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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




Hydro, bio, etc.





Onshore wind



Offshore wind



*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




Hydro, bio, etc.



 8 x 0.7


8 x 41.0

Onshore wind

8 x 1.0


8 x 44.5

Offshore wind

8 x 0.4


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












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






Hydro, bio, etc.



4 x 700


4 x 41.0

Onshore wind

4 x 1000


4 x 44.5

Offshore wind

4 x 400


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




Onshore wind




Offshore wind




Storage, distributed




Alternative No. 2, With Nuclear

2050 Times GW in 2050 $trillion
New Nuclear







Onshore wind




Offshore wind




Storage, distributed




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.

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Jarmo Mikkonen's picture
Jarmo Mikkonen on Jan 24, 2017 5:07 pm GMT

German emissions rose in both 2015 and 2016, despite addition of 30 TWh of renewable electricity. What happens when the rest of the nuke plants, worth almost 90 TWh of clean electricity, close?

Darius Bentvels's picture
Darius Bentvels on Jan 24, 2017 8:59 pm GMT

Long ago Germany’s scientists had discussions and studied (Agora) about longer winter lulls (2 months).
As usual a mix of alternatives came up as best & cheapest solution.

The two most prominent:
– More interconnection capacity with more countries +
– Substantial over-capacity of wind & solar combined with Power-to-Gas.
are not stated in the post.
Only the unsuitable battery alternative.

While the problem won’t be urgent until 2035, Germany:
– is expanding interconnection capacities (e.g. to Norway)*)
– is developing Power-to-Gas fast.
The first major pilot plant (Falkenhagen) operates since 2013. Since then major ongoing improvements (efficiency & lower costs also due to smaller volume).
MIT research contributes at a fundamental level (efficiency, stable membranes, etc)

They now have ~30 major P2G pilot plants & research facilities. ***)
The produced syn gas is partly H2 injected in the grid**), some are situated at H2 car refill stations, etc. Partly the gas is methanized, e.g. the Audi e-gas project.
They target to have a capacity of 1GW PtG running in 2022, and to start with regular roll-out in 2025. So their plan allows for years of delays.

Note that:
– in order to cover 5 weeks of a complete lull in a grid with 100GW consumption, the av. PtG production only need to be ~10GW.
– it’s cheapest to use unmanned ‘peaker’ gas turbines, as those need lowest investment and maintenance. Especially since those will run less than 10% of the time. Siemens has H2 gas turbines in development.
– nuclear is a non-option as nuclear is widely considered being extremely dangerous (their scientists confirmed some effects of Chernobyl fall-out, despite being 1000mile away; Germans have relations with German speaking farmers in the Chernobyl area). Furthermore nuclear is n-times more expensive
*) Note that there was no such lull in the wind during December in the Nordic.

**) For the climate it’s better that the renewable syn gas replaces natural gas burning immediately. First storage in earth cavities as may imply some losses.
Storage in earth cavities is extremely cheap. Germany use such stores to cover long supply interruptions of Russian gas.
In NL those allow to size the max. capacity of the gas processing plants on the average consumption, which is substantial less than the winter peak.

***) You can find out more about each through clicking on the dot.

Willem Post's picture
Willem Post on Jan 24, 2017 10:02 pm GMT


The prognosis is CO2 will continue to increase as nukes are closed down and wind and solar is not built out at a fast enough rate. Wind and solar electricity production varies from year to year, as does the weather.

My article deals with storage required for a 100-h lull of wind and solar in winter. Here in Vermont, we are having a 5-day lull, so far, and the weather report indicates 2 more days.

I just read an article that deals with storing energy at sufficient quantities for seasonal shifting, and at the same time meeting demand.

That storage capacity would be 773,388 GWh, with just 3 times the present level of wind and solar, and no increase in future consumption.

This is much larger than the 20,000 GWh for alternative no. 1.

Without seasonal shifting with storage, German wind and solar will go nowhere near 50%.

Denmark is a special case, because its energy shifting is small and Norway’s reservoirs are large.

