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Renewable Energy Sources

Renewable Energy

 

Lets establish something here, renewable energy is a really, really good idea, the less dependent we become on finite sources of energy, the better. Except of course everything is ultimately finite on Earth, the wind may blow, the sun may shine, the waves may crash and the water may flow, but the raw materials to produce electricity from these sources are ultimately finite. However, it can be generally accepted that fossil fuels and uranium/plutonium will run out before sources of iron, copper, aluminium and gypsum for cement.

 

Wind Turbines

Wind turbines are a bit like marmite or Manchester United, from an “impact on the landscape” perspective, you either love them or you hate them. A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or pumping water, the device is called a windmill or wind pump. Turbines used in wind farms for commercial production of electric power are usually three-bladed and pointed into the wind by computer-controlled motors. These have high tip speeds of over 320 kilometres per hour (200 mph), high efficiency, and low torque ripple, which contribute to good reliability. The blades are usually coloured light gray to blend in with the clouds and range in length from 20 to 40 metres (66 to 130 ft) or more. The tubular steel towers range from 60 to 90 metres (200 to 300 ft) tall. The blades rotate at 10-22 revolutions per minute. At 22 rotations per minute the tip speed exceeds 300 feet per second (91 m/s). A gear box is commonly used for stepping up the speed of the generator, although designs may also use direct drive of an annular generator. Some models operate at constant speed, but more energy can be collected by variable-speed turbines which use a solid-state power converter to interface to the transmission system. All turbines are equipped with protective features to avoid damage at high wind speeds, by feathering the blades into the wind which ceases their rotation, supplemented by brakes. A 1.5 MW wind turbine of a type frequently seen in the UK has a tower 80 meters high. The rotor assembly (blades and hub) weighs 48,000 pounds (22,000 kg). The nacelle, which contains the generator component, weighs 115,000 pounds (52,000 kg). The concrete base for the tower is constructed using 58,000 pounds (26,000 kg) of reinforcing steel and contains 250 cubic yards of concrete. The base is 50 feet (15 m) in diameter and 8 feet (2.4 m) thick near the centre.
Small wind turbines may be as small as a fifty-watt generator for boat or caravan use. Small units often have direct drive generators, direct current output, aeroelastic blades, lifetime bearings and use a vane to point into the wind.
Larger, more costly turbines generally have geared power trains, alternating current output, flaps and are actively pointed into the wind. Direct drive generators and aeroelastic blades for large wind turbines are being researched.
A quantitative measure of the wind energy available at any location is called the Wind Power Density (WPD) It is a calculation of the mean annual power available per square meter of swept area of a turbine, and is tabulated for different heights above ground. Calculation of wind power density includes the effect of wind velocity and air density.

 

 

As of 1 January 2011, there were 283 operational wind farms in the UK, with 3,153 turbines and 5,204 MW of installed capacity. A further 2,506 MW worth of schemes are currently under construction, while another 6,208 MW have planning consent and some 9,102 MW are in planning awaiting approval.
When winds are outside the optimal range for wind turbines (5 to 25 m/s), they cannot generate any power. If this happens during a winter cold snap, when electrical demand reaches its highest levels of the year, conventional power sources must have the capacity of meeting that entire demand. A wind turbine operates automatically, self-starting when the wind reaches an average speed of 3–5 m/s (7 – 11 mph). It adjusts the pitch of its rotor blades to maintain an effective operating speed regardless of the strength of the wind, and to protect itself from strong winds.
The output increases with the wind speed until it reaches 13–14 m/s (29 – 34 mph). If the average wind speed exceeds the operational limit of 25 m/s (56 mph), the turbine stops.
1. A modern wind turbine has a maximum capacity of around 2000 kilowatts (kW) or 2 Megawatts (MW)
2. There are 8760 hours in a year (365 days x 24 hours)
3. A 2 MW wind turbine will generate around 30% of its maximum theoretical capacity resulting in 5256 Megawatt hours (MWh) generated per turbine per year
4. Taking all of the above into consideration a wind turbine will generate enough electricity for the average annual needs of around 1100 homes, using an average demand of 4700 kWh per house based on electricity consumption figures from Digest of UK Energy Statistics
Wind turbines usually operate 75-90% of the time – but not at full capacity.

 

 

Advantages

• Wind is free
• To all intents and purposes wind is infinite, at least when it blows
• Considered environmentally friendly and sustainable resource
• Considered a clean source of energy for those who believe in MMGW/AGW (we don’t)
• Some people consider the turbines attractive

Disadvantages

• Typical efficiency (kinetic energy to electricity) is around 30%
• Windy area’s tend to be near beauty spots, many consider wind farms a blot on the landscape, also means they are a distance from the grid, even more so for offshore
• Limited operating capacity for wind speeds between 7 mph and 25 mph
• Dangerous to birds, such as eagles, buzzards etc

 

