Future technology for harnessing solar power

Jelle Post and Giorgos Mixoudis of Deerns MEP Consulting Engineers outline possible future technology options for solar power and considerations for MEP professionals.

The sun is the most influential energy source.
The sun is the most influential energy source.

Jelle Post and Giorgos Mixoudis of Deerns MEP Consulting Engineers outline possible future technology options for solar power and considerations for MEP professionals.

The sun is the most influential energy source for our planet. But sustainable development can only be achieved when the sun and the energy it produces are considered as such by all the stakeholders involved over a building's lifetime.

The sun provides eight thousand times more energy annually than humans consume. Although a substantial portion of that energy can and should be exploited, an even larger part can have negative implications for development.

The Middle East's climate is a clear example of the sun's contradictive influences: the potential of renewable energy systems is huge, but the sun also substantially affects the daily lives of the region's inhabitants.

Construction in general is also vastly influenced by the sun's extreme power. The operation and maintenance of buildings in the Middle East, for example, consume a vast portion of natural resources and energy, due to the extreme climate conditions.

While efforts must be made to exploit the sun for the supply of energy to buildings, ways to minimise demand by reducing the sun's influence must also be considered.

Harvesting the sun

Solar energy is found in various forms: light, heat, wind, wave energy, biomass and hydro-electricity are all alternative forms of solar energy. Various techniques to exploit this energy have been developed throughout the years.

In building applications, the use of renewable energy systems is an active way of reducing fossil fuel consumption. To date, technologies such as photovoltaic (PV) cells and solar flat plate thermal collectors have mainly been used as small-scale solutions, but other large-scale solutions are available.

Parabolic trough power plants are the most successful and cost-effective concentrated solar power plant (CSP) systems currently available. These use a curved trough, which is tilted to continually follow the sun during the day, reflecting direct solar radiation onto a hollow tube running above the trough.

A working fluid (thermal oil, water or molten salt) passes through the tube, being heated as it does so; this is then passed through a heat exchanger creating steam that drives a steam turbine.

A power tower is another example of a large-scale solar solution. This comprises a central collector consisting of an array of flat reflectors (heliostats) that concentrate light in a central receiver located on a tower.

Molten salt flows through the receiver where it is heated to temperatures of up to 1,000°C.

Storing and using solar energy

One advantage of using molten salt as a working fluid is that it enables energy storage. Energy storage of up to 12 hours is possible, enabling power supply for 24 hours per day.

Moreover, the heat that is gathered from solar collectors can also be used for powering absorption chillers and desiccant dehumidifiers in heating, ventilation and air conditioning (hvac) systems, or even for desalination systems.

Such installations can be coupled close to high-rise buildings or residential areas so that the production is carried out next to the place of consumption. These installations generally produce low noise levels and negligible by-products.

Providing protection

Solar energy in the form of heat is a big concern for building design engineers. The external heat loads in this region are vast, thus the energy needs for cooling can be double that needed in Europe.

Applying techniques to prevent these external loads from entering the building will provide a passive but effective way of reducing the building's energy demands.

Utilising outside shading is a simple and relatively efficient way to minimise the energy demand for the cooling of a building. Outside blinds will reduce heat gains from sunlight in summer, while verandas and courtyards provide extra shading.

In addition, well insulated buildings (Rc > 4m2K/W) with double-layer reflective glass and walls that are insulated from the outside are an excellent measure to reduce solar heat gains.

Evaluating design

For the evaluation of solar-related building performance, extensive use can be made of computational building performance simulation models. Digital models of varying scales and levels of detail are constructed for use in specialised software applications that have proven to give reliable results.

From the results of these software simulations a proposed building design can be tested against the requirements of daylight factor levels in sustainability standards systems such as LEED rating.

The combination of these modelling techniques has great potential because they are capable of relating the opposing performance parameters to balance the wanted and unwanted aspects of solar heat and light. These simulations are rapidly becoming more reliable.

If all feasible measures in this step have been implemented, the next step would be to use as much renewable energy as possible.

Throughout all stages, MEP professionals must work alongside the building designer and offer knowledge and expertise through dedicated collaboration to reach the desired, optimum design result.

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