Germany is the 800-lb gorilla.

Roger Arnold's picture
Roger Arnold on Jan 25, 2017 12:31 am GMT

What type of energy storage was being suggested with that magnitude of capacity? Or was the article simply pointing out the magnitude of the problem?

I know of various ways to store that much energy, but they’re not well known. Aside from large scale pumped hydro, none have been proven in any pilot demonstrations.

Darius Bentvels's picture
Darius Bentvels on Jan 25, 2017 12:41 am GMT

Gas storage in earth cavities has proven itself during many years for very cheap seasonal storage in NL, and for huge strategic reserve in Germany.
Such storage can handle more than 900TWh.

Roger Arnold's picture
Roger Arnold on Jan 25, 2017 12:50 am GMT

– in order to cover 5 weeks of a complete lull in a grid with 100GW consumption, the av. PtG production only need to be ~10GW.

That assumes 100% round trip efficiency. P2G2P is hard-pressed to get 35%, and that’s using costly hydrogen fuel cells for generation. Using cheap hydrogen-fueled peaker turbines, round trip efficiency would be closer to 15%. 20% would be generous. So you’re talking about dedicating additional power equal to more than 50% of average demand to making hydrogen for your 5 weeks of lull. That’s a complete non-starter.

Mark Heslep's picture
Mark Heslep on Jan 25, 2017 1:32 am GMT

Not any and all “gas”. Large scale methane storage is proven, and was similarly stored eons before the advent of humans.

Engineer- Poet's picture
Engineer- Poet on Jan 25, 2017 2:48 am GMT

I’d be happy to have a 5-day lull.  My area has gone through a full week of next to no wind and still has a couple more days forecast.

Willem Post's picture
Willem Post on Jan 25, 2017 3:03 am GMT


The author did a thought experiment. He added all the PHS capacity, GWh, of Germany, which is not much.

Then he assumed he had a much larger capacity, into which the present wind and solar variable energy flow would enter. At times the inflow would be high, at other times it would be low, but the energy flow from the reservoir would be in accordance with demand. Such a reservoir must be large enough to never be empty. In fact, it had to be about 13000 times greater than an average German PHS facility.
If more nukes were shut down and more wind and solar were added, then storage would increase to about 20000 times an average plant

Clearly, it is technicall’y feasible, but the cost of would be prohibitively high.

Alternative no. 2 shows how adding nuclear reduces storage and wind and solar costs by about $4 trillion.

Willem Post's picture
Willem Post on Jan 25, 2017 3:08 am GMT

You are right about gas underground storage.

Ukraine has huge underground storage capacity which has acted to provide Russian gas to Europe during winter for many decades.

Now we are talking about PHS

Nathan Wilson's picture
Nathan Wilson on Jan 25, 2017 4:36 am GMT

I saw an interesting article about P2F2P a while back, I think from MIT. Their idea was to store hydrogen for peaking power plants underground in salt caverns, but also store the co-produced oxygen in nearby caverns. This combination burns at a hotter temperature, thus allowing more efficient conversion to electricity (70% vs. 60%), as well as cutting NOx emissions.

The trick is, this was suggested for use with nuclear plants, with waste heat being used to keep the O2 warm. That way, if there is a large leak, the O2 will be lighter than air, and float high enough to disperse. Otherwise, a large O2 leak will produce a heavier-than-air holocaust plume, that drifts to the nearest city, finds an ignition source, and accelerates combustion of everything in its path.

Mark Heslep's picture
Mark Heslep on Jan 25, 2017 5:18 am GMT

Neither the battery nor the PHS storage appear to be even technically feasible to build given finite resources for the 100 hr, 20 TWh storage scenario.

For a battery solution, note that Tesla’s new battery factory will produce 53 GWh/yr and is doubling global Li-ion production capacity. With battery replacement every 10 years, 100 hr storage is never achieved even with dozens of such factories dedicated to German storage alone. BTW, the mass of 20 TWh of Li-ion battery (using Tesla’s 170 kWh/ton) would at least 100 million tons, and several times that for NAS.

