Category Archives: Renewables Confusion

A Simple Look at the Efficiency Penalty Cost of Renewables

This article is a response to a post called Wind Integration vs. Air Emission Reductions: A Primer for Policymakers.  This article claims the efficiency penalty of turning down fossil fuel power stations offsets the benefit of renewable power generation.
I found this an interesting idea – so I developed a simple model to understand what could be happening.
Renewable power generation brings a carbon benefit by generating less power in fossil fuel power stations.  Yet there is a factor working in opposition to this. Generating less in fossil fuel power stations can incur an efficiency penalty.
I don’t have data for the relationship between fossil fuel power station generation and efficiency. Instead I look at what the breakeven efficiency penalty would be to offset the benefit of renewable generation.
I created a simple model supplying 1 GW of electricity.  Renewable output is varied from 0 GW to 0.5 GW with coal supplying the balance.

I assumed the fossil fuel power station operates at a 50 % HHV efficiency at full load.  I then looked at various efficiency penalty factors in the form of reduced efficiency per reduction in load (% HHV / % load).   The efficiency penalty was modeled as linear.  You can download a copy of the model here.


Figure 1 – The effect of various assumed efficiency penalties on fossil fuel consumption
For this simple model 5 % HHV / % load is the break even.  If the efficiency really reduces at this rate then generating electricity from renewables is giving us no carbon benefit.
The real question is what is the actual relationship between fossil fuel power station output and efficiency.   It’s likely to be non-linear.  I also expect it would not be as harsh as 5 % HHV/% load – so likely renewables are providing a carbon benefit.
Is it is useful to know that this is a carbon penalty we could be paying somewhere on the system as renewables penetration increases This penalty will net off some of the maximum benefit that renewable generation could supply.
However if we can actually start permanently shutting down fossil fuel power stations then this effect doesn’t occur.  This suggests that the number of fossil fuel power stations operating could be a good metric to keep track of.

Renewables Confusion – Renewable versus Clean

 Introduction to the Series Renewables Confusion
Renewable energy is the fastest moving and most discussed topic in energy today. Unfortunately with a large amount of discussion comes a large amount of confusion. Even the educated and impartial observer struggles to get a full understanding.
This series isn’t going to inform you about the truth about renewables – because I don’t have it. A topic so fast moving requires a humble approach.
For the record – human-caused climate change is the biggest problem we face. My professional mission is to contribute towards fighting it.
Yet a mission to fight climate change does not mean blindly supporting renewables.
This series is not about bashing renewables. It’s about highlighting some of the inherent problems or areas where confusion arises.
Problems don’t mean that renewable deployment is not the way to go. In choosing a path forward we don’t need renewables to be perfect – only to be superior to the alternatives.
Highlighting problems allows us to address them. If we can see issues that may occur with high levels of renewables penetration we can start to address them now.
Confusion One – Renewable versus Clean
People often point out that no resource is renewable. When looked at on a cosmic scale even the energy provided by the sun will one day not be available.
We can ignore this facetious and unhelpful reasoning. Let’s use two simple definitions as the basis for discussion.
There are many different renewable energy technologies. We will focus on solar and wind in this series.
We define renewable as not depleting the natural resource.
We define clean as not contributing to negative environmental effects such as climate change, poisoning of rivers or loss of biodiversity.
There’s a third definition I could have included here – sustainability. Sustainability is meeting the needs of the today without compromising the ability of future generations to meet their own needs.
While I like the idea of sustainability actually applying it becomes difficult. What exactly are the needs of today? Are our needs different from the needs of future generations?
Now let’s look solar and wind in the context of the definitions above. We will take a look at both the operation and manufacture of these plants.
The operation of solar plants makes use of the sun for fuel and water for washing panels. Both are renewable and use of the sun as a fuel is clean.
The negative environmental effects generating water for panel cleaning is site specific. Best practice for generating this water will most likely have minimal environmental impact. The operation of solar panels is renewable and clean.
The manufacture of solar panels involves processing of quartz in electric furnaces to remove oxygen. The electricity used in silicon production today is non-renewable. Where the silicon production occurred will determine how non-renewable it was.
Silicon tetrachloride is a hazardous chemical that is a by-product of silicon purification. Production of hazardous wastes is not unusual in chemical processing. Best practice for disposal or reprocessing will limit environmental damage.
Solar panel manufacture uses rare earth elements such as silver, tellurium or indium. Unless we are at a position of 100% recycling then use of these will be depleting the natural resource. This makes solar panel manufacture non-renewable.
The use of carbon-intense electricity makes solar panel manufacture unclean. While this may change in the future with high levels of renewables penetration it’s not the case today – and probably won’t be for a long time.
Operation of wind plants appears renewable. Yet Vaclav Smil notes in his excellent book Energy Myths and Realities: Bringing Science to the Energy Policy Debate:

very large-scale extraction of wind (requiring installed capacities on a TW scale needed to supply at least a quarter of today’s demand) reduces wind speeds and consequently lowers the average power density of wind-driven generation to around 1 W/m2 (from 2 W/m2)

 If Smil is correct then by our definition the operation of wind turbines is not renewable. Large scale deployment of wind depletes the resource.
How clean large turbine scale deployment is an unknown. Changing wind speeds may do environmental damage but who knows?
Now let’s take a look at wind turbine manufacture. Wind turbine blades are made from fiberglass. Producing fiberglass requires non-renewable petrochemicals.
A significant amount of steel and concrete is used in building wind turbine plants. Fossil fuels are used in the production of both.
It’s not only the energy content of fossil fuels that is required. Fossil fuels are an inherent part of the chemistry of steel and concrete manufacture.

In steel production fossil fuels are required for iron smelting. Concrete production uses coal to remove carbon from calcium carbonate.


Fe2O3 + 3CO → 2Fe + 3CO2
CaCO3 → CaO + CO2
In both reactions above carbon dioxide is produced. Not only is wind turbine manufacture non-renewable it is also inherently unclean.
What does this actually mean?
At this point in the article supporters of solar and wind may be a bit upset. It looks a lot like renewables bashing!
The truth is all energy generation technologies have their problems.
In choosing a way forward, it’s not about if a technology has problems. It’s about what those problems are versus the alternative.
This is a function not only of the problem but of societies attitude towards the problem. Perhaps we don’t mind depleting our resources of rare earth elements if it means reducing carbon emissions.
To quantify the environmental benefit of renewables versus fossil fuels is a project with a massive scope. The analysis is full of uncertainty and is location & time specific.
Yet but only highlighting some of the inherent problems with solar & wind we can think about ways to address them in the future.
Perhaps we need to focus on understanding what impact large-scale wind deployment will have on wind speeds, or what quantities of rare earth elements we have left for use in solar panels.
By addressing these issues we can move forward into a brighter (but maybe less windy) future.
Our next post in this series will be about Capacity versus Generation.