Water Heating

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Solar water heater in a school in Bolivia

Households consume hot water for hygienic and cleaning purposes to prevent the spreading of diseases. Heating water is essential on a daily basis for safe water consumption since many poor households have no access to clean drinking water. Boiling remains the most common form of household-scale water treatment worldwide, having been used to treat drinking water since antiquity. If the boiling point is reached, boiling is effective at inactivating all the bacteria, viruses, and protozoa that cause diarrhoeal disease. It should be boiled for 1 minute at sea level and for 3 minutes at high altitudes.[1]

Heating water is also a small but essential element of a wide range of production processes in agricultural, industrial and service sectors. Hot water is needed, for example, in restaurants for cooking and cleaning, in industrial processes for dissolving substances or cleaning equipment, in hotels for hot showers, etc.

GIZ EnDev bolivia Warm water.jpg
Warm water in a school in Bolivia

There are various techniques available for heating water, most of which are based on fuel combustion or the use of solar power. The demand is increasing in developing countries. The market for solar water heating devices in China alone reached sales of USD 6.3 billion in 2008.[2]

Heated water may be stored in isolated tanks or in drinking water bottles, until the (hot) water is consumed. Compared to cooking, water heating is not bound to a certain time. Cooking needs to be done just before eating time, therefore and for traditional reasons, solar energy is not always a viable option.

Since in many developing countries the sunlight is strong all year round, solar energy based technologies might be a more suitable and cheaper option for water heating than fuel-based technologies. Some households in Malawi stated that the amount of firewood consumed for water heating even exceeds the one consumed for cooking.

Especially in rural areas, where access to clean water is even more difficult, common heat appliances are generally more expensive and challenging to diffuse than in urban settings.[2] Therefore, interventions of programmes should recognize these nexus between reliable access to water safety and energy supply.

Traditional and Improved Water Heaters

Traditional Water Heaters

Most households heat their water on their cooking stove. Social institutions and private firms need greater amounts of hot water and use more suitable appliances. For example in Malawi, traditional ‘Rhodesian boilers’ are usually made out of a 220 litre (oil) drum with an influx of cold water and an outlet for hot water. The water container (either a complete drum or vertically cut in half) is placed horizontally in an enclosure above an open fire. The water containers are usually not insulated, and barely shielded from the wind. The fire is made on the ground with usually low combustion efficiency.

Improved Water Heaters

Biomass Based Heaters

Although water can be heated on every biomass stove, there are also devices that were especially developed to heat water for showering and/or cleaning purposes. For more information on biomass stoves, go to: Cooking with Firewood or Cooking with charcoal.

Cookstove providing hot water in Uganda

(see Picture on page 15: GIZ Uganda 2012, http://irena.org/DocumentDownloads/events/NaplesSeptember2012/Uganda.pdf)

In Malawi, the Programme for Basic Energy and Conservation (ProBEC) improved the typical ‘Rhodesian boiler’. The ‘Rocket geyser’ adopts the Rocket Principle of cook stoves for water heating processes. This improved heater places a 220 l- water-drum above a rocket fire-chamber made of isolative bricks sized for 110 l pots (half-drum). The insulated chimney around the vertically placed drum above increases combustion and heat transfer efficiency. With less than 1 kg of wood the heater manages to heat the entire drum to ca. 40 degrees C. Because of the insulation around the water container, the water stays warm for almost the whole day. Exact fuel consumption was never quantified, as the rocket geyser remained a niche product not actively promoted by ProBEC. The rocket principle can be applied even to low-temperature uses like bath-water heating, though cleaning and clogging remains an issue.

The rocket fire chamber beneath the vertically installed water drum. (Picture: Christa Roth)

GIZ Roth Malawi RocketGeysir

  • Shia Manzi has a water heater fuelled with biomass geyser in South Africa: Shizamanzi biomass geyser. Find the video at http://www.shizamanzi.co.za/ (1kg of biomass heats up 20 l of boiling water within 10 minutes).

