AU2016206225A1 - Pre Store to store thermal energy for use with a solar thermal power plant. - Google Patents

Abstract

Abstract The invention is a new and unique configuration and manufacturing method for making practical and low cost thermal storage, for solar thermal power plant. It stores most of the thermal energy in a mixture of solid particles. The thermal energy is stored at, or close to, the temperature of the receiver of Solar Collector Assemblies (SCAs). The invention is particularly suited for use with Reciprocating Piston Steam Engines (RPS engines). The invention can be used with steam turbines provided they are of the "wet steam" type, as used for nuclear power plants. SECTION A A IWO OPM IN :::XX x 100 Steel fin plates approx. 100mm apart each 5mm 0.3m TYP thick PRE-STORE DETAILS Fins Containment for soil fill Figure 2 - Section showing container corrugations

Description

description of 2016206225 18 Jul2016

In vi

The invention is a new and unique configuration and manufacturing method for making practical and low cost thermal storage, for solar thermal power plant. It stores most of the thermal energy in a mixture of solid particles. The thermal energy is stored at, or close to, the temperature of the receiver of Solar Collector Assemblies (SCAs). The invention is particularly suited for use with Reciprocating Piston Steam Engines (RPS engines). The invention can be used with steam turbines provided they are of the "wet steam" type, as used for nuclear power plants.

The particles are whatever material is at the installation or filling site. That means soil, mud, sand, ore, silt, gravel, clay or any mixture of these. Hereafter this mixture will be referred to as "soil", to describe any and all mixtures of the materials listed above. To accommodate the low thermal conductivity of these materials they are kept in close contact with a number of metal pipes and with fins/plates connected to the pipes.

With this invention the close contact is maintained by the constraint the pipes and container provides for the soil. It prevents relative motion between the soil, pipes and the plates/fins welded or otherwise closely connected to the pipes. For small systems there may be 16 pipes of 75 mm nominal bore, four rows of four pipes, approximately evenly spaced and about 3 metres long. For the largest systems there may be 60 pipes up to 11.8 metres long.

The pipes carry a heat transfer fluid. The fluid can be one of the many used for solar thermal power plants. These include but are not limited to steam, water, hydrocarbons, halogenated hydrocarbons, silicones and molten salts. In one preferred arrangement the phase changes from steam to water and water to steam provide the smallest temperature differences and least power for pumping the fluids. The smallest temperature differences provide the highest "Round Trip Efficiency” (RTE). The average temperature of energy extracted must be close to the average temperature of energy input to achieve the highest RTE.

The fins/plates are rectangular metal plates with surfaces approximately normal to the long axes of the pipes. For small systems the plates are about 1 metre square and spaced 150 mm apart. Each fin/plate is in close contact or welded to most or all of the pipes. The pipe centrelines are not horizontal. Rather they are at an angle between 5 degrees and 90 degrees to the horizontal. In one preferred arrangement they are at an angle of 15 degrees to the horizontal and contain a mixture of steam and water. This angle is in line with good practice for boilers, to facilitate blowdown to remove sediments and corrosion products.

In one preferred arrangement the steel pipes and the steel fins/plates are connected by automated Metal Inert Gas (MIG) welding. This connection method dramatically reduces the labour costs associated with the connections. It also maintains the full strength of the fins/plates, in tension, to hold the container walls so that the soil is well constrained and that all the materials (soil, pipes and fins/plates) perform as an elastic matrix when the temperature changes and soil temperatures vary with the distance from the pipes and fins/plates. 1

To keep the materials in close contact with the pipes and fins the materials are fully contained on five of the six surfaces of a cuboid and at least partially on the sixth surface, by the pipes and some partial covering of the top. The pipe axes are parallel to the longest sides of the cuboid. By this means the number of pipe end connections is kept to a minimum. 2016206225 18 Jul2016

Meeting the challenge of constraining the soil

Unless constrained the soil fill in a Pre Store will expand and contract with thermal cycling at different rates from the steel pipes and fins. This effect can reduce thermal transfer, by producing voids. However, the major challenge is that it would tear apart the constraining container if it was not strong enough. Turner (1979) takes no account of this effect. Terzaghi (1934 and later work) proves that temperature cycling can add to the soil pressures against adjacent surfaces, such as retaining walls.

