Offshore wind design

To reduce energy costs in a twin-site extension of East Anglia ONE wind farm from 714MW to 2.4GW, a LICenergy UK consortium scoping study optimised designs for both XL monopile foundations carrying 11MW to 15MW capacity wind turbines and gravity base foundations supporting large substations and accommodation modules.

( Text content written by Twenty6 for Luke Fussell, LIC Energy )

LIC’s in-house NONLIN software optimised monopile cost and environmental impact assessments. An innovative ‘modular’ curved pillar used in groups to form gravity bases of all sizes was standardised for low-cost manufacture.

Client challenge

East Anglia ONE when finished will be one of the largest offshore wind farms in UK waters with a 714MW generating capacity. As part of a consortium examining foundation designs for future East Anglian offshore wind farms, LICenergy UK carried out a scoping study for XL monopile foundations and gravity base foundations at two new sites – East Anglia ONE NORTH and East Anglia TWO.

Each site can potentially add an additional 800 MW of generating capacity, taking the field’s total to 2.4GW. This represents approximate 75% of equivalent capacity at the proposed Hinkley Point C nuclear power station in Somerset.

Monopile foundations: -The study had to take into account the continuously increasing size of turbines deployed offshore. Five years ago, 3MW turbines were commonplace. The standard has moved on to 8MW. In the foreseeable future, 11MW to 15MW machines are anticipated with diameters of up to 15m to withstand huge operational and environmental forces.

Gravity Base foundations: – Similarly, gravity base foundation designs were required for three different sizes of substation. These ranged from typical current topside dimensions of circa 35m x 35m in plan x 20m high, to much larger structures of up to 110m x 120m x 60m.

Our response

Monopile foundations: – The study benefitted from LICenergy UK’s knowledge of the wind energy market, prevailing trends and what machines are likely to be available five years from now. Our response was to create a series of simulations for turbines ranging from 7MW to 15MW.

It was important for our client to know how much steel would reasonably be needed, likely costs and details of any environmental impacts resulting from installation work.

We provided this information through preliminary sizing designs generated by LIC’s in-house NONLIN software. NONLIN was verified independently by Bureau Veritas during earlier LICenergy UK design work for the Rampion Offshore Wind Farm.

Our study also identified the urgent need to develop innovative techniques and equipment for installing monopoles with diameters of up to 15m. Machinery to hammer the large piles needed to resist huge forces does not yet exist. Similarly, pile weights of more than 4,000 tons will be required.

Gravity Base foundations: – To make the assembly of the large gravity base foundation topsides physically and economically possible in remote deep waters, LICenergy UK has developed an innovative reinforced-concrete curved pillar modular component design.

This narrows smoothly towards its centre to optimise weight and materials before widening out again at its top.

The base is a large stiffened, hollow, reinforced-concrete box that can be fabricated in dry dock, floated to site, ballasted and sunk under controlled conditions.

LICenergy UK’s specific innovation is the modular design, that, depending on the size of future topside can be clustered in sufficient numbers to provide support.

The result is that moulds and processes can be standardised. This makes manufacture much more efficient, saving money for clients and ultimately lowering the cost of energy for consumers.

Benefits

LICenergy UK used its knowledge of current conditions and emerging trends to forecast what machines are likely to be available in the next half decade, and beyond.

This was fundamental to creating meaningful foundation design propositions within the customer’s anticipated project timeframe.