It consists of three sections with the arrows going from the first section to the second and from the second to the third. The first section shows the renewable resources, with the examples such as moving water, biomass, wind, sunshine, the Earth.

The second one presents technology and equipment showing the examples of hydroelectric and wind turbines, wood stoves and furnaces, photovoltaic panels.

The third section displays usable energy with the examples of electricity, industrial steam, heat for space and water, biofuels. The natural flow of water in rivers offers kinetic power that can be transformed into usable energy. Early usages included mechanical power for transformation activities, such as milling and sawing, and for irrigation.

As well, rivers have been used for transportation purposes, such as moving logs from forests to industrial centers. Currently, hydroelectricity is the major form of usable energy produced from flowing water. To produce hydroelectricity, the water flow is directed at the blades of a turbine, making it spin, which causes an electrical generator connected to the turbine to spin as well and thus generate electricity.

The amount of energy extracted from flowing water depends on the volume of water and its speed. Usually, a hydroelectric station is built at a sharp incline or waterfall to take advantage of the speed gained by the water as a result of gravity.

Dams are built at some locations to help regulate the flow of water and, therefore, the electricity generation. Canada has many rivers flowing from mountainous areas toward its three bordering oceans. In , Canada had hydroelectric stations with 78, megawatts of installed capacity.

These stations include small hydroelectric facilities, that is, facilities with a nameplate capacity of 50 megawatts or less, and they together represent 3. The bars of different heights show provincial capacities as follows:.

All the hydroelectric stations in Canada generated This accounted for Canada is the second largest producer of hydroelectricity in the world. Hydroelectric stations have been developed in Canada where the geography and hydrography were favourable, particularly in Quebec.

Other areas producing large quantities of hydroelectricity include British Columbia, Newfoundland and Labrador, Manitoba, and Ontario. Bioenergy comprises different forms of usable energy obtained from materials referred to as biomass.

A biomass is a biological material in solid, liquid or gaseous form that has stored sunlight in the form of chemical energy. Excluded from this definition is organic material that has been transformed over long periods of time by geological processes into substances such as coal or petroleum.

Several types of biomass can be used, with the proper technology and equipment, to produce energy. The most commonly used type of biomass is wood, either round wood or wood waste from industrial activities. Wood and wood waste can be combusted to produce heat used for industrial purposes, for space and water heating, or to produce steam for electricity generation.

Through anaerobic digestion, methane can be produced from solid landfill waste or other biomass materials such as sewage, manure and agricultural waste. Sugars can be extracted from agricultural crops and, through distillation, alcohols can be produced for use as transportation fuels.

As well, numerous other technologies exist or are being developed to take advantage of other biomass feedstock. With its large landmass and active forest and agricultural industries, Canada has access to large and diversified biomass resources that can be used for energy production.

Currently, bioenergy is the second most important form of renewable energy in Canada. Historically, the use of wood has been very important in Canada for space and water heating, as well as for cooking. It is still important today, as 4.

Every year, over petajoules of energy from wood are consumed in the residential sector, representing more than 7 per cent of residential energy use. The most important type of biomass in Canada is industrial wood waste, especially waste from the pulp and paper industry, which is used to produce electricity and steam.

Every year, more than petajoules of bioenergy are used in the industrial sector. The pulp and paper industry is by far the largest industrial user of bioenergy, which accounts for more than half of the energy used in this industry.

At the end of , Canada had 70 bioenergy power plants with a total installed capacity of 2, megawatts, and most of this capacity was built around the use of wood biomass and spent pulping liquor, as well as landfill gas.

In , 8. Most of the biomass-fired capacity was found in provinces with significant forestry activities: British Columbia, Ontario, Quebec, Alberta and New Brunswick.

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JavaScript appears to be disabled on this computer. Please click here to see any active alerts. Want to expand renewable energy use in your jurisdiction? Become a Green Power Community. Local governments can dramatically reduce their carbon footprint by purchasing or directly generating electricity from clean, renewable sources.

Local governments can lead by example by generating energy on—site, purchasing green power, or purchasing renewable energy. Green energy has the capacity to replace fossil fuels in the future, however it may require varied production from different means to achieve this.

Geothermal, for example, is particularly effective in places where this resource is easy to tap into, while wind energy or solar power may be better suited to other geographic locations.

However, by bringing together multiple green energy sources to meet our needs, and with the advancements that are being made with regards to production and development of these resources, there is every reason to believe that fossil fuels could be phased out.

