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Electric car concept running on the road.
π Mobility π Energy

“Tomorrow, roads will produce energy for vehicles”

Bernard Jacob
Bernard Jacob
Professor at the ENTPE and ESIEE (Gustave Eiffel University)

[This arti­cle is a sum­ma­ry of a note pub­lished by La Jaune et La Rouge. To read the orig­i­nal text (in French only), click here].

Road trans­port – includ­ing both roads and ther­mal vehi­cles – accounts for approx­i­mate­ly 30% of green­house gas emis­sions (GHG) world­wide. There­fore, it is a sec­tor that requires major efforts to achieve car­bon neu­tral­i­ty. Although the auto­mo­bile is in the midst of tran­si­tion in terms of ener­gy (towards elec­tric­i­ty) and use (dri­ver­less vehi­cles), roads them­selves will also need to be adapt­ed because a large pro­por­tion of the mate­ri­als used to make them, such as cement and bitu­men, are non-renew­able and require high ener­gy consumption.

Some coun­tries, includ­ing France, are try­ing to encour­age a modal shift towards rail and water­ways through pub­lic poli­cies, but the share of road trans­port remains dom­i­nant, par­tic­u­lar­ly for goods, and is even con­tin­u­ing to increase. Con­se­quent­ly, over the last ten years or so, gov­ern­ments have changed their poli­cies and sought to decar­bonise roads and vehi­cles, while encour­ag­ing the com­ple­men­tar­i­ty of modes of trans­port, each being used where it is effi­cient and eco­nom­i­cal­ly viable. As such, the road of the future (or fifth gen­er­a­tion1) is being con­ceived to meet these demands, open­ing new per­spec­tives for the 21st century.

Electric roads

Bat­ter­ies are reach­ing their phys­i­cal and eco­nom­ic lim­its, espe­cial­ly for heavy vehi­cles (trucks, coach­es), and can­not pro­vide the nec­es­sary pow­er need­ed to trav­el of sev­er­al hun­dred kilo­me­tres for the largest vehi­cles under full load. Or at unac­cept­able costs, vol­umes, and mass­es. Hence, one solu­tion is to pow­er the vehi­cles while they are run­ning, through the infra­struc­ture. Pow­er sup­ply sys­tems devel­oped for rail­ways (trains, met­ros, trams) can be adapt­ed to the road. Siemens is propos­ing a pow­er sup­ply via cate­nar­ies and pan­tographs (dou­ble cate­nary because there is no cur­rent return via the ground), Alstom is devel­op­ing a pow­er sup­ply via the ground with rails elec­tri­fied in sec­tions (trans­po­si­tion of the Bor­deaux tramway sys­tem) and Elways is propos­ing a hol­low pro­filed rail, both of which have pads or a pick-up pin installed under the vehi­cles. Con­tact­less induc­tion sys­tems already exist for bus­es and are being devel­oped or test­ed in Europe and Asia. Swe­den and Ger­many are exper­i­ment­ing with these so-called “elec­tric road sys­tems” (ERS) and a state-of-the-art report was pub­lished on the sub­ject in 2018 by the World Road Asso­ci­a­tion2.

ERS would be rel­e­vant on high-traf­fic motor­way cor­ri­dors, espe­cial­ly for heavy goods vehi­cles, which account for near­ly 30% of road trans­port emis­sions. It would not only ensure the propul­sion of vehi­cles on the equipped net­work, but also recharge their bat­ter­ies to give them suf­fi­cient auton­o­my out­side the elec­tri­fied net­work. The invest­ment costs of ERS solu­tions are esti­mat­ed (before indus­tri­al­i­sa­tion) at 2–5M€/km, and for France it is accept­ed that 3–4,000km of motor­ways would be eli­gi­ble for ERS ini­tial­ly, extend­able to 8–10,000km, i.e. an invest­ment of 10–15€bn (it would suf­fice to equip 50% of the length of the slow lanes, giv­en the pres­ence of buffer bat­ter­ies in the vehi­cles). With a repay­ment peri­od of 20–30yr and a con­ces­sion sys­tem, this does not seem out of reach. How­ev­er, ques­tions of safe­ty, sys­tem resilience and the eco­nom­ic mod­el (dis­tri­b­u­tion of costs and ben­e­fits) remain to be clar­i­fied, but no major obsta­cles have been identified. 