These challenges are solved, with the unique inventive combined application of the steel pipes (provides axial constraint) and steel fins/plates connected to the corrugated surface of the cuboid container. The container continues, to partially cover the top surface of the soil and the pipes hold down the soil, to some extent. The steel fins/plates will be in tension to provide constraint in the other two directions orthogonal with the axial direction. One direction horizontal and the other approximately vertical.

The corrugated surface of the container limits their stresses, due to temperature differences in the steel and soil. This approach is similar to Morrison tubes used for combustion spaces in drum type steam boilers. However, the corrugation shown in Figure 2 - "Section showing container corrugations" are arranged to provide maximum strength for the weight of the container surface plates as they are loaded in tension, rather than bending.

The containment is constrained, in one direction, by tension in the metal pipes. The metal fins/plates provide the strength in the other two directions. Curved metal plates, connected to at least three sides of the fins/plates, constrain the soil. On the fourth side, the top, the corner detail and pipes partially constrain the soil but spaces between them permit filling the spaces between the fins, and around the pipes. Filling the spaces can use vibration, compaction or fluidisation to facilitate transporting the soil to the spaces within the storage units. The openings also permit removing the soil when and if the storage unit needs to be relocated.

The curved plates, that contain the soil, are joined to the edges of the rectangular fins by semi-automatic or robotic MIG welding. Also, at the bottom corners of the cuboid, the curved plates are joined to one another, in the form of a "lobster back", see Figure 3 -"Container corner detail". The top corners may be similarly arranged and extend to partially cover the top surface. This "lobster back" method is commonly used to join sections of pipe to make a bend.

Cycling of the thermal storage unit will cause the soil to move and pack more tightly against the pipe outer surfaces and the fins. There will also be some separation of particles of soil of different sizes and/or density. There is a limit to this process. When the soil is packed very tightly the pipes, fins and containing walls of the cuboid may form an elastic composite matrix then all relative motion ceases. In all cases the pipes, fins and containment plates will all be strong enough to contain the soil without exceeding the elastic limit of any of the metal components. 2

The packed soil particles may eventually be packed so tightly that further packing is not possible. Packed soil is hundreds of times less stiff than steel (Soebarto, 2009) so the design and geometry ensures that the entire Pre Store can expand and contract as an elastic matrix, with thermal cycling. The partially open top of the cuboid provides the means for packed soil to be removed and/or be "topped up”. By these means the system can accommodate a wider range of soil mixtures, the ones that pack tighter and tighter until they reach some limit and the ones that always remain loose and move very slightly on the surfaces of the pipes and fins. 2016206225 18 Μ 2016

Heating and cooling the Pre Store

In one preferred arrangement the manifold piping, at the lower end of the Pre Store, is fitted with steam injectors. Some of the upper pipes, the unheated (to some extent) downcomers, will have no steam injection. This ensures that water, with few or no steam bubbles, flows readily back from the steam drum to the steam injectors. The steam heated water flows will very effectively and evenly heat all of the pipes, fins/plates and soil. This method avoids the use of circulating pumps and the power required to drive them.

When steam is allowed to flow from the steam drum to the Reciprocating Piston Steam engine(s) steam bubbles will flow from all over the locations with the hottest soil in contact. Some of the outer layers of pipes will be slightly cooler and generate less steam bubbles. Water will flow down these pipes, to increase the water flow to carry the water with more steam bubbles smoothly to the steam drum for separation. This method closely follows the practice of most water tube boilers.

Prior Art for Solar Plant with Thermal Storage

Water for Solar Thermal Storage

In 1912 a solar thermal plant was installed, at Meadi in Egypt, for pumping water (Scientific American, 1914). The plant used water, at atmospheric pressure, to store heat. A steam engine expanded steam, from the storage, to a much lower pressures in a condenser.

