The non-renewables are the three fossil fuels and nuclear:
- Natural gas
- Nuclear fuels (uranium and plutonium)
They will all 'run out' one day.
They all do damage to the environment.
They provide most of our energy.
The renewables are:
These will never run out.
Most of them do damage to the environment, but in less nasty ways than non-renewables.
The trouble is they don't provide much energy and some of them are unreliable because they depend on weather.
Burning Energy Sources
Most of the energy we use is generated from the four non-renewable sources of energy (coal, oil, natural gas and nuclear) in big power stations, which are all pretty much the same apart from the boiler.
Basic features of a typical power station:
1) The fossil fuel is burnt to convert its stored chemical energy into heat (thermal) energy.
2) The heat energy is used to heat water (or air in some fossil-fuel power stations) to produce steam.
3) The steam turns a turbine, converting heat energy into kinetic energy.
4) The turbine is connected to a generator, which transfers kinetic energy into electrical energy.
Nuclear reactors are just fanncy boilers.
1) A nuclear powerstation is mostly the same as a typical one, but with nuclear fission of uranium or plutonium producing the heat to make the steam to drive the turbines, etc.
The uranium or plutonium fuel rods heat the water to produce steam, which goes to the turbine, which returns to the boiler as water.
2) Nuclear power stations take the longest of all the power stations to start up. Natural gas power stations take the shortest time of all the fossil fuel power stations.
- 1) This involves putting lots of little windmills (wind turbines) up in exposed places like on moors or round coasts.
- 2) Each wind turbine has its own generator inside it. The electricity is generated directly from the wind turning the blades, which turn the generator.
- 3) There's no pollution (except for a little bit when they are manufactured).
- 4) But they do spoil the view. You need about 1500 wind turbines to replace one coal-fired power station and 1500 of them cover a lot of ground - which would have a big effect on the scenery.
- 5) And they can be very noisy, which can be annoying for people living nearby.
- 6) There's also the problem of no power when the wind stops, and it's impossible to increase supply when there's extra demand.
- 7) The initial costs are quite high, but there are no fuel costs and minimal running costs.
- 8) There's no permenant damage to the landscape - if you remove the turbines, you remove the noise and the view returns to normal.
- 1) Solar cells generate electrical currents directly from sunlight. Solar cells are often the best source of energy for calculators and watches which don't use much electricity.
- 2) Solar power is often used in remote places where there's not much choice (e.g. the Australian outback) and to power electric road signs and satellites.
- 3) There's no pollution. (Although they do use quite a lot of energy to manufacture in the first place.)
- 4) In sunny countries solar power is a very reliable source of energy - but only in the daytime.
- 5) Initial costs are high but after that the energy is free and running costs are almost nil.
- 6) Solar cells are usually used to generate electricity on a relatively small scale, e.g. powering individual homes.
- 7) It's often not practical or too expensive to connect them to the National Grid - the cost of connecting them to the National Grid can be enormous compared with the value of the electricity generated.
- 1) Hydroelectric power usually requires the flooding of a valley by building a dam.
- 2) Rainwater is caught and allowed out through turbines. There is no pollution.
- 3) But there is a big impact on the environment due to the flooding of the valley (rotting vegetation releases methane and CO2) and possible loss of habitat for some species (sometimes the loss of whole villages). The resevoirs can also look very unsightly when they dry up. Putiing hydroelectric power stations in remote valleys tends reduce their impact on humans.
- 4) A big advantage is it can provide an immediate response to an increased demand for electricity.
- 5) Theres no problem with reliability except in times of drought - but remember this is Great Britain we are talking about.
- 6) Initial costs are high, but there's no fuel and minimal running costs.
- 7) It can be a useful way to generate electricity on a small scale in remote areas.
- 1) Most large power stations have huge boilers which have to be kept running all night even though demand is very low. This means there's a surplus of electricity at night.
- 2) It's surprisingly difficult to find a way of storing this spare energy for later use.
- 3) Pumped storage is one of the best solutions.
- 4) In pumped storage, 'spare' night-time electricity is used to pump waterup to a higher reservoir.
- 5) This can then be released quickly during periods of peak demand such as at teatime each evening, to supplement the steady delivery from the big power stations.
- 6) Remember, pumped storage uses the same idea as hydroelectric power, but it isn't a way of generating power - it's simply a way of storing energy which has already been generated.
- 1) You need lots of small wave-powered turbines located around the coast.
- 2) As waves come in to the shore they provide an updown motion which can be used to drive a generator.
- 3) There is no pollution. The main problems are spoiling the view and being a hazard to boats.
- 4) They are fairly unreliable, since waves tend to die out when the wind drops.
- 5) Initial costs are high, but there are no fuel costs and minimal running costs. Wave power is never likely to provide energy on a large scale, but it can be very useful on small islands.
