We analyze the adoption of clean technology by heterogeneous firms subject to financing constraints. We develop a model of investment with heterogeneous capital goods, which differ in their associated energy needs and in their age. We show that, in equilibrium, cleaner and newer capital requires a larger down payment. Therefore, financially constrained, smaller firms optimally invest in dirtier and older capital than
unconstrained, larger firms. The model is consistent with the empirical patterns of technology adoption we document using data on commercial shipping fleets. Larger firms operate with higher energy efficiency, by investing in cleaner new technologies and operating newer capital, which tends to be more energy efficient. This equilibrium pattern of technology adoption implies that environmental policy has important distributional consequences.