For centuries innovative and resourceful designers and builders have recognized that the most fundamental efficient Renewable energy systemsExplore the evolution of solar thermal collectors, vital for renewable energy systems, offering sustainable heating and cooling solutions for homes. is the direct energy of the sun. They have used the heating factor of the sun both passively and actively to heat a house or building.
The earliest example I have seen of a solar thermal collector was in a house in Western Upstate New York that was built in 1735. Exactly when the solar thermal collector was installed, I do not know. The designer installed iron pipes in a series of tubes on the zinc standing seam metal roof. The pipes were on the south side facing roof. The interior dimension of these pipes was approximately 1” and the series of pipes was more than 100 feet. In the basement he had a 100-gallon tank of water which was kept heated with a fire. This supplied a closed loop radiator system that provided heat for the house.
Since then, many different variations of flat plate solar collectors have been utilized that absorb the heat from the sun using pipes full of liquid to provide domestic hot water and water source heating for the house.
In the past two decades solar thermal collectors have advanced significantly and become more than 80 % more energy efficient in capturing and using the heat of the sun than flat plate collectors. This has been advanced through the technology of Evacuated Tube Solar Thermal Collectors (ETSC) As this system has improved and the demand for thermal energy has increased so has the price decreased to make it a much more viable option than flat plate solar collectors. Furthermore, the usable energy of the sun is 53% more energy efficient than the best technology Solar Voltaic Collectors.
The highest energy consumption for residential use is in heating and cooling a house. So the first approach to addressing this issue is in lowering the house’s thermal load by making the envelope of the structure more resistant to heat loss or gain. The next step is to design a highly energy efficient heating and cooling system that most effectively uses the sun’s energy at the lowest cost for that exchange in energy both in initial cost and lifetime costs.
So most would assume that the options would be in the question of using Solar Voltaic Collectors which generate direct electricity from the sun or Solar Thermal Collectors which capture heat energy?
For many the comparison in cost between installing an Evacuated Tube Solar Thermal Collector or installing a Solar Photo- Voltaic Collector (PV) to do the same basic task of providing quiet, clean water source heating and continuous domestic hot water is all you care to know. A well-built, highly energy efficient house to best justify the initial cost of these systems is the same given. For a 1500-2000 square foot house the average cost of a Solar Photo-Voltaic Generator with inverters and back-up batteries is $30000.
For one third of the face surface to operate a heat and cooling system using Photo-Voltaic generators you can install an Evacuated Tube Solar Thermal Collector which can heat and cool your home.
In both applications the surface space is usually on the roof. For both the optimal location is where you have the longest solar exposure throughout the day and throughout the year. The roof may be the place for these installations; however, it is not always the best. In most cases the roof is not the best place for Photo-Voltaic Generators because the radiant heat from the roof affects it’s optimal function and shortens it’s life expectancy.
So for PV Collectors the circulation of air over and under the unit is best and its average life expectancy is 11-17 years, depending upon what PV technology is utilized. The lithium batteries must be replaced on an average of every five years. The production and disposal of these batteries is a big long term question concerning sustainability, which I will address in a future blog post.
For Evacuated Tube Solar Thermal Collectors, the radiant heat from the roof improves its thermal function and has no effect on its lifetime function. An Evacuated Tube Solar Thermal Collector will put out consistent direct solar thermal energy for at least 25 years. Usually, the only thing you may need to replace in such units are the evacuated tubes that might break or lose their vacuum seal. This involves the simple task of unscrewing an affected tube and screwing in a new tube.
Now back to addressing the costs differences between a Solar Photo- Voltaic generator to produce the energy needed to heat and cool your house and the costs of Evacuated Tube Solar Thermal Collectors to do the same thing. The installation costs for such a unit including storage tanks and liquid circulators for 1500-2000 square foot home is $8500. What a difference! Such a small investment for a lifetime of free thermal energy from the sun.
So, what is an Evacuated Tube Solar Thermal Collector (ETSC)?
