Why hydro power stations can help the UK manage the variability of renewables

The hydro power dam at Pitlochry
The hydro power dam at Pitlochry


One of the limitations associated with renewable energy is variability of supply, which can give rise to problems for operators of transmission and distribution grid networks. The susceptibility of renewables to extended periods of uncertain weather patterns can have drastic effects on the continuity and volume of available electricity within the grid network.

For example, sustained high pressure periods can result in a loss of generation from wind turbines and conventional hydropower subsequent to reduced wind speed and rainfall.

So is electricity storage the answer to the variability dilemma presented by renewables? Could additional storage release or enable a true renewables revolution in the UK?   The answer is a resounding ‘Yes’.

There’s general agreement within UK industry that an additional 2GW of electricity storage is needed to help balance and manage the predicted levels of renewable power by circa 2020. And we already have proven technology of appropriate scale which can meet the additional 2GW of electricity storage required – and it’s pumped storage hydro power.

See also:

Scots hydro power station celebrates 50 years of generation as Scottish Power considers investment plan to double output



What is Pumped Storage Hydro power?

Electricity network generators and network operators in the UK have been using pumped storage hydropower on a large scale since the 1960s; the technology and concept is not new.

The UK currently has four grid scale hydro power facilities in operation – Dinorwig, Ffestiniog, Cruachan and Foyers.

This small fleet of pumped storage facilities were constructed during the 1960s, 70s and 80s. Primarily, these pumped storage schemes were introduced to stabilise the power generation of the UK’s then burgeoning fleet of thermal and nuclear power stations by absorbing excess electricity generated during off-peak hours and delivering stored energy during on-peak hours.

Over the years and with deregulation of the electricity market and creation of the spot markets, the use of hydro power has greatly expanded to cover a range of ancillary benefits.

The concept of pumped storage hydro is simple but the construction is not.  Pumped Storage Hydropower systems essentially consists of two bodies of water at differing elevations (upper and lower reservoirs) connected by a pipeline/tunnel with reversible pump-turbines to generate power or return water to the upper reservoir.

When excess electricity exists within the grid the turbines go into pumping mode lifting water to the upper pond and when demand within the network exceeds available supply the turbines reverse and transition to generating mode with water released from the upper pond. The system is a net-user of electricity in lifting water to the upper reservoir but generates commercial profit through trading high value electricity during periods of high demand.


Why is hydro power so useful in managing grid issues associated with variable renewables?

Pumped Storage Hydro power can exist in a symbiotic relationship with modern renewable and nuclear electricity generation. 

Indeed, hydro power actually enables a greater development of renewable energy and contributes greatly to the decarbonisation of a nation’s power grid.  Pumped Storage Hydropower offers this symbiotic support to renewables through a number of “ancillary benefits”, namely: Load Following, Frequency Regulation, Voltage Regulation, Fast Reserve and Black Start.

Load Following is the most obvious and common ancillary benefit offered by  Pumped Storage Hydropower. The system operates like a rechargeable battery and allows the grid operator to follow the electrical load demands within the network. When electricity supply is high but demand is low the  Pumped Storage Hydropower system can be used to absorb and store the excess power. Conversely, when supply is not sufficient to meet demand the load requirements can be met by the  Pumped Storage Hydropower facility switching to generating mode.

Frequency response is a form of automated balancing that is reactive to grid frequency, increasing or reducing in output on a second-by-second basis to re-balance generation to meet customer demand.  Pumped Storage Hydropower units operating on this regime are sent a start and stop command by National Grid during agreed windows of availability. This requires that the generators are kept spinning in air in order to achieve the desired start up times.

Voltage Regulation, as for Frequency, voltages must be kept within design tolerances, regulating voltage involves balancing supply and demand of power, although in this case it involves balancing reactive power to provide a stable voltage supply.

Fast Reserve requires rapid amendment of generating levels and reliable provision of active power at very short notice to meet sudden increases in demand such as TV pickups or to meet unexpected generation shortfalls of a thermal or nuclear plants, i.e. during shutdowns.

Black Start provides power resilience. Should a large thermal power station or nuclear power station fail,  Pumped Storage Hydropower units can be used to restart the asset.


Pumped Storage hydro power in the UK – Current and Future

The UK’s existing fleet of  Pumped Storage Hydropower facilities have made a valuable contribution to the stability of the nation’s power supply for the last 52 years. The big question is, does the massive expansion of renewables within the generation mix require a significant increase in  Pumped Storage Hydropower generating capacity?

There has been no new  Pumped Storage Hydropower in the UK for the last 32 years.

However, as the UK is increasingly promoting construction of renewables the risk of power loss due to a single point failure could be up to 2GW, thus increasing variability in demand and supply indicates a growing requirement for Pumped Storage Hydropower.

Power utilities and private developers in the UK seem to support this view and over the past five years we have seen a real focus on the number of possible sites assessed for both large and small-scale Pumped Storage Hydro power.

Prior to 2010 the UK market has seen no significant activity in the  Pumped Storage Hydro power field, but a significant number of sites across the UK and Ireland are now being seriously assessed for hydro development.

Indeed across Europe, a renaissance in  Pumped Storage Hydro power is happening almost entirely driven by the increase in highly variable renewable energy. Many European countries have brought on-line large Pumped Storage Hydro power facilities to help manage the intermittency issues associated with the decarbonisation aspirations and renewable power future.

Why is the UK lagging in this  Pumped Storage Hydro power renaissance while our European neighbours forge ahead with construction and commissioning of new schemes to support their renewable future?

The answer to this particular UK question lies in policy and the electricity generation market that evolves as a consequence.

The future of  Pumped Storage Hydro power in the UK is dependent on the barriers to development, both market and regulatory.  

Whilst there is a dedicated intent to develop  Pumped Storage Hydro power in the UK, these projects face significant challenges, notably due to the long gestation periods of up to 10 years.  

The balancing principle of  Pumped Storage Hydro power means that the operating profile of the plant cannot be determined in advance, thus the lack of long term contracts makes investment prohibitively onerous, particularly as the current mechanisms are weighted towards maintaining existing generating infrastructure and are not reflective of the investment criteria for new-build projects.

Scotland is particularly well placed to capitalise on the potential  Pumped Storage Hydro power renaissance due to the topography, available land, water resource and the wider renewable energy market growth.

Pumped Storage Hydropower was introduced to the UK during the 1960s when the nationalised power industry recognised the need for a facility to help manage network issues associated with a particular type of electricity generation fleet i.e. nuclear and thermal generation.

The situation now in the 21st century doesn’t seem quite so clear or straight-forward. We have a new fleet of power stations coming on-line that also cause intermittency issues to grid operators but the lack of clear policy, regulation and long-term trading conditions cause a real dilemma for both utilities and developers.

The need for large scale storage seems as relevant today as it did in the 1960s but the dynamic within the nation’s power industry and political landscape seems more clouded.

Even despite the benefits presented by Pumped Storage Hydropower and the relatively low capacity levels in the UK, there is a lack of substantive government encouragement for Pumped Storage hydro power which is currently not recognised within the Electricity Market Reform (EMR) framework.

Imagine a future scenario, where the UK is free from all fossil fuel driven power stations; perhaps a generation mix of both renewables with a nuclear base-load all underpinned by Pumped Storage Hydropower. No reliance on gas imports and minimal reliance on continental interconnectors. The technology and the resource in the UK exists to make this sustainable vision a reality; all we need is the political and market desire to make it happen.

Craig McMaster is the MWH UK Director responsible for the firm’s Energy & Industry business


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