Large PHS has a depth of a dozen hours or so, and the largest power output is 3 GW, with typical capacity much lower.

Willem Post's picture
Willem Post on Jan 25, 2017 2:41 pm GMT


You are right regarding the unfeasibility and expense of the 20 TWh of storage required for a 100-h lull, if 8x wind and solar, and hydro, bio, etc., were used in 2050, see alternative no. 1, and regarding the 5.5 TWh of storage required for a 100-h lull, if 4x wind and solar and 75 GW nuclear, and hydro, bio, etc., were used in 2050, see alternative no. 2.

However, the storage would need to be many thousands times greater, because seasonal shifting would be required.

Much hyped flow batteries, at present in various stages of development, would be a similarly expensive solution.

Producing methane with electricity costs about 5 times the present cost of natural gas, and producing hydrogen with electricity costs about 10 times the present cost of natural gas. NG is easily storable, but H2 storage is a big challenge.

German policymakers and some elected officials are very smart people.

All are very familiar with above scenarios, but for PR reasons cannot talk about them, because it would be a political disaster to admit Germany and others have been veering off in the wrong direction for about 15 years.

Stay tuned.

Jarmo Mikkonen's picture
Jarmo Mikkonen on Jan 25, 2017 5:49 pm GMT

The late Swedish Social Democratic Prime Minister, Olof Palme, is claimed to have said that ” If the facts and the Social Democratic policy platform are in conflict, too bad for the facts.”

When sufficient capital and political capital have been invested into a project, it is usually declared a success, regardless of the problems or the facts. That’s the nature of politics.

Ryan Paulsmeyer's picture
Ryan Paulsmeyer on Jan 25, 2017 6:42 pm GMT

I believe you are referring to this article by Charles Forsberg, discussing various options of utilizing Nuclear in conjunction with fossil extraction or pairing with different storage techniques. Short read and full of interesting options. HIPES is the particular P2F2P you describe.

Darius Bentvels's picture
Darius Bentvels on Jan 25, 2017 8:23 pm GMT

…100% round trip efficiency…“??
The expert expectancy of (at least) 40% round trip efficiency will do.

‘normal’ years have say 3 weeks with wind&solar lull during which still a lot is produced by wind & solar, easily 20%. Furthermore:
– other renewable continue to produce ~10GW (~10%)
– import will deliver ~10GW (improved interconnections)
So the produced syn gas of those years is too much. The surplus will be kept in storage (earth cavities are cheap storage!).
So after a number of years there will be enough H2 in storage to cover a few real bad years.*)

Regarding economics, note that German wind & solar is now already 2 times cheaper than nuclear. That difference will be a factor >2 bigger in 2050.
So even unnecessary 25% or 50% overcapacity will then be much cheaper than nuclear!
*) note that the situation migrates during >20 towards that 100% renewable. So time enough to build up enough H2 storage.

Darius Bentvels's picture
Darius Bentvels on Jan 25, 2017 9:52 pm GMT

How come you think that it’s adequate to compare your solution for the winter lulls with a battery fantasy solution which was never taken serious in Germany as far better & cheaper solution range is available?
Which the Germans are developing actively further since roughly 2007. But you ignore those developments, while you lived in the EU and seem to know German.

Considering also your misrepresentation of the German electricity prices by not adding the remark that taxes play a major role (little tax in France, lot tax in Germany),

I get the impression you want to show the Energiewende is / will be a failure even if that story / argument doesn’t fit with reality….

Roger Arnold's picture
Roger Arnold on Jan 26, 2017 1:31 am GMT

Hmm, you’re reframing the issue on the fly, Bas. You had written:

– it’s cheapest to use unmanned ‘peaker’ gas turbines, as those need lowest investment and maintenance. Especially since those will run less than 10% of the time.