We are still some years away from this happening, but the fact remains that this is necessary to reduce climate change, improve the environment and move to a more sustainable future. Understanding the economic viability of green energy requires a comparison with fossil fuels.

The fact is that as easily-reached fossil resources begin to run out, the cost of this type of energy will only increase with scarcity. At the same time as fossil fuels become more expensive, the cost of greener energy sources is falling.

Other factors also work in favour of green energy, such as the ability to produce relatively inexpensive localised energy solutions, such as solar farms. The interest, investment and development of green energy solutions is bringing costs down as we continue to build up our knowledge and are able to build on past breakthroughs.

Efficiency in green energy is slightly dependent on location as, if you have the right conditions, such as frequent and strong sunlight, it is easy to create a fast and efficient energy solution. However, to truly compare different energy types it is necessary to analyse the full life cycle of an energy source.

This includes assessing the energy used to create the green energy resource, working out how much energy can be translated into electricity and any environmental clearing that was required to create the energy solution.

Currently, wind farms are seen as the most efficient source of green energy as it requires less refining and processing than the production of, for example, solar panels.

Advances in composites technology and testing has helped improve the life-span and therefore the LEC of wind turbines.

However, the same can be said of solar panels, which are also seeing a great deal of development. Green energy solutions also have the benefit of not needing much additional energy expenditure after they have been built, since they tend to use a readily renewable source of power, such as the wind.

Renewable energy sources are currently ranked as follows in efficiency although this may change as developments continue :. Green energy provides real benefits for the environment since the power comes from natural resources such as sunlight, wind and water.

Constantly replenished, these energy sources are the direct opposite of the unsustainable, carbon emitting fossil fuels that have powered us for over a century.

Creating energy with a zero carbon footprint is a great stride to a more environmentally friendly future. If we can use it to meet our power, industrial and transportation needs, we will be able to greatly reduce our impact on the environment. As we touched upon earlier, there is a difference between green, clean and renewable energy.

This is slightly confused by people often using these terms interchangeably, but while a resource can be all of these things at once, it may also be, for example, renewable but not green or clean such as with some forms of biomass energy.

Green energy is that which comes from natural sources, such as the sun. Clean energy are those types which do not release pollutants into the air, and renewable energy comes from sources that are constantly being replenished, such as hydropower, wind power or solar energy.

Renewable energy is often seen as being the same, but there is still some debate around this. However, a source such as wind power is renewable, green and clean — since it comes from an environmentally-friendly, self-replenishing and non-polluting source.

Readily replenished, these energy sources are not just good for the environment, but are also leading to job creation and look set to become economically viable as developments continue. The fact is that fossil fuels need to become a thing of the past as they do not provide a sustainable solution to our energy needs.

By developing a variety of green energy solutions we can create a totally sustainable future for our energy provision, without damaging the world we all live on.

TWI has been working on different green energy projects for decades and has built up expertise in these areas, finding solutions for our Industrial Members ranging from electrification for the automotive industry to the latest developments in renewable energy.

Contact us to find out more and see how we could help advance your energy project: contactus twi. enewable energy comes from sources or processes that are constantly replenished.

These sources of energy include solar energy, wind energy, geothermal energy, and hydroelectric power. Clean energy is energy that comes from renewable, zero emission sources that do not pollute the atmosphere when used, as well as energy saved by energy efficiency measures.

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This means that not all sources used by the renewable energy industry are green. For example, power generation that burns organic material from sustainable forests may be renewable, but it is not necessarily green, due to the CO 2 produced by the burning process itself.

Green energy sources are usually naturally replenished, as opposed to fossil fuel sources like natural gas or coal, which can take millions of years to develop. Green sources also often avoid mining or drilling operations that can be damaging to eco-systems.

The main sources are wind energy, solar power and hydroelectric power including tidal energy, which uses ocean energy from the tides in the sea. This common type of renewable energy is usually produced using photovoltaic cells that capture sunlight and turn it into electricity.

Solar power is also used to heat buildings and for hot water as well as for cooking and lighting. Solar power has now become affordable enough to be used for domestic purposes including garden lighting, although it is also used on a larger scale to power entire neighbourhoods.

Particularly suited to offshore and higher altitude sites, wind energy uses the power of the flow of air around the world to push turbines that then generate electricity.

Also known as hydroelectric power, this type of green energy uses the flow of water in rivers, streams, dams or elsewhere to produce electricity. Hydropower can even work on a small scale using the flow of water through pipes in the home or can come from evaporation, rainfall or the tides in the oceans.

