LONDON (Reuters Breakingviews) - Big Oil has some big numbers to back its renewable energy ambitions. France’s Total is now aiming for 35 gigawatts of wind and solar capacity by 2025, following BP’s recently announced goal of 20 GW. With deep-pocketed interlopers pouring more and more money into green projects, the question is whether there are enough wind farms and solar parks to go around, and at what price. The initial numbers give some cause for concern. Incumbent utilities like Enel, EDP and Iberdrola have 200 GW of wind turbines and solar panels, against gatecrashing oil majors’ 14 GW. But that will change quickly, with BP and Total pledging to spend $5 billion a year between them on renewable energy over the next five years. Royal Dutch Shell has yet to say, but could at least match BP’s $3 billion annually. As banks will lend up to 70% of a project’s value, the three majors’ commitments of perhaps $40 billion over five years could unleash $133 billion of new investment. A bubble is possible. Offshore wind projects can take years to plan and still fall through. Looming green targets may compel BP and Total to pay top dollar to buy up pre-existing projects, while competing also with infrastructure investors with lower return hurdles. BP paid a punchy $3 billion per GW for a stake in an Equinor offshore wind venture last month. The oil majors have ways to manage the bottleneck. BP only has to sign off its 20 GW of projects by 2025 rather than have them up and running, giving it some leeway. They could also invest heavily in solar, which is quicker to scale up than offshore wind. The bigger safety valve is the sheer amount of green energy required to decarbonise the world by 2050. The planet would need 31,000 GW of wind and solar by then, according to the Energy Transitions Commission. To get there, the world’s installed capacity of 1,400 GW in 2020 would need to grow nearly 11% a year, equivalent to an average increase of 1000 GW, costing $1 trillion every year, according to Breakingviews estimates. Unless the world falls miles short of this, the oil majors’ pledges look pretty puny.