CHP has a powerful case
If the UK is going to use energy more efficiently within buildings it must first remedy the huge losses made during power generation. David Shaw argues that we already have a tried-and-tested solution.
Every year we waste enough heat from power stations to heat most of the buildings in the country. Around 65% of the energy used to produce electricity is wasted, partly in transmission losses, but mostly in waste heat discarded via the power stations’ giant cooling towers. Europe loses the equivalent of the output of 35 power stations this way every year.
If half of the heat lost during electricity production could be captured it would meet 25% of the UK’s heat demand.
Combined heat and power (CHP) is gathering support and strength as the most efficient way of producing on-site power while also heating your building. It is an increasingly viable low-carbon alternative to the carbon-intensive Grid because the heat produced while generating electricity is not thrown away, but used as a source of low-cost heating. It is estimated to be around 30% more efficient to generate power and heat using on-site CHP rather than receiving electricity from the grid and heat from a gas boiler. This means that CHP reduces the carbon intensity of the country’s electricity generation.
Unfortunately CHP suffers from a lack of the ‘sex appeal’ enjoyed by renewables. Solar panels and wind turbines are widely hailed as solutions to the carbon-reduction challenge, but the big difference is that CHP is not dependent on the UK’s unpredictable weather conditions and is a tried-and-tested technology that is already widely used throughout Europe.
Buildings with high heating and energy demand are ideal for CHP. Leisure centres and swimming pools, hotels, hospitals, sheltered housing, fire stations, schools and many others with long running hours or periods of intense demand will keep a CHP unit working almost continuously.
This is when CHP is at its most efficient, for all the time the engine is running it is producing electricity. A buffer tank will absorb and store excess heat for release into the heating system when required and, importantly, reduces the frequency of on/off cycling that can reduce the efficiency of the engine.
The CHP unit can be easily integrated with existing services and controlled via an integral module that monitors the condition of the system and ensures optimum operating efficiencies. CHP systems can also form the heart of a trigeneration system that will provide cooling as well as heating with the addition of an absorption chiller.
The Dachs mini-CHP engines made by Baxi-SenerTec, for example, are designed to be robust and reliable so will run for thousands of hours, delivering up to 440 MWh of electricity and 1200 MWh of usable heat at a combined efficiency of over 90% over their life. They will also reduce carbon emissions by over 100 t during their operating life, compared with conventional methods of delivering heating and electricity separately.
The latest CHP models are designed to reduce installation and commissioning time because they are delivered to site as complete packages. For example, the Dachs SE comes complete with a buffer vessel and all heating- system components, including an integrated control unit.
London Fire Brigade is already enjoying the benefits of CHP. It is upgrading all its stations with a combination of low-carbon technologies, and 18 stations have already installed Dachs mini-CHP SE kits consisting of a CHP unit, a condenser and a buffer vessel.
At one fire station, the CHP also works in tandem with a photo-voltaic (PV) array, and the two systems combined are expected to reduce a station’s carbon footprint by 13 t a year.
This fire station registers the energy produced and carbon saved by the CHP system in real time on a prominently displayed digital panel reports a £2500 annual saving on fuel costs. This means that the payback on the purchase cost of the CHP system will be less than six years.
With widespread blackouts expected in the near future, it is increasingly important that we replace as much of the capacity of the National Grid as possible with more efficient and low-carbon sources of electricity. The more energy we produce from decentralised sources, the less comes from a Grid that wastes as much as 65% of its production through rejected heat and transmission losses. CHP captures waste heat and re-uses it, and there are no transmission losses as electricity is generated on site.
In the longer term, the Grid will become less carbon intensive owing to wider use of renewables. However, it is unrealistic to expect that it will ever be completely de-carbonised because of the enormous volumes of renewables this would require and the stupendous cost. There will always be a need for some conventional power generation, and the ideal scenario is to generate electricity locally using CHP, which is efficient, reliable and is not at the mercy of our fickle weather.
David Shaw is business manager of Baxi-SenerTec UK.
