February 25, 2014 by Robert Wilson @ theenergycollective.com
The current feasibility of 100% renewable energy is easily tested by asking a simple question. Can you build a wind turbine without fossil fuels? If the machines that will deliver 100% renewable energy cannot be made without fossil fuels, then quite obviously we cannot get 100% renewable energy.
What are windmills made of? Lots of steel, concrete and advanced plastic. Material requirements of a modern wind turbine have been reviewed by the United States Geological Survey. On average 1 MW of wind capacity requires 103 tonnes of stainless steel, 402 tonnes of concrete, 6.8 tonnes of fiberglass, 3 tonnes of copper and 20 tonnes of cast iron. The elegant blades are made of fiberglass, the skyscraper sized tower of steel, and the base of concrete.
To rapidly transition to 100% wind electricity over a 20 year period given an average global electricity demand of 2.6 TW, we’d need around 10 TW of wind capacity to provide this electricity. That would take about 50 million tonnes of steel, 200 million tonnes of concrete and 1.5 million tonnes of copper each year. These numbers sound high, but current global production of these materials is more than an order of magnitude higher than these requirements.
Fossil fuel requirements of cement and steel production
For the sake of brevity I will only consider whether this steel can be produced without fossil fuels, and whether the concrete can be made without the production of carbon dioxide. However I will note at the outset that the requirement for fiberglass means that a wind turbine cannot currently be made without the extraction of oil and natural gas, because fiberglass is without exception produced from petrochemicals.
Let’s begin with steel. How do we make most of our steel globally?
There are two methods: recycle old steel, or make steel from iron ore. The vast majority of steel is made using the latter method for the simple reason that there is nowhere near enough old steel lying around to be re-melted to meet global demand.
A quick summary of how we make steel:
- We take iron ore out of the ground, using powerful machines that need high energy density diesel fuel, and the machines that do all of this work are almost made entirely of steel.
- After mining, the iron ore will need to be transported to a steel mill. If the iron ore comes from Australia or Brazil then it most likely will have to be put on a large bulk carrier and transported to another country on an enormous steel ship powered by diesel fuel.
- We then convert this iron ore into steel. How is this done? There are only two widely used methods. The blast furnace or direct reduction routes, and these processes are fundamentally dependent on the provision of large amounts of coal or natural gas.
- The blast furnace route is used for the majority of steel production globally. Here coal is key. Iron ore is unusable, largely because it is mostly iron oxide. This must be purified by removing the oxygen, and we do this by reacting the iron ore with carbon monoxide produced using coke: Fe2O3 + 3CO → 2Fe + 3CO2. Production of carbon dioxide therefore is not simply a result of the energy requirements of steel production, but of the chemical requirements of iron ore smelting.
This steel can then be used to produce the tower for a wind turbine, but as you can see, each major step of the production chain for what we call primary steel is dependent on fossil fuels.
By weight cement is the most widely used material globally. We now produce over 3.5 billion tonnes of the stuff each year. One of the most important uses of cement is in concrete production. Cement is only 10 to 20% of concrete’s mass, but from an embodied energy and emissions point of view it makes up more than 80%.
We make cement in a cement kiln, using a kiln fuel such as coal, natural gas, or quite often used tires. Provision of heat in cement production is an obvious source of greenhouse gases, and providing this heat with low carbon sources will face multiple challenges.
Even more challenging to overcome is that about half of emissions from cement production come not from the energy to make cement, but from chemical reactions in its production.
The key chemical reaction in cement production is the conversion of calcium carbonate (limestone) into calcium oxide (lime). The removal of carbon from calcium carbonate inevitably leads to the emission of carbon dioxide: CaCO3 → CaO + CO2. These chemical realities will make total de-carbonisation of cement production extremely difficult.
Total cement production currently represents about 5% of global carbon dioxide emissions, to go with the almost 7% from iron and steel production.
In conclusion, we obviously cannot build wind turbines on a large scale without fossil fuels.
Robert Wilson is a PhD Student in Mathematical Ecology at the University of Strathclyde.