Solar Thermal Water Heaters

Solar thermal energy can be used to heat water with the help of specially designed collectors and tanks, which capture and store heat from the sun. Since it depends on the sun shining, solar cookers are ideal if cooking is not bound to happen at a certain time, e.g. for pasteurization of drinking water. In the autonomous region of Tibet, families store the water heated by the solar cooker during the day within thermos flasks. The hot water is used for preparing both morning and evening meals (mainly soup and porridge) enabling the solar cooker to fulfil almost all the household energy needs.

The technology of solar thermal water heaters is present worldwide and significant deployments occur already in emerging economies and developing countries. Regions without experiencing freezing temperatures can use the simplest and most cost-effective kinds of this technology.[3]

Simple passive solar water heaters without pumps or any other electricity need are well suited for the developing world. These ‘batch collectors’ are effective and practical. The water is contained in a collector tank and heated by the sun’s energy.

The simplest form is a black plastic bag to lie in the sun to heat up. A solar collector usually consists of various pipes, isolated within a box covered with a glass front.[4]

A newly installed water tank in Bolivia. (Picture: GIZ Energising Development Bolivia)

GIZ EnDev bolivia Bolivien Solarthermie

A more sophisticated solar water heater (SWH) consists of an array of collectors, an energy transfer system and a thermal storage system. While active SWH use a pump to circulate the heat-transferring fluid through the solar collectors, passive thermosiphon systems use the natural circulation of working fluid. As hot water rises above cold water, the water in a tank gets heated when placed above the solar collector. Design and climatic parameters such as solar radiation, ambient temperature and wind speed define the possible amount of hot water produced from a solar water heater.

There are two types: the Flat-Plate Collectors (FPC) and the Evacuated Tube Collectors (ETC). FPCs are more common and heat the water in many tubes that are placed on a dark absorber plate. ETCs achieve higher temperatures, but are more expensive (1.2-2 times). In the UK a 3m2 FPC costs around 3,600 £ and an ETC about 3,462 £. In ETCs, the dark absorber tubes are placed inside a glass vacuum pipe. The vacuum allows for all the heat to be transferred to the water, eliminating convective and conductive heat losses.[5] In regions with very low winter temperatures, ETCs are the better option, but generally both types are suitable. For further technical information about solar thermal collectors please refer to Solar Thermal Technologies: Solar water heaters.

Productive use applications of solar water heaters arise in various industries, notably in the food service and hotel industries. As solar water heaters are a relatively low-cost technology and involve zero running costs, they are ideally suited to micro and small enterprises. Reliable and sufficient availability of hot water usually implies higher service quality, which allows restaurants and hotels to attract more clients or increase prices. An example of productive use of solar water heaters in the agriculture sector is pasteurisation of milk and cheese, which requires hot water (ADA/MEI 2011).

For pictures and examples in Spanish: visit http://termoinox.com/.

Market Development and Barriers for Solar Water Heaters

The current commercial market for modern SWH is predominantly households (high income), hospitals, commercial establishments and tourist facilities, but small passive thermosiphon systems are spread out in households throughout the world.

The leading countries in cumulated water collector capacity in operation in 2010 per 1,000 inhabitants were Cyprus (577 kWth/1,000 inhabitants); Israel (397 kWth/1,000 inhabitants); Austria (388 kWth/1,000 inhabitants); Barbados (323 kWth/1,000 inhabitants), Australia (271 kWth/1,000 inhabitants), Greece (266 kWth/1,000 inhabitants), Turkey (120 kWth/1,000 inhabitants), Germany (118 kWth/1,000 inhabitants), Jordan (109 kWth/1,000 inhabitants) and Switzerland (93 kWth/1,000 inhabitants). The vast majority of the total 2010 capacity was installed in China (117.6 GWth) and Europe (36.0 GWth). But also the United States and Canada (16.0 GWth), Asia, excluding China (9.4 GWth), Australia and New Zealand (6.0 GWth), Central and South America (5.5 GWth), the MENA countries Israel, Jordan, Lebanon, Morocco and Tunisia (4.4 GWth) as well as some Sub-Saharan African countries (0.8 GWth), namely Namibia, South Africa and Zimbabwe have installed capacities of solar water collectors.[6]

It is expected that these capacities will rise significantly with a growth rate world wide of 25 per cent. Many governments adopted policies to foster consumer’s choice towards solar water heaters instead of electrical water heaters with lesser initial costs.

