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Sector coupling: district energy comes of age
Sector coupling is the logical progression for district energy. It has huge potential for the ongoing, wholesale reduction of carbon and the integration of renewable and waste energy sources in our energy supply. A number of countries have started to embrace this approach, but in the UK the possibilities are yet to be fully explored and harnessed. Neil Parry, global head of district energy, Armstrong Fluid Technology elaborates
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t is a startling fact that globally more than 40% of our building energy requirements could be supplied from the energy that we waste every day. This energy is wasted by industry processes, data- centre cooling, power generation, wastewater etc. Sector coupling has enormous potential in this regard, as the linking of the energy streams allows energy to be stored in various forms to match the changing demands AND changing outputs during a typical 24 hour period. Sector coupling splits energy supply into 4 key power grids: Electricity, Gas (This can be a mix of natural, hydrogen, biogas etc.), district cooling and district heating. These four networks are divided into four areas where the energy is ‘obtained’, stored, converted or used. The source and the use are straightforward. The storage and conversion however, are the two key areas that create flexibility and allow for energy to flow across the four different power grids. .
Designing for sector coupling
The four grids and the four stages are connected. Even the end users can be consumers or prosumers, taking or giving energy into the system. Sector coupling therefore can be thought of as a spider’s web with energy travelling in all directions across every strand. Let’s look more closely at the four stages: energy source, energy storage, energy conversion and energy end use. Energy of all types can move from, or to, the storage, conversion and end use sectors. Energy sources: These could include biogas,
hydro-electric, nuclear, geothermal, wind, solar, large scale CHP etc. Some sources will be available 24 hours a day, every day, such as nuclear for example, whilst the availability of some sources could fluctuate wildly, for example solar or wind. Geothermal, solar and heat pumps could supply energy directly into the district heating network. If renewable energy is in abundance, at a particular time, then this excess energy can be stored. Energy storage: Storage is extremely important as
it increases the flexibility of the supply. Wind energy could be stored as electrical energy in batteries or can be used to pump water up to high reservoirs and stored, as potential energy ready to be released to produce hydro-electricity via turbines. Gas, biogas and hydrogen can be stored using traditional methods,
30 April 2023
whilst thermal storage allows energy to be stored as LTHW, for example. In a similar way, chilled water can be stored for cooling networks, possibly even in the same vessels, or in aquifers, switching from heating to cooling seasonally. However, ‘smart’ sector coupling will also be able to predict peaks in the requirement for certain types of energy. Heating and DHW demand in domestic homes normally peaks early morning and again later in the evening. Knowing this allows the smart network to increase thermal storage ahead of this known peak in demand. Energy conversion: Energy from either the source or
from storage can be converted into different types of energy depending on what is required at any particular time. Electrical energy directly from solar or wind, or indirectly from storage batteries in the storage phase, can be used to produce hydrogen or used by heat pumps to create LTHW or chilled water, for example. Consumer waste can be incinerated and turned into LTHW or electricity at waste to energy plants Electrical energy (be that directly from source, such as solar or wind, or energy from storage, from batteries or gas powered CHP from the conversion sector) can all be used to pre-charge LTHW thermal stores in the storage sector ready to meet the predicted district heating peak. The CHP, of course, also produces electricity. Why not use this electrical output to also power heat pumps that can further augment the LTHW store?
Neil Parry, global head of district energy, Armstrong Fluid Technology
End users: The first question to ask is, are these
all consumers? The answer is no. Depending on the time of day, they could be either consumers or prosumers. Industry end users often have energy intensive processes that produce heat as a by-product of that process. Very often this heat is wasted. A better approach would be to direct this waste energy back into the district heating system, or to LTHW stores for use at a later time. Typically, electrical power plants send their heat to atmosphere, but why not send it to a district heating network instead? Why don’t we capture the heat from wastewater processes for use in the storage, conversion or end use phases? How about a business with a large fleet of electric powered vehicles? Why not use the electricity stored in their batteries and send it back into the storage or conversion sectors for use elsewhere? Very often these vehicles are not required from 6pm to 6am, plenty of time to use their stored electricity and re- charge them again prior to 6am. Sector coupling is the logical progression of district
energy. It helps in the decarbonisation process, increases flexibility of energy supply, increases resilience and improves reliability. It also reduces the costs and increases the speed of decarbonisation, both locally and globally (something that cannot be said of the ‘hard electrification approach’). Indeed this was the finding of the ITRE, the European Parliament Committee on Industry, Research and Energy in a report in 2018.
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