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Wind And Solar Energy Lulls: Energy Storage in Germany
Germany aims to have almost all of its domestic electricity consumption from renewable sources by 2050. The Energiewende targets are 35% RE by 2020, 50% by 2030, 65% by 2040, and 80% by 2050. Thus, about 20% of domestic electricity consumption could continue to be from fossil fuels, such as natural gas, in 2050.
In 2016, gross electricity generation was 652 TWh, of which 456 TWh was from conventional generators and 196 TWh was from renewables, i.e., about 30% of gross electricity generation was from renewable sources, such as wind, solar, hydro, bio, etc.
In 2016, Domestic electricity consumption was gross generation (652), less self-use (30), less net exports (52), less transmission and distribution (30), less pumped storage and misc. (19.4), or about 520.6 TWh.
Of the 196 TWh, about 88 TWh was from wind, about 38 TWh from solar, for a total of 126 TWh. About 70 TWh was from hydro, bio, etc. On an annual basis, wind and solar (stochastic sources) was 126/652 = 19.3% of electricity generation.
German CO2 Emissions: Germany’s CO2 emissions are about the same as in 2009. The increase in RE over this period did not have the desired effect, but did increase household electric rates. The electricity sector contributes only about 45% of Germany’s total emissions. The 100% decarbonizing of the electricity sector, which is already about 45% decarbonized (if we add nuclear) would reduce total emissions by about another 25%. Yet Germany’s efforts to decrease emissions continue to concentrate on the electricity sector. Germany likely will not meet its 2020 and 2030 emissions reduction targets.
German Household Electric Rates: German household electric rates are the SECOND highest in Europe, about 28.69 eurocent/kWh in 2015; Denmark is the leader with about 30 eurocent/kWh. Both are RE mavens. France, about 80% nuclear generation, has one of the lowest.
Electricity in 2050: At present, electricity is about 35 percent of all energy, but after implementation of heat pumps for almost all buildings and replacing almost all fossil fuel vehicles with electric vehicles, electricity would become about 60 percent of all energy.
Wind and Solar Energy is Stochastic: When Germany has one of its sunny and windy days, RE proponents usually mention Germany obtained a large percentage of its electricity generation from renewables. They usually do not mention “for up to about one hour around noontime”. RE proponents often say, wind and solar can generate almost all electricity. All that is needed is more build-outs and energy storage.
With increased future reliance on weather-dependent wind and solar electricity, it would be useful to determine the required energy storage system capacity, GWh, if nuclear and fossil plants were closed in the near future. This article shows what might be required during two consecutive wind and solar lulls in December 2050, as occurred in December 2016.
Below is a comparison of the following alternatives:
Alt. No. 1: The same lulls in December 2050, without conventional generators.
Alt. No. 2: The same lulls in December 2050, with 50 GW of nuclear generators
Existing Conditions, Wind and Solar Lulls in December 2016: At present, during periods of almost no wind and little sunshine, conventional generators provide the electricity to meet the demand.
Such was the situation, when high-pressure winter weather caused extremely low outputs of wind and solar electricity in Germany and surrounding countries during 2 periods in December 2016.
The above figure shows:
- Such weather events can persist for several days. The first lull lasted about 100 hours, the second about 50 hours.
- Germany exported electricity during almost all hours of the 16-day period. Those exports likely went to Denmark, as it relies on imports from Norway, Germany, the Netherlands, etc., during its wind lulls. Germany exported 85 TWh and imported 34 TWh, during 2015.
The power from different sources quoted in the Agora article are summarized in the table.
| Lull, 3-6 Dec 2016 | GW | Installed GW |
| Demand | 70.0 | |
| Supply | ||
| Conventional* | 59.9 | |
| Hydro, bio, etc. | 8.0 | |
| Solar | 0.7 | 41.0 |
| Onshore wind | 1.0 | 44.5 |
| Offshore wind | 0.4 | 3.3 |
*Conventional includes fossil, nuclear, imports and exports.
Alt. No. 1, Wind and Solar Lulls in December 2050: RE proponents claim wind, solar, hydro, bio, etc., generate almost all electricity, and fossil fuel and nuclear generators are not needed. However, if fossil fuel and nuclear generators were closed down and wind and solar were minimal, hydro, bio, etc., whether in Germany or abroad, would not be able to meet Germany’s electrical demand without massive, bulk energy storage systems.
