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Widening the spark gap

In sites with high constant demand for heat and power, a well-designed CHP system holds the key to significant financial savings and safer maintenance. That's according to Mark Gibbons, national sales manager for CHP at Baxi Heating


Mark Gibbons, national sales manager for CHP at Baxi Heating

As lockdown restrictions ease, businesses and organisations across the UK will be making plans to reactivate their buildings. While safety will be the major concern, implementing energy efficiency measures will also be a priority, both to reduce building running costs and to meet environmental commitments.

In sites with high, constant demand for high grade heat, one technology that can help organisations achieve significant cost and efficiency savings while providing greater energy control and security is Combined Heat and Power (CHP). Let’s consider the benefits.

Efficiency and emissions savings

Like a micro power station, only twice as efficient, CHP generates lower carbon, lower cost electricity and useful heat simultaneously at the point of use. While traditional power stations reject ‘waste’ heat to atmosphere, CHP captures and re-uses it for heating or hot water pre-heat, meeting the building’s heat demand more efficiently.

When replacing old or inefficient plant in existing buildings, CHP can typically reduce a building’s total primary energy usage and bills by 30% and CO² emissions by up to 20% compared with traditional heating plant and electricity supplied solely from the grid. Indeed, most natural gas CHP engines nowadays will emit almost zero CO² due to the set-up of the engine and lambda sensors. As a low carbon technology, CHP can also be used in new build developments to comply with low carbon requirements in Building Regulations Part L.

Spark spread

In addition to the considerable efficiency savings, the ability of CHP to generate on-site electricity at lower gas prices boosts returns still further. The operating cost benefit of CHP will depend on the difference in gas and electricity prices, which is often referred to as the ‘spark gap’ or ‘spark spread’.

The wider the spark spread, the greater the financial return. With gas prices currently at around a quarter of the cost of electricity, a trend that is predicted to continue, the economic case for CHP is still more attractive, especially with payback achievable within three years. 

An added advantage of onsite generation is the opportunity to offset fluctuations of wholesale energy prices, ensuring greater energy resilience and control over energy costs at a time when cash is king. 

CCL exemption

CHP can also financially benefit organisations that are in scope of the Climate Change Levy (CCL). Introduced to encourage improved energy efficiency, CCL is a government tax on electricity, gas, LPG and solid fuels supplied to businesses and organisations that can make up around 5% of their total energy costs.

CHP schemes registered and meet ‘Good Quality CHP’ status are exempt from CCL payments on the gas they use to generate electricity, helping reduce environmental tax bills and mitigate energy costs. The exemption applies when the CHP is registered with the Combined Heat and Power Quality Assurance (CHPQA) standard (

Remote monitoring

Aside from efficiency concerns, building operators and FM providers will need to adhere to increased safety requirements when operating and maintaining a building in the ‘new normal’. 

The good news is that experienced CHP suppliers will provide remote monitoring as a standalone service or as part of a comprehensive service plan.

Obvious as it may sound, a CHP only delivers savings when it’s operating. So, at all times, remote monitoring provides building operators and FM providers with peace of mind that if a problem should occur, it can be quickly and easily resolved. 

In the current climate, however, this service takes on added importance. As an estimated 85% of reported CHP faults are able to be corrected and reset remotely, remote monitoring largely removes the need for a site visit. 

Sizing is key

The financial case for CHP is compelling. But for a CHP to deliver maximum efficiency benefits, it’s essential that it is sized accurately.

While it can be tempting to size a CHP to meet winter demand, this will result in it shutting down in summer months when demand is low. Similarly, oversizing the CHP to cover a building’s poor energy performance will reduce its efficiency, CO² savings and operating hours, affect stop/start operations, increase servicing costs, and deliver poor financial paybacks. 

The CIBSE Applications Manual AM12 on Combined Heat and Power for Buildings offers a host of useful information and guidance on how to go about selecting, installing and operating CHP plant.

It reaffirms there is no straightforward way to size a CHP as each building or site will have different requirements. As designers are faced with the task of deciding the size of the CHP, it recommends that they seek support on accurate sizing from experienced suppliers at an early stage of design.

15 July 2020


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