Novelty of the EnerTwin and technology
Smallest commercially available “micro” turbine is the Capstone C30 that delivers 30 kW electricity with over 10.000 units sold worldwide. Yet, 30 kW is way beyond the power requirement of MTT’s actual micro CHP markets. Reducing the output power, however, creates serious technical challenges: the negative effect of so-called tip clearances becomes more dominant leading to lower shaft efficiencies, rotational speed needed to achieve a reasonable efficiency raises exponentially, the hot parts (turbine wheel) and the parts that need to stay cool (compressor and generator) have to be placed at a very short distance causing unwanted heat transfer and resulting in lower performance or no performance at all. In addition, these technical challenges have to be solved within constraints of limits of materials and rotor dynamics.
With its micro gas turbine, MTT has solved these technical problems and developed a compact micro-gas-turbine using available turbocharger components (Commercial Off-The-Shelf). MTT has tested these micro gas turbines extensively, having operated them for long times without any measurable deterioration in materials and performance. Micro-CHP systems equipped with this micro gas turbine that were deployed in the field trials have proven to be very reliable. In addition, to the low-cost benefit of turbochargers, the main advantages of using a gas turbine for the EnerTwin micro CHP system are:
a) Gas turbines have only one single rotating part and require very little maintenance. From current stage of development, MTT can conclude that maintenance cost will be around 1,3 Eurocent per kWh electricity, which is only a fraction (< 20%) of maintenance cost of competing micro CHP systems. This maintenance is based on the full maintenance schedule and in agreement with specifications of subcomponents.
b) Gas turbines have a superior power density, allowing lightweight and small micro CHP systems to be built. This is important for low cost mass production, where material cost become a dominant factor.
c) Lifetime of gas turbines is substantially longer than that of other energy conversion technologies. As industrial gas turbines have a typical lifetime of 80.000 hours, the average reciprocating piston engine is generally designed for 5.000 to 6.000 hours. This increases the attractiveness of a micro turbine based micro CHP system, since condensing boilers (the benchmark device for EnerTwin) have a typical lifetime of more than 50.000 hours.
Reducing cost level, Total Cost of Ownership
MTT develops its products not with the sole aim of achieving high electrical efficiency, but with a strong focus on obtaining the lowest “Total Cost of Ownership (TCO)”. This approach is crucial for commercial success of micro CHP that will bring about all mentioned benefits for the society (energy efficiency, lower CO2 emissions, lower cost of energy etc.) achievable through a large-scale implementation of micro CHP.
MTT has translated this into a cost-effective solution: The EnerTwin offers a very reliable and more cost-effective micro CHP solution with a very competitive target price. In addition, with the low maintenance cost a payback time between 3 and 6 years for the end user in most EU member states will be possible.
