Towards the Green Power System

The installation of new renewable generation capacity was at first dominated by wind-power. But as most of the more profitable sites in northern and east-ern Germany were allocated, or not included for development due to political

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0 20 40 60 80 100 120 140

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

Renewable Generation [TWh]

Hydro Wind Biomass

Biogenic Waste PV Geothermal

0 10.000 20.000 30.000 40.000 50.000 60.000 70.000

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

Renewable Generation Capacity [MW]

Hydro Wind Biomass

Biogenic Waste PV Geothermal

2011: 123,186 TWH 2011: 65,698 MW

Figure 2.1: Development of renewable electricity generation and capacity in Germany since 1990, BMU (2012a).

reasons, Photovoltaics (PV) increasingly contributed to the new capacity as in-stallation prices dropped from 2006 on to the present day in 2013. Biomass and especially Biogas contributed increasingly, reaching a level of 5.4 GW of installed capacity at the end of 2011 (BMU, 2011). Wind-power topped 29 GW and PV more than 25 GW in 2011 while installation rates for 2012 kept growing even though the feed in tariff for PV was substantially lowered to slow down instal-lations for reasons of cost control and grid stability, resulting in a installed PV capacity of over 29.7 GW in mid-2012 (BSW, 2012). Through this increasing dy-namic in the installation of renewable generation sources, Germany was able to cover more than 20 % of its gross yearly power consumption by renewable sources at the end of 2011 (BMU, 2012a). The German power sector is thus being reshaped continuously by three major driving forces: the market liberalization process which now focuses on a stronger connection and synchronization with the surrounding countries, the dynamics of the renewable generation develop-ment and by the stepwise nuclear phase-out until 2022.

These developments put a high pressure of the conventional power system ar-chitecture. This architecture was defined by the needs of centralized integrated utilities formed by the developments in the beginnings of the power system as described above. The main structure relies on three general voltage levels, a high voltage (HV) transmission and subtransmission network (including voltages be-tween 35 - 110 kV, and 230 - 380 kV for Extra-HV), a medium voltage distri-bution network (voltages of 1kV - 30 kV) for regional and shorter interregional connection, and the low voltage network with 0.22-0.38 kV for the connection of end-customers (Erdmann and Zweifel, 2007; El-Hawary, 2008).

The transmission and in particular the distribution networks were designed

Institute of Information Systems and Management 14 25.10.2012 A. Schuller – R2V: Price Based Charging Coordination for EVs

High Voltage (HV) Medium Voltage (MV) Low Voltage (LV) TSO

System  Balance

Conventional Power System

Unidirectional  Energy Flow

Figure 2.2: Structure and value chain of the conventional power system. (Own illustra-tion and according to Valocchi et al. (2007))

to deliver the energy from the centralized power generation unit to the more or less distant customers on the medium and low voltage network. This included only a unidirectional flow of energy from the source to the consumer, cf. Figure 2.2. In this system distribution level companies would serve their customers and also communicate a forecast of the expected load based on historic data and weather conditions of their control region to the respective transmission system operator (TSO) or independent system operator in the North American power system. The TSO/ISO would then determine for at least one day ahead for each 5-15 minute time interval of the next day, which load was expected and would dispatch the available generation accordingly. This generation used to be, and still is in large parts constituted by thermal power plants that can be controlled in their output in order to follow the load in every time step. The economic dispatch will be further addressed in section 2.5. Also the TSO or ISO is operating the system and purchases ancillary services in order to guarantee a stable system frequency of 50 Hertz (Hz) in Europe, or 60 Hz in the U.S.. This is achieved by balancing system load and generation in every instant during operation.

The general value creation chain and service delivery was organized accord-ing to this centralized energy delivery paradigm. The vertically integrated util-ities often combined several or all of these steps in their company, from

gener-ation to transmission and distribution as well as sales, marketing and metering of end-customers. In this architecture the customer was mainly passive and not metered on a real time basis. As there was only a unidirectional power flow, there also was only a mostly unidirectional information flow, from the utility to the consumer, in general only for administration or billing purposes (Valocchi et al., 2007). The mentioned drivers are increasingly altering the requirements to the power system, which with a growing share of intermittent generation, needs do become more flexible in balancing load and generation as it is cur-rently capable of when relying on the conventional system structure. Balancing requirements are mostly met by flexible generation units like combined cycle gas turbines (CCGT) or pumped hydro generation that can respond with high power change gradients to the requirements of the grid. These resources though are limited in their availability, be they constrained by the geographic properties of a country or the costs for keeping power plants on stand-by for renewable generation drop-outs or sudden load changes that they have to balance. There-fore, with increasing intermittent resources on the grid, a more flexible demand side is technologically necessary and also economically required, (Stoft, 2002;

Ramchurn et al., 2012).

The development of the internet and its tremendous impact on nearly all sec-tors of the economy and society also enables a different way to operate and co-ordinate the power system. The increasingly distributed structure of generation and incrementally added flexible demand resources need to be coordinated to respond to fluctuations in the power grid. This requires an additional layer of ICT infrastructure for communication between these resources and the TSO / ISOs and with each other. Enabling communication and coordination between distributed generation and demand resources and the conventional actors in the power system can be facilitated by the infrastructure and the concept of the

"Smart Grid", which will be explained in the next section.