Energy Insights is a series where we highlight interesting energy content from around the web.
The previous post in this series was about the 2017 BP Annual Energy Outlook.
These three Energy Insights come from a TED talk titled ‘How to save the energy system’ given by André Bardow. André is a fantastic speaker and his talk is well worth a watch.
Below are three of the many interesting things André discusses. I really enjoyed writing this – I find all of this fascinating.
As humanity burns more oil the amount of oil left to recover should decrease. This is logical – right?
Figure 1 below shows the opposite is true. Estimated global oil reserves have actually increased over time. The key is to understand the definition of oil reserves.
Figure 1 – Estiamted global oil reserves 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 therefore a function of a number of variables that change over time:
- 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 (1950 – 2010)
Only the physcial 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 physcial reserves but by climate change. I find this worrying – it would be much better if humanity was forced to swtich to renewables!
A lot of the advantages in systems are from economies of scale – energy systems are no different. Larger plants are more energy efficient and have lower specific capital & maintenance costs.
Figure 3 – Effect of gas engine size [kWe] on gross electric efficiency [% HHV]
This is also why part load efficiency is worse than full load efficiency. Energy production reduces but fixed energy losses remain constant.
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 are not able to do this. The problem is the prime movers in both wind & solar plants.
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. It’s the fact that fossil fuels:
- share most of these economies of scale.
- use high energy density fuels, which gives a fundamental advantage in the form of large maximum prime mover sizes.
We need to decarbonise the supply of heat & power as rapidly as possible. Renewables are going to be a big part of that. The great thing is that even with this disadvantage wind & solar plants are being built around the world!
Average 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 your own estimates based on experience with the inputs or outputs of models.
Thanks for reading!