For this alternative, we assume Germany would:
- Consume the same quantity of energy in 2050, as in 2016, i.e., increased due to population and gross product growth, but reduced due to energy efficiency.
- Increase its electricity generation from 35% of all energy to 60% of all energy.
- Have 8 times the installed capacity, MW, of wind and solar systems and associated transmission, in 2050.
- Experience the same wind and solar lulls in December 2050, as in December 2016.
Below is the 2050 power balance for the first wind and solar lull; the second lull is assumed identical for analysis purposes.
| 1st Lull, Dec 2050 | GW | Installed GW | |
| Demand | 120.0 | ||
| Supply | |||
| Storage* | 91.2 | ||
| Hydro, bio, etc. | 12.0 | ||
| Solar | 8 x 0.7 | 5.6 | 8 x 41.0 |
| Onshore wind | 8 x 1.0 | 8.0 | 8 x 44.5 |
| Offshore wind | 8 x 0.4 | 3.2 | 8 x 3.3 |
*Storage includes imports and exports
The energy supplied by the storage system to cover the entire 100-hour lull would be 100 hour x 1.1 x 91.2 GW = 10032 GWh, assuming a 10% discharge loss. Imports and exports would be minimal, as nearby countries also would have wind and solar lulls.
The actual energy in the storage system would need to be about 20000 GWh, because we cannot assume the batteries to be fully charged at the start of the lull, and batteries should not be frequently discharged to less than 50%, as it would significantly shorten battery life.
Standard 1 MW battery units can deliver about 1 MW for 6 hours. They are about the size of a 40-ft trailer. The turnkey cost is about $1.5 million/unit*. Multiple units can be located at a site. See page 1 of URL.
*Whereas the cost of batteries for vehicles likely would decrease in the near future, due to mass production, that likely would be much less so for engineered, 25 to 100 MW, utility-grade, bulk energy storage systems, which require up to ten acres of land.
The battery systems would be:
- Charged with solar energy during peak generating hours and would discharge energy, as needed to meet demand, during other hours, on a daily basis.
- Charged with wind energy and discharge energy, as needed to meet demand, during all hours of the year.
- Charged by the other generators (nuclear, hydro, bio, etc.), as needed, during all hours of the year.
The turnkey capital cost of the utility-grade storage systems would be 20,000,000/6 x $1.5 million = $5 trillion. They would be distributed throughout Germany. A significant percentage of this capital cost would be repeated every 15 – 20 years.
The Agora graph shows, the second wind and solar lull occurred a few days later. That means, either there must be enough electricity generation (mostly wind and solar, and some hydro, bio, etc.) to charge the batteries in a few days, plus serve the demand (a very tall order), or even more storage must be available to serve demand during the 2nd lull. The safe approach would be to have available the additional storage.
NOTE: Germany policymakers are beginning to realize expensive, bulk energy storage systems are not an economically viable option in the near future. Germany will place:
- Up to 4400 MW of plants in “capacity reserve” to ensure the security of power supply in case of unforeseeable and extreme. Payments for such back-up services were 67 million euro and 168 million euro in 2014 and 2015, respectively, and are estimated to increase to about 260 million euro per year.
- Up to 2700 MW of lignite plants in “security reserve” in the case of long-lasting, extreme weather events. The “security reserve” will cost an estimated 230 million euros per year, on average, and will last for about seven years.
NOTE: Germany RE curtailments, mostly wind energy during windy days in north Germany, likely will increase, as more wind and solar build-outs are added in future years. See table.
| Year | TWh | $million |
| 2012 | 0.38 | 23 |
| 2013 | 0.55 | 33 |
| 2014 | 1.58 | 94 |
| 2015 | 2.69 | 160 |
Alt. No. 2, Wind and Solar Lulls, Plus 75,000 MW of Nuclear Generation in December 2050: Germany may change its collective mind regarding nuclear energy, once the people realize the cost and environmental impacts of the required wind, solar and transmissions system build-outs by 2050, as shown in Alternative No. 1.
The nuclear plants would have standard 1100 MW units, which reduces turnkey costs. The plants would be a mix of base-loaded and load-following plants, similar to France. Hydro, bio, etc. plants would be operated as at present.
Instead of 8 times, only about 4 times the wind, solar and transmission system build-outs would be required.