While this resource requires drilling to access, thereby calling the environmental impact into question, it is a huge resource once tapped into. Geothermal energy has been used for bathing in hot springs for thousands of years and this same resource can be used for steam to turn turbines and generate electricity.

The energy stored under the United States alone is enough to produce 10 times as much electricity as coal currently can.

Find out more about geothermal energy. Biomass power plants use wood waste, sawdust and combustible organic agricultural waste to create energy.

While the burning of these materials releases greenhouse gas these emissions are still far lower than those from petroleum-based fuels. Rather than burning biomass as mentioned above, these organic materials can be transformed into fuel such as ethanol and biodiesel.

Having supplied just 2. Green energy is important for the environment as it replaces the negative effects of fossil fuels with more environmentally-friendly alternatives.

Derived from natural resources, green energy is also often renewable and clean, meaning that they emit no or few greenhouse gases and are often readily available.

Even when the full life cycle of a green energy source is taken into consideration, they release far less greenhouse gases than fossil fuels, as well as few or low levels of air pollutants.

This is not just good for the planet but is also better for the health of people and animals that have to breathe the air. Green energy can also lead to stable energy prices as these sources are often produced locally and are not as affected by geopolitical crisis, price spikes or supply chain disruptions.

The economic benefits also include job creation in building the facilities that often serve the communities where the workers are employed. Renewable energy saw the creation of 11 million jobs worldwide in , with this number set to grow as we strive to meet targets such as net zero.

Due to the local nature of energy production through sources like solar and wind power, the energy infrastructure is more flexible and less dependent on centralised sources that can lead to disruption as well as being less resilient to weather related climate change.

Green energy also represents a low cost solution for the energy needs of many parts of the world. This will only improve as costs continue to fall, further increasing the accessibility of green energy, especially in the developing world.

There are plenty of examples of green energy in use today, from energy production through to thermal heating for buildings, off-highway and transport. Many industries are investigating green solutions and here are a few examples:.

These include solar water heaters, biomass fuelled boilers and direct heat from geothermal, as well as cooling systems powered by renewable sources. Renewable heat for industrial processes can be run using biomass or renewable electricity.

Hydrogen is now a large provider of renewable energy for the cement, iron, steel and chemical industries. Sustainable biofuels and renewable electricity are growing in use for transportation across multiple industry sectors.

Automotive is an obvious example as electrification advances to replace fossil fuels, but aerospace and construction are other areas that are actively investigating electrification.

Green energy has the capacity to replace fossil fuels in the future, however it may require varied production from different means to achieve this. Geothermal, for example, is particularly effective in places where this resource is easy to tap into, while wind energy or solar power may be better suited to other geographic locations.

However, by bringing together multiple green energy sources to meet our needs, and with the advancements that are being made with regards to production and development of these resources, there is every reason to believe that fossil fuels could be phased out.

Heat is extracted from geothermal reservoirs using wells or other means. Reservoirs that are naturally sufficiently hot and permeable are called hydrothermal reservoirs, whereas reservoirs that are sufficiently hot but that are improved with hydraulic stimulation are called enhanced geothermal systems.

Once at the surface, fluids of various temperatures can be used to generate electricity. The technology for electricity generation from hydrothermal reservoirs is mature and reliable, and has been operating for more than years.

Hydropower harnesses the energy of water moving from higher to lower elevations. It can be generated from reservoirs and rivers. Reservoir hydropower plants rely on stored water in a reservoir, while run-of-river hydropower plants harness energy from the available flow of the river.

Hydropower reservoirs often have multiple uses - providing drinking water, water for irrigation, flood and drought control, navigation services, as well as energy supply.

Hydropower currently is the largest source of renewable energy in the electricity sector. It relies on generally stable rainfall patterns, and can be negatively impacted by climate-induced droughts or changes to ecosystems which impact rainfall patterns.

The infrastructure needed to create hydropower can also impact on ecosystems in adverse ways. For this reason, many consider small-scale hydro a more environmentally-friendly option , and especially suitable for communities in remote locations. Ocean energy derives from technologies that use the kinetic and thermal energy of seawater - waves or currents for instance - to produce electricity or heat.

Ocean energy systems are still at an early stage of development, with a number of prototype wave and tidal current devices being explored. The theoretical potential for ocean energy easily exceeds present human energy requirements.

Bioenergy is produced from a variety of organic materials, called biomass, such as wood, charcoal, dung and other manures for heat and power production, and agricultural crops for liquid biofuels.

