Solar Thermal Water Heating

Solar thermal energy in Rio de Janeiro

Building installed solar thermal water-heating systems in Rio are technically feasible and can potentially payback investment costs in a few years. Photo by frogart licensed under creative commons.

Solar thermal water heating uses energy from the sun to heat water, which can be used for washing and domestic purposes. The energy in sunlight is captured by collectors, usually placed on roofs. Liquid is circulated in the collector, is warmed by the sun and transfers heat to water in a thermal reservoir.

In this way, water is progressively heated when the sun shines and stored in an insulated tank for convenient use.

Solar thermal water heating is a much more efficient process than generating electricity by means of solar photovoltaic technology – converting a high proportion of the incident energy to usable heat. Furthermore, solar thermal heating of domestic water is effective even when sunlight is diffuse.

Solar thermal systems are a clean and renewable way of decentralizing energy production. Such systems can deliver significant savings of electrical energy even when water is only partially heated by the solar-thermal system.

By reducing the requirement for electric water heating, solar thermal systems can help reduce peak demands on the electricity supply system. More widespread adoption of the technology as the Brazilian economy expands would also help reduce the requirement for new electricity generation capacity. This would have significant environmental and economic advantages.

Solar Thermal Water Heating in Rio

In the context of Rio de Janeiro, solar thermal water-heating is extremely significant. A large percentage of Brazilians use electrically heated showers on a daily basis – usually after work, during the peak hours between 18:00 and 21:00. These showers have a typical power consumption of up to 5,400 Watts.

This energy usage is extremely significant – it has been estimated that electric shower usage accounts for 22.6% of the electric energy consumption of the Brazilian residential sector – about 6% of the total national electric energy consumption [1]. Using solar energy to heat water for showers reduces demand on the electrical system and frees up more energy during peak hours. According to GIZ, solar thermal systems in Brazil may reduce energy consumption for heating water by up to 35%.

Many governments around the world have recognised that solar thermal water heating is an excellent way to reduce electrical demand and mitigate GHG emissions. In January 2008, the state government of Rio de Janeiro approved a law that makes the installation of solar water heating systems mandatory for public buildings. Under state law Lei N° 5184 (in effect from January 2008), solar thermal systems are mandatory for new and refurbished public buildings in Rio de Janeiro. Solar energy must cover 40% of the annual hot water demand. Exemption is made for public buildings in which it is technically impossible to install a solar thermal system. The materials and equipment used in implementing the system have to comply to the Brazilian norm NBR, and the Brazilian Technical Standards Association (Portuguese: ABNT) [2].

Solar heating has grown rapidly in Brazil, with an area of over 5 million square meters of solar collectors installed in recent years [3]. Indeed, more than 1 million square metres of solar collectors were set up in 2011 [4].

Case Study: Mangueira, Rio de Janeiro

As part of the re-housing of Favela residents from Manguira, solar thermal water heating was installed in low-rise residential units (4-5 storey). The solar thermal units installed consisted of 2 square metre  flat panel collector plates, with a 200 litre hot water reservoir situated on the roof. Each unit is plumbed in to an individual apartment. The project was carried out by GIZ (Deutsche Gesellschaft für Internationale Zusammenarbeit GmbH) Projeto 1000 Telhados. The following video provides an overview of the project:

State Support for Solar Water Heating

One of the targets of the Brazilian National Plan for Climate Change is 15 million square meters of solar panels to installed by 2015 [5]. The Miha Casa Miha Vida project aims to improve availability of housing units for for families with monthly income of up to R $ 1,600. Caixa Economica Federal pays up to 2,000 R$ per installed solar thermal water heating unit to project developers under the scheme.

Economic Benefits of Solar Thermal Water Heating

The savings generated by solar thermal water heating systems need to be balanced against the relatively high purchase & installation cost. A typical solar thermal unit may cost in the region of R$ 2,000, whereas a 4.4 kW electric shower retails in Brazil for approximately R$ 35 [6].

There is evidence that solar thermal systems can reduce gas consumption by up to 50% in multi-family housing units, and that systems can pay-back in less than four years.  The Mundo Apto Cambuci building in São Paulo was built in 2007, consisting of three towers of 142 residential units each. A total of 589 m² of roof-installed solar collectors provide the energy for domestic hot water, which is stored in three 12,000 litre tanks. The design avoids shading and allows for easy and safe maintenance. The installation saves 13,700 m³ of gas per year, amounting to R$ 34,000. Payback time has been calculated as 3.3 years [7].

