Are offshore grids the key to the UK’s energy independence?

The Russ­ian inva­sion of Ukraine has fuelled the urgency of ener­gy tran­si­tion ambi­tions. For the UK and EU, off­shore wind tur­bines could pro­pel their advances – but only if grid inno­va­tion keeps pace.

The UK wants to gen­er­ate 40GW of off­shore wind by 2030. The recent ScotWind seabed leas­ing round award­ed a record-break­ing 25GW of poten­tial projects, enough to pow­er about 1.5 mil­lion homes, set­ting the coun­try on a path to meet­ing this tar­get. The EU is tar­get­ing at least 60GW by 2030 and 300GW by 2050.

But while off­shore wind tech­nol­o­gy costs are falling rapid­ly, grid inno­va­tion must keep up, or we risk miss­ing these tar­gets. Stud­ies show that when off­shore wind pow­er assets are built at the scale planned, sin­gle point-to-point con­nec­tions from off­shore wind farms to the onshore grid (as is cur­rent­ly stan­dard) will be inef­fi­cient, more expen­sive, and less envi­ron­men­tal­ly friend­ly.

What does inte­gra­tion mean? One idea is for a mul­ti-coun­try con­nect­ed off­shore meshed grid in the North Sea, built using nov­el tech­nol­o­gy. This would enable much high­er lev­els of ener­gy to be trans­port­ed with low­er loss­es. Cru­cial­ly, sup­ply would be more eas­i­ly shift­ed to meet demand across the five major Euro­pean off­shore wind play­ers – the UK, Bel­gium, the Nether­lands, Ger­many and Den­mark.

There are already a grow­ing num­ber of point-to-point inter­con­nec­tors trans­port­ing ener­gy from one Euro­pean coun­try to anoth­er – the UK cur­rent­ly has four. How­ev­er, a meshed off­shore grid would be like “the Lon­don to Brighton main line” says Fay Lel­liott, a glob­al prac­tice leader for pow­er trans­mis­sion and dis­tri­b­u­tion at Mott Mac­Don­ald, a con­sul­tan­cy firm.

“It’s not only point-to-point; it’s pos­si­ble to trav­el from Lon­don to Brighton by lots of dif­fer­ent routes,” she explains.

Integration innovation

Dr Cor­nelis A. Plet is a prin­ci­pal con­sul­tant at DNV, who coor­di­nat­ed the PRO­MO­TioN Hori­zon 2020 project to advance the devel­op­ment of high-volt­age direct-cur­rent (HVDC) meshed off­shore grids. He explains what inte­gra­tion means in prac­tice. “It’s two lines com­ing togeth­er at the same loca­tion, rather than hav­ing two sep­a­rate links with their own con­vert­er sta­tions.” Com­bin­ing them can save hun­dreds of mil­lions of euros, he says, “and doing this con­sis­tent­ly across the North Sea low­ers costs sig­nif­i­cant­ly.”

UK elec­tric­i­ty sys­tem oper­a­tor Nation­al Grid ESO has deter­mined that tak­ing an “inte­grat­ed approach” for wind farms deliv­ered from 2025 could save con­sumers approx­i­mate­ly £6bn in cap­i­tal and oper­at­ing expen­di­ture between now and 2050, with cables and onshore land­ing points reduced by around 50%. It is devel­op­ing a Holis­tic Net­work Design (HND) due in June that is expect­ed to incor­po­rate some of these learn­ings and rec­om­mend how to facil­i­tate the 2030 tar­get, includ­ing 11GW from ScotWind.

Inte­gra­tion ideas are tak­ing shape. Ten­neT, Europe’s largest trans­mis­sion net­work oper­a­tor (TSO), advo­cates an inter­na­tion­al­ly coor­di­nat­ed mod­u­lar hub-and-spoke con­cept. This would be cre­at­ed by the North Sea Wind Pow­er Hub, which con­sists of sev­er­al Euro­pean TSOs. The idea would see wind farms con­nect­ed to mul­ti­ple coun­tries, as well as to pow­er hydro­gen con­ver­sion sta­tions.

Sask­ia Jaars­ma, head of off­shore devel­op­ment at Ten­neT, says this kind of expan­sion is impor­tant.

“We will not achieve the Paris cli­mate change agree­ment with one-or two-gigawatt sys­tems. It makes sense to com­bine it inter­na­tion­al­ly, and this [hub-and-spoke plan] is a suf­fi­cient solu­tion,” she says.

While such a con­cept is years away from real­i­sa­tion, grid inte­gra­tion at the coun­try lev­el is start­ing to take shape. TenneT’s 2GW Pro­gram, which has just start­ed the ten­der­ing process, will build at least six off­shore grid con­nec­tion plat­forms – three in Ger­many and three in the Nether­lands – that will use a new cable sys­tem and have a trans­mis­sion capac­i­ty of 2GW.