You’re right to be concerned about the cost of the G2P leg of the system, since at a 10% capacity factor, the cost of power will be dominated by the cost of capital. But a cheap peaker unit will only give about 27% thermal efficiency. And that’s from gas that was produced from low voltage DC to the electrolysis cells at an optimistic efficiency of 80%. (It’s possible to split water with somewhat higher efficiency than that, but it requires operating the cells at very low current. Totally demolishing their capital productivity.)

Factor in’ perhaps 92% conversion efficiency for grid AC to LVDC distributed to the electrolysis cells, and your “cheap” P2G2P system is operating at .27 x .80 x .92 = 19.8% round-trip efficiency. Oh, and that’s ignoring the considerable energy required to compress the hydrogen for storage in “earth cavities”.

(BTW, did you really mean “cavities” — i.e., salt caverns of the type used for oil and gas storage in the US Gulf Coast region — or did you mean depleted gas fields of porous rock below an impermeable cap? I believe the latter are much more common for gas storage than the former, and they certainly have more capacity, but I don’t know that they’ve ever been used for hydrogen storage. They likely have issues with the fraction of stored gas than can be recovered, and they certainly would have issues with purity of the gas recovered from storage. It would contain substantial amounts of methane and other light hydrocarbons. Wouldn’t be a problem for burning the gas in a turbine, but would be for a PEM fuel cell. Salt caverns might save a bit on compression energy, but I’m not sure there’s enough storage capacity there for the magnitude of hydrogen storage one would need for P2G2P over one-year timeframes.)

Siemens has H2 gas turbines in development.

I don’t know what Siemens may be developing. I’m pretty sure, however, that if it’s cheap, it won’t be efficient, and if it’s efficient, it won’t be cheap.

The expert expectancy of (at least) 40% round trip efficiency will do.

As to that, 40% is indeed do-able, but it means you’re back to using expensive fuel cells, or at least high efficiency CCGT units, for the G2P leg. It will be a lot more expensive than firing up a gas-fueled peaker to supply power during lulls. If it’s mandated by German law, it will be done (in Germany). But it will push the overall cost of electricity still higher. And you’re already getting pushback from German businesses over the high cost of electricity.

And now I’ll do a little reframing of my own.

We’ve been talking about the impact of extended lulls in wind and solar power, of the sort that hit Germany this winter. An implicit assumption has been that production from wind and solar vary stochastically around an overall yearly average. I don’t know to what extent that holds for wind in Europe, but I know it does not hold even remotely for solar.

At the latitude of Frankfurt, there are 16 hours of daylight in summer and 8 in winter. But that 2:1 ratio understates the summer to winter variance by a wide margin. The winter sun has a low elevation angle even at noon, and delivers only about half the wattage per square meter as the summer sun, even in clear air with a tracking array. If there’s any haze or cloud cover, it’s worse. Of course Frankfurt is in the north of Germany, but things aren’t very much better even at Germany’s southern border. 5:1 seems a conservative estimate of the solar power variance between the mid summer and mid winter.

So it’s not just 5 weeks of non-production every few years that your stored energy system needs to cover. It’s more like four months of average consumption every year. Good luck maintaining a competitive economy with the cost of electricity that that order of energy storage is going to mean.

Willem Post's picture
Willem Post on Jan 26, 2017 2:05 am GMT


Thank you for your comments.

Storing expensive, pressurized hydrogen in caverns is a pipe dream.

Solar production in Germany has a best month divided by worst month ratio of about 6; in Vermont it is about 4. Those numbers are from many existing installations. Those ratios would be much greater on a weekly or dally basis.

For the past 150 years, nature has provided us with stored energy in the form of fossil fuels. We just take them, process them and feed them into the economy, as needed.

Now we have to create our own energy storage facility, into which we feed our weather dependent renewable and not so renewable energy, and from which we draw energy, as needed.

For Germany, such energy storage facility would have a capacity of hundreds of TWh of electrical and thermal energy to cover seasonal variations.

Roger Arnold's picture
Roger Arnold on Jan 26, 2017 2:16 am GMT

Link to “this article” failed to come through. Googling for “Charles Forsberg HIPES” will get one immediately to the abstract, but the contents have to be purchased. I found this presentation to be adequately informative, with the advantage of covering more options.

