Fiona Riddoch,
Managing Director COGEN Europe
The simultaneous provision of both heat and electricity in combined heat and power is a reliable high efficiency approach to getting the most value out of primary fuels. Where society has a demand for electricity there is typically also a demand for heat, where there is a demand for heat (such as an industrial process or a large building complex) there is also a demand for electricity.
Societies’ demand for heat is considerable. Heat at high temperature or steam is needed in both heavy and light industrial processes, while buildings of all sizes and uses require space heating or cooling at relatively low temperatures by comparison.
A quick review of the use of combined heat and power (also known as CHP or cogeneration) in providing space heating shows a growing use of systems in the kW and low MWs ranges of capacity in specific types of applications. CHP is widely used in hospitals and in sports facilities or leisure centres, where there is a reliable heat load throughout based on long operating hours. Small engine based CHP operating in the range of 50kW to 500kW can supply these facilities with the heat they require and generate a surplus of electricity for the network. University campuses are also showing interest in CHP where units of the low MW range can replace the traditional boiler in the campus boiler house of and supply heat to a range of buildings on the campus site, generating electricity for own use or export. Major individual buildings or groups of buildings are good candidates for CHP and a city setting can contemplate supplying heat to neighbouring buildings. Once an organisation has the facility of generating heat and selling electricity as a business prospect in its own right, then supplying heat not just for their own needs but to supply other commercial and private users becomes a reasonable proposition.
A whole new departure for the sector is in micro CHP (1kW to 5kW) where new products are currently entering the market which greatly improve the efficiency of fuel use of traditional individual home boilers. This sector has seen a surge of interest and confidence in the past 12 months and several new European products based on modern engine design and supplied by well established appliance manufacturers. The micro CHP provides a step-change of efficiency in energy performance over the traditional condensing boiler and as a like-for-like replacement solution offers immediate energy efficiency gains in a market which currently sells 400,000 units per year in The Netherlands alone.
The low carbon heat and electricity supply from CHP is finding new roles in a world of increasing renewables. CHP on natural or biogas provides a very low carbon form of heat and electricity. It also has the advantage of being fast responding to peaks in demand or anticipated drops in supply from intermittent sources such as wind. There are a growing number of cases where CHP units of a range of sizes with or without heat stores are finding that they can offer services in the grid balancing functions necessary in a supply system with an increasing quantity of renewables. Micro CHP, because of its fast response and associated thermal storage, in particular could have a key role to play in the virtual power station designs now under investigation.
CHP is sometimes most familiar to citizens in the EU through its links to space heating in Europe’s district heating (DH) networks. Europe is home to the strongest examples of CHP penetration in the energy supply network in the world and some of these countries notably Denmark have achieved this position with a high penetration of CHP in DH. The DH networks in Denmark have been largely converted to CHP in the past 20 years. In Denmark 46% of the space heat is provided through DH today and the DH sector is strong. These companies published in 2008 their “Heat plan Denmark”, an ambitious document which outlines how the heat sector of the Danish economy can be decarbonised by 2050. The DH sector claims that DH is the least cost solution for heating in new planned urban districts. In the plan DH is increased to supply up to 63-70% of heat by 2050, this recognising that there will be 25% drop in heat demand overall. Energy sources for the DH schemes will include an increasing range of renewables and the DH scheme technology and management will be improved to keep the return temperature of the DH scheme to less than 35°C hence improving the energy efficiency and the overall energy extraction of the system.
The DH sector is not standing still. As providers of heat to a range of customers this sector knows the challenges of the energy market. Over the past few years the sector has responded to Europe’s climate and energy challenges by investigating new fuels and new business models. DH schemes have advantages in meeting the new challenges of a diverse fuel, high renewable electricity and heat supply which may not be immediately apparent. DH is one of the best methods for introducing solid biomass into the heat supply system. Centrally located heating/CHP plant and co-firing with other fuels improves the logistics and efficiency of use of biomass and DH schemes can take advantage of this. The urban challenges of waste management have led to a growing interest in waste-to-energy plants which are now well established in several EU Member States. In Denmark waste-to-energy is integrated into their supply system with urban centres such as Copenhagen having waste-to-energy (with flue gas condensation) plants centrally located in the cities geography.
DH networks are also finding new products and services in the more diverse electricity supply world of today. A DH network incorporates heat storage and short term storage of energy as heat is very attractive in a world where an increasing proportion of the electricity supply is intermittent and the demands from customers remain time-of-day dependent. DH networks can also help accelerate the penetration of renewables by acting as a central distribution of renewable heat and electricity which can deploy an optimal mix of renewables and low carbon heat, solving some of the structural and capital problems of other approaches. Geothermal boosted by biogas and large scale solar are being considered while electric heat pumps supplying the DH network can absorb over supply of electricity from wind at time of the day when electrical demand is low.
DH networks can also take advantage of waste heat opportunities. The high temperature heat associated with industrial processes is an ideal base for CHP. Additionally, the vented process water or steam is frequently at a sufficiently high temperature at the end of the process to provide space heating and hot water for local buildings, offices and homes. This cascading down of temperature from industry to domestic/commercial use is still considerably underdeveloped although there are some classic best practise cases to learn from. The city of Dunkirk in northern France is a good example. In Dunkirk, the DH system recycles surplus energy from France’s largest steel mill. The city has added three CHP units and a second surplus heat capture unit at the steel plant and increased the share of recovered energy in the network to 90%, significantly lowering overall CO2 emissions.
The DH sector has responded robustly to the forecast drop in demand for space heating as buildings become better insulated and hence demand for heat drops. By improving their customer services and incorporating increasing quantities of renewables into their supply, DH networks can provide their customers with options on arguably choices of low carbon heat and electricity.
However, challenges still remain including the central one of the high cost of establishing a heat network. Funding such networks demands a large capital investment and requires strong market and policy leadership on an extended timescale to develop the full network and infrastructure. A further issue exists in several new EU Member States where traditional DH networks and also the buildings they supply require major upgrade, to improve their reliability and efficiency and extend their lifetime. Moreover, poor business practises still exist with histories of customer non-payment being common, and a resulting lack of funds in the business. Underinvestment over time has led to poor performance and consequently poor customer satisfaction and this spiral of decline leads to customers leaving the scheme and accelerating the decline cycle. The contrast between these histories and the situation in the main cities of Finland or Denmark is striking. In these latter countries the DH sector is strong and planning for growth.
CHP is a highly efficient use of primary fuel for heat and electricity. It is possible to find a CHP solution over a wide range of different capacities and meeting the needs of a preferred fuel type. Given the challenge which remains to meet Europe’s energy and climate objectives the wider use of CHP in applications ranging from industrial processes to domestic heat supply will continue to a compelling option.