The sta­tions will require half as many grid con­nec­tions and great­ly reduce space com­pared to com­bin­ing two 900MW plat­forms, as was pre­vi­ous­ly pro­posed. The com­pa­ny is also work­ing with 50Hertz, anoth­er Ger­man TSO, to deliv­er 4GW of ener­gy from two off­shore wind parks into one onshore mul­ti-ter­mi­nal hub, so only one AC/DC con­vert­er sta­tion, instead of the usu­al three, needs to be built.

Denmark’s Energinet has pro­posed build­ing two arti­fi­cial ener­gy island hubs in the North Sea, where around 200 wind tur­bines with a com­bined capac­i­ty of 3GW would be installed in the first phase of the project. The hope is there will even­tu­al­ly be the poten­tial for 10GW and the abil­i­ty to con­nect to oth­er coun­tries.

In the UK, Alice Etheridge, off­shore coor­di­na­tion senior man­ag­er at Nation­al Grid ESO, says the oper­a­tor is con­sid­er­ing off­shore wind farm project shar­ing con­nec­tions to the main­land for the HND, poten­tial­ly con­nect­ing off­shore cables from projects in Scot­land to Eng­land and Wales, instead of just direct­ly to Scot­land, plus high­er-capac­i­ty con­nec­tions and poten­tial­ly mul­ti­pur­pose inter­con­nec­tors.

A phased approach to offshore grids

Tak­ing a Europe-wide approach “absolute­ly has its ben­e­fits”, Etheridge says, but progress should be phased.

“That’s like­ly some­thing we’ll build up to in the future. As we get a more endur­ing path, we will prob­a­bly head towards increas­ing lev­els of inte­gra­tion with Europe. We all have sim­i­lar decar­bon­i­sa­tion tar­gets and hav­ing a diverse sup­ply is going to be real­ly ben­e­fi­cial,” she explains. “This will also help us with secu­ri­ty of sup­ply and real­ly get­ting val­ue from this low-car­bon gen­er­a­tion.”

Etheridge doesn’t think Brex­it is pro­hib­i­tive. How­ev­er, she says it might require some “prac­ti­cal mat­ters to be clar­i­fied”. In the short to medi­um term the UK and EU Trade Coop­er­a­tion Agree­ment should be help­ful, she says.

While there appears to be Euro­pean con­sen­sus for devel­op­ing a North Sea high-volt­age grid, cre­at­ing such an expan­sive, mul­ti-stake­hold­er, inter­na­tion­al infra­struc­ture using nov­el tech­nol­o­gy – some of which may not be ready until 2030 – throws up tech­ni­cal, reg­u­la­to­ry and polit­i­cal com­pli­ca­tions, as well as sup­ply chain chal­lenges.

To accel­er­ate the con­cept, col­lab­o­ra­tive plan­ning between nation­al stake­hold­ers and coun­tries needs to hap­pen now. “It seems like an emp­ty sea, but it’s real­ly crowd­ed with users and stake­hold­ers – this can nev­er be devel­oped with­out a strong gov­ern­men­tal back­up,” warns Jaars­ma.

Challenges ahead

Work­ing with­out mul­ti-stake­hold­er coor­di­na­tion could cre­ate chal­lenges lat­er. For exam­ple, HVDC grids with dif­fer­ent volt­ages are very expen­sive or impos­si­ble to con­nect.

Col­lab­o­ra­tion between tech­nol­o­gy ven­dors is also a key chal­lenge. There are only three lead­ing region­al man­u­fac­tur­ers for the nec­es­sary HVDC tech­nol­o­gy need­ed – Siemens, Hitachi Ener­gy and GE – and man­u­fac­tur­ers are not always forth­com­ing in shar­ing infor­ma­tion between them­selves. The costs will also be high – the PRO­MO­TioN project esti­mat­ed that the trans­mis­sion infra­struc­ture off­shore alone would cost approx­i­mate­ly €1bn (about £850m) per gigawatt.

And time is run­ning out. The time­lines for build­ing grids are typ­i­cal­ly more than 10 years, with ini­tial inte­grat­ed con­nec­tions not expect­ed until 2030. In its assess­ment, Nation­al Grid ESO warns the delay in devel­op­ing such infra­struc­ture could poten­tial­ly risk miss­ing the UK’s 2030 tar­gets.

“The soon­er that coor­di­na­tion starts, the greater the ben­e­fits, but there are prac­ti­cal­i­ties to con­sid­er such as that many of the projects to meet the 2030 tar­get are already in progress,” says Etheridge. “But this kind of coor­di­na­tion will be real­ly impor­tant to help oth­er projects get their con­sent and there­fore reach the tar­get.”

To gal­vanise devel­op­ment of a meshed North Sea grid by tra­di­tion­al­ly con­ser­v­a­tive TSOs, gov­ern­ments will like­ly need to facil­i­tate more pilot projects for test­ing tech­nol­o­gy. This would help increase con­fi­dence and dri­ve down costs.

Despite the chal­lenges, how­ev­er, Plet says an off­shore grid in the North Sea is “now inevitable”, with Amer­i­ca and Chi­na also con­tem­plat­ing the con­cept to sup­port their own green ener­gy ambi­tions.