Solar, By Ian McEwan

A climate scientist's priapic urges eclipse his professional drive in Ian McEwan's tepid farce

Physicist Michael Beard, the unlikely seducer at the centre of Ian McEwan's latest novel, won the Nobel Prize for his Beard-Einstein Conflation, a brilliant theory that allowed him to be sucked along in the slipstream of Einstein's hurtling importance. Celebrity in his field and honorary degrees ensued, while he coasted through two decades without producing any further original hypotheses, "vaguely weary of himself, bereft of alternatives".

His latest appointment, as head of the Government's new National Centre for Renewable Energy, is already mired in a wrong-headed project to build domestic roof-mounted wind turbines, launched after one of Beard's glib throwaway comments, and now too personally embarrassing to reverse. To add insult, his ponytailed junior colleague, Tom Aldous, is becoming a nag, relentlessly proselytising his own world-saving work on carbon-free photovoltaic (solar) energy.

While Beard's professional career shows rapid detumescence, his private life is still packed with "excitement and unpredictability". Patrice, his gorgeous young wife, has just moved into the guest-room of their well-appointed Primrose Hill abode and embarked on a flagrant affair with a builder, seemingly to repay Beard for humiliating her with years of clumsily hidden infidelities. For the first time in five marriages, Beard is forlorn, unable to dislodge his wife from his libidinous cravings by the habitual method of a little light philandering. When Beard happens upon Patrice's latest lover – Tom Aldous, nag-turned-opportunistic stud, guiltily wearing Beard's robe in his own living room – matters come swiftly to a head.

Although the overarching context of Solar is the search for clean energy, which is presented with McEwan's usual liberal salting of plausible research, it serves as little more than a proscenium for the turgid drama of sex, compromised integrity and serial irresponsibility played out by Beard's shambling figure. As a weak sybarite in thrall to his appetites and overly fond of his own voice, Beard could have been the richly flawed character that would carry Solar. However, despite the many ponderous ruminations on his own sensual and moral weaknesses, his smug lack of any humility or self-reproach gives the reader little purchase for any enduring interest.

Beard briefly wonders what Melissa – the willing doormat who accommodates him after Patrice – sees in "a man as faintly absurd, short, tubby, ageing, as scalded by public disgrace, corrupted by a whiff of failure" as he is. Bewildering indeed, since Beard proffers no appealing characteristic, physical or spiritual, in compensation. Yet his lovers afford him indulgence untethered from any meaningful form of responsibility. Portly on first appearance, but carrying wobbling wattles of fat by the novel's end nine years later, Beard is a ridiculous figure and a highly unconvincing Lothario. One could imagine Philip Roth or Howard Jacobson giving an interesting degree of psychological unease to the sexual incontinence of such "a monster of insincerity", but Beard seems to be played only for laughs. From the early scene of Beard's penis welding to his snowsuit during an al fresco micturition in the Arctic, a farcical tone dominates, occasionally goosed by a judicious spot of slapstick.

The sprawling mess of Beard's priapic career contrasts starkly with the fraught and prurient conduct of sexual relations that framed McEwan's last work, On Chesil Beach. That precisely crafted novella, held in its mildly claustrophobic, mid-century period by sharp characters and difficult mores, showcased the fine textures and nuanced sensibilities that McEwan is capable of. Before that, Saturday, a sententious novel whose sudden violence ripped into a coterie of urbane, privileged lives during London's anti-Iraq war protests, made state-of-the-nation claims and delivered a flawed but rich meditation on McEwan's familiar themes. Ideas of obsession, loss, moral responsibility, innocence and guilt throng much of his largely impressive canon and are predicated upon strong interpersonal relationships and the individual's understanding of how to engage with society. But Beard's farcical character and serial pratfalls glibly shrug off this engagement, thereby denuding Solar of the credible or meaningful relationships that would add colour and depth to its essentially two-dimensional plot.

Beard coasts through a string of vignettes, which build into a listless plot that remains rather less than the sum of its parts. There are no breath-taking, cinematic moments (such as the openings of Saturday or Enduring Love) and Beard's bland fulminations, despite a certain defiant joie de vivre, soon begin to grate. Forgive the pun, but Solar is purely light entertainment – no bad thing in itself but lacking the scope and tenacity that one might expect from McEwan. Farce, perhaps thankfully, may not be his métier, and one cannot help thinking that a writer of, say, Barbara Trapido's comedic skills would give Beard more punch than paunch.