German electricity generation would be 60/35 x 652 = 1,118 TWh by 2050, of which the nuclear plants would provide about 75000 x 8755 x 0.85/1000000 = 559 TWh, or about 50% of total generation.
NOTE: In France, nuclear plants generate about 75% of total electricity. France has among the lowest household electric rates in Europe. Germany has the second highest, about 30 eurocent/kWh, after Denmark, about 31 eurocent/kWh.
The Agora graph shows, the 2016 average demand was about 70 GW from the 3rd to 7th of December 2016. We assume the 2050 demand would be 60/35 x 70 = 120 MW, and the annual generation would be 60/35 x 652 = 1118 TWh. By multiplying the existing wind and solar by 4 and adding the nuclear plants, about 1217 TWh would be generated, for a 9% margin.
Below is the 2050 power balance for the first wind and solar lull; the second lull is assumed identical for analysis purposes.
| Period | Dec 2050 | GW | Installed GW |
| Demand | 120.0 | ||
| Supply | |||
| Nuclear | 75.0 | ||
| Storage* | 24.6 | ||
| Hydro, bio, etc. | 12.0 | ||
| Solar | 4 x 700 | 2.80 | 4 x 41.0 |
| Onshore wind | 4 x 1000 | 4.00 | 4 x 44.5 |
| Offshore wind | 4 x 400 | 1.60 | 4 x 3.3 |
*Storage includes imports and exports
The energy supplied by the storage system to cover the entire 100-hour lull would be 100 hour x 1.1 x 24.6 GW = 2706 GWh, assuming a 10% discharge loss. Imports and exports would be minimal, as nearby countries also would have wind and solar lulls.
The actual energy in the storage system would need to be about 5500 GWh, because we cannot assume the batteries are fully charged at the start of the lull, and batteries should not be frequently discharged to less than 50%, as it would significantly shorten battery life.
The turnkey capital cost of utility-grade storage systems would be 5500000/6 x $1.5 million = $1.38 trillion. They would be distributed throughout Germany. A significant percentage of this capital cost would be repeated every 15 – 20 years.
Pumped Hydro Plants to Shift Seasonal Energy Variations: According to a study titled “Buffering Volatility: A Study on the Limits of Germany’s Energy Revolution”, in 2014:
Germany would have required about 11.29 TWh of pumped hydro storage to store/smooth all of its wind and solar energy. If all nuclear plants had been shut down and replaced by W&S, about 15.25 TWh of PHS would have been required. If all fossil plants had been shut down and replaced by W&S, about 40 TWh of PHS would have been required, or 40/0.038 = 1053 times Germany’s 2014 PHS capacity of about 0.038 TWh.
In 2050, with 6.5 times W&S, about 100 TWh of PHS would be required, or 100/0.038 = 2632 times Germany’s 2014 PHS capacity.
Seasonal energy shifting requires much greater storage than do W&S lulls, such as the 100-h lull of Alternative no. 1, which required only 13.65 TWh of storage.
Producing Methane Syngas by Electrolysis: Wind and solar electricity can be used to split water into hydrogen and oxygen by means of electrolysis. The hydrogen can be converted to methane, CH4, and stored in underground caverns. At present, process development is conducted in various power-to-gas, P2G, pilot plants.
Producing hydrogen from electrolysis, with electricity at 5 cents/kWh, will cost $28/million Btu, slightly less than two times the cost of hydrogen from natural gas.
NOTE: The cost of hydrogen production from electricity is a linear function of electricity costs, so electricity at 10 c/kWh means hydrogen will cost $56/million Btu.
German wind and solar is 10 c/kWh. 1 million Btu of methane to a CCGT would produce 500000 Btu of electricity, or 146 kWh for $56, or 38 c/kWh,
The methane has to be piped to a storage reservoir, stored, then discharged, then piped to CCGTs, for a loss of about 20%, so the cost becomes 38 c/kWh/0.8 = 47.5 c/kWh, plus utility mark-up and taxes, fees and surcharges.
Very significant overbuilding of wind and solar would be required to ensure adequate storage for seasonal shifting and extended wind and solar lulls.
Synthetic Gas to Cover Wind and Solar Lulls: Wind and solar electricity could be used to split water into hydrogen and oxygen by means of electrolysis. The hydrogen can be converted to methane, CH4, and stored in underground caverns. At present, process development is conducted in various power-to-gas, P2G, pilot plants.
