Heat supply through Solar Thermochemical Residential Seasonal Storage (Heat-STRESS)

The Renewable Heat Incentive (RHI) scheme encourages uptake of renewable heat technologies in the UK to support the ambition of 12% of the heating coming from renewable sources by 2020, and solar energy is one of the forms of renewable energy that has great potential. The amount of solar radiation incident on the roof of a typical home exceeds its energy consumption over a year. However, the longstanding barriers to the utilisation of solar thermal energy technology lie in the noticeable miss-match between energy supply and demand. The Heat-STRESS project aims to deliver the maximum benefits of solar thermal energy by means of short-term (diurnal) and long-term (seasonal) thermal energy storage and thermochemical heat transformer technology to significantly reduce energy demands for individual and/or multiple residential buildings, such as a local community or multi-storey development. The concept proposes to significantly advance phase change material (PCM) storage and thermochemical technology in a holistic system such that it has the potential to provide both a technically and economically viable solution.
With sensible heat storage systems, the storage volumes required will be large and difficult to integrate into existing domestic dwellings. The latent heat storage has higher energy density than sensible heat system, and thermal-chemical thermal storage has much higher energy density than latent heat. Moreover, thermochemical sorption technologies seldom suffers from long-term heat loss and provide a preferable option for solar seasonal energy storage, i.e. using excess solar heat collected in the summer to compensate for the heat supply insufficiency during the winter time. One of the significant advantages of a thermochemical sorption system is that it is inherently an integrated heat pump and energy storage system. It is a pure heat-driven heat pump cycle and the heat source can be the seasonally stored solar energy, which would provide the potential to avoid electricity or gas use and off-peak grid loading resulting from the deployment of integrated air and ground source heat pumps, electric boiler, gas boiler and storage technology currently being developed. The thermal transformation provides the opportunity to upgrade heat, which may be suitable for domestic heating, so that it can provide higher temperature domestic hot water.
The Heat-STREES project is aiming at a new high level of cutting-edge technologies despites with lower Technology Readiness Level. It should be envisaged with long-term vision: one of imperative measures to realise decarbonisation and to cut energy bills is to avoid the conventional generated electricity and gas consumption due to the continuously increasing demands, aggravating energy poverty and the forthcoming strengthened carbon taxes. In order to tap all appealing potential of thermal-chemical sorption and PCM thermal storage to make contribution for a better advanced world, more immediate collective efforts from both academia and industries is required to address important research issues.

The proposed project focusses on delivering more efficient heating and hot water for single dwellings and multi-dwelling communities, however there is also significant potential for scale-up and scale-out of the technology to meet the demands of a wide range of other potential domestic, commercial and industrial energy consumers.
Global investments in thermal energy storage are expected to total $1.8bn by 2020 (Market projections for Thermal Energy Storage Market - Global Industry Analysis, Size, Share, Growth, Trends, and Forecast 2014 - 2020, Transparency Market Research, 2014). As such, the sector is experiencing rapid growth and will continue to grow as installer/consumer attitudes toward such solutions become more progressive as the evidence base grows. To date, the full exploitation of solar thermal energy has yet to be realised despite a) its potential to offset GHG emissions, and b) benefit of increasing national energy resilience through decentralised infrastructure. This market failure is in part due to the intermittency of solar energy and relatively high capital costs, therefore any improvements to diurnal and seasonal thermal storage may well unlock its potential for UK deployment.
In 2013 there where around 27 million UK dwellings and we still have a legacy of some of the least thermally efficient housing in Europe. Domestic heating accounts for 23% of UK energy demand, and almost 80% of total domestic energy consumption (around 500 TWh per year). Thermal energy demand has continued to increase over the past 40 years from 400 TWh/y to 450 TWh/y, even though home thermal energy efficiency has been improving. Over 95% of UK homes are heated by a boiler, with the fuel type dependent on location; some 23 million homes (80%) are connected to the gas grid (The Future of Heating: Meeting the challenge. DECC, March 2013).
Heat supply through Solar Thermochemical Residential Seasonal Storage (Heat-STRESS) aims to ensure the maximum exploitation of solar energy through thermal/chemical storage which can be a) used to satisfy transient domestic heating demands, b) upgraded for hot water and, c) used to offset electricity and gas demand within the home. This research programme has the potential to impact in a positive manner upon a wide range of societal beneficiaries from policymakers, manufacturers down the supply chain to the consumer and their corresponding energy bills. These benefits are expected to manifest through the development of (and IP associated with) novel and innovative technologies, control and system optimisation methodologies.
The storage and heat pump system topologies proposed are well positioned to dovetail the new STRESS subsystem for thermal storage development into the existing state-of-the-art Glen Dimplex Hybrid Heating System (HHS). In this way a clear route to market can be established with the STRESS subsystem acting as a natural successor to Glen Dimplex's Quantum Boiler thermal storage system currently utilised in the HHS system. It also provides not only a carbon emission and energy running cost performance baseline to assess potential environmental and fuel poverty impacts, it will also provide a baseline for maintenance costs, ease of installation and capital cost. All of which can normally prove difficult to assess in academic led research of this nature. It also brings the benefit of having a UK based manufacturer engaged in the research at an early stage which hugely increases the potential take up of the technology. Finally Glen Dimplex involvement also brings a years of experience in getting thermal storage technologies approved in building regulation procedures such as the SAP procedure. With Dr Counsell (previously a SAP Scientific Integrity Group member) and Glen Dimplex, the performance and final reports of the project can be made to align easily with building regulation approval, without which no technology can easily make it to market.