The water, that stored the thermal energy, remained at atmospheric pressure at all times. That limits the maximum thermal efficiency of the system to a theoretical maximum of 18.7%, even with a condenser operating at 30°C. The actual efficiency, solar to mechanical energy was probably less than 8%, assuming the average trough solar to thermal efficiency was 65%.

Water can be practically used to store thermal energy at temperatures up to 355°C (17.57 MPa or 2533 psig). Beyond that storage temperature it becomes necessary to use pipes above Schedule 80 thickness or alloy steels and the cost increases significantly. However, the economic limit of pressure, for thermal storage, is much less.

The economic pressure and temperature optimum for thermal storage in water contained by steel, with the current price of vessels, is about 1.5 MPa (203 psig) and a saturation temperature of 198°C (388°F). That means that the theoretical efficiency of 3 thermal energy recovery, with 30°C heat rejection, is limited to 35.7% and practical efficiency with Rankine Cycle and reciprocating piston engines to about 23%. These figures change with the price of steel for the vessels and the cost of labour. The optimum pressure may be higher when assembly of vessels uses mass production methods, such as for Liquefied Petroleum Gas storage vessels. 2016206225 18 Μ 2016

Most Concentrating Solar Power (CSP) plant uses steam turbines. To provide protection for the steam turbine and ensure high system efficiency most use superheating of the steam and sometimes reheating. Using reciprocating steam engines operating at 6 MPa (855 psig and saturation temperature of 276°C) provides a temperature range of 79 K, for thermal storage, with no effect on energy conversion efficiency. A wider temperature range can be used to reduce the cost of thermal storage, to some extent.

Water and steam is most commonly limited, for coal-fired plants, to a pressure of 10 MPa (1436 psig) and a saturation temperature of 311°C. That pressure limit can support practical thermal to mechanical efficiency of 29% using only saturated steam supply and reciprocating piston engines with engine efficiencies widely demonstrated before 1922, (Gebhardt, 1928).

Steel Pipes with Sand and/or Soil for Solar Thermal Storage

Work in the USA from 1977, by Richard Turner (1979) demonstrated that using sand or soil, for thermal storage, is practical using steel pipes surrounded by moving or stationary sand or soil.

Turner recognized the need to contain sand and described concrete retaining walls, for one horizontal direction and corrugated steel walls with reinforcing columns and steel tie rods for the other direction. The tie rods were arranged parallel with the steel pipes. The description makes no mention of the steel pipes providing any of the constraint of the corrugated steel walls. Rather steel tie rods provide the additional constraint required. The tie rods described need to be high tensile steel just to restrain the hydraulic pressure from the depth and density of sand. No allowance is made for compacting of the sand increasing that pressure. That problem is well documented in grain silos.

Turner (1979) makes no mention of restraining the sand in the vertical direction. Also he makes no mention of how the pipes are constrained in the vertical direction other than at the ends of the long pipes. These are major limitation that are well managed in the Pre Store configuration and manufacturing methods.

Temperature ami pressure limits for thermal storage

Parabolic trough solar collectors are currently the most widely used. Provided the solar plant system needs no superheating or reheating of the steam supply the cheapest and most efficient heat transfer method is Direct to Steam (DTS). DTS systems set a practical upper limit to Solar Collector Assembly (SCA) temperatures of about 355°C.

The optimum saturated steam supply temperature for reciprocating piston steam engines is in the range 253°C to 276°C (saturated steam pressure of 4.2 MPa or 594 psig to 6.0 MPa or 855 psig), Gebhardt, 1917. Given those limits then whatever material is at 4 a solar thermal power plant site is the only material economically practical for thermal storage. All other materials cost too much to be relevant. 2016206225 18 Jul2016

Steel Pipes end Concrete for Solar Thermal Storage

Kuravi et al (2013) states that concrete, as a solar thermal storage material, is limited to an upper temperature of 500°C. A lower temperature of 260°C can be assumed for a lowest steam pressure of 4.0 MPa (253°C saturation temperature).

Researchers at the University of Arkansas (Brown, N., 2012) claim to have achieved a breakthrough in thermal storage, using concrete.

