Are Electric Cars and Solar Panels Complements?
研究发现电动汽车和家用太阳能电池板在需求上存在互补关系：每增加一个太阳能用户，约带动0.184辆电动汽车销售；每增加一辆电动汽车，约带动0.26个太阳能安装。
Both electric cars and residential solar panels are environmentally friendly durable goods that are often subsidized. The relationship between the two in demand will affect the efficiency of a range of green policies. This study explores the complementarity between the two goods, taking an instrumental variables approach. Using global horizontal irradiance as an instrument, I find that each existing solar adoption leads to approximately 0.184 additional electric car sales, including 0.121 battery electric vehicles and 0.063 plug-in hybrid electric vehicles. Utilizing availability of high occupancy vehicle lanes and gasoline prices as instruments, I find that each electric vehicle ownership leads to roughly 0.26 additional solar installations. The complementarity mainly comes from lack of charging stations and insufficient compensation for excess solar energy sold back to the grid. The findings imply substantial spillovers from policies affecting either choice, changing the cost-benefit calculus for a range of green policies.