Test 4 : Testing the technical feasibility of aggregating Micro-CHPs in the German residential sector
This test is related to Business model 2 investigated in EU-DEEP, which addresses the aggregation of Micro-CHP at residential clients in the German context.
The aggregation of 10 Micro-CHP units installed in selected residential buildings was tested under real conditions to provide the necessary data and feedback to validate the business case of Micro-CHP aggregation.
Installed heat storage allowed a flexibility
The field test confirmed that the flexibility regarding residential customers is limited to the size of the heat storage. Thus the maximum operation time of the Micro-CHP without having any instantaneous heat demand from the site was approximately 1 to 2 hours. Depending on the load profile of the heat demand it was possible to use this flexibility several times a day. During summer time, when only hot water was needed by the customers, in many cases the storage could be filled only once or twice a day. Contrasted control strategies were assessed during the field test. They showed a limited usability of the flexibility. The heat supply of the customers had the highest priority during the field test: the acceptance of the external aggregator signal was limited to the period when the heat storage was half empty, up to the point where the local heat controller started the Micro-CHP unit to reload the storage.
The remote-control system using GPRS is reliable
The field test proved that the selected communication system via GPRS is suitable for the business and is extremely reliable, with availability of over 99%. Even with data collection every minute there were only very few data points lost during the entire operation of the 10 systems.
The control strategy should be improved to increase the available power for the aggregator
The performance of the Micro-CHP units was lower than expected. The electrical efficiency was in the range of 7% rather than the specification of 12%. The overall efficiency was approximately 85 % rather than 90%. The low electrical efficiency is caused by the self-consumption of the unit and the low average running time per start. In particular, during the start up of the unit, this takes up to 15 minutes until full load is reached. The steady state efficiency is much lower when compared to continuous operation at full load. Considering the nominal electrical output of 1 kW, the field test showed an average usable output of 0.75 kW. This means a loss of 25% compared to the theoretical calculations. The control strategy should be improved in order to increase the running time per start, which was approximately 70 minutes during autumn and winter. In many cases, especially during summer time, the running time was less than 30 minutes. This has high potential to increase the general performance, by optimising the control strategy. The total availability of most units (from an aggregator point of view and for self-consumption) was 100%.
A common standard for the control signal to run the Micro-CHP unit is a key issue
The field test showed that it would be useful to determine a common standard for the control signal towards the Micro-CHP unit. The local heating controller should have a common interface to accept and process the start and stop signals coming from the local Distributed Energy Resources (DER) controller.
In general, the whole installation process, measurement and control equipment should be optimised and standardised as much as possible in order to reduce investment costs, as well as ongoing costs for maintenance and troubleshooting.
A wider variety of Micro-CHP units suitable for use in residential applications would create competition and might lead to lower investment costs and a better technical performance. In addition different Micro-CHP sizes might help to choose the right unit for a given site in order to optimise both performance and economics of the system.
- Otto BERTHOLDGASAGWP4 & WP5email
- Uwe DIETZERWE EnergyWP4 & WP5email
- Marc BERGERGDF SUEZWP4 & 5 Leaderemail