It is a market failure. The incentives of the owner need to be aligned with the incentives of the tenant, that is the failure. Either, as you point out, tenan

It is a market failure. The incentives of the owner need to be aligned with the incentives of the tenant, that is the failure. Either, as you point out, tenants need to be given powers to install solar panels, and given security of tenure to take advantage of the long term investment, (which seems to me would go further than mere planning regs). Or incentivise the owner to install solar panels, this seems more straight forward, although might not necessarily benefit the tenant.