1 residential fuel cells for distributed generation · future distributed generation system....

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Fuel Cell and Distributed Generation, 2007: 1-26 ISBN: 978-81-308-0179-7 Editor: Francisco Jurado Melguizo

1 Residential fuel cells for distributed generation

Beatriz Alzueta1, Raquel Garde1 and Mónica Aguado2 1CENER, National Renewable Energy Centre, c/ Ciudad de la Innovación 7 31621 Sarriguren, Spain; 2Public University of Navarre, Electrical Engineering Department, Campus Arrosadía s/n, 31006 Pamplona, Spain

Abstract Current worldwide electric power production is based on a centralised power generation system. This system has several disadvantages such as high emissions, transmission losses and large and long term financing requirements. Distributed generation (DG) can reduce the energy supply problems in some regions (weak networks,remote places) and allows making good use of local resources, increasing sustainable development. Indeed,DG introduces the use of modern technologies, such as fuel cells.

Correspondence/Reprint request: Dr. Beatriz Alzueta, CENER, National Renewable Energy Centre, c/ Ciudad de la Innovación 7, 31621 Sarriguren, Spain

Beatriz Alzueta et al. 2

Statistics on energy consumption have pointed out that residential sector is one of the most pollutants end-use sectors, as around 30% of the world energy consumption, mostly produced by fossil fuels, is due to it. Hydrogen and fuel cells will be introduced in this sector considering their high efficiency, small size, reliability and general performance. Fuel cells can produce combined heat and power (CHP) increasing this way the overall efficiency of energy conversion and reducing the fuel consumption. The owners of the household, who are generating heat and electricity for their own needs, by means of using a CHP fuel cell, could feed surplus electrical power into the grid or share excess heat via a distributed heating grid constituting a small DG system. In spite of all the benefits that DG can provide, nowadays exists a number of technical problems that can affect the stability of the network and quality of electricity supplied if a lot of small generators fed their power into the grid. It is necessary to analyze all this issues to make a correct DG integration in the system. When hydrogen is obtained from renewable sources, fuel cells could increase the contribution of renewable sources in the electricity grid and reduce the dependency on fossil fuels. It is also necessary to develop standards and codes to increase the share of DG into the grid and to introduce residential fuel cells as a DG technology option. Introducción In a centralised power generation, large central generators feed electrical power up through generator transformers to a high voltage interconnected transmission network. The transmission system is used to transport the power, sometimes over large distances, for delivery to the customers. In recent decades, there has been a considerable interest in distributed generation (DG) to avoid some of the disadvantages of these systems. DG can offer to consumers and the whole society a wide variety of benefits, including economic savings, improved environmental performance, and greater reliability. Approximately 30 % of the world energy consumption is due to the residential sector, most of this energy coming from fossil fuels. Fuel cells will be introduced in this sector because they have many advantages over conventional power generating systems and because of their efficiency and environmental advantages. Residential fuel cells are suited for DG in small scale. The DG permits the owners of the household, who are generating heat or electricity for their own needs, to feed surplus electrical power into the grid or share excess heat via a

Residential fuel cells for distributed generation 3

distributed heating grid. Residential fuel cells will play an important role in the future distributed generation system. Different types and sizes of fuel cells are suitable for distributed generation based on residential sector. However, it is difficult to predict the success of one fuel cell type and size versus another given the immature development and commercialization of these technologies and because each type of household (in each country) has different styles and demands. Features of residential sector The energy consumption of Spanish household’s trends points to an annual increase around 3%. However, important technological progresses in development and use of renewable energies are taking place as well in energy efficiency of electrical appliances and buildings. That permits to foresee a trends change in the short-medium time. In Europe, the average energy consumption per house (tep/house) is around 1.7. Spain, with 0.74 tep/house is one of the countries that consumes less in this sector. That could be due to a benign climate, with moderate average winter temperature that favours the reduction of energy demand for heating. Characteristics of household consumption Space heating and hot water together represent approx. 70 % of end-energy-use of Spanish households. According to IDAE (The Institute for Energy Diversification and Saving) [1] the residential energy consumption could be distributed in the following way: heating (40.4 % of the total consumption), followed by domestic hot water (DHW) (26.9 %), electrical appliances (12.0 %), cooking (11.6 %) and lighting (8.7 %). Nowadays the air conditioning is becoming more relevant (0.4 %), as shown in Figure 1. In any case, the heat consumption for dwelling varies very much depending on the geographic zone, for instance in Spain there are regions where heating is not almost necessary along the year.

Figure 1. Distribution by consumptions in a typical Spanish household.


That applies also for the rest of the energy consumption. The climatic zone where the house is sited, the use given to the dwelling, the construction quality and isolating materials, among other factors, determine the familiar energy expenses. Indeed, the cost of systems and equipments and their use, also contribute in a decisive way on the energy consumption and costs. The energy consumption in houses depends, mainly, on the size and members of the family. Regarding to the uses, ones depend on size, as lighting and heating, and others depend only on number of people as D.H.W. or cooking energy. It is assumed an energy sources distribution of 70 % fuel (to cover hot water and heating) and 30 % electricity. Typical energy demand during the day is shown in figure 2. The average consumption per hour in Spanish household in the range of 250-500 W but peak power is around 3-5 kW; these punctual demands are mainly due to electrical appliances as microwaves for instance. The average power of usual autonomous devices used is 1 kW and the average consumption of cold equipments is around 240 Wh.

