Combined Heat and power systems

Technical issues - specifications
There are many heat and power generation concepts. Many of these can produce heat (in the form of steam or hot water) or power (through, for example, the Rankin steam cycle), or both (in CHP applications). These advanced heat and power generation concepts have two central aims: to improve the fuel conversion efficiency of the process and to reduce emissions, whilst maintaining high availability and low operating costs. It should be noted that improving efficiency itself has a positive environmental effect by reducing the amount of raw material that has to be used for the same net energy output; small improvements in efficiency can lead to substantial environmental benefits.

The technologies can either be used in new applications, or can be used to refurbish and improve the operation (efficiency, emissions, availability or cost) of existing plant.

Many of the technologies can be used for the conversion of a wide range of fuels, including renewable energy feedstocks such as biomass and wastes. Increasingly, interest is being shown in the use of technology that can offer fuel flexibility, to enable operators to use a wide range of fuels, and to use fuels in combination -cofiring. This idea is covered in more depth under the heading of Renewables.

The status of commercial development of the key heat and power technologies varies. Only PF combustion (well established and reliable), AFBC and NGCCs are currently fully commercially available, although many of the other technologies are approaching commercial viability.

The production of heat and power from fossil fuel is based on natural gas, fuel oil (light and heavy) and solid fuels like hard coal, lignite, peat and residues from refineries. In the future biomass and wastes could be additional fuel sources in fossil power plants.

Barriers:

• Advanced power plants have high initial investment costs.

• Actual or perceived risks associated with innovative technologies and their potential environmental impacts may deter investors, and make it difficult to raise finance.

• Aspects of market operation, relevant regulations and lack of an appropriate infrastructure may restrict or prevent deployment.

Small scale Combined Heat and Power systems

Technical issues - specifications
Cogeneration, or combined heat and power (CHP), is the production of both heat and power from a single source. Usually, both forms of energy are used on site but surplus electricity from large installations is sometimes sold back to the grid, and heat can be used to supply district heating systems. Small-scale cogeneration (capacity under 1MWe) typically converts about 30% of the input fuel energy into electricity and 50% into usable heat.

The main components of small-scale cogeneration system are;

• a generator to produce electricity

• a prime mover (engine) to drive the generator

• a heat recovery system to recover waste heat from the engine

• a control system, an exhaust system and an acoustic enclosure.

Highly efficient cogeneration technology for the commercial sector is now mature and well established. For the domestic sector, where cogeneration units might serve individual houses, further technology development is needed. Cogeneration can work in conjunction with absorption chilling to provide cooling, heating and power.

It should be noted that cogeneration works best where the building(s) in question have significant heat and electricity requirements for a substantial part of the year. When evaluating cogeneration, it is important to consider other measures that might affect the energy loads in the future. The economics of a prospective cogeneration scheme need to be assessed carefully in the context of other energy conservation measures,

e.g. improvements to lighting and thermal insulation.

On a practical level, there is a requirement for development of;

- a gas supply network;
- smaller, highly efficient units for smaller energy users, possibly including the domestic sector; Stirling engines and fuel cell cogeneration have potential;
- packages with an absorption chiller to provide summer cooling in commercial buildings. In Cyprus there are no prospects of gas introduction in the energy system are expected during the near future.


Solar cooling systems - Absorption cooling units

Technical issues - specifications
The solar-powered air-conditioning of buildings is a promising opportunity for Cyprus and the services sector is well suited for this type of applications.

Air-conditioning is the dominant energy consuming service in buildings. Demand for cooling-dehumidification of indoor air is growing due to increasing comfort expectations and increasing cooling loads.

Growing demand for air-conditioning has imposed a significant increase in demand for primary energy resources. Besides the high-energy consumption, conventional cooling induces two additional problems: high electricity peak loads, and the use of refrigerants, which have serious negative environmental impacts (depletion of ozone layer).

The use of heat for cooling is not a new idea. In the past, different technologies have been tested, mainly using absorption processes. In the years of the great surge in solar energy R&D following the energy crisis of the 1970’s there have been several attempts at building solar-driven cooling systems. These solutions did not find significant practical usage due to substantial technical problems related mainly to the need of high temperatures and the cost of the whole system.

Today several new ideas concerning both collectors and chillers have gained ground. It is widely recognised that, with suitable technology, solar-cooling can help alleviate, if not eliminate the problems related to conventional air-conditioning systems.

Beyond technological issues, the potential for solar space conditioning applications in Cyprus hotels may increase rapidly in the near future given that:

- Solar radiation potential is sufficient,
- New opportunities exist in financing projects which exploit solar energy,
- A significant rate of hotel owners is already familiarized with solar applications (solar hot water systems),
- It is a good application since the greatest demand for air-conditioning occurs during the greatest insolation periods (of the day and year).

Solar water heating

Technical issues - specifications
Energy consumption for heating domestic water is, after space heating, the second largest energy user in the residential sector. The average human uses daily 36 litres of 50-60°C hot water and his average energy consumption for hot water is about 950 kWh per year (prepared at a temperature of 60°C from cold water at 10°C).

Variations in hot water consumption patterns are also observed through the week and through the seasons.