Municipal Energy TransitionTurning prohibited?

The dis­tri­b­u­tion net­works were planned as one-way streets. Now there is a threat of heavy two-way traf­fic. Self-suf­fi­cient or decou­pled grids are one way to relieve the upstream grids.

Stand-alone or “island” grids, self-suf­fi­cient local grids, decou­pled low-volt­age grids—these are buzz­words that are being heard more and more fre­quent­ly in con­nec­tion with the ener­gy tran­si­tion. The idea is that as more and more gen­er­a­tion capac­i­ty migrates to local grids, they should become increas­ing­ly inde­pen­dent of upstream grids. The advan­tages: On the one hand, these “self-suf­fi­cient” local grids would no longer be affect­ed by the uncer­tain­ties and volt­age fluc­tu­a­tions of the upstream grids. And on the oth­er hand, they them­selves would no longer place such a heavy bur­den on the upstream net­works from fluc­tu­at­ing feed-in, since dis­tri­b­u­tion grids are still designed for elec­tric­i­ty that only flows in one direc­tion.

What sounds sim­ple in the­o­ry, how­ev­er, turns out to be a tech­ni­cal­ly high­ly demand­ing under­tak­ing in prac­tice. How­ev­er, a num­ber of projects are show­ing how sup­ply can suc­ceed at the munic­i­pal lev­el, whether through com­plete­ly self-suf­fi­cient sys­tems (Feld­heim), iso­lat­ed solu­tions (Mau­ri­tius) or a decou­pled local grid (Nieder­bobritzsch). The com­mon denom­i­na­tors in these solu­tions are mod­ern con­vert­er sys­tems and bat­ter­ies for stor­age.

Feldheim: An energy-self-sufficient village

One of the show­case projects when it comes to ener­gy self-suf­fi­cient com­mu­ni­ties is the Feld­heim vil­lage of the Bran­den­burg town of Treuen­bri­et­zen. Here, the Ger­man project devel­op­er Energiequelle has imple­ment­ed one of the most ambi­tious over­all con­cepts for a decen­tral­ized, regen­er­a­tive ener­gy sup­ply for com­pa­nies, pri­vate house­holds and munic­i­pal­i­ties over the past 20 years.

Feldheim independent energy
Feld­heim project: This dis­trict of Treuen­bri­et­zen is already com­plete­ly self-suf­fi­cient, mak­ing it one of the world’s show­case projects for regen­er­a­tive ener­gy sup­ply.

The indi­vid­u­al­ly con­nect­ed house­holds here are sup­plied with elec­tric­i­ty and heat autonomous­ly via their own dis­tri­b­u­tion net­work. All ener­gy is gen­er­at­ed on site exclu­sive­ly from renew­able sources. A wind farm is the basis for the local pow­er sup­ply; heat is sup­plied by a bio­gas plant. And if it gets par­tic­u­lar­ly cold in win­ter, a wood­chip heat­ing plant is also avail­able. The spe­cial fea­ture of this ener­gy con­cept is that the heat and elec­tric­i­ty gen­er­at­ed on site are fed direct­ly to con­sumers and any sur­plus is fed into the upstream grid. Fluc­tu­a­tions in the grid are pre­vent­ed by a region­al reg­u­lat­ing pow­er plant and a bat­tery stor­age sys­tem. As Doreen Rasche­mann from project devel­op­er Energiequelle told Deutsch­land­funk radio: “The stor­age sys­tems ensure that we real­ly do have a sta­ble grid, and that the fre­quen­cy of 50 Hz is main­tained.”


Tom Fricke and his team are active in many dif­fer­ent parts of the world. He is Head of Ener­gy Stor­age at DHYBRID, a solu­tion provider for renew­able ener­gies and bat­tery stor­age sys­tems. Based in Gaut­ing, Bavaria, the com­pa­ny designs hybrid sys­tems world­wide that intel­li­gent­ly com­bine bat­tery stor­age and renew­able ener­gies. For this pur­pose, DHYBRID sup­plies its own devel­oped con­trol solu­tion as well as turnkey bat­tery stor­age sys­tems, thus shap­ing the future of ener­gy sys­tems, espe­cial­ly in South Amer­i­ca, Africa and Asia.