Figure 2. Average electrical consumption in a typical Spanish household. Source data: REE. Cogeneration technologies for residential applications As we say before, space heating and hot water together represent approx. 70 % of end-energy use of households in Spain. Considering the usually poor energetic quality of the existing building stock, significant energy saving potentials can be found. With regard to new buildings, various concepts for ultra-efficient houses are available and practically proved such as passive houses, solar architecture, zero-energy houses, etc.


The growing worldwide demand for less polluting forms of energy has led to a renewed interest in the use of cogeneration technologies in the residential sector due to their potential to significantly reduce the quantities of pollutants emitted in supplying residential electricity and heating. Cogeneration systems in the residential sector have the ability to produce useful heat and generating electricity simultaneously at the point of use from a single fuel. This means that the efficiency of energy conversion to useful heat and power is potentially significantly greater than by using the traditional alternatives of boilers or furnaces and conventional fossil fuel fired central electricity generation systems. Cogeneration applications in the residential sector offer opportunities in terms of improving energy efficiency and reduction of GHG emissions. Several technologies are available for residential cogeneration. The most promising technologies in this sector are:

• Internal combustion engine (ICE) converts heat from combustion of fuel into rotary motion to drive a generator. ICE uses two types of cycle: the Diesel one using compression ignition and the Otto one using spark ignition. Spark ignition engines operate natural gas, propane, gasoline or landfill gas. Compression ignition engines use diesel fuel or heavy oil. ICE presents a low capital cost, has a good efficiency and is used in cogeneration. As barriers, it has a great maintenance cost and its NOx emissions are the highest among the DG technology. • Stirling engine where an external flame heats a sealed amount of working gas. The gas drives a power piston and is cooled down by the cold return flow of the hydronic heating. • Steam engine works similarly: water is evaporated by external combustion, and the steam generates power in an expander. Thermal energy is transferred to the heating system in the condenser where the vapour liquefies and is then pumped back into the steam generator. • Micro turbine is a Brayton cycle engine using atmospheric air and natural gas fuel to produce shaft power. The key barrier to micro-turbine usage is its maintenance cost. The last three CHP configurations show low emissions due to the continuous combustion and minor maintenance costs because of oil free lubrication. • Fuel cell is a device that produces heat and electricity by a combination of oxygen and hydrogen in an electrochemical process. It is similar to a conventional battery except that the fuel and oxidant are stored externally. A fuel cell can be classified as renewable or non-renewable according to the type of fuel used. Its main barriers are the capital costs, the technological development needed (fuel choice and availability, fuel storage, reliability) and lack of standards and regulations.


Fuel cells offer several technical advantages, such as modularity, good partial load characteristics, dynamic response or high heat levels which are favourable for industrial and cooling applications. In addition, advantages that are common to all cogeneration technologies, such as reduced transmission losses, reduction of required grid capacity, etc. can be made accessible. The potentially high electrical efficiency of fuel cell power plants is one of the major advantages of these systems. However, conventional systems are constantly optimised, too. Since fuel cells contain only few rotating parts, noise emissions and vibration are low. The noise is produced especially by the balance of plant components (that means the periphery of the plant, e. g. the gas processing, air compressor, AC/DC converter, etc.), particularly the compressor. It can be attenuated with appropriate noise protection devices. In residential applications, where conventional small reciprocating engines are too noisy for households, fuel cells could offer significant advantages. As fuel cells have to succeed in an already competitive market, cost is seen as the major market entry barrier. Stationary fuel cells are still between 2.5 to 20 times more expensive than competing technologies, with the balance of plant being responsible for a large share of total capital cost.[2] The extended use of CHP residential fuel cells is limited by the high initial cost, the low level of commercialisation, and the competition with other technologies which are at an advanced stage of development. Fuel cells are only one option among others that may contribute to increasing energetic efficiency and environmental performance of the energy system. Hence, fuel cell policies must not stand alone but have to be integrated into an overall guiding strategy for a sustainable development of European energy systems towards a much more efficient use of energy and the expansion of renewable energy sources. CHP Fuel cell systems for households The advantages of fuel cell cogeneration systems include low noise level, potential for low maintenance, excellent part load management, low emissions, and a potential to achieve an overall efficiency of 85-90% even with small units. [3] The domestic micro cogeneration sector could, if the right market and economic factors support this segment, represent a considerable market. The FutureCogen project estimated that under optimistic assumptions, by 2020 up to 50 GWel in EU15 could be installed in this sector. In addition, some 700.000 units could be installed in Central and Eastern European countries. [2] The use of fuel cells in this sector brings important advantages, such as good efficiency in operation with no nominal load, the adaptability capability


to variable loads, a high efficiency which is independent of the power rating of the cell, low acoustic contamination and vibrations, near-zero level emissions (depending on the fuel), etc. One of the key factors for economic viability is the electricity price which enters the calculation because either domestic electricity consumption is displaced, and thus associated costs eliminated, or because electricity is fed into the electricity grid with a corresponding feed-in tariff. There is no clear technological leader in residential sector amongst the five main types of fuel cells, although PEMFC (Proton Exchange Membrane Fuel Cell) and SOFC (Solid Oxide Fuel Cell) are most applicable and these are likely to be the dominant types in this sector of the market. Nowadays most of the fuel cell operates on natural gas reformer hydrogen. It has the lowest greenhouse gas emissions per energy unit of all fossil fuels. Even though natural gas is not a sustainable energy source, it does represent an efficient way of economising the inevitable fossil energy input during a transition period to a renewable energy supply system. Moreover, natural gas can bridge the gap between our fossil system and a more renewable system based on hydrogen. Fuel cells for the residential applications will supply power in the range of 1 kW to 10 kW. As we can see in Figure 3 below, different size units are being developed to this market because each country has different housing styles and demands from the grid. The majority of 1kW units are being used to provide base load electricity for an 8-hour period and 24-hour hot water heating, for a single family house. In this system the units are switched off daily and the peak demand and night time demand is met by the grid. [4] In residential applications, the design of systems poses a significant technical challenge due to the potential non-coincidence of thermal and electrical loads; that creates the need for electrical/thermal storage or connection in parallel to the electricity grid.

