Bi-Directional Solar Chimneys by Robert J. Rohatensky The Solar Heat Pump Electrical Generation System (SHPEGS)
This page of the website is still under construction
The main focus of the design is to build a feasible renewable base load power station for moderate climates like Canada and the northern U.S.A., Asia and Europe where there is high solar insolation during the summer, but very cold temperatures and little daylight in winter.
A convection tower (bi-directional chimney) allows the large quantities of air to move across the heat exchangers taking advantage of buoyancy to improve air exchanger efficiency over a forced air system. A large heat storage system (water, sand, stone or earth, either natural or man-made) is used to store both the heat from the air and the heat collected from the solar/geothermal source until the air is cooler (either day/night cycle or seasonal). This stored heat is relatively close to the system (as compared to deep geothermal) and the energy to pump the heat is relatively low.
How it Works
A tower is built to allow large quantities of air to move across heat exchangers by natural convection due to buoyancy.
Solar thermal or deep geothermal heat is used to power a heat pump which moves a much larger amount of heat from the air.
Both the heat from the air and the heat powering the heat pump are stored in shallow heat storage.
The thermal storage is used to exploit the difference in temperature changes due to day time heating between the air and shallow underground, either day/night or seasonally. In effect this creates a local geothermal source and the low media transfer energy allows for an efficient geothermal power generation system. This source is reliable and may be used for base load electrical generation and structure heating.
In moderate climates where there is substantial differences in air temperature through day/night and/or seasonally, the system would function bi-directionally.
"Hot Air" cycle (ambient air warmer than ground)
A low boiling point fluid (ammonia) is expanded in the heat exchanger in the tower and where it boils (anhydrous ammonia boils at -33C) and expands. The ammonia is then absorbed into cool water. This aqueous ammonia solution is heated by solar thermal collectors or deep geothermal heat and the ammonia boils off under pressure. The ammonia vapor is condensed and the pressurized anhydrous ammonia is then returned to storage. Some of the heat is converted to electricity and the subsequent heat is stored. The cooled air falls in the tower creating wind and this energy is also captured in the wind turbines.
Step by step detail (PDF format)
"Cold Air" cycle (ambient air colder than ground)
Flow Animation (requires FlashPlayer)
The heat stored underground is used in a turbine very similar to existing geothermal systems. The turbine is air cooled with heat exchangers in the tower and the heat causes convection in the tower and this is also captured in the wind turbine and converted to electricity.
In high humidity tropical climates, the ambient air temperature remains relatively close to the shallow surface earth temperature and the temperature gradient would not make a bi-directional system feasible. The extraction of clean water from the humid air at a height is a major benefit of this system in a tropical location. A twin-tower in a "U" shaped system with a continual down and updraft air flow would be a design intended to dissipate as much heat as possible in the hot climate. The system would use large anhydrous ammonia storage to allow night operation and require large solar collectors to recover the ammonia in the day. During sunlight periods the solar collectors and ammonia storage would need to be large enough to allow sufficient ammonia to be recovered/re-pressurized to allow for continual operation. The system wouldn't use thermal storage and the ground would only be utilized as a heat sink to dissipate excess heat.
Many people have difficulty visualizing why this system in net energy positive, because when refrigerants (low boiling point fluids) are mentioned they lose the concept of the steam engine and start thinking about refrigerators and air conditioners. Refrigerators and Air Conditioners require energy (are not net energy positive) because they are moving heat from a cold area to a warmer one (like pumping water uphill), but this system is always moving heat from a warmer area to a colder (like water flowing downhill) and is energy positive.
In an arctic climate where there is access to medium temperature geothermal a much simpler system than existing low-boiling-point fluid steam turbines can be built with a convection tower. The major benefits of this system are simplicity potentially could have lower construction and maintenance cost than complicated low-gradient fluid turbine systems.
This system would perform well through the cold season and the temperature gradient from 70ºC geothermal to -30ºC ambient air allows for high efficiency. For this system to be efficient in a convection only system, the tower would need to be extremely tall.
Introduction of moisture to the air lowers density and increases buoyancy, but will probably cause snow and ice crystals to fall in the local area.
