Coatings for efficient photothermal conversion of solar energy should have high absorption at wavelengths &lgr;<&lgr;cand low absorption at &lgr;≳&lgr;c, where &lgr;cis ∼2 &mgr;m. For granular metals, we show by computation that &lgr;cdepends strongly on the shape of the metal particles. Increasing eccentricity of ellipsoidal grains is seen to displace &lgr;ctowards the infrared. A similar shift is found also for spherical metallic shells surrounding dielectric cores of increasing size. Some implications for practical absorber surfaces are pointed out.