CO2 per year or 150 tons of CO2 over a 25 year life.
This should trigger two questions; How much of the sun’s energy would have been absorbed by the surface of the earth and turned into heat regardless of the solar panel and what importance does CO2 have on climate change. To answer the first question is rather complicated. It depends on the color of the surface, the angle of the sun striking the surface and the atmospheric insulative effect. The second question is a little easier to answer
CO2 in the production of solar panels
It takes about 3.6 years (in average insolation) for a PV cell to make the energy used in its production. Therefore, over a PV cell’s 25 year life, it will produce electricity and contribute 86% less CO2 than electricity generated by fossil fuels. This reducing in CO2, a known Green House Gas (GHG) which is thought to be significantly contributing to the global rising in temperatures more than off sets the local heat island effect that PV panels have.
Solar thermal panels take much less time to payback because they are made mainly from copper (absorber plate and piping), aluminum (frame and mounting), insulation and glass. These materials are readily recyclable which greatly reduced the energy required for extraction and refining. Additionally, a solar thermal panel is much more efficient at collecting energy, so the energy payback comes in about 1.5 years. Most solar HW systems have some type of AC pump. Taking that into consideration, the Energy Returned on Energy Invested (EROEI) while the system is operational is about 15, or for every 1 watt of electricity used, 15 watts of energy are gained. In the Hudson Valley, a two panel SDHW system can expect to save about 3,350 kWh per year. That equals about 5,690 pounds of CO2 per year or 71 tons of CO2 over a 25 year life span.
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Tags: climate change, Environment, photovoltaics, solar thermal
The other Solar Thermal; Solar Hot Air Collectors
22 Apr 08 | solar thermal
We have written a good deal about solar thermal on this blog. One thing that has not been covered are Solar Thermal air collectors. These units look similar to hot water collectors, only they use air as the Heat Transfer Fluid (HTF).
Solar hot air collectors have several advantages; They are easier to install and many do-it-yourselfers can install one or two hot air panels in a weekend. They can be mounted on south facing walls or roofs. Shading by deciduous trees is not an issue, since summer time heat production, in most cases, is not desired. They do not contain liquid, so freeze protection is not necessary. They also can most often be power by a small PV panel, which means they require no outside energy input.
The main disadvantage is they have no heat storage capacity, nor can their heat output be transported easily to another part of the building. When the sun is shining, you get the full effect of the sun’s energy (about 1 KW per M2), minus the incident angle losses. For the average solar hot air collector in a category C environment, that is about 10-14 KBTU/day per Ft2. They are also slightly less efficient than liquid flat plate collectors because water is a better HTF than air.
There are two companies that make SRCC certified solar air collectors, Your Solar Home and Environmental Solar Systems. They consist of a flat plate collector with solar selective coating in and aluminum frame. Both units have DC powered fans, one comes with a 14 watt PV panel, the other comes with a wall transformer for 120 VAC. They look comparable in size/output and price. One is made in Canada, the other in Massachusetts.
A real DIY person could potentially make their own solar thermal panel if they had the proper motivation.
Update: Stephen let me know that my research was not a through as it should have been:
You missed the solar hot air units from Newfoundland Canada. I am a reseller of the product.They have over 1000 of them out in the real world. They work well in Newfoundland where they only get 1500 hours of sunlight.
Their website:
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Tags: solar thermal
Solar Thermal Systems
21 Feb 08 | GeneralWhen you say solar, most people assume that you are talking about photovoltaics. Solar thermal systems have been around for longer than photovoltaics and have a proven track record of working well and paying back there costs many times over.
I install both types, and lately I have been receiving quit a few calls regarding solar thermal (i.e. solar hot water, or radiant floor heating) systems. I think this will continue as the price of energy goes up.
A solar thermal system move fluid through solar collectors, which collect heat. The fluid is then stored or used in the building. In reality, a solar thermal system is about plumbing. A Solar Domestic Hot Water (SDHW) system has three unique parts that other hot water systems or heating systems don’t have. The first is the solar collectors, the second is some type of heat exchanger and the third is some type of controller. As regarding the solar collectors, I believe that SDHW systems work best with flat plate collectors.
The flat plat collector design has been around for many years. Newer solar selective coatings have been created that increase the system efficiency. In addition to that, better insulation and better high transmisity glass have all improved on the flat plate collector design. Evacuated tubes run at higher temperatures and have problems with the seals between the glass tube and the copper pipe on the inputs and outputs of each tube.
The next unique thing in a solar system is the heat exchanger. The heat exchanger takes the hot fluid from the solar collector and cools it with the fluid from the solar hot water tank. This can be implemented in a number of ways. Some heat exchangers are part of the solar storage tank, some are a part of a drainback tank, and some are external. All heat exchangers are made of metal (stainless steel or copper) and use counter-flow properties to move the heat from one fluid reservoir to another.
Finally, the system controller, which measures the temperature of the collector outputs and the solar storage tank. If there is enough energy in the collectors to transfer to the storage tank, the controller turns the system on, which begins collecting energy.
Beyond that, a solar system is copper piping, valves, drains, hot water tanks, pumps, and other miscellaneous hardware which is all available at the local plumbing supply house.
Solar thermal systems that are designed for space heating are very similar to SDHW, only they are usually quit a bit larger with more storage.
In most cases, all solar thermal systems should have some way of operating in backup mode in case there is a long period of inclement weather. These back up systems entail some type of conventional heating system installed in parallel with the solar system. For example a SDHW system may have an electric tank or electric element in the solar tank designed to turn on if the water temperature gets too cool. A radiant floor heating system may have a small oil or gas fired backup furnace in standby duty.
A well designed solar system should be designed to produce about 80 to 85 percent of the energy needs. More than that and the system design will be too large, causing it to over produce and over heat under normal operating conditions. Less than that and you are leaving a good deal of money on the table, to be taken by the gas/oil companies.
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Tags: radiant floor heat, SDHW, Solar Hot Water, solar thermal
Does solar hot water work in cold climates?
03 Jan 08 | Solar Hot WaterI was at a lecture this past September when the speaker stated “Solar thermal just doesn’t work in this climate (the Northeast), it is not a consideration…” I wanted to stand up, raise my hand and say “Um, excuse me, but you are wrong.” There is a persistent misconception that solar thermal only works in temperate climates. The truth is that is works in cold climates as well. As evidence I submit the following:
It is January, the temperature outside is 17 degrees (that was the high temperature of the day) with a foot of snow on the ground.
The water temperature coming back from the solar collectors on my roof is 150 degrees.
Furthermore, last night it was 0 degrees and I suffered no freeze damage to the collectors or piping, even though I use distilled water as my heat transfer fluid.
This is no accident, of course. A properly designed and installed solar hot water (solar thermal) system can work in almost any climate. The snow surrounding the collector reflects sunlight unto the collector itself, making it more efficient. I have a drain back system, so when the sun goes down and the temperature drops, all the water drains out of the collectors into a reservoir inside the house. The collectors and piping all are sloped so that the water drains out properly thus providing excellent freeze protection without the use of expensive anti freeze.
Naturally, I didn’t say anything to the photovoltaic guy who made the above statement. After all, we are playing on the same team.