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What sort of green grid system?

By Dave Elliott

It’s clear that we will need energy transmission grids and networks to help balance variable renewables and link up locations where there is excess to areas where there are temporary lulls, but what sort of energy is best for transmission? And for storage? Both are important and can interact: in some cases storage may be better as a local option than long distance transmission, while in other cases, long distance transmission may allow access to areas where storage (e.g. pumped hydro reservoirs) is easier.  However, electricity isn’t necessarily always the best option for either: for example, gas can be transmitted long distances with low losses and, once installed, gas pipelines are less invasive than power grid tower links. Gas can also be stored in bulk in underground caverns and the gas grid itself is a store. So as we move to a new energy system, we need to think about all the possible energy vectors – and that also includes heat.

Electricity, heat and gas each have their pros and cons in different contexts. Heat is actually often the best storage medium, but it is hard to transmit over long distances (>30miles). Gas is easy to store and transmit (in the UK, 3-4 times more energy is transmitted by gas than by electricity), electricity less so – there are significant transmission/distribution losses (up to 10%/1000km for AC) and storage is expensive. So electricity may not be the way ahead in all cases. We need to look at all the energy vectors, including also non-fossil gasses such as green hydrogen and syngas/biogas.

So it’s good that the UK Energy Technologies Institute is investing £300,000 in an 11-month energy infrastructure analysis project led by Element Energy aiming to improve understanding of the opportunity for, and implications of moving to, more integrated multi-vector networks. It says that ‘Future energy systems could use infrastructure very differently to how they are employed today. Several individual energy vectors – electricity, gas and hydrogen – are capable of delivering multiple services and there are other services that can be met or delivered by more than one vector or network. This project will explore how this could become a reality over the coming decades.’

Pity there’s no direct mention of heat there, but the ETI is keen on heat networks, and the UK Department for Business, Energy & Industrial Strategy has launched the first part of a 5-year £320m programme to supply low-carbon and recycled heat in towns and cities in England and Wales, in a £39m pilot scheme for the Heat Networks Investment Project.

So hopefully heat will be covered in the new study, especially since CHP/district heating systems with storage can play a role in integrated energy system balancing, along with other energy storage and demand management systems. Certainly the ETI is looking at better integration: ‘Currently the networks themselves are operated independently, but their role in the future energy system is expected to evolve and new networks are also set to emerge. Closer and more complex interactions between these different vectors, including partial or complete transitions from one vector to another, are a distinct opportunity. The full benefit of employing a multi-vector approach to energy supply will only be clear once the impacts on each part of the energy system are understood. So far multi-vector energy systems analysis has focused on generation or demand side technologies. Understanding the implications for networks and their ability to contribute to multi-vector energy systems will help to provide a more complete picture. The results of this project will help to inform the best way to deploy new networks alongside existing networks, how best to transition from existing to new networks and what opportunity there is to make use of existing assets.’

While the ETI is looking more broadly at all the energy vectors, there are also more focused projects looking at optimal power grid management for variable renewables. For example IRENA’s report, Scaling up Variable Renewable Power: The Role of Grid Codes, looks at best practices and lessons learned from different countries on developing power grid codes and rules for stable operation/integration.

Certainly integrating a higher share of variable renewable energy (VRE) into the electricity grid is an issue concerning many countries. Some worry that VRE will disturb business-as-usual procedures for managing power systems, resulting in power supply interruptions or system problems. But some countries have already shown that a higher share of VRE is possible today with the right technical measures. The report offers case studies from several countries, including:

*Barbados: early stages of grid code development for a country with rising VRE targets;

*Germany: policy and technical co-ordination to resolve the ‘50.2 Hertz problem’ triggered by rapid penetration of solar PV, which has little frequency-stabilising system inertia, unlike big rotational-turbogenerator power plants. Wind plants offer some but not much.

*Ireland: challenges posed by wind power in an island system without strong cross-border grid interconnections. VRE has been limited initially to 50% to avoid problems.

It does seem inevitable that power from wind farms and the like will be transmitted by electricity grid, including from offshore projects, with HVDC supergrids allowing for more efficient long distance transmission, but of course, there may be some merit in converting that power to hydrogen either offshore or on shore for subsequent transmission by pipe. Indeed, some see hydrogen, produced from a range of energy sources, as a key new energy vector, with multiple possible end-uses.

Microwave plasma generation of hydrogen from methane, producing no CO2 gas, is amongst the ideas outlined in a new OU-led report on hydrogen futures from the UK Institute of Physics, Next Steps for Hydrogen.

The report accepts that earlier drives to push hydrogen as a new energy vector have slowed, with battery EVs dominating in the key transport sector. That may change with new fuel cell technology, but for now it looks to a range of new industrial niche markets for hydrogen to help rebuild momentum. For example, it says liquid hydrogen at 20 degrees K may be better and cheaper than helium for cryogenic cooling. There are safety issues, but if ideas like this worked then a hydrogen economy could pick up, linked to the use of hydrogen produced via Power to Gas electrolytic conversion of excess wind/PV output.  Physics to the rescue! There is certainly a lot of new stuff emerging.

All of which makes for an interesting mix of options as we rethink the overall energy system. Certainly views are changing. The once favoured idea of decarbonisation just by electrification is getting a bad press. Green gas looks like a better, less disruptive option. Labour’s Green Gas booklet also argues that case: see my earlier post. Also see these earlier studies: and And this challenging overview.

All that said, there will still also be a need for electricity grids and, in my next two posts, I will be looking at some developing ideas and plans for new power grid systems in the EU and elsewhere.

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