The Optimal Mix for a Powerful Europe
The recent financial and economic crisis shows that unlimited and unregulated growth is not sustainable. Increasing energy prices, dependency on energy imports and the need to mitigate climate change require joined-up thinking within Europe to promote a sustainable and climate-friendly power supply system that is driven by solar, wind and other renewable energies. Smart investors will soon be inspired by this vision to make it happen. The central insight is that wind, solar, pan-European transmission and storage form an interdependent system. This system has to be optimised according to the specific costs of each of these technologies.
By Lueder von Bremen, ForWind – Center for Wind Energy Research, University of Oldenburg, Germany. Co-authors: Jens Tambke, Jan De Decker and Kurt Rohrig
The complexity of today’s power system is vast in operation and difficult to model. In our studies that focus on 100% renewable electricity in Europe, we have to determine (i.e. to compute) where wind and solar power plants can be sited favourably and which capacities of interconnectors and storage capacities are needed. Future electricity consumption is estimated to be unchanged from today; that is, higher energy efficiency and energy savings are thought to balance the increased demand resulting from E-Mobility. Positive effects resulting from demand-side management, smart-grids, hydro-electric plants and other controllable renewables (e.g. biogas, geothermal) or back-up power plants will decrease the needed storage and transmission capacity, but these components have not been considered in this study.
Despite the fact that the weather (and thus energy) is hard to predict one week in advance, we are confident that the spatio-temporal pattern of generation from wind and solar resources will be virtually unchanged from what we know today. Thus, the characteristics of wind flow and solar radiation in the past are used to simulate the power that will be made available by large-scale onshore and offshore wind farms and photovoltaic (PV) plants.
Time Series of Wind and Solar Power
A mesoscale atmospheric model provides wind speed (Figure 1), global radiation and ambient temperature to simulate wind and PV power at each grid point. Several grid points of the weather model are aggregated to regions, giving more weight to grid points (sites) with greater resources (wind, solar radiation). The regions are fully interconnected with their neighbours. Some countries (e.g. Germany) are subdivided into up to six regions. In total, we have simulated 33 offshore and 50 onshore regions. The hourly temporal resolution considers the diurnal cycle in PV (and wind).
Scenarios
The scenarios of onshore and offshore wind power capacities in 2020 follow national targets and the TradeWind study and recent EWEA scenarios. The capacity of PV is estimated to have grown to nearly 70GW by 2020 for the EU-27. The 100% renewables scenario is based on the spatial distribution estimated for 2020, but the total of wind and PV power is scaled to meet the average consumption. It can be assumed that the spatial concentration of wind and solar power capacities decreases from 2020 onwards as more and more diverse sites in all countries are utilised. This will have the favourable effect that short-term fluctuations will decrease as well.
Team Play of Solar and Wind
In the past the change of seasons affected consumption in Europe, with highest demand in winter (Figure 2). With the increasing proportion of wind and solar power and, especially, in a 100% renewable scenario, the seasonal cycle of renewable resources like wind and global radiation has to be considered. Model results show that the variation from winter to summer is of high amplitude, with the solar power maximum in summer and the minimum in winter. It is fortunate that the seasonal cycle of wind power in Europe is complementary, with sufficient wind during the winter months. The mix between solar and wind power has been adjusted in Figure 2 to best match the consumption; that is, 60% of the energy is generated by wind power and 40% by PV. These shares are similar to results recently published in Renewable Energy by Heide et al. (doi:10.1016/j.renene.2010.03.012) )who used the same wind and PV power simulations for their work). It is shown that a storage capacity that holds roughly 11% of Europe’s annual consumption is required to balance the inherent seasonal cycle of wind and PV.
It is currently being suggested that this high amount of storage can be reduced efficiently by a smart ‘over-installation’ of wind and solar (e.g. 130%) and/or by other sources of power (e.g. hydro-electric, biogas, back-up power by efficient combined heat and power plants (CHP) and natural gas plants). The use of excess wind and solar power in the heating sector might also be an option.
Transmission Reduces Storage Needs
The trade-off between transmission and storage in high renewables scenarios is being widely discussed, particularly with respect to operating costs and the investments needed under the constraints of grid stability and feasibility (political and technical). The demand for storage has been investigated for two extremes (Figure 3). Firstly, Europe is modelled as a ‘copperplate’, with unlimited transmission capacities between the regions; that is, only the total European imbalance between generation and consumption has to be covered by stored energy. In the second case each region uses its own storage and energy exchange between regions is disabled.
Transmission between regions reduces the demand for stored energy up to 45% depending on the mix between wind and solar. The reduction in stored energy avoids a lot of energy losses (depending on the storage efficiency) and is better invested in a ‘Supergrid’.
