1!Electricity production Source: World Energy Outlook 2009!0 4000 8000 12000 16000OilBiomassOther renewablesNuclearHydroGasCoalWorld electricity generation by fuel in the Reference Scenario200720152030TWhImage by MIT OpenCourseWare.Source: World Energy Outlook 2008!Coal Gas Oil Nuclear Hydro Wind Rest ofrenewables250200150100500Power - Generation Capacity Under Construction WorldwideTotal = 613 GWNon - OECDOECDNote: Includes power plants considered as under construction in 2007Source: Platt's World Electric Power Plants Database, Jaunary 2008 versionGW4!Generation technologies!• Hydro plants"• with reservoir"• run-of-the-river"• pump storage"• Thermal plants"• Nuclear"• Coal, oil"• Gas"– simple cycle"– combined cycle"• Other plants: wind, thermo solar, photovoltaic, fuel cells, biomass, geothermal, wave & tidal power, etc. "Image by MIT OpenCourseWare.5!Why a mix of generation technologies?!• Economic reasons"– The uneven demand profile provides opportunities for the different technologies, since they offer different combinations of fixed & variable costs"• Strategic / political reasons"– Fuel diversification is a reasonable strategy "• Environmental reasons"– Generation technologies have very diverse environmental impacts"6!Load-duration curve!base load!medium load!peak load!reserve capacity!operational hours/year!available capacity!In general terms, the generating units in a power system are called to operate (are “dispatched”) in order of the increasing operating costs until all demand is met & some units (or part of them) are kept on “operating reserve” !Pros & Cons of different sources of electricity !“An energy policy for Europe”, EU, January 2007!22!Principle of a thermal unit!generator electricity heat combustion chemical energy (fuel) (boiler) (steam) steamturbine mechanical energy (rotating shaft) !Steam cycle!fuel pump condensor cooling water water, low pressure water, high pressure hot steam, high pressure boiler cold steam, low pressure turbine + - electricity generator 24!Energy balance!fuel generator pump energy hot gases electricity heated cooling water other lossesCombined-cycle units!Gas turbine development led to combined-cycle units: ʻsteam and gasʼ. Such units have high (electric) efficiencies (up to 60%)."Sale of heat less important""Smaller units make on-site electricity production competitive"Combined-cycle generator!compressor air hot gases: source of energy for steam cycle combustion chamber fuel power turbine + - electricity generator1!The electricity distribution network 3!Distribution!• One can distinguish between subtransmission & true distribution networks"• Subtransmission networks cover a region & they have a some kind of meshed topology. They feed distribution networks & some large consumers"• Distribution networks must reach every single end consumer"– Rural distribution networks have a radial topology"– Urban distribution networks are meshed but they are operated radially"9!Storage Main properties of electric storage technologies!Electricity supply comprises many activities… 11!Supply of electricityClassification of the required activities!12!"Commercialization (retailing, supply (UK))!Diversity of services: "• Retailers of captive consumers"• Retailers of consumers that are qualified to choose supplier"– and choose supplier"– but stay with the regulated tariff (if any)!• Traders"• Brokers"13!System Operation!• Coordination activity at system level: To guarantee system security while meeting the market requirements"• System Operator (SO) implements the dispatch of generation & determines the network operation, subject to prescribed technical rules"• SO applies prescribed criteria for network access & informs about estimated access conditions in the short, medium & long run"14!Market Operation (power exchange, PEX)!• PEX facilitates transactions among agents in an organized market"– In principle, this is a non regulated activity"• Typically: management of day ahead transactions"– Hourly (typically) matching of purchasing & selling bids for the next day"• Also: management of other markets"– Shorter term: intra-daily markets, regulation market, etc. "– Longer term: future contracts, forward contracts"• Economic settlement of transactions"15!Service quality 16!Different dimensions of quality of service!• Technical quality of the product"– Continuity of supply"– Technical characteristics of the waveform"• Over-voltages, harmonics, mini-interruptions, flicker"• Commercial quality of service"– Connection / disconnection time, response to queries, metering, general attention to customers, other services"17!Quality of service at delivery!18!Quality of service at wholesale level !• Metric 1: Non served energy (NSE)"– Annual non served demand (MWh) in the entire system because of service interruptions (longer than 1 minute) at wholesale (i.e. transmission network) level Typical reference value that has been used in centralized generation expansion planning: 1day equivalent of non-served demand/10 years • Metric 2: Average interruption time!– This is the NSE divided by the average power (MW) supplied by the system, and it is expressed in minutes TIM = 8760 x 60 x NSE / E E = annual supplied system demand (MWh) Typical reference value could be 15 m/year (e.g. Spain) 19!Quality of service of the transmission network !• The unavailability of a network can be measured by the total amount of time that its lines, transformers & control devices have not been available during the year. Computation of the Unavailability Index (UI) (a component of the remuneration of transmission may be related to this index): ti= Unavailable time for the ith component (line, transformer or control device) (hours) n= Total number of lines, transformers and control devices in the transmission network T= Duration of the considered time period (hours) PNi= Rated capacity (MW) of the lines, transformers and control devices"20!n Σ t · PN UI = i ii = 1 n ·100 Reference value = 3% T Σ PN i i= 1Environmental implications of electricity supply & consumption References: For instance see J.W. Tester et al. “Sustainable energy. Choosing among options”, MIT Press, 2005.