Most biomass is used in rural areas for cooking, lighting and space heating, generally by poorer populations in developing countries. Modern biomass systems include dedicated crops or trees, residues from agriculture and forestry, and various organic waste streams.

Energy created by burning biomass creates greenhouse gas emissions, but at lower levels than burning fossil fuels like coal, oil or gas.

However, bioenergy should only be used in limited applications, given potential negative environmental impacts related to large-scale increases in forest and bioenergy plantations, and resulting deforestation and land-use change.

International Energy Agency Renewables. Using sawmill or logging residues however is not contentious. Some EU states have developed biomass sustainability criteria. A new technology, Pavegen , uses pavement tiles about one metre square to harvest energy from pedestrian traffic.

A footfall on a tile will flex it about 5mm and result in up to 8 watts of power over the duration of the footstep. Electricity can be stored, used directly for lighting, or in other ways. In the context of sustainable development it shares many of the benefits of many renewables, it is a low-carbon energy source, it has a very small environmental impact, similarities that are in sharp contrast to fossil fuels.

Nuclear fission power reactors do use a mineral fuel, and demonstrably but minimally deplete the available resources of that fuel. In the future nuclear power will make use of fast neutron reactors.

As well as utilizing about 60 times the amount of energy from uranium, they will unlock the potential of using even more abundant thorium as a fuel. In addition, some 1. The consequence of this is that the available resource of fuel for fast neutron reactors is so plentiful that under no practical terms would the fuel source be significantly depleted.

Most also tend to make very large demands on resources to construct the plant used for harnessing the natural energy — per kilowatt hour produced, much more than nuclear power. Wind turbine plants need over ten times the amount of steel, 15 times the amount of copper and more than twice the amount of other critical minerals than nuclear power per kWh output.

Inertia is a key element of electricity grid stability. To compensate for the lack of synchronous inertia in generating plant when there is high dependence on wind and solar sources, synchronous condensers, sometimes known as rotating stabilisers, may be added to the system.

These are high-inertia rotating machines that can support the grid network in delivering efficient and reliable synchronous inertia and can help stabilize frequency deviations by generating and absorbing reactive power.

They behave like a synchronous motor with no load, providing reactive power and short-circuit power to the transmission network. Synchronous condensers syncons are like synchronous motors with no load and not mechanically connected to anything.

They may be supplemented by a flywheel to increase inertia. They are used for frequency and voltage control in weak parts of a grid or where there is a high proportion of variable renewable input requiring grid stability to be enhanced.

Adding synchronous condensers can help with reactive power needs, increase short-circuit strength and thus system inertia, and assure better dynamic voltage recovery after severe system faults. They can compensate for either a leading or lagging power factor, by absorbing or supplying reactive power measured in volt-ampere reactive, VAr to the line.

Static synchronous compensators STATCOM have a voltage control function, but not the full syncon function. A leading application is in Germany, where a highly variable flow from offshore wind farms in the north is transmitted to the main load centres in the south, leading to voltage fluctuations and the need for enhanced reactive power control.

The reduced inertia in the entire grid made the need to improve short-circuit strength and frequency stability more critical. Amprion has ordered two MVAr static synchronous compensators STATCOM from Siemens for Polsum in North Rhine-Westphalia and Rheinau in Baden-Württemberg to help stabilize the power grid as conventional plant closures increase the loss of inertia risk with increasing volatility from renewables.

Also a large GE synchronous condenser is installed at Bergrheinfeld in Bavaria. Following a state-wide blackout, South Australia is installing two GE synchronous condensers at Davenport near Port Augusta and two Siemens units at Robertstown to compensate for a high proportion of wind input to the grid and reduce the vulnerability to further problems from this.

These are connected to the kV grid. Also a MVAr Siemens machine is installed at the MWe Kiamal solar PV farm just across the Victorian border near Ouyen. GE has converted a MWe generator retired from a coal-fired plant to a synchronous condenser of over MVAr, and such conversions, powered from the grid, are often cost-effective.

After the MWe Biblis A nuclear power plant in Germany was retired in its generator was converted to a synchronous condenser. In the UK, Statkraft plans to install two GE rotating stabilisers to provide stability services to the transmission network in Scotland.

These would draw about 1 MWe from the grid and enable many times that of intermittent renewable input, replacing the role of inertia in fossil-fuel or nuclear plants for frequency control.

The project is among five innovative grid stability contracts awarded by the National Grid electricity system operator in January GE quotes rotor mass of tonnes for its horizontal axis 65 MVAr machine and t for a MVAr vertical axis machine compared with over t for a large conventional power plant.

