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Heat networks: a flexible approach to decarbonisation

In a mere 5 years time, renewable energy is expected to overtake coal and become the largest source of electricity generation worldwide. This will mean renewables will supply one third of the world’s electricity. This exponentially increasing share of renewables in the global energy mix will require more flexible energy systems for successful integration, says Andrew Cripps, Director of Sustainability, Buildings and Places at AECOM, part of Triple Point Heat Networks Investment Management delivering the Heat Networks Investment Project.

The International Energy Agency (IEA) released a report in May 2020 that analysed the impact of Covid-19 on renewable energy deployment in 2020 and forward into 2021. Although Covid-19 has drastically caused many sectors to grind to a halt, this is not the case for renewables.

Covid-19 is reported to be ‘hurting – but not halting – global renewable energy growth’ and renewable technology costs are continuing to decline, changing the investor landscape. It is predicted that the share of renewables’ growth coming from purely market-based settings, outside of policy programmes like auctions and feed-in tariffs, will triple from less than 5% today to more than 15% through 2025.1 This shows the resilience of renewable energy markets in the electricity, heat and transport sectors.

This resilience, adaptive capacity and forecasted growth of renewables needs to be harnessed and utilised to drive global emissions down to net zero.

The intermittency of some forms of renewable energy makes the generation of electricity/heat harder to predict or control which calls for a more flexible energy system in order to integrate renewables into the energy mix.

Luckily, there are solutions available to enable this transition with a flexible energy system.

The Committee on Climate Change in their Sixth Carbon Budget stated that “the shift to electrification and heat networks can also deliver improved energy security and improved air quality”. Heat networks allow a range of low-carbon heat sources, including renewable energy, heat pumps and otherwise wasted heat from a variety of sources, to be used individually, or in combination in a single network. Thermal energy storage can be used to help match supply to demand in heat networks, improving their efficiency and flexibility. Despite being technology agnostic, heat networks are increasingly being supplied by heat pumps which provide an efficient way of heating multiple homes, utilising renewable electricity generation.

Heat network flexibility – the capability of shifting energy use in time and/or magnitude – can be obtained, amongst other methods, by integration of thermal energy storage in district heating systems. Adequate control of storage systems allows a scheme to take advantage of periods of high availability (and potentially low cost) of renewable energy, by increasing power take to build up storage in these conditions. Similarly, the scheme can reduce power demand and rely on stored heat when renewable energy is less available, potentially earning income from grid services. By supporting the grid in these ways, a heat network can help in a way that single building heat pumps cannot, or at least not on the same scale.

Centrally located, thermal energy storage can provide value to district heat systems by reducing the size of heat generation. However, the potential for flexibility from district heating has not yet been fully exploited.

Energy flexibility in thermal networks can be offered by many sources, ranging from dedicated storage systems, e.g. tanks and aquifers, to the thermal energy storage inherently present in the network, building thermal inertia and network pipes containing warm water. In some countries, the majority of district heating systems have sensible thermal storage tanks. For example, in Sweden as much as 64 % of their capacity is available for flexibility services.

There is a growing interest, both in Europe and China, for the use of short-term storage in district heating to provide flexibility, particularly in the form of ancillary services to the electricity grid, but implementations of these techniques are rare.

The recent announcement from the Climate Change Committee (CCC) of their Sixth Carbon Budget highlights the opportunity for heat network development. The sector will need to embrace demand side response and flexibility. A number of heat networks applying for Heat Networks Investment Project (HNIP) funding are incorporating thermal storage and mechanisms to support a more flexible energy system as we transition towards net zero.

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