Saving for the future

Renew­able ener­gies are volatile. Decar­boniza­tion will not be pos­si­ble with­out stor­age tech­nolo­gies across all grid lev­els.

Envi­ron­men­tal pro­tec­tion and the reduc­tion of green­house gas­es, par­tic­u­lar­ly CO 2 , require far-reach­ing changes in ener­gy pro­duc­tion around the globe. The expan­sion of renew­able ener­gies, espe­cial­ly solar and wind ener­gy, play a key role in the ener­gy rev­o­lu­tion, because the sup­ply of these environ­mentally friend­ly ener­gy sources vast­ly exceeds the cur­rent glob­al need for pri­ma­ry ener­gy, cur­rent­ly at about 170,000 ter­awatt hours (see ONLOAD 07).

Accord­ing to data acquired by the IEA (Inter­na­tion­al Ener­gy Agency), emis­sions-free pow­er already accounts for approx­i­mate­ly 37% of the pow­er flow­ing through grids around the world. How­ev­er, elec­tric ener­gy only makes up a fifth of the total glob­al ener­gy con­sump­tion. There­fore, how renew­able sources can sub­sti­tute con­ven­tion­al ones in the trans­port and heat­ing sec­tors is also cru­cial for the ener­gy rev­o­lu­tion.

There­fore, how renew­able sources can sub­sti­tute con­ven­tion­al ones in the trans­port and heat­ing sec­tors is also cru­cial for the ener­gy rev­o­lu­tion.

In order to reach our cli­mate goals, a whole array of chal­lenges must be over­come. In the words of Markus Riepl, who devel­ops solu­tions for the grids of the future at Rein­hausen: “Many ques­tions are about how the grids of the future can trans­port this mas­sive amount of ener­gy, and how the volatile pro­duc­tion of solar and wind pow­er can be aligned with cur­rent needs in the right place at the right time. These ques­tions have both glob­al and region­al dimen­sions.”

In the future, many indus­tri­al­ized nations, such as Ger­many, will have to import “green ener­gy” in the form of “green hydro­gen” pro­duced in windy and sun­ny regions. At the same time, grid capac­i­ties are already reach­ing their lim­its and can­not always trans­port envi­ron­men­tal­ly friend­ly pow­er from the pro­duc­er to the con­sumer as need­ed. One option for off­set­ting these fluc­tu­a­tions are ener­gy accu­mu­la­tors. Below, this arti­cle shows how grid prob­lems asso­ci­at­ed with renew­able ener­gies can be solved with stor­age systems—from high-volt­age and extra-high-volt­age to medi­um-volt­age and low-volt­age lev­els.

The challenge of sector coupling

Even at the extra-high-volt­age lev­el, bat­tery stor­age can buffer trans­mis­sion bot­tle­necks in grids. For exam­ple, in Ger­many, elec­tric­i­ty has to get from off-shore wind parks in the windy north to high-con­sump­tion areas in the south. While oper­a­tors are con­stant­ly expand­ing trans­mis­sion grids, this alone is not enough. The trans­mis­sion pow­er must also be opti­mized using what are called “grid boost­ers”. These are gigan­tic bat­tery sys­tems in the pow­er range of sev­er­al hun­dred megawatts.

For con­text: Trans­port­ing large amounts of elec­tric­i­ty from the north to the south over lines results in over­load­ing indi­vid­ual line sec­tions again and again, which makes expen­sive redis­patch mea­sures nec­es­sary. This means that pro­duc­ers upstream of a bot­tle­neck must reduce their pro­duc­tion and those down­stream of the bot­tle­neck must increase their pro­duc­tion by the same amount. The costs for these mea­sures add up to more than 100 mil­lion euros annu­al­ly in Ger­many alone.

Pow­er gen­er­a­tion and con­sump­tion: When bal­anc­ing the gaps or sur­plus­es between gen­er­a­tion and con­sump­tion, redis­patch costs arise. Grid boost­ers help to min­i­mize these.

Grid boost­ers help bal­ance out these gaps by sav­ing the excess quan­ti­ties that occur upstream of bot­tle­necks and can­not be trans­port­ed, nd then pro­vid­ing the pow­er down­stream of the bot­tle-necks. Since this all hap­pens with­in an extreme­ly fast response time, safe­ty reserves in the grids intend­ed for these kinds of mal­func­tions can be used for elec­tric­i­ty trans­port.

Grid boosters for transmission grids

Due to the depen­dence on wind and weath­er, there is usu­al­ly either too much or too lit­tle elec­tri­cal ener­gy avail­able. Grid oper­a­tors want to off­set this by cou­pling or inter­lock­ing the ener­gy sec­tors of elec­tric­i­ty, heat and transport—using the ener­gy source of gas. Excess renew­able ener­gy is decou­pled to the trans­port and heat­ing sec­tors using pow­er- to-gas or pow­er-to-heat sys­tems.

The gas grid has enor­mous stor­age capac­i­ty for this. For exam­ple, the hydro­gen pro­duced with renew­able ener­gy in fuel cells for cars or through con­ven­tion­al uti­liza­tion in nat­ur­al gas con­sumers can reduce dam­ag­ing green­house gas emis­sions.

Pro­fes­sor Veroni­ka Grimm of the Uni­ver­si­ty of Erlan­gen-Nurem­berg is one of the lead­ing forces behind sec­tor cou­pling in Ger­many. In an inter­view with the online plat­form sech­snull. de, she explains that green hydro­gen in par­tic­u­lar will play a cru­cial role when it comes to the decar­boniza­tion of the trans­port and heat­ing sec­tors.

