Solar energy pros and cons: Solar thermal systems

Solar energy systems are classified into three system categories: Solar thermal, passive solar and Solar Photovoltaic systems (see “renewable energy sources: solar energy systems”). In this article we review the operation of Solar Thermal technologies and identify the main Advantages and Disadvantages of Solar thermal systems.

Solar Thermal Technology Systems

Solar Thermal systems constitute an important renewable green energy technology by exploring the naturally renewable energy of the sun.

Solar Thermal systems use thermal energy absorbed by sun radiation (heat) and use it to heat up water or other medium e.g. oil or special molten salts. This Thermal energy contained in the material at high temperature can be used for a range of applications such as:

• For providing hot water in buildings (HW for use)
• For heating of buildings and spaces (solar heating systems)
• For cooling of buildings and spaces (solar cooling systems)
• For the generation of electric power (Power Industry); such systems are called Concentrated Solar Thermal (CSP)

The basic operation of solar thermal systems incorporates a means of absorbing solar radiation by different technological applications. In general the solar collectors may be flat plate collectors or evacuated tube collectors examples of which are typically seen on building roof tops with a hot water storage tank. In CSP systems, used for electrical power generation, different applications exist such as Power towers, parabolic dishes or parabolic troughs.  These solar thermal systems use different technological configurations to gather solar energy in the form of heat. It is normal to expect a variation of performance levels amongst the different configurations in terms of efficiency, environmental impact and cost. In conjunction to other energy systems (using renewable or non-renewable energy sources) solar thermal systems can offer several advantages.

Advantages of Solar Thermal Systems

 As all renewable green energy technologies, Solar Thermal Systems, contribute to reducing consumption of fossil fuels. Thus towards reduction of CO2 emissions into the atmosphere and help combat “green-house” challenges.

1. Solar collectors used for heating are a mature technology offering a high energy contribution at a fairly low cost. That is why solar thermal systems have formed an established norm in the construction industry.
2. Solar thermal systems exhibit in general high efficiency levels when it comes to solar heating applications. In combination to their moderate costs they offer a good return on investment at short repayment periods. Depending on environmental conditions repayment of initial investment is expected within first five years; in cases of available subsidy funding repayment is even earlier.
3. Moreover, solar systems can easily store thermal energy by use of storage tanks and use it when it is required without interference from immediate environmental conditions; e.g. overnight or during cloudy periods. This is especially important in power generation with concentrated solar power plants (CSP).
4. Concentrated Solar technology is particularity suitable for Power generation because it makes it possible to reach very high temperatures. High temperatures can supply a steam turbine to produce electricity without the consumption of fossil fuels.
5. In general, solar thermal panels can easily be used in a modular manner and on a wide range of technological configurations. As a renewable green energy source they are expected to grow even further with a higher contribution in the global energy mix.

As in everything in real life, solar thermal systems also have disadvantages.

Disadvantages of Solar Thermal Systems

Although we have noted that storage tanks are an important advantage which can be used to provide for an uninterruptible energy supply, the fact that sun only shines during the day is an inherited disadvantage for all solar energy systems. The degree to which this can influence a solar system’s performance depends on the technology used.

1. Depending on the place of installation and environmental conditions, seasonal variation of solar radiation may be of high influence to the reliability of a solar system. In general, conditions near the equator increase solar systems’ reliability where as at extreme latitudes solar reliability is decreased (you may refer to solar radiation maps).
2. For power generation it is important to note that CSP systems come at large scales of about 100 MW or larger, thus they involve an extremely high initial cost.  Consequently, economical viability of concentrated solar power (CSP) will continue to remain a main disadvantage before costs can be reduced, or before costs for alternative energy solutions increase (e.g. increase of oil prices, depletion of fossil fuels).

In review of the advantages and disadvantages of solar thermal systems it is important to understand that pros and cons are variable attributes depending on comparable alternatives available and on other external factors – see the ultimate list of solar energy pros and cons. Comparable alternative systems may refer to within the solar family systems (e.g. solar thermal, Concentrated CSP, or photovoltaic), or to other renewable green energy systems (e.g. wind energy systems) or to other non-renewable energy systems that use fossil fuels. External factors influencing are variables such as the price of oil or natural gas thus cost of energy fuels. However, the decision on energy issues and on optimizing our energy mix is no longer a matter of economical viability, but also of environmental and social sustainability.