In the small Denmark grid, five machines are required to dampen the effect of about 5 GWe of wind capacity. It has a MVAr Siemens syncon at Bjaerskov. Siemens quotes horizontal axis units up to MVAr, ABB up to MVAr, and GE to MVAr.

Some newer wind turbines are directly coupled and run synchronously at fixed grid-defined rotation speeds, providing some frequency stability, although less total energy output than with DC output.

Centralised state utilities focused on economies of scale can easily overlook an alternative model — of decentralized electricity generation, with that generation being on a smaller scale and close to demand. Here higher costs may be offset by reduced transmission losses not to mention saving the capital costs of transmission lines and possibly increased reliability.

Generation may be on site or via local mini grids. In some places pumped hydro storage is used to even out the daily generating load by pumping water to a high storage dam during off-peak hours and weekends, using the excess base-load capacity from low-cost coal or nuclear sources.

During peak hours this water can be used for hydro-electric generation. It is not well suited to filling in for intermittent, unscheduled generation such as wind, where surplus power is irregular and unpredictable. In , GWh was supplied from pumped storage according to IRENA. There is increasing interest in off-river pumped hydro ORPH storage, with pairs of reservoirs having at least metres height difference.

Building power storage emerged in as a defining energy technology trend. See companion information paper on Electricity and Energy Storage. It is clear that renewable energy sources have considerable potential to meet mainstream electricity needs.

However, having solved the problems of harnessing them there is a further challenge: of integrating them into the supply system where most demand is for continuous, reliable supply. Obviously sun, wind, tides and waves cannot be controlled to provide directly either continuous dispatchable power to meet base-load demand, or peak-load power when it is needed, so how can other, dispatchable sources be operated so as to complement them?

If there were some way that large amounts of electricity from intermittent variable renewable energy VRE producers such as solar and wind could be stored efficiently, the contribution of these technologies to supplying electricity demand would be much greater — see preceding subsection.

The only renewable source with built-in storage and hence dispatchable on demand is hydro from dams. The storage can be enhanced by pumping back water when power costs are low, and such dammed hydro schemes can be complemented by off-river pumped hydro.

This requires pairs of small reservoirs in hilly terrain and joined by a pipe with pump and turbine. There is some scope for reversing the whole way we look at power supply, in its hour, 7-day cycle, using peak load equipment simply to meet the daily peaks.

Conventional peak-load equipment can be used to some extent to provide infill capacity in a system relying heavily on VRE sources such as wind and solar. Its characteristic is rapid start-up, usually apart from dammed hydro with low capital and high fuel cost.

Such capacity complements large-scale solar thermal and wind generation, providing power at short notice when they were unable to.

This is essentially what happens with Denmark, whose wind capacity is complemented by a major link to Norwegian hydro as well as Sweden and the north German grid. West Denmark the main peninsula part is the most intensely wind-turbined part of the planet, with 1.

In , 3. On two occasions, in March and April, wind supplied more than total demand for a few hours. In February during a cold calm week there was virtually no wind output. However, all this can be and is managed due to the major interconnections with Norway, Sweden and Germany, of some MWe, MWe and MWe respectively.

Furthermore, especially in Norway, hydro resources can normally be called upon, which are ideal for meeting demand at short notice. though not in after several dry years. So the Danish example is a very good one, but the circumstances are far from typical.

The report from a thorough study commissioned by the German Energy Agency DENA looked at regulating and reserve generation capacity and how it might be deployed as German wind generation doubled to The study found that only a very small proportion of the installed wind capacity could contribute to reliable supply.

This all involves a major additional cost to consumers. The performance of every UK wind farm can be seen on the Renewable Energy Foundation website.

Note particularly the percentage of installed capacity which is actually delivering power averaged over each month. If hydro is the back-up and is not abundant, it will be less available for peaking loads. If gas is the back-up this will usually be the best compromise between cost and availability.

But any conventional generating plants used as back-up for VRE sources has to be run at lower output than designed to accommodate the intermittent input, and then the lower capacity factor can make them uneconomic, as is now being experienced with many GWe of gas and coal capacity in Germany.

The higher the proportion of intermittent input to a system, the greater the diseconomy. This incidentally has adverse CO 2 emissions implications. See sections below.

This value decline caused by wind and solar generating most of their output during times of self-imposed electricity oversupply is marked and it magnifies with their share increasing. This price effect is not compensated by the price peaks enjoyed by reliable producers when those renewables are insufficient.

