Biogas Energy Storage

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I am always on the lookout for energy storage solutions, so I am very interested in this aspect of Mich Hein’s (Nidus) “Renewable Natural Gas” lecture (Coursera (MOOC): Our Energy Future, U of San Diego, Oct 2014).

Biogas contains approximately 50% methane and 50% carbon dioxide.  Biogas is a natural product of organic material decomposition.  Commercially biogas is produced in anaerobic digesters (food, human and animal waste) and landfill gas collection.

Methane is a very potent greenhouse gas, about 20 times more so than CO2, but less abundant or long lived in the atmosphere.

Harvesting biogas has the dual benefit of preventing it vent to atmosphere and it’s use as a green fuel.  Since the feedstocks are not fossil fuels, but derived from recent plant growth, it is not adding carbon to the atmosphere, so long as the source plant matter is replaced by replanting.

Upgrading of the biogas CO2 component to Methane (CH4) which requires energy input can bring the total methane content up to 98%, which is comparable to that of natural gas (fossil fuel).  This seems to have great potential in several ways:

  • Use excess renewable energy from wind, tidal and solar (possibly nuclear) when demand is low to upgrade CO2 to methane, thus storing energy in high quality biogas.
  • Add value to raw low grade biogas.
  • Bring quality of biogas up to conventional natural gas levels for direct substitution into existing infrastructure.
  • Displacement of fossil fuel natural gas.
  • No need to alter existing gas fuel infrastructure or equipment.

I am most enthusiastic about the storage capability, which on its own could be used to store the excess energy from renewables and nuclear electricity production, and used in gas turbine plant to provide electricity on demand.

Prof Mayfield, in the follow-up lecture, proposed that instead of upgrading the CO2 component of biogas, other sources of CO2, conventional power-plant stacks for example, could be upgraded to methane in a similar manner.

It seems possible that CO2 from power stations could be continuously collected, upgraded as an energy storage solution in tandem with renewables, and used to generate electricity.  Some number crunching and flow models would help to determine the viability of such a scheme.

As always, the economics of these technologies would be greatly improved with a realistic tax on carbon emissions.

Whether upgraded biogas can significantly displace natural gas in sufficient quantities to effectively reduce fossil carbon emissions on a significant scale is less clear.  Are there enough sources of biogas raw materials to feed demand?

Persistence of Atmospheric CO2

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In the Coursera (MOOC) class ‘Global Warming: The Science of Climate Change‘ by Prof David Archer (University of Chicago), the long life of Carbon Dioxide in our atmosphere was explained and is a real cause for concern.

The concentration of atmospheric CO2 reached 400ppm last year, a fossil-fuel induced historical high.  Pre-industrial concentrations were relatively stable at around 280ppm.

Global temperatures have been rising in step with CO2.

Chart 1 _ Atmos CO2 v Temp 1000 years

University of Chicago oceanographer David Archer, who led the study with Caldeira and others, is credited with doing more than anyone to show how long CO2 from fossil fuels will last in the atmosphere. As he puts it in his new book The Long Thaw, “The lifetime of fossil fuel CO2 in the atmosphere is a few centuries, plus 25 percent that lasts essentially forever. The next time you fill your tank, reflect upon this”

Nature: Climate Change, ‘Carbon is Forever’, 2008

So the effects on Climate from Global Warming, induced by high levels of atmospheric CO2, will persist for centuries after pollution is curtailed.  With rates of emissions of CO2 set to increase, the worst effects on Climate are on the horizon and will become the normal conditions for hundreds of years to come.

An interesting dataset of Historic CO2 emissions since the beginning of industrialisation is available from CDIAC: Carbon Dioxide Information Analysis Centre which is the primary climate-change data and information analysis center of the U.S. Department of Energy (DOE).

Table 1 _ Historic CO2 by Country

Chart 2 _ Historic CO2 by Country

As can be seen from the CDIAC graph below, the bulk of CO2 emissions have been in the last 50 years.

Chart 3 _ CDIAC GHGs

Please remember when examining data on carbon emissions that the quantity of Carbon is not the same as that of CO2.  Carbon dioxide has additional oxygen atoms to take into consideration, so:

One ton of carbon equals 44/12 = 11/3 = 3.67 tons of carbon dioxide.

Wind Energy in Scotland

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Written for the Coursera (MOOC) Class ‘Wind, Waves and Tides‘ by the University of Toronto (Nov 2014).

Scotland has 25% of Europe’s wave and wind power potential [1] [2] [3] [4], and has a theoretical total wind energy capacity of 159 GW [5].