With a share of 80% wind and 20% solar energy the demand for stored energy is smallest. The difference between this figure and the seasonal mix of 60/40% is due to the high turnover induced by the solar diurnal cycle. A highly efficient storage to level out the intra-daily cycle of solar would separate the two timescales; that is, an optimal mix between solar and wind can be found for all timescales.
Investigating the Supergrid for Wind Power
The OffshoreGrid project is a techno-economic study to analyse different offshore grids in Northern Europe along with a suitable regulatory framework that considers technical, economic, policy and regulatory aspects. The geographical scope is, at first, the windy regions around the Baltic and North Seas, the English Channel and the Irish Sea. For all European countries specific wind power capacity scenarios have been developed (Figure 4). In a second phase, the results will be applied to the Mediterranean region. The experiences and methodologies gathered in OffshoreGrid will serve as the backbone to further renewable integration studies including solar power and other renewables.
Different blueprints for offshore grids in the Baltic and North Sea (Figure 5) are developed taking into account: (a) the costs of the various options, (b) their socio-economic value, (c) the regional/internal power market designs and (d) the regulatory framework for the remuneration and operation of the grid. It is within the scope of OffshoreGrid to achieve acceptance and acknowledgement of the results by the main stakeholders including the European Commission, national policy makers, transmission system operators (TSOs), regulators, offshore generation developers and other users of the sea.
Acknowledgements
We thank Siemens AG for funding the study carried out at the division of Energy Economy and Grid Operation at the Fraunhofer Institute for Wind Energy and Energy System Technology (IWES). The European Agency for Competitiveness and Innovation – Intelligent Energy for Europe (IEE) supports the ‘OffshoreGrid’ Project. ForWind is supported by the Federal Ministry for Sciences and Culture of Lower Saxony (Germany).
Biography of the main Author
Dr Lueder von Bremen is a meteorologist and worked from 2001 to 2005 at the European Centre for Medium-Range Weather Forecasts, where he became an expert on Numerical Weather Forecasting. Since 2005 he has developed various wind power forecasting models and renewable energy scenario simulations.{/access}
The recent financial and economic crisis shows that unlimited and unregulated growth is not sustainable. Increasing energy prices, dependency on energy imports and the need to mitigate climate change require joined-up thinking within Europe to promote a sustainable and climate-friendly power supply system that is driven by solar, wind and other renewable energies. Smart investors will soon be inspired by this vision to make it happen. The central insight is that wind, solar, pan-European transmission and storage form an interdependent system. This system has to be optimised according to the specific costs of each of these technologies.By Lueder von Bremen, ForWind – Center for Wind Energy Research, University of Oldenburg, Germany. Co-authors: Jens Tambke, Jan De Decker and Kurt Rohrig
{access view=!registered}Only logged in users can view the full text of the article.{/access}{access view=registered}In the long term, European electricity will dominantly be supplied by solar and wind power. Both power sources fluctuate with the weather, so we will inevitably have to think carefully about the infrastructure of Europe’s future power supply system. A Supergrid (on and offshore) will have to be in place besides new flexible units and storage facilities to balance fluctuations and to transfer wind and solar energy from places where they are abundant. Furthermore, to alleviate the inherent seasonal characteristics of wind and solar power generation in Europe and to secure the power supply, large-scale storage will be needed. A study that has been funded by Siemens AG shows that an optimal mix of solar and wind power generation exists which determines a minimum investment into storage and transmission capacities.
Modelling the Future Power Supply SystemThe complexity of today’s power system is vast in operation and difficult to model. In our studies that focus on 100% renewable electricity in Europe, we have to determine (i.e. to compute) where wind and solar power plants can be sited favourably and which capacities of interconnectors and storage capacities are needed. Future electricity consumption is estimated to be unchanged from today; that is, higher energy efficiency and energy savings are thought to balance the increased demand resulting from E-Mobility. Positive effects resulting from demand-side management, smart-grids, hydro-electric plants and other controllable renewables (e.g. biogas, geothermal) or back-up power plants will decrease the needed storage and transmission capacity, but these components have not been considered in this study.
Despite the fact that the weather (and thus energy) is hard to predict one week in advance, we are confident that the spatio-temporal pattern of generation from wind and solar resources will be virtually unchanged from what we know today. Thus, the characteristics of wind flow and solar radiation in the past are used to simulate the power that will be made available by large-scale onshore and offshore wind farms and photovoltaic (PV) plants.
Time Series of Wind and Solar Power
A mesoscale atmospheric model provides wind speed (Figure 1), global radiation and ambient temperature to simulate wind and PV power at each grid point. Several grid points of the weather model are aggregated to regions, giving more weight to grid points (sites) with greater resources (wind, solar radiation). The regions are fully interconnected with their neighbours. Some countries (e.g. Germany) are subdivided into up to six regions. In total, we have simulated 33 offshore and 50 onshore regions. The hourly temporal resolution considers the diurnal cycle in PV (and wind).