The price volatility is a major disincentive to investment in new plant, whether nuclear or renewable, if not regulated or subsidized. Since wind and solar PV output correlates with meteorological conditions across a wide area, an increased proportion of them also means that the average price received by those producers — especially solar PV — declines significantly as their penetration increases, magnifying this value decline.

At a penetration level of Nevertheless, VRE sources make an important contribution to the world's energy future, even if they cannot carry the main burden of supply. The Global Wind Energy Council expects wind to be able to supply between In the OECD International Energy Agency IEA published a report on this issue : The Power of Transformation , wind, sun and the economics of flexible power systems.

It said that the cost-effective integration of variable renewable energy VRE has become a pressing challenge for the energy sector. Meanwhile Germany provides a case study in accelerated integration of VRE into a stable system, with both politically- and economically-forced retirement of conventional generating capacity.

See also the information paper on Energiewende. Thus the PTC meant that intermittent wind generators could dump power on the market to the extent of depressing the wholesale price so that other generators were operating at a loss.

This market distortion has created major problems for the viability of dispatchable generation sources upon which the market depends.

Grid management authorities faced with the need to be able to dispatch power at short notice treat wind-generated power not as an available source of supply which can be called upon when needed but as an unpredictable drop in demand.

Thus, building 25 GWe of wind capacity, equivalent to almost half of UK peak demand, will only reduce the need for conventional fossil and nuclear plant capacity by 6.

Also, some 30 GWe of spare capacity will need to be on immediate call continuously to provide a normal margin of reserve and to back up the wind plant's inability to produce power on demand — about two-thirds of it being for the latter. Ensuring both secure continuity of supply reliably meeting peak power demands and its quality voltage and frequency control means that the actual potential for wind and solar input to a system is limited.

Doing so economically, as evident from the above UK figures, requires low-cost back-up such as hydro, or gas turbine with cheap fuel. Nuclear power plants are essentially base-load generators, running continuously. Where it is necessary to vary the output according to daily and weekly load cycles, for instance in France, where there is a very high reliance on nuclear power, they can be adapted to load-follow.

For BWRs this is reasonably easy without burning the core unevenly, but for a PWR as in France to run at less than full power for much of the time depends on where it is in the 18 to month refueling cycle, and whether it is designed with special control rods which diminish power levels throughout the core without shutting it down.

So while the ability on any individual PWR reactor to run on a sustained basis at low power decreases markedly as it progresses through the refueling cycle, there is considerable scope for running a fleet of reactors in load-following mode.

Generation III plants and small modular reactors have more scope for load-following, and as fast neutron reactors become more established, their ability in this regard will be an asset. If electricity cannot be stored on a large scale, the next logical step is to look at products of its use which can be stored, and hence where intermittent electricity supply is not a problem.

In contrast to renewable hydro, the feed-in of wind and solar output is uncontrollably intermittent due to the uncertainty of meteorological conditions. In grid management terms they are not dispatchable.

Therefore the energy system needs backup capacity from the on-demand-sources to bridge periods with high or low generation from renewables. To some extent battery storage can help, though most grid-scale battery installations are more for ancillary services frequency control etc.

rather than energy storage. See also Electricity and Energy Storage information page. But that is not the main problem. Wind and solar power supply is largely governed by wind speed and the level of sunlight, which can only loosely be related to periods of power demand.

It is this feature of intermittent renewable power supply that results in the imposition of additional costs on the generating system as a whole. The third category of intermittent renewable integration cost is grid interconnection.

Wind and solar farms are ideally sited in areas that experience high average wind speeds and high average solar radiation respectively.

These sites are often, even typically, distant from areas of electricity demand. Transmission and distribution networks will often need to be extended significantly to connect sources of supply and demand - this is a current challenge in UK and North Germany.

The impact of high levels of intermittent, low cost power will be to reduce the load factors of base-load power generators, and thereby increase their unit costs per kilowatt-hour.

Given the high capital costs of nuclear, such an impact will significantly increase the levelised generation costs of nuclear. Hydrogen is widely seen as a possible fuel for transport, if certain problems can be overcome economically. It may be used in conventional internal combustion engines, or in fuel cells which convert chemical energy directly to electricity without normal burning.

Making hydrogen requires either reforming natural gas methane with steam, or the electrolysis of water. The former process has carbon dioxide as a by-product, which exacerbates or at least does not improve greenhouse gas emissions relative to present technology. With electrolysis, the greenhouse burden depends on the source of the power.

