Semiconductors in the grid

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At first glance, the dis­trict of Nieder­bobritzsch, Ger­many is a com­mu­ni­ty like thou­sands of oth­ers: a church, farms, busi­ness­es, a small fac­to­ry, a few super­mar­kets and about 800 house­holds. If you look close­ly, how­ev­er, you will also find a gray con­tain­er. This is the vis­i­ble sign that the future is being writ­ten in Nieder­bobritzsch, near the Sax­on city of Freiberg, where elec­tricity sup­pli­er MITNETZ STROM and Rein­hausen, togeth­er with two uni­ver­si­ties, are research­ing how to suc­cess­ful­ly imple­ment the ener­gy rev­o­lu­tion.

“The ener­gy rev­o­lu­tion is tak­ing place pri­mar­i­ly in dis­tri­b­u­tion grids. That is why we need research.”Jens Schwedler, Project Man­ag­er at MITNETZ STROM

To man­age this, tremen­dous quan­ti­ties of addi­tion­al elec­tri­cal ener­gy will have to be trans­port­ed through grids in the future. In par­tic­u­lar, the decar­boniza­tion of the heat­ing and trans­porta­tion sec­tors will strain the grids in the years and decades to come (see ONLOAD 07). Grid oper­a­tors are look­ing for new solu­tions to expand the grids. At Rein­hausen, Stephan Rupp and Dirk Wüsten­berg are work­ing intense­ly on the top­ic. “We’re look­ing for new answers to the ques­tion of how grids will be able to absorb the grow­ing amounts of ener­gy and how, at the same time, to close the gap between gen­er­a­tion and demand that results from the increas­ing volatil­i­ty,” says Busi­ness Devel­op­er Rupp.

Smart distribution grids

Over the course of the ener­gy rev­o­lu­tion, solar elec­tric­i­ty will have to be great­ly expand­ed in the future. A major­i­ty of sys­tems can be found on roofs and facades, mean­ing that they are in local grids. Direct­ing this solar cur­rent through dis­tri­b­u­tion grids to trans­porta­tion grids is not a use­ful solu­tion. The grid expan­sion would be extreme­ly cost­ly and it would be hard to find cus­tomers for the over­sup­ply of solar cur­rent around noon­time. By the same token, in the evening hours, large quan­ti­ties of elec­tric­i­ty must be drawn from the grid as the demand grows on the con­sumer side due to charg­ing sta­tions for elec­tric vehi­cles and elec­tri­cal­ly pow­ered heat pumps.

The solu­tion might be to make the dis­tri­b­u­tion grids more flex­i­ble, which means the option to store solar cur­rent near the source, i.e. in local grids. Anoth­er option for ensur­ing flex­i­bil­i­ty is to adjust the demand for elec­tric­i­ty to the sup­ply with the help of intel­li­gent load con­trol. And solu­tions that also offer autonomous oper­a­tion of dis­tri­b­u­tion grids in the event of a mal­func­tion would be able to increase the sup­ply reli­a­bil­i­ty.

Jens Schwedler, who works as a project man­ag­er on the local grids of the future at dis­tri­b­u­tion grid oper­a­tor MITNETZ STROM in cen­tral Ger­many, says, “Around 55,000 sys­tems for renew­able ener­gy are con­nect­ed to our dis­tri­b­u­tion grids.” There­fore, for Schwedler, it is obvi­ous: “In addi­tion to off­shore appli­ca­tions, the ener­gy rev­o­lu­tion is tak­ing place pri­mar­i­ly in dis­tri­b­u­tion grids. In order to main­tain the pow­er qual­i­ty in the future with the increas­ing volatil­i­ty of sup­ply and demand, there is an urgent need for action and research today!”

Decoupled local grids

For cost rea­sons, ful­ly expand­ing the grids and lay­ing them out with new cables and new trans­form­ers for load or gen­er­a­tion peaks is not a viable approach. “It takes more intel­li­gent solu­tions to get the volatil­i­ty under con­trol than just build­ing up expen­sive over­ca­pac­i­ty,” says Schwedler’s col­league Jan Schön­feld. In order to research exact­ly these solu­tions, MITNETZ STROM began a research project two years ago. Since then, Schwedler and Schön­feld have worked togeth­er with Mit­twei­da Uni­ver­si­ty of Applied Sci­ences, TU Dres­den and Rein­hausen as tech­nol­o­gy part­ners. As part of the project, spon­sored by the Ger­man Fed­er­al Min­istry for Eco­nom­ic Affairs and Ener­gy, they research the advan­tages of decou­pling local grids.

“It takes more intel­li­gent solu­tions than just build­ing up over­ca­pac­i­ty.” Jan Schön­feld, Project mem­ber, MITNETZ STROM

The project has the some­what clunky name “Flex­i­bil­isierung des Net­z­be­triebs durch entkop­pelte Ort­snet­ze” (Eng­lish: Flex­i­bi­liza­tion of Grid Oper­a­tion through Decou­pled Local Grids), which is short­ened to “FlexNet-EkO.” It focus­es on the tran­si­tion from medi­um-volt­age to low-volt­age grids. In order to test this future solu­tion in a field test, MITNETZ STROM chose the com­mu­ni­ty of Nieder­bobritzsch. It is like thou­sands of oth­ers in Ger­many and else­where in the world. There is also an increas­ing num­ber of solar pan­els on roofs here. Par­tic­u­lar­ly in the sum­mer, the momen­tary pro­duc­tion pow­er exceeds ener­gy con­sump­tion. “Here, we have the phe­nom­e­non of load flow rever­sal, and the remain­ing renew­able ener­gy does not appear when the res­i­dents actu­al­ly need the elec­tric­i­ty,” says Schön­feld.

