Energy Storage Systems (BESS) – what and why?

As we strive to achieve the renewable energy targets for the UK of over 20% renewable energy (this includes both electricity, heating and transportation and depending on the scenario equates to 30% renewable electricity usage) by 2020 and reduce carbon emissions by 80% of 1990 levels by 2050, the Government and private companies are investing considerably in the likes of solar panels and wind turbines, as well as nuclear. Whilst this is without a doubt a noble quest that only a minority would argue with, renewable energy sources pose quite a challenge to the National Grid. Take for example solar power, which we get from the Sun’s energy. This is only generated when the sun is above the horizon and unimpeded by clouds with a large peak being achieved during the middle of the day. At night solar generates zero power. Wind power similarly depends on whether the wind is blowing or not, which although is planned for when selecting the best areas for wind turbines is still unreliable. One day all your wind turbines could be generating their near maximum capacity and the next they could be outputting 10% or less of their capacity. Non-renewable power stations, on the other hand, such as gas and coal are pretty constant at outputting the same output day in day out.

solar power output

Example of how power output from solar varies during the day

The unpredictability of renewable energy means that the Grid has to cope with these surges of power (which often occur when the actual UK demand for energy is quite low in comparison to its peak) potentially having to pay operators to disconnect their systems from the Grid. At the other end, a lot of renewable energy capacity is not available when the daily peaks in power usage occur. Energy storage promises to solve this by storing excess energy from renewables and feeding this into the grid when the peak power demand occurs. This is all part of a Smart Grid, which can automatically decide when to store the energy and when not to.

tesla powerwall

Tesla has entered the energy storage market with its Powerwall

When it comes to energy storage systems, there are a number of different storage technologies that are used. Current technologies include:

  • VRLA or valve regulated lead acid batteries. These are the batteries used in Uninterruptible Power Supplies and as they have been around since 1934, their cost is relatively low in comparison to other battery technologies. Deep cycle VRLA batteries are the type most suited to energy storage to ensure that they have a long enough life span for this use.
  • Lithium Ion batteries. This is the type of battery that is commonly found in modern consumer electronics such as your smartphone. They have a high energy density with the potential for even higher capacities (lithium ion technology is constantly changing and improving). The main benefit with lithium ion batteries are that they can be charged and discharged more often that VRLA batteries with less deterioration in terms of storage capacity of longevity of product. The main downside is cost although this is coming down progressively.
  • Vanadium Flow batteries. This battery uses vanadium ions to store chemical potential energy. They are currently quite bulky in size but offer the ability to completely discharge without any adverse effects and a long life time (20+ years).
  • Sodium Nickel batteries. These batteries use molten salt as the electrolyte. This allows the batteries to withstand greater temperature extremes as the cells themselves operate at 270+ degrees Celsius and are insulated so that the external chassis is just above ambient temperature.
  • Liquid metal batteries.  This battery technology uses liquid metals as both the electrodes and the electrolyte. As there is a constant regeneration between cycles, the electrodes do not degrade with time. The cost of liquid metal is currently the main stumbling block.

 

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