Using Hydrogen as a Battery
In 2 previous articles we showed that EVs can be a useful tool in reducing CO2 in our atmosphere. In the second article we saw that, in addition to getting people into EVs, we also need to clean up the grid approximately 60% from where we are now. This implies adding more CO2 free sources of electricity into the grid mix.
Renewables provide that source but at very high penetration rates renewables would benefit from having a way to store the energy to smooth out the intermittent nature of wind and solar.
Could Hydrogen be used as a very large battery? Is anyone doing it? How much does it cost?
Germany has Ambitious Plans for Renewables
Germany has plans to increase their percentage of renewables from a current mix of approximately 25% to 45% by 2025 and 60% by 2035.
With an increasing percentage of renewables in the grid mix, the intermittency problem associated with wind and solar becomes more difficult to manage. Some way of storing energy from peak periods where there is a surplus would be very advantageous. Hydrogen could provide that storage medium. The official term for hydrogen storage is P2G, power to gas.
Why not batteries?
Batteries can be useful in smaller decentralized applications where the frequency between charging and discharging is short ie on a daily basis. With further cost reduction from Tesla’s giga factort we will see Li batteries being used more frequently to smooth out the daily fluctuations in solar. Day to day fluctuations require smaller battery sizes than seasonal fluctuations where very large storage requirements make a battery system too expensive.
Hydrogen storage could be used in these situations where the charge/discharge frequency is higher than a 1 day, sun up, sun down scenario.
Is anyone actually building a P2G Plant?
Germany already has multiple demonstrator plants up and running. One of the larger ones is in Falkenhagen, Germany and it is 2 MW capacity. Germany plans to have 1000 Mw of P2G plants running by 2022.
How does this Plant Work? What about the high cost of the Hydrogen infrastructure?
The plant uses electrolysis to produce the hydrogen. The electrolyzer is an alkaline fuel cell manufactured by Hydrogenics. Their plan is to move to PEM elecrolyzers which offer a more compact design as shown on figure 5.
The plants main purpose is convert EXCESS electricity from a wind farm into hydrogen. During period of very high wind activity the cost of electricity is essentially zero since without storage the wind generators would need to be shut down. Using excess electricity makes energy conversion efficiency a less important variable.
The infrastructure cost issue is addressed by injecting the hydrogen into the existing natural gas system of lines and storage tanks. Concentrations as high as 20% (page 7 ref 1) can be used with little or no change to the existing natural gas distribution system or to the combustion characteristics of natural gas. Using existing natural gas infrastructure mitigates cost. The 2 MW plant in Falkengagen has successfully demonstrated the entire process, including hydrogen injection into the natural gas system.
Is P2G Cost Effective?
Studies have shown that it is. The study (ref 1) showed that payoff period as low as 3.5 years (ref 1 p17) can be achieved under the proper conditions: where the cost of electricity is low and the cost of natural gas is high. This is exactly the situation in Germany.
A tornado chart which shows the effect of the primary variables is shown in figure 6. Cost of electricity and cost of natural gas have the highest effect on payoff time. A complete list of all the variables is shown in figure 7
Could P2G be in our Future?
I would say that under the correct conditions the answer is definitely YES. If P2G can be used as an effective tool in making renewables work then why not use it? Why not add this tool to our war chest of tools in our fight against Global Warming?
Here is a link to Hydrogenics product catalog. All the specs for one module worth of equipment at the Falkenhagen P2G plant are in the catalog found here.