Project Mau­ri­tius: The con­struc­tion of an island grid with solar pan­els, bat­tery stor­age and con­vert­ers offer­s­the solu­tion here to become inde­pen­dent from the unsta­ble upstream grid.

Only recent­ly, the spe­cial­ists set up a stand-alone grid on Mau­ri­tius. There, the local ener­gy sup­pli­er CEB pro­hibits pho­to­volta­ic sys­tems from being con­nect­ed direct­ly to the grid. Fricke reports: “For cost and sus­tain­abil­i­ty rea­sons, our cus­tomer Kalac­hand want­ed to move away from diesel gen­er­a­tors and the unsta­ble pow­er grid and cov­er its needs pri­mar­i­ly with solar pow­er. From a pure­ly legal point of view, how­ev­er, this was only pos­si­ble if we phys­i­cal­ly decou­pled the local grid from the upstream pow­er grid and set up an inde­pen­dent island grid.” That’s because the sun shines on Mau­ri­tius for 2,900 hours a year. And dur­ing mid­day, the plant pro­duces up to 535 kW. In order to save the ener­gy into the night hours, the spe­cial­ists from Dhy­brid built a bat­tery stor­age sys­tem with around 613 kWh and com­bined it with two Rein­hausen GRIDCON® PCS con­vert­ers, which set up an island grid that is phys­i­cal­ly sep­a­rat­ed from the pub­lic grid. Now the oper­a­tor saves almost 214,000 liters of diesel per year and no longer has any pow­er out­ages, which means that the entire sys­tem will pay for itself in just under four years. The advan­tage of this solu­tion is that, as a pure con­sumer, it can still access the elec­tric­i­ty in the upstream grid if nec­es­sary.

“Sce­nar­ios of severe volt­age fluc­tu­a­tions and pow­er out­ages last­ing from sec­onds to more than 72 hours are no longer unthink­able.”
Tom Fricke, DHYBRID

The require­ments are sim­i­lar for oth­er projects spread around the world. Fricke explains: “Many of our cus­tomers want to sup­port their diesel or gas gen­er­a­tors with renew­ables and thus reduce costs and con­sump­tion. For oth­ers, the issue is reli­ability, because either the upstream grid is unsta­ble or they oper­ate safe­ty-crit­i­cal appli­ca­tions that don’t tol­er­ate down­time.” Look­ing at Ger­many and the Euro­pean net­works, Fricke makes inter­est­ing obser­va­tions, “Here we’ve always had incred­i­bly sta­ble net­works.” For this rea­son, this mar­ket was not very prof­itable for Dhy­brid. “But in the mean­time,” Fricke says, “the sit­u­a­tion has changed and there is a rethink­ing in indus­try and pol­i­tics. Sce­nar­ios of severe volt­age fluc­tu­a­tions and pow­er out­ages last­ing from sec­onds to more than 72 hours are no long­er unthink­able. Our solu­tion port­fo­lio can help bridge these dis­rup­tions sus­tain­ably.”

Niederbobritzsch makes it!

FlexNet-EkO — mak­ing net­work oper­a­tion more flex­i­ble by means of decou­pled local net­works — is also con­cerned with the issue of sup­ply qual­i­ty and reli­a­bil­i­ty of the local net­work. As part of this research project fund­ed by the Ger­man Fed­er­al Min­istry of Eco­nom­ics and Cli­mate Pro­tec­tion (BMWK), the dis­tri­b­u­tion net­work oper­a­tor MITNETZ STROM has set up a local net­work in Nieder­bobritzsch whose only con­nec­tion to the upstream net­work is via a pow­er-elec­tron­ic net­work cou­pling from Rein­hausen (see ONLOAD 10).