Brown wrote: "... a structured thermocline system in which there are parallel plates of concrete with steel pipes running through them. The steel pipes transfer heat absorbed by solar panels into the concrete, which stores it until it is needed to boil water and produce steam (which is usually the case), or supply heat to other heat-powered generators such as Stirling engines or thermoelectric modules.

This thermocline concept survived temperatures up to 600 degrees Celsius (1,112 degrees Fahrenheit) and absorbed heat at an efficiency of 93.9%.

It has an impressively low cost of $0.78 per kWh, far less than the U.S Department of Energy’s goal of $15 per kWh.

To give a clearer idea of how this compares to batteries: Lead-acid batteries cost upwards of $25 per kWh, lithium-ion batteries cost $50 to $100 per kWh. Lithium-ion batteries can last 4 times longer than lead-acid batteries depending on the type and usage. "

The figures in the University of Arkansas report appear to be seriously in error. They may relate only to the storage material costs. The battery cost figures are much more mysterious. Elon Musk has announced a battery price breakthrough, the Tesla "Powerwall" battery. The price announced is USD 3,500 for a 10 kWh-electrical unit. That converts to USD 350 per kWh-electrical, not the USD 50 to USD 100 per kWh stated by Brown. A European company "HID" offers a 1 MWh battery system for AUD 682,000 but advises that the warranty for 4,500 cycles (12.3 years of daily cycles) is invalidated if the battery is cycled over more than 700 kWh-electrical. That means the system cost is AUD 974 per kWh, approximately USD 730 per kWh-electrical. Clearly, the University of Arkansas report is very confusing.

Note that the USA Department of Energy (DOE) target for thermal storage is $15 per kWh-thermal (p27 of nrel.gov/docs/fyl3osti/58484.pdf). That figure must be corrected for thermal to electric conversion efficiency. At a practical average figure of 33% the figure $15/kWh-thermal becomes USD 45.45/kWh-electrical. It appears that Smith et al (2014) publication predicts this figure can be achieved, using thermocline molten salt storage.

For confirmation, a large Exide deep cycle battery, DC6V375, operating over 70% of its full discharge at the 20-hour rate, costs AUD 477 per kWh-electrical. This battery costs AUD 750.75 and will deliver, over a 20-hour discharge cycle, up to 375 ampere-hour at nominally 6 volts. The remainder of the system for safe and reliable operation with long life approximately doubles the cost of the battery. 5

Predicting the cost of their system per tonne of concrete. First assume that the specific heat of their concrete is very high, about 1.4 kJ/(kg*K) and the temperature of all of the concrete varies from 320°C to 500°C. There is no evidence yet that the concrete will survive many cycles above 500°C. The lower temperature is selected to suit the lowest common saturation temperature of steam power plants, 311°C, for steam pressure of 10 MPa (1436 psig). 2016206225 18 Jul2016

Then the concrete will store 252 kj/kg ((500-320)*1.4)=252 kj/kg) (0.0700 kWh/kg) of thermal energy. If the system is to cost $0.78 per kilowatt-hour the concrete, and all other elements must cost less than $0.0546 per kilogram of concrete (0.78*0.07) or $54.60 per tonne.

Readymix concrete cost USD 46.78 per tonne (USD 93 per cubic yard concretenetwork.com/concrete-prices.html) in California, assuming 2.6 tonne per cubic metre. Assuming that the concrete can be mixed and placed to reliably perform to 500°C, for many thousands of cycles, this system cost appears feasible. However, it appears there is no allowance for the remainder of the thermal storage system that must transfer heat in and out of the concrete.

Also, it appears that the researchers are comparing costs per kWh-thermal, for thermal storage, with costs per kWh-electrical for batteries. However, the concrete storage costs above are all costs per kWh-thermal. The critically important cost, for comparison with batteries, is cost per kWh-electrical output.

Graphite for Thermal Storage

Graphite is a relatively expensive material. It has a high specific heat, about half that of water. It can be operated at very high temperatures; up to 1200°C is practical. To operate at these temperatures parabolic trough collectors are impractical. Heliostat tower systems and paraboloidal dishes could be used but most low-cost heat transfer fluids cannot handle these temperatures.