Intelligent, energy-positive roads

Roads con­sume ener­gy, both for their con­struc­tion, main­te­nance, and oper­a­tion (light­ing and sig­nalling) and for the vehi­cles that use them. But it can also pro­duce ener­gy: its sur­face, which receives the sun’s rays, could in fact be a source of ener­gy. With con­ser­v­a­tive assump­tions of 25% sun­shine (i.e. half the day), 0.5% of the road sur­face used and 300 W/m² of ener­gy received, the aver­age pow­er received would be of the order of 2.25 GW, i.e. 3.5% of the elec­tri­cal pow­er installed in France, or a lit­tle more than half that con­sumed by road trans­port. Of course, the real­ly recov­er­able part of this ener­gy is prob­a­bly small, but it could nev­er­the­less con­tribute to the decar­bon­i­sa­tion of the road sec­tor, or even meet lim­it­ed ener­gy needs in the vicin­i­ty of an equipped road. 

Solar ener­gy recov­ery via roads could be ther­mal, with stored heat, or pho­to­volta­ic, with cells insert­ed in the sur­face course made trans­par­ent to allow inci­dent light to pass. The first solu­tion is suc­cess­ful­ly mar­ket­ed in France by Eurovia for the ther­mal reha­bil­i­ta­tion of build­ings. The sec­ond solu­tion, pro­posed by Colas (Wattway), can be used to pow­er sen­sors or con­tribute to light­ing. The two solu­tions can be com­bined on the same site. Nev­er­the­less, the yield of these tech­nolo­gies remains lim­it­ed and the invest­ments quite heavy, espe­cial­ly for the pho­to­volta­ic solution.Finally, the road of the 21st Cen­tu­ry is no longer a sim­ple strip of bitu­men sup­port­ing vehi­cles and equipped with safe­ty and sig­nalling devices. In addi­tion to its phys­i­cal func­tions, roads will increas­ing­ly be equipped with sen­sors, infor­ma­tion and com­mu­ni­ca­tion sys­tems, and con­nect­ed to the vehi­cles that use it and to the oper­a­tors who man­age it. This so-called ‘intel­li­gent’ road will have to be self-diag­nos­tic, even self-repair­ing, com­mu­ni­cat­ing infor­ma­tion with regards to its con­di­tion and evo­lu­tion. Its func­tion will be col­lab­o­ra­tive, inso­far as it will par­tic­i­pate in the man­age­ment or con­trol of traf­fic, in the ener­gy sup­ply of cer­tain vehi­cles and in the guid­ance or mon­i­tor­ing of autonomous vehi­cles. Fur­ther­more, it will be inte­grat­ed into a true glob­al sys­tem of mobil­i­ty ser­vices. Nev­er­the­less, each solu­tion and the asso­ci­at­ed busi­ness mod­el must be stud­ied to avoid tech­no­log­i­cal myths.

1Hau­tière N., de La Roche C. & Piau J.-M. (2015), Les routes de 5e généra­tion, Pour la Sci­ence, n° 450, April 2015, pp. 26–35.
2PIARC (2018), Elec­tric Road Sys­tems: A Solu­tion for the Future, Report of a Spe­cial Project, 2018SP04EN, 138 pp.

Contributors

Bernard Jacob

Bernard Jacob

Professor at the ENTPE and ESIEE (Gustave Eiffel University)

Bernard Jacob started working at SETRA on the safety of bridges and load codes, then joined the Laboratoire Central des Ponts et Chaussées (LCPC) where he led projects on the fatigue of metal bridges under traffic. He has led European and international projects on the weighing of heavy goods vehicles, dynamic interactions between infrastructures and vehicles, the safety and behaviour of heavy goods vehicles, their weights and dimensions (expertise for the European Commission) and was technical director of road operation and safety at LCPC and then transport and infrastructures at IFSTTAR before joining the Research vice-presidency of Gustave Eiffel University.