An online clean technology database

Solar technologies

Solar technologies facilitate the extraction of a renewable energy source by harnessing power from the sun. There are two technological principles that can be used to achieve this: (1) Collecting thermal energy from the sun, known as solar thermal; and (2) Converting light into electricity, through the photovoltaic process. Both solar thermal and photovoltaic (PV) can be integrated into buildings. Applications for PV include building integrated photovoltaic (BIPV), solar home systems (non-grid connected) and solar charging stations. Solar home systems and solar charging stations are most suitable for application in rural and remote areas where grid power is not readily available. Most BIPV applications are grid connected enabling surplus energy produced to be exported to the grid.

Introduction top

Solar thermal water heater. In its most basic form, the system consists of a collector and a water storage tank. The collector is a flat plate comprising a black coloured metal sheet with metal tubes attached to it. The metal sheet is backed by a thermal insulation layer, and covered on top with a glass panel to reduce convective heat loss and provide protection from the weather. The collector tube is connected to a water tank which is located on top of the collector. The collector absorbs solar heat radiation, which is transmitted to the water circulated in the metal tube. The heated water then rises and is stored at the water tank through natural convection. Cool water automatically fills the space in the metal tube.

Recently, the use of solar thermal energy has expanded to include dual use systems, combining both water heating and space heating (combi-systems). These systems reduce energy consumption for space heating during the winter season for buildings located in temperate regions. One disadvantage is that the systems have to discharge surplus heat during the hot summer season. This issue has been overcome by combining solar cooling and combi-systems, which maximises the usage of solar thermal technologies year-round (Troi et al., 2008). Solar cooling makes good sense for application in hot climatic regions. During a typical day, the peak demand for space cooling matches the peak of solar radiation. As such, the large scale implementation of solar cooling technology will contribute to reduced electricity peak loads.

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Figure 1: Solar thermal water heater (left), photovoltaic panels (right).

BIPV. A BIPV system consists of PV panels and a DC-AC inverter. A PV panel includes a series of connected cells made of semiconductor materials. When PV modules are exposed to sunlight, they generate direct current (DC) electricity, which is most often converted to alternating current (AC) electricity – a common form of electricity that can be used in most current appliances and lighting systems. The AC electricity can then be fed into one of the building’s AC distribution boards, or connected to the main electricity grid. PV panels, which are integrated into the roof, façade, skylight or sun-shading devices, are referred to as building integrated photovoltaic technologies (BIPV). With BIPV, PV modules are usually used as a substitute for other building components, e.g., sun-shading devices, thereby offsetting some of the cost.

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Figure 2: PV panels as integral part of building design.

Although considered to be a proven technology, PVs are still under research and development, especially to increase the efficiency of energy production and to reduce manufacturing costs. The common PV technologies can be broadly categorised into two groups – crystalline silicon and thin film. Crystalline silicon technologies account for the majority of PV cell production, whereas thin film is newer, less efficient, but growing in popularity (EMA & BCA, 2009).

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Figure 3: BIPV: PV modules sandwiched between glass panels of skylight over an atrium.

Solar home system: is developed based on photovoltaic (PV) technologies and integrated with DC-electricity-based appliances. It is the most suitable technology used in remote and rural areas, which are not served by the electricity grid (Grimshaw & Lewis, 2010). The technology has been implemented in villages and remote settlements in Africa and Asia. A typical system consists of a 10 to 50 Watt Peak PV module, charging controller, storage battery, and various end-use equipment that operate with DC electricity (e.g., fluorescent lamps, radio, television, fan, etc.).

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Figure 4: Diagram of a typical solar home system.

Solar charging station: is another application for PV technologies. A typical solar charging station includes PV module(s) to generate electricity, a charging controller to normalise the voltage, and a battery bank to store the DC electricity. The electricity from the battery bank can then be used to charge batteries for various uses, such as lights, mobile phones, and other DC-electricity-based appliances.

Feasibility of technology and operational necessities top

Solar technologies perform better in regions and seasons with the highest sun intensity and long sunlight hours. Building rooftops are the most logical location for the installation of solar thermal and PV technologies. Prior to the installation of a large number of solar panels, it is important to ensure a roof’s structure is strong enough to hold their weight. Accessibility for maintenance should also be planned for. It is recommended that preventive inspections and maintenance are carried out every 6 to 12 months. Inspection includes checking for signs of damage, dirt build-up or shade encroachment (EMA & BCA, 2009).

Solar thermal water heater. These systems are most often used in urbanised areas, which have access to a stable water supply. Water supply stability is required for automatic operation of solar thermal water heaters. In these systems, pressure from the water supply system must be high enough to allow for automatic refilling of water into the heating pipes. The water supply pressure can be provided by the city main water supply system, or locally produced by pumping water up to a level higher than the installed solar thermal water heater. The second option requires electricity for pumping, and this will reduce the cost-effectiveness and energy-efficiency of the system. However, solar thermal water heaters do not require extensive maintenance, once installed.

