In the following it shall be shown that a decentralized energy supply from 100% renewable sources is physically and economic feasible and reasonable and can be realized till 2030.
The proposed system has numerous advantages compared to the current one.
Firstly and obviously there is the ecological aspect. Power production from nuclear and fossil fuels cause severe environmental damages. An energy supply based on wind and sun on the other hand makes a sustainable environmentally friendly economy possible.
By using renewable energies the negative health impact and hazards for the population caused by radioactive exposure (operating nuclear plants, nuclear meltdowns, radioactive waste) and air pollution (causing 7 million deaths worldwide annually) can be avoided.
Renewable energies are available in every country. By using them autarky in the energy sector is possible and international conflicts about fossil fuels (e.g. oil) are prevented. Thus renewable energies can contribute to peace worldwide.
Renewable energies make a stable energy supply possible with lower costs in the short- and long-term – for the whole economy and for the individual consumers.
First, one should know how big the current total energy demand is (divided into the sectors electricity, heat and transport). Renewable energies have to be able to satisfy this demand.
In Germany approx. 600 TWh of electricity are produced annually. This corresponds to approx. 20 % of the total energy demand. Over 20% of the electricity demand is already supplied by renewable energies.
The annual heat demand in Germany is 1200 TWh. This corresponds to approx. 50 % of the total energy demand.
The annual energy demand of the transport sector in Germany is 730 TWh corresponding to approx. 30 % of the total energy demand.
The total annual energy demand in Germany therefore is approx. 2500 TWh..
Is there enough wind and sun in Germany to produce the needed 2500 TWh annually?
In Germany a photovoltaics (pv) power plant has an average of 900 full load hours. Thus approx. 2800 GWp installed solar power is needed to supply the complete energy demand solely from photovoltaics. Depending on the used technology and type of installation 10 to 30 square meters are needed for every kWp installed solar power. This translates to 28 000 - 84 000 km² or 7.8-23.5 % of the total area of Germany for a pure solar energy supply.
As a comparison: The accumulated settlement and traffic area in Germany is 46 789 km² or 13.1 % of the total area. The area for bioenergy crops is 22 800 km² or 6.4 % of the total area.
A study commissioned by the German Federal Environmental Agency assumes that 13.8 % of the total area of Germany is suitable for wind turbines. This is enough for 1 190 GWp of installed wind power and an annual energy production from wind power of 2900 TWh.
The complete energy demand of Germany of 2500 TWh annually can therefore be supplied by photovoltaics and wind turbines.
An increase in power efficiency can additionally considerably reduce the energy demand.
The power efficiency of electric appliances can be increased (LED-lights, more efficient stand by mode, Off-switch in stead of standby,…).
When electrifying the transport sector there is an increase of power efficiency just because of the electrification (electric motors are much more efficient than combustion engines). A traffic system based more on public transportation, bicycles (tricycles, e-bikes) and intercity transport by bus and train (and potentially Hyperloop) and less on cars can significantly reduce the energy demand.
The heat demand can be reduced by stricter energy standards for buildings and by energetic redevelopment. Technically this is possible amongst others by a better heat insulation and an efficient ventilation system with heat recovery.
Operating reserves and electricity storages are generally needed because of the fluctuating electricity consumption. In the current electricity system with large central power plants there is the problem that the output of these plants can not or only insufficiently be regulated. Therefore an electricity storage is needed to be able to run the plants at full power during periods of reduced power consumption (e.g. during night) and thus to insure the economic operation of the plants.
An energy supply from 100 % renewable energies (mainly sun&wind) with fluctuations of the electricity production (s. Fig. 1 and 2) will initially have a much higher storage demand.
Fig. 1: Annual and daily fluctuations of electricity production of wind turbines in Germany
Fig. 2: Annual and daily fluctuations of electricity production of solar plants in Germany
The fluctuations of the solar and wind electricity production can however cancel each other out (s. Fig. 3). Across the board one can say for Germany: Much wind in winter, much sun in summer. Therefore a combination of wind and solar energy production is reasonable. In Germany, due to the high heat demand, the energy consumption is high in winter. Therefore it will probably be more economic to have more wind electricity compared to solar electricity (e.g. 60/40 or 70/30 ratio). In sunnier countries closer to the equator (e.g. Spain, Tanzania) with a higher cooling and much lower heating demand a higher solar share is reasonable.
Fig. 3: Electricity production from wind turbines and solar power plants in Germany in 2012 (source: FfE e.V.)
