Resource Documents: Grid (164 items)
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Author: Cardoso Marques, António; Alberto Fuinhas, José; and André Pereira, Diogo
• The econometric technique takes into consideration both short- and long-run effects.
• The installed capacity of wind power preserves fossil fuel dependency.
• Natural gas is the main fossil fuel used to back up renewable energy sources.
• The installed capacity of hydropower and solar PV has been substituting fossil fuels.
• Electricity consumption intensity and its peaks have been satisfied by burning fossil fuels.
The electricity mix worldwide has become diversified mainly by exploiting endogenous and green resources. This trend has been spurred on so as to reduce both carbon dioxide emissions and external energy dependency. One would expect the larger penetration of renewable energies to provoke a substitution effect of fossil fuels by renewable sources, in the electricity generation mix. However, this effect is far from evident in the literature. This paper thus contributes to clarifying whether the effect exists and, if so, the characteristics of the effect by source. Three approaches, generation, capacity and demand, were analysed jointly to accomplish the main aim of this study. An autoregressive distributed lag model was estimated using the Driscoll and Kraay estimator with fixed effects, to analyse ten European countries in a time-span from 1990 until 2014. The paper provides evidence for the substitution effect in solar PV and hydropower, but not in wind power sources. [emphasis added] Indeed, the generation approach highlights the necessity for flexible and controllable electricity production from natural gas and hydropower to back up renewable sources. Moreover, the results prove that peaks of electricity have been an obstacle to the accommodation of intermittent renewable sources.
António Cardoso Marques, José Alberto Fuinhas, Diogo André Pereira
University of Beira Interior and NECE-UBI Management and Economics Department, Rua Marquês d′Ávila e Bolama, 6201-001 Covilhã, Portugal
Energy Policy, Volume 116, May 2018, Pages 257-265
Download original document: “Have fossil fuels been substituted by renewables? An empirical assessment for 10 European countries”
Author: Holttinen, Hannele
[abstract] The variations of wind power production will increase the flexibility needed in the system when significant amounts of load are covered by wind power. When studying the incremental effects that varying wind power production imposes on the power system, it is important to study the system as a whole: only the net imbalances have to be balanced by the system. Large geographical spreading of wind power will reduce variability, increase predictability and decrease the occasions with near zero or peak output. The goal of this work was to estimate the increase in hourly load-following reserve requirements based on real wind power production and synchronous hourly load data in the four Nordic countries. The result is an increasing effect on reserve requirements with increasing wind power penetration. At a 10% penetration level (wind power production of gross demand) this is estimated as 1·5%–4% of installed wind capacity, taking into account that load variations are more predictable than wind power variations.
Hannele Holttinen, Technical Research Centre of Finland
Wind Energy 2005; 8:197–218. DOI: 10.1002/we.143
Download original document: “Impact of Hourly Wind Power Variations on the System Operation in the Nordic Countries”
Author: Paatero, Jukka; and Lund, Peter
[abstract] Irregularities in power output are characteristic of intermittent energy, sources such as wind energy, affecting both the power quality and planning of the energy system. In this work the effects of energy storage to reduce wind power fluctuations are investigated. Integration of the energy storage with wind power is modelled using a filter approach in which a time constant corresponds to the energy storage capacity.The analyses show that already a relatively small energy storage capacity of 3 kWh (storage) per MW wind would reduce the short-term power fluctuations of an individual wind turbine by 10%. Smoothing out the power fluctuation of the wind turbine on a yearly level would necessitate large storage, e.g. a 10% reduction requires 2–3 MWh per MW wind.
Jukka V. Paatero and Peter D. Lund
Helsinki University of Technology, Advanced Energy Systems, Espoo, Finland
Wind Energy 2005; 8:421–441. DOI: 10.1002/we.151
Download original document: “Effect of Energy Storage on Variations in Wind Power”
Author: Ongena, Jozef; István Markó; Koch, Raymond; and Debeil, Anne
If the aim is to decarbonize the electricity sector and phase out nuclear power, then renewable energy remains as the only source of electricity. As wind and solar photovoltaics (PV) are a major fraction (in Germany about 65% of the total renewable electricity production) one then must cope with strong intermittency. The consequences show up most prominently during dark and cloudy periods without wind.
The reality of this last statement is illustrated in Fig. 1, showing the evolution of the electricity production in Germany for January 2017. Due to lack of wind and sunshine in the second half of January most of the German electricity during that whole period was produced by conventional power sources – lignite, coal, gas and nuclear power. On the morning of the 24th of January 2017 a nearly total collapse of the German electricity supply took place. It could have had consequences throughout Europe and was only avoided by putting into operation all possible fossil power plants in Germany, including the oldest and dirtiest ones.
Fig. 1: Electrical power consumption and production in Germany (in MW) by various sources for January 2017: grid load (brown), sum of onshore and offshore wind (blue), solar PV (yellow), installed iRES [intermittent renewable energy sources] capacity (light green background color). Although the iRES capacity is exceeding the grid load, it could only provide a fraction of the German electrical power needs during this dark period without sufficient wind and most of the power was produced by conventional power sources (fossil and nuclear). Especially the period 16-25 January 2017 demonstrates the need for large additional backup power systems (that are evidently non-renewable) or storage.
