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Renewables and Natural Gas are Partners, Part II: Proof of Concept

Ed Dodge's picture
  • Member since 2013
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  • Dec 10, 2013

Wind, solar and biogas combine to keep the lights on in Germany

In Germany a test has been successfully conducted of a 100% renewable energy power plant using wind, solar and biogas to provide round the clock electric power. The Kombikraftwerk 2 is a “Combined Renewable Energy Power Plant” that links together geographically dispersed assets into a virtual power plant.  Unlike plans for 100% renewable energy written by activists such as Mark Jacobson that are designed to influence the political debate but could never actually function, this plan is designed by engineers to actually work in the real world.   Many climate activists reject all carbon based fuels but the Germans recognize the crucial role played by methane as a renewable that can both fill in for the intermittency of wind and solar as well as providing much needed energy storage.  This novel new renewable energy model demonstrates the need for natural gas backup, energy storage in the gas pipeline network, carbon capture and utilization and renewable natural gas.

The Kombikraftwerk 2 is a pilot study funded by the German government and conducted by a consortium of leading companies including Siemens and SMA along with academics and the weather service.  The main focus of the study was to demonstrate on live facilities that grid stability could be maintained as the power outputs from wind and solar fluctuated.  Through a combination of slight curtailment and biogas power, precise voltages and frequencies were successfully maintained on the power grid.  The test system linked together 37 wind turbines, four biogas CHP plants, twelve PV systems and one pumped hydro reservoir into a virtual 80 MW plant intended to meet the power demand of one small town or equivalently  1/10,000th of Germany’s overall power demand.  All of the plants were active commercial facilities.  Most of the documentation for the project is in German, but here are links to English videos and papers.  The videos provide an excellent overview of the operations and a vision for how the system is meant to work in the future including the advanced power to gas systems. 



Wind, Solar and Biogas 100% Renewable Energy Power Plant

In America the discussion over energy storage is generally focused on batteries or pumped hydro. The Department of Energy lists batteries, flywheels, capacitors, control systems and some others technologies in its Energy Storage Program, but no mention is made of using the natural gas pipelines as a storage medium.  The Germans on the other hand embrace the idea of power to gas completely and lead the world in the technology.  Power to gas plays an important but often overlooked role in the Energiewende.  Power to gas offers substantial benefits in minimizing curtailment when wind and hydro are overpowered by using the diverse, abundant, long-term storage capacity of the pipeline networks.  There are real limitations in batteries and pumped hydro, aside from their expense, they can only store a few hours of power, these technologies have their role but neither can offer the massive storage potential of the gas pipeline network that is already in place.  Gas pipelines also offer alternative long distance transport options to the power grid that is less expensive and lower impact than power lines.

Power to gas works in a variety of ways.  The simplest method is basic electrolysis; electric power is used to separate water into hydrogen and oxygen.  The hydrogen can then be used directly, injected in small quantities directly into the natural gas pipelines or combined with carbon to form methane.  Pilot projects are currently being run in Germany to assess direct injection of hydrogen.  A more advanced option is to combine hydrogen with CO2 captured from coal or other fossil fuels to form methane, which is CH4.  This process requires some energy to break apart the carbon bonds, but it would be done with surplus or low cost power.


Power-to-Gas flowchart
Power-to-Gas flowchart

Making use of captured CO2 is a topic rarely mentioned in the American policy debates.  The discussion is dominated by Carbon Capture and Sequestration (CCS) and how difficult and expensive it is.  Carbon Capture and Utilization (CCU) offers an alternative model for carbon recycling.  Using low cost power from surplus renewables or nuclear, CO2 can be broken apart and used for fuels or in the chemical industry.  Methane is not the only option and other chemicals may offer better economics or efficiencies.  An interesting study was performed by DNV and can be found here.  The main products that can be produced from CO2 include chemicals, plastics, carbon fiber, graphene, fuels, carbonated beverages and Enhanced Oil Recovery (EOR).  EOR has been the most successful use so far for CCS, but sequestering CO2 just to produce more fossil fuels does seem to defeat the purpose from a climate change perspective.  CCU is an idea that should be explored far more actively in this country as carbon is valuable life giving molecule, not toxic waste.