But if these sources are used for electricity to make hydrogen, then they can be utilised fully whenever they are available, opportunistically. Broadly speaking it does not matter when they cut in or out, the hydrogen is simply stored and used as required.

However, electrolysers are inefficient at low capacity factors such as even dedicated wind or solar input would supply. A quite different rationale applies to using nuclear energy or any other emission-free base-load plant for hydrogen.

Here the plant would be run continuously at full capacity, with perhaps all the output being supplied to the grid in peak periods and any not needed to meet civil demand being used to make hydrogen at other times.

About 55 kWh is required to produce a kilogram of hydrogen by electrolysis at ambient temperature, so the cost of the electricity clearly is crucial. Renewable energy sources have a completely different set of environmental costs and benefits to fossil fuel or nuclear generating capacity.

On the positive side they emit no carbon dioxide or other air pollutants beyond some decay products from new hydro-electric reservoirs , but because they are harnessing relatively low-intensity energy, their 'footprint' — the area taken up by them — is necessarily much larger.

Whether Australia could accept the environmental impact of another Snowy Mountains hydro scheme providing some 3.

Whether large areas near cities dedicated to solar collectors will be acceptable, if such proposals are ever made, remains to be seen.

Beyond utilising roofs, MWe of solar capacity would require at least 20 square kilometres of collectors, shading a lot of country. In Europe, wind turbines have not endeared themselves to neighbours on aesthetic, noise or nature conservation grounds, and this has arrested their deployment in UK.

At the same time, European non-fossil fuel obligations have led the establishment of major offshore wind forms and the prospect of more. However, much environmental impact can be reduced.

Fixed solar collectors can double as noise barriers along highways, roof-tops are available already, and there are places where wind turbines would not obtrude unduly.

In an open market, government policies to support particular generation options such as renewables normally give rise to explicit direct subsidies along with other instruments such as feed-in tariffs, quota obligations and energy tax exemptions.

In the EU, feed-in tariffs are widespread. Corresponding to these in the other direction are taxes on particular energy sources, justified by climate change or related policies.

For instance Sweden taxes nuclear power at about EUR 0. European Environment Agency figures in gave indicative estimates of total energy subsidies in the EU for solid fuel coal EUR Thus, various schemes are operating in Europe, mainly feed-in tariffs, fixed premiums, green certificate systems and tendering procedures.

These schemes are generally complemented by tax incentives, environmental taxes, contribution programs or voluntary agreements. France had a feed-in tariff of EUR 8. Germany's Renewable Energy Sources Act gives renewables priority for grid access and power dispatch.

It is regularly amended to adapt feed-in tariffs to market conditions and technological developments. For wind energy an initial tariff applies for up to 20 years and this then reduces to a basic tariff of EUR 5.

The initial tariff is EUR 9. Denmark has a wide range of incentives for renewables and particularly wind energy. It has a complex 'Green Certificate' scheme which transfers the subsidy cost to consumers. However, there is a further economic cost borne by power utilities and customers.

When there is a drop in wind, back-up power is bought from the Nordic power pool at the going rate. Similarly, any surplus subsidised wind power is sold to the pool at the prevailing price, which is sometimes zero. The net effect of this is growing losses as wind capacity expands.

Spain has different levels of feed-in tariffs depending on the technology used. A fixed tariff of EUR 7. The tariffs for renewables are adjusted every four years. Greece has a feed-in tariff of 6. The UK has not used any feed-in tariff arrangement, but is to do so from Meanwhile a specific indication of the cost increment over power generation from other sources is given by the 4.

In addition there is a Climate Change Levy of 0. Sweden subsidises renewables principally large-scale hydro by a tax on nuclear capacity, which works out at about EUR 0. For wind, there is a quota system requiring utilities to buy a certain amount of renewable energy by purchasing certificates.

In the USA the wind energy production tax credit PTC of 1. In Australia energy retailers are required to source specified quantities of power from new non hydro renewables. In India ten out of 29 states have feed-in tariffs, eg 2.

OECD NEA , Nuclear Energy and Renewables — system effects in low-carbon electricity systems. Ryan Zimmerling et al. Renewable Energy and Electricity Updated August There is widespread popular support for using renewable energy, particularly solar and wind energy, which provide electricity without giving rise to any carbon dioxide emissions.

Harnessing these for electricity depends on the cost and efficiency of the technology, which is constantly improving, thus reducing costs per peak kilowatt, and per kWh at the source.