Locally and chronologically there can be stronger fluctuations as Fig. 3 might suggest. It shows regional (whole Germany) and temporal (monthly) average values. The data shows however that at least the demand for seasonal electricity storage can be reduced by a combination of wind and solar energy production.
Additionally the fluctuations of wind and solar energy electricity production can be significantly reduced by an appropriate optimization of the power plants.
Instead of installing solar systems only on roofs facing south (north for the southern hemisphere) they can also be installed on west and east facing roofs and faces of buildings. Thus more solar electricity is produced during the morning- (east facing) and evening-hours (west facing) or in winter (south facing face for northern hemisphere, north facing face for southern hemisphere). When reducing the feed-in power (e.g. to 70% or 50% of the theoretic maximum power output) fluctuations of the electricity feed-in will be reduced. The operator of the solar power plant can use the peak power locally or store it in batteries for later use.
The full load hours of wind turbines can technically easily be increased. When building the wind turbines higher, layers with stronger and more constant winds are reached. Thus sites previously unsuitable can be opened up for wind energy production (e.g. southern Germany). Additionally smaller generators can be used while keeping the rotor diameter constant. The maximum power is reduced but the wind turbine produces electricity already at lower wind speeds. The power production thus occurs more constantly. A full realization of this strategy are airborne wind turbines which fly or float in heights of several hundred meters. While they are still in development the reduced material and ground usage and stronger more constant winds promise to further reduce the price of wind energy significantly.
For the reduced demand of electrical storage a fast variety of technologies are available. Some of these technologies are discussed in the following.
Fig. 4: Dam of the pump storage power plant Ottenstein, Germany
Pump storage plants store electricity by pumping water to a higher level. When energy is needed the water flows down again passing turbines and producing electricity. The advantage of this type of storage is the relatively high efficiency (electricity to electricity) of 75-80% and the fast reaction time. In Germany the total storage capacity of pump storage plants is 0,04 TWh. It can not be significantly increased and traditional pump storage plants also result in unwanted environmental damages (permanent flooding for the water reservoirs). There are however approaches to realize pump storage plants more ecological friendly. Old coal mines could be utilized for lower and the towers of wind turbines for upper water reservoirs (s. Fig. 5).
Fig. 5: Wind turbines as upper water reservoir for pump storage plants (Source: http://www.naturstromspeicher.de/)
Batteries store electricity electro-chemically. They are superior to pump storage plants regarding total efficiency and millisecond fast reaction. There are many different battery technologies. Rather cheap and field-tested are lead acid batteries. A potential successor for grid electricity storage are Lithium based batteries (e.g. LiFePO4 batteries). They are still more expensive than lead acid batteries but excel with a lower maintenance demand and a longer lifetime. For larger systems redox-flow-batteries are also suitable. The storage capacity for these batteries can easily be increased (while keeping the maximum power output constant) by adding larger electrolyte(fluid)-tanks.
Fig. 6: The electric car Renault Zoe
Cars are only driven 5% of their lifetime. The time the cars are not driven (which would however be reduced on average with an increase in car sharing) could be utilized. After an electrification of the motorized traffic a large portion of the vehicle batteries could be used for grid electricity storage. Assuming an available storage capacity of 20 kWh per car and 20-40 million electric cars (currently there are 52 million cars in Germany) the resulting accumulated storage capacity will be 0.4-0.8 TWh.
The costs for solar systems and batteries are constantly decreasing (s. Chapter Costs). Consumption of the solar electricity locally by the system owner becomes more and more attractive. In Germany there is an approximated potential for building integrated photovoltaics of 200 GWp. Assuming 1-3 kWh battery storage per kWp installed solar power the accumulated storage capacity for solar systems optimized for own consumption will be 0.2-0.6 TWh.
Together with the electric car batteries this adds up to a potentially 15-35 times higher storage capacity compared to current pump storage plants.
Fig. 7: Biogas plant, gas tank ad wind turbine of the hybrid plant Prenzlau (Enertrag), Germany
A possibility to store electricity for weeks and months is the so called power to gas technology. Water is split into oxygen and hydrogen using electricity (electrolysis). The hydrogen can then be stored locally ore fed into the existing natural gas grid up to a portion of 5 % per volume. In an additional step the hydrogen can react with CO2 (extracted from biogas or directly from the atmosphere) to form methane. This can be fed into the grid and can completely replace the natural gas. Compared to other storage technologies the efficiency (electricity to electricity plus heat) of 40-50% is low. The important advantage of the technology however is the huge storage capacity of 200 TWh when using the existing natural gas grid in Germany. This is sufficient to store enough electricity to meet the electricity demand for weeks and months of reduced sunshine and wind.
