In this paper, an efficient solar selective absorber based on a tungsten sphere array and a tungsten grating is proposed and demonstrated numerically. The proposed structure has a spectral range of 300-1777 nm, with an absorption higher than 95% and an infrared thermal emittance as low as 0.03% at wavelengths greater than 6.15 gm. As a result, the solar thermal conversion efficiency of the optimized solar absorber can obtain 92.23% at an operating temperature of 373.15 K. In addition, the proposed absorber is polarization-independent and can maintain a high solar absorption in a wide range of incident angles from 0 to 50 for both transverse electric and transverse magnetic waves. A detailed analysis by 3D full-wave simulations indicates the broadband absorption mechanism can be attributed to the coupling effect of multi-plasmon resonance modes. The optimized absorber shows great potential for solar thermal applications that require wide-angle polarization-independent ultra broadband absorption and low infrared thermal emittance.