Converting waste CO₂ into fine chemicals and/or fuels is an exciting prospect for green-house gas mitigation. Electrocatalytic CO₂ conversion is a leading candidate for this application because it operates at ambient conditions with extremely high reaction rates, product selectivity and faradaic efficiency. Carbon balance is a major consideration for any CO₂ conversion technology because the majority of the United States' electricity is derived from burning fossil fuels. This necessarily shifts most CO₂ conversion technologies into the carbon positive regime because CO₂ emissions associated with fossil-fuel derived electricity will likely exceed that consumed by the conversion process. This limitation is an important challenge that must addressed before CO₂ conversion technologies can be implemented on an industrial scale. Here, we describe a “carbon negative” (more CO₂ consumed than produced) electrochemical CO₂ conversion system based on atomically-precise Au₂₅ nanocatalysts. The catalytic system operates on inexpensive (ca. $10-20 USD), consumer-grade photovoltaic cells and solar-rechargeable batteries. We show stable CO₂ → CO conversion activity with turnover numbers (TON: mol CO₂/mol catalyst) surpassing 5x10⁶, rates exceeding 800 L CO₂ /gram catalytic metal/hour, and faradaic efficiencies and product selectivities around 90%. These performance metrics correspond to 1-2 kg CO₂ converted per gram of catalytic metal every hour. We can also tune product selectivity to favor CO or H₂ production by varying the catalyst loading and/or operating voltage. We show stable operation for 12 hours with photovoltaic cells to represent daylight operation, and 24 hours with a solar-rechargeable battery to mimic low-light or night-time hours. This study provides proof-of-principle example that renewable-powered electrocatalysis is a viable strategy for CO₂ conversion applications. The results were published in ACS Applied Materials and Interfaces 2015, 7, 15626.