Pumped Thermal Electricity Storage

Lead Research Organisation: Durham University
Department Name: Engineering and Computing Sciences

Abstract

The increasing use of renewable energy technologies for electricity generation, many of which have an unpredictably intermittent nature, will inevitably lead to a greater need for grid-scale electrical energy storage schemes. The UK government's target (as part of the EU Renewable Energy Directive) is for 20% of energy to come from renewable sources by 2020. This will require a much a higher proportion of electricity to be generated from uncontrollable sources such as wind, and one of the associated challenges will be providing sufficient electricity storage capacity to deal with the resulting variability in supply. Currently there is about 30 GWh of electricity storage capacity in the UK, with a maximum power output of around 3 GW. Nearly all of this is in the form of Pumped Hydro Storage (PHS), which is expensive and its scope for extension is limited by geographical constraints. Estimates vary, but the expert view is that our storage inventory will need to at least double over the next decade or so in order to efficiently accommodate the expanding fraction of wind and other renewable generation technologies. There is thus strong motivation to develop new, efficient and cost-effective electricity storage methods.

This project is aimed at investigating a novel storage technology known as Pumped Thermal Electricity Storage (PTES). PTES uses a high temperature-ratio heat pump to convert electrical energy into thermal energy which is then stored in two large reservoirs - one hot and one cold. The reservoirs contain gravel, or a similar high heat capacity material, and are able to store the energy much more compactly than PHS. When required, the thermal energy can be converted back into electrical energy by effectively running the heat pump backwards as a heat engine. The projected round-trip efficiency is approximately 75%, which is a little lower than PHS, but PTES has a number of potential benefits, including low capital cost and no geographical constraints. Compared to chemical energy storage methods (batteries and flow batteries) it also has the advantage of not requiring any hazardous or scarce substances.

The success of PTES will hinge upon minimising the effect of various thermodynamic irreversibilities (for example, heat transfer across substantial temperature differences and losses associated with compression and expansion of the working fluid) whilst simultaneously keeping capital costs low. Accordingly, the proposed work focuses on investigating fundamental thermodynamic, fluid flow and heat transfer processes using a combination of experimental, theoretical and computational methods. An important aim of the work is also to develop and validate an overall system model and to use this to optimise the design and operation strategy, and to examine the benefits that PTES might bring to the electricity supply chain.

Publications

10 25 50
 
Description Commonly in energy systems modelling, a simple model of a storage unit is used which includes input and output efficiencies and losses, but no more complex properties associated with specific storage technologies. This work has developed a simplfied proxy for the physical model of the project's Cambridge collaborators, which is suitable for embedding in energy systems models.
Exploitation Route This modelling approach might be used by others in including thermal electricity storage in energy system models. Thinking on modelling physically complex storage systems and other technologies is informing thinking in the UK Centre for Energy Systems Integration.
Sectors Energy,Government, Democracy and Justice

 
Description Invited presentations to UK industrial mathematics community 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Dr Chris Dent has given invited presentations at:
- Turing Gateway to Mathematics event on "Maths and Public Policy - Cities & Infrastructure", see http://www.turing-gateway.cam.ac.uk/mpci_mar2015-programme
- KTN Industrial Mathematics community event, to stimulate interest in links between the mathematical sciences community and energy systems applications
- KTN "Mathematics in Energy Systems" workshop, see https://www.eventbrite.co.uk/e/energy-catalyst-brokerage-event-london-tickets-19192257559?aff=erelexporg

This outreach activity drew together experience from a number of different EPSRC projects.
Year(s) Of Engagement Activity 2015,2016