One point that the presentation brings out is that the pure oxygen co-product of any P2G scheme does carry a high value. I don’t know about storing large quantities of it; that’s a little scary. But using it for oxy-fueled combustion of hydrocarbons with sequestration of the CO2 output stream makes sense.

Nathan Wilson's picture
Nathan Wilson on Jan 26, 2017 4:17 am GMT

For stationary applications, flow batteries seem more attractive than numerous small cells, especially in their apparent ease of recycling the active materials.

That said, I think the growing BEV market will push solid batteries down in cost so rapidly that flow batteries will fall far behind.

Another problem is that batteries are entering the grid storage market at the 0.2-1 hour range (spinning reserves), and slowly shifting to 5 hours, to serve peak evening hours. Flow batteries have better economics at longer run-time (which give more daily energy for the same pumps and membranes), but longer run-time storage will compete mostly with cheap nighttime power, and only be relevant at high solar penetration. And at high solar penetration, solar loses it’s capacity value, even with storage, so a storable-fuel backup is needed.

In other words, after the 5 hour market segment, the next category is not 12 hours, it’s weeks as Willem suggests (the exception is thermal energy storage at CSP and nuclear plants, where that 12 hour thermal storage is backed up with weeks of combustion fuel). Note that li-ion batteries (and therefore the improved flow battery in the article) have an energy density an order of magnitude worse than liquid ammonia (a storable fuel).

So flow batteries get stuck between cell batteries and methane/ammonia/hydrogen storage, and can never gain a foothold.

Jarmo Mikkonen's picture
Jarmo Mikkonen on Jan 26, 2017 7:48 am GMT


Having read the post and the comments, it seems obvious that the Germans are going to have capacity markets, in other words, fossil fuel plants are going to kept in reserve and their owners compensated for keeping the plants in running order.

The German goal of 80% renewable power in 2050 does not mean that there are natural gas and coal plants providing a steady 20% stream of the power 24/7 and steady 80% of renewable generation.

In practice, Germany will need 200-300 GW of solar and wind capacity to provide that 80%. That means massive oversupply at times. Then there are those lulls when wind and solar generation is close to zero the fossil capacity is needed. And lots of it.

Short-term storage will be developed but if lulls continue for over 12 hours, storage becomes prohibitively expensive. The German system will probably become some sort of a hybrid. The fossil fuel plants already exist so there is no need for new investment.

Finally, I must say that one leg of Energiewende, namely increased efficiency gains that supposedly decrease electricity demand, is unlikely. Power supply is just one source of emissions. Germany needs to clean up transportation emissions (oil) and heating emissions (natural gas). France and Finland use a lot of electricity for heating and I think that is also the way Germany will choose. Add millions of BEVs and the equation is clear.

Darius Bentvels's picture
Darius Bentvels on Jan 26, 2017 10:53 am GMT

We talk about a fictitious situation which won’t become an issue in next decade. So we won’t know who is right.

Since I feel we won’t agree on the numbers, I don’t want to spend more time on this imagined issue.

We in NL store the processed gas (to cover higher demand in winter) in a few salt domes (we have more).

Darius Bentvels's picture
Darius Bentvels on Jan 26, 2017 10:58 am GMT

Seems to me Germany is more prone to follow Denmark where only energy neutral new buildings are allowed, etc.

Willem Post's picture
Willem Post on Jan 26, 2017 12:47 pm GMT

In my article I mention Germany already makes capacity payments, which likely will significantly increase in the near future.

These are separate from payments relating to curtailments, when some wind and solar energy could be produced, but is not needed in Germany and cannot be exported.

Jarmo Mikkonen's picture
Jarmo Mikkonen on Jan 26, 2017 1:45 pm GMT

I have a particular gripe about energy efficient and energy neutral buildings. In Finland, they started building those after the oil crisis in the ´70s and 80s.

