This article was originally published on LinkedIn on the 29th of January 2021. This version has been updated based on some of the comments and feedback received.
As Energy Transition is the buzzword of the moment and we slowly move from debating the reality of climate change and who is to blame to debating the best way to tackle it and who will pay for it, I took some time to look through old notebooks from working on the Kingsnorth-Hewett CCS project. (This was dropped by main developer E.On after the UK government cancelled the £1bn CCS competition and Kingsnorth ceased power generation in 2012 ). About the same time, and as a side project, I took an interest in the Mauna Loa Observatory Carbon Dioxide data  to see how CO2 in the atmosphere had been increasing over the last few decades – I suppose just to confirm to my self that climate change was real and that we were in fact to blame. (Spoiler – yes, it is and yes, we probably are).
Figure 1 below shows the increasing levels in the atmosphere between 1999 and 2010, around the time I started working on CCS projects. I’ve also included an exponential trend line up to the end of 2020 which indicates that the extrapolated high for 2020 should be 415.6 ppm. The good news is that this correlation fits quite well with the actual value of 418 ppm measured on 1st June 2020. The bad news is that the trendline under predicts the actual albeit not by much.
If we take this as a reasonable correlation, then extrapolating it forward to 2050 (the goal for a carbon-neutral planet) indicates that we can expect CO2 levels in the atmosphere to be in the order of 487.5 ppm – assuming we do nothing.
Fortunately, we have quite a few options available to try and tackle this seemingly overwhelming challenge. All and none of which are viable technical and or commercial / economic options depending on what or who you believe. The trick is not to fall into the trap of believing that any one of them is a panacea for managing CO2. All will be necessary in order to arrest the rise of CO2 in the atmosphere.
What better place to start than actually grabbing the offending gas at source and burying it underground. The truth is that you can build as many wind farms and solar arrays as you like, but there will always be a part of the economy that will generate CO2, even if it is in relatively small amounts by today’s standards.
Nobody gets beyond a petroleum economy. Not while there’s petroleum there.Dan Simmons, Hyperion
One of the big challenges from my perspective as an experienced oil and gas engineer is the selection and management of the ‘storage site’, i.e. the underground ‘reservoir’ where the CO2 will be stored.
One of these challenges is that if we utilise depleted hydrocarbon reservoirs then we have a number of high-risk leakage paths built into our proposed storage site. These are in the form of the existing wells, some of which may be decades old, have limited P&A information and were never designed to be part of a Carbon Dioxide storage system anyway. Depending on the number of wells in a given site, the remedial work required to ensure that existing well integrity is maintained (assuming this can even be achieved) can be crippling to a proposed storage site development.
Nonetheless, there are numerous operational CCS sites around the globe  with Sleipner and Gorgon being amongst the largest at 1 and 4 million tonnes of CO2 injection per year respectively. Note that there are other large scale injection projects, such as Ras Laffan with 2.1 MT/year injection, but as this is for EOR it could be argued that it’s contribution to CO2 reduction is significantly lessened by the fact that the produced hydrocarbons will be burned and simply adding to the cycle.
While these numbers seem impressive it is important to remember that global CO2 emissions from fossil fuels and industry in 2019 were 33 GT . There are now 51 CCS facilities globally – 19 in operation, four under construction, and 28 in various stages of development with an estimated combined capture capacity of 96 million tonnes of CO2 per annum 
So even if all these current facilities were fully operational and running at maximum capacity, they would only account for capturing 0.26% of CO2 emissions – which when you think about it is a little depressing. That said, CCS when combined with electric power generation (especially coal powered fire stations and to a lesser extent gas) does have the potential to significantly reduce emissions for that industry sector  as shown in Figure 2 below.
This then brings us onto the next part of the puzzle – reducing the CO2 emissions in the first place. CCS is a useful stop gap on our way to a renewable power generation economy but the removal of hydrocarbon based power generation should be the main focus and the first stop on that journey is…
Wind, solar, wave, tidal, geothermal and even at a push hydro have very little in the way of emissions – if you include the carbon cost of manufacture and maintenance it is not zero but over their lifetime the cost is between 5 and 25 gCO2eq/kWh for say, and offshore windfarm . That is to say that for every kWh of electricity generated by a wind turbine, there is an equivalent 25g of CO2 emitted as part of the manufacture, installation, maintenance and decommissioning of the turbine. Compare that to that of traditional electric generation which, while reducing, in 2008 were still 500 gCO2eq/kWh  with a ‘proposed’ reduction to 50 gCO2/kWh by 2030 (still double the upper level of offshore windpower).
I always enjoy reading the naysayers comments on renewable energy, from the pedestrian “When you need the power the wind won’t below and the sun won’t shine” to the trainspotter’s, “Ah, yes but when you factor in the land requirements due to the inefficiency of the system and taking cognisance of the exergy associated with these renewables…”. They are of course correct.
First of all efficiency. A typical solar panel can generate about 200 W/m2 of power. This is based on a solar radiance of 1,000 W/m2 and a panel efficiency of 20%, a perfectly reasonable level for today’s technology. Let’s say we go somewhere near the equator where it’s:
- Nice and sunny!