Very Basic Concepts
Warm humid air is less dense than cool dry air and this causes convection due to buoyancy
Water vapor is less dense and lighter than air (this is a little counter-intuitive for many people)
The heat from the air is "upgraded" by the ammonia system and the system output is all of the heat from the air plus all of the heat to move it
Geothermal, Biomass Coal or other waste heat may be substituted for or supplimented to the Solar Thermal Collection
When a liquid boils, it takes more heat than normal raising of it's temperature and it greatly expands in volume creating pressure
Boiling point increases with pressure
When the sun shines, the air warms up quicker than the earth (shallow underground)
At night or in winter, the air cools off quicker than the earth (shallow underground)
Heat moves from hot to cold with a force, when this happens some of the energy can be converted to mechanical energy
The Concepts in More Detail
When the temperature of the air is changed compared to the surrounding air, the density changes and it makes the air heavier or lighter than the surrounding air and this causes convection. Wind.
Matter that is more more dense takes more energy to change temperature than matter that is less dense. The temperature of the earth below the surface or in bodies of water changes temperature slower than the air does because they are more dense and they also take longer to cool off.
To "capture" mechanical (electrical) energy from heat, heat has to be moved from hot to cold. It doesn't matter where the heat is moving, but the mechanical energy captured is always a percentage of the heat that is moved based on the absolute temperature of the "cold" sink. The more heat that moves between matter and the larger the difference between the hot and cold sinks, the more mechanical (electrical) energy can be captured. An easy way to visualize this is by imagining a hydroelectric dam on a river. Some of the water may be used to generate power, but because the output of the dam is usually above sea level, you cannot use all of it. Getting mechanical energy from heat works the same way, it is always a percentage of the heat being moved and the amount of energy that can be converted is a function of the quantity and the difference in temperature between the hot and cold source. The difference between the cold sink and absolute zero determines the efficiency of the system. Water flows downhill with a force and heat moves from hot to cold with a force and both require energy to reverse the process.
During day/night or seasonal changes, there are substantial differences in temperature between the earth and the air. That difference in temperature can be moved from hot to cold and some of that energy can be used to generate electricity.
Except for a very small portion of the earth, the ocean (or ground) isn't always colder than the surrounding air. The air temperature in Western Canada swings from +30C to -30C, but the earth temperature a few meters below ground stays at around +3C. Just as much power can be generated from -30C air as +30C air.
Water freezes and the transport media has to have a lower freezing point than the coldest ambient air to have a location independent system.
If the thermal storage is either a natural or man-made underground system, it won't harm the environment. Denser materials like rock or metals will hold even more heat than water.
The system is base load electrical generation.
The solar energy collected is used to move a much larger amount of heat from the air.
The heat pump system can be powered from multiple sources (solar, geothermal or waste heat).
This system will be available in sub-zero temperatures and can generate as much power when it is really cold as when it is really hot.
Due to the reversible cycle, the energy stored or removed from the earth is used in the opposing cycle.
The system should be scalable from the single dwelling or remote equipment power source up to the MW grid project.
The system is "tuned". The more heat transferred through the heat pump, the more convection occurs. The more convection that occurs, the more heat transferred through the heat pump. The more heat that moves the more mechanical energy that can be "harvested" and converted to electricity.
The condensation on the cooling coils may be used to provide a clean domestic water source or for irrigation as a by-product during the air cooling cycle.
The system should operate in a wide range of climates with the limitation that there is sufficient solar heat above ground level and sufficient thermal transfer below ground level .
A rotating or finned air intake/output leveraging prevailing winds would increase performance and it should also improve system startup.
The system could be integrated with biomass methane production or with algae agriculture.
Actively "cooling" the pumps, turbines and generators and using the heat will make it very efficient. (contributed by Mark Smith, September 2006).
In colder climates where the ambient air temperature is below freezing for 6 months of the year, the system is really "renewable" because the amount of heat added and removed from the ground balances on an annual cycle.
In some locations there are natural geothermal heat sources at deeper levels that may be used in low solar isolation areas.
The physics of this design have not yet been in question, but the economics of the capital investment has. In calculating the economics of non-trivial renewable energy systems the traditional study using current market prices of goods and services is flawed. Our current economy is based on non-renewable energy and therefore it is a large portion of the "cost" of goods and services for common materials and construction. Eventually non-renewable energy systems run out of supply or cause damage to the ecosystem and the "cost" of damage to the environment is hidden for the short term comparison.
A fair evaluation of a non-trivial renewable energy system is energy input for materials, construction and maintenance versus energy output or EROEI. If a system can be constructed from common materials that will not be in short supply, the feasibility of the system is whether that system can produce enough renewable energy to construct a like system within a reasonable length of time. The initial capital cost is largely irrelevant if the energy output criteria is met and the system is a maintainable and a renewable energy source.