Figure 3. Size of small fuel cell manufactured in 2005 [4].


It can be expected that even in a business-as-usual case the heat demand will be reduced significantly whereas more ambitious climate policies may trigger further achievements. As a direct effect of a decreasing demand for space heating, however, the relatively constant consumption of hot water gains importance. Hot water demand represents a base load for fuel cells even in summer time, so that the annual heat demand profile will show less seasonal unbalances. In this regard it will be easier to dimension the CHP units with a reasonable load factor. Target cost of fuel cells he main challenge for fuel cells is to achieve the competitive cost goals. In stationary applications, cost targets are not quite as strict as in mobile applications. Residential applications have to fulfil higher standards because in typical applications, higher stack lifetimes are demanded, and the high electric efficiencies of the competing technologies will require operating the systems at much lower current densities than in mobile applications. The target costs of fuel cells, i. e. the allowable costs at which fuel cells will become competitive, are determined by the market segment, by the costs of the competing technologies and by the energy economic developments, to bring down investment costs of fuel cell systems, various measures have to be taken into account as improved fuel cell stack design, used lower cost materials, reduced degradation and increased tolerance towards gas contaminants, streamlined manufacturing processes. Basics of distributed generation Current worldwide electric power production is based on a centralised power generation system. This system has several disadvantages such as high emissions, transmission losses and large and long term financing requirements. Distributed generation (DG) can reduce the energy supply problems in some regions (weak networks, remote places) and allows making good use of local resources, increasing sustainable development. Indeed, DG introduces the use of modern technologies, such as fuel cells. Moreover, because DG could replace or reduce the demand for traditional utility service, DG could also pose an economic risk to some incumbent utilities and their consumers. That has created a conflict between industry stakeholders and other interest groups. [5] On one hand, proponents of DG are telling decision makers that utilities and regulators have imposed technical and economic barriers to the development, installation, and interconnection of DG facilities with the electricity grid.


They are asking regulators and legislators to act to remove those barriers so that consumers can benefit from DG. On the other hand, some utilities have insisted that if decision makers adopted the DG proponents’ recommendations, it would significantly degrade the safety and stability of electric systems and would require utilities and their residential and small commercial consumers to subsidize uneconomic technology investments by others. Traditional and distributed generation network layout Much of the energy generated today is produced by large-scale, centralised power plants, with energy being transmitted and distributed over long distances to consumers. Electricity grids in Europe are laid out rather uniformly as a top-down supply system. The distribution networks are designed for unidirectional flows of power and sized to accommodate customer loads only. The transmission grid (operated by the transmission system operator or TSO) is a high voltage grid for high power flows. In Spain it operates typically at 400kV and 220kV. This high transmission voltage reduces grid losses. Interconnections between EU countries are made at the transmission grid level and large power stations are directly connected to the transmission grid Figure 4.

Figure 4. Conventional networks and flows of power.


The boundary voltages that define the distinction between high, medium and low vary according to country. In Spain the distribution grid can be divided into a high voltage distribution grid (typically 132, 66 and 45 kV), a medium voltage distribution grid (typically 20, 15 and 6.6 kV) and a low voltage distribution grid (380, 220V). Distribution grids are operated by distribution network operators (DNOs). However, in a power system composed by distributed energy resources, much smaller amounts of energy are produced by numerous small, modular energy conversion units, which are often located close to the point of end use. Most of DG based systems are connected to the distribution grid. According to this, whit significant penetration of distributed generation the power flows may become reversed and the distribution network can no longer be considered as a passive appendage to the transmission network but an active system whit power flows and voltages determined by the generation as well as the loads. This is shown in Figure 5. Distribution grid operators have an obligation to connect users to the grid and to ensure the security of supply. They are also responsable for the power quality from the grid. Most countries have developed standards and practices to deal with technical issues of connecting and operating generation on a distribution system. In general the approach adopted has been to ensure that any

Figure 5. Networks and flows of power with distributed generation.


any distributed generation does not reduce the quality off supply offered to other customers and to consider the generators as a “negative load”. Technical impacts on the distribution systems The main technical impacts of DG on the distribution system are listed above [6]

• Network voltage changes. A matter of concern for the grid parallel operation of a fuel cell source, which is fundamentally a DC source, is the issue of the possible injection of DC currents into the power system. DC injection into the power system may cause saturation of existing power and metering or protection measurement transformers and could lead to mal-operation of protection devices and a more onerous breaking duty for components such as circuit breakers. IEEE 1547 Standard specifies acceptable limits for DC injection into the power system of 0.5% of the DG full rated output current. Typically the method employed to reduce DC injection would be to incorporate a conventional isolating transformer in the design of the inverter output, prior to the grid coupling, but this in turn adds to the overall inverter system cost. • Power quality. When power is injected into the network at the distribution level flows of electricity are changed and this leads to technical issues affecting the stability of the network and the power quality. Power quality refers to the degree to which the customer’s service voltage continuously approximates a normal 50 Hertz sine wave at the expected normal voltage. Of course, some degree of power quality deterioration has always been present on the grid from time to time. Causes include lightning pulses, faults and system recloser operations, and in certain applications voltage drops at the end of long lines and wave form disturbances due to customer loads like welders or arc furnaces. Two aspects of power quality are usually considered to be important: transient voltage variations and harmonics distortion of the network voltage. Voltage flicker and variation caused by fluctuating loads or production are the most common cause of complaint on power quality. Flicker could occur if there were widely and rapidly fluctuating amounts of power being exported to the grid, this is felt to be much more of a concern from wind system fluctuations than from residential fuel cell installations. Harmonics are a measure of the distortion of the voltage sine-wave and are becoming more important to power quality. They are produced by many types of electrical equipment including power electronics such as linear drive motors and personal computers and affect both supply and demand sides. • Protection. DG flows can reduce the effectiveness of protection equipment and create operational difficulties under certain conditions. A number of different aspects of DG (in this case, the fuel cell) protection can be identified:


Protection of the generation equipment from internal faults Protection of the faulted distribution network from fault currents supplied

by distributed generator Anti-islanding or loss-of-mains protection Impact of distributed generation on existing distribution system protection

Protecting the DG from internal faults is usually rather obvious from the fault current flowing from the distribution network. However, protection of the faulted distribution network from fault current from DG is often more difficult. Loss-of-mains protection is a particular issue in a number of countries, particularly where autoreclose is used in the distribution circuits. For a variety of reasons, both technical and administrative, the prolonged operation of a power island feed from the DG, but no connected to the main distribution network is generally considered to be unacceptable. Finally, DG may affect the operation of existing distribution networks by providing flows of fault current which were not expected when the protection was originally designed. • Stability and network operation. One important parameter is the stiffness of the grid relative to the fuel cell generator. This stiffness concept is a good indicator of the degree to which the distributed generator can influence the grid. “Stiffness” is, in effect, the ratio of the grid fault current available at the fuel cell interconnect point to the maximum rated output current of the residential fuel cell. In this instance, the stiffness ratio would be equivalent to the sum of the distribution transformer available fault kilovoltamperes plus the fuel cell fault kilovolt-amperes divided by the fuel cell fault current. The greater the stiffness ratio, the less likely the fuel cell can affect the grid.[7] Finally, the DG also has important consequences for the operation of the distribution network in that circuits can now be energised from a number of points. This has implications for policies of isolation and earthing for safety before work undertaken. There may also be more difficulty in obtaining outages for planned maintenance and so reduce flexibility for work on a network with DG connected to it. Small scale distributed generation based on fuel cells Residential fuel cells are suited for distributed generation (DG). The DG permits the owners of the household, who are generating heat or electricity for their own needs, to feed surplus electrical power into the grid or share excess heat via a distributed heating grid. Small CHP fuel cells can replace the conventional boiler found in each dwelling house. Not only it is more efficient in use of fuel but the network losses can be reduced or avoided as well. On the environmental side the emissions of CO2 and NOx are much lower than in conventional systems.


The modification of Building regulations to allow for DG may spread the use of DG. The lack of public awareness of the benefits provided by small CHP and trigeneration (when cold is generated in addition to heat and electricity) is one of the main barriers. Efficient use of energy and less environmental impact are among these benefits. In addition, the technical connection requirement should allow people with DG to export and make money with the excess of electricity. Nevertheless, the fault level restrictions in urban areas may limit the connection of DG, especially CHP, to the network. It is expected that the market introduction of fuel cells in the residential sector will depend on a supply push by manufacturers, promoters, and authorities in order to develop standards and a legal framework to introduce fuel cells into the residential sector. It is foreseen that manufacturers, licensed installation contractors and/or utilities will take care of installation, operation and maintenance of the device and will coordinate the integration of the CHP into the public grid. Features of distributed generation based on residential CHP fuel cells

• Reduced transmission and distribution losses. One of the potential benefits of DG is a reduction of line losses. Depending on the load of a grid, its capacity, the weather conditions etc., a considerable amount of energy might be lost because of transmission and distribution of electricity. Whereas in many countries, these losses are in the range of 5 to 8 %, under certain conditions (high load, low voltage, weak grid, etc.) they might be as high as 15 % [2]. In effect, this can be viewed as a direct multiplier of fuel cell efficiency. For example, if a fuel cell power plant has a site fuel-to-power efficiency of 33% but its operation concurrently eliminates 10% of line losses, then the power plant’s apparent efficiency is 0.33/0.9, or 36.7%. • New options for supply of backup power. Fuel cells can be used to manage the end-users’ electric load curve, especially when several units are interlinked through information technologies and centrally controlled. Appropriate timing of operation can contribute to peak load shaving, compensation of seasonal load asymmetries and provide the option to balance the increasing share of intermittent generation from renewable energy sources. Grid-related operation strategies of fuel cells, therefore, are of special interest for systems operators and distribution utilities. They are obliged to purchase expensive back-up power from reserve capacity in order to balance the differences between load prognosis and factual demand. In this context, the load management of fuel cells creates specific added value that adds to the profitability of installations.


