Difference between revisions of "Types of renewable energy"

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==Wind energy==
 
==Wind energy==
  
Wind is a form of indirect solar energy, produced by convection currents in warmed air. Wind has been used for millenia to produce mechanical power for milling corn and pumping water, but nowadays increasingly big wind turbines are used to produce electricity. The power available from wind depends very strongly on the wind's speed – it is proportional to the cube of wind speed – and wind speeds are faster the higher one gets above the ground, so taller turbines can produce much more power than shorter ones. Wind tends to be more consistent (less intermittent) at higher altitudes so taller turbines also have slightly higher capacity factors. Wind speeds at sea also tend to be higher than on land so offshore wind farms such as those in the  
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Wind is a form of indirect solar energy, produced by convection currents in warmed air.  
[https://en.wikipedia.org/wiki/List_of_offshore_wind_farms_in_the_North_Sea North Sea] can have capacity factors up to about 45%, although around 30% is more common for wind farms in general.
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Wind has been used for millenia to produce mechanical power for milling corn and pumping water,  
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but nowadays it is widely used to generate electricity, mostly via the familiar wind turbine.
  
However offshore wind farms are more expensive to build, and also more dangerous (in common with other maritime occupations, from fishing to oil and gas rig operations). Wind turbines also kill birds and bats. The numbers of birds killed are far fewer than those killed by domestic cats and by collisions with windows, but they tend to kill rarer, sometimes endangered, species such as eagles and other raptors.
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There are other designs of wind generator such as vertical axis machines, and also some work being done in using large tethered kites.
 
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The potential for wind energy in the UK is estimated by David MacKay in [[Sustainable Energy Without The Hot Air]]
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[https://withouthotair.com/c4/page_32.shtml pages 32-34], and Professor MacKay explains the physics of Wind Energy in  
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[https://withouthotair.com/cB/page_263.shtml pages 263-268].
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''More on [[Wind energy]]''
 
''More on [[Wind energy]]''

Revision as of 20:01, 30 November 2019


What is Renewable Energy?

Definitions vary but generally comprise energy sources which will last indefinitely from a human perspective. (There are no sources of energy which can actually be renewed from nothing – that would violate basic laws of Physics[1], and the concept of "renewable energy" has been criticised for the way its use has affected the way energy policy is debated and conducted[2]). Energy sources considered "renewable" include solar, wind, wave, tide, hydro, geothermal, and biomass. Wind, wave and biomass are derived from solar energy hitting the Earth and providing energy for plants to grow, evaporating water to create rain, and creating winds, which create waves. Geothermal energy comes partly from the decay of radioactive isotopes of Uranium, Thorium and Potassium in the Earths core, and partly from the heat remaining in the core from the time our whole planet was red hot. Tidal energy is derived from the kinetic energy of the Moon's orbiting of the Earth and the Earth's orbit of the Sun, and has the effect that very slowly the Moon is moving further away from the Earth.

Not all renewable energy is carbon-free, environmentally friendly, small-scale, or safe, and the word is often used politically to mean any non-fossil fuel energy source except nuclear energy. A more useful term would be "sustainable energy" (the term chosen by the late David MacKay for his excellent book Sustainable Energy Without The Hot Air) – energy which we can continue to use as much of as we need, without harmful consequences such as climate change, air pollution, and other environmental degradation, for the forseeable future.

Important qualities of energy sources are:

  • Despatchability – can it be turned on (and off) when needed?
Despatchability matters because supply of electricity has to be exactly matched to demand at every instant, so sources of energy which can be turned on and off – or up and down – at will are essential to avoiding power cuts.
  • Capacity Factor (or load factor) – what proportion of its maximum output it produces on average.
Capacity factor is important because when a generator, such as wind or solar, is producing less than its maximum output, then demand for energy has to be met from other sources — which are generally fossil fuels or biomass.
  • Energy Density – how much land is required to produce a given amount of energy.
Energy density tells us what proportion of our land is needed to meet our energy needs from a particular source. For example Britain simply does not have enough land to grow enough biomass to supply all our energy needs even if we wanted to.
The overall EROEI of all our energy sources determines how much energy our civilisation has to spare for activities like producing food, housing, transport, education, industry etc.

Various schemes have been proposed for powering regions, countries or even the entire world using only "renewables" – some further restricting choices by excluding hydro or biomass. Most of these plans are non-scientific offerings of anti-nuclear "environmentalist" organisations; those that have been peer-reviewed have not been found favourable by the IPCC's assessments.

Solar energy

The sun's energy can be exploited through passive solar buildings, for water heating or even cooking. Most usefully it can be used to generate electricity, via various technologies. Photovoltaic (PV) panels are the most familiar and widespread, but there are also concentrating solar power (CSP) plants and solar wind energy which uses convection currents in heated air to drive wind turbines in a large chimney structure.