Uses for Captured CO2

Uses for Captured CO2

While I am personally very excited to see this concept of a gas-electric renewable power model brought to life, I do have a couple of comments about the limitations of the Kombikraftwerk.

First, this model is for electricity only, they state in the video that “most” transportation will be electric, but obviously not all.  Electricity is great for light duty passenger vehicles and commuter trains, but hydrocarbons are still needed for heavy duty and long distance vehicles such as trucks, construction equipment, airplanes and ships (Rod Adams passionate appeal for nuclear shipping duly noted).  Clean fuels for transportation are still needed and not provided for in this model.

Secondly this model is not a prescription for a high energy future.  This model presumes (without saying) that energy use will be reduced through efficiency measures, which may be possible but it is not clear that it is desirable.  The production of wind, solar and biomass simply do not add up to provide the massive quantities of energy that will be required to lift billions of people out of poverty.  Bulk heat and power in a high energy future will need to be provided by nuclear power and on this point I break with German energy policy.  A high energy future opens up new possibilities for improving living standards by enabling energy intensive projects like water desalination, toxic waste cleanup and aluminum production.

A hybrid gas-electric clean energy model offers opportunities for every type of technology to find its niche according to its utility and scalability.  We must stay focused on replacing coal and oil with clean energy solutions.  I am convinced that these solutions exist and will enable us to clean up the environment, lift up the poor and open up vast new energy resources and economic growth.  The Kombikraftwerk is very encouraging and shows us some pieces that are missing from the American energy policy debate but should be encouraged here like renewable natural gas, carbon utilization and power to gas.

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Simon Friedrich's picture
Simon Friedrich on Dec 9, 2013

Hi Ed,

What feedstocks did they use in the four biogas facilities?

At what volume and pressure ranges did they store the biogas?


Simon Friedrich

Bob Meinetz's picture
Bob Meinetz on Dec 9, 2013

Ed, again Energiewende entrepreneurs are performing logical gymnastics in order to justify a “renewable” label for biogas:

By far the most important source of bioenergy in Germany is wood. Domestic consumption of wood resources has increased continuously over the past two decades and currently amounts to 130 million cubic metres per year.

European firms are scouring the Earth for wood. Europe consumed 13m tonnes of wood pellets in 2012, according to International Wood Markets Group, a Canadian company. On current trends, European demand will rise to 25m-30m a year by 2020...

Tim Searchinger of Princeton University calculates that if whole trees are used to produce energy, as they sometimes are, they increase carbon emissions compared with coal (the dirtiest fuel) by 79% over 20 years and 49% over 40 years; there is no carbon reduction until 100 years have passed, when the replacement trees have grown up. But as Tom Brookes of the European Climate Foundation points out, “we’re trying to cut carbon now; not in 100 years’ time.”

Ed Dodge's picture
Ed Dodge on Dec 10, 2013


No one was suggesting to that wood was the only biomass source.  There is no question that humans are capable of taking too much wood and creating deforestation, this was true long before the industrial revolution.  Biomass has lots of competing demands on it as a resource and we have to be cognizant of only taking as much as mother nature freely offers and nothing more.

The biogas plants in this study were on farms processing manure I believe.  There are lots and lots of resources available to manufacture methane from.  Sewage, garbage, food waste, animal waste, coal, biomass, algae and more.  As long as you have some source of carbon and water you can make CH4, there is no upper limit on how much methane we can produce synthetically.  It can be a great way to dispose of waste like petcoke.

The key takeway is that methane is renewable and our natural gas infrastructure can carry renewable gas in great quantities.  Power-to-Gas offers the ability to leverage the gas pipeline networks for vast energy storage without needing to invent any new technologies.

