This week at Clean Energy Capital we take a look at some of the problems surrounding clean energy storage and the newest technologies being developed to further drive the advancement of a sustainable future.
Written by our in-house Project Manager, Mack Harter.
Traditionally the biggest challenge facing the renewable energy sector has been intermittency - how do we produce sustainable energy without constant wind or sunlight? Existing energy storage technologies are part of the solution but have limitations of their own - Lithium-ion batteries are not suitable for long-duration storage and pumped hydro can only be installed in very specific locations. We must, therefore, look to new energy storage technologies if we are to unlock the potential of a fully renewable electricity network.
What are the current problems facing clean energy storage?
Utility scale Li-Ion batteries have been readily adopted globally. According to BloombergNEF, growth in the Global Energy Storage Market is expected to be dominated by batteries in the midterm. Whilst this is welcome news, high upfront installation costs create a requirement for high utilisation to provide return on investment. This means the primary uses of battery assets remain frequency response and load-shifting, not long duration storage.
Pumped hydro is by far the most developed long-duration energy storage solution, with over 25.8GWh currently installed in the UK and planning approved for a further 30GWh system system in the Scottish Highlands. The technology involves pumping water from a lower altitude reservoir to a higher altitude reservoir when there is surplus generation on the grid, then releasing the water to produce hydroelectricity. Undoubtedly, pumped hydro has a significant part to play in realising the potential of offshore wind. However, as the technology is limited to locations with particular geographics, new solutions will be required in other areas of the country.
New clean energy storage solutions
Other Material Batteries
Solid state batteries work in the same way as lithium-ion, ions pass from the positive to the negative side of the battery to produce current; and pass in the opposite direction when charging. The main difference between Li-ion batteries and solid-state is that Li-ion has a liquid electrolyte between the positive and negative sides of a battery, whereas solid-state batteries have a solid ceramic electrolyte. This greatly increases the power density of the battery and simultaneously removes the dangerous liquid component of Li-ion batteries.
Flow batteries have been considered for decades but until recently the technology had never been developed at scale; the technology works by transferring electrons between two electrochemically reacting liquids. They have two key advantages over lithium-ion. Firstly, they are manufactured from less expensive materials and secondly, their quality does not degrade as quickly. Vanadium flow batteries, in particular, have the potential to penetrate the utility battery market owing to near zero degradation.
Compressed Air Energy Storage
Compressed Air Energy Storage (CAES) is a proven solution, however it is yet to be deployed at scale due to the current use of gas-turbines to make up for shortfalls in renewable energy. When there is surplus renewable generation on the grid, electric compression is used to drive air into underground storage containers at high pressures. When the demand on the grid increases, the process can be reversed to rotate turbines and generate electricity. As increasing amounts of renewable generation is connected to the grid, curtailment and negative spot market prices are expected to increase. This could make compressed gas a financially viable long-duration energy storage solution.
Green hydrogen is considered by many as potentially the most versatile form of energy storage. Renewable powered electrolysis can be used to produce hydrogen gas, which can then be stored as a liquid in pressurised silos or as a gas within salt caverns, which are present across the UK. Hydrogen can be used to power large vehicles and machinery, feed into the gas network, or be used to generate electricity via combustion or fuel cells. A recent report completed by The Royal Society suggests that by 2050, 900 hydrogen filled salt caverns would be required to mitigate variation in wind and sunshine year-round. However, it is important to remember than in order for hydrogen to be considered green, it must be produced in a sustainable manor, as set out in the UK Low Carbon Hydrogen Standard.
What does this mean for the future?
As the world continues to drive towards a sustainable future, in particular looking at robust electricity grids powered by renewables, clean energy storage solutions will become an ever-important factor. Clean energy storage technologies can be separated into three distinct categories:
1) High Density - Lithium-ion and solid-state batteries will be vital for EVs and portable devices.
2) Grid Ancillary Services - Frequency response and localised load shifting will be dominated by lithium-ion batteries for the foreseeable future, with the potential for flow batteries to break into the market.
3) Long Term-Storage - CAES could be the first long-duration electricity storage solution to be deployed at scale, if the UK is serious about reducing its reliance on gas turbines during periods of low renewable generation. If UK and global hydrogen production ambitions can be realised, utilising the UKs existing salt caverns as a long-duration energy storage solution would be an effective way to unlock the potential of a fully renewable electric grid.