Solar thermal technologies deployed in around 400 million dwellings by 2030

Worldwide, dwellings using solar thermal technologies for water heating reached 250 million in 2020. To achieve the milestone of 400 million dwellings by 2030 in the Net Zero Emissions by 2050 Scenario (NZE Scenario), 290 million new solar thermal systems will need to be installed this decade. This deployment target takes into account the expected decommissioning of solar thermal systems which will happen during 2020s. According to the IEA Solar Heating and Cooling (SHC) TCP, 170 million new solar thermal systems using standard technologies and 120 million new solar thermal systems using emerging technologies will need to be installed by 2030.

Therefore, the deployment of solar thermal technologies in the 2020s will need to at least match the total deployment from the previous two decades for the 2030 milestone to be met. The contribution from emerging solar thermal technologies will be critical to meet this goal. Targeted innovation (technology, regulatory, and market) directed towards bringing these emerging technologies into their growth phase will be necessary in the next five years.

To achieve the 400 million dwelling target, a hybrid approach of deploying standard and emerging solar thermal technologies by 2030 will be required. Government support for large-scale pilot projects of the emerging smart solar-powered heat storage systems in the 2020s could direct this technology towards the 9^th Technological Readiness Level (TRL) internationally by the end of the decade. 

Solar thermal technologies can provide high fractions of water heating demand at low capital cost, even in cold climates. They can be used stand-alone or integrated into virtually any type of heating system, regardless of the primary heat source (direct electricity, heat pumps, district heating, biomass, or clean fuels). Exemplary uses of standard solar thermal technologies (evacuated tube and flat plate) with water-based heat storage include: 

• High-density housing developments because standard collectors, including hybrid photovoltaic-thermal collectors, have a high useful heat output per meter square of collector.
• District heating networks (with and without seasonal storage) can provide a very low levelised cost of heat using centralised MW-scale solar thermal plants.
• Rural low heat demand housing in low- and middle-income countries as low-cost solar thermosiphon and solar swimming pool heaters can provide quicker financial payback than other water heating technologies.
• Very high solar fraction combi systems (space heating and hot water) for single-family buildings are particularly suitable for rural houses in middle- and high-income countries.

Many of the 100 million households targeted in the NZE Scenario to rely on rooftop solar PV by 2030 could have power-to-heat related technologies installed that work intelligently to optimise self-consumption. These emerging solar thermal technologies are:

• Electrical heat storage (including hot water tanks and compact heat stores, both residential scale and district heating scale) using the power from solar photovoltaics (on-site and/or off-site). These types of smart solar-powered heat storage systems are suitable for rural and urban housing in middle- and high-income countries and are currently at the 7^th TRL in Europe.
• Heat pumps (heating, cooling and dehumidification) and direct electric heating using the power from solar photovoltaics (on-site and/or off-site). These are particularly suitable for rural houses in middle- and high-income countries.
• Centralised solar power combined with air conditioning is particularly suitable for high-density housing in the sunbelt regions (±10ᵒ from both the Northern and Southern Tropic).

Deployment growth rates for standard solar thermal technologies have generally declined globally in recent years, however, 2021 did show a change in this downward trend with a positive growth rate of 3%. Some markets in 2021 have demonstrated that significant year-on-year deployment growth rates of standard solar thermal are still achievable, with Italy, Brazil and the United States posting growth rates of 83%, 28% and 19%, respectively.

Data is scarce on the current deployment of emerging solar thermal technologies (e.g. solar photovoltaic to heat), however markets such as South Africa have already reached 10 MWp since the start of data collection in 2018.

The major challenges to achieving the 2030 milestone are the certification and installation standards for solar thermal technologies (standard and emerging), which are currently not sufficiently harmonised across all regions. The discontinuous deployment and promotion policies are not conducive to the efficient development of the solar thermal industry; and innovation spending is often not aligned with industrial strategy, leading to poor allocation of research funding and weak internal markets for solar thermal technologies. 

• Advancing solar thermal support schemes towards achieving the 2030 deployment milestone, whilst also securing prosperity and creating sustainable employment opportunities.
• Enabling the comprehensive integration of solar energy considerations into local planning and buildings energy codes (new building and renovation of existing buildings).
• Research and demonstration that would result in the lowering of capital cost, improving the technical performance, enhancing the installation experience, and removing the market barriers of emerging and standard solar thermal technologies.