From Passive Buildings to Active Flexibility Assets
Power-to-heat solutions foreseeing integration of local PV, heat pumps and thermal energy storage (TES) can turn buildings from passive energy users into active partners of the electricity system, allowing the surplus locally produced renewable electricity at household level to be converted into heat and stored for later use.
This increases local self-consumption, limits curtailment, congestion and grid-quality problems at DSO Level, in addition to giving distribution system operators a new source of flexibility. Furthermore, aggregating many units (in a local grid managed by a DSO or energy community) could shift demand without compromising indoor comfort, and offer a relevant grid flexibility potential of a Demand Response asset “more or less” always present along the day. The question is at what cost.
A thermo-economic analysis conducted by the University of Genova through the ThumbsUp project confirms there is great potential for compact TES in residential buildings, however it also revealed significant economic barriers. The analysis was done on a series of buildings located in different climates (from Spain to Sweden), type of buildings (from single family homes to large multifamily buildings) and electric markets.
The results show that TES enables heat pumps to use local PV production and operate at favourable times. Yet storage costs remain high, particularly for phase-change-material (PCM) based solutions. Although PCMs offer high energy density by mass and volume, limited heat transfer constrains their charging and discharging rates. They may therefore provide substantial thermal-energy capacity but relatively low thermal power, increasing the size and cost required to offer relevant flexibility potential.
For example, the ThumbsUp FractLES which is a bio-based PCM solution that enables daily storage of heat using short duration latent TES for intraday use with a high energy density storage. This solution can be more sustainable than electrochemical batteries, but the complete heat pump (HP) and TES systems are currently often too expensive to install.
Energy-bill savings alone consequently produce long payback periods. In several of the analysed cases, simple payback exceeded 20 years; incentives for locally consumed renewable electricity reduced it, sometimes to about 9–16 years which is still too long return on investment for an average household.. Attractive business models may therefore require support to cover the initial investment and remuneration for system benefits, such as Italy’s Renewable Energy Community incentives of around €70–100/MWh locally self-consumed, or the possibility to work (as previously mentioned) via aggregation schemes that could enable to offer to local grids/DSOs flexibility services worth up to €400–600/MWh during high-value periods.
Economics, however, should not be the only purchasing driver to introduce innovative thermal energy storage solutions like the ones being developed in the ThumbsUp project or its sister projects in the TES Cluster. Greater awareness, appealing design and simple controls could transform smart heat pumps coupled with TES into attractive green appliances: visible signs of a low-carbon and energy-independent lifestyle in buildings. Ideally these technologies should become desirable and trusted, environmental identity and social status can complement financial savings (as it is happening for many other low carbon technologies that are becoming more and more common at building level). This would accelerate their adoption and multiply their value for consumers and the grid operator/EsCos/Buildign managers who can invest in such solutions.
Written by Stefano Barberis
Researcher at the University of Genoa
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