It appears that graphite thermal storage is only relevant for heliostat tower systems operating at very high collector temperatures. This approach is not relevant for smaller systems operating with steam engines.

Soften Salt Thermal Storage

The challenge for molten salt systems is the high cost of materials and the systems that prevent the salt solidifying in pipework, pumps and tanks.

Wikipedia (2015) provides some information on the most common thermal storage for solar power plant, "Molten salt can be employed as a thermal energy storage method to retain thermal energy collected by a solar tower or solar trough of a concentrated solar power plant, so that it can be used to generate electricity in bad weather or at night. It was demonstrated in the Soiar Two project from 1995-1999. The system is predicted to have an annual efficiency of 99%, a reference to the energy retained by storing heat before turning it into electricity, versus converting heat directly into electricity.i9i|10!i,1i The molten salt mixtures vary. The most extended mixture contains sodium nitrate, potassium nitrate and calcium nitrate. It is nonflammable and nontoxic, and has already been used in the chemical and metals industries as a heat-transport fluid, so experience with such systems exists in non-solar applications. 6

The salt melts at 131 °C (268 °F). It is kept liquid at 288 °C (550 °F) in an insulated "cold" storage tank. The liquid salt is pumped through panels in a solar collector where the focused sun heats it to 566 °C (1,051 °F). It is then sent to a hot storage tank. This is so well insulated that the thermal energy can be usefully stored for up to a week." 2016206225 18 Jul2016 A report (Azcarraga. G., ca 2012) prepared by Torresol and the International Solar Energy Society (ISES) provides clear evidence of the effectiveness of thermal storage for solar thermal power plant. Power can readily be provided to meet demand at all times. The high capital cost is the unsolved problem. The Pre Store invention solves that problem.

Phase change material storage

These systems can provide energy at close to constant temperature. The challenge with this approach is the high cost of the materials and its containment.

The paper by Smith et al (2014) indicates that Phase Change Material (PCM) "Pre-store" thermal storage can reduce the capital cost to USD 50 per kWh-thermal. That converts to approximately USD 151 per kWh-electrical (AUD 202 per kWh-electrical).

On the 27th of May 2014 USD 1.00 had a value equivalent to AUD 1.0794. On the 30th of May 2015 one USD had a value equivalent to AUD 1.3083. That shows an increase in storage costs for Phase Change Material (PCM) from AUD 53.97 to AUD 65.42 per kWh-thermal. Assuming a high conversion efficiency of 35% that indicates that thermal storage costs AUD 186.90 per kWh-e. At a lower recovery efficiency of 22%, readily exceeded by Reciprocating Piston Steam engines, the pricing predicts a cost of $245.32 per kW-hr (electrical).

Abengoa Heliostat Tower Plant

Abengoa announced, 9th of January 2014, the following about their thermal storage system. "Solar-thermal tower technology uses a series of mirrors (heliostats) that track the sun on two axes, concentrating the solar radiation on a receiver on the upper part of the tower where the heat is transferred to the molten salts. The salts then transfer their heat in a heat exchanger to a water current to generate superheated and reheated steam, which feeds a turbine capable of generating around 110 MW of power.

The solar plant will also have a pioneering thermal storage system with 17.5 hours of storage that has been designed and developed by Abengoa. This makes the technology highly manageable, enabling it to supply electricity in a stable way, 24 hours a day, responding to all periods of electricity demand.”

Current Cost of Solar Thermal Storage

It is very difficult to find definitive overall cost figures for the current "State of the Art" thermal storage for solar thermal power plant. It is clear that the current "State of the Art" is molten salt in steel tanks. Kuravi et al (2013) in their review show that 49% of the cost is the salt, 13% is the pumps and 4% is the heat exchangers.