• Reduced vulnerability of the energy system. In this context the development of a robust and “self-healing” transmission and distribution system (capable of automatically anticipating and responding to disturbances, while continually optimising its own performance) will be critical for meeting the future electricity needs. In combination with new information and communication technologies, sophisticated sensors, and operation and management practices, distributed power generation by fuel cells can make a contribution to the avoidance of widespread network failure due to cascading and interactive effects. • Modularity of the system. CHP fuel cells systems can be installed in a modular way. Thus, instead of installing large-scale power plants with a sudden high increase in installed capacity, a step-wise build-up of capacity can be realised. Under certain circumstances, this may be of economic advantage, caused be reduced forecasting risks, reduced financial risks and reduced risk of technological or regulatory obsolescence. Technical aspects of grid connection Together with other technologies for DG, stationary fuel cells represent a technology that could fundamentally change the designs and business models of power delivery systems. To do so, however, fuel cells must be properly integrated into the distribution system so that it enhances system value for all stakeholders. First concept studies are currently underway but it has to be recognised that still significant technical, organisational and regulatory obstacles have to be removed. Particular problems results from the prospect that a large number of generation units of 1-10 kW (power range in the residential sector) will be operated in parallel to the distribution grid. The current system of low voltage grids are not ideally suited to the broad integration of distributed generation and beyond a certain threshold will suffer critical impacts on grid operation unless modifications for grid adaptation take place. In order to avoid limitations and bottlenecks for market growth, these critical impacts have to be investigated in detail and the envisaged technical and institutional solutions have to be explored and implemented early enough. There exists numerous electrical matters associated whit the connection of distributed generation based on residential fuel cells and the most significant are shown in Table 1. A typical fuel cell stack produces power at low Direct Current (DC) voltage, but with high direct current capacity. To be useful in the households, this energy should pass through an inverter to produce the normal 220 V Alternating Current (AC) supply.


Table 1. Significant connection criteria and impact in the electricity grid by residential fuel cells [2].

It may be possible to utilise the common low voltage DC, for example, in modern buildings to provide a low voltage private wire circuit to service modern equipment needs. In this case, however, the major barrier would not be the fuel cell but the standardisation of voltage and connectivity for the various devices. The necessary power electronic inverter for fuel cells is a major barrier as it typically can be ~30% of the total fuel cell system cost. [8] The inverter design is heavily influenced by the characteristics of the fuel cell itself. If the load demand in a typical household could be controlled in some fashion, then the overall design ratings and hence cost of the inverter could be reduced.


The practical design needs for a grid-parallel fuel cell are the relatively straightforward development of IEEE 1547 Standard and a related detection and control card capable of interrupting the unit’s inverter in the event of a grid upset. In most cases, the technical solutions are already available today but any upgrading of grid infrastructures induces significant investment costs to grid operators. Institutional and regulatory arrangements have to be made in order to guarantee a fair and discrimination-free allocation of these costs. It can be expected that the issue of grid access and grid management will become a key problem for a large scale diffusion of stationary fuel cells and other distributed generation technologies. DG economics The biggest potential market for distributed generation is displacing power supplied through the transmission and distribution grid. On site power production circumvents transmission and distribution costs for the delivery of electricity. These costs average about 30% of the total cost of electricity. This share, however, varies according to customer size. For very large customers taking power directly at transmission voltage, the total cost and percentage are much smaller; for a small household consumer, network charges may constitute over 40% of the price.[9] Distributed generation has other economic advantages for particular customers. For example, customers with sizeable heat loads may produce both heat and power economically. Some customers have access to low cost fuel (such as landfill gas or local biomass, wind and solar energy), compared with commercially delivered fuel (which usually has a higher unit cost than for large central generators). Distributed generation can also encourage greater competition in electricity supply, allowing even customers without DG greater choice in suppliers. However, small generators used in DG cost more per kilowatt to build than larger plants used in central generation and the costs of fuel delivery are normally higher. Virtual power plant The idea of a virtual power plant (VPP) is a cluster of distributed energy resources, which are connected to a control and communication system. The central control station optimises the operation of the whole system by yielding surplus value e.g. by reducing maximum load and generating valuable peak time power. Virtual power plants promise a more efficient utilisation in the field of DG.


The concept of a VPP is not itself a new technology but a method of organising decentralised generation and storage in a way that maximises the value of the generated electricity to the utility. Virtual power plants using DG, renewable energy sources (RES) and energy storage have the potential to replace conventional power stations step by step until a sustainable energy mix has been developed. Figure 6. Decentralised power production with small units may also have some social effects. First of all, the awareness for power related problems is raised. The customers will try to optimize their energy demand and electricity is no longer a "low interest" product. In the VPP, transactions between buyers and sellers of electricity would be handled in a non-traditional manner, participants can switch the role of customer and supplier; a customer of energy and heat can become a supplier by offering his excess production on the (local) market. For example, an operator of VPP could own several distributed energy resource units such as stationary fuel cells and remotely dispatch energy and capacity in accordance with contractual agreements made with the buyers of its services. This operator would act as a virtual utility as long as he is able to remotely monitor and control the fuel cell units and the consumer’s energy management system as well as to respond to external signals, e.g. price signals from buyers in the spot market. In a more general case, the virtual operator may also own other types of equipment that enable it to provide other types of services like improved power quality or load management. Most or all functions necessary for the operation of the VPP, such as maintenance, billing, and information technology system, could be outsourced. In fact, the distributed generation units and other equipment used to provide services could be owned by other

Figure 6. Virtual power plant design.