Figure 1 _ EU Wind Map_2

Figure 1: Europe Wind Energy Potential (EEA 2008) [6]

The Scottish Government has set ambitious energy targets to de-carbonise electricity generation and reduce energy consumption [7].

  • 100% of Electricity demand to be met by Renewable Energy sources by 2020.
  • Interim target of 31% by 2011 was exceeded
  • Next target of 50% by 2015 is expected to be met.
  • Energy Efficiency improvements by reducing final energy consumption by 12% (years 2005-07 baseline) by 2020.
  • Reductions of 9.2% were achieved by 2011.

The Fossil Fuel portion of electricity generation is largely met by one coal fired station, Longannet (2.4 GW) and by one natural gas station, Peterhead (1.5 GW) [8] [9]. The target of meeting Scottish demand for electricity from renewable sources leaves the door open for fossil fuel and nuclear in exports of electricity to England and Northern Ireland.

Retention of some of this non-renewable capacity will help in balancing the grid as renewable sources fluctuate. Scotland currently has pumped storage capacity of 16.3 GWh with scope and plans for expansion [10] [11].

Both Longannet and Peterhead power stations have been considered for Carbon Capture and Storage technology. UK government investment was withdrawn for the Longannet pilot project, but has funded a study for the Peterhead facility [10] [11].

Nuclear Power is generated at two facilities, Hunterston B (1.3 GW) and Torness (1.4 GW). Both are towards end of life and have had extensions granted for another 10 years [12] [13]. The current Scottish administration is opposed to any new nuclear power facilities being built [14].

Energy Storage is an essential technology in matching intermittent renewable energy sources with variable consumer demand. Scotland currently has two large Pumped Storage facilities, Cruachan (440 MW, 10 GWh) and Foyers (300 MW, 6.3 GWh) [15] [16].

Feasibility studies are underway on another four locations, Cruachan expansion [17], Sloy conversion (60 MW, 0.4 GWh) [18], Coire Glas (600 MW, 30 GWh) [19] and Balmacaan (600 MW, 30 GWh) [20]. Note that power transfer, the rate at which electricity can be stored from or released back to the grid is indicated in MW. Actual storage capacity (energy) is shown in GWh. Divide GWh by MW / 1000 and this is the amount of stored energy in hours at maximum power.

The Scottish government has set emissions targets, in law, to reduce production of greenhouse gasses responsible for climate change, in ‘The Climate Change (Scotland) Act of 2009, (using 1990 levels as the benchmark).

  • Target of reducing emissions by 80% by 2050.
  • Target for 2020 is set at 42% reduction.

Besides Electricity Generation, Scotland plans to have 30% total energy consumption, 10% transportation (EU target of 10%), 11% of heat energy, powered by Renewable Energy sources. Guidance on how the country shall achieve these targets is provided in the Scottish government publication ‘2020 Routemap for Renewable Energy in Scotland’.

Wind Energy Progress

There are currently two offshore and more than 100 onshore windfarms operating in Scotland. In addition to this, another 200 are either under construction, have planning permission or are in planning[21].

Figure 2 _ Scotland Windfarm Map 2013_DUKES ch6

Figure 2: Scotland Installed Wind Energy (UK Gov) [22]

Table 1 _ Operational Wind Farms Scotland 2014

Table 1: Operational Facilities 2014.

Table 2 _ Future Known Wind Farms Scotland 2014

Table 2: Future Facilities 2014.

The two largest Onshore Facilities are:

Whitelee Wind Farm (Scottish Power) [23], near Glasgow is the largest onshore wind farm in the UK, second in Europe.  Completed in 2009, it operates 215 turbines each rated at 2.3 MW, giving it a total installed capacity is 539 MW. The total project cost was £300 million, or around £0.56 million per megawatt.

Clyde Wind Farm (SSE) [24], south east of Glasgow, was completed in 2011. It is Europe’s fourth and the UK’s third largest onshore facility. It has 152 turbines and an installed capacity of 350MW. The project cost was £500 million.

A similar large scale facility is currently in construction:

Viking Wind Farm (SSE & Community) [25], Shetland Islands, is due for completion in 2019. It will operate 103 turbines and produce 370 MW. The project includes a new high voltage sub-sea cable linking with the UK electricity grid. The wind conditions on Shetland estimate the capacity factor to be 0.44.