Smith et al (2014) predict that thermocline molten salt thermal storage could cost $20.60 per kW-h (thermal). That figure is based on 2010 pricing in Australia and converts to a cost of $62.44 per kW-electrical output, assuming that 33% recovery 7 efficiency can be achieved. At a practical lower recovery efficiency of 22%, readily exceeded by Reciprocating Piston Steam engines, the 2010 pricing predicts a cost of $93.64 per kW-hr (electrical). The molten salt thermal storage system priced was based on 100 MW-electrical power plant. The operating temperature range of these systems are commonly 250°C to 550°C and the technology relies heavily on economies of scale and stable prices of the potassium and sodium nitrate and nitrate salts used. The high temperatures significantly reduce the efficiency of single axis tracking trough SCAs and this encourages the use of heliostat-tower systems. The cost advantages of the latter system are yet to be proven commercially. 2016206225 18 Jul 2016

The figures from Smith et al (2014) are comparable the USA Department of Energy target of < USD15 per kW-hr (thermal).

Energy in ths Prs Store Thermal

The smallest unit planned has overall dimensions of 1.2 metres by 1.2 metres by 4 metres, selected for practical handling and maintenance. The maximum weight, when filled with compacted dense soil, will be 10.5 tonne.

The volume of soil contained is 4.16 cubic metres, when compacted by cycling to 100 mm below the "water line". The average weight of soil contained is 6,032 [kg], assuming a compacted density of 1,450 [kg/mA3].

The steel pipes will weigh 343 kg. The steel fins and end end plates will weigh 1233 kg and the containment sides and bottom 495 kg. Total weight of steel is 2,975 kg.

The water in the storage unit will weigh 240 [kg], at 350°C with the steam drum half full.

When the thermal storage operates across the upper range 275°C to 350°C the storage unit can be charged by adding 762 [MJ] of energy in the form of heat. The energy is stored in about the following percentages: soil - 71%, water - 14% and steel - 15%.

Note that the specific heat of carbon steel assumed is 0.498 [kJ/(kg*K)] (Umino, 1925).

When operated across the lower range, 200°C to 275°C, the storage unit can be charged by adding 690/3.6 [MJ]. The specific heat of steel, at these temperatures is 0.478 [kJ/(kg*K)]. For the lower range the energy is stored in very similar percentages.

The energy stored can be converted to electrical output at constant efficiency of at least 22%, for the upper range, and this reduces to 20% at the lower limit of the lower range. These values assume that the temperature differences when recovering energy reduces the conversion efficiency to 90% of the direct use efficiencies.

The amount of electrical energy output available from one thermal storage unit is then at least 85 kW-hour-electrical (762,000/3,600*22% + 690/3.6*20%).

The steel pipes, fins, tube plates and containment provide a total surface area of 73.3 square metres. Many system designs will use storage for 12 hours at average output. During a six-hour discharge, of the upper range of storage temperature, the soil to steel heat transfer is 342 [W/mA2] (71%*762,000,000/6/3600/73.3). With thermal conductivity at only 1.25 [W/(m*K)] (Soebarto, 2009) there will be an approximate temperature difference of 2.7 [K] in the first 10 mm of soil. It is this effect that reduces the Round Trip Efficiency. This simplistic analysis is more conservative than onedimensional transient thermal conduction analysis already completed. A full three dimensional transient thermal conduction model will predict performance more accurately and guide design refinement to reduce the cost of storage. 8

During operation in the upper range of temperatures there is trivial effect on system efficiency as the steam engine upper limit for pressure, 6 MPa for the Spilling engines, sets a constant efficiency. 2016206225 18 Jul2016

References

Abengoa, 2014 January 09, "Abengoa to develop South America’s largest solar-thermal plant in Chile", abengoa.com/web/en/noticias_y_publicaciones/noticias/historico/2014/01_enero/abg _20140109.html.

Azcarraga. G., 2012, "Evaluating the effectiveness of molten salt storage with solar plants", ises.org/fileadmin/user_upload/PDF/Molten_salt_tower_plant_GA_Azcarraga.pdf

Brown, N., 2012, "Solar thermal storage: A concrete cost breakthrough?" Renew Economy/CleanTechnica.