The prin­ci­ple of pow­er-to-gas tech­nol­o­gy

For this renew­able ener­gy spe­cial­ist, it is also clear that there can be no ener­gy rev­o­lu­tion with­out inter­na­tion­al con­nect­ed­ness. “As an indus­tri­al­ized nation, we will still not be self-suf­fi­cient in a 100 per­cent renew­able world. We will import hydro­gen and syn­thet­ic ener­gy sources that were pro­duced in pre­ferred regions all around the world,” says Prof. Grimm.

Buffering with community batteries

Today, sta­tion­ary accu­mu­la­tors, also known as com­mu­ni­ty bat­ter­ies, usu­al­ly buffer the fluc­tu­at­ing amounts pro­duced by renew­able ener­gy sources on the medi­um-volt­age lev­el, thus con­tribut­ing sig­nif­i­cant­ly to the ener­gy rev­o­lu­tion. They offer total­ly new oppor­tu­ni­ties for ener­gy and load man­age­ment in indus­tri­al oper­a­tions and dis­tri­b­u­tion grid sec­tions.

Wind or solar parks can be cou­pled to pro­duc­tion units using these ener­gy accu­mu­la­tors, allow­ing them to bring ener­gy into the grids con­stant­ly and pre­dictably. They help sta­bi­lize micro­grids or poor­ly devel­oped grids by com­pen­sat­ing for fluc­tu­at­ing load and infeed amounts. From an eco­nom­ic point of view, com­mu­ni­ty bat­ter­ies make sense at many node points on the grids, says Rein­hausen expert Markus Riepl.

“Grid oper­a­tors avoid invest­ment in grid expan­sion, and sup­pli­ers of wind and solar ener­gy can use the mar­ket imbal­ances to sell their elec­tric­i­ty when it brings in the most prof­it. Pow­er sta­tions can cre­ate reserves and com­pen­sate for demand peaks in the grid.”

The bat­tery invert­er com­bines three func­tions in a sin­gle unit: stor­age, reac­tive pow­er com­pen­sa­tion and active fil­ter­ing. Due to this sys­tem ser­vice capa­bil­i­ty, these invert­ers are clas­si­fied as grid com­po­nents by the reg­u­la­to­ry author­i­ty. This clas­si­fi­ca­tion offers advan­tages to the oper­a­tor in terms of invest­ment costs and stor­age man­age­ment. Remote regions with a weak grid con­nec­tion can also achieve a more sta­ble pow­er sup­ply using stor­age tech­nol­o­gy.

Ener­gy stor­age sys­tems (ESS) can store ener­gy pro­duced by var­i­ous pro­duc­ers, like solar and wind sys­tems or diesel gen­er­a­tors, and out­put it to the grid as need­ed. As a result, these sys­tems guar­an­tee a smooth, con­tin­u­ous pow­er sup­ply. This requires invert­er solu­tions, such as GRIDCON® PCS from Rein­hausen, for exam­ple, which Autarsys installs in bat­tery sys­tems that are cur­rent­ly being used in the pow­er sup­ply of a remote area in the Philip­pines (read more on this in online issue 05

Andreas Plenk of the Dutch stor age sys­tem man­u­fac­tur­er Alfen sees even more ver­sa­tile appli­ca­tions for bat­tery sys­tems. “More and more Euro­pean cities are set­ting up green zones and want to ban diesel gen­er­a­tors for envi­ron­men­tal rea­sons. But mar­kets, fes­ti­vals and large events still need to be sup­plied with elec­tric­i­ty. We have a sim­i­lar sit­u­a­tion at ports. Green zones are set up here in order to reduce the num­ber of diesel gen­er­a­tors port oper­a­tors and ship­ping com­pa­nies need. In this way, new mar­kets are cur­rent­ly emerg­ing.”

Charging stations relieve distribution grids

The ener­gy trans­for­ma­tion can­not be done with­out elec­tric mobil­i­ty, at least as an inter­me­di­ate step. Ana­lysts expect that, by 2030, there will be more elec­tric vehi­cles on the road in most indus­tri­al­ized coun­tries than those with com­bus­tion engines. In fact, Cal­i­for­nia would like to get rid of con­ven­tion­al vehi­cles entire­ly by that point. For dis­tri­b­u­tion grids, in par­tic­u­lar, this devel­op­ment presents tremen­dous chal­lenges which can only be mas­tered with intel­li­gent charg­ing infra­struc­ture.

For exam­ple, expen­sive expan­sion of line capac­i­ties would be nec­es­sary in many cas­es in order to charge mul­ti­ple vehi­cles in a park­ing garage or pub­lic park­ing spaces. The alter­na­tive is charg­ing sta­tions that keep a bat­tery ready and there­fore accel­er­ate the charg­ing process while simul­ta­ne­ous­ly reliev­ing the low-volt­age grids. There is a glob­al mar­ket here for which Rein­hausen is pro­vid­ing solu­tions.

This con­cept can also ben­e­fit from swarm intel­li­gence. The fluc­tu­at­ing, weath­er-depen­dent ener­gy pro­duc­tion from renew­able ener­gy sources can also bal­ance fluc­tu­a­tions on the local grid lev­el through smart bat­tery solu­tions. For this pur­pose, vehi­cles in their down­times pro­vide their bat­tery capac­i­ty to the pow­er grid in the event of bot­tle­necks. In turn, in cas­es where the pow­er grid would have more than enough ener­gy to sup­ply to the vehi­cles, sup­ply and pro­duc­tion peaks could be smoothed over. Bat­tery stor­age can there­fore help mas­ter the chal­lenge of the ener­gy rev­o­lu­tion on all grid levels—from high-volt­age grids to local grids. Rein­hausen wants to do its part here.


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