Developing efficient systems for the conversion of carbon dioxide to valuable chemicals using solar power is critical for mitigating climate change and ascertaining the worlds future supply of clean fuels. Here, we introduce a mesoscopic cathode consisting of Cu nanowires decorated with Ag islands, by the reduction of Ag-covered Cu2O nanowires prepared via galvanic replacement reaction. This catalyst enables CO2 reduction to ethylene and other C2+ products with a faradaic efficiency of 76%. Operando Raman spectroscopy reveals intermediate formation of CO at Ag sites which undergo subsequent spillover and hydrogenation on the Cu nanowires. Our Cu-Ag bimetallic design enables a similar to 95% efficient spillover of intermediates from Ag to Cu, delivering an improved activity toward the formation of ethylene and other C2+ products. We also demonstrate a solar to ethylene conversion efficiency of 4.2% for the photoelectrochemical CO2 reduction using water as electron and proton donor, and solar power together with perovskite photovoltaics to drive the uphill reaction.