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Figure 5: Solar thermal system installed on building’s rooftop.

BIPV, solar home system and solar charging station. The core technology of these three systems is PV. The crucial condition of PV applications is that the locations must be exposed directly to sunlight and are not shaded. The reason is that PV modules, crystalline silicon technologies in particular, are very sensitive to shading. Taking a module consisting of 36 PV cells as an example, if one cell is shaded, the cell, instead of producing, can consume the energy produced by other cells, due to their string connectivity. Electricity production of the whole module, in this case, can be reduced by up to 50%. Therefore, shading must be avoided. Preventive measures include periodic maintenance to clean the surface of the modules (e.g., accumulated dust and/or bird droppings).

In order to maximise the yield, PV panels should be mounted so that they face the sun directly. In temperate regions, such as Eastern Europe, PV panels should be mounted with a suitable sloping angle toward the South, whereas, in the tropical regions, especially in the regions near the equator, flatmounted PV panels provide the best yield. However, the flat-mounted PV panels will result in poorer self-cleaning performance and tend to accumulate dust, which in times causes shading to the cells and diminishes the system’s outputs. A slight inclining angle of 3 to 5 degrees, to allow for rainwater properly drained off and promote self-cleaning, is useful and acceptable. Regular maintenance is required.

Feasibility for implementation

Experience suggests that the availability of strong institutional supports, especially incentivising policies and supportive financial mechanisms, are the key first steps to make solar technologies mainstream. These include but are not limited to:

  1. Reducing/removing subsidies for fossil-fuel-based electricity supply.
  2. Reducing/removing import tariffs on solar technologies’ components.
  3. Cleary identifying power grid expansion plans (for rural and remote areas) and communicating these plans clearly to the public. This is necessary for calculating payback periods used in decision making processes to invest and implement off-grid solar technologies, such as solar home systems and solar charging stations.
  4. Setting up smart grids and incentivising feed-in tariffs (in urbanised areas) as a platform to promote on-grid application of PV technologies, such as BIPV.

In the regions, where the solar technologies have not been or only ad hoc implemented, research and development is an important first step to determine the feasibility of implementation. The areas to be given priority include:

  1. Collecting local solar radiation, intensity and sunlight hours available during various seasons.
  2. Researching the most suitable, efficient, and cost effective solar technologies and products for large-scale deployment.
  3. Establishing viable business models and financial mechanisms for a reasonable return on investment.

These activities can be done through establishing a research institute, which can be in the form of collaboration with local government and universities. Capacity building should be in the area of technical knowledge, design techniques for building professionals, installation skills for technicians, and routine inspection and maintenance for home/property owners and facility management personnel.

Status of the technology and its future market potential top

Solar energy is considered one of the most promising renewable energy technologies. The International Energy Agency estimates that the contribution of solar energy to the global electricity demand will increase from about 0.02% in 2007 to approximately 1% by 2030 (IEA, 2009). The IPCC reports that in 2003, there were more than 132 million square metres of solar collector surface for space and water heating worldwide (Levine et al., 2007). China accounts for closed to 51.4 million square metres, followed by 12.7 million square metres in Japan, and 9.5 million square metres in Turkey (Weiss et al., 2005) Recognising the high potential of solar energy, governments around the world are paying attention to and preparing for its large-scale implementation. This creates a strong market penetration for solar technologies. For example, in China the annual growth rate of the installed area of solar panels has been steady at around 27% from 2000 to 2005. (Abbaspour et al., 2005). The Chinese solar market initially targeted installations in villages and small towns, but has recently gained a strong foothold in urbanised areas.

The present and potential markets for large scale implementation of solar technologies are in rural settings and areas not served by the power grid. In these areas, the cost to install solar power can usually be justified when compared to the high infrastructure cost to extend the power grid or to build a power plant.

Solar thermal water heater. Solar thermal water heaters have enjoyed good market penetration, compared to PV technologies, which are considered more costly. In Rizhao, China, for example, 99% of homes are reported to use solar water heaters (Grimshaw & Lewis, 2010).

The supply of hot water in non-temperate regions can be regarded as a less crucial issue and can even as luxurious, such as in the case of Africa. It is observed that the bulk of solar thermal water heaters in use there are bought by high-income households and large commercial establishments such as hotels. The use of hot water, and thus the need and potential market for solar thermal water heaters, are more pressing in colder climate regions, such as villages or towns in north-eastern European countries, mountainous areas of the Andes and the Himalayas.

PV technologies: PV-related technologies, such as BIPV, solar home systems, and solar charging stations, are more capital intensive to invest in and require more stringent installation requirements due to their sensitivity to being shaded, when compared to solar thermal. Therefore, PV technologies at the present have smaller market penetration. However, research findings show that almost all developing countries have enormous solar power potential. For example, many regions of Africa have 325 days of strong sunlight each year. This can lead to an average of more than 6kWh energy harvested per square metre a day (Grimshaw & Lewis, 2010).

