Power-to-Gas concept. According to the white paper, an important distinction between P2G and other forms of energy storage is that P2G allows conversion of energy amongst a variety of sectors and end-uses (e.g., electric grid, gas grid, transportation fuel) and takes advantage of the natural gas grid as an existing and inexpensive storage resource to augment, and in some instances replace, dedicated hydrogen storage infrastructure. Defining grid electricity storage to include conversion and later use in non-electrical forms of energy is critical to achieving emissions and climate goals in a least-cost, best-fit manner. Constraining storage solutions to “electricity-in, electricity-out” only will increase the cost of intermittency. Click to enlarge.

The stored chemical energy can be used to generate electricity via a fuel cell or other generation device, as a transportation fuel, or for any other purpose for which hydrogen or methane is used. The water consumption of the P2G process is small, with about 50 gallons of water required to convert 1 MWh of power into 20 kg of hydrogen.

Power-to-Gas energy storage leverages an already existing storage infrastructure that has a vast amount of capacity—i.e., the natural gas grid—making P2G an excellent candidate for long-duration storage applications. It is a multi-functional technology that serves use cases that support the electricity, transportation and heating sectors, the paper notes.

Among the other conclusions of the analysis:

• Electrolysis is the only viable and commercially proven method of producing hydrogen from highly variable renewable electricity generation. Electrolyzers can provide a dynamic response to supply and load fluctuations – a critical factor in grid stabilization.

• Once produced, hydrogen can be used for high-value applications such as for clean transport fuel therefore turning electricity into a high value road fuel capable of extended range and rapid fueling characteristics.

• Hydrogen, or methane generated from hydrogen, can also be injected into the natural gas pipeline system providing a flexible method of storing renewable energy for all the traditional uses of natural gas.

• The use of widespread electrolysis in California will not adversely affect the drought situation as the water converted by the electrolyzers is modest in amount, can be reclaimed water, and can be recovered in some cycles such as when used in a fuel cell.

• The need (and opportunity) for bulk energy storage in California is potentially in the TWh range, given the developing “duck curve”, the mandate for energy storage procurement and the state’s goals to transition to non-petroleum vehicle fuels. (The duck curve to the shape of the CAISO net load (grid supplied power) plotted against time of day. It looks like the profile of a duck.)

  
  

• The cost of fuel produced via Power-to-Gas is competitive with other pathways to produce renewable fuel and the cost competitiveness will increase as the need for (and value of) grid services increases.

• P2G can be cost effective for electricity storage if the cost of input electricity is low such as at times of surplus supply.

• The value proposition for P2G as grid storage is being developed along with other forms of energy storage, but important market-structure, regulatory and policy issues must be addressed in the near term to capture this value starting with increased awareness of the multiple facets and successful international deployment of P2G.

Resources

• Power-to-Gas: The Case for Hydrogen White Paper