Generating clean energy for remote communities is challenging. The easy solution is to install solar cells and batteries, but the cost/kWh is excessive. Now there is a cheaper way.
It is a fact that the energy from large concentrated solar thermal (CST) generators is up to 40% cheaper than energy from solar cells and batteries, essentially because CST generators use thermal storage to store energy instead of expensive batteries. A cheaper solution for remote communities would therefore be to use a CST generator with thermal storage. The problem, however, is that today’s CST generators are typically too large for remote communities, leaving expensive solar cells and batteries as the only remaining option. Why therefore don’t we think outside the square and build smaller CST generators so that remote communities can also have access to the cheaper clean energy possible through CST generation and storage?
To meet that need, my solution is to build
small portable CST generators housed in shipping containers. In addition to being
suited to the needs of remote communities, a small CST generator also has the
advantage that the limited output of the generator allows for a hot air engine to
be used to convert the stored heat into electrical output instead of a less efficient
steam engine. Hot air engines are 25%
50% more efficient than steam engines
at the same operating temperature. Using a small hot air engine instead of a
steam engine therefore gives a potential 25%
50% more electrical output from
the same quantity of collected heat. That in turn leads to a potential 20% -
33% reduction in electricity costs compared with a conventional CST
installation. Since CST generation is already up to 40% cheaper than solar
cells and batteries, clean energy from a ‘container generator’ ultimately has
the potential to be less than half the cost of energy from
solar cells and batteries once reasonable production levels are reached.
Using hot air engines instead of steam is the key to reducing the cost of clean energy for CST generators. The best known type of hot air engine is the Stirling cycle engine which was invented over 200 years ago. Stirling cycle engines have in recent years been developed to remarkable levels of efficiency. Some Stirling cycle engines have achieved efficiencies of up to 32% at 700ºC, well above the 17% efficiency typical of steam based CST installations. While an efficiency of 32% will not be achievable when operating at the lower temperature available from stored thermal energy, it is clear that Stirling cycle hot air engines still offer significant potential for improved efficiency over steam, even when powered by stored heat. Unfortunately, in order to achieve these efficiencies, Stirling cycle engines require the use of hydrogen as the working fluid which has also lead to some reliability issues. To overcome these problems, my approach uses a different hot air engine.
The engine to be used in the container generators is a new patented Brayton cycle rotary displacement hot air engine that does not require the use of hydrogen. The problems associated with the use of hydrogen are therefore avoided. This new engine will provide both the efficiency and durability required to make it ideal for solar thermal generation, both at remote locations and in modern industrial situations, without the need to use hydrogen.
The more efficient engine and cheaper thermal storage are however not the only advantages of the container generator. There are in fact several more advantages. Having a relatively small collector area, the collectors for a container generator can be better positioned to collect more solar energy than is possible with large CST generators. Properly manufactured, these smaller collectors will also be lighter and cheaper. Having both the generator and thermal storage package permanently housed in a shipping container is also a cost-effective way of providing a durable enclosure for the generator, while ensuring easy low-cost delivery and rapid installation. Having all generators essentially identical will also allow for the generators to be mass- manufactured on a fully-automated factory production line for minimum cost. All these advantages will ultimately contribute to lower energy costs.
Container generators, however, will have even further advantages at remote locations. Because the generators store heat at high temperature to drive the engines, the stored heat could also be used for cooking purposes if required. In addition, either the stored heat and/or waste heat from the engine could be used for general heating purposes to avoid the need to burn wood, charcoal or animal waste for those purposes.
While burning wood inefficiently for heating and/or cooking is to be avoided, the container generator has yet a further advantage in that it can also be made to efficiently burn biomass when no stored solar thermal energy is available. While this is perhaps something that ought to be avoided except in emergencies, it is nevertheless a distinct advantage of the container generator over the alternative. Once stored clean energy is exhausted with solar cells and batteries, a separate small generator operating on a hydrocarbon fuel of some sort would be required. Operating the container generator on biomass is almost certainly the better of the two options.
In conclusion, the container generator is a new approach to generating renewable solar powered energy. Container generators use essentially existing technology and require very little development to bring them to market. Their size is suited to the energy needs of remote communities or anyone who wants to generate and store their own clean energy at lower cost than using solar cells and batteries.
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