Tidal and wave power is the next frontier for renewable energy, with the potential to significantly contribute to the global energy mix. A recent study by the International Renewable Energy Agency (IRENA) estimates the potential from 20,000TWh to 80,000TWh, or 100% to 400% of current global demand for electricity, i.e. “more than sufficient to meet present and projected global demand well into the future”. [Engerati-Ocean Energy Technology In The Spotlight]
The challenge is in harnessing these resources, with differing technologies required according to the resource type. Of these the most mature are tidal technologies, with tidal stream prototypes under development while tidal range technologies have a proven track record but limited deployment due to site availability.
The tidal concept is now being taken a step further forward with a tidal lagoon project in Swansea Bay in the UK, for which planning consent was recently approved by the UK government and promises to be a world first.
Swansea Bay tidal lagoon
Swansea Bay is located on the southwest coast of Wales, within the Severn Estuary, which holds the second highest tidal range in the world and Swansea Bay benefitting from an average tidal range during spring tides of 8.5m.
The proposal is to construct a 9.6km horseshoe shaped sea wall looping 3km out to sea with a nominal 240MW generation capacity that could provide around 500GWh per year (with an estimated 14 hours of reliable generation per day) – enough to power over 155,000 homes. Existing technology will be used in the form of low-head bulb turbines which have been widely used in hydropower applications. The primary difference with the tidal lagoon application is the efficiency of electricity generation in both directions, on ebb and flood tides. The proposed 16 turbines will have a span in the region of 7m and be permanently submerged below the low water level in Swansea Bay.
Swansea Bay project costs
The project has an anticipated lifetime of 120 years with a cost of around £1 billion.
The project is now subject to a Contract for Difference (CfD) assessment to establish its affordability and value for money. CfD was introduced by the government as a mechanism to support renewable energy development by giving investor certainty to electricity generators by reducing their exposure to volatile wholesale prices, whilst protecting consumers from paying for higher support costs when electricity prices are high. Under CfD a generator is paid the difference between a ‘strike price’ – which reflects the cost of investing in a particular technology – and the ‘reference price’ – a measure of the average market price for electricity in the market.
A study by consultants Pöyry for the project company, Tidal Lagoon Power, estimates a strike price of £168/MWh for the project with a 35-year CfD duration. The support requirement is estimated at £50 million per year. Taking into account social discounting, the project is cost comparable with offshore wind, the study suggests. The study also argues that further developments of larger capacity would be cheaper than gas-fired power, with the strike price dropping to £130/MWh for the second and £92/MWh for the third, with this also broadly similar to those for onshore wind, large scale solar PV and nuclear.
Potential for tidal lagoon energy
A 2012 UK government study estimated the capacity of tidal lagoon resources at 14GW with a generation potential of 25TWh/year, almost all on the kingdom’s west coast.
Tidal Lagoon Power is developing plans for five other tidal lagoon projects in the UK. Two others in the Severn Estuary, at Cardiff and Newport with proposed capacities of between 1,800MW to 2,800MW and annual outputs of 4TWh to 6TWh, are the most advanced. An Environmental Impact Assessment scoping report has been submitted for the former. Others are at Bridgwater Bay in Somerset, Colwyn Bay in North Wales and West Cumbria in northwest England.
Together these could generate 30TWh of electricity per year, meeting around 8% of the UK’s needs by 2030, the company believes.
“We see [Swansea Bay] as a game-changer, a scalable blueprint, paving the way for a fleet of lagoons that can work in harmony with nature to help secure the nation's electricity for generations to come,” says Mark Shorrock, chief executive of Tidal Lagoon Swansea Bay. “The tidal lagoons that follow – at Cardiff, Newport, elsewhere in the UK and overseas – must each make their own compelling social, environmental and economic case to proceed. But they have a pilot project to guide them and a blossoming technical and industrial network to support them.”
Construction at Swansea Bay is expected to begin in Q1 of 2016 and the project to become operational in Q4 of 2018. General Electric and Andritz Hydro have been named as the preferred bidders to provide the turbines and power generation facilities. China Harbour Engineering Company Ltd will provide the marine works.