Grid stabilization through hydropower plants

In 2022, the last nuclear pow­er plants in Ger­many will be tak­en off the grid — mean­ing that the pow­er sup­ply sys­tem will also lose instan­ta­neous reserve. This sys­tem ser­vice — in addi­tion to con­trol pow­er — ensures the sta­bil­i­ty of the grids in the event of dis­rup­tions. As a study by the RWTH Aachen Uni­ver­si­ty has now shown, the hydropow­er plants in Ger­many can com­pen­sate for a dis­rup­tion, for exam­ple due to an unplanned pow­er plant out­age of up to 500 megawatts (MW), in terms of instan­ta­neous reserve. This cor­re­sponds to the out­put of a medi­um-sized coal-fired pow­er plant. They thus make a rel­e­vant con­tri­bu­tion to future grid sta­bil­i­ty and secu­ri­ty of supply.

Instan­ta­neous reserve is the term used to describe the pow­er reserve avail­able with­out delay in a pow­er trans­mis­sion sys­tem. It results from the iner­tia of the rotat­ing fly­wheel mass­es of the syn­chro­nous gen­er­a­tors of con­ven­tion­al pow­er plants. If there is an abrupt change in load in a pow­er grid, the pow­er deficit can­not be com­pen­sat­ed imme­di­ate­ly by reg­u­lat­ing pow­er plant out­put. This is because this is always asso­ci­at­ed with a cer­tain delay time. There­fore, in order to pre­vent insta­bil­i­ties and inter­rup­tions, suf­fi­cient kinet­ic ener­gy from rotat­ing fly­wheel mass­es of pow­er plants must be avail­able in the sup­ply sys­tem imme­di­ate­ly after the disturbance.

Hydropower plants as a balance to volatile power generators

From the point of view of gen­er­a­tion vol­umes, wind ener­gy and pho­to­volta­ic plants are con­sid­ered to be the main pil­lars of future renew­able ener­gy pro­duc­tion. How­ev­er, these plants, which are usu­al­ly con­nect­ed by pow­er elec­tron­ics, do not yet pro­vide instan­ta­neous reserve accord­ing to the cur­rent state of the art. Hydro­elec­tric pow­er plants, on the oth­er hand, are capa­ble of doing so.

A team led by Pro­fes­sor Albert Moser, Chair of Trans­mis­sion Net­works and Ener­gy Eco­nom­ics at the Insti­tute of Elec­tri­cal Sys­tems and Net­works, Dig­i­tal­iza­tion and Ener­gy Eco­nom­ics (IAEW) at RWTH Aachen Uni­ver­si­ty, has now deter­mined and quan­ti­fied the instan­ta­neous reserve of hydropow­er plants in Ger­many. The cal­cu­la­tions are based on 7,988 hydropow­er plants with a total of 6.28 gigawatts net nom­i­nal capac­i­ty record­ed in the mar­ket mas­ter data reg­is­ter of the Fed­er­al Net­work Agency. Among oth­er things, the sci­en­tists deter­mined the stored kinet­ic ener­gy of the hydropow­er plants, which can be deter­mined from the iner­tia con­stant and the rat­ed pow­er of the generators.

Accord­ing to the cal­cu­la­tions, a kinet­ic ener­gy of around 10.32 gigawatt sec­onds (GWs) is stored in the rotat­ing mass­es of the hydropow­er plants in Ger­many. By way of com­par­i­son, the Weisweil­er Block H lig­nite-fired pow­er plant has a kinet­ic ener­gy of 2.4 GWs, while the Isar/Ohu 2 nuclear pow­er plant has 8.88 GWs. The kinet­ic ener­gy pro­vid­ed by the hydropow­er plants thus cor­re­sponds to the instan­ta­neous reserve of a nuclear pow­er plant.

The study was led by Mar­tin Knecht­ges and Ste­fanie Samaan. It fur­ther shows that a dis­tur­bance event of 462.5 MW could be absorbed by the hydropow­er plants alone in terms of instan­ta­neous reserve, tak­ing into account the fre­quen­cy depen­dence of the grid loads. Their held instan­ta­neous reserve is suf­fi­cient to suf­fi­cient­ly lim­it the result­ing fre­quen­cy change rate and devi­a­tion. “Ger­man hydropow­er plants also con­tribute at this lev­el to the con­trol of larg­er pow­er deficits, for exam­ple grid dis­con­nec­tions. Fur­ther con­tri­bu­tions to mas­ter­ing must then still be pro­vid­ed from oth­er plants,” sum­ma­rizes Mar­tin Knecht­ges, research asso­ciate at IAEW.

Small decentralized hydropower plants stabilize Bavarian power grids

In addi­tion, the researchers point out, par­tic­u­lar­ly for Bavaria, that in terms of future grid struc­tures and the self-suf­fi­cient sup­ply of small cel­lu­lar grids, the decen­tral­ized hydropow­er plants avail­able can con­tribute to sta­ble grid operation.

“The study shows once again that hydropow­er plants ful­fill impor­tant sys­tem ser­vices for grid sta­bi­liza­tion, espe­cial­ly against the back­ground of the shut­down of nuclear pow­er plants in 2022 and sub­se­quent­ly of coal-fired pow­er plants. In addi­tion to instan­ta­neous reserve, black start capa­bil­i­ty is also worth men­tion­ing in this regard, for example.”

- Fritz Schweiger, Chair­man of the Board of the Asso­ci­a­tion of Hydropow­er Plants in Bavaria (VWB) e.V.

This means that after a large-scale pow­er out­age, hydropow­er is tech­ni­cal­ly capa­ble of sup­port­ing the recon­struc­tion of the pow­er sup­ply. “How­ev­er, the study also shows that exist­ing hydropow­er alone can­not pro­vide the nec­es­sary momen­tary reserve in the pow­er sup­ply sys­tem. Expand­ing elec­tric­i­ty gen­er­a­tion from hydropow­er would already have an effi­cient solu­tion com­po­nent for this. How­ev­er, the oth­er renew­able ener­gy sources will also have to make their con­tri­bu­tion in the future. Now it is up to the engi­neers to find out how this can be ensured with mod­ern pow­er elec­tron­ics,” states Detlef Fis­ch­er, Man­ag­ing Direc­tor of the Asso­ci­a­tion of Bavar­i­an Ener­gy and Water Indus­tries (VBEW) e.V..

The study “Deter­min­ing the instan­ta­neous reserve of hydropow­er plants in Ger­many” at the Insti­tute of Elec­tri­cal Sys­tems and Net­works, Dig­i­tal­iza­tion and Ener­gy Eco­nom­ics at RWTH Aachen Uni­ver­si­ty was car­ried out on behalf of the Ger­man Hydropow­er Asso­ci­a­tion (BDW) e.V., the “Hydropow­er Yes Please!” ini­tia­tive in the Bavar­i­an Ener­gy and Water Man­age­ment Asso­ci­a­tion (VBEW) e.V. and the NRW Water Uti­liza­tion Inter­est Group.