- 1) Tidal barrages are big dams built across river estuaries, with turbines in them.
- 2) As the tide comes in it fills up the estuary to a height of several metres - it also drives the turbines. This water can then be allowed out through the turbines at a controlled speed.
- 3) The source of the energy is the gravity of the sun and the moon.
- 4) There is no pollution. The main problems are preventing free access by boats, spoling the view and altering the habitat of the wildlife, e.g. wading birds, sea creatures and beasties who live in the sand.
- 5) Tides are pretty reliable in the sense that thy happen twice a day without fail, and always near to the predicted height. The only drawback is that the height of the tide is variable so lower (neap) tides will provide significantly less energy than 'spring' tides. They also dont work when the water level is the same either side of the barrage - this happens four times a day because of the tides. But tidal barrages are excellent for storing energy ready for periods of peak demand.
- 6) Initial costs are moderately high, but there are no fuel costs and minimal running costs. Even though it can only be used in some of the most suitable estuaries tidal power has the potential for generating a significant amount of energy.
- 1) This is only possible involcanic areas where hot rocks lie quite near to the surface. The source of much of the heat is the slow decay of various radioactive elements, including uranium, deep inside the Earth.
- 2) Steam and hot water rise to the surface and are used to drive a generator.
- 3) This is actually brilliant free energy with no real environmental problems.
- 4) In some places, geothermal heat is used to heat buildings directly, without being converted to electrical energy.
- 5) The main draw back with geothermal energy is there aren't very many suitable locations for power plants.
- 6) Also, the cost of building a power plant is often high compared to the amount of energy we can get out of it.
1) Biofuels are renewable energy resources. They're used to generate electricity in exactly the same way as fossil fuels - they're burnt to heat up water.
2) They can be also used in some cars - just like fossil fuels.
3) Biofuels can be solids (e.g. straw, nutshells and woodchips), liquids (e.g. ethanol) or gases (e.g. methane 'biogas' from sludge digesters).
Sludge digesters are used in sewage processing.
4) We can get biofuels from organisms that are still alive or from dead organic matter - like fossil fuels, but from organisms that have been living much more recently.
5) E.g. crops like sugar cane can be fermented to produce ethanol, or plant oils can be modified to produce biodiesel.
Non-Renewables - Environmental Problems
- All three fossil fuels (coal, oil and gas) release CO2 into the atmosphere when they're burned. For the same amount of energy produced, coal releases the most CO2, folowed by oil then gas. All this CO2 adds to the greenhouse effect, and contributes to global warming.
- Burning coal and oil releases sulfur dioxide, which causes acid rain. Acid rain can be harmful to trees and soils and can have far-reaching effects in ecosystems.
- Acid rain can be reduced by taking the sulfur out before the fuel is burned, or cleaning up the emissions.
- Coal mining makes a mess of the landscape, especially "open-cast mining".
- Oil spillages cause serious environmental problems, affecting mammals and birds that live in and around the sea. We try to avoid them, but they'll always happen.
- Nuclear power is clean but the nuclear waste is very dangerous and difficult to disspose of.
- Nuclear fuel (i.e. uranium) is a relatively cheap but the overall cost of nuclear power is high due to the cost of the power plant and final decommissioning.
- Nuclear power always carries the risk of a major catastrophe like the Chernobyl disaster is 1986.
1) Bio fuels are a relatively quick and 'natural' source of energy and are supposedly carbon neutral.
2) There is still debate into the impact of biofuels on the environment, once the full energy that goes into the production is considered
- The plants that grew to produce the waste (or to feed the animals that produced the dung) absorbed carbon dioxide from the atmosphere as they were growing. When the waste is burnt, this CO2 is re-released into the atmosphere. So it has a neutral effect on the atmospheric CO2 levels (although this only really works if you keep growing plants at the same rate you're burning things). Biofuel production also creates methane emissions - a lot of this comes from the animals.
3) In some regions, large areas of forest have been cleared to make room to grow biofuels, resulting in lots of species losing their natural habitats. The decay and burning of this vegetation also increases CO2 and methane emissions.
4) Biofuels have potential, but their use is limited by the amount of available farmland that can be dedicated to their production.
1) Carbon capture and storage (CCS) is used to reduce the amount of CO2 building up in the atmosphere and reduce the strength of the greenhouse effect.
2) CCS works by collecting the CO2 from power stations before it is released into the atmosphere.
3) The captured CO2 can then be pumped into empty gas fields and oil fields like those under the North Sea. It can be safely stored without adding to the greenhouse effect.
4) CCS is a new technology that's developing quickly. New ways of storing CO2 are being explored, including CO2 dissloved in seawater at the bottom of the ocean and capturing CO2 with algae, which can then be used to produce oil that can be used as a biofuel.
