Comment by Dr Chris Harrison and Huw Thomas, Modelling and Simulation Engineers at Energy Systems Catapult.

As we transition to Net Zero and a greater dependence on electricity, the increased demand on the grid will be a major challenge that we’ll need to overcome. The increased network reinforcement and generation required will result in increased cost, impacting the consumer. Flexible electrolysers (for example, Polymer Electrolyte Membrane/Proton Exchange Membrane (PEM) electrolysers or Anionic Exchange Membrane electrolysers) connected to the local distribution grid rather than at the national transmission level have the potential to reduce that impact.

As part of the Hydrogen Innovation Initiative, we have used Living Lab homes and the Whole Energy System Accelerator (WESA) to explore the potential benefits that co-located hydrogen generation and storage at small industrial sites can provide to electricity networks through the provision of flexibility services.

Our simulations show that reducing the hydrogen produced during peak electrical demand can have a significant positive impact on a local electricity distribution network in 2050. By carefully sizing the electrolyser output and hydrogen storage volume, the capacity of the site’s grid connection could be lowered and/or the total peak electricity demand on the network reduced.

In this blog post, we refer to the electrolyser ‘operating point’, ‘nominal operation’ and ’turn down’.

The ’operating point’ refers to controlling the electrolyser operation to adjust input power consumption and output hydrogen production, ‘nominal operation’ is defined as the electrolyser operating at its nameplate rated capacity, and ‘turn down’ is the act of limiting the electrolyser operation to an operating point below its nominal value to reduce power consumption and hydrogen production.

Peak load is significantly impacted by the amount of electrolyser turn down

The electrolyser provides flexibility to the network by turning down its operating point at peak times to reduce its power consumption. The flexibility offered by the electrolyser can have a significant impact on the peak load of the electricity distribution network. The table below compares the impact on the network and the calculated hydrogen storage capacity required in five scenarios. The hydrogen storage required is calculated as the capacity needed to ensure the hydrogen demand of the industrial site is met whilst the electrolyser is turned down. These scenarios have been compared with a baseline scenario, where the electrolyser does not offer any demand turn down at peak times, and there is no hydrogen storage required.

In the simulations for a 1 MW electrolyser, by reducing the operation of the electrolyser from 50% to 25% of its nominal operating point (scenarios 1 and 2), the reduction in distribution network peak load more than tripled from 3.01% to 9.14% compared with the baseline scenario. However, further reductions appear to provide diminishing returns – turning the electrolyser off at peak times only provides an additional 0.85% reduction in peak load compared to the scenario where it operated at 25% (scenario 3).

For a smaller 500 kW electrolyser, reducing to 25% of the nominal operation (scenario 5) was found to result in the greatest peak load reduction, achieving a 12.7% reduction in peak load. In addition, the 500 kW electrolyser enables a 38% decrease in the site’s grid connection size, regardless of whether the electrolyser provides flexibility (scenarios 4 & 5).

Peak network load and time at high loads are reduced by more turn down of the electrolyser, but more storage is required.

Time at high network load is reduced

Reducing the operating point of the electrolyser is successful at reducing the time that the electricity network is operating at high loads. We investigated the percentage of time that total network demand is above the 90th percentile of the Baseline scenario, to give an indication of the duration at which the network will be operating at higher demand. This reduced from 10.1% of the time to just 4.2% (a 58% reduction) in scenario 5 (500 kW electrolyser and 25% of the nominal operation during peak times).

More turn down requires more storage

As the electrolyser operation is turned down more, the required hydrogen storage capacity grows dramatically.  For the 1MW electrolyser with a turn down to 50% of nominal operation, there is a requirement for 0.8 MWh of storage (25 kg of hydrogen), but when operation is limited to 25%, five times more storage capacity is required (125 kg). If the electrolyser completely shuts off, ten times more storage is required (250 kg). The 500kW electrolyser with a turn down to 25% requires the greatest storage capacity (300 kg of hydrogen). While this will increase the cost to the industrial site of operating the system, there is the potential that participation in flexibility markets could result in income to offset these costs.

Inclusion of hydrogen storage can reduce the impact on the local grid

We have shown that offering flexibility through reducing the operating point of the electrolyser at times of peak electricity demand can offer a significant positive impact to the local electricity distribution network while decarbonising the industrial site. By carefully sizing the electrolyser and hydrogen storage capacity the industrial needs can be met while decreasing the peak load on the network by over 10%. This would reduce or delay local network upgrades and reinforcement, and the amount of generation required would be reduced. Together these will reduce infrastructure and operating costs, reducing the burden on consumers.

Ultimately the optimum setup will depend on the application, costs of electrolysers and storage and the flexibility offerings available. But the advantages to the network of using a setup that includes hydrogen storage are clear. We plan on further investigating the relationship between relative industrial and domestic loads and the impact that the electrolyser can provide to the network.