Finland’s LUT University has looked in detail at long-term inter-annual renewable power balancing, which it says goes beyond just seasonal balancing, as longer muti-year time frames must be investigated which can significantly increase the necessary storage infrastructure and overall energy system costs.
In its new report it notes that ‘inter-annual variations are either caused by natural resource fluctuation or potentially unpredictable mutations due to climate change impacts,’ and it looks at storage of electricity-derived green gases and fuels as options- focussing on methane (CH4) and hydrogen (H2), using the British Isles as a context.
Interestingly, and a bit controversially, it says that ‘inter-annual variations of solar PV have been excluded for simplification and due to the fact that lower variations are expected than for wind power’. Well yes, wind does vary a lot in the UK and Ireland, annually and also maybe inter-annually, but so does solar (this year was particularly bad).Then again, overall, sadly, there is less of it than in some other places.
A previous LUT study, based mostly on wind and solar use, looked at an energy transition towards 100% renewables across all sectors up to 2050, which was shown to be possible in the British Isles at a lower cost than the business-as-usual approach, even with seasonal balancing costs include. However, LUT has now accepted that ‘inter-annual variabilities and thus, necessary balancing requirements, have not been considered for the applied scenarios.’ That is what this study tries to remedy.
Its initial analysis of seasonal balancing looked at hydrogen as an option, but said that conversion of hydrogen to methane might offer a cheaper storage option. In its new analysis of the even tougher Inter Annual Storage (IAS) systems requirements, it is even more convinced that methane would be better than (just) hydrogen.
That is not to say that to two routes do not have different technical/equipment needs and issues. For example, LUT says ‘if hydrogen is used as an IAS medium, electrolysers and H2 storage facilities are required in addition to the existing energy system components' whereas 'if methane is used, electrolysers, methanation units, CO2 direct air capture (DAC), & methane storage facilities are required to produce and store e-methane.’
So, a lot of different bits of kit, with different operational implications depending on which approach is used and what is done with the stored gas- converting it back to power involves further losses. One option is to just use it for feedstock, fuel for heating or transport, not convert it back to power for direct balancing. However, leaving that end-use issue aside, LUT found that, overall, the IAS scenario with e-hydrogen as a storage medium had the highest cost: it increased the total annual system costs by 14–23%, whereas for e-methane it only rose 7–8%. That’s better, but it is still quite significant, and LUT suggest that e-fuel trading between countries with different renewable regimes might be needed, with methanol and ammonia production and trading also being options.
Even so, there are still uncertainties about which storage medium will be best and about the costs and viability at scale of some of the energy conversion technologies- for example e-gas compressors and DAC systems. So the route forward is still far from resolved, although LUTs preliminary conclusion, that using green gas storage to deal with occasional inter year events will be expensive, is interesting, and so is LUT’s more general view that the ‘hydrogen economy’ concept has to be revised and widened.
It says that, usually, ‘hydrogen is discussed more prominently than methane, in terms of long-term seasonal storage, though it is acknowledged that other energy carriers can solve the energy density drawback of hydrogen’. In addition, hydrogen is sometimes assumed to be able to ‘replace hydrocarbons for many end-use applications, including road transportation and space heating, although heat pumps and battery electric vehicles are known to be significantly more efficient technologies’. However it says ‘describing hydrogen as the key energy carrier for many to all end-use applications and intuitively assigning hydrogen to hard-to-abate sectors bears the risk of neglecting potentially better suited options’.
Certainly, given its conclusion that the hydrogen storage route will be higher cost, it is a little uncertain about the role of hydrogen in the IAS context, and also possibly in some others. It says ‘recent debates challenge the role of hydrogen as an energy carrier by highlighting that hydrogen will mostly be used as an intermediate product to produce e-methane/LNG, e-liquids, or e-chemicals, or for various applications only in cases where direct electric solutions are not suited, creating the term Power-to-X Economy’. And it adds, its efforts to assess the suitability of methane and hydrogen for Inter Annual Storage ‘may add one more example where the use of hydrogen is questioned’.
It's an interesting, and ongoing, debate, with many new ideas and options being discussed for optimal green gas production and use, including methanol with DAC. For example, it has been claimed that, with a well-sited wind farm, plus DAC, electrolysis & catalyst upgrades, costs may fall from ~$1k to $300 per tonne of methanol, comparable to using fossil gas, but with net negative carbon emission. The Power to Gas/DAC use/storage performance and costs trade-offs in this area are fascinating (not least since you need power to run DAC), though there is still a way to go before we can be certain about the best route ahead. And hydrogen is often still somewhere in the process mix!
*In the UK, the Autumn budget included ‘support for the first round of electrolytic hydrogen production contracts, harnessing renewable energy to decarbonise industry across the length & breadth of the UK’. But it also backed some ‘blue hydrogen’ projects, synthetic hydrogen produced from fossil gas with CCS to make it low carbon, despite the hostility of some to that approach. The battle over blue versus green hydrogen is a global one, with blue mostly being seen as cheaper for now, especially in the industrial context, but green as probably winning out soon, as renewables get cheaper. But all options for the subsequent use hydrogen, or synfuels derived from it, are still up for grabs, with balancing grids, via short or long term storage, obviously only being one of them.
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