Solar Photovoltaic electric conversion (stand-alone, hybrid and grid connected systems)

Photovoltaics have a very large potential and are widely used for decentralized applications by populations not yet connected to the main electricity girds. Another potential market is related to grid connected small PV plants to support distribution networks in rural areas. This type of application could become more competitive in the coming decade, when the cost of PV modules becomes less expensive.

PV applications

PV	Average size	Average cost (EURO)	Applications
Roof top systems	3 kWp	3,000/kWp	Individual houses, buildings, schools
Building facades	30 kWp	4,000/kWp	Commercial buildings, institutional public buildings
Grid connected applications	Multi MW	2,500/kWp
Stand alone rural development	10W-10kW	5,000/kWp	Isolated homes, small islands electrification, summer houses

The use of photovoltaic solar energy in Cyprus is still in its infancy. Photovoltaics has been used by the Cyprus Telecommunication Authority (CYTA) for the telephone kiosks and transmitters. The Cyprus Radio-Telephone Authority has also used photovoltaics for transmitters. The nowadays installed capacity of photovoltaics is estimated at 0.2MW.

 

Solar thermal electric conversion

Electricity production using high temperatures obtained through the concentration of solar radiation has a great potential, although these systems are in a demonstration phase. Two types of solar thermal installations are going to be considered. Solar Energy System Generation Stations (SEGS) consists of a linear collector with a parabolic cross-section and a conventional steam turbine. The combination of parabolic trough technology with a gas turbine combined cycle is called Integrated Solar Combined Cycle system (ISCCS). The electricity production, in very good sites with solar energy can reach up to 2500 kWh per kW installed. The land requirement is about 1 km² for a 80MW plant and the cost is estimated about 3000 EURO per kW installed [33].

Solar hot water systems

Efficiency and cost effectiveness of Solar hot water systems contribute to their wide expected penetration in urban, rural and isolated communities.

Cyprus is one of the leading countries in the use and construction of solar water heating systems. Local industry is characterized by high quality of standards in the construction and know-how in this field.

In Cyprus the manufacturers provide their products to the end users. The average market price of a typical system of 150lt - 3m² is about 850 € +15% VAT. This price includes the installation costs and the water storage tank.

Table 3.4. Solar systems

Solar collectors	Average size	Average cost (EURO)	Applications
Domestic hot water	2.4-10m2	300/ m2	All European countries
Large collective solar system	>100m2	200/ m2	All European countries
Space heating	25-50m2	200/ m2	Northern and Southern countries
District heating	>500 m2	150/ m2	Northern and Southern countries
Air conditioning and industrial process heating		350/ m2	All European countries

Given the solar radiation in Cyprus the expected annual energy production is 0.578MWh/m² per year [40].

Solar systems for space heating and cooling

These systems can be installed either in existing or new buildings. The design characteristics and the investment cost are different in the various buildings. The collector performance is depending heavily on the local conditions. An average performance of 750kWh/m²/year is expected. Costs ranges from 500 to 600 EURO per m² of collector area. The attractiveness of the technology opens significant prospects for its wide penetration into the market. The wide application of such systems will smooth the profile of the power electricity curve and will substitute peak loads. These systems are mainly composed by the solar heat collectors, the storage tank, the cooling unit and the drying unit. Such systems can be applied in hotels, apartments, offices, traditional buildings, industrial and commercial sector.

Bioclimatic architecture - Solar energy for passive use in architecture

The interventions are expected to be incorporated into both the existing and new buildings. The techniques adopted for application during next years are:

• Roof insulation
• New air-tight frames, favourable for natural and night ventilation
• Reasonable use of the movable shading devices
• Reasonable use of the apertures for ventilation purposes
• Ceiling fans
   

It is obvious, that interventions in buildings are to be adjusted in its community due to differences in their style and traditional conditions, as well as due to different climatic conditions.

On the other hand different building types are identified: Terraced house, attached detached or semi detached house, traditional or modern design, insulated or noninsulated, different construction period and different prescriptions during construction, number of households and others. Different interventions are suitable for the various types of buildings.

For the hotel sector, a greater implementation is expected, due to the fact that in this sector, refurbishment is more often realized.

 

Batteries

Nickel/ metalhydride, lithium/ carbon

Hydraulic/ pneumatic accumulators

Hydraulic/ pneumatic accumulators are devices, which allow energy to be stored as compressed gas in a pressure tank and recovered later when needed. The process is facilitated by use of a hydraulic pump/motor, which is used to transfer the energy to and from the gas.

Flywheels

Flywheels are storage devices, which are particularly well suited to high power applications, but not for holding large amounts of energy. Flywheels are a good match to the requirements of smoothing the power fluctuations. Two types of flywheel have been applied to wind-diesel systems.

In the first, the flywheel is attached to the shaft of the diesel’s synchronous generator. A power dissipator, such as a dump load, is also generally included for power fluctuations, which are to great for the storage to absorb. When there is surplus wind power the diesel is stopped and disconnected from its generation. The latter continues to run as a synchronous condenser, providing reactive power to the wind turbine’s power fluctuations and can be used to start-up the diesel when it is needed. In this system the flywheel stores the energy equivalent of between a few seconds to a few minutes of operation at rated power.

A second type of flywheel storage, which is still at the experimental stage, uses a separate flywheel driven by an a.c motor, which operates asynchronously. By allowing large speed variations the amount of energy which can be removed from a given size of flywheel increases dramatically. This configuration consists of an ordinary induction generator, the flywheel, and a variable speed regenerative a.c. motor drive. In this system the grid frequency does not have to vary for the stored energy to be used. Disadvantages include the introduction of added complexity and increased with the power electronics of the motor drive.

 

Pumped storage

A pumped storage unit can be used for storage in medium or long term basis. The main advantage of such unit is the quality of the produced energy. On the other hand the capital costs are quite high and special location features are required for its installation. Another disadvantage is the overall inefficiency of the operation cycle.

Water is stored by pumping it against a net hydraulic head to be discharged at a more propitious time. Surplus of power derived by wind farms, or by conventional thermal units working in their technical minimums is used for pumping during the hours of low demand. A hydro turbine generates energy, which is used to cover peak loads [30].

PSU transforms the intermittent and variable energy from the wind farms into a uniform electricity flow to be used at predetermined hours and provides the electrical system with an additional peak power. The definitely predicted operation and the negligible time needed for setting out (Black start), the PSU improves the behavour of the electrical system in extreme conditions (Black-out).