Setting Up a Power Station
Because coal and oil are running out fast, many old coal- and oil-fired power stations are being taken out of use. Often they're being replaced by gas-fired power stations because they're quick to set up, there's still a lot of gas left and gas doesn't pollute as badly as coal and oil.
But gas is not the only option.
When looking at the options for a new power station, there are several factors to consider:
How much it costs to set up and run, how long it takes to build, how much power it can generate, etc.
Then there are also the trickier factors like damage to the environment and impact on local communities. And because these are often very contentious issues, getting permision to build certain types of power station can be a long-running process, and hence increase the overall set-up time. The time and cost of decommisioning (shutting down) a power plant can also be a crucial factor.
Renewable resources often need bigger power stations than non-renewables for the same output.
And as you'd expect, the biggeer the power station the more expensive.
Nuclear reactors and hydroelectric dams also need huge amounts of engineering to make them safe, which bumbs up the cost.
Set Up / Decommissioning Time
The set up / decommissioning time are both affected by the size of the power station, the complexity of the engineering and also the planning issues (e.g. discussions over whether a nuclear power station should be built on a stretch of beautiful coastline can last years).
Gas is one of the quickest to set up.
Nuclear power stations take by far the longest (and cost the most) to decommission.
All the non-renewables are reliable energy providers (until they run out).
Many of the renewable sources depend on the weather, which means they're pretty unreliable here in the UK.
The exceptions are tidal power and geothermal (which don't depend on weather).
Running / Fuel Costs
Renewables usually have the lowest running costs, because there's no actual fuel involved.
If there's a fuel involved, they'll be waste pollution and you'll be using up resources,
If it relies on the weather, it's often got to be in an exposed place.
- Amospheric Pollution: Coal, Oil, Gas
- Visual Pollution: Coal, Oil, Gas, Nuclear, Tidal, Waves, Wind, Hydroelectric
- Using Up Resources: Coal, Oil, Gas, Nuclear
- Noise Pollution: Coal, Oil, Gas, Nuclear, Wind
- Disruption of Habitats: Hydroelectric, Tidal, Biofuels
- Disruption of Leisure Activities (e.g. boats): Waves, Tidal
- Other Problems: Nuclear (dangerous waste, explosions, contamination), Hydroelectric (dams bursting)
A power station has to be near to the stuff it relies on.
- Solar - pretty much anywhere, the sunnier the better
- Gas - pretty much anywhere there's piped gas (most of the UK)
- Hydroelectric - hilly, rainy places with floodable valleys, e.g. the Lake District, Scottish Highlands
- Wind - exposed, windy places like moors and coasts or out at sea
- Oil - near the coast (oil transported by sea)
- Waves - on the coast
- Coal - near coal mines, e.g. Yorkshire, Wales
- Nuclear - away from people (in case of disaster), near water (for cooling)
- Tidal - big river estuaries where a dam can be built
- Geothermal - fairly limited, only in places where hot rocks are near the Earth's surface
1) The National Grid takes electrical energy from power stations to where it's needed in homes and industry.
2) It enables power to be generated aywhere on the grid, and then supplied anywhere else on the grid.
3) To transmit the huge amount of power needs, you need either a high voltage or a high current.
4) The problem with a high current is that you lose loads of energy through heat in the cables.
5) It's much cheaper to boost the voltage up really high (to 400000 V) and keep the current very low.
Pylons and Transformers
1) To get the voltage to 400000 V to transmit power requires transformers as well as big pylons with huge insulators - but it's still cheaper.
2) The transformers have to step the voltage up at one end, for efficient transmission, and then bring it back down to safe, usable levels at the other end.
3) The voltage is increased ('stepped up') using a step-up transformer.
4) Then its reduced again ('stepped down') at the consumer end using a step-down transformer.
Different Way to Transmit Electricity
Electrical energy can be moved around by cables buried in the ground, as well as over head power lines. Each of these different options has its pros and cons.
PROS: low setup cost, easy to access, easy to set up, minimal disturbance to land.
CONS: lost of maintenance needed, they look ugly, can be affected by weather, less reliable.
PROS: minimal maintenance, hidden, not affected by weather, more reliable.
CONS: higher setup cost, hard to access, hard to set up, lots of disturbance to land.
Supply and Demand
1) The National Grid needs to generate and direct all the energy that the country needs - our energy demands keep on increasing too.
2) In order to meet these demands in the future, the energy supplied to the National Grid will need to increase, or the energy demands of consumers need to decrease.
3) In the future, supply can be increased by opening more power plants or increasing their power output (or by doing both).
