Comment by Daniel Murrant, Practice Manager – Networks and Energy Storage, at Energy Systems Catapult.

Looking forward, climate change will have an increasing impact on many aspects of our life, even with decarbonisation measures in place. This is because many of the effects of climate change are already “baked into the system” due to historical greenhouse gas emissions. One area which climate change can impact is access to, and availability of water, particularly freshwater.

Our energy system is already heavily dependent on water, for example for boiler feed and to provide cooling for thermal power generation (e.g. where heat is produced to generate power such as in gas or nuclear power stations). However, as we move into a Net Zero world this reliance on water will change but it won’t go away, with water still being required for some thermal generation (e.g. nuclear power plants or generation with carbon capture and storage) but also for new methods of energy generation such as hydrogen production or the growth of bioenergy crops.

In a recent study Energy Systems Catapult and our partners HR Wallingford worked with National Grid Electricity Transmission and National Gas Transmission to explore the impacts of future water availability on a Net Zero energy system, especially the impact on energy networks.

We did this using a methodology (Figure 1) which incorporated future water availability and accessibility projections into our whole system modelling capability, and then focused on identifying energy system changes which would likely impact energy networks.

This analysis first focused on the whole energy system impact of future water availability where we modelled over 40 individual energy scenarios out to 2050, each with different assumptions around future water availability and water demand. We found that one area which was most sensitive to water availability was the cooling methods used for thermal generation.

The main water requirement for thermal generation is for providing cooling. Therefore, the total water abstracted and consumed by a power station is largely driven by the cooling method it uses. Cooling technologies vary from (a) abstracting large volumes of water and consuming little as the water only passes through once before being returned to the water source (once-through cooling), to (b) abstracting less but consuming more as the water is recirculated through the cooling circuit multiple times leading to some of the water evaporating and not returning to the water source evaporated (evaporative cooling). There is also air cooling where air fans are used, as well as hybrid systems which alternate between evaporative and air cooling. Large amounts of water are typically the most efficient coolant so moving from once-through cooling to evaporative and then air tends to result in higher costs. Where enough water is available, once-through cooling is therefore usually used.

We found that with limited freshwater available, when environmental regulations and other siting constraints also limited access to coastal and estuarine waterbodies then there was a shift to using less water-intensive cooling methods. This is highlighted by Figure 2 which shows electricity generation in 2050 broken down by cooling method, for a sensitivity with (left) good access to coastal and estuarine water and (right) limited access to these resources. Moving left to right there is a shift away from once-through cooling (turquoise) with the other cooling methods making a larger contribution in most regions.

Additionally, when there was less water available more offshore wind was also deployed. This additional installed capacity alongside the change to more costly cooling methods resulted in a modest increase in system cost for those scenarios with the least water available.

We then considered how the findings of the whole system analysis may impact future energy networks. Figure 3 shows the change in cooling water source for thermal electricity generation capacity (GW), for a scenario with good access to coastal and estuarine resource. In order to access adequate water to utilize the cheapest, most efficient but most water-intensive once-through cooling there is a considerable increase in capacity at the coast.

This move to the coast can exacerbate several existing electricity network challenges:

1. Network operation and stability: Relocation of significant thermal generation, and therefore inertia, towards the coast can change the distribution of inertia on the network and cause difficulties relating to network operation and stability inland.
2. Voltage control: Siting thermal generation on the coast could move synchronous generation further away from other areas, making it harder to correct voltage levels in those areas.
3. Change in boundary transfers: If the distribution of generation assets changes significantly, this can change directions of power flow across boundaries, impacting where network reinforcement is needed.
4. Short circuit levels: These will increase near new thermal generation sites, although if these are on the coast then challenges may arise in power system protection operation inland.

But it is not only electricity networks which will be impacted by future water availability, we found that total hydrogen consumption reduced slightly as water availability fell which in turn could have a small impact on hydrogen networks. We also found that the heat source for district heat networks was dependent on water availability, as heat offtake from thermal generation plants (including nuclear plants), was heavily restricted under scenarios with low total water availability leading to greater electrification of district heat network under thee scenarios, this in turn can have additional electricity network impacts.

In total this analysis identified 31 individual insights covering whole system and network impacts but boiling it own to 3 essential points we found:

1. If access to estuarine and coastal water is limited then freshwater resource constraints will result in the deployment of additional renewable capacity and more expensive but less water-intensive cooling methods.
2. Increased thermal generation capacity on the coast and estuaries, if this is possible, may result in a more resilient whole energy system, although it is likely to increase operational and stability challenges for the electricity network.
3. Water-related constraints also impact other energy networks, such as hydrogen and district heat.

This work is an important step in enabling a future Net Zero energy system and energy networks which cost effective and resilient to future water availability driven by the impact of climate change. However, we recognise there is more work to do particularly in ensuring that climate change impacts, specifically future water constraints, integrated into future energy system planning.

Energy Systems Catapult would welcome further conversations and collaboration in this area. For more details on this analysis find the full reports and executive summary here, or reach out to us.