Thursday, 30 September 2021

Part 1 – The Role of Renewable Energy to Combat Climate Change

So if reducing to a minimum carbon dioxide emissions from the burning of fossil fuels is necessary to mitigate the effects of climate change, the questions which remain to be settled are how is this to be done and what will replace fossil fuels.

Tricastin nuclear power station and a wind turbine 

Whilst we can make some progress within developed economies by improvements in efficiency, conservation and demand management, the net result of these measures will be grossly insufficient to counter increasing global demand arising from the legitimate requirement for more energy from developing economies. In this video “The Magic Washing Machine” by Hans Rosling (now sadly deceased) he explains why we in the developed world have no right to tell people in developing economies that they can’t use more energy because of Climate Change, since it’s a major key to lifting poor people out of poverty.

The role of renewables

So as well as conservation measures what is the best way forward? Clearly renewables have a significant part to play in the future of energy production, and they are getting cheaper, but many are still being subsidized and, in common with other energy production technologies, they are not without an impact on the environment.

Global primary energy by source
Primary energy is an energy form found in nature that has not been subjected to any human engineered conversion process. It is energy contained in raw fuels, and other forms of energy received as inputs to a system. Primary energy can be non-renewable or renewable.
Where primary energy is used to describe fossil fuels, the embodied energy of the fuel is available as thermal energy and around 70% is typically lost in conversion to electrical or mechanical energy. There is a similar 60-80% conversion loss when solar and wind energy is converted to electricity, but today's UN conventions on energy statistics counts the electricity made from wind and solar as the primary energy itself for these sources.

The following graphic shows the global primary energy consumed for all purposes including electricity generation. Energy generated from nuclear, hydropower, biomass and other renewables is directly measured as electricity outputs whilst coal, oil and gas need efficiency factors to be applied when they are used for electricity generation, as opposed to industrial process heat or to power vehicles. The vertical axis is in Mega Tonnes of Oil Equivalent Mtoe.

The proportion of carbon free energy i.e. renewables, biomass, hydro and nuclear, is projected in 2030 to be only 20.5% of total primary energy consumed. So, to replace the other 79.5% of primary energy from fossil fuels, an enormous investment in energy from carbon free sources, of all types, is therefore required to meet decarbonization targets and it was needed yesterday!

Except in particular locations bio-fuels are heavy consumers of agricultural land and are unlikely to provide more than marginal amounts of electricity on a global scale but they have a role to play. In Brazil, for example, they are successfully replacing fossil fuels for vehicles with blends of gasoline and ethanol derived from sugar cane. Biodiesel, in various blends, is established in North America and Europe. Biofuels are being encouraged by the EU, but there are concerns that by displacing food production from agricultural land and clearing forests, which are net absorbers of CO2, the production of biofuels could actually release more carbon dioxide than they save.

Tidal power
Tidal power could also contribute more to renewable energy production, and some sites have been in operation since the 1960's. Tidal power generation is, of course, very predictable and could remove much of the need for back up fossil fuel generation for other less predictable renewables, but tidal barrages and lagoons have an impact on ecosystems and the energy generated is on a lunar cycle, which does not coincide with diurnal demand.

Submerged tidal turbines
Submerged turbines placed in locations where currents are created by tidal flows are another possible source of tidal power. Studies are ongoing but environmental impacts are likely to be much less than tidal barrages.

Wave power 
Wave power is a source of renewable energy which could be further developed and wave farms have been installed in a number of coastal locations. Currently the largest operational wave farm has a capacity of 2.4MW and most are in the fraction of a MW range. The graphic below shows the potential in terms of kW/m for the world's oceans and it’s clear that some locations, such as the North Atlantic and Northern Pacific are potentially much more productive than others.

Hydro electricity has, along with nuclear and wind, one of the lowest rates of carbon dioxide generated at 18.5g CO2 per kWh. What’s more it is dispatchable power which can be rapidly varied to suit the demand and compensate for variable generation from wind and solar PV. It’s therefore an attractive investment for governments to make.

Hydropower in Europe
As of 2020 in Europe there were:-
254 GW of installed generation capacity,
55 GW of pumped storage capacity and
676 TWh of electricity were generated in the year representing 13% of total European electricity generation.

During the year 2020, 3GW of capacity were added across the European region, made up mainly by new hydropower plants commissioned in Turkey and other additions in Norway and Albania. Generation from hydropower was almost 4 per cent higher in 2020 than the previous year, owing largely to increased production in the Nordics and Iberia.

Adding major amounts of capacity in Europe involves damming rivers and creating lakes and because there are few “natural habitat-rich” rivers left, this is controversial and unpopular with some environmentalists.

Hydropower internationally
Installed global hydropower capacity rose by 1.6 per cent to 1,330 gigawatts (GW) over the past year 2020 and generated a record 4,370 terawatt hours (TWh) or 19% of world consumption.

