How to save the energy system - André Bardow

These Energy Insights come from the TED talk ‘How to save the energy system’ by André Bardow. Below are three insights from the talk.

Why peak oil won’t save the planet

The more oil we burn, the less oil we have, right? Figure 1 below shows the opposite is true. Estimated global oil reserves have increased over time. To understand why we need to understand what an oil reserve is defined to be.

Figure 1 – Estimated global oil reserves (1980 – 2014)

Oil reserves are defined as the amount of oil that can be technically recovered at a cost that is financially feasible at the present price of oil.

Oil reserves are a function of

• total physical oil in place – physical production of oil reduces the physical amount of oil in the ground
• total estimated oil in place – the initial estimates are low and increased over time
• oil prices – historically oil prices have trended upwards (Figure 2). Oil reserves defined as a direct function of the present oil price
• technology – the oil & gas industry has benefited more than any other energy sector from improved technology. Improved technology reduces the cost of producing oil. This makes more oil production viable at a given price

Figure 2 – Crude oil price

Only the physical production of oil has had a negative effect on oil reserves.

The other three (total oil estimate, technology & oil price) have all caused oil reserve estimates to increase.

We are not going to run out of oil any time soon. The limit on oil production is not set by physical reserves. The limit will ultimately be set either by the oil being too expensive to recover or climate related limits on oil extraction.

Wind & solar lack an inherent economy of scale

Economy of scale is a key advantage in many systems – energy systems are no different. Larger plants are more energy efficient and have lower specific capital & maintenance costs.

Energy efficiency improves with size because the ratio of fixed energy losses to energy produced improves. Figure 3 shows an example of this for spark ignition gas engines.

This is also why part load efficiency is worse than full load efficiency. Energy production reduces but fixed energy losses remain constant.

Figure 3 – Effect of gas engine size [kWe] on gross electric efficiency [% HHV]

Specific capital & operating costs also improve with size. For example, a 10 MW and 100 MW plant may need the same land area at a cost of £10,000. The specific capital cost of land for both projects is £1,000/MW versus £100/MW respectively.

Fossil fuel plants use their economy of scale to generate large amounts of electricity from a small number of prime movers. Wind & solar plants don’t an economy of scale on a single prime mover level.

The maximum size of a wind or solar prime movers (wind turbines or solar panels) is small comapred with fossil fuel prime movers. For example GE offer a 519 MWe gas turbine – the world’s largest wind turbine is the 8 MWe Vestas V164.

Figure 4 – The Vestas V164

A single gas turbine in CCGT mode is more than enough to generate 500 MWe. A wind farm needs 63 wind turbines to generate the same amount.

The reason for the difference is fundamental to the technologies – the energy density of fuel. Fossil fuels offer fantastic energy densities – meaning we can do a lot with less fuel (and less equipment). Transportation favours liquid fossil fuels for this reason.

Wind & solar radiation have low energy densities. To capture more energy we need lots more blade or panel surface area. This physical constraint means that scaling the prime movers in wind & solar plants is difficult. The physical size increases very fast as we increase electricity generation.

This means that wind turbines & solar panels need to very cheap at small scales. As wind & solar technologies improve there will be improvements in both the economy of scale & maximum size of a single prime mover.

But to offer a similar economy of scale as fossil fuels is difficult due to low energy density fuel. It’s not that wind & solar don’t benefit from any economy of scale – for example grid connection costs can be shared.

Wind and solar can gain an economy of scale advantage through production. The mass production of wind and solar can give an economy of scale advantage that individual panels and turbines lack.

German capacity factors

Andre gives reference capacity factors for the German grid of

• Solar = 10%
• Wind = 20%
• Coal = 80%

This data is on an average basis. The average capacity factor across the fleet is usually more relevant than the capacity factor of a state of the art plant.

It is always good to have some rough estimates in the back if your mind. A large part of engineering is using rough estimates based on your own or others experience.

Thanks for reading!