It’s like living in a plastic bag. The buildings don’t “breathe”, condensation builds up easily in the structures. Worst are the indoor air problems. Any problems in the mechanical air circulation and that’s it.

The is even an organisation in Finland advocating for the so-called “mold refugees”:

Jarmo Mikkonen's picture
Jarmo Mikkonen on Jan 26, 2017 1:59 pm GMT


Germans talk about “capacity reserve” which is different from capacity market as in the UK. At least that is my understanding.

Darius Bentvels's picture
Darius Bentvels on Jan 26, 2017 3:35 pm GMT

We had similar in NL. But those designs improved during >30years, Now those issues are very rate, if they occur at all.

Darius Bentvels's picture
Darius Bentvels on Jan 26, 2017 3:48 pm GMT

Jarmo, agree.
German authorities rejected capacity market ideas as being unnecessary high subsidies for incumbent utilities with old plants, keeping those plants longer open than necessary.*)

But they do create temporal reserves if necessary.
When Merkel closed 8 NPP’s after Fukushima (spring 2011), they arranged cold standby with 2 already closed plants during next winter (2011/’12). During that winter one was asked to become hot standby during a week. But none had to deliver electricity.
*) The utilities then united with more utilities from other countries (Spain, UK, etc), arranged a study which showed such capacity markets would be necessary, mobilized publicity and political support and then requested the EU to implement those.

So German authorities had to explain in Brussels that those are a waste of money. As the issue was not solved, Brussels decided that countries can decide themselves.

Now you see only capacity markets in countries such as UK and Spain, where incumbent utilities have prime influence on politics.
Btw. those also have high whole sale prices…

Willem Post's picture
Willem Post on Jan 26, 2017 4:26 pm GMT


I did not use the words “capacity market”.

The capacity payments are made to have “capacity reserve”, i.e., units available to provide energy, i.e., they are “on call”.

That means those units are staffed, fueled, kept on good order, to be ready to go, as needed.

Jarmo Mikkonen's picture
Jarmo Mikkonen on Jan 26, 2017 4:53 pm GMT


Just making sure apples are apples. Personally, I think Merkel & co are playing with semantics. Market or reserve, the result is identical.

Willem Post's picture
Willem Post on Jan 26, 2017 7:56 pm GMT

Addition to comment:

At present, Germany has 35 pumped storage hydro plants with a total capacity of about 37695 MWh = 0.0377 TWh.

According to a study “Buffering Volatility: A Study on the Limits of Germany’s Energy Revolution”, in 2014, Germany would require about 11.29 TWh of PHS to store/smooth all of its wind and solar energy.

If all nukes were shut down and replaced by W&S, about 15.25 TWh of PHS would be required.

If all fossil plants were shut down, about 40 TWh of PHS would be required.

In 2050, with 8 times W&S (see alternative no. 1), about 100 TWh of PHS would be required, which is about 2600 times present PHS. Alternative no. 1 indicated 20 TWh or storage for the 100-hour lull.

Harry Degenaar's picture
Harry Degenaar on May 11, 2017 12:13 am GMT

@Bentvels – Nuclear power generation has the smallest deathprint, rarely discussed. The deathprint is the number of people killed by one kind of energy per kWhr produced, coal is the worst and nuclear is the best. Nuclear is NOT n-times more expensive, when excluding the first built Westinghouse AP1000’s and the first built Areva EPR’s. South Korea and China have already proven this. Furthermore, GEN III and GEN IV reactors are no longer considered to be dangerous. Nuclear power generation in Germany (when taking the capacity factors into account) is still well over twice that of Wind and Solar combined. GLOBAL LIVE POWER USEAGE:

Darius Bentvels's picture
Darius Bentvels on May 11, 2017 6:41 pm GMT

Harry, Death print
Sorry, but the idea that nuclear would have a small deathprint is imagination. It’s only true when one accepts the unrealistic estimations of pro-nuclear.
A typical example is the publication by (in nuclear circles extolled) climate guru James Hansen & Pushker Kharecha: 43 deaths for Chernobyl.
While other estimates are up to 4-8 million until the end of this century.