Scenarios
The scenarios of onshore and offshore wind power capacities in 2020 follow national targets and the TradeWind study and recent EWEA scenarios. The capacity of PV is estimated to have grown to nearly 70GW by 2020 for the EU-27. The 100% renewables scenario is based on the spatial distribution estimated for 2020, but the total of wind and PV power is scaled to meet the average consumption. It can be assumed that the spatial concentration of wind and solar power capacities decreases from 2020 onwards as more and more diverse sites in all countries are utilised. This will have the favourable effect that short-term fluctuations will decrease as well.
Team Play of Solar and Wind
In the past the change of seasons affected consumption in Europe, with highest demand in winter (Figure 2). With the increasing proportion of wind and solar power and, especially, in a 100% renewable scenario, the seasonal cycle of renewable resources like wind and global radiation has to be considered. Model results show that the variation from winter to summer is of high amplitude, with the solar power maximum in summer and the minimum in winter. It is fortunate that the seasonal cycle of wind power in Europe is complementary, with sufficient wind during the winter months. The mix between solar and wind power has been adjusted in Figure 2 to best match the consumption; that is, 60% of the energy is generated by wind power and 40% by PV. These shares are similar to results recently published in Renewable Energy by Heide et al. (doi:10.1016/j.renene.2010.03.012) )who used the same wind and PV power simulations for their work). It is shown that a storage capacity that holds roughly 11% of Europe’s annual consumption is required to balance the inherent seasonal cycle of wind and PV.
It is currently being suggested that this high amount of storage can be reduced efficiently by a smart ‘over-installation’ of wind and solar (e.g. 130%) and/or by other sources of power (e.g. hydro-electric, biogas, back-up power by efficient combined heat and power plants (CHP) and natural gas plants). The use of excess wind and solar power in the heating sector might also be an option.
Transmission Reduces Storage Needs
The trade-off between transmission and storage in high renewables scenarios is being widely discussed, particularly with respect to operating costs and the investments needed under the constraints of grid stability and feasibility (political and technical). The demand for storage has been investigated for two extremes (Figure 3). Firstly, Europe is modelled as a ‘copperplate’, with unlimited transmission capacities between the regions; that is, only the total European imbalance between generation and consumption has to be covered by stored energy. In the second case each region uses its own storage and energy exchange between regions is disabled.
Transmission between regions reduces the demand for stored energy up to 45% depending on the mix between wind and solar. The reduction in stored energy avoids a lot of energy losses (depending on the storage efficiency) and is better invested in a ‘Supergrid’.
With a share of 80% wind and 20% solar energy the demand for stored energy is smallest. The difference between this figure and the seasonal mix of 60/40% is due to the high turnover induced by the solar diurnal cycle. A highly efficient storage to level out the intra-daily cycle of solar would separate the two timescales; that is, an optimal mix between solar and wind can be found for all timescales.
Investigating the Supergrid for Wind Power
The OffshoreGrid project is a techno-economic study to analyse different offshore grids in Northern Europe along with a suitable regulatory framework that considers technical, economic, policy and regulatory aspects. The geographical scope is, at first, the windy regions around the Baltic and North Seas, the English Channel and the Irish Sea. For all European countries specific wind power capacity scenarios have been developed (Figure 4). In a second phase, the results will be applied to the Mediterranean region. The experiences and methodologies gathered in OffshoreGrid will serve as the backbone to further renewable integration studies including solar power and other renewables.
Different blueprints for offshore grids in the Baltic and North Sea (Figure 5) are developed taking into account: (a) the costs of the various options, (b) their socio-economic value, (c) the regional/internal power market designs and (d) the regulatory framework for the remuneration and operation of the grid. It is within the scope of OffshoreGrid to achieve acceptance and acknowledgement of the results by the main stakeholders including the European Commission, national policy makers, transmission system operators (TSOs), regulators, offshore generation developers and other users of the sea.
Acknowledgements
We thank Siemens AG for funding the study carried out at the division of Energy Economy and Grid Operation at the Fraunhofer Institute for Wind Energy and Energy System Technology (IWES). The European Agency for Competitiveness and Innovation – Intelligent Energy for Europe (IEE) supports the ‘OffshoreGrid’ Project. ForWind is supported by the Federal Ministry for Sciences and Culture of Lower Saxony (Germany).
Biography of the main Author
Dr Lueder von Bremen is a meteorologist and worked from 2001 to 2005 at the European Centre for Medium-Range Weather Forecasts, where he became an expert on Numerical Weather Forecasting. Since 2005 he has developed various wind power forecasting models and renewable energy scenario simulations.{/access}
