Storing Wind Energy as Hydrogen

By David Anthony and Ken Brown

Wind turbines capture the energy contained in wind.  The turbine rotates a shaft which powers an electric generator.  The electricity that flows from the generator can go to the wind farm’s grid connection to be consumed immediately or go to storage.  We have previously discussed the advantages of storage.  Let’s look at storage using hydrogen.

Water electrolysis produces hydrogen.  As the electricity flows through the water in an electrolysis unit, oxygen and hydrogen are evolved as gases at separate electrodes. In a 100% efficient unit, it takes about 39 kilowatt hours (kWh) of electricity to create 1 kilogram (kg) of hydrogen.  In the real world, electrolysis units are about 80% efficient at best.  With an 80% efficient unit, it takes about 50 kWh of electricity to create 1 kg of hydrogen.  The hydrogen is piped to a hydrogen storage unit.  To avoid the high cost of compressing hydrogen or of cooling and liquefying hydrogen, a good alternative is to store the gas in a metal hydride slurry.  Safe Hydrogen uses magnesium as the metal and mineral oil as the liquefying agent.  With the use of small particles and a suitable dispersant, the particles will stay in suspension almost indefinitely.  Using a hydriding reactor, hydrogen is absorbed by the Magnesium Slurry with suitable pressure and temperature that ensures rapid reaction.  The Magnesium Hydride Slurry that is created in this reactor then can be stored in large quantities at ambient conditions.  The hydriding reaction to create the magnesium hydride slurry creates heat.  This heat is about 30% of the heating value of the hydrogen gas.  About 10 percentage points of this heat, or one-third of the heat, can be used to perform useful work such as generating more electricity.  The rest of the heat can be used for space heating or to produce hot water.  Thus the hydriding step in the process can be from 110-130% efficient.

There are a number of options for the stored slurry.  One, the hydrogen can be recovered on site and the hydrogen can be used to power a gas turbine-generator.  The wind farm owner has the option of selling into the real time and day ahead electric market at a time and price of his choosing.  Since wind blows more at night than during the day on average, and since consumers use more electricity during the day than at night, the wholesale price at night is often $0.02 per kWh or less.  It was reported in Business Week in September 2009 that year to date in the Texas Grid, the wholesale price of electricity was zero or below for 11% of the time.  During those times, the generation facilities on line were paying to put power on the grid.  The Electric Reliability Council of Texas (ERCOT) controls the wholesale price of electricity in the real time and day ahead markets to balance generation and load.  Why would generators pay to put power on the grid?  Large base-load coal and nuclear plants do not want to vary their loads.  Cycling the plants leads to premature wear and high costs.  Wind farms get a $0.022 production federal tax credit.  Until the price passes down through a negative $0.022, wind farms still receive revenue if the turbines generate power.

Another option is to use the hydrogen slurry to “firm” the wind power.  Wind does not blow consistently from hour to hour, day to day, week to week, or season to season.  The ISO that supervises the grid cannot count on the full power of the wind farm’s output.  Typically, only 15% of a wind farm’s output can be counted on as reliable capacity—likely to be available in any given time period.  This means that for a 500MW wind farm, only 75MW is counted as generating capacity by the ISO.  Often, to “firm” the wind farms output, a natural gas fired plant needs to be constructed—partially negating the carbon free output of the wind farm.

With storage, the picture can be different.  Below is an example of a 500MW wind farm delivering 150MW dispatchable power 100% of the time by using storage and gas turbines(GT) powered by hydrogen.  In this example, the ISO can count on 30% of the wind farm’s output.

Wind Storage in Hydrogen Slurry

 

The beige portion of the power generated is stored, the blue portion is delivered by the wind turbines to the grid, and the red portion comes from gas turbines powered by hydrogen.  The horizontal axis represents a probability of power going to the grid from the wind or gas turbine.  About 45% of the time in the year, 100% of the 150MW will come from wind with the excess going to storage.  About 40% of the time, power comes from both the wind and gas turbines.  About 15% of the time, all of the power comes from the gas turbine.  In any give hour or day, power may flow in any of these ways.

Advantages:

  1.  Dispatchable power can demand a higher price.
  2. The grid connection can have smaller capacity—it no longer has be sized for maximum wind farm output.
  3. Firming natural gas fired plants do not need to be built.
  4. The gas turbines can provide the regulation that natural gas fired turbines now provide.
  5. The wind turbines can spin 100% of the time the wind blows (excluding the time when the weather is too violent to operate).

 

David Anthony is Managing Director of 21Ventures.  21Ventures has made over 40 clean tech investemtns  across the globe since 2004. 21Ventures is a co-investor  in Safe Hydrogen, LLC 

Ken Brown  is CEO  of Safe Hydrogen, LLC, a developer  of  safe, transportable  hydrogen.  

5 replies
  1. AgentG
    AgentG says:

    Thank you for this article. Storage is a fantastic opportunity for clean energy and hydrogen storage might hold great promise.

    However, statements like "110-130% efficient" only rob you of professional credibility. The literature is full of improper recitations of efficiency that serve no one.

    Heat generated storing H2 in MG means a lower energy state. To release the H2, heat must be applied. So, the energy balance will be negative, requiring more heat to release the hydrogen than was given off previously. In this case, it appears that the overall electrical efficiency for hydrogen storage is *substantially* less than 50%, when calculating properly as electrical energy output vs. electrical energy input for the entire hydrogen storage system in aggregate, which is really the fundamental metric here. This highly relevant fact is never presented, because it likely undermines the economic case for hydrogen storage. Even worse, we get an impression that those promoting hydrogen storage are not being completely forthcoming and are selectively obscuring key facts. If I am mistaken, please show me where and how.

  2. William Basore
    William Basore says:

    What is missing here is that hydrogen can be a raw material ingredient used to make products of higher value than grid electricity. The puzzle here is economics, not power generation. This is an opportunity cost problem. The wind mills produce no economic benefit when they are furled.

    The stored hydrogen can be combined with CO2 from coal or natural gas fired power plants to make synthetic hydrocarbon fuels. The fuel produced has a much higher value than grid electricity: Electricity is cheaper than oil, so making more valuable gasoline or diesel from waste CO2 and H2 produced with low cost or even free electricity makes the economic business case feasible.

    This concept is also critical as it provides us with the one element that can help stabilize the price of oil: a viable alternative that we can use in our vehicles today. The effect of not sending billions of dollars out of our economy for oil is mind boggling.

  3. pagan
    pagan says:

    Before you plan on storing energy from windmills they first have to produce it., most dont. I am amazed at all the money thrown at usless wind and solar technology that is so costly and ineffective it will never pay for itself, where getting produced energy if any, to the grid and maintanace is a financial nightmare.
    Without free wasteful funding from the puffed up administration of the all knowing Obamas DOE who have an astonishing record of funding fancyful technology that will never work or pay for its self, while at the same time throwing real energy producing technology under the bus. With out DOE funding windmills and solar would be in the junk yard. However a new technology is coming soon, that will kill off these two hidious money wasters, thats if they dont commit suicide first. It looks like its starting to happen.

Leave a Reply

Want to join the discussion?
Feel free to contribute!