IN­CUR­ABLE EN­GI­NEER

Once con­sid­ered utopian, elec­trol­y­sis is now a se­ri­ous en­ergy pos­si­bil­ity.

Cosmos - - Contents - ALAN FINKEL is an elec­tri­cal en­gi­neer, neu­ro­sci­en­tist and the chief sci­en­tist of Aus­tralia.

— Hy­dro­gen gets a lift

WHEN I WAS VERY YOUNG, our gas stove ran on town gas. I didn’t know it at the time but it was a mix­ture of hy­dro­gen and car­bon monox­ide pro­duced from coal.

One day a ser­vice­man came round to change the noz­zles on our stove and gas heater, and very quickly our house, and even­tu­ally the city, were con­verted to nat­u­ral gas (meth­ane). It was a leap into moder­nity. Not only did it elim­i­nate pol­lu­tants emit­ted dur­ing gasi­fi­ca­tion, it promised a seem­ingly un­lim­ited sup­ply of clean burn­ing meth­ane from off­shore gas fields.

But that was in an era where “clean” meant “free of the toxic chem­i­cals and par­tic­u­lates re­leased by coal gasi­fi­ca­tion”.

To­day, clean also means free of car­bon diox­ide. As the global com­mu­nity works to de­car­bonise its elec­tric­ity sup­ply, one of the big­gest re­main­ing sources of car­bon diox­ide emis­sions will be from burn­ing meth­ane for heat­ing and cook­ing. In a back-to-the-fu­ture step, many fu­tur­ists are con­tem­plat­ing a variation of town gas – pure hy­dro­gen.

To­day, most hy­dro­gen is pro­duced from fos­sils fu­els, emit­ting large quan­ti­ties of car­bon diox­ide as a by-prod­uct, so that’s no help. But there’s in­creas­ing in­ter­est in pro­duc­ing it from pure wa­ter. In a well-known process called elec­trol­y­sis, ex­cess elec­tric­ity from wind or so­lar farms is passed through wa­ter to crack it into its atomic con­stituents – hy­dro­gen and oxy­gen.

When the hy­dro­gen is used for stoves, or space heat­ing, the only com­bus­tion prod­uct is wa­ter vapour! So what’s stand­ing in the way of this utopian fuel?

Prob­lem one is that pro­duc­ing hy­dro­gen from elec­tric­ity is only 70% ef­fi­cient, so you need a very cheap elec­tric­ity sup­ply. It could be com­ing. As our elec­tric­ity is in­creas­ingly sourced from wind and so­lar, the amount avail­able will of­ten exceed the elec­tri­cal load. Own­ers of the gen­er­a­tors will seek an eco­nom­i­cally worth­while pur­pose for this ex­cess, such as charg­ing bat­ter­ies, de­sali­nat­ing wa­ter, or mak­ing hy­dro­gen.

Prob­lem two is that the cur­rent largescale elec­trol­y­sis units are so ex­pen­sive that the cost of pro­duc­ing hy­dro­gen is sev­eral times more than nat­u­ral gas. But one thing we know for sure is that as man­u­fac­tur­ing vol­umes in­crease, costs come down. We’ve seen it al­ready in re­lated in­dus­tries.

Wind tur­bine prices have halved in the past five years and so­lar prices have dropped even faster. Sim­i­lar cost re­duc­tions are likely for elec­trol­y­sis units.

Prob­lem three is that steel pipes – a ma­jor part of the cur­rent gas de­liv­ery in­fra­struc­ture – aren’t suited to trans­port­ing hy­dro­gen. They be­come brit­tle be­cause the hy­dro­gen mol­e­cules work their way into the spa­ces be­tween the iron atoms and even­tu­ally cause cracks to form. For­tu­nately, mod­ern pip­ing used for gas dis­tri­bu­tion is mostly made from polypropy­lene and does not suf­fer from this prob­lem.

Hy­dro­gen can be mixed at up to 10% with the meth­ane in the ex­ist­ing gas dis­tri­bu­tion net­work with­out any risk of cor­ro­sion nor need to change the noz­zles on stoves or space heaters. Above 10% hy­dro­gen con­cen­tra­tion it’s eas­ier to com­mit and con­vert all gas ap­pli­ances to run on pure hy­dro­gen.

The city of Leeds in the UK has a plan to do this in the late 2020s.

In­stead of burn­ing the hy­dro­gen, an al­ter­na­tive use would be to use it to store en­ergy, like in a bat­tery, then re­gen­er­ate elec­tric­ity in a tur­bine gen­er­a­tor or a fuel cell. But it makes for a very in­ef­fi­cient bat­tery.

The round-trip ef­fi­ciency – elec­tric­ity to stor­age medium and back to elec­tric­ity – is about 35%, much worse than the 90% ef­fi­ciency of a lithium ion bat­tery. So this is a less at­trac­tive use for the hy­dro­gen than us­ing it to re­place nat­u­ral gas in our cities for space heat­ing and cook­ing.

If we can suc­cess­fully make the tran­si­tion to hy­dro­gen for heat­ing and cook­ing we will have a win­ning fuel that we can keep us­ing lit­er­ally for­ever. The main im­ped­i­ment to­day is cost.

I used to be scep­ti­cal that hy­dro­gen use would be­come wide­spread, but given the rapid rate of re­duc­tion in the price of re­new­able elec­tric­ity, and a rea­son­able ex­pec­ta­tion that the price of elec­trol­y­sis will con­tinue to fall, the eco­nomics might in­deed work out.

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