Energy storage has the potential to contribute to the operation of power systems in a number of ways. The most important are:   

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    Managing intermittency caused by the integration of time variable renewable sources of generation,      and thereby facilitating improved decarbonisation of the electricity supply system.   

    Providing solutions in grid constrained areas.   

    Supporting energy security.   

    Operational cost savings and financial/commercial opportunities. 

  

Short Term Cycle Uses (seconds to minutes)   

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Short term uses of energy storage are mostly associated with maintaining the stability of the power system, e.g emergency reserve to cover loss of plant or transmission lines. Such an application requires large power ratings, but only for seconds or minutes. Conventionally this is supplied by spinning reserve (i.e. part loaded plant), pumped storage, or open cycle gas turbines. Other storage technologies like flywheels could be an alternative. A key economic issue is that use of this supply is only occasional – at most a few times per year. Other uses include power system frequency regulation or voltage control and also providing angle stability (which relates to the electromechanical connection between the electrical generator and the grid that must be maintained if generation is not to be interrupted).  

  

Intermediate Cycle Uses (hours to days)   

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Energy storage in electricity systems is most commonly aimed at intermediate time scales. These, most often larger scale systems, are usually for high energy use and thus on the scale of MWh of storage. There are a few key applications.   

Load shifting, load levelling or peak shaving are all part of a subset of load management activities that can be delivered by storage. This use focuses on moving or shifting pieces of the load often to reduce the peak load. Commonly, peak shaving involves storing surplus energy from renewables and discharging the storage during a time of high demand. Load levelling, on the other hand, which may also reduce the peak, usually involves charging the storage from the grid during times of low demand and then discharging during a peak. The other key usage for storage of intermediate cycle length is the ability to store energy generated from renewable sources, usually when more electricity is generated than can be absorbed by the power system at a given time. The energy generated through renewable sources is much less responsive to supply and demand, and thus flexible conventional generation is required, or perhaps energy storage, to ensure a secure supply.   

 

After conducting a thorough literature review on energy storage technologies and associated matrices for storage solutions we narrowed down the current market options to li-ion and REDOX flow batteries as being the most favorable. This fell in line with what Scottish Water have been looking to deploy recently on their asset sites. They also represent, currently the most convenient/accessible solutions available on the market from an operational perspective.    

 

A good overview for energy storage options in Scotland is the Infield, D., Hill, J., 2014. Literature Review: Electrical Energy Storage for Scotland.  

  

We decided to create our own energy storage matrix around the cases study WWTW site we had data for regarding Li-ion and a REDOX flow Battery solutions. We received information regarding a proposed solution that SW were looking to implement including technical specifications and capital cost’s.