Features of an electricity supply system based on variable input

Abstract. Wind and solar electricity is produced without direct CO 2 emissions. However, the introduction of this electricity in the grid is delicate due to the intermittent character of its sources. Wind and solar production is characterized by multiple, strong variations in the electric power. These variations put stress on the grid where the total production of electricity must always be equal to the consumption. We present a synthesis of five studies conducted for Germany and France with different assumptions of electricity mixes, all with large shares of wind and solar power. These mixes are subjected to the dynamics of wind and solar production as recorded in 2010 (Germany), 2012 and 2013 (Germany and France). Common structural trends are exhibited when the results of simulations (instantaneous power distributions and average annual values) are expressed as a percentage of the annual reduced load to be produced by these intermittent energies. We focus on the evaluation of these trends and the resulting constraints on the grid. The results obtained make it possible to anticipate the problems brought about by a large share of renewable intermittent energies in the production of electricity. They show the need for backup production in order to complement the intermittent sources. This leads to CO 2 emissions unless storage systems of large capacity are available.World electricity production relies mainly on fossil fuels and, consequently, is a big contributor to CO 2 emissions. Electricity use is growing and will continue to grow, as more recent applications develop, e.g. internet and electric cars. In order to reduce their carbon footprint, many countries encourage and subsidize the development of electricity production from wind and solar photovoltaic energy sources. After construction of their infrastructure, both are free of direct emission of CO 2 while operating. However, their production depends directly on intermittent fluxes: solar irradiation and wind, caused by the rotation of the earth and the thermodynamics of the atmosphere. Constraints arise from these intermittent (periodic and stochastic) productions and from the present impossibility to store electricity in large quantities. When available, storage is not direct but is linked to conversion to another form of energy and thus requires two transformations, each with losses. The management of electricity in the grid requires the equilibrium of production and consumption at all times. Any imbalance results in variations of the voltage or frequency of the electric power that can be detrimental to the consumer and even lead to power outages. Thus, power variations must be studied, known and managed, before large quantities of intermittent energy can be injected into the grid.In order to study these power variations, a method has been developed in ref.[1] based on the temporal evolutions of consumption and of wind and solar production during one year. After a brief summary of the method, we present and compare the results obtained from the data obta...

Section: For Re 100% Share and Installed Capacitiessupporting

confidence: 86%

Section: Counteractive Measuresmentioning

confidence: 99%

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Electricity production by intermittent renewable sources: a synthesis of French and German studies

Grand¹,

Brun²,

Vidil³

et al. 2016

“…No specific storage technology is assumed. The capacity is lowest in case of the optimal mix because the storage can be filled in both seasons -during winter with wind and during summer predominantly with PV power [19] allowing thus two periods per year where the storage level is minimal. A complete storage of the surplus energy for the optimal-mix case would require a storage capacity of 33 TWh.…”

Section: Surplus Power Storage and Demand-side Managementmentioning

confidence: 99%

Electricity by intermittent sources: An analysis based on the German situation 2012

Wagner

2014

Abstract. The 2012 data of the German load, the on-and offshore and the photo-voltaic energy production are used and scaled to the limit of supplying the annual demand (100% case). The reference mix of the renewable energy (RE) forms is selected such that the remaining back-up energy is minimised. For the 100% case, the RE power installation has to be about 3 times the present peak load. The back-up system can be reduced by 12% in this case. The surplus energy corresponds to 26% of the demand. The back-up system and more so the grid must be able to cope with large power excursions. All components of the electricity supply system operate at low capacity factors. Large-scale storage can hardly be motivated by the effort to further reduce CO 2 emission. Demand-side management will intensify the present periods of high economic activities. Its rigorous implementation will expand the economic activities into the weekends. On the basis of a simple criterion, the increase of periods with negative electricity prices in Germany is assessed. It will be difficult with RE to meet the low CO 2 emission factors which characterise those European Countries which produce electricity mostly by nuclear and hydro power.

“…The general procedure for the present analysis is described in [2] and applications for Germany, France, Italy and several European countries are given in [3][4][5][6][7]. Furthermore, recent studies on the gross wind situation in the European countries [7] have shown that further inter-countries distribution net connections can only partly take up the intermittent wind surplus simply because the European, and in particular, the northern European countries have a rather similar wind pattern.…”

Section: Introductionmentioning

confidence: 99%

Study on a hypothetical replacement of nuclear electricity by wind power in Sweden

Wagner

Rachlew

2016

The Swedish electricity supply system benefits strongly from the natural conditions which allow a high share of hydroelectricity. A complete supply is, however, not possible. Up to now, nuclear power is the other workhorse to serve the country with electricity. Thus, electricity production of Sweden is basically CO 2 -free and Sweden has reached an environmental status which others in Europe plan to reach in 2050. Furthermore, there is an efficient exchange within the Nordic countries, Nordpol, which can ease possible capacity problems during dry cold years. In this study we investigate to what extent and with what consequences the base load supply of nuclear power can be replaced by intermittent wind power. Such a scenario leads unavoidably to high wind power installations. It is shown that hydroelectricity cannot completely smooth out the fluctuations of wind power and an additional back-up system using fossil fuel is necessary. From the operational dynamics, this system has to be based on gas. The back-up system cannot be replaced by a storage using surplus electricity from wind power. The surplus is too little. To overcome this further strong extension of wind power is necessary which leads, however, to a reduction of the use of hydroelectricity if the annual consumption is kept constant. In this case one fossil-free energy form is replaced by another, however, more complex one. A mix of wind power at 22.3 GW plus a gas based back-up system with 8.6 GW producing together 64.8 TWh would replace the present infrastructure with 9 GW nuclear power producing 63.8 TWh electricity. The CO 2 -emission increases to the double in this case. Pumped storage for the exclusive supply of Sweden does not seem to be a meaningful investment.