While adopting solar water heaters in industrialised countries helps to reduce the risk of peak loads of electricity, in developing counties solar water heaters aim at replacing inefficient ways of heating water with biomass.

China is responsible for the majority of the world’s demand. Over 30 millions Chinese households have a solar water heating system, nearly one out of ten households. SWH cost only 20 per cent of what to pay in Western countries, starting at around 1,500 Yuan (US 235).[7] Per-capita leaders are Israel and Cyprus, with coverage of 90 per cent of all households. Israel implemented a favourable legislation: since 1980, every new house must be built with a SWH.[8]

In the Middle East and North Africa (MENA), SWHs are well developed and mostly manufactured locally; several manufacturing facilities are established in most MENA countries. In Jordan, an estimated 30 per cent of houses are equipped with solar water heaters. Low tariff of conventional energy in some MENA countries, manufacture material pricing, legislations, awareness, availability of skilled labour prevent further adoptions. Another reason why there are so few solar water heaters in other regions, despite an abundance of sunshine in some countries, is the lack of trust in this technology. Also, technology must always be adapted to the specific traditions (e.g. housing conditions) and needs of people in the region.

Barriers that prevent faster dissemination of SWHs are the following:[9]

  • Initial costs
  • Technical Barriers
  • Lack of Awareness
  • Economic/Financial Barriers
  • Institutional & Legislative Barriers
  • Research & Development Challenges
  • Marketing Considerations & Social Barriers

Fellow, P. (2012): Technical Brief: Solar Water Heating by Practical Action.

This publication explains how solar energy may be used to heat water and how the technology works, it also includes some success stories.
practicalaction - solar water heating

Women in Europe for a Common Future (2010): Construction of solar collectors for warm water.

This brochure shows how to use the energy from the sun for heating water, how to construct a solar water heater and gives an overview of other solar collector models.

Construction of solar collectors.pdf

Experiences of GIZ Projects

Malawi: Rocket ‘geysers’ as Medium-scale Wood-fuelled Water Heaters

Project Approach

The Programme for Basic Energy and Conservation (ProBEC) promoted improved energy solutions for low-income households through market development and policy support in the SADC region. In order to do so, ProBEC adopted a commercial approach in as much as it built capacity by training producers to manufacture energy saving cooking devices, who in turn sell the stoves and hence a market was developed.

A private Tea company from Malawi, Satemwa Tea Estates assessed in 2005 that the firewood consumed for water heating exceeded the wood consumed for cooking. Trying to reduce this wastage, they approached the ProBEC technology development centre in Mulanje to inquire if the rocket principle that they were successfully using for their larger cook-stoves could be applied to water heating. ProBEC asked the local producer of Rocket stoves, Ken Steel Engineering, if he could build a ‘Rocket geyser’. In 2006, the tea company was able to provide hot water to all their management-level houses in the Thyolo district.


Rocket geysers are medium-scale biomass-fuelled water heaters to provide quantities above 20 litres (up to 200 l) of water heated to 40-70 degrees C, suitable for bathing. The rocket stove builder constructed a prototype at his own house with a rocket fire-chamber out of insulative bricks sized for 110 l pots (half-drum). He placed a 220 l-drum vertically into an insulated chimney, thus increasing combustion and heat transfer efficiency.

The selling price of then 95,000 MK (ca. 800 USD) was high, as the inner drum was made out of stainless steel.

Experiences/ Lessons Learnt

The rocket principle can be applied even to low-temperature uses like bath-water heating, though cleaning and clogging remains an issue. However the technology remained a niche product. Only where solar or electric heating is not feasible, it can compete economically.

Producer Ken Chilewe, who built the first model in his own house, managed to heat the entire drum to ca. 40 degrees C with less than 1 kg of wood. Because of the insulation around the water container, the water stays warm for an extended period of time.

According to the managing director of Satemwa Tea Estates, Alexander Kay, the rocket geysers considerably reduce the consumption of firewood. The challenges they observe is clogging and burning out of the drum-bottoms. To overcome this, they had to widen the recommended gap between the chimney and the drum slightly decreasing the efficiency of the system. Clogging occurred especially when people used wet firewood that causes a lot of soot.

