Font Size

- Aa +

Mon 17 Mar 2008 04:00 AM

Font Size

- Aa +

Panel connections

Continuing our special feature on solar power, Murat Aydemir outlines some of the technical and installation issues to consider with the technology.

Continuing our special feature on solar power, Murat Aydemir outlines some of the technical and installation issues to consider with the technology.

To protect fuel reserves accumulated over millions of years, the MEP sector is now committed to finding responsible ways of handling these precious resources. One rational way of achieving this aim is to make direct use of solar energy.

Thanks to the availability of highly sophisticated collectors and overall systems the economic use of solar energy is a reality today. And considering that fuel prices will continue to rise in the years ahead, installing in a solar system is a genuine investment for the future.

Solar radiation represents a flow of energy, irradiated evenly in all directions by the sun. Of that energy an output of 1.36kW/m2, the so-called solar constant, permanently hits the outer earth's atmosphere.

The amount of solar energy reaching the earth is split into two types - direct and diffused solar radiation - the sum of which is termed global radiation. With today's solar panels as much as 75% of global radiation can be utilised depending on the type of collector and the system size.

System formats

Photovoltaic (PV) systems are generally designed and provided as a package for connection to the electrical grid. This provides several advantages including the lack of need for a battery, plus all electricity generated by the system can be used in the building or returned to the grid if local utility firms permit.

For this type of application the electrical network supplier should allow the connection of the photovoltaic system with the electrical grid. Energy prices are increasing and the production costs of PV cells are expected to continue to fall in future, therefore PVs are expected to have a bright future in the Middle East.

Thermal solar systems have been used widely for many years to provide domestic hot water, swimming pool heating and process hot water for commercial and industrial use. If the design of these systems is done correctly they will work for many years without any problem.

The great challenge of a solar thermal system is to create a design that balances the energy income from the sun with the hot water consumption needs of an individual application. You cannot turn off the sun, you have to use or store the energy when the sun shines.

In a solar thermal system the collector is connected to a dual-mode calorifier or cylinder tank, where a heating coil heats the stored water. The solar circuit operates on a closed loop; the cylinder's second coil can be connected to an oil or gas-fired backup boiler to ensure water can be supplied at the desired temperature regardless of the available sunshine.

An electrical backup heater can also be installed if there is no oil or gas available, however care should be taken when making this choice. Although electricity is clean when used, its production has a very high CO2 emission so the overall sustainability of the project will be affected.

This type of closed loop solar thermal design can provide 65-80% of the annual hot water demand of a hotel or residential house depending on the location, consumption profile and selection of the solar system.

Making use of solar power in the Middle East

Viessmann has completed several solar installations in the Middle East, with several systems in the UAE having been operational for more than eight years. These include systems for varying applications such as residential properties on the Palm Jumeirah, Dubai and an industrial factory in Jebel Ali.

On the Palm Jumeirah, a total of 14 apartments in the Shoreline Apartments development are being provided with domestic hot water from a system of Viessmann Vitosol 100 flat collectors. With a total installed absorber surface of more than 2500m2, the system operates through the use of gas-fire condensing boilers.

The firm has also supplied 117 Vitosol 100 flat collectors with a total surface area of 300m2 for the Master Foods factory in Jebel Ali. Here the system is used to provide process heating and has resulted in CO2 savings of more than 130,000kg.

The system provides hot water for a closed loop circuit that maintains a setpoint temperature to keep chocolate as a liquid. Due to the long operation periods used in the factory the system includes three buffer tanks and a boiler backup system for night-time operation. The installation and after-sales support for the system was carried out by Viessmann's authorised distributor Value Addition.

In order to most accurately select the optimum solar system for a project, simulation software should be used. It is not possible to make an optimum selection without this simulation.

A solar system for an individual villa can be delivered by using a simple combination of a solar collector, pump group, domestic hot water cylinder, controls and a wall-hung gas condensing backup boiler. This again can generally be provided as a package solution.

Solar collectors

The main equipment in any solar system is the collector. Various factors must be considered at the planning stages in order to select the correct type of collector for an application. These include the availability of space, installation conditions and the temperature differential between the average collector temperature and that of the external air.

Such factors will influence the efficiency of the collector; the higher the collector operating temperature, the higher its output and therefore the yield of vacuum tube compared to flat plate collectors.

Flat collectors have a very good proven performance in solar energy systems. If the temperatures reach levels of more than 90°C they will lose energy; this may be a disadvantage in cold countries, but in the Middle East it creates a big advantage as it guarantees a reliable operation under the high temperature conditions experienced in the region.

Plug-in connectors can be used to join flat plate collectors to save installation costs, time and reduce the amount of pipework needed.

Evacuated tube collectors are widely installed. This type of collector is good for locations that have low ambient temperatures (below 0°C) or applications that need very high temperatures of above 110°C. They have the advantage that they produce very low energy losses.

To find out what type of collector is most suited to an application it is best to do a simulation for both flat and evacuated collectors beforehand. By comparing the simulations it is easier to make a decision.

A high quality solar collector alone cannot guarantee the optimum operation of an installation, this depends on the overall system as a whole. Further components that must be carefully considered are:

• a control unit that is tailored specifically for solar heating systems;

• a domestic hot water cylinder that incorporates a solar heat exchanger at a low height;

• system technology that is aimed at achieving fast responding control, therefore maximum yields from the solar system.

When collectors heat up they transfer energy to the ambience through thermal conduction, thermal radiation and convection. Some solar radiation that hits the collectors will also be lost through absorption and reflection off the surface.

The optical efficiency level takes into account these losses plus those created during the transfer of energy into the medium. The optimum efficiency occurs when the difference between the collector and ambient temperature is zero, so the collector will lose no energy to the environment.

Murat Aydemir is general manager of Viessmann Middle East.

Legislation changesThe UK's newly launched 17th Edition of the IEE Wiring Regulations (BS 7671: 2008) provides specific instructions and guidance for the safe installation of solar photovoltaic (PV) systems.

Some specific risks of this type of installation include the need to work on a live system as PV systems cannot be switched off. Other considerations include the need to work with dc wiring, which many installers are unfamiliar with.

BS 7671 comes into force in the UK in July.

Related Article: Sunshine solutions

For all the latest construction news from the UAE and Gulf countries, follow us on Twitter and Linkedin, like us on Facebook and subscribe to our YouTube page, which is updated daily.