Helen Gavin

09 December, 2019

Environmental Change Institute, University of Oxford

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How can hot water tanks help balance the National Grid?

Researchers at Oxford University have teamed up with energy industry partners Upside, Powervault, Mixergy and the Eden Project in a pioneering trial funded by BEIS and Innovate UK. Called the PETE Project (Power, Energy, Technology, Efficiency), it explores how smart, efficient, hot water tanks can help balance the National Grid.

Providing electricity for everyone, whenever it is needed, is a tricky balancing act. The demand for electricity must be matched by a supply, otherwise there may be a blackout. It’s also true that where the supply of electricity is greater than the demand for it, the excess must be removed from the national grid for safety reasons.

“Using smart and efficient hot water tanks means we can heat during periods where energy is abundant…” 

There has been a significant increase in the amount of renewable energy sources plugged into the UK grid over the past 10 years to the point where renewables generated more electricity than fossil fuels for first time ever, over July-Sept 2019. This is fantastic from the perspective of decarbonising our energy supply, and moving towards net zero emissions. However more renewables on the grid poses challenge to the balancing act between supply and demand. This is because of the variability of renewable energy: there may be shortfalls if the sun or wind is not as strong as expected, or too much if the amount of available electricity isn’t matched by demand for it. Further, the lack of inertia of renewable energy technologies means that there may be very sudden imbalances that need to be managed.

One way to address this variability, and to balance supply and demand, is to turn off the supply from wind turbines and solar farms. But this is an incredible waste of clean, cheap energy. It is much better to make use of this energy using storage technologies so that we can use it at a later date when demand exceeds available supply. This storage can take many forms: batteries, pumped hydropower, flywheels, super capacitors… and smart, hot water tanks.

The idea is that when there is excess electricity available, the smart tanks will use this to heat water. Not only does this make use of electricity from renewable sources that may otherwise be turned off, it also provides hot water to the households without any perceptible impact. Further, it reduces the pressure on the grid infrastructure and allows more renewable energy sources to be connected.

Data from Eurostat indicates that of all the energy used in the house, 15% is used to heat water. 48% of gas used in the home is for water heating; or 11% of oil in households using it as a fuel source. Using excess renewable energy to heat water therefore can play a critical role in reducing greenhouse gas emissions and household costs.

According to Dr Pete Armstrong, CEO of Mixergy, “Using smart and efficient hot water tanks means we can heat during periods where energy is abundant and electricity prices are negatively priced, a phenomenon which is becoming increasingly prevalent. This enables the energy system to accommodate more renewable power whilst reducing primary energy consumption”.

The PETE Project has placed around 300 smart hot water Mixergy tanks and 100 Powervault home batteries, into houses mostly in London and Cornwall, which are all connected together via the cloud. Aggregating large number of tanks and batteries together in this way creates an energy capacity equivalent to a power plant. This virtual power plant means considerable savings can be realised by deferring capital expenditure on new generation equipment.

The data from batteries deployed to some households help us determine how to integrate thermal and battery storage. When there is a surplus of energy, the tanks use the energy to heat water. When there is less supply than demand, the batteries can provide power to the grid and the hot water tanks will stop heating. This approach is termed ‘demand side response’ in that, rather than turn on or increase supply from a fossil fuel plant, the demand for power is managed instead.

Dr Sivapriya Bhagavathy, a researcher with the Oxford Martin Programme on Integrating Renewable Energy, is part of the Oxford University team that is analysing data from the trial. She is looking to ascertain the success of the approach, patterns of household consumption of hot water, the potential residual capacity of the tanks to see how much storage could be used, and how the concept could be scaled.

Priya Mothilal Bhagavathy

She says, “A key aim of the trial is to test how the storage assets can be run collectively as an interoperable and scalable system, that can offer 1 MW of balancing capacity to the National Grid. Another aim is to quantify true multi-vector storage potential in the households.”

If the concept is proven, it could allow operators to access new revenue stream such as the National Grid’s frequency response market, and also from the distribution network operator in terms of managing constraints on the network. Some of this revenue would be passed to the property owner participating in the scheme. Alternatively, it could mean that operators approach a property owner to host a tank in order for both partners to derive benefit: low cost hot water for the property owner, and additional revenue streams for the operator.

Further digitalisation of energy production and storage assets is a key way in which we can decarbonise our energy supply in a cost-effective way, for the benefit of all. There are lots of challenges to overcome however, and the PETE project is a fantastic example of how Oxford University is working with partners to explore and find solutions to these new challenges, from getting the technology to work, agreeing standards and data protection, to building hyper efficient new energy economies that have a positive impact on people’s everyday life and the environment.

Written by Helen Gavin, Manager and Knowledge Exchange Researcher Oxford Martin Programme on Integrating Renewable Energy

This article also appears on Oxford University’s True Planet website.

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