entities and managed by the virtual operator. Collectively, the changes will mandate the overall physical infrastructure of the distribution system to evolve into something that is capable of supporting the business arrangements of the virtual utility.[2] Renewal sources in distributed generation system When hydrogen for fuel cells is produced from renewable energy using electrolysis, there are clear benefits as the carbon emissions are far lower. However, a question arises as to whether it is preferable to use renewable energy directly rather than use it to produce hydrogen because unfortunately the conversion of renewable electricity into hydrogen and then back into electricity is associated with significant energy losses and additional costs. One of the advantages of a hydrogen energy infrastructure is its capacity to store hydrogen thus overcoming some of the problems of intermittent energy flow from renewable sources. In the situation where renewables form a large proportion of the energy used, for example in a small distributed network, the production of hydrogen from excess renewable energy will be environmentally beneficial. This could be a solution in countries as Spain, where the share of wind power into the network continues increasing. The wind power installed in Spain was 10,028 MW on 1 January 2006, with an annual increase of 1,524MW [10]. But nowadays the main barrier to the wind power integration into the grid is not economical but technical. In Spain the major barrier to connect RES to the grid in the case of high power installations, particularly wind power, is the evacuation capacity lack of generated energy to the transport or distribution lines. In addition, some regions in Spain have set temporary suspensions in the handling of requests for installations for new wind farms or in approving new strategic wind farms due to the large number of requests for administrative authorisations made after the approval of the appropriate regional standards. This moratorium is related to the temporary saturation of the capacity for evacuation of the electrical grid and also with planning criteria for implementing new wind farms. Solar and wind energy are only available when the sun shines or the wind blows. Therefore, they are not a continuous source of electricity. However, when they are producing a surplus of electricity or when the system manager operator limits the energy share from renewable sources to avoid any management trouble due to the intermittence of this energy, it is possible to design a system which produces hydrogen via electrolysis and then, the hydrogen can be fed to a fuel cell to produce heat and electricity when renewable energies are not available.


Related to this proposal, in CENER (National Renewable Energy Centre) we are working in an European project supported by Intelligent Energy Europe programme with 12 partners from 5 European countries. The project is “Regional markets of RES-fuel cell systems for households”. The scope of this project is to make a contribution for changing the development of RES fuel cell household systems (FCHS) from R&D also to include market development and in this way accelerate the development of the technology and its economic performance. The Spanish task in this project is to use wind power excesses to produce hydrogen by means of using an electrolyser during night time when energy availability is high and price of electricity is low. The hydrogen produced by electrolysis, is stored as compressed gas in high pressure tanks to be later used in a 1 kW PEM fuel cell CHP to provide part of the household energy demand, when energy prices are high. [11] By using hydrogen produced by renewable sources, several targets can be achieved at the same time: an increase in the use of renewable energies, a reduction in fossil fuels dependence and a reduction of greenhouse gas emissions. Spanish legal framework The current legislative framework establishes the suitability of the retribution considered for the sale of surplus electricity from CHP fuel cell to the distribution company. In Royal Decree 436/2004 of 12th March fuel cells are cited as the means by which hydrogen can be exploited in high efficiency cogeneration. Article 2) defines, among others, category a) of autoproducers “who utilize cogeneration or other forms of electricity generation associated with non electric activities, and which must exhibit high efficiency”. Category a) includes group a.1) Installations that include a cogeneration plant” which is further divided into groups:

• subgroup a.1.1) “Cogenerators which use natural gas, once this comprise 95% of primary energy used, measured by low heating value”; • subgroup a.1.2) which classifies all other cogenerators. (This group includes micro-generation and hydrogen fuel cells). This Royal Decree regulates the purchased of surplus electricity supplied by CHP fuel cell systems to the distribution company at a price calculated as 90% of the of the average Reference Tariff (TMR in Spanish) ) which is a weighted average of the different regulated electricity tariffs in Spain (in 2006; 7.6588 c€/kWh). That payment is maintained for the fist ten years from the start of the project after which the payment is reduced to 50% of the TMR. These systems must have a minimum of 10% auto-consumption of the electricity generated and an equivalent electrical efficiency over 59%.


Where:

• EEE is the equivalent electrical efficiency, • E is the electricity generated, • Q is the consumption of primary energy measured by the fuel’s Low Heating Value(LHV) and • V is the heat energy obtained from the cogeneration and used to meet thermal needs.

Regulations, codes and standards Commercial products require laws and regulations to meet all applicable codes and standards to demonstrate that they are safe, perform as designed, and are compatible in systems in which they are used and most of the countries in the world are working to establish these laws. The use of hydrogen as an energy carrier on a large-scale commercial basis remains largely untested and undeveloped even though it has an established history of industrial use as a chemical feedstock. A major challenge and a potential institutional barrier to the commercialization of hydrogen technologies is the availability of appropriate codes and standards to ensure consistency and, if possible, uniformity of requirements and facilitate deployment. Certification to applicable standards facilitates approval by local code officials and safety inspectors. Uniform standards are needed because manufacturers cannot cost-effectively manufacture multiple products that would be required to meet different and inconsistent standards. It is recognized that domestic and international codes and standards must be established along with affordable hydrogen and fuel cell technologies to enable the timely commercialization and safe use of hydrogen technologies. The development and promulgation of codes and standards are essential to establish a market-receptive environment for commercial, hydrogen based products and systems. International standards There are three separate but related international organizations working on the development of new technology standards: the International Organization for Standardization (ISO), the International Electrotechnical Commission (IEC) and the World Forum for Harmonization of Vehicle Regulations. We are not taking into account the last one devoted to hydrogen for transport applications.


• International organization for standardization. ISO is a worldwide federation of national standards bodies from more than 140 countries. Established in 1947, its mission is to promote standardization to facilitate the exchange of goods and services, and to facilitate cooperation in intellectual, scientific, technological and economic activities. ISO standards are developed through a consensus process.[12] The following ISO Technical Committees are working on standards related to hydrogen and fuel cells for stationary applications

TC 197 - hydrogen technologies: Working groups address standards for systems and devices for the production, storage, transport, measurement, and use of hydrogen (ultimodal transport of liquid hydrogen, hydrogen safety, hydrogen and hydrogen blends, hydrogen fuel quality, water electrolysis, fuel processing, etc.). TC 58 - gas cylinders: fittings and characteristics related to the use and

manufacture of high-pressure gas storage. The working group on gas compatibility and materials coordinates with TC 197.

