Picture: Roland Goslich, ISFH

Range exten­sion of an e‑delivery vehi­cle through vehi­cle-inte­grat­ed photovoltaics

An elec­tric vehi­cle (almost) with­out depen­dence on charg­ing sta­tions — that sounds like dreams of the future, but the first steps towards it are being tak­en right now. The con­sor­tium of the “Street” research project, in close coop­er­a­tion with Con­ti­nen­tal Engi­neer­ing Ser­vices, has now put a pro­to­type of a light com­mer­cial vehi­cle on the road that is equipped with high­ly effi­cient vehi­cle inte­grat­ed pho­to­voltaics (VIPV). What’s spe­cial about it is that the ener­gy con­vert­ed from sun­light can be fed into the high-volt­age vehi­cle elec­tri­cal sys­tem and thus used direct­ly to extend the range.

Pho­to­volta­ic mod­ules con­vert sun­light into elec­tri­cal ener­gy. Mod­ern bat­tery-elec­tric vehi­cles always have two pow­er stor­age units on board: a small 12 V bat­tery that can sup­ply elec­tri­cal con­sumers, lights and pow­er steer­ing, and a large trac­tion bat­tery that oper­ates at a high­er volt­age of 400 V and sup­plies the elec­tric dri­ve with ener­gy. In order for the ener­gy gen­er­at­ed by VIPV to be fed into the large trac­tion bat­tery and thus con­tribute to extend­ing the range, it is nec­es­sary to cou­ple the PV mod­ules to the high-volt­age vehi­cle elec­tri­cal sys­tem. This is tech­ni­cal­ly very demand­ing, as it requires a con­ver­sion from 12 V to 400 V and is linked to many safe­ty aspects. It is pre­cise­ly this chal­lenge that the Street Con­sor­tium has now suc­cess­ful­ly addressed. The basis for this was the com­bi­na­tion of dif­fer­ent com­pe­tences: The con­ver­sion of solar ener­gy into elec­tri­cal ener­gy takes place in PV mod­ules devel­oped by a2-solar for auto­mo­tive use. These are based on high­ly effi­cient sil­i­con het­ero­junc­tion solar cells from Mey­er Burg­er, which were inter­con­nect­ed at the ISFH using Smartwire inter­con­nec­tion tech­nol­o­gy. This tech­nol­o­gy, devel­oped in Europe, not only enables max­i­mum cell and mod­ule effi­cien­cies, but also max­i­mum mod­ule yields due to a low­er tem­per­a­ture coef­fi­cient. Con­trol to the point with max­i­mum pow­er is pro­vid­ed by elec­tron­ics from Vitesco Tech­nolo­gies, which has also devel­oped the DC/DC con­vert­er from 12 V to 400 V as a cen­tral inno­va­tion. Con­ti­nen­tal Engi­neer­ing Ser­vices was respon­si­ble for the inte­gra­tion of all com­po­nents and their inte­gra­tion into the vehi­cle elec­tri­cal system.
The “WORK L” light com­mer­cial vehi­cle from the StreetScoot­er com­pa­ny used as a demon­stra­tor offers ide­al con­di­tions for VIPV: a total area of 15 m² is avail­able for the 10 PV mod­ules. In con­trast to inte­gra­tion on pas­sen­ger cars, the mod­ules did not have to be curved or coloured. Their nom­i­nal total out­put is 2180 Wp. At the same time, the ener­gy require­ment for dri­ving, at approx. 19 kWh / 100 km, is sim­i­lar­ly low to that of pas­sen­ger cars.

“We expect an annu­al range exten­sion of about 5200 km for trips in Low­er Sax­ony, and sig­nif­i­cant­ly more in more south­ern regions. This would save more than one in four grid-based charg­ing stops,” says Prof. Rob­by Peib­st, coor­di­na­tor of the Street project. “Our results will show the attrac­tive­ness of vehi­cle-inte­grat­ed pho­to­voltaics first for such light com­mer­cial vehi­cles. In addi­tion, how­ev­er, they also pro­vide impor­tant insights into the trans­fer of VIPV to oth­er vehi­cle classes.”

The demon­stra­tor vehi­cle has road approval in accor­dance with the Ger­man Road Traf­fic Licens­ing Reg­u­la­tions (StV­ZO) and has com­plet­ed ini­tial tests. It is equipped with numer­ous sen­sors to accu­rate­ly track ener­gy flows. By the end of the project, all com­po­nents will have been put through their paces in test dri­ves at dif­fer­ent times of the day and year and under dif­fer­ent weath­er con­di­tions. In the near future, the vehi­cle will there­fore often be seen on the roads of the Weser­ber­g­land, the Han­nover region and in the state cap­i­tal itself. The num­ber plate “HM-PV-30E” refers to the poten­tial for solar ener­gy in Low­er Sax­ony: stud­ies by the ISFH show that in a cost-opti­mized sus­tain­able ener­gy sys­tem in Low­er Sax­ony, up to 30 % of the final ener­gy demand can be pro­vid­ed by PV.

The research project “Street” is fund­ed by the Ger­man Fed­er­al Min­istry for Eco­nom­ic Affairs and Ener­gy (fund­ing code 01183157). The results of the project also flow into the inter­na­tion­al work­ing group “Task 17 — PV for Trans­port” in the Pho­to­volta­ic Pow­er Sys­tems Pro­gramme of the Inter­na­tion­al Ener­gy Agency (IEA). There, experts from all over the world exchange ideas on how to reduce CO2 emis­sions in the trans­port sec­tor by means of photovoltaics.

Vehi­cle inte­grat­ed pho­to­voltaics (VIPV) was already con­ceived in the six­ties. How­ev­er, for many years the main appli­ca­tion was in the niche of com­pe­ti­tions of spe­cial stream­lined light­weight solar vehi­cles. For some years now, var­i­ous man­u­fac­tur­ers have also been offer­ing car mod­els with solar roofs or PV mod­ules inte­grat­ed on truck refrig­er­a­tor box­es. In this case, the PV-con­vert­ed ener­gy is used for “addi­tion­al func­tions” such as air con­di­tion­ing or cool­ing. These appli­ca­tions run on a low volt­age lev­el of typ­i­cal­ly 12 V, the sys­tems avail­able on the mar­ket are not suit­able for charg­ing the high volt­age trac­tion bat­tery of an elec­tric vehicle.

With cur­rent­ly 155 employ­ees in two depart­ments, the ISFH devel­ops inno­v­a­tive tech­nolo­gies for the use of solar ener­gy. The pho­to­voltaics depart­ment devel­ops new indus­try-ori­ent­ed solar cell tech­nolo­gies, high­ly effi­cient pho­to­volta­ic mod­ules that can be indus­tri­al­ized and, as in this case, research­es the inte­gra­tion of PV into inno­v­a­tive sys­tems. The ISFH is a mem­ber of the Forschungsver­bund Erneuer­bare Energien (FVEE) and the Zuse-Gemein­schaft as well as an affil­i­at­ed insti­tute of the Leib­niz Uni­ver­sität Hannover.