Storage matters

Scott McGregor, CEO of redT energy storage, discusses different forms of energy storage and how each type has its own benefits and disadvantages.

Storage matters

Long-duration (>3 hours) energy storage is transforming how the world generates and consumes energy. The infrastructure it provides enables renewable energy sources to be used on-demand, 24/7 and allows clean, plentiful and cost-effective energy to come online in greater quantities without compromising the transmission and distribution network. Simply put, energy storage technologies, deployed correctly, both in-front and behind the meter, will allow renewables to compete with conventional coal, gas and nuclear generation for an even larger share of baseload generation as part of a smarter, more flexible energy system in the UK.

The business case for storage remains very strong, with industry experts estimating that “by 2024, roughly 81GWh of energy storage will be installed globally”. The incentives are obvious, with solar and wind generation now trending towards levelised cost of energy figures far below that of traditional baseload generation sources. For instance, according to DECC, (now BEIS) 2016 levelised cost of energy figures, solar sits at 5.9p/kWh with wind at 4.7p/kWh, compared to coal and CCGT at 12.5p/kWh and 6.5p/kWh respectively. For perspective, the Hinkley Point C strike price is 9.25p/kWh, almost twice DECC’s figures for PV and wind. Food for thought. 


Different technologies

From a technology perspective, there are many different forms of energy storage with a plethora of different chemistries and processes, making it somewhat difficult to make an assessment of which approach is correct for the specific needs of a customer. Due to its widespread use within consumer electronics and electric vehicles, lithium-ion batteries are probably the best known of these. However, lithium has its limitations, only being viable for high power, short duration (<3 hours) applications. As such, if lithium is used too heavily, it degrades rapidly and requires replacement – a fact that many of us can relate to through experience of mobile phone batteries! We believe that lithium is a good technology, and alongside lead acid batteries, flow machines and pumped hydro, it is one of the few tried and tested mature technologies available. However, it is well suited to certain applications, a fact the market is now waking up to, evidenced by the recent “derating” discussion surrounding capacity market auctions.

The word battery is banned in our office. We develop and supply vanadium flow machines, not batteries. Where lithium and lead acid batteries contain power and energy within a cell, our machines separate these two elements, storing charged vanadium electrolyte (which is 70 per cent water) in tanks, which is then pumped through “stacks” that provide the power element. The set up is similar to an engine and fuel tanks, except the fuel never runs out, because vanadium electrolyte does not degrade, no matter how much you use it (unlike lead and lithium solutions). Flow machines are ideal for high-energy applications, requiring discharging or charging duration of three hours or more on a daily basis, which is what’s required for time shifting multiple hours of solar power or for providing all types of grid support services. 


Highlighting costs

Another stumbling block in the energy storage industry is cost. The standard industry metric, using price per kilowatt hour, does not take into account all of the costs involved. To get a comprehensive understanding of the cost of storage, we need to look at levelised cost of storage – which takes into account how you will use the system and the resulting effect on elements such as maintenance, depreciation and replacement costs. Energy storage, especially at grid level, needs to be thought of as infrastructure, in just the same way as pylons, cabling and substation equipment – it needs to last for 25 years or more in order to provide all grid services – and it needs to create an investable, attractive return. This is what’s termed a “flexible platform asset” and that’s what a flow machine provides, as opposed to being a consumable like a conventional battery.

However, there is no one panacea technology when it comes to energy storage. We recently announced a hybrid energy storage project, which combines flow machines with lithium technology. Because flow machines address the weaknesses of conventional, power-centric batteries, this solution can accommodate short term power spikes as well as longer duration, energy-focused needs. By using a flow machine as a workhorse, covering 60-80 per cent of the work on a daily basis, with lithium batteries being employed to cover occasional peaks, the lithium usage can be carefully managed to prolong its life, whilst providing the short sharp bursts of power that the site requires.

Energy storage is the key to solving the energy trilemma of access, affordability and de-carbonisation. Renewable energy can be deployed centrally as baseload generation or on a decentralised basis, behind the meter as part of a smarter, more flexible energy system. The future is energy and storage is at its heart, so make sure you select the right technology for your needs.  



CASE STUDY: UK’s largest flow battery system connected to the grid

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The Hawkey family runs a 600-acre farm and 28-cottage holiday retreat called The Olde House in Wadebridge, North Cornwall. Their agri-business is grid-connected and has a peak demand of over 100kW. The site has traditionally been an early adopter of new renewable energy generating technology and to help offset costs, generates its own electricity from an on-site 350kWp solar array.  


Much of the site’s energy use occurs during the evening and at night (when guests return to their cottages and start cooking dinner, etc.) Therefore, in order to make the most of their solar generation and to avoid peak electricity costs, the site needs to store excess solar generation produced during the day for use at night. We call this “firming” solar. 


redT’s Vanadium Redox Flow Machines are ideally suited to this situation. As excess solar needs to be stored over a long period during the day and discharged over a long period during the night, liquid energy storage machines, such as redT’s, don’t degrade and are therefore ideal. 


In addition to making savings by utilising their own generation instead of importing from the grid, The Olde House will also be able to generate useful revenue by providing grid services to the local network and trading energy as part of Centrica’s Local Energy Market project. redT are the first storage technology to be signed up to this scheme, which will allow asset owners to take control of their energy use and trade excess generation with both the grid and each other. 


redT’s machines are flexible platform assets, which means they can be used to perform different services at different times, depending on what provides the greatest net benefit to the asset owner. In this context, The Olde House can use the machines to engage in frequency response services, bid into the capacity market and engage in merchant energy trading and arbitrage activity. Importantly, because these machines don’t degrade, layering on new services or changing what activities the machine performs, does not have an associated cost in terms of degradation.   


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