In 2050, during the 2 lulls, Germany would need to generate about (3 TWh/day/24 h) x 150 h = 18.75 TWh.
The generators of Alternative no. 1 would produce about 65650 MW x 150 h = 9.85 TWh, for a shortfall of 8.90 TWh, which has to be made up with syngas-fired CCGTs.
The required capacity of the CCGTs would be 8.9 TWh/(150 h x 0.85) = 69,824 MW.
The required syngas would be 8.9 TWh/0.5 = 17.8 TWh, equivalent to 60.7 billion cubic feet.
At a maximum operating pressure of about 100 bar (1470 psig) the underground volume would be about 0.61 bcf. The quantity of stored syngas would be double that to provide adequate operating cushion.
This approach may not be attractive with a CF of about 0.20 for wind energy in Germany, and a P2G a-to-z process efficiency of 60%, and pumping into storage at 90%, and discharging from storage at 90%, and burning the gas in a CCGT at 50%.
Germany Seasonal Energy Shifting: Below are estimates of the storage that would have been required in 2014:
- If all of Germany’s wind and solar energy had been stored/smoothed, about 11.29 TWh.
- If all nuclear plants had been closed and replaced by W&S (resulting in 2 times 2014 W&S), about 15.25 TWh.
- If all fossil plants had been closed and replaced by W&S (resulting in 3.5 times 2014 W&S), about 26.6 TWh.
In 2050, at 6.5 times W&S, about 69.9 TWh would be required. Note: The US 2016 gross electricity generation was 4000/648 = 6.2 times Germany’s gross generation.
The seasonal storage quantities would need to be increased by up to 20% for round trip losses, in case of pumped hydro storage. In case of syngas storage, to generate the above 69.9 TWh, the required gas input to CCGTs would need to be 69.9 TWh/(CCGT efficiency, 0.55 x 0.845 LHV/HHV) = 150.4 TWh, and the storage caverns would need to hold at least 300 TWh for operational purposes.
NOTE: The energy loss to produce the syngas, compressing and piping it into storage caverns, discharging it from the caverns, recompressing and piping it to CCGTs, almost all of it performed with wind and solar energy, was omitted to reduce complication of the analysis.
Losses Due to Seasonal Storage Requirements: At present, any energy sent into storage is less than 1% of gross electricity generation, and associated losses are minimal. This would not be the case in 2050, when much greater storage flows and storage capacity, TWh, would be required.
In 2050, all wind and solar electricity would need to be sent into storage throughout the year to ensure adequate electricity supply, 24/7/365, year after year, which involves a total loss of 1.02, self-use x 1.07 T&D x 1.1, charging x 1.1 discharging = 32%, i.e., wind and solar capacity, MW, plus associated grid expansions, would need to be 32% greater to offset these losses. The required turnkey capital costs were NOT included in the tables of below section.
Summary of Capital Costs of Alternatives: Below is a summary of the capital costs of the two alternatives. The capital cost of the nuclear alternative is less costly by about 6.71 – 2.68 = $4.03 trillion.
Alternative No. 1, Without Nuclear
| 2050 | Times | GW in 2050 | $trillion |
| Solar | 8 | 328.0 | 0.82 |
| Onshore wind | 8 | 355.8 | 0.78 |
| Offshore wind | 8 | 26.3 | 0.11 |
| Storage, distributed | 5.00 | ||
| Total | 6.71 |
Alternative No. 2, With Nuclear
| 2050 | Times | GW in 2050 | $trillion |
| New Nuclear | 75.0 | 0.45 | |
| Solar | 4 | 164.0 | 0.41 |
| Onshore wind | 4 | 177.9 | 0.39 |
| Offshore wind | 4 | 13.1 | 0.06 |
| Storage, distributed | 1.38 | ||
| Total | 2.68 |
At a cost of about $0.45 trillion for nuclear plants (with almost no CO2 emissions), implementing the Energiewende would be about $4.03 trillion less costly, plus the environmental adversities of wind turbines, solar panels and associated transmission lines would be significantly less intrusive.
German electricity generation would be about 90% without CO2 emissions by 2050; bio-electricity has CO2 emissions). There can be no hope of achieving that without nuclear plants, and with continued operation of coal, oil and gas plants.
Thank Willem for the Post!
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