FEEDBACK Fossil-fuel energy sources are required when renewable energy is unable to meet demand The issues of polluting neighbours and carbon factor calculations A different approach Join the conversation We want to hear from you. Talk to us. @CIBSEJournal CIBSE LinkedIn www.cibse.org Subscribe to our newsletter Receive our top stories about building services engineering. Sign up at cibsejournal.com I read the opinion article by Mike Hefford (Other factors, CIBSE Journal, February 2019) with interest, and certainly agree with his call for wider decentralisation of power generation using CHP integrated with other low carbon technologies. However, I cannot agree with his endorsement of the use of averages for grid carbon value, be it over a month, year or any other period. This is because focusing on average carbon content disguises the high carbon content of the dispatchable power being used every day to top up low carbon sources, such as wind and solar. To clarify, dispatchable sources of electricity are thosethat can be dispatched at the request of power-grid operators and used on demand when renewable energy sources are unable to meet demand. Dispatchable power also provides our insurance againstthe lights going out when the wind isnt blowing and the sun is obscured by cloud. The fact that so much of our renewable capacity is at the mercy of the vagaries of the weather means we will always need this dispatchable capacity, irrespective of the installed renewable capacity. In fact, increased useofelectrical/electronic technologies, electric cars, heat pumps and so on will increase the UKs power demands in coming years, which increases the backup capacity requirement. The energy source of this dispatchable power is known as the marginal energy source. Even with the significant increases weve seen in renewable capacity over the past few years, that marginal energy source is still predominantly inefficient, gas-fired power stations, with a little coal thrown in when demand is high. So I believe it is this marginal carbon factor that we should be focusing on, rather than an average carbon factor from all power sources (wind, solar, nuclear, gas, coal). Moreover, I would argue that focusing on the dispatchable marginal carbon factor, rather than the average carbon factor, is the only way we can effectively resolve the UKs energy trilemma namely, the need to simultaneously reduce carbon emissions, cut energy costs and ensure security of supply. Focusing on the marginal energy source reinforces our continued dependence on gas and, crucially, the imperative to use that gas more wisely and efficiently. Such a focus naturally leads us to wider use of prosumer buildings that produce and consume energy. Typically, these would use decentralised CHP combined with heat pumps and electric boilers, in a smart system that can avail itself of green grid electricity when appropriate. As well as taking pressure off the grid and making more efficient use of fossil-fuel energy sources, decentralising a higher proportion of our dispatchable power meets all of the requirements of the energy trilemma. This approach also has implications for the proposed SAP 10, in terms of using a more realistic carbon factor based on marginal energy sources. In parallel, there is a need to enhance the functionality of SAP software tofacilitate the use of the mixed hybrid systems described above, which are not supported in the current version of SAP. The fact that the Department for Business, Energy and Industrial Strategy is now reconsidering the lower carbon factor proposed in the draft SAP 10 is clearly to be welcomed. Lars Fabricius Managing director, SAV Systems Hard to breathe I was very interested in the article regarding wood burning. I suffer first hand from a neighbours chimney that manages to engulf our house in smoke that eventually enters through window and underfloor vents. Apart from the disgusting smell, I am now wondering ifwe are breathing in any nasties . I appreciate there is nothing we can do to stop the burning, but I am enquiring of your readers to see if theyhave had similar experiences and would welcome any advice. Colin Smith, ACIBSE CIBSE Journal welcomes readers letters, opinions, news stories, events listings, and proposals for articles. Please send all material for possible publication to: editor@cibsejournal.com or write to: Alex Smith, editor, CIBSE Journal, CPL, 1 Cambridge Technopark, Newmarket Road, Cambridge CB5 8PB, UK. We reserve the right to edit all letters. 20 March 2019 www.cibsejournal.com CIBSE Mar19 pp20 Letters.indd 20 22/02/2019 16:33