There is also experimental work on using solar energy to make chemical fuels.

Main article on Solar energy

Wind energy

Wind is a form of indirect solar energy, produced by convection currents in warmed air. Wind has been used for millenia to produce mechanical power for milling corn and pumping water, but nowadays it is widely used to generate electricity, mostly via the familiar wind turbine.

There are other designs of wind generator such as vertical axis machines, and also some work being done in using large tethered kites.

More on Wind energy

Hydropower

The water cycle

Hydropower is another form of indirect solar energy, produced by the sun's radiation heating water (on land and in the oceans) making it evaporate and rise into the atmosphere where it condenses into clouds and falls as rain (or snow). Some of it falls in hills and mountains where it has the potential to release energy as it descends to lower altitudes (and eventually back to the sea).

The main ways of exploiting this energy are with water-wheels or turbines in flowing rivers, or by building dams creating artificial lakes or reservoirs which store large amounts of water which can drive turbines as it is released. Dams with turbines driving electrical generators can produce large amounts of electricity with good capacity factor and despatchably: they are turn-on-and-off-able, very quickly.

See also the EIA's article Hydropower explained, and main Hydropower article on this site.

Articles announcing that a country has run for so-many days on renewables alone, such as this and this about Costa Rica, often feature pictures of wind turbines and solar panels when the prime energy source is actually hydro.

Pumped hydro

A hydroelectric dam where water released from the dam is collected in a lower dam (or goes to the sea) can be arranged so that water can be pumped back from the lower reservoir (or sea) to the upper reservoir, where it can generate electricity again later. These sorts of pumped storage schemes act like enormous batteries, effectively storing electricity (although there is a trade-off: only about three-quarters of the electricity put into pumping up the storage comes back as electricity generated). Pumped storage schemes such as that at Dinorwig in North Wales and Diablo Canyon in California have long been used to match the constant output from baseload power stations, especially nuclear, to demands which tend to be lower at night, when the pumped system can use surplus electricity to pump water and then release it for extra generation during peak periods in the the daytime.

Pumped storage may also be able to partner with solar to provide electricity 24*7, in certain parts of the world such as the proposed Valhalla project in Northern Chile.

Safety and environmental

Hydroelectricity generally has a very low carbon footprint. Hydro dams are mostly quite safe, but when they do go wrong they can be very dangerous: the world's worst energy disaster (massively worse than Chernobyl) was the collapse of the Banqaio dam which killed around 200,000 people and made about 12 million homeless. Building dams often floods homes and displaces communities, and has large ecological impacts, especially downstream where patterns of river flow and flooding are disrupted by the dam. Silt carried in the river feeding the dam can also deposit in the dam reservoir, reducing its storage capacity. Climate change is likely to alter patterns of rainfall and is already impacting hydroelectric production in some parts of the world.

Wave energy

Wave energy is derived from the Sun's energy, via wind which acts on seas and other bodies of water to create waves. Like wind, wave energy is intermittent.

There are a variety of machines which have been designed to harness wave energy.

The physics and potential of wave energy, and ways to harvest it, are discussed in David MacKay's Sustainable Energy Without The Hot Air and Wikipedia's article on Wave power.

More on wave energy projects

Tidal energy

Unlike other energy sources tidal energy harnesses the kinetic energy of the Earth's rotation in the gravitational field of the Moon and the Sun. Tidal forces acting on Earth slow its rotation, very slowly increasing the length of our day. Harnessing tidal energy adds minutely to this slowing.

One way of harnessing tidal energy is to place turbines - like wind turbines - underwater, in the path of strong tidal currents. Another is to create a dam or lagoon to hold a body of water which can be allowed to flow to or from the sea when the tide has created a difference in level between the lagoon and the sea.

Like wind and solar, tidal energy is variable, but its fluctuations follow a precisely known pattern, increasing and decreasing twice a day. There is also a 14 day variation in how big the maximum is because of variation in the height between Spring and Neap tides. With suitable placing of tidal energy installations it should be possible to more-or-less even out the daily fluctuations, but not the Spring/Neap differences.

More on Tidal energy

Geothermal energy

Geothermal energy comes from the heat of the radioactive decay of isotopes in the Earth's crust, and heat from the Earth's molten core, which itself is partly due to the friction of the Moon's and Sun's tidal effect's on the Earth, but mostly the heat stored in the the core from when the Earth itself was red-hot as it had just formed.

David MacKay discusses the potential for either sustainable or short term geothermal energy in Sustainable Energy Without The Hot Air.

Some Geothermal energy projects are discussed in the article Geothermal energy

Biomass

The burning of wood, crop wastes and animal dung are the most widespread and ancient forms uses of this form of renewable energy. Their use causes air pollution which damages the health of billions of people, particularly women and children where the use of indoor stoves for cooking by the world's poorest people is widespread. Particulates from smoke can travel long distances and darken ice increasing the melting of glaciers and even ice caps. Demand for fuel drives deforestation and soil erosion. And burning biomass releases CO2 which could be sequestered in trees, grasses and soils if other fuels were available.