This graph also leaves no doubt about the storage problem. During the 10 days between 16 and 25 January, equivalent to 240h, the difference between the iRES produced electrical power and the electrical power needs of Germany varied between 50 and 60GW, i.e. between 12000 and 14400 GWh of electrical energy was missing. German electrical storage systems could not have supplied this large amount of energy, as the total storage capacity in Germany is about 40GWh (mainly hydro). The missing electrical energy represents thus 300-360 times the German electrical storage capacity. Including also the 12 dark and wind still days in December 2016, the missing energy would increase to about 32TWh, i.e. about 800 times the currently existing storage capacity in Germany. Note that such long low iRES power production intervals are not an exception; similarly, long periods of low combined solar PV and wind power production were observed regularly in the past years, not only in Germany but in several EU countries and predominantly simultaneously, see also below. …
The electricity production from renewable systems is characterized by a low capacity factor. In Germany with its large fleet of wind and solar PV systems, this is ~15%, resulting from ~11% for solar PV and ~18% for wind (sum of offshore and onshore wind). The consequences are shown in Fig. 2, documenting the evolution in Germany of the installed capacity and power production from solar PV and wind; also indicated are the minimum and maximum power load of the grid. It is clear (i) that although the iRES installed capacity is huge (exceeding at the moment already the maximum power load on the German grid), its contribution to the German electrical energy needs is limited and (ii) that the peaks of the iRES production increasingly cross the lines of minimum load, thus leading to more and more excess production. For the moment export to neighboring countries is still a solution. But this will have to change when the iRES production in other EU countries also will increase in the near future.
Fig. 2: Electrical power production (in GW) by wind (blue) and the sum of solar PV and wind (red) compared with maximum and miminum grid load. As the installed renewable capacity increases, the minimum grid load is increasingly exceeded, leading to overcapacity and export of surplus energy, often at negative prices. …
Export of electricity is needed not only on days with a large iRES power production, but paradoxically also on days with a minimal iRES power production. Indeed, on such days the backup production is maximal and cannot be easily regulated in the short time intervals, which characterize the intermittency of the renewable power from sun and wind. At low iRES production most of the iRES power serves only to increase the export (in several cases at negative prices) as illustrated in Figs. 4a and b and discussed in detail in D. Ahlborn, H. Jacobi, World of Mining, Surface and Underground 68, 2-6 (2016). Thus it comes as no surprise that there is a clear correlation between iRES power production (low or high) and export of electricity from Germany, as illustrated in Fig. 4b. This power is not totally lost, as it can help other countries to reduce their CO₂ output. However, the German taxpayer pays for this, and such a solution can only be temporary. Contrary to what one would expect, these massive and rather unpredictable imports are not really welcomed in the concerned neighboring countries as (i) local power plants have to reduce or shut down, reducing their profitability, and (ii) it increasingly causes overloads in the national grids of those countries. For such reasons Poland and the Czech Republic are installing phase shift transformers at their borders (paid by Germany) to reflect any dangerously high excess electrical energy imports back to Germany.
Fig. 4a: Example of the time evolution of iRES renewable electricity production during a dark and wind still period and compared to the electricity export for Germany (16-25 Jan 2017)
Fig. 4b: Hourly correlation between electricity production from renewable sources (wind + PV) and electricity export in Germany (February 2015)
These exports can only be a temporary solution because the same weather patterns often cover large surfaces of Europe. The consequence thereof is illustrated in Fig. 5, showing a comparison between the instantaneous wind power production from Germany and the sum of the wind production in 15 other EU countries: except for Spain, the correlation in the electricity production between the different countries is clearly visible. Excess wind power in Germany signifies thus also excess wind power in neighbouring countries. The difference in the timing of the maxima and minima in wind production in Spain compared to the rest of Europe, can help to average the fluctuations to a certain, albeit limited extent. One could wonder if the averaging effect of solar photovoltaic power could contribute. In fact, such an effect is nearly absent, as shown by a recent study. The same study shows that if one would use a EU wide 100% iRES electrical network, able to transport excess electrical energy production between the various European countries, typical German grid fluctuations could be reduced by 35% and the maximal storage capacity by 28% (with a 30% fluctuation level on those numbers due the varying weather conditions from year to year). Interconnector lines with a capacity of tens to hundreds of GW will then be needed throughout Europe. The export (and storage) problem can thus indeed be somewhat reduced but they will be far from totally eliminated. Other solutions to avoid the enormous excess energy will have to be found.
Fig. 5: Instantaneous wind power production in MW in Germany (dark blue) compared to the wind power production from 15 EU countries (various colors), illustrating the close correlation between wind power Europe wide. This graph clearly shows consequences for export of excess intermittent electrical power between EU countries in the future, and the very limited extent of possible ‘averaging’ of excesses throughout Europe. …
A large fraction of the produced iRES power in Germany is exported. The export was nearly stable and negligible in the years before the massive introduction of renewable power and has increased ever since, with a rapid increase in the last 5 years up to about 25% of the produced renewable energy or about 55TWh (Fig. 8). The exported energy matches the yearly produced photovoltaic energy or 2/3 of the produced wind power. However, export of excess energy can only be temporary if renewable energy is to be deployed in all EU countries, given the strong correlation between the weather in neighboring countries as already discussed in Section 2.
Fig. 8. Evolution of the total iRES electrical energy production and net electrical energy export (in TWh) over the last 26 years in Germany. The total photovoltaic production (dotted orange curve) or 66% of the total wind energy production (dashed blue curve) follows remarkably close the export curve.
Go to original document: “Hidden consequences of intermittent electricity production”