• International electrotechnical commission. IEC is a leading global organization for preparing and publishing international standards for electrical, electronic and related technologies. The IEC is developing standards for the electrical interface to fuel cells. [13] The following IEC Technical Committees are working on standards related to hydrogen and fuel cells for stationary applications:

TC 105 – fuel cell technology: Is primarily addressing stationary fuel cell power plants, but has also addressed portable and propulsion fuel cells. The working groups in TC 105 include: Terminology, Fuel Cell Modules, Stationary Safety, Performance, Installation, Propulsion, and Safety and Performance of Portable Fuel Cells. Current status of international standards In U.S. for instance, stationary fuel cell standards are the most comprehensively available standards within hydrogen technologies, as the phosphoric acid fuel cell has been commercially available for more than 20 years. Standards are being revised or developed to more adequately represent emerging fuel cell technologies but installation and performance of these equipments is mainly regulated. Nevertheless, most of the international standards remain yet in development or even not available. We following present a brief description of some suitable standards for residential applications. For installation and approval of stationary Fuel Cell Power Systems, the US published the standard NFPA 853. The 2003 Edition has been expanded to


include stationary fuel cells below 50kW. The new chapter, “Fuel Cell Power Systems 50 kW or Less” gives requirements for both outdoor and indoor installations as well as ventilation and fire protection for these smaller systems. The international standard, which is in development is, IEC TC105 WG5. “Fuel Cell Power Systems – Installation”. It provides performance based requirements for the minimum safe installation of indoor and outdoor fuel cell power plants. All comments to the CD by member nations were addressed at a March 2006 meeting, and are now being documented for submittal to TC105. In the US, for electrical interface with house, the standard is NFPA 70, Article 692 and for electrical interface with grid IEEE 1547 Series and State Interconnect Regulations. Interconnecting Distributed Resources with Electric Power Systems. This standard established criteria and requirements for interconnection of distributed resources with electric power systems and provide requirements relevant to the performance, operation, testing, safety considerations and maintenance of the interconnection. The 2005 US Energy Policy Act cited and requires IEEE 1547 on interconnecting distributed energy systems to the electric grid. This IEEE standard was published in July 2003 and designated as ANSI American National Standard in October 2003. For performance of stationary Fuel Cell Power Systems, the US published the standard, ASME PTC 50 which addresses efficiency. The international standard developed by IEC TC105 WG4 is “Test Methods for the Fuel Cell Power System – Performance” IEC 62282-3-2 (2006-03)/EN 62282-3-2:2006. Describes how to measure the performance of stationary fuel cell power systems for residential, commercial and industrial applications. It was published in 2006 as IEC 62282-3-2 (2006-03) and has been adopted as a European Standard as EN 62282-3-2:2006. For Hydrogen Generators, the international community is taking the lead with design standards under development addressing:

• Electrolysis: ISO TC197 WG8. “Hydrogen Generators using Water Electrolysis Process” ISO/CD 22734. 22734-1 “Part 1: Industrial and Commercial Applications”. It is expected to be published as International Standard in July 2007. ISO TC197 WG8. “Hydrogen Generators using Water Electrolysis Process” ISO/CD 22734. 22734-1 22734-2 “Part 2: Residential Applications”. It is expected to be published as International Standard in July 2008 • Fuel Processing: ISO TC197 WG9 developed 16110-1 “Hydrogen Generators Using Fuel Processing Technologies– Part 1 Safety”. This standard applies to packaged, self-contained or factory matched hydrogen generation systems with a capacity less than 400 Nm3/hr (normal cubic meters per hour) that convert a fuel to a hydrogen rich stream of composition and condition


suitable for the type of device using hydrogen (e.g. a fuel cell power system or a hydrogen compression, storage and delivery system). ISO/DIS 16110-1 was approved by TC197 15 to 1 with 6 countries providing comments. The Final Draft International Standard is out for vote until February 21, 2007. There is currently only one standard under development addressing Hydrogen Generator performance (Fuel Processing), developed by ISO TC197 WG9, ISO 16110-2 “Test Methods for the Performance (Efficiency) of Hydrogen Generators Using Fuel Processing Technologies.” This standard covers operational and environmental aspects of the performance of hydrogen generators described in ISO 16110-1. The major issues included efficiency definitions (H2 output/fuel input but also include fuel in, H2 out, steam in and electricity in), operating modes, hydrogen composition measurement and hydrogen impurity levels during transients. The target date for publication is the end of the year 2008. The following standards are under development for Hydrogen Storage, Piping and Handling (Safety): ISO TC197 WG7 “Basic Considerations for the Safety of Hydrogen Systems” ISO/TR 15916:2004. It provides guidelines for the use of hydrogen in its gaseous and liquid forms, identifies the basic safety concerns and risks, and describes the properties of hydrogen that are relevant to safety. Detailed safety requirements associated with specific hydrogen applications are treated in separate international Standards. IEC/TC105 WG3 “Safety”. It is an International standard providing minimum design, construction, operating and quality requirements for stationary fuel cell power plants. All comments (~150) to the CDV by member nations were addressed at a March 2006 meeting, and are now being documented for submittal to TC105. ISO TC197 WG12 “Hydrogen Fuel – Product Specification”. This activity is to update the current standard ISO 14687-1999 that specifies the quality characteristics of hydrogen fuel in order to assure uniformity of the hydrogen product as produced and distributed for utilization in vehicular applications or other fueling applications. ISO TC197 WG13 “Hydrogen Sensors“. While IEC 61779 covers requirements for flammable gas detectors, it doesn’t address all issues critical to hydrogen detectors. This work, which will be known as ISO 24162, will build on 61779 and address measuring range, selectivity, poisoning, concentration levels, and modifications to 61779’s calibration curve and accuracy range. Committee draft ISO/CD 26412 is out for comment until May 9, 2007. IEC/TC31, cooperating on this work, have been asked to comment. IEC/TC31 – “Equipment for Explosive Atmospheres” IEC 61779-1 “Electrical Apparatus for the Detection and Measurement of Flammable Gases – Part 1. General Requirements and Test Methods”. It specifies general