Solar thermal systems are well established in Brazil, with 34 Brazilian companies manufacturing solar thermal systems approved by INMETRO, the National Institute of Metrology, Quality & Technology [8]. Solar thermal systems should certainly be considered for building projects in Rio de Janeiro.

Legionella

Legionella pneumophila is a pathogenic water-borne bacterium which causes legionnaire’s disease. The illness is typically acquired by exposure to contaminated aerosols and can be fatal in vulnerable populations. Legionella grows most rapidly at lukewarm temperatures (i.e. 25 – 40° C) and the warm water in solar thermal systems may harbor dangerous concentrations of the organism. In Rio de Janeiro, this is probably more likely to occur in winter, when the temperature of water storage tanks is lower. Showering with contaminated water is likely to increase risk for Legionella infection. Cases of Legionnaires disease are frequently misdiagnosed, and it is likely that the prevalence of the disease has been under-reported [9], [10].

Care should be taken to ensure that solar thermal hot water systems do not promote legionella growth. Chemical disinfection procedures are possible, but perhaps the simplest method of legionella control is pasteurisation. This is achieved by heating the hot water reservoir to 60° C for one hour per day, which effectively sterilises the system. It is important that all water within the tank is heated to the correct temperature. According to the UK Water Regulations Advisory Scheme, solar hot water systems should be designed so that water in the storage tank can be pasteurised on a regular basis [11], [12].

System Design: Size Considerations

Care should be taken when designing solar thermal systems, paying particular attention to the size of the expected demand. If systems are too large this can cause very high water temperatures and flashing to steam.

Additional Resources

References

  1. E. Salvador, “The Energy Efficiency Evolution of the Water Heating Process in Brazil´s Residential Sector: The PROCEL Seal Program contribution,” (PDF) in Eurosun, 2008.
  2. “Solar obligation by the state of Rio de Janeiro, Brazil | Solarthermalworld.” [Online]. Available: http://www.solarthermalworld.org/content/solar-obligation-state-rio-de-janeiro-brazil [Accessed: 18-Sep-2012].
  3. “The solar heating sector | DASOL | Department of National Solar Heating ABRAVA.” [Online]. Available: http://www.dasolabrava.org.br/informacoes/o-setor/ [Accessed: 27-Sep-2012].
  4. “Brazil: Collector Area Exceeds 1 Million a Year,” Solarthermalworld. [Online]. Available: http://www.solarthermalworld.org/content/brazil-collector-area-exceeds-1-million-year [Accessed: 27-Sep-2012].
  5. GOVERNO FEDERAL, “PLANO NACIONAL SOBRE MUDANÇA DO CLIMA BRASIL,” 2007. [Online]. Available: http://www.mma.gov.br/estruturas/smcq_climaticas/_arquivos/plano_nacional_mudanca_clima.pdf [Accessed: 16-Oct-2012].
  6. “Maxi Shower Bath – Lorenzetti – Americanas.com.br.” [Online]. Available: http://www.americanas.com.br/produto/388772/chuveiro-maxi-banho-lorenzetti [Accessed: 16-Oct-2012].
  7. “Brazil: Solar Water Heater Case Studies in Multi-family Housing,” Solarthermalworld, 2012. [Online]. Available: http://www.solarthermalworld.org/content/brazil-solar-water-heater-case-studies-multi-family-housing [Accessed: 16-Oct-2012].
  8. INMETRO and PROCEL, “SISTEMAS E EQUIPAMENTOS PARA AQUECIMENTO SOLAR DE ÁGUA – COLETORES SOLARES – EDIÇÃO,” 2012.
  9. B. S. Fields, R. F. Benson, and R. E. Besser, “Legionella and Legionnaires’ disease: 25 years of investigation.,” Clinical microbiology reviews, vol. 15, no. 3, pp. 506–26, Jul. 2002.
  10. “Legionnaire’s disease,” 2011. [Online]. Available: http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001641/. [Accessed: 08-Nov-2012].
  11.  T. Makin, “LEGIONELLA BACTERIA AND CONDITIONS FOR ITS GROWTH AND,” Report for the Water Regulations Advisory Scheme, 2009. [Online]. Available: http://www.wras.co.uk/PDF_Files/Preheated_Water_Report.pdf. [Accessed: 08-Nov-2012]
  12. “STORAGE OF PREHEATED DOMESTIC HOT WATER AND POSSIBLE GROWTH OF LEGIONELLA BACTERIA,” Water Regulations Advisory Scheme (UK). [Online]. Available: http://www.wras.co.uk/Preheated-Water.htm. [Accessed: 08-Nov-2012].