Utilising electricity from solar and wind in a grid becomes problematical at high levels for complex but now well-demonstrated reasons. Supply does not correspond with demand.

Back-up generating capacity is required due to the intermittent nature of solar and wind. System costs escalate with increasing proportion of variable renewables. Policy settings to support renewables are generally required to confer priority in grid systems and also subsidise them, and some 50 countries have these provisions.

Utilising solar and wind-generated electricity in a stand-alone system requires corresponding battery or other storage capacity. The possibility of large-scale use of hydrogen in the future as a transport fuel increases the potential for both renewables directly and base-load electricity supply off-peak.

System effects are often divided into the following four broadly defined categories: Profile costs also referred to as utilisation costs or backup costs by some researchers. Balancing costs.

Grid costs. Connection costs to the grid sometimes included in LCOE. Demand for clean energy There is a fundamental attractiveness about harnessing such forces in an age which is very conscious of the environmental effects of burning fossil fuels, and where sustainability is an ethical norm. The prospects, opportunities and challenges for renewables are discussed below in this context.

Load curves for typical electricity grid source: VENcorp This load curve diagram shows that much of the electricity demand is in fact for continuous supply base-load , while some is for a lesser amount of predictable supply for about three-quarters of the day, and less still for variable peak demand up to half of the time; some of the overnight demand is for domestic hot water systems on cheap tariffs.

Source: Vencorp Most electricity demand is for continuous, reliable supply that has traditionally been provided by base-load electricity generation. Rivers and hydroelectricity Hydroelectric power, using the potential energy of rivers, is by far the best-established means of electricity generation from renewable sources.

Green Rigg wind farm in the UK Image: EDF Energy In Germany, with high dependence on wind, there is corresponding high uncertainty of supply.

Solar energy Solar energy is readily harnessed for low temperature heat, and in many places domestic hot water units with storage routinely utilise it.

Photovoltaic PV systems The best-known method utilises light, ideally sunlight, acting on photovoltaic cells to produce electricity. Solar thermal systems, concentrating solar power CSP Solar thermal systems need sunlight rather than the more diffuse light which can be harnessed by solar PV.

Both Dii and MSP appear to be moribund. CSP boost to fossil fuel power, hybrid systems Solar energy producing steam can be used to boost conventional steam-cycle power stations. Solar updraft tower Another kind of solar thermal plant is the solar updraft tower, using a huge chimney surrounded at its base by a solar collector zone like an open greenhouse.

Direct heating A significant role of solar energy is that of direct heating. Geothermal energy The core of the Earth is very hot, and temperature in its crust generally rises 2. Ocean energy This falls into three categories — tidal, wave and temperature gradient, described separately below.

Tidal energy — barriers, tidal range Harnessing the tides with a barrage in a bay or estuary has been achieved in France MWe in the Rance Estuary, since , Canada 20 MWe at Annapolis in the Bay of Fundy, since , South Korea Sihwa , MWe, since , and Russia White Sea, 0.

Tidal energy — tidal stream Placing free-standing turbines in major coastal tidal streams appears to have greater potential than barriers, and this is being developed. Wave energy Harnessing power from wave motion has the potential to yield significant electricity.

Ocean thermal energy Ocean thermal energy conversion OTEC has long been an attractive idea, but is unproven beyond small pilot plants up to 50 kWe, though in a kWe closed cycle plant was commissioned in Hawaii and connected to the grid. Biomass Beyond traditional direct uses for cooking and warmth, growing plant crops particularly wood to burn directly or to make biofuels such as ethanol and biodiesel has a lot of support in several parts of the world, though mostly focused on transport fuel.

Pedestrian traffic A new technology, Pavegen , uses pavement tiles about one metre square to harvest energy from pedestrian traffic. Rotating stabiliser synchronous machines Inertia is a key element of electricity grid stability. Large batteries can provide some virtual inertia for frequency control.

Decentralized energy Centralised state utilities focused on economies of scale can easily overlook an alternative model — of decentralized electricity generation, with that generation being on a smaller scale and close to demand.

Electricity storage at utility scale In some places pumped hydro storage is used to even out the daily generating load by pumping water to a high storage dam during off-peak hours and weekends, using the excess base-load capacity from low-cost coal or nuclear sources.

Intermittent renewables in relation to base-load demand It is clear that renewable energy sources have considerable potential to meet mainstream electricity needs.

Case study: West Denmark West Denmark the main peninsula part is the most intensely wind-turbined part of the planet, with 1.