Pete Mills, Commercial Technical Operations Manager, Bosch Commercial & Industrial explains why CHPs are becoming less attractive for district heating and what alternatives there are.
CHP (Combined Heat & Power modules) have long been a staple of district heating scheme plant rooms across the UK, due to a highly efficient process that captures and utilises the heat as a by-product of the electricity generated.
However, CHP is becoming harder to justify as a future solution based on its carbon impact.
The electricity grid has decarbonised much quicker than was imagined even a few years ago and large amounts of renewable energy have quickly come onto the grid. The risk is that any CHP installed now could be in a negative carbon situation in a few years.
With the new Building Regulations imminent, for some time we have had a draft release to review (SAP 10.1).
This projects significantly reduced carbon factors for grid electricity. CHP will not easily work within this framework, especially as the more aggressive target has already been adopted by the Greater London Authority ahead of the official release of SAP10.2 (as it will be known).
There has been some work looking into what actual generating technology CHP would be offsetting and if they would still have a future for district heating schemes. However, it is likely that BEIS will not accept these arguments, although at this stage that is purely conjecture.
What alternatives are there?
If CHP is superseded, there are several technologies that are available to take its place. One being heat pumps which many believe could be the sole heat source for a new heat network project.
In our view, a more future-proof solution could be a hybrid solution, in this case between heat pumps and peak-load boilers. These can deliver significant carbon savings, whilst ensuring costs are kept under control.
Experience has shown that with around 50% to 60% of the peak demand covered by heat pumps, over 80% of the kilowatts can typically be provided through heat pumps.
Heat networks tend to operate below 25% of their peak demand for over half of the year, which is well suited to a heat pump. On the small number of days each year when temperatures are coldest, demand can be taken up by peak-load boilers.
If we consider the future energy landscape as well, hybrid solutions with a boiler involved can support even further carbon emission reductions in the future. One of the unique abilities of a heat network is its straightforward adaptation to multiple forms of heat that may become available in the mid to long term, such as Hydrogen gas.
Other alternatives include waste heat, which is often cited as the catalyst that sparked the very first heat networks to be built. Using a supply of heat that would otherwise be discarded makes perfect sense; something that has not gone unnoticed by policy makers. We are likely to see more policy moving towards incentivising this valuable resource.
However, currently the trend is for smaller unconnected heat networks to be built; not ideal for the use of waste heat that is better introduced into a larger distribution network.
Leaving strategic connection points that would aid future hook up to a wider district-heating scheme makes sense and represents minimal capital outlay at the start of a project.
If, at a later date an opportunity arises to connect to a much larger district-heating scheme, the transition is a much simpler prospect. However, keep in mind that many larger schemes will have strict guidelines about connection arrangements and in particular the return temperatures that can be accepted. Leaving plant room space for associated plate heat exchangers and hydraulic control equipment will be necessary.
As the UK moves towards a net zero future, the importance of district heating will no doubt become more and more prominent. Its ability to power whole areas and multiple buildings can already help efficiency levels, however its potential may be even greater in the future.
Many cities have already implemented district heating schemes in their regions, which will most likely increase the implementation of them across the country. CHP has been effective to date and will still run efficiently in existing schemes but the technologies discussed, as well as future innovations, will take heat networks to the next level in terms of carbon reduction.
One key energy transformation that is looking more and more likely is the decarbonisation of the gas grid to hydrogen blends and ultimately 100% hydrogen. If these can be utilised in heat networks, then the benefits will definitely put us in a good place as we continue our journey towards net zero. Particularly if a hybrid approach is applied.
Combined Heat and Power may have been the choice in the past, but a collaborative hybrid one could well be the future,