Electricity Generation and Consumption

Electricity generation in Scotland remains fairly constant at around 50 TWh per annum [26].  All of the coal generation is from the 2.4 GW Longannet Station with some of the remainder from earlier years intermittently supplied by the 1.2 GW Cockenzie Station which was closed in March 2013 [27]. Much of Cockenzie’s electricity was exported to neighbouring Northern Ireland.

Figure 3 _ Scotland Elect Gen & Cons 2004 _ 2012

Figure 3: Electricity Generation and Consumption (UKgov DECC Statistics) [26]

Nuclear power provides an annual average base load of just under 16 TWh, from Torness (1.4 GW) and Hunterston B (1.3 GW) stations[28] [29].

The Peterhead power station (1.5 GW) generates the majority of gas sourced electricity at around 10 TWh annually[28] [29].  The Grangemouth petrochem complex is supplied by the 130 MW gas power station.  It provides electricity and steam locally, as well as exporting excess electricity to the grid.

Permission was granted in 2011 for a 1 GW combined cycle gas power plant at the Cockenzie site, it will be equipped with carbon capture and storage CCS) technology [30].

Table 3 _ Elect Gen byFuel Perc 2004 _ 2012

Table 3: Electricity Generation Share [26]

Table 4 _ Elect Gen byFuel GWh 2004 _ 2012

Table 4: Electricity Generation Quantity [26]

Table 5 _ Elect Cons and Export GWh 2004 _ 2012

Table 5: Electricity Consumption and Export [26]

Installed capacity for renewable sourced electricity is rapidly increasing in Scotland in line with targets set out by the Scottish government [22].  The graph below illustrates this expansion, with hydro capacity remaining constant and wind being responsible for the majority of the increase.  Tidal power is at the prototype testing stage and currently contributes very little, but the potential from tidal energy, especially in the Pentland Firth is estimated at 1.9 GW [31].

Figure 4_ Scotland Elect Gen by Renewables MW 2004 _ 2013

Figure 4: Electricity Generation by Renewables, Installed Capacity MW (UKgov DECC Statistics) [26]

Renewable Electricity Production and Energy Efficiency

The Scottish government target of generating 100% of national electricity consumption from renewable sources by 2020 appears to be very achievable.  The two pronged approach of reducing consumption and increasing renewable capacity is already having the desired affect.

In the 2010 Scottish government publication ‘Conserve and Save: The Energy Efficiency Action Plan’ [32], provision is made to encourage public participation in the broad objective to reduce energy consumption.  Resources are provided to better educate the general public on energy conservation and climate change matters, as well as provision of financial aid to improve domestic energy efficiency, by increasing home insulation for example.

‘Action 2.1 Within available resources, we will continue to provide ongoing support and financial assistance for energy efficiency in existing housing, levering investment from energy companies and private householders wherever appropriate.’

Scotland, as with all northern European countries, has a cool climate and much of the domestic energy use is for heating.  Well insulated homes drastically reduce heat energy consumption.

Scotland is a net exporter of electricity, to neighbouring England and Northern Ireland.  In recent years the trends, shown in the graph below, are for reduced national consumption and increased exports.

Figures 1 shows an 11.5% reduction in electricity consumption between 2012 and 2004. This is an indication that reduction initiatives may be working, but may also be a result of thrift during an economic downturn.

The rapid increase in wind turbine installation, and grant assisted improvements in home insulation plus micro renewable generation, indicate that the continuation of trends towards lower consumption and increased renewable share are highly probable.

Short-Term Wind Installation Estimates

The current installed onshore wind generation of 4.7 GW is soon to be augmented by a further 0.5 GW under construction, 3.3 GW approved for construction, 4.3 GW currently in planning.  The current known potential of 12.8 GW can be included for the short term [33].

Fig 5 _ Wind Installed Const Approved Planning 2014

Figure 5: Scotland Wind Power (UKgov Statistics)

There are also great opportunities currently being reviewed in offshore wind energy.  This is both a more technically challenging and resource rich sector.  Currently in Scotland there are two offshore wind developments: the 5 MW Beatrice demonstrator project and the 180MW Robin Rigg installation.

The Scottish government initiative ‘Blue Seas – Green Energy A Sectoral Marine Plan for Offshore Wind Energy’ [34], has identified 5 GW of development in six areas which exhibit favourable potential.

In addition to this, the ‘Sectoral Marine Plan’ has identified 25 areas for offshore wind development.  Estimates of Scottish total offshore wind energy potential are in the region of 206 GW.

