Lagoon power in UK System

Assessment of the UK future power system - to meet the 2050 zero carbon target - has just been issued by the National Infrastructure Commission.  It includes an assessment of the proposal for a fleet of tidal lagoons.

Swansea is the small red blip, Cardiff-Penarth assumed to start in 2027

The NIC assessment gives a critical look at the Hendry review, outlining its “major limitations”. Hendry used a comparison with costs of offshore wind in the mid 2020s, which are now known to be far lower.  “Strike price” comparison was fudged to make it appear lower by not indexing fully to inflation.  Hendry argued for other benefits of regeneration, recreation and flood protection, but ignore the lost opportunities of using the same money.  Hendry discounted the strongly variable (on-off) power generation; the NIC finds (National Infrastructure Commission (2017), Congestion, Capacity, Carbon: Priorities for National Infrastructure) the gaps cannot be covered by a ‘fleet’ of lagoons around the coast, so they could not contribute much to power security.

The analysis for the NIC was recently carried out by Aurora Energy Research, said to be separate from the government’s work underpinning its rejection of funding for the Swansea Lagoon.  It considered Lagoon-power in alternatives of much nuclear power, 40% renewables and only Hinkley nuclear with 90% renewables.

"Balancing" gaps with battery storage or interconnectors is higher for off-shore wind, but network costs for distributing the local peaks in generation are higher for lagoons.

Tidal Lagoon Power described the extra subsidy as minimal.  This shows it's 

an extra £39bn or 38% on the total 'low carbon' energy subsidy up to 2040 (and more after that!)

Here is how the side panel summarises the case:

▪ Replacing offshore wind with tidal is a more costly way for government to meet carbon targets

▪ Offshore wind becomes economic in 2030s without subsidies, tidal never becomes competitive without government support

▪ Consequently, additional government subsidies are required to procure the same amount of low carbon generation with tidal rather than offshore

▪ Whilst tidal can be considered a more predictable source of generation than offshore wind, it adds additional constraints to the system as it is only able to generate power at fixed times of the day. This leads to low load factors and 10.2 GW more tidal capacity to generate the same amount of electricity as the displaced offshore wind.

   Thus tidal power is predictable but not dispatchable; offshore wind is hardly predictable but in combination with storage it's dispatchable to meet peak demands.  It's not clear that the variation of lagoon power between spring and neap tides is taken into account; serious if you have to accommodate low period generation 50% below the average.