Renewable Energy – Electricity
Renewably sourced electricity has increased enormously in recent years from approximately 9% in 2011 to 37% in 2019. The renewable electricity technologies currently delivering electricity in the UK can now be considered mature and new projects are being installed on a market basis with little or no subsidy.
Of all electricity generated in 2019, 20% came from wind power – half from onshore, and half from offshore, bioenergy (mostly wood chip with some biogas from anaerobic digesters) 11.4%, solar photovoltaic 4%, and hydro 1.9%.
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The figures for 2020 are expected to be even higher due to a combination of new capacity installed after the beginning of 2019, and reduced demand due to the COVID 19 lock down. (The author is writing in June 2020).
In total in 2019, the UK used 324 TWh of electricity of which 119.3 TWh was categorised as renewable.
In the future, there will be two opposing trends re the use of electricity. The first is improved energy efficiency in lighting, appliances and industry, whilst the second of a trend towards energy use currently provided directly by burning fuels moving towards electrification. The later will almost certainly dominate as electric vehicles are increasingly adopted, heating is increasingly driven by electrically powered heat pumps, and industrial processes likewise are increasingly driven by electricity.
In addition to the mainstream renewables listed above, there are a number of technologies not yet mature enough to be economically viable without further research and development – some of which are likely to form part of the electricity mix in future years, and one which is not suitable to the UK geography and climate.
Less Common or Developing Renewable Technologies
Both tidal dams running off the rise and fall of the tide, and tidal stream powered by the movement of water in currents.
Advantages – a high degree of predictability and the potential for cost effective generation at scale.
Disadvantages – not yet mature, there may well be significant impacts on intertidal ecosystems from tidal dams, and potential marine life impacts from tidal stream turbines.
Using a wide variety of systems to convert the movement of water in waves into electricity.
Advantages – available for a larger proportion of the time than offshore wind with better predictability as waves continue for quite some time after wind has died down.
Disadvantages – many of the experimental devices deployed so far to develop the technology have been destroyed and sunk by extreme waves due to the very harsh environment of waves in a storm, and those which have succeeded technically still need refinement and learning curve to bring their cost down.
In theory, geothermal power could offer reliable baseload power anywhere on the planet. In practice, it is currently difficult and expensive to generate geothermal power outside geologically active zones i.e. areas with hot springs and volcanism.
In order for geothermal power to be generally and widely available in the UK, several technologies will need to be refined and made more cost effective.
Improved drilling techniques – preferably non-contact drilling capable of drilling deeper and faster than before at lower cost.
Improved resource identification – whilst the UK is not great for accessible geothermal resources, in certain areas, rocks get hot at shallower depths than others, whilst some localities will have fractured wet rocks, and others un-fractured dry rocks. Picking the best locations and avoiding the cost of abortive drilling can help lower cost.
Improved techniques for creating a heat exchanger – the areas in the UK with a reasonable thermal gradient tend to have dry rocks with minimal fracturing. If heat is to be extracted by deep drilling, there needs to be either a naturally occurring supply of steam or pressurised hot water, or the ability to create one by fracturing rock to create a heat exchanger between an injection well and an extraction well.
Whilst no geothermal power project is yet operating in the UK, The Eden Project has a geothermal system out for tender involving a first well to provide heat to the domes followed later by a second well and an engineered heat exchanger between the two wells 4.5 km down where the rock is at around 180 centigrade which will allow extraction of sufficient heat to run a power plant.
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Solar Thermal Power
In the right geological location solar thermal power produced by focusing the sun's rays to generate high temperatures can offer a cost effective reliable and predictable source of electricity when thermal storage is included. Unfortunately, there are two reasons why this system is poorly suited to the UK. First, the UK is not especially sunny so that a large proportion of potentially available solar power is delivered when the sky is at least partly overcast, and second, there is around a 5-fold difference in available solar energy between summer and winter meaning that even when conditions are sunny, solar thermal power cannot offer the reliable always available performance that can be obtained in North Africa, India and the like.