Gebhardt, G.F., 1928, "Steam Power Plant Engineering, 6th Edition. John Wiley, USA.

Kuravi, S., Trahan, J., Goswami, D.Y., Rahman, M.M., Stefanakos, E.K., 2013, "Thermal energy storage technologies and systems for concentrating solar power plants", Elsevier.

Scientific American, 1914, “The Sun Power Plant in Egypt”, Vol. 110, No. 3, Jan. 17, 1914, p60.

Smith, C., Sun, Y., Beath, A., Bruno, F., 2014, "Cost analysis of high temperature thermal energy storage for solar power plant", Proceedings of the 52nd Annual Conference, Australian Solar Energy Society (Australian Solar Council) Melbourne May 2014, solar.org.au/papers/14papers/%2342_final.pdf

Soebarto, V., 2009, “Analysis of indoor performance of houses using rammed earth walls”, Eleventh International IBPSA Conference Glasgow, Scotland July 27-30, 2009.

Terzaghi, K., "Large Retaining Wall Tests", Engineering News Record Feb.l, March 8, April 19 (1934).

Turner, R.H., 1979, “High Temperature Thermal Energy Storage in Steel and Sand”. Jet Propulsion Laboratory - California Inst. Of Tech. Pasadena, Ca. (JPL Publication 80-35).

Umino, S., circa 1925, “On The Specific Heat of Carbon Steels”, publikationen.ub.uni-frankfurt.de/files/14044/E001892563.pdf 9

Claims (14)

1. The connection of multiple metal pipes, with large metal fins/plates supporting metal containment of soil, provides high thermal conduction and more thermal storage per unit mass of metal than other configurations and methods of manufacture. This provides high Round Trip Efficiency by keeping average temperature differences to a minimum.

2. The connection of inclined multiple metal pipes, with large metal fins/plates supporting metal containment of soil, provides high thermal conduction and more thermal storage per unit mass of metal than other configurations and methods of manufacture. This provides high Round Trip Efficiency by keeping average temperature differences to a minimum.

3. Connection of multiple steel pipes for thermal storage, with large steel fins/plates for soil containment by automated MIG welding is cheaper than other methods of construction strong enough to constrain the soil.

4. A system as in Claim 1 or 2, above, and the operation of the Pre Store thermal storage with steam heating provides a high Round Trip Efficiency for steam power plant.

5. As in Claim 1 or 2, above, and the operation of the Pre Store thermal storage with steam extraction directly from the thermal storage provides a high Round Trip Efficiency for steam power plant with thermal storage.

6. As in Claim 1 or 2, above, and the operation of the Pre Store thermal storage with steam extraction directly from the thermal storage provides a high Round Trip Efficiency for steam power plant with thermal storage.

7. As in Claim 1 or 2, above, and the operation of the Pre Store thermal storage with steam heating and with Reciprocating Piston Steam engines provides a high Round Trip Efficiency for steam power plant.

8. As in Claim 1 or 2, above, and the operation of the Pre Store thermal storage with steam extraction directly from the thermal storage and with Reciprocating Piston Steam engines provides a high Round Trip Efficiency.

9. As in Claim 1 or 2, above, and the operation of the Pre Store thermal storage with steam heating and steam extraction directly from the thermal storage provides a high Round Trip Efficiency for steam power plant.

10. As in Claim 1 or 2, above, and the operation of the Pre Store thermal storage with steam heating and steam extraction directly from the thermal storage and with Reciprocating Piston Steam engines provides a high Round Trip Efficiency.

11. As in Claim 1 or 2, above, and the operation of the Pre Store thermal storage with Reciprocating Piston Steam engines provides a high Round Trip Efficiency as superheating is not required or used.

12. As in Claim 1 or 2, above, and the operation of the Pre Store thermal storage with Wet Steam Turbines providing a higher Round Trip Efficiency as superheating is not required or used.

13. As in Claim 1 or 2, above, combined with energy storage using water storage pumped to a higher dam or tank and allowed to return to a lower dam or tank.

14. As in Claim 1 or 2, above, combined with energy storage by using batteries to store electrical energy.