Is it possible that renewables can supply 100% of our energy needs? One study that looked at this question was here:
A Plan to Power 100 Percent of the Planet with Renewables
This study proposes a mix of wind and solar for 100% of our energy. It mentions we would need to make 200k wind turbines each and every year to get wind power to provide 50% of our energy by 2030. That's about 10x more wind turbines installed per year than we are doing currently. Is that even possible? The article thinks so. Looking at raw materials first:
Enough concrete and steel exist for the millions of wind turbines, and both those commodities are fully recyclable. The most problematic materials may be rare-earth metals such as neodymium used in turbine gearboxes. Although the metals are not in short supply, the low-cost sources are concentrated in China, so countries such as the U.S. could be trading dependence on Middle Eastern oil for dependence on Far Eastern metals. Manufacturers are moving toward gearless turbines, however, so that limitation may become moot.
Photovoltaic cells rely on amorphous or crystalline silicon, cadmium telluride, or copper indium selenide and sulfide. Limited supplies of tellurium and indium could reduce the prospects for some types of thin-film solar cells, though not for all; the other types might be able to take up the slack. Large-scale production could be restricted by the silver that cells require, but finding ways to reduce the silver content could tackle that hurdle. Recycling parts from old cells could ameliorate material difficulties as well.
Three components could pose challenges for building millions of electric vehicles: rare-earth metals for electric motors, lithium for lithium-ion batteries and platinum for fuel cells. More than half the world’s lithium reserves lie in Bolivia and Chile. That concentration, combined with rapidly growing demand, could raise prices significantly. More problematic is the claim by Meridian International Research that not enough economically recoverable lithium exists to build anywhere near the number of batteries needed in a global electric-vehicle economy. Recycling could change the equation, but the economics of recycling depend in part on whether batteries are made with easy recyclability in mind, an issue the industry is aware of. The long-term use of platinum also depends on recycling; current available reserves would sustain annual production of 20 million fuel-cell vehicles, along with existing industrial uses, for fewer than 100 years.
Gearless turbines solves the neodymium issue, but shortages of Indium, tellurium, Lithium, and platinum could pose a problem. We already have a Lithium thread here and I do not really want to go through that whole discussion again. As for Indium, tellurium and platinum, I don't see any easy solution to that problem other than reducing the amount needed and/or going with alternate forms of solar and fuel cells. I already read about work being done along these lines. Manufacturers of solar and fuel cells are putting out models that use a fraction of the rare materials that previous models used. Will this be enough of a reduction? Possibly. The study did not delve into this issue too deeply.
Aside from the raw material needs, can our infrastructure even produce that many turbines/solar panels a year? Currently, no, we would have to expand our current infrastructure. I don't see this as a problem however. We produce 93 million cars and trucks every year, so I don't see a problem producing 200k wind turbines a year. The power grid would have to be upgraded as well. It currently would not be able to handle the intermittent nature of wind/solar providing 100% of our electricity needs. We would need larger lines to transfer power from areas of the country where wind is not blowing to areas where it is blowing. We would need energy storage to store energy for when the sun is not shining. Batteries are too expensive for this, so compressed air storage is probably the most likely candidate for this.
It would not be wise to trash all of our current power plants. They represent sunk costs that have already been paid and we should continue to utilize them to the end of their life. With the exception of those 60 year old coal dinosaurs that belch many times more pollution that a modern plant would. As old plants are retired, we should replace them with renewable energy.
It has been argued by some that renewable energy is a misdirection of resources. With biofuels, I could see the argument. With solar, wind, hydro, geothermal, tidal, etc, I am having trouble seeing the argument. All power generation despoils the environment to some extent. So in the strictest sense, none of them are green. However these renewables are orders of magnitude greener than coal, tar sands, etc. I am not convinced renewables can/will be scaled up in time to counter the effects of fossil fuel depletion and allow BAU. And I have concerns about the supply of rare earths and costs of grid energy storage. But I do not see renewables themselves as a misdirection of resources.
It has also been argued that renewables provide only energy. They do not provide us with food, raw materials, etc. I think that goes without saying. No one has argued renewable energy is some kind of star trek style replicator that can provide for all of our wants and needs. Renewable energy can keep the lights on. But it does not solve the issue of our consumer disposable society that digs resources out of the ground, briefly uses them, and then buries them in landfills. This is unsustainable and needs to be corrected.
The final point I wanted to address was that renewables are not really renewable. The materials to build them were mined by fossil fueled mining equipment. They factories that build them were powered by coal power plants. The vehicles that transported them were powered by diesel. Again, I don't see this as an issue. Our current infrastructure in place uses fossil fuels everywhere. Of course everything we do is powered by fossil fuels. But our fossil fueled infrastructure did not spring up from nothing. It was created by an earlier infrastructure. Everything from biomass to old fashioned muscle power. Pointing out that renewable energy is being built by fossil fueled powered infrastructure is no more relevant than pointing out that the fossil fueled infrastructure was built by muscle, biomass, etc. Burning through the incredible energy bonanza of fossil fuels in a few centuries seems incredibly wasteful to me. However using this energy to power a transition to a more sustainable energy future seems like a very wise move.