Tag Archives: evacuated tube collector

Solar Water Heating as an Energy Service – Part 1 – Technology Choices and Markets

Solar water heaters as a product have the potential to contribute considerably to energy demand reduction in developing countries. This exists both as a household-scale technology, and in industrial applications such as desalination in countries such as the UAE and Saudi Arabia, and industrial process heat in both developed and developing countries. A number of developing countries around the world, notably those in Sub-Saharan Africa, have had success in disseminating solar water heating products on a commercial basis, in addition to a number of large-scale government dissemination programs. Countries such as South Africa (with around 500,000 systems installed as of 2016) and China (which has over 85 million installed SWH units as of 2016) have developed a robust network of commercial installers and manufacturers of solar water heating units and parts, selling products on a market basis to households and businesses.

Solar water heater installed by ESKOM, South Africa. Image: gmourits, Flickr, via http://inhabitat.com/eskom-installs-solar-powered-heaters-on-south-african-roofs/


There are a number of opportunities in developing country markets to develop a solar water heating sector. A number of developing countries, particularly those in Sub-Saharan Africa, have high levels of insolation (sunlight kWh/m2/day), and a consistent demand across income segments of the population for water heating. Industrial process heat is another sector where solar water heating could have an impact, as is institutional process heat, for example heat exchangers for hospital refrigeration, and hot water for use in health centres and schools.

Entrepreneurs and companies looking to enter the solar water heating market space need to consider a number of questions before starting their operations. Firstly, an appropriate technology choice is essential for succeeding in the SWH market, perhaps more so than many other renewable energy technologies. Deciding which consumer segment or income bracket to target informs the technology decision somewhat, but thorough research needs to be done on what the market and consumers can afford before deciding on a technology. Main technology streams for SWH include flat-plate solar collectors, and evacuated tube solar collectors. Both work on similar principles, heating water that passes through the collector, either through capillary action or through the use of an electric pump. Flat-plate collectors can be slightly less efficient than evacuated tube designs due to heat loss through convection, however they are also less expensive and simpler to produce. Evacuated tube designs are generally more efficient at heating water, but are also more expensive to compensate for the increased complexity in manufacture.

Flat-plate solar collector installed on a house in the United Kingdom. Image: uk.solarcontact.com

Flat-plate solar collector efficiency vs evacuated tube efficiency at various temperature ranges for a typical North American location. Source: https://blog.heatspring.com/solar-thermal-flat-plate-or-evacuated-tube-collectors/


When designing a new solar water heating business or intervention, therefore, it is important to consider which variant on the technology is to be used, and at what scale (household, institutional, industrial etc.), in order to plan dissemination based on affordability for the consumer. The next blog in this series will investigate business and financing models that can assist in improving the sustainability and replicability of solar water heating energy service companies.

– Daniel Kerr, UCL Energy Institute


Clean Technica (2015) World’s Largest Solar Powered, Jellyfish-Fightin’ Desalination Plant To Be Built in Saudi Arabia. Available at: https://cleantechnica.com/2015/01/22/worlds-largest-solar-powered-desalination-plant-under-way/

Urban, Geall & Wang (2016) Solar PV and solar water heaters in China: Different pathways to low carbon energy. Renewable and Sustainable Energy Reviews, Vol. 64, pp. 531 – 542

EE Publishers (2016) Solar water heater rollout programme gains momentum. Available at: http://www.ee.co.za/article/solar-water-heater-rollout-programme-gains-momentum.html