During 2020, hydropower projects totalling 21 GW were put into operation, up on 2019’s 15.6 GW. Nearly two-thirds of this growth came from China, which saw 13.8 GW of new capacity. Among other countries that added new capacity, only Turkey (2.5 GW) contributed more than 1 GW.

Wudongde in operation

The single biggest project was Wudongde in China, which put eight of its 12 units online, adding 6.8 GW to the Chinese grid. The remainder are expected to be commissioned in 2021.

China remains the world leader in respect of total hydropower installed capacity with over 370 GW. Brazil (109 GW), the USA (102 GW), Canada (82 GW) and India (50 GW) make up the rest of the top five. Japan and Russia are just behind India, followed by Norway (33 GW) and Turkey (31 GW).

Nevertheless the International Hydropower Association in their 2021 Status Report states that much faster growth is necessary:

Quote <<to limit dangerous global warming and achieve net zero by 2050, the International Energy Agency (IEA), however, says the water power sector will need to double in size to 2,600 GW. This equates to building the same amount of capacity in the next 30 years as was built in the last 100 years.

“At the present rate of hydropower development, the global energy pathway to net zero emissions will not be realised,” warn IHA President Roger Gill and IHA Chief Executive Eddie Rich in the report’s foreword. “This is a wake-up call for policy-makers, hydropower developers and project financiers and provides clarity for the public.

“Investment in sustainably developed and responsibly operated hydropower is essential to support the massive expansion of variable renewables like wind and solar. However annual growth rates of 1.5 to 2 per cent cannot meet the doubling of installed capacity proposed by the International Energy Agency to achieve net zero by 2050.”

According to the report, the Covid-19 crisis has further underlined how the power system flexibility provided by hydropower is now a prerequisite for the clean energy transition. Hydropower’s critical role was illustrated by a recent near blackout incident in Europe in January 2021.
>> Unquote.

The emphasis on using hydropower, which is quickly increased or reduced, to support grid power systems having an increasing proportion of variable renewables is enlightening and significant.

There are geothermal power installations of 10MW capacity or more on 72 sites in 16 countries with a total installed electrical output capacity of 10.9 GW. This is proven technology which has been in operation for decades and the total output is equivalent to about 18 typical coal fired power stations. There are almost certainly more opportunities to expand the output of geothermal power and, as carbon reduction policies begin to harden, more plants will be built, but on a worldwide scale its contribution to reducing fossil fuel use will not be very significant.

Wind power has expanded rapidly in recent years and in 2020 reached 743 GW of installed capacity worldwide. 

Quoting from the Global Wind Energy Council, << 2020 was the best year in history for the global wind industry with 93 GW of new capacity installed – a 53 per cent year-on-year increase – but this growth is not sufficient to ensure the world achieves net zero by 2050. The world needs to be installing wind power three times faster over the next decade in order to stay on a net zero pathway and avoid the worst impacts of climate change.....

......Today, there is now 743 GW of wind power capacity worldwide, helping to avoid over 1.1 billion tonnes of CO2 globally – equivalent to the annual carbon emissions of South America.

Yet, as the clean energy technology with the most decarbonization potential per MW, the report shows that the current rate of wind power deployment will not be enough to achieve carbon neutrality by the middle of this century, and urgent action must be taken by policymakers now to scale up wind power at the necessary pace.
>> Unquote.

There is, however, an element of misleading “sales talk” in these figures. The capacity factor of a wind turbine is its average power output divided by its maximum power capacity. On land, capacity factors range from 0.26 to 0.52. In the U.S. the fleet wide average capacity factor was 35%, so applying this to the global total of 743 GW would give an equivalent electrical output of only 260 GW or about a third of the installed capacity. 

Whilst one can understand the Global Wind Energy Council’s enthusiasm for their technology, it would be better for them to be more honest and realistic, and to quote the total energy generated as TeraWatthours (TWh) instead of talking up generation capacity! As a result one has to question their calculations in general and specifically their assumption that wind power is the only option. They also make no reference to its variability and the need to have backup generation available when wind power reduces unexpectedly.
Nevertheless, on an international scale, one can expect wind power to represent a larger and growing proportion of energy supplies.

Solar Photo-Voltaic

Power generation from solar photo-voltaic globally is estimated to have increased by 22% in 2019, to 720 TWh. With this increase, the solar PV share in global electricity generation is now almost 3%. In 2019, PV generation overtook bio-energy and is now the third-largest renewable electricity technology after hydropower and onshore wind.
Solar PV generation rose by 22% in 2019

Quoting from the International Energy Alliance June 2020 report << Solar PV electricity generation increased by 131 TWh globally in 2019, to account for 2.7% of the electricity supply. This growth was significantly lower than in 2018, however, because global solar PV capacity additions stalled in 2018 and China’s deployment further contracted in 2019.