In a stove, where the pot gets regularly removed for cleaning, the soot-deposits on the stove wall are cleaned out easily from the inside. In a geyser the situation is different as the drum becomes permanently fixed, once the plumbing is done and the pipes for cold-water influx and hot-water outlet are fitted to the drum. This makes cleaning impossible, unless the gap is widened and the ‘roof’ of the system can be removed, so that the cleaning can be done from above.

Peru: Solar Water Heaters

Project Approach

Energising Development Peru (EnDev) supports the installation of solar water heaters in schools, health centres and communal institutions and strengthens the existing market of solar heaters. EnDev assessed the solar potential by indicating the solar radiation per region and the companies’ activities in the solar heater industry. EnDev subsidises up to 20per cent of the investment and installation costs in the region of Arequipa. The remaining costs are covered by mining companies, micro finance institutions, social institutions, the community, the local government and private companies.

The aim of this intervention line is to facilitate the access to hot water with solar energy in 200 social institutions and to strengthen the existing market of solar heaters. Until December 2010, over 540 schools, 460 health centres und 500 communal institutions profited. Additionally, 250 households bought a solar water heater (90-360l).


Commercial solar heaters cost between 1.500 (90 litres) and 1.850 (120 litres) Soles (between € 400 and 500). In comparison an electric boiler costs around 300 Soles (or around € 75).

Market Situation in the intervention region: There are around 60 enterprises in Arequipa producing solar water heaters. Sales of the solar heaters are concentrated on the urban and peri-urban market.

Thermosophon solar water system on the roof in Peru. (Picture: GIZ Verena Brinkmann)

GIZ Brinkmann Peru SWH Themosyphon


Further information and a project example can be found in Solar Water Heaters – Project Examples.

Mexico: 25,000 Solar Roofs Programme

Project Approach

In August 2007, the Mexican Energy Commission (CONUEE) unveiled its Programme to Promote Solar Water Heating (PROCALSOL) with the goal of tripling the installed surface area of solar collectors by 2012. This corresponds to an increase of 1.8 million square metres. The objective is to reduce GHG emissions of up to 161,250 tCO2e, compared to use of conventional gas systems.

The unique features of PROCALSOL are its consistently integrated approach to developing the market and the fact that public institutions, manufacturers, activities, financial institutions and other stakeholders are pooling their efforts for the first time.

By improving the legislative and regulatory environment, developing quality standards and giving its support to information and public awareness campaigns, the GIZ programme provided technical and conceptual advice from 2007 – 2009.

Promotion mechanism: A subsidy of 100 Euros will be permissioned for up to 25,000 SWH through the ‘Green Mortgage Programme’ from Infonavit.


A solar water heater (calentador solar de agua) is a system that heats water only with solar energy without gas or electricity. A typical system of SWH consists basically of three components: a solar collector, where the solar energy is captured and transferred to the water, a hot water tank, that stores the hot water, and piping and valves that "transports" the water between collector, the hot water tank and sanitary system by natural circulation.


Figure1: Solar water heater on page 21.

Source: http://www.conuee.gob.mx/procalsol/dictamen_procalsol.pdf

Info-commercial de Infonavit (in Spanish)


Experiences and Lessons Learnt

The legal environment, especially the quality standards, has improved and the high quality of installation has been ensured through the creation of the relevant training courses. Moreover, the surface-area of newly installed solar collectors is growing each year (from 53,183 m2 in 2008 to 132,934 m2 in 2010). The population is becoming aware of the issues of solar thermal energy and renewable energies.

The Green Mortgage programme (Hipoteca Verde) organized by the Infonavit Bank offered low-interest loans. This way, 37,000 households profited alone in 2009 – that means almost every second collector in the residential sector.


GIZ is working on certification and standardisation of SWHs in the Middle Eastern and North African (MENA) countries. The Regional Center of Excellence for Renewable Energy was established in Cairo, Egypt and will facilitate RE technology transfer. See: http://www.rcreee.org.

