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Basking in the sun: emissions-free heat production

Four in five Israeli households use solar water heaters. © OECD/IEA, 2014

Much fossil fuel is burnt to produce heat, but renewable options abound, from wood pellets to geothermal. Solar hot water is already a winner.

2 May 2014

More than 40% of the world’s primary energy supply of natural gas, and 20% of both coal and oil supplies, go to producing heat. Using renewable energy sources would cut CO2 emissions and increase energy security, especially for countries heavily reliant on fossil-fuel imports.

Renewable sources already play a large role, at almost one-quarter of global energy use for heat. But most of this is in the form of traditional, inefficient use of biomass in developing countries to heat and cook, leading to deforestation and indoor smoke pollution. Modern biomass, such as wood pellets, plus solar thermal and geothermal heat, accounted for only 3% of the total global energy use for heat in 2011, though use grew dynamically in the last decade.

There are several reasons why modern renewables are little used for heat in buildings and industry. One is that policy makers have paid considerably less attention to the renewable heat sector than the electricity sector. Only about 35 countries have dedicated policies to encourage renewable heat, while more than 100 have policies for renewable electricity.

As a new IEA Featured Insight, Heating Without Global Warming: Market Developments and Policy Considerations for Renewable Heat, explains, solutions to enhance the contribution of renewable heat abound. Some are basic and already mature, such as solar water heating, geothermal energy from hot springs for district heating, and efficient wood-burning stoves and heating systems. Though not entirely renewable, heat pumps, which extract low-temperature heat from the ground, water or ambient air, are increasingly popular: global heat-pump capacity has doubled since 2005 to 42 gigawatts (GW) in 2011, equivalent to the heat capacity of 15 large-scale combined heat and power plants.

Concentrating on big potential

Many of these technologies can be competitive under favourable circumstances and in applications such as domestic hot water provision, swimming pool heating, even space heating. But a number of issues hinder development, such as subsidies for fossil fuels, the lack of a price on CO2 emissions, or poor consumer awareness.

A range of renewable heat technologies exists, but solar thermal heat has been the most dynamic growth market in recent years. Solar energy theoretically could provide 6 200 times the current world primary energy supply.

Numerous technologies exist to harvest this potential for heating and cooling, ranging from simple solar stoves for cooking, to flat-plate collectors and evacuated tube collectors for hot water production and space heating, up to concentrating solar thermal installations for future use in high-temperature industrial applications.

In the last decade, global use of solar thermal heat in buildings almost quadrupled to 0.7 petajoules – equivalent to 7% of the annual heating demand of US households – produced from a global total of 235 GW thermal of installed solar collectors. Countries such as Israel and Austria have long histories of deployment and the highest per-capita installed solar heat capacities. In Israel, which has required installation of solar water heaters in new buildings since 1980, 80% of households now obtain their hot water from solar thermal systems, thanks also to their cost-competitiveness with fossil fuel-based systems.

But with a ten-fold increase in solar thermal heat capacity in the last decade, China now accounts for two-thirds of global use of solar heat in buildings. Most systems there provide hot water only, and installation is driven by their cost-competitiveness. More recently, several cities and municipalities, including Beijing, have adopted solar obligations for larger building complexes, meaning that solar thermal systems next need to be better integrated into high-rise buildings, such as facade or balcony systems.

In all countries with considerable solar thermal energy use for heat, support policies such as solar thermal obligations and investment subsidies, as well as more general support measures such as CO2 taxes on fossil fuels, drove initial deployment. In several countries, the initial market push provided by the policies made solar thermal water heating cost-competitive with fossil fuel or electricity-based systems even in the absence of support policies.

Impediments to a global success story

Does this mean that such success stories can easily be replicated anywhere in the world?

As Heating Without Global Warming points out, the resource availability (sunshine) obviously is important, but so are factors such as the costs of solar thermal systems compared with fossil fuel-based heating systems. In China, mass production of solar thermal water heaters lowered system costs considerably and led to a wide network of retailers and installers.

Solar thermal heat in buildings has mainly been for hot water systems, with more modest growth in space heating or combined installations.

One reason is the complexity of solar thermal heating systems, requiring significant up-front investment and extending the payback period through fuel savings compared with a fossil fuel-based heating system. Further technology improvements and cost reductions will increase circumstances where solar thermal heating systems are cost-competitive.


This article by Anselm Eisentraut, Bioenergy Analyst in the IEA Renewable Energy Division, appears in the new issue of IEA Energy: The Journal of the International Energy Agency.  The IEA produces IEA Energy, but analysis and views contained in the journal are those of individual IEA analysts and not necessarily those of the IEA Secretariat or IEA member countries, and are not to be construed as advice on any specific issue or situation. Click here to read the new and earlier issues of IEA Energy, and click here to send a request a free subscription.


The statistical data for Israel are supplied by and under the responsibility of the relevant Israeli authorities. The use of such data by the OECD and/or the IEA is without prejudice to the status of the Golan Heights, East Jerusalem and Israeli settlements in the West Bank under the terms of international law.

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