From left to right solar PV additions - years 2017-2019

In China, solar PV capacity additions slowed for the second year in row to 30.1 GW in 2019. This expansion is significantly lower than the 53.1 GW in 2017, when the government phased out feed-in tariffs and introduced deployment quotas (in June 2018) to control costs and tackle grid integration challenges. Overall, this policy shift is expected to make solar PV technology more cost-competitive within and outside China, leading to more sustainable development over the longer term. A large number of subsidy-free projects were already in development in multiple provinces in 2019.

Solar PV generation rose sharply in Southeast Asia, driven by a surge in new capacity in Viet Nam from 0.1 GW to 5.4 GW. Capacity additions increased in the United States, the European Union, Latin America, the Middle East and Africa, which together compensated for the slowdown in China, resulting in a record year for PV deployment – 109 GW were installed in 2019.

Solar PV is well on track to reach the Sustainable Development Scenario (SDS) level by 2030, which will require electricity generation from solar PV to increase 15% annually, from 720 TWh in 2019 to almost 3 300 TWh in 2030.
>> Unquote.

Land area
Electricity generation from wind and solar energy is based on diffuse energy sources and on-shore based wind power is consequently land hungry. The graphic below illustrates the areas required for different energy generating sources for a capacity of 1000MW (1GW). The units are in square miles. To generate 1GW from wind would require about 300 square miles and from solar about 60 square miles.

In contrast fossil fuel power plants, and those using nuclear energy, are burning energy dense substances and so require only about 1 square mile. In terms of area, a gas fired plant would be comparable with a nuclear power station and a coal fired plant would be a little bigger due to the space required for stockpiling coal and ash.
In Europe, where most non-urban land is already farmed, I question the overall viability and acceptability of covering fields with solar panels. Near us, in South West France, there is an application to do just that on an area of land that we visit each spring to hear nightingales and look at orchids.

Offshore wind
Offshore wind turbines like the Dogger Bank, Wind Farm in the North Sea, have the advantage of not requiring land which could be used for other purposes although, as is reported from the USA, conflicts with fishing industries due to the presence of underground cables are likely.

Offshore wind turbines cost twice as much to install but they are also are more productive since there's almost always more wind off-shore than on land. It follows that countries with long coast lines in comparison with their land area, like the UK, are favourably placed to benefit from off-shore wind power but other countries, don’t have the same opportunities. 
Floating turbines would be able to take advantage of the higher wind velocities further out to sea if they are able to overcome disadvantages due to cost.

Variability of wind and solar
Wind power installations are normally expected to produce electricity 30-50% of the time depending on their location, but output is variable over both short and long term timescales. 

The daily mean wind power output for Great Britain during the summer of 2018.
based on data from

The variability of energy production by location can be an advantage since, if the grid network is sufficiently extensive, having installations in a diversity of locations can result in a degree of smoothing of output power levels.

On dull overcast days, however, solar photovoltaic (PV) power can be largely unproductive, especially in northern latitudes. So when demand peaks on cold winter evenings when there is no sunlight, if there is also no wind, these sources will not supply power.

Solar photovoltaic panels produce most efficiently in hot sunny places, like sparsely inhabited deserts. In certain places, if geo-political constraints involving distance and international borders can be overcome, it may be an economic proposition to generate solar power in one country and transfer it to another. Long transmission lines, with their associated costs and losses (in the USA in 2007 transmission losses were estimated at 6.5%), would then be needed to deliver the power to centres of population.

High Voltage DC lines have been used in some long distance situations. These have the advantage that the capacitance of the line and hence its charging current is no longer a length limiting consideration as it is with alternating current systems. One of the disadvantages is that DC voltages cannot be easily reduced by transformers without first utilizing inverters, with their associated costs and efficiencies, to recreate alternating current.

Dispatchable power
So both solar and wind power are, by their nature, highly variable and rarely provide continuous reliable output. In almost all electricity supply grids at present there is no significant storage capacity so, to meet the varying demand from consumers, electricity utility operators therefore have to schedule the right mix of flexible and inflexible power generation capacity from different types of generators. As part of the day to day management of the grid, this requires them to predict the weather conditions and hence the output from renewables. If there is an unpredictable drop in output from renewables, then flexible generation capacity must be very quickly brought on line. Electricity from flexible sources, known as “dispatchable power”, commands a much higher price in wholesale electricity markets than that from inflexible base load plants, so getting this right is therefore important for both utility companies and consumers. This paper from the US National Renewable Energy Laboratory explains the problem in detail.

If, as in Germany, there's a law forcing utilities to accept energy from renewables as a priority then, as the proportion of total generating capacity that wind and solar power provide increases, there will be an increasing need to maintain backup power supplies, in the form of spinning reserves, with their associated costs and energy consumption. If not the system would become unstable and power cuts would result.

Grid scale energy storage
In effect, without grid scale energy storage, to satisfy the demand when renewables can't, there will be a limit to the overall proportion of electricity production that can be provided by these non-dispatchable sources. At present grid scale storage is minimal so gas fired turbines are kept spinning at low power, in anticipation of a requirement for bringing higher outputs on line very rapidly.

The next article will deal with some of the many and varied ways of storing energy.


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