Project Approach

GIZ is supporting the establishment and organisational development of the Regional Centre for Renewable Energies and Energy Efficiency (RCREEE), which is based in Cairo. So far 13 countries have joined the RCREEE: Algeria, Bahrain, Egypt, Iraq, Jordan, Lebanon, Libya, Morocco, the Palestinian Territories, Sudan, Syria, Tunisia and Yemen.

At the End of 2011, the Arab Ministerial Council for Electricity (AMCE) raised a request to the Regional Center for Renewable Energy and Energy Efficiency (RCREEE) and the Arabian Industrial Development and Mining Organization (AIDMO) to work on standardization and certification program for SWHs. Together with the University of Stuttgart in Germany, they will develop an accreditation system and quality label for Solar Water Heaters. The Project wants to ensure a specific quality for solar thermal products and services in the Arab region. Solar water heaters usage should expand through the Arab world.



Solar Water Heating (SWH) systems are simple and cost-effective renewable energy technology that is widely used for water heating for domestic and industrial. Thus, SWHs systems are great means to governments seeking less dependency on gas and electricity in heating water. Also, SWHs can reduce pressure on the national power system as they decrease energy consumption in the residential sector as one of the most energy consuming sectors in the Arab region.

Experiences and Lessons Learnt

Solar Water Heaters Certification and Standardization: In 2011, RCREEE operated the planning process to produce national and regional certification models for the Arab region. With Jordan being the first case study, the other Arab countries can then adopt these models.

Further Reading/ Links


This article was originally published by GIZ HERA. It is basically based on experiences, lessons learned and information gathered by GIZ cook stove projects. You can find more information about the authors and experts of the original “Cooking Energy Compendium” in the Imprint.

  1. World Health Organization (2011): Evaluating household water treatment options, Heath-based targets and microbiological performance specifications http://www.who.int/water_sanitation_health/publications/2011/household_water/en/.
  2. 2.0 2.1 Elzinga, D. et. Al., (2011): ADVANTAGE ENERGY Emerging Economies, Developing Countries and the Private-Public Sector Interface, IEA. Available at: http://www.iea.org/publications/freepublications/publication/advantage_energy.pdf. Cite error: Invalid <ref> tag; name "Elzinga" defined multiple times with different content
  3. Elzinga
  4. Punter, Amy (2002): Solar thermal energy, A technical Brief of Practical Action, available at: http://practicalaction.org/solar-thermal-energy-1.
  5. GIZ India (2011): Identification of Industrial Sectors Promising for Commercialisation of Solar Energy, Commercialisation of Solar Energy in Urban and Industrial Areas – ComSolar, New Dehli, India.fckLRThis study examines the potential of solar energy appliances within Indian industrial sectors. Also the reduction potentials of other energy resources through solar thermal energy are discussed. http://mnre.gov.in/file-manager/UserFiles/identification_of_insdustrial_sectors_promising_for%20_commercialisation_of_solar_energy_ComSolar.pdf.
  6. Gadonneix, Pierre, Survey of Energy Resources (London, UK: World Energy Council (WEC), 2010), p. 411ff. http://www.worldenergy.org/documents/ser_2010_report_1.pdf.
  7. Energy and Security Group for U.S. Department of Commerce,fckLRInternational Trade Administration (2008): Clean Energy: An Exporter’s Guide to China, available at: http://trade.gov/publications/pdfs/china-clean-energy2008.pdf.
  8. Siderer, Y., and Dann, R. (2010): National Survey Report of PV Power Applications in Israel 2009. Israel: IEA PVPS & Ben-Gurion University. Retrieved from http://www.iea-pvps.org/index.php?id=9&eID=dam_frontend_push&docID=433.
  9. Kordab, Mohamad (2009): Solar Water Heaters Development In MENA Region, Solar Thermal Application in Egypt, Palestine, Lebanon, Syriaq and Jordan: Technical Aspects, Framework conditions, and private Sector NeedsfckLRThis is a presentation from Dr. Kordab (Energy Expert of the Damascus University) during the “Solar Thermal Applications workshop” held in Syria. The event was jointly organized by the Regional Center for Renewable Energy and Energy Efficiency (RCREEE), regional organizations from Syria and Egypt and the German Development Cooperation (GTZ). Available at http://www.solarthermalworld.org/taxonomy/term/22121.

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