Regulating Brazil’s solar boom

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With around 21 mil­lion inhab­i­tants, Minas Gerais is one of the largest states in Brazil. It is also home to Brazil’s most impor­tant indus­tri­al cen­ters. Min­ing, steel and auto­mo­tive indus­tries as well as food pro­cess­ing and agri­cul­ture have ensured steady eco­nom­ic growth in recent years. The grid oper­a­tor CEMIG (Com­pan­hia Energéti­ca de Minas Gerais S.A.), one of the largest ener­gy sup­pli­ers in South Amer­i­ca with more than nine mil­lion cus­tomers, not only has to cope with this growth, but also with geo­graph­i­cal and cli­mat­ic pecu­liar­i­ties such as rainy and dry sea­sons and strong weath­er fluc­tu­a­tions.

In 2024, CEMIG also installed 4.2 GW of solar pow­er, mak­ing it the mar­ket leader in decen­tral­ized pow­er gen­er­a­tion in Brazil. William Alves de Souza, Engi­neer­ing Man­ag­er at CEMIG, says: “The increase in decen­tral­ized pow­er gen­er­a­tion pos­es major chal­lenges for dis­tri­b­u­tion grids. Main­tain­ing pow­er qual­i­ty with­in the stan­dards has become a nation­al chal­lenge.”

Grid stability vs. decentralized generation

Souza is not the only one fac­ing these chal­lenges. In recent years, Brazil has cre­at­ed strong incen­tives for the expan­sion of pho­to­volta­ic (PV) sys­tems, par­tic­u­lar­ly through the net-meter­ing pro­gram “Ger­ação Dis­tribuí­da”. This pro­gram enables house­holds and com­pa­nies to feed the ener­gy they gen­er­ate into the local pow­er grid. In return, they receive cred­its on their elec­tric­i­ty bill. Thanks to these sup­port mea­sures and falling pho­to­volta­ic costs, decen­tral­ized solar ener­gy has devel­oped rapid­ly in South America’s largest econ­o­my and, accord­ing to cal­cu­la­tions by Abso­lar, the Brazil­ian asso­ci­a­tion for pho­to­volta­ic solar ener­gy, has already reached more than 36 gigawatts of installed capac­i­ty in the decen­tral­ized sec­tor.

As in many oth­er coun­tries, Brazil’s dis­tri­b­u­tion grids are uni­di­rec­tion­al and there­fore not designed to absorb large amounts of volatile solar ener­gy. The results of an increas­ing num­ber of decen­tral­ized gen­er­a­tion feed-ins: Volt­age fluc­tu­a­tions, over­loads and vio­la­tions of the volt­age band.

Rena­to Tanaso­vi­ci, Head of Sales South & Cen­tral Amer­i­ca, is famil­iar with these prob­lems and also knows a solu­tion: “Despite the high solar poten­tial, weath­er fluc­tu­a­tions and inter­mit­tent cloud cov­er affect the con­sis­ten­cy of pow­er gen­er­a­tion. This is why dis­tri­b­u­tion grids in par­tic­u­lar need to become more adapt­able, and their con­trol mech­a­nisms more robust. There is a great need for con­trol sys­tems that are capa­ble of man­ag­ing bidi­rec­tion­al ener­gy flows. The VRDT (Volt­age Reg­u­lat­ing Dis­tri­b­u­tion Trans­former) is an effi­cient way to solve these prob­lems.” The VRDT is designed to auto­mat­i­cal­ly reg­u­late fluc­tu­a­tions in gen­er­a­tion and load, and stud­ies and field analy­ses have also shown that, under cer­tain con­di­tions, the grid absorp­tion capac­i­ty can be increased by up to 50 per­cent.

These are argu­ments that con­vinced CEMIG Engi­neer­ing Man­ag­er Souza, who man­ages a grid with over 970,000 dis­tri­b­u­tion trans­form­ers: “We need to pre­pare our grid for decen­tral­ized gen­er­a­tion and have looked at var­i­ous options, such as volt­age reg­u­la­tors. We are now test­ing a promis­ing device: the VRDT with ECOTAP® VPD®. In 2024, we start­ed direct­ly with two pilot projects.” When select­ing the two loca­tions for the reg­u­lat­ed trans­form­ers in which the man­u­fac­tur­er Trael installed the Rein­hausen tap-chang­ers, the grid spe­cial­ists chose two com­plete­ly dif­fer­ent sup­ply areas where there were repeat­ed vio­la­tions of the volt­age band due to new PV feed­ers. The first trans­former sup­plies 92 cus­tomers in the urban area of Uber­a­ba, a town in the min­ing tri­an­gle in the south­west of Minas Gerais. The sec­ond trans­former is locat­ed in the more rur­al town of Bocaiú­va and sup­plies only one com­mer­cial cus­tomer, who feeds the elec­tric­i­ty from his installed PV sys­tem into the dis­tri­b­u­tion grid.

CEMIG Engi­neer­ing Man­ag­er Souza com­ments: “We replaced both unreg­u­lat­ed trans­form­ers with VRDTs with ECOTAP® VPD® III. The instal­la­tion was as straight­for­ward as that of a con­ven­tion­al trans­former. As imbal­ances can occur in the sys­tem, it is impor­tant to select the cor­rect volt­age. We there­fore rec­om­mend that you first study the volt­age pro­file so that you can then set the device accord­ing­ly.”

Operating equipment with great potential

For Rein­hausen man­ag­er Tanaso­vi­ci, the sup­port pro­vid­ed by the sup­pli­ers dur­ing the intro­duc­tion of this new oper­at­ing equip­ment plays an impor­tant role: “MR pro­vid­ed sup­port in select­ing the para­me­ters and also dur­ing the ini­tial com­mis­sion­ing on site. There was also train­ing for the grid operator’s tech­ni­cians.” In addi­tion, grid oper­a­tors can ben­e­fit from work­ing with man­u­fac­tur­ers, research cen­ters and aca­d­e­m­ic insti­tu­tions to gain the nec­es­sary exper­tise for imple­ment­ing, mon­i­tor­ing and opti­miz­ing VRDT solu­tions.

From Souza’s point of view, the deci­sion in favor of VRDT with ECOTAP® VPD® was a good option: “We see the great­est poten­tial at grid points where there are strong volt­age fluc­tu­a­tions due to PV feed-ins.” And this poten­tial exists far beyond CEMIG’s dis­tri­b­u­tion grids through­out Brazil and ulti­mate­ly all of Latin Amer­i­ca.

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