Solar Power

Solar power is the conversion of sunlight into electricity. Sunlight can be converted directly into electricity using photovoltaics (PV), or indirectly with concentrated solar power (CSP), which normally focuses the sun’s energy to boil water which is then used to provide power, and other technologies, such as the sterling engine dishes which use a sterling cycle engine to power a generator. Photovoltaics were initially used to power small and medium-sized applications, from the calculator powered by a single solar cell to off-grid homes powered by a photovoltaic array.
The early development of solar technologies starting in the 1860s was driven by an expectation that coal would soon become scarce. However development of solar technologies stagnated in the early 20th century in the face of the increasing availability, economy, and utility of coal and petroleum. In 1974 it was estimated that only six private homes in all of North America were entirely heated or cooled by functional solar power systems. The 1973 oil embargo and 1979 energy crisis caused a reorganization of energy policies around the world and brought renewed attention to developing solar technologies. Deployment strategies focused on incentive programs such as the Federal Photovoltaic Utilization Program in the US and the Sunshine Program in Japan. Other efforts included the formation of research facilities in the US (SERI, now NREL), Japan (NEDO), and Germany (Fraunhofer Institute for Solar Energy Systems ISE).
Between 1970 and 1983 photovoltaic installations grew rapidly, but falling oil prices in the early 1980s moderated the growth of PV from 1984 to 1996. Since 1997, PV development has accelerated due to supply issues with oil and natural gas, global warming concerns, and the improving economic position of PV relative to other energy technologies. Photovoltaic production growth has averaged 40% per year since 2000 and installed capacity reached 10.6 GW at the end of 2007, and 14.73 GW in 2008.

 

 

Solar powered electrical generation relies on heat engines and photovoltaics. Solar energy’s uses are limited only by human ingenuity. A partial list of solar applications includes space heating and cooling through solar architecture, potable water via distillation and disinfection, daylighting, trickle charging batteries and torches, solar hot water, solar cooking, and high temperature process heat for industrial purposes. To harvest the solar energy, the most common way is to use solar panels.
Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic panels and solar thermal collectors to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favourable thermal mass or light dispersing properties, and designing spaces that naturally circulate air.
By 2008, there was just over 5,000 megawatts of solar PV cells installed worldwide. Operating at average efficiency of 20%, the combined output of all the PV cells in the world is now equal to the output of a single coal fired power-plant
It would take close to 220,000 square kilometres of solar panels to power the global economy via solar power. This may sound like a marginally manageable number until you realize that the total acreage covered by solar panels in the entire world right now is a paltry 10 square kilometres.

 

Tidal and Surge Energy

Tidal power, also called tidal energy, is a form of hydropower that converts the energy of tides into electricity or other useful forms of power. The first large-scale tidal power plant (the Rance Tidal Power Station) started operation in 1966.
Although not yet widely used, tidal power has potential for future electricity generation. Tides are more predictable than wind energy and solar power. Among sources of renewable energy, tidal power has traditionally suffered from relatively high cost and limited availability of sites with sufficiently high tidal ranges or flow velocities, thus constricting its total availability. However, many recent technological developments and improvements, both in design (e.g. dynamic tidal power, tidal lagoons) and turbine technology (e.g. new axial turbines, crossflow turbines), indicate that the total availability of tidal power may be much higher than previously assumed, and that economic and environmental costs may be brought down to competitive levels.

Tidal power can be classified into three generating methods:

1. Tidal stream generator

Tidal stream generators (or TSGs) make use of the kinetic energy of moving water to power turbines, in a similar way to wind turbines that use moving air. This method is gaining in popularity because of the lower cost and lower ecological impact compared to tidal barrages.

2. Tidal barrage

Tidal barrages make use of the potential energy in the difference in height (or head) between high and low tides. Barrages are essentially dams across the full width of a tidal estuary, and suffer from very high civil infrastructure costs, a worldwide shortage of viable sites and environmental issues.

3. Dynamic tidal power

Dynamic tidal power (or DTP) is a theoretical generation technology that would exploit an interaction between potential and kinetic energies in tidal flows. It proposes that very long dams (for example: 30–50 km length) be built from coasts straight out into the sea or ocean, without enclosing an area. Tidal phase differences are introduced by the dam, leading to a significant water level differential (at least 2–3 meters) in shallow coastal seas featuring strong coast-parallel oscillating tidal currents such as found in the UK, China and Korea. Each dam would generate power at a scale of 6 – 15 GW.

Wave power is the transport of energy by ocean surface waves, and the capture of that energy to do useful work — for example for electricity generation, water desalination, or the pumping of water (into reservoirs).
Wave power is distinct from the diurnal flux of tidal power and the steady gyre of ocean currents. Wave power generation is not currently a widely employed commercial technology although there have been attempts at using it since at least 1890. In 2008, the first experimental wave farm was opened in Portugal, at the Aguçadoura Wave Park.

Marine energy or marine power (also sometimes referred to as ocean energy or ocean power) refers to the energy carried by ocean waves, tides, salinity, and ocean temperature differences. The movement of water in the world’s oceans creates a vast store of kinetic energy, or energy in motion. This energy can be harnessed to generate electricity to power homes, transport and industries.
The term marine energy encompasses both wave power — power from surface waves, and tidal power — obtained from the kinetic energy of large bodies of moving water. Offshore wind power is generally confused as a form of marine energy, but is not as wind power is derived from the wind, even if the wind turbines are placed over water.
The oceans have a tremendous amount of energy and are close to many if not most concentrated populations. Many researches show that ocean energy has the potentiality of providing for a substantial amount of new renewable energy around the world.