Of course, our economy currently is not based on renewable energy and until a substantial portion of our energy supply is met by truly renewable sources, real world economics are very important. The design criteria for this system allows for this by allowing for simple integration with other clean energy systems. The seasonal thermal storage may be used to heat buildings, ethanol fermentation or methane bioreactors. Biomass pyrolysis gas and methane can be burned in reciprocating or gas turbine engines and the heat output readily integrated. Biodiesel and Ethanol production facilities can also become more feasible with integration into this system.
Our current economy is based on finite resources. As an example, if an oil or gas well is drilled, there is an exploration cost and drilling cost. Eventually the well runs dry and again there is an exploration and drilling cost. This same problem is appearing with semiconductor supplies in Solar PV. As more finite resources are used it becomes more difficult and expensive to locate and collect and the economy continues in inflation. The constant increase in the price of fossil fuels also increases it's own exploration and extraction cost.
If a completely renewable system can be built from common materials and can produce enough renewable energy to build a like system within a reasonable length of time, it is feasible.
Why This is Published Openly
Although this idea has huge potential and it could be exploited for personal gain, there are several reasons for putting this idea forth on the Internet.
Economics. We are not running out of coal or uranium in the near future and we probably won't run out of oil prior to a normal patent expiry. A commercial venture into renewable energy is competing against these relatively cheap energy solutions and currently is not a very viable business. An example of this is the Athabasca Oil Sands. This is a scheme to extract oil from petroleum tar sand using large amounts of petroleum to extract, build infrastructure and construct processing plants and processing the sludge into oil takes huge volumes of natural gas. From the environmental point of view, this is insane. In reality the tar sand projects have been able to attract billions of dollars of investment, turned Fort McMurray into a boom town and are going forward very quickly. The reason that this type of mega-project is able to proceed is that it is still much more profitable than most renewable energy ideas. A new idea in renewable energy is priceless to society and worthless to an individual with a normal lifespan at the same time due to these types of projects. In areas without tar sands, renewable energy has a difficult time competing with coal or uranium.
One has to look at pre-oil age construction techniques and materials that built the pyramids and the castles and cathedrals in Europe and not at modern oil based construction. Prior to 1900, everything was built without petroleum and lack of stones didn't end the stone age. This is an example of 190 feet (3000ft2) of stucco wall built by one person by hand in their spare time over a summer, but you can't be afraid of a shovel.
To create a commodity out of this system as soon as possible. Competing against non-renewable energy takes a large amount of innovation, efficiency and in a very long timeframe renewable systems will not run out of fuel and prevail over non-renewable systems. It is very difficult for a single commercial venture to sustain operation until that time.
The principles and project management of Linus Torvalds with Linux and the many other contributors to Open Source and Free Software have shown such success with large projects. This actual construction of this type of project is very different than software, but the concept and design of the system can be managed the same way as open source software and show the same rapid development of new ideas.
There are many people with good ideas and a willingness to help, but Mechanical and Electrical Engineering and Physics are not their field. In this type of project, there are social, economic, environmental, political, information technology and financial tasks and the engineering and construction of the system is actually a small portion of the development and deployment. The project spirit is based on bringing people together to work on something that has benefit for everyone.
People want to live in a world where there is clean, cheap energy and they will help to bring that about.
Solving the problem, not getting rich. We don't have a practical alternative to fossil fuels because most people and companies are trying to make a lot of money solving the problem. They concentrate too much on the financial gains and not enough on solving the problem.
Energy is fundamental to modern society and should be owned by the people not the corporation. People have morals, corporations have responsibilities to their shareholders to show large profits.
Although the entire project is being managed in a not-for-profit manner, the intent is to work with business. The detailed design, manufacture of the sub-assemblies, construction, system operation and integration with existing operations and waste heat sources can create many economic opportunities.
I learned very early and painfully that you have to decide at the outset whether you are trying to make money or to make sense, as they are mutually exclusive.
- R. Buckminster Fuller GRUNCH of Giants, 1983
The Project Goals and "What Can I Do?"
The energy problem and the project to solve it are large and complex and require resources from many fields. The initial design and prototype require engineering resources, but there are many portions of the project that require diverse skills from administration, project management, software and web development, marketing, financial organization or even just fresh baking. But please, don't send money. At this point the project is in research and development and the minimal costs of web hosting don't require any external funding. There are many "free energy" scams in the world and this isn't one of them. If you have an interest in donating some of your time and skill, the project is looking for resources that see the merit in the system and want to help.
Contact Robert J. Rohatensky
if you have an interest in helping with this project.