In the developed world the widespread use of biomass in power stations drives the destruction of old growth forests, in Europe and America, driven by European Union rules which classify it as carbon neutral. In Eastern Europe demand for wood for fuel may be driving illegal logging and the murder of forest rangers.

See pages on Biomass

Intermittency, capacity factor, grid integration

Renewables and grid reliability Challenges integrating renewables

ANALYSING TECHNICAL CONSTRAINTS ON RENEWABLE GENERATION TO 2050 A report to the Committee on Climate Change; Mar 2011

Huge Boost For Renewables' Output And Reliability Just From Location Planning Jeff McMahon; Forbes; 22 Apr 2016

California could boost its solar and wind energy output by nearly 50 percent and reduce volatility just by planning where new plants are installed, according to a Stanford economist. Solar and wind developers tend to cluster installations in locations that offer the highest revenues, said Frank Wolak, director of Stanford University’s Program on Energy and Sustainable Development. But these same locations accentuate volatility, raising the peaks when all are producing and deepening the troughs when all shut down.

Europe has adopted clean energy with so much gusto they've created a strange new problem Rebecca Harrington; Business Insider; 30 Mar 2016

Europe gets so much of its energy from renewables that many leading countries are now facing a new problem: updating their energy grids to handle it all.

Managing Flexibility Whilst Decarbonising the GB Electricity System - Executive Summary and Recommendations Energy Research Partnership; Aug 2015

The Energy Research Partnership has undertaken some modelling and analysis of the GB electricity system in the light of the carbon targets set by the Committee on Climate Change. Firstly a brief examination was made of the German and Irish markets with the hope of learning from their advanced penetration of variable renewables. Secondly a new model, BERIC, was written to simultaneously balance the need for energy, reserve, inertia and firm capacity on the system and its findings compared with simpler stacking against the load duration curve. The intention was to assess the need for flexibility on the system but some broader conclusions also emerged: A zero- or very low- carbon system with weather dependent renewables needs companion low carbon technologies to provide firm capacity
The modelling indicates that the 2030 decarbonisation targets of 50 or even 100 g/kWh cannot be hit by relying solely on weather dependent technologies like wind and PV alone. Simple merit order calculations have backed this up and demonstrated why this is the case, even with very significant storage, demand side measures or interconnection in support. There is a need to have a significant amount of zero carbon firm capacity on the system too - to supply dark, windless periods without too much reliance on unabated fossil. This firm capacity could be supplied by a number of technologies such as nuclear, biomass or fossil CCS

The Duck Pond Bonnie Marini; Power Engineering; 22 Mar 2016

The use of renewable power generation continues to grow around the globe. The challenge introduced with renewable generation is that it can be interrupted by timing and weather, and this variance affects the stability of the power produced. The sum of all generation must meet the demand at the very instant the demand is manifested-simply put, most of the electricity around the globe is produced and used in the very same moment. Without a solution for large-scale, cost-effective energy storage, the only way to fill the gaps in fluctuating generation from renewable resources is by partnering dispatchable power generation.
The California duck curve has become synonymous in the industry with the shape of renewable generation. The renewable duck generation rides on top of the rest of the generation portfolio, which is referred to as the duck pond. This paper discusses the changes in demand for this pond of dispatchable generating resources as they react to the presence and growth of the duck.

The Biggest Solar Breakthrough You've Never Heard Of William Pentland; Forbes; 12 Nov 2015

The breakthrough is a business model used to integrate distributed energy technologies into the mainstream electric grid.
For the first time in the history of the modern power grid, a non-utility, non-RTO entity called GridSolar is managing a part of the electric power grid. This would be illegal in any state other than Maine. GridSolar is demonstrating the value distributed generation, demand response and energy efficiency can provide to the power grid and ratepayers. In the process, it is turning the central argument made by utility trade groups against distributed energy on its head. Rather than imposing additional costs on ratepayers, distributed energy can significantly reduce the economic burden borne by ratepayers.

