SSE combined heat and power (CHP) feasibility

Wattcraft carried out for SSE a technical and economic assessment of options for a multi megawatt combined heat and power (CHP) system serving a new mixed-use development


The following services were provided:

  • Energy demand modelling

  • CHP plant sizing

  • Thermal store sizing

  • Auxiliary boiler plant sizing

  • Lifecycle economic modelling to determine the most economically viable system

    The first part of the assessment was to model heat and electricity consumption over the year for the mixed-use development, using energy performance indicators based on building type, building energy standards and building configuration. Energy consumption was modelled over the day and over the year in accordance with projected building use and, in the case of heat energy, external temperature data. CHP and auxiliary boiler plant was sized in relation to the heat demand profile, taking into account limitations of plant operational ranges, such as level of turndown and also the optimum number of units to meet the target heat output rating. Provision was also made for system resilience, with the inclusion of standby plant to be costed. Thermal storage was sized to maximise the run-time of CHP plant in meeting the varying daily heat demand and also optimising the revenue from electricity generation. Economic costing was carried out over the project lifecycle in order to be able to provide SSE with a comparison of commercially viable options to take forward to project delivery, including processing the following factors:

  • Plant capital cost

  • Maintenance cost (including how this varied with plant unit selection)

  • Fuel cost

  • Revenue from supply of heat and electricity through CHP

    Gas-fired CHP can represent an environmental improvement compared to the supply of fossil-fired heating and grid electricity supply, through the use of the waste heat from electricity generation. Its commercial viability depends on whether the balance between the value of energy generated offsets the combination of increased capital and operational costs compared to a gas boiler and grid electricity supply. The difference between electricity and gas prices in the market varies over time and so this needs to be taken into account in establishing the ongoing viability of a CHP project. Whilst future energy prices are very difficult to predict, given that they are subject to multiple global factors, Wattcraft applies sensitivity analysis to cost models, taking historical trends into account, to support the client in arriving at a resilient solution.