Emission and economic performance assessment of a solid oxide fuel cell micro-combined heat and power system in a domestic building

Combined heat and power (CHP) is a promising technological configuration for reducing energy consumption in the domestic built environment. In CHP applications, both electrical and thermal power are generated from a single fuel source, with the view to using both products. CHP in decentralised energy generation (DEG) applications can produce improved system efficiency, reduce transmission losses and increase energy security. CHP in domestic buildings is often referred to as micro-CHP (mCHP) and is commonly defined as anything with a power output of less than 5kWe. Fuel cells, on account of their: high electrical efficiency, low emissions and useful heat output have been identified as a key technological option for improving both building energy efficiency and reducing emissions in domestic mCHP applications. Many papers have optimised the size of fuel cell mCHP systems for domestic built environment applications; however limited work has been conducted on the assessment of a commercial system in a real working environment. This paper aims to assess the emission and economic performance of the commercially available BlueGEN 1.5 kWe solid oxide fuel cell (SOFC) mCHP system, which has been installed at The University of Nottingham’s Creative Energy Homes. The performance assessment evaluates, over a one year period, the associated carbon (emission assessment) and operational costs (economic assessment) of the BlueGEN SOFC mCHP case compared to a ‘base case’ of grid electricity and a highly efficient gas boiler. Results from the assessment show that that the BlueGEN SOFC mCHP system can generate annual emission reductions of up to 56% and cost reductions of 177% compared to the base case scenario. However support mechanisms such as; electrical export, feed in tariff and export tariff, are required in order to achieve this, the results are significantly less without. A simple pay back analysis shows that the BlueGEN SOFC mCHP system will pay for itself within 10 years. However, in order for the payback period to fall to a more reasonable level of around 5 years, the capital cost of the BlueGEN SOFC mCHP system needs to be around £10,300. Additionally, a net present value (NPV) analysis has been employed to compare the economic feasibility of each case over a 15 year lifetime. Results show that the base case is still more profitable over the 15 years, even though the BlueGEN SOFC mCHP system generates annual revenue; this is on account of the BlueGEN’s high capital cost. A secondary aim of the paper is to assess the impact the heat to power demand ratio (H:P) of the home has on the SOFC mCHP system’s environmental and economic performance. The H:P of a home is the ratio of how much thermal energy to electrical energy is required. Traditionally UK homes are characterised by a H:P. However, it is now widely accepted that in newer houses this ratio is falling on account of reduced thermal demand (improved building practice and materials) and increased power demand (more electrical appliances with higher power ratings). Two H:P scenarios, low and high, have been assessed. The results show that the BlueGEN SOFC mCHP performs best in a low H:P home (<2), generating greater relative savings with the base case. Thus, the recommendation would be to focus BlueGEN SOFC mCHP deployment in newer domestic homes with a lower H:P.