Balancing Europe’s wind-power output through spatial deployment informed by weather regimes Christian M. Grams, Remo Beerli, Stefan Pfenninger, Iain Staffell, Heini Wernli; Nature Climate Change letters; 17 July 2017

As wind and solar power provide a growing share of Europe’s electricity1, understanding and accommodating their variability on multiple timescales remains a critical problem. On weekly timescales, variability is related to long-lasting weather conditions, called weather regimes2, 3, 4, 5, which can cause lulls with a loss of wind power across neighbouring countries6. Here we show that weather regimes provide a meteorological explanation for multi-day fluctuations in Europe’s wind power and can help guide new deployment pathways that minimize this variability. Mean generation during different regimes currently ranges from 22 GW to 44 GW and is expected to triple by 2030 with current planning strategies. However, balancing future wind capacity across regions with contrasting inter-regime behaviour—specifically deploying in the Balkans instead of the North Sea—would almost eliminate these output variations, maintain mean generation, and increase fleet-wide minimum output. Solar photovoltaics could balance low-wind regimes locally, but only by expanding current capacity tenfold. New deployment strategies based on an understanding of continent-scale wind patterns and pan-European collaboration could enable a high share of wind energy whilst minimizing the negative impacts of output variability.

Weatherwatch: can we keep the lights on when the wind fails to blow? Kate Ravilious The Guardian; 9 Jan 2018

Rapid growth in both solar and wind (the UK now has more offshore wind power capacity than any other country in the world) has enabled the UK to achieve these impressive statistics, but will the rise in renewables also make UK power more vulnerable to the whims of British weather?
Researchers working on the European Climatic Energy Mixes project have been investigating future risk by assessing how the UK would fare with a repeat of the unusually cold winter of 2009-10. From mid-December 2009 a southward-displaced jet stream allowed cold air to pour in from eastern Europe, bringing widespread snow and plunging temperatures. The mean UK temperature for the entire winter was just 1.5C, the lowest since 1978-79 when it was 1.2C . As a result power demand surged, with electricity consumption between 10 and 20% above average on a number of occasions.
Back in 2010 renewables provided less than 10% of UK electricity. But similar weather now might create a strain. “The low wind conditions in a repeat of winter 2009-10 would lead to a substantial reduction in wind power production over the season, which could lead to increased risks to electricity supply availability when combined with an increased demand due to low temperatures,” writes meteorologist Emma Suckling from the University of Reading. Winters like this might be getting rarer, but we still need a contingency plan when the wind fails to blow.
China

China proposes $50+ trillion Global UHV grid connecting all power generation including massive wind farm at the North Pole by 2050 Next Big Future; 31 Mar 2016

China is proposing a $50+ trillion global energy grid. Global Energy Interconnection (GEI), a vision of a world power grid, was outlined by the State Grid Corporation of China ("State Grid"). It would be based upon a global network of Ultra High Voltage power lines connecting global power generation including massive wind farm at the North Pole and solar power from equatorial areas to energy users around the world.

China’s Vision of a Global Grid Zhenya Liu; The Energy Times; 22 Mar 2016

This is the first of a two-part series, excerpted and edited, from a speech by Zhenya Liu, chairman of the State Grid Corp. of China, delivered recently at IHS CERAWeek in Houston.

Marine - Tide and Wave

Will Tidal and Wave Energy Ever Live Up to Their Potential? SOPHIA SCHWEITZER; Yale Environment 360; 15 Oct 2015

As solar and wind power grow, another renewable energy source with vast potential — the power of tides and waves — continues to lag far behind. But progress is now being made as governments and the private sector step up efforts to bring marine energy into the mainstream.

IPCC special report on renewables

Special Report on Renewable Energy Sources and Climate Change Mitigation IPCC Working Group III; 2012

The IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation (SRREN) provides a comprehensive review concerning these sources and technologies, the relevant costs and benefits, and their potential role in a portfolio of mitigation options.
For the first time, an inclusive account of costs and greenhouse gas emissions across various technologies and scenarios confirms the key role of renewable sources, irrespective of any tangible climate change mitigation agreement.

Footnotes and References

  1. The Laws of Thermodynamics, which are as well-proven as Gravity, tell us that we cannot get energy from nothing, and that valuable forms of energy (such as electricity) inevitably degenerate into less useful forms (such as low-grade heat) - see for example this explanation at The Khan Academy
  2. "Abandoning the concept of renewable energy", Atte Harjanne, Janne M. Korhonen, Energy Policy, 29 Dec 2018 (The full article can be downloaded from this coauthor download link)
    Abstract
    Renewable energy is a widely used term that describes certain types of energy production. In politics, business and academia, renewable energy is often framed as the key solution to the global climate challenge. We, however, argue that the concept of renewable energy is problematic and should be abandoned in favor of more unambiguous conceptualization.
    Building on the theoretical literature on framing and based on document analysis, case examples and statistical data, we discuss how renewable energy is framed and has come to be a central energy policy concept and analyze how its use has affected the way energy policy is debated and conducted. We demonstrate the key problems the concept of renewable energy has in terms of sustainability, incoherence, policy impacts, bait-and-switch tactics and generally misleading nature. After analyzing these issues, we discuss alternative conceptualizations and present our model of categorizing energy production according to carbon content and combustion.
    The paper does not intend to criticize or promote any specific form of energy production, but instead discusses the role of institutional conceptualization in energy policy.