How renewable are renewables really?

Renewables are on the rise. The International Energy Agency (IEA) forecasts global capacity of wind, solar and hydropower will grow 43% in the next five years. Such technologies are called renewable since their source of energy (e.g. sun, wind or flowing water) naturally replenish themselves. This can be contrasted with fossil-fuel generation, whose fuels (e.g. coal or gas) can be depleted and take millions of years to regenerate.

The classification into renewable and non-renewable refers only to the process of electricity generation. Over their whole lifecycle, renewable technologies use resources that can both be depleted and lead to greenhouse gas emissions in their extraction process. Furthermore, they need a lot of them: per unit of electricity, wind turbines require 6-14 times more iron and 11-40 times more copper than fossil fuels. Meeting one quarter of global electricity demand from wind by 2050 would require an additional 1 million onshore and 100,000 offshore wind turbines, and the IEA estimates that decreasing energy related greenhouse gas emissions by 50% doubles the material requirements per unit of electricity. Obtaining the additional materials required may negatively impact the environment in their extraction and in their processing.

Furthermore, renewable energy production requires materials that may be scarce, toxic, or required for domestic electronic devices. An important example is the lithium and cobalt required for lithium ion batteries. The demand for these is expected to grow exponentially because of their use in portable electronics, electric cars and storing renewable electricity (see a previous article on this topic). Both metals are available only in a small number of countries, with cobalt a particular concern; more than half of world supply comes from DR Congo, a country infamous for its political instability and plagued by civil war. The combination of high demand and supply uncertainty has even lead to deep-sea mining pilots, worrying many environmentalists. Clearly, the environmental impacts of a massive renewable transition should be considered carefully — we must be careful that one source of environmental damage (greenhouse gases emissions) is not substituted for another.

Figure 1: Lifecycle greenhouse gas emissions per unit of electricity generated for different renewable and non-renewable energy sources. Source: IPCC, 2011 Special Report on Renewable Energy Sources and Climate Change Mitigation (Chapter 9).

In this backdrop, shrinking renewable technologies’ material requirements is a key priority. Many approaches fall under the age-old mantra Reduce, Reuse, Recycle. One strategy is to design new technologies that require fewer scarce resources. The lithium ion battery is itself an improvement on its lead acid predecessor, and the race to build a new battery, free of lithium and cobalt, is in full swing. Another is to increase the effective lifecycle of existing technologies. As everyone with an old mobile phone recognises, battery performance declines over time, and this is usually the first reason to discard an otherwise working model. The same applies to wind power: the harsh conditions experienced by turbine blades, including lightning strikes, storms and ice, decreases the efficiency of wind turbines 60% in their first 15 years of operation. Replacing blades periodically or making them more resilient lowers material requirements, but comes with considerable technical challenges.

A third option is to recycle materials. The first generation of large-scale renewable projects built in the 1990s are reaching the end of their lifetimes, meaning millions of tonnes of old wind farm and solar panel materials will be decommissioned. Estimates suggest that by 2030, there will be 300,000 tonnes of waste from old wind turbines annually in Europe alone, and most of these parts are made from costly unreformable plastic that cannot be melted down or given a second life. Reusing components both reduces demand for mining and prevents costly materials ending up in landfill sites. Examples include a planned recycling centre in Texas where old wind turbines are cut up and given a second life in composite panels and a French chemical firm building blades from reformable plastic. In the EU, research funding and targeted landfill bans have lead to pilot projects into the recycling of solar panels and batteries. Some of these batteries have even been given second lives in grid-scale storage. However, recent attempts have been slow to get off the ground, and for many of these technologies, mining new materials remains cheaper than recycling. Furthermore, recycled materials typically cannot be reused in renewable technologies again and must be sold to other sectors.

Many of the issues outlined above relate to the fact that these technologies are still in their infancy. Fossil fuel technologies have been the dominant energy source for more than a century, and trillions of dollars have been invested to maximise their efficiencies. If and when such sums start being spent on renewables, technologies are expected to improve significantly. These improvements have already sent the price of renewables plummeting, and they may make the renewable resource question disappear altogether in the future.

Furthermore, despite the hefty material requirements, a study by the Norwegian University of Science and Technology estimates that the planet has enough resources to support the large-scale transition to renewables, and it’s not the case that fossil fuels don’t use any materials for their infrastructure — imagine, for example, the amount of metal and energy required to build on oil rig. In terms of lifecycle greenhouse gas emissions, renewables are a clear improvement on non-renewables (see Figure 1). However, having enough resources for the foreseeable future does not mean this will be the case forever.

Becoming a truly renewable society requires not just the adoption of renewable technologies, but also their improvement. Otherwise, it may be that in solving one sustainability issue, we are creating another.

Adriaan Hilbers – PhD student researching Mathematics of Power Systems at Imperial College London

Mariana Clare – PhD student researching numerical fluid and sediment transport models at Imperial College London