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Solar Thermal

Principle & How it works

Solar thermal systems produce thermal energy which can be used directly as heat or converted into electricity.

The most common and recognizable use of solar thermal technology in buildings around the world is solar water heating, which can typically provide almost all hot water requirements for households during the summer months and about 90 % year round in Mediterranean countries. Solar hot water systems can also be used on larger applications such as swimming pools.

The three main components for domestic hot water systems are solar panels, a heat transfer system, and a hot water cylinder. The solar panels, or collectors, are usually fitted to the roof and convert solar irradiation into thermal energy. Depending on the water temperatures and efficiencies needed, the solar panels can either be a simple absorber, a flat-plate collector or an evacuated tube collector. This heat is used to raise the temperature of the household water and is delivered by the heat transfer system which takes the heated water to the hot water cylinder for storage until use. The performance of a solar thermal system is best when the solar collectors are installed on a southeast to southwest facing roof receiving solar radiation for the main part of the day.

To benefit from solar thermal energy for electricity generation, sunlight is reflected by mirrors and concentrated onto a receiver. The high temperature energy produces heat which boils water to make steam. The steam's pressure flows through a turbine, turning the shaft that is connected to a generator in which electricity is produced. There are three solar electric thermal technologies being developed: parabolic troughs, central receivers, and parabolic dishes. All of these technologies depend on tracking mirrors to reflect and concentrate sunlight and can operate independently or as part of a hybrid system.

Parabolic troughs are long rows of concentrators that are curved in only one dimension forming troughs. Central receivers, commonly called power towers, consist of a fixed receiver mounted on a tower surrounded by a large array of mirrors called heliostats. Parabolic dishes consist of parabolic-shaped point focus concentrators that reflect solar irradiation onto a receiver mounted at the focal point. Along with central receivers, parabolic dishes typically achieve higher conversion efficiencies than parabolic troughs.

Advantages

Solar thermal technologies minimally impact the environment and expel few greenhouse gas emissions.

Disadvantages

The sun's intermittent nature and the fact that solar thermal technologies are not fully commercialized tend to be a disadvantage, but Constructing systems as hybrids fueled by other energy sources tend to resolve part of this problem.

Where it's working (Syria, Abroad)

The global solar thermal market is dominated by China, Europe, Japan and India. Installation of solar hot water heating has become the norm in countries with an abundance of solar irradiation, like Cyprus and Greece, as well as in Japan and Austria, where there is less. Solar hot water systems have become popular in China, where basic models are much cheaper than in Western countries (around 80 % cheaper for a given size of collector). It is said that at least 30 million Chinese households now have one, and that the popularity is due to the efficient evacuated tubes which allow the heaters to function even under gray skies and at temperatures well below freezing. In 2005, Spain became one of the first countries in the world to require the installation of solar hot water systems in new buildings.

The solar thermal market for hot water has boomed in Syria in the past year due to the rise in the cost of diesel. In the past, it had remained stable for many years mainly because of the hard competition that it faced from the conventional energy sources. Oil, electricity and gas are offered in abundance in the country and in very low prices. The electricity supply for domestic use is still very cheap in Syria as well, despite the many infrastructure problems. Hotels and other public sector buildings commonly use boilers for domestic hot water supply because of the low cost of the fuel. The expected payback period is estimated to be three to four years but some studies have shown that a problem exists in Syria because the systems produced locally are not durable, and after two or maximum three years their inherent defects begin to show.

There are several solar power plants in the Mojave Desert, southwestern United States, which supply electrical energy to the electricity grid. Solar Energy Generating Systems (SEGS) is the name given to nine solar power plants in the Mojave Desert which were built in the 1980s. These plants have a combined capacity of 354 megawatts (MW) making them the largest solar power installation in the world. Nevada Solar One is a new solar thermal plant with a 64-MW generating capacity, located in Nevada. There are also plans to build other large solar plants in the Mojave Desert. The Mojave Solar Park will deliver 553 MW of solar thermal power when fully operational in 2011.

Since 2004 there has been renewed interest in solar thermal power stations and two plants were completed during 2006/2007: the 64 MW Nevada Solar One and the 11 MW PS10 solar power tower in Spain. Three 50 MW trough plants were under construction in Spain at the end of 2007 with 10 additional 50 MW plants planned. In developing countries, three World Bank projects for integrated solar combined-cycle gas-turbine power plants in Egypt, Mexico, and Morocco were approved during 2006/2007.

There are no solar thermal power plants for electricity generation in Syria but many countries are embarking on these kinds of projects at present. There is no reason why Syria cannot benefit from solar thermal power generation.

Future Development & integration

For electricity generation, the future for solar thermal technology looks to incorporate hybridization methods and increased storage capacities. Hybridization includes the use of additional firing with natural-or biogas or usage of the hot exhaust gas of a gas turbine. This is simple and cost effective. There are many opportunities for extended applications in the technology for chemical high temperature processes.

As for solar thermal technology for hot water, there is not a lot more to be done as the efficiencies are already quite high. However the application of the technology for solar thermal cooling is a new field of development and has huge potential in all hot sunny countries around the world.

Local Factors & Conditions

Syria, like other Mediterranean countries, is rich in solar irradiation. The average solar irradiation on a horizontal surface is about 5 kWh/m2 per day. This is a relatively high value especially when compared with the average irradiation in Germany which is about half that amount. The sun shines about 2800-3200 hours per year and the cloudy days are about 40 days per year. The important point is that all the Syrian regions have high irradiation and the number of sunny days are relatively high. These indicators lead to a promising outlook for solar energy exploitation in Syria.

The following map illustrate the mean irradiation level in Syria:

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