SOLAR VALUE CHAIN
The term “solar value chain” generally refers to a set of interconnected systems and processes that convert solar radiation into energy forms that are useful to our societies.
For more than a century, scientists and engineers have worked to develop technologies that would enable us to derive useful energy from the solar resource. During the past 50 years or so these efforts have intensified, with the result that many new and important technology developments have been achieved. However, these advanced solar technologies have never been brought together in a way that provides a complete solar value chain capable of cost-effectively providing us with all of the energy that we need, in the forms that we need it, whenever we need it. In the past, the chain has always had missing links.
But now that has changed. We now have at our disposal critical technologies that can be linked together to make solar the primary energy resource that countries all over the world can rely on to meet their energy needs. We don’t need new technology developments or scientific breakthroughs. To complete the solar value chain, we just need systems that effectively integrate technologies that we already have.
At SEA, that’s what we’ve been working towards. We’ve combined our own innovations with existing technologies to create systems that can be deployed and cost-effectively operated anywhere people live, regardless of population density, even in locations where latitude or weather conditions greatly reduce available sunlight. SEA systems efficiently convert solar radiation into the types of energy our societies must have in order to function, and more importantly, our systems provide for long-term storage of that energy so we’ll have it whenever we need it.
The figure below shows how the work we have done at SEA can be integrated with some other amazing technologies that have been developed during the previous half century. The result of this integration process is a complete solar value chain that can be deployed and cost-effectively operated anywhere on Earth, providing benefits in the form of millions of rewarding jobs, greatly improved standards of living, and a better quality of life..
The first link in the chain is the SEA solar energy conversion system, a highly efficient cogeneration system which combines state-of-the-art photovoltaic (PV) technology with proven Concentrating Solar Power (CSP) technology. The system has parabolic trough reflectors that focus sunlight onto actively cooled arrays of solar cells. Nearly 25 per cent of the radiation incident on the cells is converted directly to electricity. The rest is collected as low-grade thermal energy in coolant circulating through cooling channels that support the solar cells. The SEA system converts more than 90 per cent of incident direct solar radiation into useful output. Also, since the concentrated sunlight produced by the trough reflectors is 25 to 30 times more intense than unfocused sunlight, the area, and thus the cost, of the solar cells required to generate a given amount of electrical power is reduced to only 3 or 4 per cent of what would be required in a flat-panel solar cell array receiving unfocused sunlight.
The next links in the chain relate to storage of the thermal energy and the electricity energy provided by the SEA cogeneration system.
Regarding the storage of low-grade thermal energy, the SEA system interfaces easily and efficiently with proven Borehole Seasonal Thermal Energy Storage (BSTES) technology. The integrated technology consists of a fluid carrying thermal energy from the SEA system’s solar cells to borehole heat exchangers which transfer the energy to underground storage reservoirs (undisturbed layers of soils, gravel, rock, etc). This easily stored/easily reclaimed energy, which is usually discarded as waste heat, has extremely high value because it can completely displace the large quantities of electricity and the fossil fuels that are currently used for low-grade thermal applications in our homes, businesses, and industries. Measured Coefficient of Performance (COP) numbers for the BSTES technology are quite large, with values above 30 commonly reported. (High COP values are to be expected because, when BSTES technology is used, heat is always transferred from high to lower temperature materials, so no thermodynamic work is necessary for accomplishing the transfer.)
An important characteristic of low-grade thermal energy is that, after it is collected, it can be stored directly as thermal energy, then reclaimed from storage as thermal energy, and ultimately utilized as thermal energy in end-use applications. Conversion to another energy form is unnecessary at any point. In the case of the SEA cogeneration system, the thermal energy collected from the solar cells is stored as thermal energy in underground reservoirs and then reclaimed as needed for use in space heating, hot water heating, and industrial drying and processing operations. This direct use of thermal energy greatly simplifies the end-to-end sequence of operations and significantly reduces the cost of the energy provided to domestic, retail, and industrial customers.
Direct storage of electricity, as in super capacitors or superconducting inductors, is not feasible on any meaningful scale. Storage of electrical energy always involves conversion to another energy form.
The figure above shows that some of the electrical energy generated by SEA cogeneration systems will be used as it is generated. However, the variability of the solar resource means that a large fraction of the electricity produced by our systems must be stored—either for the short term (overnight or for a few days) or for the long term (season to season). For short-term storage, where relatively modest quantities of energy are involved, batteries are a reliable, convenient, and very efficient storage option. However, even for the best batteries available today, the cost of each kilowatt-hour of storage capacity is so high that batteries are not an economically viable option for storing the huge quantities of energy involved in seasonal storage.
The lack of seasonal storage capabilities for electrical energy has, in the past, prevented solar from becoming the preferred primary energy resource of societies all around the globe. Because there has not previously been a solution to this problem, solar has always been relegated, as it is today, to fulfilling the needs of small, specialized energy markets; and solar installations have, in nearly all instances, required complete backup in the form of fossil fuel infrastructure.
The only viable option for season-to-season storage of electrical energy involves conversion to the chemical energy of fuels. (See our page on Long-Term Energy Storage.) The conversion process involves electrolysis of a chemical compound, usually water, to produce a combustible fuel, such as hydrogen. Hydrogen, or inorganic fuels derived from hydrogen, can be stored for long periods of time and then burned in heat engines that drive electrical generators. This sequence of operations is usually referred to as an Electrolysis/Storage/Reconversion (ESR) process. (See our page on ESR Processes.) In the past, ESR processes have not been considered viable energy storage technologies because of the inefficiencies associated with commercially available heat engines and electrolysis units.
As recently as ten or fifteen years ago, the efficiency of industrial-scale water electrolysis units was, at best, in the range of 55 to 65 per cent. The highest efficiency for heat engines was in the range of 50 percent, as reported for Brayton/Rankine combined-cycle engines. However, during the past few years, industrial-scale electrolysis units with efficiencies above 82 per cent have become available (Thyssenkrupp). And now, SEA has designed a two-stroke reciprocating piston engine which could have efficiencies of nearly 70 per cent for a broad range of expected operating conditions. These two developments are the final links in the solar value chain represented in the figure. The chain is now complete—from collection to conversion to long-term storage. We now have the ability to harness and fully exploit the most valuable, most uniformly distributed energy resource on our planet.