The four part­ners have now been work­ing togeth­er on the idea for more than two years and imple­ment­ed it in a field test in Octo­ber 2021: How can a mod­u­lar dis­tri­b­u­tion grid be set up with a pow­er-elec­tron­ic grid coup­ling? Fur­ther­more, can the pro­duc­tion-side and con­sumer-side peaks be buffered using bat­tery stor­age units in order to bring demand and sup­ply into har­mo­ny with­in the dis­tri­b­u­tion grid, and reduce reper­cus­sions on the upstream medi­um-volt­age lev­el?

“A grid-form­ing invert­er would act like a diesel gen­er­a­tor or a small pow­er plant.” Stephan Rupp, Busi­ness Devel­op­er, Rein­hausen

To find the answers to these ques­tions, Rein­hausen con­tributed its exper­tise in stor­age tech­nol­o­gy and pow­er qual­i­ty man­age­ment to the project. “The decou­pling of a local grid with Rein­hausen tech­nol­o­gy offers us a whole range of pos­si­ble advan­tages as a grid oper­a­tor. What we dis­cov­ered, first in the­o­ry and then under lab­o­ra­to­ry con­di­tions, has now been test­ed in a local grid with 200 house­holds under real-world con­di­tions for the first time,” says project mem­ber Schön­feld.

Semiconductors stabilize load flows

In the tri­al grid in Nieder­bobritzsch, a bat­tery stor­age unit from Rein­hausen is now in use that stores the excess renew­able ener­gy. The project also focus­es on the sta­bi­liza­tion and har­mo­niza­tion of load flows with­in dis­tri­b­u­tion grids. For this pur­pose, Rein­hausen also placed a pow­er-elec­tron­ic grid cou­pling with a grid-form­ing invert­er in the gray con­tain­er, in addi­tion to the bat­ter­ies.

This Rein­hausen tech­nol­o­gy is already sta­bi­liz­ing load flows with­in the dis­tri­b­u­tion grid under real-world con­di­tions. “Now, our task is to gain expe­ri­ence with this new equip­ment and see whether real­i­ty match­es our sim­u­la­tion results,” explains grid expert Schwedler, adding, “The the­o­ry sug­gests that inter­fer­ence com­ing from the medi­um-volt­age lev­el will be fil­tered out, pro­vid­ing a clean volt­age range. We’re now test­ing what pow­er qual­i­ty can actu­al­ly be reached with an invert­er and deriv­ing plan­ning and oper­at­ing cri­te­ria from this infor­ma­tion.”

“Our con­trol tech­nol­o­gy is also mak­ing the grid more intel­li­gent.” Dirk Wüsten­berg, Project Man­ag­er, Rein­hausen

Anoth­er aspect is that the tech­nol­o­gy is also intend­ed to make the grid as a whole more intel­li­gent. MITNETZ tech­ni­cian Schön­feld says, “We can bal­ance the sup­ply and demand using intel­li­gent con­trol. We con­sume the elec­tric­i­ty we pro­duce local­ly, thus reliev­ing the bur­den on the upstream medi­um-volt­age grid. To do so, the con­trol sys­tem of the invert­er com­mu­ni­cates direct­ly with the con­trol box­es installed in the cus­tomer sys­tems with sig­nals in the range of 10 MHz over the pow­er grid. This means that, when a lot of elec­tric­i­ty is gen­er­at­ed, elec­tric vehi­cles are charged, heat pumps are start­ed up, and the bat­tery in the con­tain­er is charged. If more ener­gy is required lat­er than what is being pro­duced, it is avail­able.” It sounds like a real win-win sit­u­a­tion for grid oper­a­tors and cus­tomers.

The semi­con­duc­tor tech­nol­o­gy required for this, how­ev­er, intro­duces the next chal­lenge: the short-cir­cuit capac­i­ty. Schwedler says, “In order to pro­vide suf­fi­cient short-cir­cuit capac­i­ty with semi­con­duc­tor tech­nol­o­gy, we designed the pow­er of the sys­tem to be twice as large as would actu­al­ly be need­ed. We played it safe and want­ed to avoid neg­a­tive effects for our cus­tomers dur­ing the field test at all costs.” His col­league Schön­feld adds, “This first step was about test­ing the tech­nol­o­gy under real-world con­di­tions. As a result, eco­nom­ic con­sid­er­a­tions were not yet a high pri­or­i­ty. We can use the find­ings to lat­er dimen­sion the pow­er actu­al­ly required. These are also need­ed lat­er to be able to com­pare the dif­fer­ent tech­no­log­i­cal alter­na­tives with each oth­er.”

Rein­hausen spe­cial­ist Wüsten­berg is opti­mistic, say­ing, “With our con­trol tech­nol­o­gy, we are also mak­ing the grid more intel­li­gent. If we net­work pro­duc­ers, con­sumers, and bat­tery stor­age units with­in a dis­tri­b­u­tion grid with each oth­er using con­trol tech­nol­o­gy, this alone pro­duces com­pelling advan­tages.” Rein­hausen strate­gist Rupp is think­ing one step fur­ther, say­ing, “If the grid-form­ing bat­tery stor­age units prove their worth in dis­tri­b­u­tion grids, this would make it pos­si­ble to relieve the bur­den on high­er-lev­el grids, since solar pow­er from the local grid can be stored and con­sumed in the dis­tri­b­u­tion grid. This also secures high­er sup­ply reli­a­bil­i­ty since the grid-form­ing invert­ers can sup­ply the grid exact­ly like a diesel gen­er­a­tor or small pow­er plant.” Cur­rent­ly, it seems that this is so.

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YOUR CONTACT

Do you have ques­tions about the project?
Dirk Wüsten­berg is avail­able for you:
D.Wuestenberg@reinhausen.com