The aim of Solar thermal collectors is to absorb as much solar heat energy as possible and to retain that heat in a liquid medium. In other words, solar collectors convert solar radiation into thermal energy and reduce energy loss. ETSC’s improve this energy efficiency over flat plate absorption collectors by using glass or plastic cylindrical clear tubes that have within them copper tubes with a reflective backing that absorbs the radiant heat from the sun.
These absorption tubes maintain their radiant energy by being sealed inside a clear vacuumed tube. This acts as a diathermia wall. The internal absorber is a copper heat pipe that contains a vaporized fluid that makes it possible for the heat transferred fluid to reach temperatures that exceed 250 degrees (F).
This means that this heat has the possibility of running a steam electric generator or hydrolyzing hydrogen from water to be collected in pressurized tanks to operate an electric generator instead of being dependent on back up batteries which when spent has to be disposed of as hazardous waste.
I see the future of truly renewable sustainable energy as a micro-grid for individual residential use or for a system that may power a neighborhood or a city as in a hybrid approach of using the direct energy of the sun in ETSC, PV, and wind generators with the end goal of the most efficient means to power hydrogen fuel cells which can produce electricity to power whatever size grid during low light conditions. It is my opinion that the most cost efficient and energy efficient route to this end is using direct thermal energy from the sun.
In moderate climates the most efficient use of this thermal heat is in direct heating water as the vaporized liquid. This provides direct heat for domestic hot water and for water source heating for the home either through radiant tubes or hot water run through coils in the air handler to heat the home.
In climates especially that have a high gradient temperature between day and night or climes which have many days without sun or temperatures below freezing, then a liquid like glycol is the absorbent liquid. The vaporized liquid rises to the condenser and the heat manifold and turns back to liquid and falls back to the solar exposed space. In such a system there is a built-in storage tank that maintains this cycle with natural thermal convection.
In most closed loop systems, the heated fluid circulates through a water heater and through a system of radiant tubes either in direct radiant heat or through coils in the air handler and returns to the ETSC using a circulating pump to supply domestic hot water and for water source heating for the home. We recommend a dedicated low wattage circulating pump supplied by a photo-voltaic generator.
Since the heat absorption tubes are protected within the evacuated tubes that prevent the loss of thermal energy and maintain the maximum heat absorption and because the evacuated clear tubes are cylindrical this system works effectively from sunrise to sunset and even on overcast days. Furthermore, the vacuum seal makes the system impervious to energy loss on cold days or the flow of air around the tubes.
This system using cylindrical tubes optimizes the total thermal surface area for collecting thermal energy. The vacuum seal also prevents corrosion from the effects of the environment or from collection of condensation. This translates into continuous production of thermal energy every day, every season for a lifetime.
This means this system saves you in energy costs consistently for many years directly using the free thermal energy of the sun. Now with solar thermal collectors surrounded by a clear cylindrical vacuum tubes consistently provides heat for heating water for domestic hot water and for heating the home is a no brainer for this purpose, but it can also be utilized for a cooling system through desiccant cooling as well.
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A desiccant cooling system uses a material that removes moisture from the air with resulting cooling of the space where the relative humidity is extracted. A common readily accessible and inexpensive desiccant could be silica gel. Here is how a desiccant cooling system would work in conjunction with Evacuated Tube Solar Thermal Collectors.
The ETSC provides consistent heat through the heated liquid medium which is produced by direct thermal energy of the sun. This heat is transferred to a desiccant wheel or rotor. The desiccant wheel rotates between the air flow and the heated fluid, which allows the desiccant material to absorb the moisture from the air.
As the desiccant absorbs the moisture from the air it releases latent heat, which cools the air passing over it. The cooled dehumidified air provides effective cooling for your living space. In all our eco-sustainable plans we integrate the use of Evacuated Tube Solar Thermal Collectors as an integrated part of our heating and cooling system because it captures the direct thermal energy of the sun as a highly consistent, energy efficient and inexpensive heating and cooling system year round.