Operational data from an installation in Germany:
Below operational data is from a CraftEngine connected to a system of two wood gasifiers and two gensets running on wood gas. The system is located in the north of Germany. The maximum available thermal power is about 540 kW. The special requirement for this setup was that the system also had to be able to run using only one set of wood gasifiers and gensets.
Figure 4 shows a summary of 5 months of continuous operation. This overview gives a good insight into the behaviour of the system with different heat sources and heat sink conditions.
The heat source supplies hot water at about 92 °C and requires a return temperature of 75 °C. This temperature level is sufficient for running the CraftEngine efficiently. A possible increase in the return temperature from by 5 °C, would increase the average power output and efficiency by about 10 per cent, which means about a 0,8 per cent absolute increase in efficiency and 3 to 4 kW more in electrical output.
The heat sink performance is affected by the ambient conditions, mainly the ambient temperature but also by sun radiation and rainfall.
During this five-months period, one of the heat sources was switched off and on several occasions by the customer. Hence, the available amount of heat changed fast from 270 kW to 540 kW, and vice versa. Simultaneously, the effects of varying ambient conditions on power output are clearly visible in the diagram.
The ambient temperature during the first part of September was more than 25°C during daytime. This leads to a power output of about 25 kW net into the grid, and an efficiency of about 4.7 per cent. During the winter months, with ambient temperatures below 10°C, the power output is about 40 kW and an efficiency of around 7.5 per cent. The calculated average yearly power output for this system is 32 kW.
This means that with an assumed running time of 8,000 hours per year, a total electric production of 256,000 kWh can be expected. This is enough to supply about 70 households with electricity produced from waste heat.
Figure 5 shows an overview over one week of operation in a late summer week with good weather conditions. The ambient temperature rose to about 25°C during daytime and decreased to about 10°C during the night. The heat source runs continuously on maximum power with a constant inlet temperature. The return temperature is controlled by the CraftEngine to about 75°C. The relatively high difference between day and night temperature correlates directly with the electrical output of the system.
Due to its innovative and flexible control system, the system is always able to run with the maximum possible efficiency. The system is able to achieve this by automatically changing the expansion ratio of the expander in order to ensure a thermodynamically optimal expansion. The generated electricity that can be delivered and sold to the grid varies between 25 kW and 35 kW.
Figure 6 shows an overview of a week of operation in the winter. In comparison to the summer week, there is only a very small difference between night and day temperature. This leads to a very constant system power output of about 40kW and an efficiency of about 7.5 per cent. At the end of the week, one heat source system was switched off by the customer due to maintenance work carried out to one of the wood gasifiers. The drop in available heat was immediately registered by the CraftEngine and the system quickly and automatically adapted to the new conditions. The electrical output then dropped to about half, because only half of the available heat remained. During this part-load condition, the CraftEngine was still able to maintain the same high level of efficiency as it had under full load conditions.
After 5 months of continuous operation, the CraftEngine shows a very good power output and efficiency under all ambient conditions. The CraftEngine demonstrates its unique ability to adapt very fast to changing conditions, regardless of whether they happen on the heat source or heat sink side. The achieved electrical efficiency of up to 7.5 per cent net into the grid based on a heat source temperature of about 92 °C to 75 °C, demonstrates the attractive potential of the low-temperature waste heat to power application. It also shows that continuous operation during the summer is viable. The observed lower efficiencies around 4.7 per cent at 25 °C ambient condition are only applicable for a few hours during daytime. The average efficiency on summer days end up at around 5.5 per cent. The efficiency can further be improved by using slightly higher heat source temperatures. An increase of 5°C will lead to about 10 per cent higher power output and efficiency.