Read the Annals of the New York Academy of Sciences when you want to have a more realistic view regarding the huge death print of nuclear.

Darius Bentvels's picture
Darius Bentvels on May 12, 2017 6:30 am GMT

Except that the costs for capacity markets are factor 2 -4 higher…

Darius Bentvels's picture
Darius Bentvels on May 12, 2017 7:33 am GMT

Harry, Nuclear is expensive
Check the huge cost increase in France in last century, when nuclear had to become more safe. So FOAK hardly seem to play a role, as confirmed when one checks the new reactor generation:
– Hinkley C are 5 and 6 of the EPR. Still the price is 2-5 times that of wind & solar.
– The AP1000’s in USA are number 3-6. Not clear what the costs are but calculating with the official costs deliver already <10cnt/KWh (not including the costs of the loan guarantee subsidy. neither the $15B loss of Westinghouse.
So in the end the AP100) will costs similar as the EPR or even more.

China, S.Korea
We don’t know the real costs in communist China, neither those in S.Korea as there the utility is building himself, which delivers excellent options for invisible cross-subsidies. Considering their wide-spread fraud with nuclear parts, we can assume that they use those.

Anyway when you want to compare, you have to compensate for the really low wages and much higher productivity (longer working hours, more dedicated) of workers in China (have experience with that). Assume similar with S.Korea.

Those are also the cause Chinese (& Korean) products are so cheap that they compete us (in the west) off the market.
For solar panels they compete even while:
– we have import tariffs of ~45%, and
– those are far less labor intensive than NPP’s.

Not dangerous. GEN III and GEN IV no longer???
Same was promoted before Chernobyl.
Same was promoted for the Fukushima generation after Chernobyl…
Meanwhile even GEN III+ will end in similar disaster when attacked with a big freight plane loaded with steel, etc. Nowadays attackers, e.g. IS, may use more advanced weapons incl. drones and remote controlled planes.

Furthermore: didn’t see measures with GEN III+ against the regular spreading of radio-activity, which nuclear facilities incl nuclear power plants, do.
Which brings highly significant genetic, hence also health, damage to newborn up to 40km away. Especial important as genetic damage is transmitted to next generations.

Pro-nuclear seem to care little about health and intelligence of their next generations.
German govt does.
So they closed their prime dry cask nuclear waste store, Gorleben, prematurely (while the huge building was still half empty) because of that damage

Click “Jahresbericht Umgebungsüberwachung 2014” at the link and you can see pictures of the Gorleben site with its huge building with 0.5m thick walls in which the dry casks are stored and the high dike around it, as well as the excellent radiation measurement network, incl. neutrons, in and around it.

Darius Bentvels's picture
Darius Bentvels on May 12, 2017 7:57 am GMT

flow batteries get stuck between cell batteries and methane/ammonia/hydrogen storage
Sorry, don’t share your opinion. Even German grid installs flow batteries, while they also have ~35 pumped storage facilities…
Together with pumped storage, they fill the gap between ‘normal’ batteries and Power-to-Gas which supports seasonal storage. Their benefit is that they can be installed everywhere and have higher round trip efficiency than pumped storage.

With the increasing penetration level of solar panels, cheap night time rates are ending. Here the difference between the day-time and night-time rates decreased already a lot in past decade. So much that I was questioning myself whether it was worth the extra costs of the double tariff meter. But we get a smart meter before 2020, so more flexibility. Hence we may see lower tariffs during sunny days (so I will then adjust the hours my dish washer, washing & dry machines run).

Helmut Frik's picture
Helmut Frik on May 12, 2017 8:15 am GMT

Well the quality of the article is shown in the size of existing pumped storage being too low by factor 4 – the main pumped storage is missing, maybe because it’s not a short time storage but a weeks-storage. (Schluchseewerke).
Beisde this, main balancing of lulls etc is done by grid, not by storage. Storages are just needed when grids are forbidden in the model.

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