Commercialisation Options

The key feature of this engine design that would make it attractive to potential buyers is its ability to run on a variety of low grade heat sources that are potentially free, however for it to be successful in the marketplace it must be very cost competitive as an outright purchase. If a small version (1-4 kW output) was able to be produced cheap enough then it could potentially find its way into applications such as off-grid domestic power generation, competing with current technologies such as solar panels, wind turbines and even other Stirling engine technologies such as WhisperGen. In such an application it would most likely be driven by hot water sourced from inexpensive solar collectors and may also be used in conjunction with the domestic hot water system. Other potential heat sources may include geothermal hot springs (though this would be very limiting in market potential) or direct heat from the likes of a wetback wood fireplace. In New Zealand, an off-grid solar power system rated at 1kW typically will cost $25,000 — $30,000 installed, of which $10,000 — $13,000 is the cost of the actual solar panels and the rest is battery banks, controllers and inverters and installation [44] which is assumed to remain the same for a Stirling engine based system of similar output. That means that an equivalent 1kW Stirling engine generator and the necessary heat collection system would need to be sold to the end user for around $10,000. To be profitable these would need to be produced for around half of that, and at this stage of design this seems like a very reasonable proposition though it is difficult to say without a final design. This is undoubtedly a growing market in itself, as evidenced by the large number of manufacturers and retailers of photovoltaic panels and associated equipment to service this demand.

An even larger market share is those who still wish to remain grid connected but also generate their own electricity either for reasons of saving money on electricity over the long term, security of supply or environmental consciousness. This situation would offer a further advantage to the Stirling engine based system as it would simply send the generated power back through the customer’s electricity meter into the grid at 50Hz, earning them revenue without the need for batteries, inverters and controllers that are still required by the photovoltaic systems which generate DC power. This makes the installation a lot cheaper and hence offers a more attractive payback period to potential buyers.

If a scaled up version were to be investigated then many more commercial possibilities become available. In the tens to hundreds of kilowatts range there is scope for pumps that are driven partially or wholly by the heat contained in the fluid that they are pumping. Pumps that drive hot fluid are found in many industrial processes such as production and processing plants and power stations. Some industrial processes may have such a great output of waste heat that it would be possible to drive a Stirling engine in the megawatts range, and in such applications it is an added bonus to remove this heat as it is often problematic and of environmental concern when dumping it to rivers or lakes.

There is further scope for auxiliary power generators on the likes of small to medium sized boats, particularly private yachts where quiet operation is a big plus. In such an application the heat source could be provided either from gas, engine waste heat or both and the cooling would be from the surrounding water.

A further option is on a utility scale, generating power in the tens of megawatts range for the national grid from a suitable heat source, which would most likely be geothermal heat. As discussed in the introduction, there is plenty of geothermal heat available that is currently unutilised due to a lack of an economical way of extracting the energy from it. It is unknown at this stage how well the engine would scale up to the sizes required for this level of output, although a quick calculation shows that if the power to volume ratios hold as size increases then a 5 MW machine would require a gas volume of 1500 m3, which equates to a cylinder roughly 20 metres in diameter and 24 metres long — a big ask but certainly not outside the realms of possibility.

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