In micro gas turbines with power-heat cogeneration the methane can be efficiently converted into electricity and heat close to the consumer. Micro gas turbines are suitable for this application as they have low maintenance, long lifetime, an easily controllable power output and rather high efficiency under partial load. Thus they can complement the fluctuating solar and wind power production.
During the transition to 100 % renewable energies there might not be enough electricity surplus from renewable sources to justify the large scale application of power to gas. During these few years the micro gas turbines could be run with natural gas. Thus in the short term they can quickly substitute less efficient large power plants (coal, nuclear) which are not suitable for partial load operation. With growing renewable energy production the natural gas can then be replaced gradually by methane produced by power to gas and biogas.
An economic problem of power to gas are either the low efficiency or the low expected degree of utilization when the power to gas plants (micro gas turbines) are only in use when there is an excess (lack) of electricity. A lower degree of utilization leads to a reduced profitability. This can only partially be solved technologically: e.g. by the use of micro turbines which are optimized for partial loaded operation.
But optimizing solar and wind power plants (s. chapter Fluctuations of electricity production) can lead to a largely reduced need for (seasonal) electricity storage. If only a relatively small part of the total consumed electricity has to be stored using power to gas the influence on the average electricity price can be minimized.
Instead of only adjusting the power production to the consumption or store in access produced electricity it might be more economic to also adjust the consumption to the production. This so called demand side management is easily realized in the following areas.
Cooling and air conditioning contribute with 14 % to the German electricity demand1. In countries with a warmer climate this percentage will be significantly larger. This corresponds to approx. 80 TWh annually. A very exact temperature is only needed in very few cases. Thus the systems can cool down to a slightly lower temperature when there is an access of electricity and temporally reduce the cooling power when there is a lack of electricity – leading to slightly higher temperatures. Therefore the 80 TWh annual power consumption can be managed in order to compensate for fluctuation of the electricity production in the minute and hour range.
The heat demand in Germany is approx. 1200 TWh annually. If one assumes a 50 % reduction (better heat insulation, heat pumps, etc.) and an extensive electrification of the heat sector this corresponds to an electricity demand of approx. 600 TWh annually. Equivalently to the cooling sector this demand can be managed in order to compensate for fluctuations in the electricity production.
In addition heat storage tanks can be installed in order to store heat for longer periods. Fluctuations in the electricity production with durations of days and weeks can be compensated in this way. The costs for heat storage tanks of approx. 20-30 € per kWh heat storage capacity are much lower than for batteries (>300 €/kWh). This is still to expensive for a seasonal heat storage (where the storage is charged with solar power in the summer in order to use heat in winter). But with approx. 25 full charge cycles per year or more and a life expectancy of 20 years heat storage systems can become competitive to natural gas heating (assuming a low enough electricity price).
The transport sector contributes with 730 TWh to the annual energy demand in Germany. Assuming again a reduction of 50 % (electrification, more public transportation, bus&train) and an extensive electrification this corresponds to 370 TWh annual electricity demand which can be managed in the minute and hour range.
The bulk of the future electricity demand can therefore be managed. Fluctuations with durations of (mili)seconds, minutes, hours and (with heat storage tanks) days and weeks can be compensated.
The electrification of the heat and transport sector and the resulting increase of electricity consumption will most probably necessitate an expansion of the electricity grid. The extent and type of the expansion is however still under discussion.
Currently the German government plans a grid expansion mainly in the high and highest voltage level. The expansion is publicly justified by the need to transport future offshore wind electricity from the north to the south of Germany. But the main reason might be to transport electricity from new coal power plants planned mostly in the west and north to the south and east of Germany. Generating the electricity directly in the south with higher wind turbines instead of transporting expensive coal or offshore wind electricity with new and expensive power lines would be the more economic solution.
The costs for a transition to 100% renewable energies shall now be discussed and compared to the costs of the current energy supply system
Production costs for non-renewable energy as of 2012 are: 6-10 ct/kWh (nuclear), 4,5-10 ct/kWh (coal) and 4,5-7,5 ct/kWh (natural gas). The English government has guaranteed a feed-in tariff of 11.2 ct/kWh for a duration of 30 years (plus compensation for inflation) for the planned new nuclear power plant Hinkley Point C. This feed-in tariff is necessary for the economic operation of the plant and is significantly higher than the current feed-in tariffs for large solar plants and onshore wind turbines in Germany (with no compensation for inflation and only a duration of 20 years).