“The sys­tem builds up a com­plete­ly sta­ble grid; inter­rup­tions are com­pen­sat­ed for by the bat­tery.”
Jens Schwedler, MITNETZ STROM

Project man­ag­er at MITNETZ STROM, the largest region­al dis­tri­b­u­tion sys­tem oper­a­tor in east­ern Ger­many, is Jens Schwedler. The ques­tion he has been work­ing on for almost three years togeth­er with Mit­twei­da Uni­ver­si­ty of Applied Sci­ences, Dres­den Tech­ni­cal Uni­ver­si­ty and Rein­hausen as a tech­nol­o­gy part­ner: How can a mod­u­lar dis­tri­b­u­tion net­work with a pow­er-elec­tron­ic grid cou­pling be con­struct­ed? To this end, the par­tic­i­pants have been re­searching a sys­tem tech­nol­o­gy basis for the use of pow­er elec­tron­ic net­work cou­plings (eNCs). The basis is the decen­tral­ized and cus­tomer-ori­ent­ed pro­vi­sion of the required volt­age qual­i­ty. In addi­tion, the aim is to achieve sim­ple and cost-effec­tive reg­u­la­tion of con­trol­lable con­sumers, gen­er­a­tors and stor­age units in the dis­tri­b­u­tion net­work.

Highest voltage quality

Since Sep­tem­ber 2021, as part of a tech­ni­cal fea­si­bil­i­ty study, a gray con­tain­er has been the heart of the dis­tri­b­u­tion net­work in this Cen­tral Sax­on munic­i­pal­i­ty. It con­tains the stor­age units and a pow­er-elec­tron­ic grid cou­pling with a grid-form­ing con­vert­er. Schwedler reports: “The sys­tem has been run­ning smooth­ly for four months. One pos­i­tive aspect is that we are mea­sur­ing excel­lent volt­age qual­i­ty which we could nev­er have got­ten from the pub­lic grid. The sys­tem sim­ply fil­ters out asym­me­tries from the medi­um-volt­age grid and builds up a com­plete­ly sta­ble low-volt­age grid. Inter­rup­tions are seam­less­ly com­pen­sat­ed for by the bat­tery.”

mitnetz kommunale energyversorgung schwedler onload
Nieder­bobritzsch project: Jens Schwedler from MITNETZ STROM is con­vinced that many prob­lems can be solved with bat­tery stor­age sys­tems in com­bi­na­tion with pow­er elec­tron­ic grid cou­pling and grid-form­ing con­vert­ers.

The con­trol sys­tem devel­oped byRein­hausen is also impres­sive. It com­mu­ni­cates via the pow­er grid with sig­nals in the 100 mil­li­hertz range. MITNETZ STROM was able to win sev­er­al cus­tomers for a field test who have equipped inert loads such as wall­box­es for e‑cars or heat pumps with a con­trol box. If the pow­er pro­duc­tion falls below a crit­i­cal val­ue or is cur­rent­ly run­ning on bat­tery pow­er due to an inter­rup­tion, the charg­ing process or the heat pump sim­ply stops for this peri­od. The cus­tomer is not even aware of this. Schwedler empha­sizes: “This is about con­trol tech­nol­o­gy for sta­bi­liz­ing the net­works. For com­mu­ni­ca­tion, I need a secure path. The results show that this can be fre­quen­cy.”

Rein­hausen tech­nol­o­gy has thus prov­­en itself in Nieder­bobritzsch, mak­ing decou­pling, grid build­ing, stor­age and con­trol all pos­si­ble. In Schwedler’s view, the sys­tem thus has the poten­tial to estab­lish itself as the oper­at­ing resource of the future: “The next ques­tion is whether the sys­tem can also assert itself eco­nom­i­cal­ly against com­pet­ing sys­tems.” But here, too, the ener­gy expert is opti­mistic.


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