The total power of waves breaking on the world’s coastlines is estimated at 2-3 million MW. In favourable locations, wave energy density can average 65 MW per mile of coastline. Three approaches to capturing wave energy are:

  1. Floats or pitching devices – these devices generate electricity from the bobbing or pitching action of a floating object. The object can be mounted to a floating raft or to a device fixed on the ocean floor.
  2. Oscillating water columns – these generate electricity from the wave-driven rise and fall of water in a cylindrical shaft. The rising and falling water column drives air into and out of the top of the shaft, powering an air-driven turbine.
  3. Wave surge or focusing devices – these shoreline devices, also called ‘tapered channel’ or ‘tapchan’ systems, rely on a shore-mounted structure to channel and concentrate the waves, driving them into an elevated reservoir. Water flow out of this reservoir is used to generate electricity, using standard hydropower technologies.

Ocean thermal

Oceans cover more than 70% of the Earth’s surface, making them the world’s largest solar collectors. Each day, the oceans absorb enough heat from the Sun to equal the thermal energy contained in 250 billion barrels of oil. Ocean Thermal Energy Conversion Systems (OTEC) convert this thermal energy into electricity – often while producing desalinated water.
Three types of OTEC systems can be used to generate electricity:

  1. Closed-cycle plants circulate a working fluid (such as ammonia which has a low boiling point) in a closed system, heating it with warm seawater, flashing it to vapour, routing the vapour through a turbine, and then condensing it with cold seawater.
  2. Open-cycle plants flash the warm seawater to steam and route the steam through a turbine.
  3. Hybrid plants flash the warm seawater to steam and use that steam to vaporise a working fluid in a closed system.

OTEC systems can be land-based, mounted on the ocean shelf or floating.

 

 

Geothermal Energy

Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is energy that determines the temperature of matter. Earth’s geothermal energy originates from the original formation of the planet, from radioactive decay of minerals, from volcanic activity, and from solar energy absorbed at the surface. The geothermal gradient, which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of heat from the core to the surface.
From hot springs, geothermal energy has been used for bathing since Paleolithic times and for space heating since ancient Roman times, but it is now better known for electricity generation. Worldwide, about 10,715 megawatts (MW) of geothermal power is online in 24 countries. An additional 28 gigawatts of direct geothermal heating capacity is installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications.

 

 

Geothermal power is cost effective, reliable, sustainable, and environmentally friendly, but has historically been limited to areas near tectonic plate boundaries. Recent technological advances have dramatically expanded the range and size of viable resources, especially for applications such as home heating, opening a potential for widespread exploitation. Geothermal wells release greenhouse gases trapped deep within the earth, but these emissions are much lower per energy unit than those of fossil fuels. As a result, geothermal power has the potential to help mitigate global warming if widely deployed in place of fossil fuels.
The Earth’s geothermal resources are theoretically more than adequate to supply humanity’s energy needs, but only a very small fraction may be profitably exploited. Drilling and exploration for deep resources is very expensive. Forecasts for the future of geothermal power depend on assumptions about technology, energy prices, subsidies, and interest rates.

 


Ground Heat Pump

Ground source heat pumps (GSHP) are a proven renewable energy technology, designed to take solar energy from the ground, and use it to meet the heating and hot water requirements of an entire household. They are set to revolutionise the way homes are heated in the future.

The heat pump replaces the need for a boiler and can satisfy all a households heating and hot water requirements.

 

A GSHP circulates water and antifreeze around a loop of pipes which is buried in your garden, this loop of pipes is commonly known as a ground loop. The heat in the ground is then absorbed into the fluid and is pumped through a heat exchanger which is located in the heat pump. The lower grade heat is then passed through the heat pump compressor and is concentrated into a higher temperature which can then heat your home. Ground loop fluid which then cools, passes back into the ground where it then absorbs more energy from the ground. This process then begins again, it is continuous whilst the heating is required. You can have a small amount of ground loop or a larger amount depending on the size of your home and depending on the size of your garden. The ground loop can either be laid flat in your garden, coiled or if you are limited in space you can install a vertical loop into the ground about 100 metres in depth. Although heat pumps do use electricity when they are running, the heat that they extract is renewed naturally. They do not use high temperatures like boilers as their temperature is much lower over longer periods. Radiators powered by GSHP are never red hot to touch like boiler powered radiators so in winter they have to be left on all the time in order to heat your house sufficiently.

Alternative Energy Feasability

Energy Density Few people realize how much energy is concentrated in even a small amount of oil or gas. A barrel of oil contains the energy-equivalent of almost 25,000 hours of human labour. A single gallon of petrol contains the energy-equivalent of 200-to-500 hours of human labour. Most people are stunned to find this out, …

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