The Challenge of Intermittency
As a higher and higher proportion of electricity is generated by intermittent sources of renewable energy such as solar and wind, increasing challenges and grid balancing costs arise in regards to matching electricity supply and demand.
As sources such as wind and solar have no fuel cost, there is very little incremental cost incurred by keeping them running, so they are always given priority on the grid over gas and coal fired power which consequently have to ramp their output up and down to ensure supply and demand are matched.
Hydro power is typically also ramped in counter point to solar and wind output as it can largely be dispatched according to need thereby acting as a “battery” storing gravitational potential energy. There is also a special class of hydro – pumped storage in which at times of low demand and high output, water is pumped from a low reservoir to a high reservoir, with the reverse happening later at times of peak demand.
Other means helping to balance the grid are demand response - in which energy intensive industrial or commercial processes are on occasion started or stopped at the request of the grid operator to either absorb excess power, or make power available by cutting demand, (examples include large thermal loads, the production of industrial gases, and the charging of electric vehicles, and the installation of stationary batteries manageable in conjunction with the grid operator to similar effect).
Opponents of renewable energy tend to exaggerate grid management costs and to argue that intermittent power sources such as sun and wind are unreliable, however in a well-run power grid with a broad range of power sources, quite high levels of intermittent renewables can be accommodated at reasonable cost.
It should always be remembered that fuel will always be saved when wind and sun reduce the demand for fossil fuel electricity, and that such sources have their own issues with hidden costs in the form of pollution, and climate change.
Even with the above, it is sometimes necessary to curtail some output from wind and solar for the stability of the grid i.e. to turn off some solar farms and wind turbines. When this occurs owners are generally compensated to some degree for lost revenue depending on the details of their grid supply contract. This again is used by opponents of renewable energy as a stick to beat the industry with, though in reality curtailment usually affects a relatively small percentage of potential generation, and the payments received by developers for curtailment are contractual arrangements not too different from the availability payments received by gas power generators for standing by to ramp their output up or down to balance the grid.
As with anything, renewable energy carries some potential for adverse environmental impact, and no generation technology is ever likely to beat energy efficiency measures for low environmental impact. Also, not all renewable energy is equal, and in a few cases such as large dams in relatively flat regions of the tropics (large amounts of methane and CO2 are given off by decomposing vegetation), the production of corn ethanol, (high energy inputs during cultivation and processing) or palm oil used for biodiesel (if poorly managed, land use change and degradation of tropical rainforest), environmental impacts can be as damaging as conventional fuels.
It should be noted however that overall, the adverse impacts of well-designed and managed renewable energy systems are substantially less than for fossil fuel plant.
For this reason, as with any other projects, responsible project planners need to identify likely environmental impacts and seek to both manage and mitigate said impacts.
In the future, renewable electricity will continue to increase – most likely at increasing speed as generating costs per kWh are generally lower than any other system so that an ever greater proportion of intermittent power will be fed into the grid.
A number of increasingly smart technologies will be used in order to enable this expansion whilst maintaining the stability and reliability of the grid and keeping grid management costs acceptably under control.
These will include
Smart charging of an increasingly large fleet of electric vehicles to absorb power at less busy times mostly avoiding charging at times of peak demand.
Vehicle to grid where EVs will be able to earn revenue by exporting a proportion of their charge to the grid at times of peak demand. As a secondary benefit with the right systems, EVs will be able to provide resilience and backup during power outages.
Static batteries acting together under the control of an electricity supplier as a virtual power station.
Other longer term electricity storage technologies like new pumped storage plants, electricity to hydrogen, and thermal storage technologies such as liquid air and high temperature heat stores for use in conjunction with steam turbines.
Thermal storage technologies such as very large hot water tanks on heat networks,
Increased international electricity transmission capacity over long distances so that excess production in one place can be transmitted to another location with a deficit. (Typically if there is very little wind in Scotland, there is likely to be more wind in Spain or Morocco or vice versa).
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