requirements for construction and testing and describes the test methods that apply to portable, transportable and fixed apparatus for the detection and measurement of flammable gas or vapour concentrations with air. The apparatus, or parts thereof, are intended for use in potentially explosive atmospheres. It was published in 1998. At present is under revision and to be reissued as: IEC 60079-29-1 “Electrical apparatus for explosive gas atmospheres-Part 29-1 Electrical apparatus for the detection and measurement of flammable gases- General requirements and test methods”, and IEC 60079-29-2 “Electrical apparatus for explosive gas atmospheres- Part 29-2 Electrical apparatus for the detection and measurement of flammable gases – Guide for the selection, installation, use and maintenance”. Hydrogen safety, codes and standards challenges From a safety, codes and standards perspective, the fundamental challenges to the commercialization of hydrogen technologies are the lack of safety information on hydrogen components and systems used in a hydrogen fuel infrastructure, and the limited availability of appropriate codes and standards to ensure uniformity and facilitate deployment. [14] Some of the specific challenges include:

• Limited Safety Data for Hydrogen Systems. Only a small number of hydrogen technologies, systems and components are in operation and many are in the pre-commercial development phase and still proprietary. As such, only limited data are available on the operational and safety aspects of these technologies. In addition, the historical data used in accessing safety parameters for the production, storage, transport, and utilization of hydrogen are several decades old and need to be assessed and validated. • Liability/Insurability Issues. Lawsuits and insurability are serious concerns that could affect the commercialization of hydrogen technologies. New technologies not yet recognized in codes and standards will have difficulty in obtaining reasonable insurance, and may not be approved in some cases. • Lack of Understanding of Hydrogen Systems. There is currently a general lack of understanding of hydrogen and hydrogen system safety needs among local government officials, fire marshals, and the general public. In addition, there is no comprehensive Handbook of Best Management Practices for hydrogen safety for officials to refer to. • International Competitiveness. International code development is usually complicated and difficult to achieve because of international competitiveness and licensing issues. Governments have a limited role in the development of ISO standards. Inadequate representation by government and


industry at international forums leads to difficulties in promoting the findings of international technical committees to domestic industry experts. Conclusions Faced with the obvious change in the traditional centralised power generation system towards a DG, it is necessary to analyse this new form of power generation to know which are the most suitable technologies and its problems about the integration into the network. Residential Fuel cells are suited for DG in small scale. The owners of the households become the manager of this own energy, producing energy when they need it (or when the energy price is low) and feeding into the grid when they have excess (or when the energy price increase). But furthermore, if fuel cell produces combined heat and power (CHP) every end-user will be able to contribute to a more efficient energy use, reducing CO2 emissions, and achieving a more sustainable energy system. In spite of all the benefits that fuel cell can provide, nowadays is not a cost-effective option because of its high cost. It is believed that mass production of fuel cells will reduce these costs but this would obviously require a growing and sustained market demand. The use of fuel cells into the households as a DG system has some problems to solve related to the stability of the network and quality of electricity supplied. When hydrogen is obtained from renewable sources, fuel cells could increase the use of renewable sources and thus hydrogen would offer a solution to renewable energy's key deficiency, since it's not always available when we need it. In this way it is possible to obtain a major contribution of the renewable sources into the grid electricity and reduce the dependency on fossil fuels. The development and promulgation of codes and standards are essential to establish a market-receptive environment for commercial, hydrogen based products and systems, making possible that hydrogen and fuel cells will play a significant role in the future distributed generation system. References 1. www. idae.es 2. Pehnt, M., and Ramesohl, S. 2003, Fuel cells for distributed power: benefits,

barriers and perspectives, Commisioned by WWF, in co-operation with Fuel Cell Europe, from: www.panda.org/epo

3. Knight, I., Ugursal, I., and Beausoleil-Morrison, I. 2005, Residential Cogeneration Systems:A Review of The Current Technologies.. Annex 42 of the International Energy Agency Energy Conservation in Buildings and Community Systems Programme, from: www.cogen-sim.net.


4. Adamson K.A. 2005, Fuel Cell Today Market Survey: Small Stationary Applications., from: www.fuelcelltoday.com

5. White paper on distributed generation. NRECA (National Rural Electric Cooperative Asociation), from: www.nreca.org

6. Jenkins, N., Alla, R., Crossley, P., Kirschen, D., and Strbac, G. 2000, Embedded generation, The Institution of Electrical Engineers, London.

7. Torrero, E., and McClelland, R. 2002, Residential Fuel Cell Demonstration Handbook.NREL/SR-560-32455, from: www.nrel.gov

8. Graham,G., Druden,Dr A., and Hart, J. 2002, Assessment of the implementation issues for fuel cells in domestic and small scale stationary power generation and CHP applications.ETSU F/03/00235/00/00

9. Galal, D. 2004, Distributed generation (DG)- An option for sustainable energy, available at: www.worldenergy.org

10. Wind power 2006 AEE, from: www.aeeolica.org 11. www.resfc-market.eu 12. www.iso.ch 13. www.iec.ch 14. www.hydrogen.energy.gov

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