“Tomorrow, roads will produce energy for vehicles”

[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.

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. 

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 21^st 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.