- Has little change in the average hours of sun per day (let’s call it 6 hours to cover an overly optimistic irradiance value)
Every day we would have 1,200 Wh per square metre of energy which equates to 438,000 Wh per year per square meter. Global energy consumption in 2017 was 113,009 TWh so to generate this we would need 258,000 km2. To put that in perspective I’ve drawn a square over North West Africa. Please note I am not suggesting that we cover Mali in solar panels and that all our problems would be solved – in fact what I am trying to highlight here is the scale of the challenge given the inefficiencies of the tools we have to work with.
Similarly, for wind turbines, a lot of space is needed. Aberdeen Bay recently (commissioned September 2018) installed eleven Vestas V164 wind turbines with a nameplate capacity of 8.4 to 8.8 MW. The spacing required for a windfarm suggests that the distance between turbines normal to the prevailing wind direction is 2-4 times the rotor diameter and 8-12 times the rotor diameter in the direction of the wind. Thus, for the giant 164m rotor diameter of the Vestas, each turbine requires about 850,000 m2. Let’s say that each turbine is operational 50% of the time. Then for our massive Vestas we get 43,800 Wh/m2 per year. Again, this is a huge area requirement (2,580,000 km2) but remember a) not trying to solve all the power consumption with one type of renewable and b) not trying to put it all in one place.
My point is that despite their inefficiencies both in terms of power generation and space requirements, the focus needs to be on reduction in carbon emissions (and also energy consumption). A strong mix of renewables from solar and wind power to geothermal and hydro is what is required. And also a variance in the scale of these developments to meet regional needs based on their resources and energy requirements.
Wind, solar, wave etc. don’t work without wind sunshine or waves. Again this is true which brings us nicely to the next part of the energy transition train, but first…
The Nuclear Question
Yes, but what about Nuclear – it’s clean! I hear to say. And I have to agree, in terms of CO2 emissions, nuclear is a clean alternative. However, it brings along a whole bunch of other really scary problems. Mayak and Windscale (Sellafield) both 1957, Three Mile Island 1979, Chernobyl 1986, Fukushima 2011 all with an INES (International Nuclear Event Scale) level of 5 or higher. So let’s just not go there, OK?
So on to…
If the wind won’t blow and the sun won’t shine, just when we need a cup of tea then we have to have a means of storing our lovely clean energy until such times as we need it. One option is to use hydrogen.
There are different colours of hydrogen! Did you know that? I only found out yesterday. Believe it or not there is green, blue, pink, grey and even turquoise. No seriously, turquoise hydrogen is the name given to hydrogen derived from the pyrolysis of natural gas.
As we are talking about wind turbines and solar farms then green hydrogen is where we want to focus. This is where hydrogen is generated using electrolysis with the power being supplied by renewable energy – negligible CO2 is generated (only lifetime CO2 costs as mentioned previously).
For some countries the jump to green hydrogen may be more attractive than others, depending on the scale of their renewable supply and hydrogen power strategy. For example, Scotland has a significant portion of its power generation from renewables, about 90% of Scotland’s energy demand in 2020 , so a move to green hydrogen might be more attractive than blue hydrogen. But what’s the difference?
As already mentioned, green hydrogen is produced by electricity from renewable energy sources (wind or solar) through electrolysis. Blue hydrogen is created through the reforming of natural gas (Methane) with steam to produce Hydrogen and Carbon Dioxide where the CO2 is stored as part of a CCS development. (Note that if reforming is used to generate hydrogen without CCS this is referred to as grey hydrogen). However, the ability to generate green hydrogen in a robust renewables environment is only half the picture. Compared with reforming, electrolysis is less efficient and more costly. So the decision, assuming a government hydrogen strategy is in play, will be down to the current power generation types and capacities.
But why do we care about hydrogen? Simple, it is a massively abundant clean energy source. When combined with oxygen it produces water and power which can be used to drive electric motors or even supply electricity to the grid. Last year a 10MW capacity fuel cell opened in Fukushima  (yes, that Fukushima) which operates from green hydrogen generated from a 20MW solar farm using electrolysis – see Figure 5
If we do move to a hydrogen economy, then storage will become a key factor in its success. Similar to CO2 storage in so much that hydrogen can be stored in underground caverns. Germany’s EWE gas provider is currently ‘building’ a pilot hydrogen storage project  with a capacity of 500 m3 by washing out salt caverns which is due to come online in 2022.
Although there are domestic boilers which can handle a certain amount of hydrogen, manufacturer’s are already looking at developing boilers which can fully run on hydrogen. The future may see gas mains replaced with hydrogen mains or hydrogen storage tanks in remote rural areas. Not only could our electric be generated by hydrogen but also our heating requirements.
All that said, hydrogen should not be seen as a panacea in the fight against climate change.
So, what would the new components of an energy transition look like, based on the above? Figure 6 below shows the various connections that may need to be established in order to start moving away from a hydrocarbon reliant power generation mix.
Renewables continue to grow and start to provide hydrogen for power generation or storage. Hydrocarbon’s clean-up their act with reforming and CCS which reduces their emissions and provides additional clean power from hydrogen. As Renewables continue to grow, hydrocarbons are slowly phased out until only the cleanest remain.
I’ve already pointed out that renewables compared to burning hydrocarbons are inefficient and this is one of the key arguments against pursuing a renewable energy environment. But the greatest inefficiency we face is our inability to make a decision and act, but hopefully we will still have enough time left to make those choices.
 Global Status of CCS 2020 – The Global CCS Institute (download link)