Joris van Dorp's picture
Joris van Dorp on Dec 10, 2013

Ed, (great article by the way)

Concerning the following:

The biogas plants in this study were on farms processing manure I believe. “

I think you’ll find that these farmers spike their manure with significant amounts of corn in order to be able to produce economical quantities of biogas. In a way, this endeavour is similar to the US corn-ethanol plan (or should I say the us corn-ethanol boondoggle?).

Concerning the kombi-kraftwerk concept: I’d like to see the biogas plant and pumped hydro replaced by fast ramping modular nuclear power plants. Trees shouldn’t be burned by the milions of tons in the name of sustainability, IMO. They should be left to prosper and be pretty in the form of forests.

Simon Friedrich's picture
Simon Friedrich on Dec 11, 2013

Please note most of these biofuel “renewables” only exist because of human activities and the resulting emissions still contribute to greenhouse gases either as carbon dioxide or methane.

Nathan Wilson's picture
Nathan Wilson on Dec 13, 2013

It looks like the Kombikraftwerk2 project has done some very useful simulations.  Unfortunately the English write-up leaves out most of the good data (particularly the trade-off between more batteries & pumped hydro storage versus more inefficient power-to-gas-to-power). 

They also glossed over a lot of really bad news, for example cost. When combined with smart meters with real-time pricing, the storage in this system will produce painfully large price swings that could be fully visible to the end users (even though the current feed-in tariffs hide such swings from customers with on-site solar PV systems).  The power-to-gas idea will produce methane that is much more expensive than imported pipeline natural gas.   The average cost of electric power will also be very high (for example, solar PV costs much more than on-shore wind, but provides 20% of the energy in their reference portfolio).

Unfortunately, in their push to declare that the system would make reliable power, they also were quite shy about making recommendation for the technology choices that would be required to make it work.  They mentioned needing a lot of storage, but there is no meaningful detail.  Here’s a subtle jab a residential solar,”…to optimise the results, the renewable energy systems should be connected to the highest voltage levels possible. Ideally, a certain proportion should also be provided by central systems…”.  The owners of rooftop solar system like to imagine themselves as being in command of their own electricity supply, but in order for the entire grid to function, the report hints that the utility must be in control of the inverters and in many cases batteries attached to such systems. 

That they could achieve reliable power should come as no surprise.  To supply the stated average load of 61 GWatts, they assumed 43 GWatts of methane power stations would be available, about 6 GWatts of geothermal, 7 GWatts of hydro, somewhere around 8 GWatts of solid biomass fired generation, plus an unstated amount of batteries and pumped-hydro (I estimated the nameplate capacity based on stated generation and reasonable estimated capacity factors of geothermal at 75%, hydro 40%, and solid biomass 50, but they could be much worse).

Like the high renewable study done for the US by NREL (Re Futures), it assumes the desired amount of biomass will be available, with no interference from the spacing heating or transportation fuel sectors.  The biomass numbers assumed should raise flags for all environmentalists, since according to David MacKay, biomass has an energy yield of only 0.2 W/sq.m, which means each GWatt of average yield requires 5,000 square km or 1,922 square miles.  This is approximately true whether one is burning wood to make electricity directly, or converting to bio-methane as an intermediate.

An important lesson we should take away from this work is that early phase out of nuclear power is not necessary for the development of the renewable technologies, and in fact gives them much higher fossil fuel use for any given level of renewable development.  For any given level of fossil fuel use, the nuclear phase out means higher cost and much larger environmental footprint for their energy system.

The most worrying thing about the German plan is that unlike the French plan (in which the expensive parts happen upfront: reactor construction), the German plan mostly defers the expensive part (energy storage) until the nuclear phase out is mostly complete.  This puts a large cost burden on future generations, and increases the likelihood that the implementation will slowdown or stop due to unacceptable costs, leaving an energy system that is even more dependent on fossil fuels than before. 

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