External cost which are hard to numeralize have still to be added. Estimates of the German Environmental Agency from the year 2012 give 9-10 ct/kWh for electricity from coal power plants and 5 ct/kWh for electricity from gas power plants. The external costs for solar and wind electricity is much lower with 1 and 0.3 ct/kWh respectively. Estimations for nuclear plants were not given because of strongly varying numbers from different studies. Considering the costs of nuclear meltdowns like Tchernobyl and Fukushima and extrapolating the current costs for the storage of radioactive waste for the next million years it is obvious that nuclear energy is by far the most expensive form of electricity production.
The production costs for renewable energies as of 2013 are: offshore wind: 11.9-19.4 ct/kWh; onshore wind: 4.5-10.7 ct/kWh and photovoltaics: 7.9-14.2 ct/kWh.
Onshore wind and photovoltaics are already competitive to coal and nuclear electricity – even when not considering external costs.
One should also bear in mind that the cost of nuclear and fossil energy has been rising the last decades (because of amongst others higher security standards and rising natural resource prices) while the costs for renewable energies are continuously falling.
The German Renewable Energy Act (REA) obligates the transmission system operators to buy electricity from renewable energy plants for a fixed price. This so called feed-in tariff is guaranteed for 20 years. The transmission system operators then sell the electricity at the (spot) market – most of the time for a lower price. The costs for the operators which arise from this price difference are allocated to the end-consumer price for electricity. This REA allocation amounts to 6.2 ct/kWh as of 2014 and is often cited as proof for the high costs of the transition to 100% renewable energies. It is however ignored, that the higher supply of electricity (generated by renewable sources) lowers the average price at the electricity market (the so called Merrit-Order-Effect). This decrease of the average market price for electricity leads to a higher REA allocation even though no additional costs were generated. If this price decrease was considered, the REA allocation would be significantly lower (s. Fig. 9). Energy-intensive industries already profit from the transition to renewable energies in Germany. They can buy electricity for a lower price at the market and are mostly exempt from paying the REA allocation.
Fig. 9: Price portion of the REA allocation with (turqouise) and without (blue) considering Merrit-Order-Effect
When comparing the costs of renewable and non renewable energies one should bear in mind that production costs are not equal to end-consumer prices. Alleged cheap electricity from amortized nuclear and coal power plants is sold at the same high price as the other electricity during peak consumption hours. Consolidated profits, network charges, taxes and fees are added to the consumer price.
In Germany it is already more economically to directly use the produced electricity of a rooftop photovoltaic system instead of feeding it into the grid. Instead of 28 ct/kWh for grid electricity you only have to pay 14 ct/kWh for electricity produced with a rooftop solar system. If one has to first store the electricity in batteries (e.g. for evening or night consumption) additional costs of approx. 15-25 ct/kWh occur. For consumers like offices, shops, super markets, etc. the main consumption is during the day as is the solar electricity production. A high degree of own consumption is here therefore possible.
With further falling costs for solar and battery systems the option of own consumption becomes more and more attractive. Unfortunately the German government seems to try to stop or at least significantly slow down the transition to 100 % renewable energies at all costs. They already have reduced the feed-in tariff too fast, resulting in the loss of half the jobs in the German solar energy industry. Additionally in 2014 they decided that the REA allocation has to be payed for electricity which is produced by rooftop solar systems and consumed locally by the operator, too. A much more ecological and economic sound financing of the REA would be through a resource tax (s. next chapter Measures for a fast and effective implementation).
Building-integrated solar or wind power plants (and local plants with power-heat cogeneration) don't need to have electricity production costs lower than large-scale power plants. They are competitive if the produced electricity is cheaper than electricity from the grid (end-consumer grid electricity price = production costs + network charges + profits + taxes + fees). This is already the case in many cases.
Systems with additional battery storage optimized for own consumption of the produced electricity and a more constant feed-in of electricity can contribute to the grid stability and a higher degree of capacity utilization of the grid and thus to lower total system costs and to lower energy prices for all consumers.
Finally some measures shall be mentioned with which an efficient, cost effective, sustainable and fast transition to 100% renewable energies is possible.
Firstly all direct and indirect market-distorting subsidies for fossil and nuclear energies have to be abolished.
A resource tax on natural (non renewable) resources leads to a more efficient resource usage and better sustainability and should be introduced. The tax is justified because: (a) Natural resources are commons and mining them often generates rents/unearned income. The community should therefore have a share in those rents. (b) Natural resources are finite. The tax can reduce the extraction rate, optimize the extraction path and lead to more generational justice. (c) The mining for natural resources causes external costs, which should be included by a tax as good as possible.
