Power Surge & CHP

The fact remains that (at best) CHP is only a little better than conventional supplies

Your article regarding Combined Heat and Power perpetuates the myth that this is a low carbon technology. From your figures, the savings in Carbon Dioxide Emissions are only 10% better than conventional supplies, (which is hardly a reason for the Government to promote this technology) however even this figure is incorrectly calculated since it uses the wrong reference values.

The European Directive on Co-Generation (Directive 2004/8/EC) has now passed into statute and CHP must report its CO2 savings against a ‘same fuel source’. The majority (80%) of Good Quality CHP in the UK is gas fired, which means that the calculated energy savings (from gas fired CHP) should be measured against centralised Combined Cycle Gas Turbines (CCGT) and SEDBUK A boilers. In effect, the CHPA figures in your article are quoted against the full spectrum of fuel sources (including a substantial portion of coal – 28%) and, as a result, the real reason why CO2 savings are claimed is because natural gas is a significantly lower carbon fuel than coal (not that CHP is so much better than conventional supplies).

Combined Cycle Gas Turbines installed in the UK have a measured efficiency of 47.6% GVC (DUKES 2010) and SEDBUK A boilers are 90% efficient. When the statistical Data from DUKES 2010 for all good quality CHP schemes is tested against these criteria there are no energy savings when using the EU Directive calculation given that the average CHP electrical efficiency is just 24% and the average heat efficiency is 43% GCV.

Whilst the CHPA might argue against the EU Directive analysis, the fact remains that (at best) CHP is only a little better than conventional supplies and the vast majority of CHP schemes are less efficient than conventional supplies (usually because they dump heat).  Since the stated aim of the Government is to reduce the UK’s CO2 footprint by 80% by 2050, it is clear that CHP is not the answer. Investment in future energy converters needs to be at least 80% less CO2 intensive than the current schemes otherwise the UK will fail to meet its climate change obligations.

It’s time for the IMechE to step up and advise the government.

James Thonger, Hampshire