Consequently, the optimal level of subsidies for R&D on low-carbon technologies depends on the magnitude of knowledge spillovers from these technologies, relative to the spillovers generated by other technologies, in particular the fossil technologies they replace. It also needs to cover not only the public sector, but also the private one. The intellectual property argument, while valid in some cases, should not impede the development of standardised mechanisms to collect, compile and publish urgently needed global data on budgets for energy technology innovation.