Solar and wind power plant, energetic redevelopment of buildings and building with a higher energy standard are characterized by high initial investment and low running costs. Low interest loans can therefore lead to a significantly improved profitability and should be implemented or extended. This can happen in form of low interest loans from a state bank (as is done by the German Kreditanstalt für Wiederaufbau, Reconstruction Credit Institute) or by a currency reform with the introduction of Freiwirtschaft and the resulting generally reduced interest costs.
For new buildings the energy plus standard should apply. The building has to have a very good heat insulation and produce its complete annual energy demand from local solar, wind or power-heat cogeneration power plants. The industry committee of the European parliament plans to have this implemented for buildings built after the 31th December 20181. It has still to be passed to national law.
Public transportation should be expanded. Furthermore higher subsidized ticket prices should be considered. A completely tax financed public transportation system might be the best ecological and economic solution.
The use of electric buses for public transportation can easily be realized because of the planned and regular routes involved.
The bike infrastructure should be expanded.
An inner-city speed limit of 30 km/h can also bring numerous advantages. It results in a reduced noise exposure and a higher capacity of the streets. This higher capacity reduces the traffic jams and traveling times during rush hours. The number of traffic accidents and deaths will also be reduced. The speed limit should be considered especially for inner-city streets without a separate bike lane.
The German REA has proven to be a very cost effective measure for the transition to more renewable energies. It should however be made sure, that the cost savings resulting from a reduced electricity market price are passed on to the end-consumer. A financing of the REA through the resource tax might be a better solution than the current REA allocation mechanism.
A feed-in tariff guaranteed for 20 years reduces the risks for investors and insures the profitability of the power plants. The amount of the feed-in tariff can be reduced continuously to accommodate cost reductions, while still insuring the profitability.
Incentives for the optimization of wind and solar power plants as described in the chapter Fluctuations of electricity production can also be given by the feed-in tariff.
For solar systems this can be realized as follows:
The feed-in tariff for wind turbines will be set corresponding to the number of their annual full load hours. The more full load hours (= more constant power production) the higher the feed-in tariff. The full load hours can be increased with higher wind turbines and smaller generators from 2500 h/a to over 4000 h/a. This will result in a more constant feed-in of wind electricity and a significantly reduced need of energy storage and operating reserves.
The feed-in tariff for power-heat cogeneration plants and battery storages (and other power plants) will not be fixed but depend on the current need for electricity. The current need for electricity can technically easily be determined locally at each feed-in point. (This also applies for the application of power throttle and automatic disconnect of solar systems as mentioned above.) At each feed-in point the grid voltage and frequency is measured. Values above the nominal values correspond to a power overproduction and values below the nominal value correspond to a power underproduction. In the current German REA the automatic disconnection of photovoltaics systems is initialized when the grid frequency reaches 50.2 Hz (nominal 50.0 Hz). The lower the grid frequency (and voltage) the higher the feed-in tariff.
Flexible electricity prices should be introduced in order to adapt the electricity consumption to the production. The electricity price could be set corresponding to the current electricity demand and production. This can measured the same way as described above for the feed-in tariffs of cogeneration and battery plants. The lower the grid frequency (and voltage) the higher the electricity price.
A smart meter with permanent Internet connection is not needed. Each power meter can save the number of consumed kWh at a specific grid frequency. This data – which does not include any chronological consumption curves and thus enables a better protection of data privacy – can then be send to the power supplier in regular intervals. This can be done with an Internet connection or with a manual meter reading common today.
It is physically, technically and economically feasible to transit to 100% renewable energies in a relatively short time frame (till 2030). Fluctuations in the power production of wind and solar plants can be reduced by an optimization of the plants (solar: throttling of the feed-in power, solar systems on east and west roofs and faces of buildings; wind: more full load hours by higher wind turbines with smaller generators) and can be compensated by demand side management and energy storages.
Measures for an efficient, cost effective, sustainable and fast transition to 100 % renewable energies include: a resource tax, low interest loans, strict energy standards for buildings, feed-in tariffs which incentivize a more constant feed-in of solar and wind electricity and flexible electricity prices (for demand side management).
The costs for renewable energies is continuously falling. Renewable Energies enable a decentralized power production near the consumer and a energy supply which is – in the short and long term – cheaper for the end consumer and the whole economy. They are hereby more environmental friendly and sustainable than the current nuclear and fossil based energy supply.