Future markets for PV technologies include urban settings, in particular when smart grid systems and policies that provide incentives for a feed-in tariff from renewable energy become mainstream.

How the technology could contribute to socio-economic development and environmental protection top

Solar technologies hold a prominent and promising role in climate change mitigation by replacing fossilfuel-based electricity production. Taking solar home systems as an example, a typical system of 10 to 50 Wp (Watt peak) will directly displace about 0.15 to 0.3 tonnes of CO2 annually through fossil fuel substitution (Kaufman, 1990).

Regarding the social development aspect, solar technologies improve the quality of life and contribute to a healthy environment. Solar thermal heaters provide hot water to millions of people in the mountainous Himalayas and in China. The use of solar home systems reduces the need to store and burn kerosene for lighting, improving health and reducing fire hazards for villagers in Africa and rural Asia. Solar home systems also make information and entertainment accessible to rural areas with the use of radio and television.

In terms of economic development, solar technologies bring direct benefits to households, and to regional/national economies. The IPCC’s Fourth Assessment Report estimates that BIPV could generate enough energy to meet 15% of total national electricity demand in Japan, and close to 60% in the US (Levine et al., 2007). At the household level, the application of BIPV reduces monthly electricity expenses and provides the opportunity for building owners to sell surplus electricity to the grid. The implementation of solar charging stations provides opportunities for new businesses that are environment-friendly. Large-scale implementation of solar technologies, through capacity building, provides new skills and sources of income for local work forces. Studies have shown that investment in solar technologies would create additional jobs even in oil-rich Middle East countries such as Iran (Abbaspour et al., 2005).

Financial requirements and costs top

Financial requirements for solar technologies include the investment costs of the products and installation, and maintenance costs. In general, it is expected that the investment cost of solar technologies will decline as a result of improved technology and increased mass production, made possible through higher market demand. The cost components also vary depending on the technologies and whether the products are produced locally or imported. The following includes some indicative figures and considerations:

Solar thermal water heater. In the Caribbean region, a solar thermal water heater for a typical household costs between US$1,500 to over US$2,000. This initial investment cost has a payback period of 2 to 2.5 years in most Caribbean islands. In India, the investment cost of a solar thermal water heater is about INR15,000 to INR 45,000.

BIPV. The initial investment cost of a BIPV system is high, whereas the operational costs are negligible during the warranty period. As a rule of thumb, after the warranty period, the annual maintenance cost may amount to 0.5 to 1% of the investment cost. It is also observed that historically the cost of PV has been falling by about 4% yearly. If the same trend continues, it will take about ten more years for PV to be competitive (EMA & BCA, 2009). In Singapore, the investment cost for PV ranges from S$8 to S$12 per Wp with a normal warranty period of 25-30 years (DLS, 2009).

Solar home systems. The investment cost of a full solar system in Africa typically ranges from US$250 to US$630 (Davies, 2010).It has been reported that a solar home system in Africa has a payback period of less than two years in combination with the right financial mechanisms (Grimshaw & Lewis, 2010).

References top

Abbaspour M., Hennicke P., Massarrat M. & Seifried D. (2005). Case Study: Solar Thermal Energy in Iran Saving energy, realising net economic benefits and protecting the environment by investing in energy efficiency and renewable energies. Heinrich Böll Foundation. [Online]:

Davies C. (2010). Solar energy brings power to rural Africa. CNN News. [Online]:

DLS. (2009). Green Building Products and Technologies Handbook. Singapore: Davis Langdon & Seah Singapore Pte Ltd.

EMA & BCA (2009). Handbook for Solar Photovoltaic (PV) Systems. Singapore: Energy Market Authority & Building and Construction Authority.

Grimshaw J. D. & Lewis S. (2010). Solar power for the poor: facts and figures. Science and Development Network. [Online]

IEA (2009). World Energy Outlook 2009. Paris: International Energy Agency.

Kaufman S. (1990). Rural Electrification with Solar Energy as a Climate Protection Strategy. Renewable Energy Policy Project. [Online]:

Levine M., Urge-Vorsatz D., Blok K., Geng L., Harvcey D., Lang S., Levermore G., Mongameli Mehlwana A., Mirasgedis S., Novikova A., Rillig J. & Yoshino H. (2007). Residential and Commercial Buildings. In Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Metz B, Davidson O. R., Boshch P. R., Dave R. & Meyer L. A. (eds)]. United Kingdom & United States: Cambridge University Press.

Troi A. Vougiouklakis Y., Korma E., Jahnig D., Wiemken E., Franchini G., Mugnier D,. Egilegor B., Melograno P. & Sparber W. (2008). Solar Combi+: Identification of most promising markets and promotion of standardised system configurations for small scale solar heating & cooling applications.Solar Combi+. [Online]

Weiss W., Bergmann I. & Faninger G. (2005). Solar Heating Worldwide, Markets and Contribution to the Energy Supply 2003. Austria: IEA Solar Heating and Cooling Programme.