Some Technical and Political Issues

The majority of large scale renewables projects are located near the larger urban areas of Scotland, where the interconnecting transmission grid has the capacity to link new generators to existing large loads, towns and cities.  However, the areas with the greatest potential for wind and wave power lie at the sparsely populated and infrastructure poor northern and western extremities of the country, including the Western Isles which confront the fierce open Atlantic.

Significant infrastructure investment would be required to tap into this vast resource.  As I have illustrated, the more easily accessible sites near urban centres are being developed, and significant further development here is possible.  Once this has been exhausted, then the more expensive to connect, remote areas, may be developed.

The limit to urban developments is affected by density of turbines and the tolerance of people living close by.  Currently the majority of people in Scotland and the UK are in favour of wind energy.  As reported in the Guardian newspaper in 2012, an Ipsos Mori poll found that 66% were in favour and only 8% against [35].

Tourism contributes £11 billion towards the Scottish economy annually [36], and some have claimed that wind turbines will discourage tourists from visiting.  However, another Ipsos Mori poll surveyed tourists in 2002: Unaware of windfarms (60%), Windfarms have positive effect (55%), Ambivalent (32%) and Negative effect (8%).  In fact 80% of tourists said they would like to visit a windfarm [37].



[1] Carbon Trust/Black and Veitch Report (Phase II UK Tidal Stream Energy Resource Assessment), 2005

[2] Offshore Valuation Study (The Offshore Valuation), 2010

[3] Scottish Energy Review 2006 (Stephen Salter, Kerr Macgregor, Clifford , Jones)

[4] Garrad Hassan report “Scotland’s Renewables Resource”, 2001

[5] Newsnet Scotland “Scotland continues to lead the way on renewable energy”, 12 June 2013

[6] European Environmental Agency, “Europe’s onshore and offshore wind energy potential”, 2009

[7] Scottish Government “2020 Routemap for Renewable Energy in Scotland – Update 2013

[8] Scottish Power Website: Longannet Power Station

[9] Scottish & Southern Energy Website: Peterhead Power Station

[10] BBC website, “Longannet carbon capture scheme scrapped”, 19 Oct 2011

[11] UK Gov DECC, “Peterhead Carbon Capture and Storage Project”, 24 February 2014

[12] BBC website, “Hunterston B nuclear power plant will run until 2023”, 4 Dec 2012

[13] BBC website, “Scotland’s nuclear stations could stay open”, 5 March 2012

[14] The Scottish Government’s position on nuclear power, 9 Oct 2007

[15] “Sustainable Energy Without the Hot Air”, p191, David MacKay

[16] Scottish Renewables website, Hydro: What is Hydro?

[17] BBC website, “Cruachan hydro power station output could double”, 11 February 2014

[18] Water Power magazine, “SSE submits Sloy expansion plan”, 17 September 2009

[19] SSE website, “Coire glas hydro scheme”, December 2013

[20] SSE Renewables, “New Pumped Storage Proposals

[21] Renewable UK, “UK Wind Energy Database”, October 2014

[22] UK Gov DECC, Digest of UK Energy Statistics, chapter 6 Renewable Energy, 2014

[23] Scottish Power, “Whitelee Wind Farm

[24] SSE, “Clyde Wind Farm

[25] SSE, “Viking Wind Farm

[26] UK Gov DECC, “Sub-national energy consumption statistics

[27] BBC website, “Cockenzie coal-fired power plant closes”, 15 March 2013

[28] UK Gov DECC, Digest of UK Energy Statistics, chapter 5 Electricity, 2014

[29] UK Gov DECC, Energy Trends: December 2013, special feature article – Electricity generation and supply figures for Scotland, Wales, Northern Ireland and England, 2009 to 2012

[30] BBC website, “Coal power plant at Cockenzie to be replaced by gas”, 5 October 2011

[31] The Scotsman, “Pentland Firth tides can power half of Scotland”, 19 October 2014

[32] Scottish Gov, “Conserve and Save: The Energy Efficiency Action Plan”, 2010

[33] Scottish Renewables, “Scotland’s Renewable Energy Sector in Numbers”, Oct 2014

[34] Scottish Gov, ”Blue Seas – Green Energy A Sectoral Marine Plan for Offshore Wind Energy in Scottish Territorial Waters”, 2011

[35] The Guardian, “Wind power: new poll finds 66% of UK public in favour”, 19 April 2012

[36] Visit Scotland, “Tourism Delivering for Scotland”, October 2014

[37] Ipsos Mori, “Tourists ‘Not Aware’ Of Wind Farms”, October 2002