4) Demand can be reduced by consumers using more energy-efficient appliances, and being more carfeul not to waste energy in the home (e.g. turning off lights or running washing machines at cooler temperatures).
Amplitude, Wavelength & Frequency
Waves transfer energy from one place to another without transferring any matter (stuff).
1) The amplitude is the displacement from the rest position to the crest (NOT from a trough to a crest).
2) The wave length is the length of a full cycle of the wave, e.g. from crest to crest.
3) Frequency is the number of complete waves passing a certain point per second OR the number of waves produced by a source each second. Frequency is measured in hertz (Hz). 1 Hz is 1 wave per second.
Most waves are transverse:
- Light and all other EM waves
- Ripples on water
- Waves on strings
- A slinky spring wiggled up and down
In TRANSVERSE waves the vibrations are perpendicular (at 90 degrees) to the direction of energy transfer of the wave.
Examples of longitudinal waves are:
- Sound waves and ultra sound
- Shock waves, e.g. seismic waves
- A slinky spring when you push the end
(Rarefractions and Compressions)
In LONGITUDINAL waves the vibrations are parallel to the direction of energy transfer of the wave.
Wave Speed = Frequency x Wavelength
UNITS: (m/s) = (Hz) x (m)
v = f x λ
Speed (v is for velocity) = Frequency x Wavelength
The speed of a wave is usually independent of the frequency or amplitude of the wave.
Reflected, Refracted, Diffracted
When waves arrive at an obstacle (or meet a new material), their direction of travel can be changed.
This can happen by reflection or by refraction or diffraction.
1) Reflection of light is what allows us to see objects - light bounces off them into our eyes.
2) When light travelling in the same direction reflects from an uneven surface such as a piece of paper, the light reflects off at different angles.
3) When light travelling in the same direction reflects from an uneven surface (smooth and shiny like a mirror) then it's all reflected at the same angle and you get a clear reflection.
4) The law od reflection applies to every reflected ray:
Angle of INCIDENCE = Angle of REFLECTION
Note that these angles are ALWAYS defined between the ray itself and the normal.
The normal is an imagery line that's perpendicular (at right angles) to the surface at the point of incidence (where light hits the surface).
Drawing a Ray Diagram
How an image is formed in a PLANE MIRROR.
Learn these important points:
1) The image is the same size as the object.
2) It is as far behind the mirror as the object is in front.
3) The image is virtual and upright. The image is virtual because the object appears behind the mirror.
4) The image is laterally inverted - the left and right sides are swapped, i.e. the object'sleft side becomes its right side in the image.
Diffraction & Refraction
1) Reflection's quite straightforward, but there are other ways waves can be made to change direction.
2) They can be refracted - which means they go through a new material orr change direction.
3) Or they can be diffracted - the waves'bend round' obstacles, causing the waves to spread out.
1) All waves spread out ('diffract') at the edges when they pass through a gap or pass an obstacle.
2) The amount of diffraction depends on the size of the gap relative to the wavelength of the wave. The narrower the gap, or the longer the wave length, the more the wave spreads out.
3) A narrow gap is one that is the same order of magnitude as the wave length of the wave - i.e. they're about the same size.
4) So whether the gap counts as narrow of not depends on the wave in question.
5) Light has a very small wavelength (about 0.0005mm), so it can be diffracted but it needs a really small gap.
1) When a wave crosses a boundary between two substances (e.g. from glass to air) it changes direction.
2) Whwn light shines on a glass window pane, some of the light is reflected, but a lot of it passes through the glass and gets refracted as it does so.
3) Waves are only refracted if they meet a new medium at an angle.
4) If they're travelling along the normal (i.e. the angle of incidence is zero) they will change speed, but are NOT refracted - they don't change direction.
Spectrum of EM Waves
Electromagnetic waves with different wave lengths (or frequencies) have different properties. We group them into seven basic types, but the different regions actually merge to form a continuous spectrum. They're shown with increasing frequency and energy (decreasing wavelength) from left to right.
Radiowaves, Microwaves, Infrared, Visible Light, Ultra Violet, X-Rays, Gamma Rays
Ronald McDonald Invented Veggie Lunches Using Extra Garlic
1) EM waves vary in wavelength from around 10-15m to more than 104m.
2) All the different types of EM wave travel at the same speed (3 x 108 m/s) in a vacuum (e.g. space).
3) EM waves with higher frequencies have shorter wavelengths.
4) Because of their different properties, different EM waves are used for different purposes.
- 1) Radio waves are EM radiation with wavelengths longer than about 10 cm.
- 2) Long-wave radio (wavelengths of 1-10 km) can be transmitted from London, say, and received halfway around the world. That's because long wavelengths diffract (bend) around the curved surface of the Earth.
- 3) Long-wave radio wavelengths can also diffract around hills, into tunnels and all sorts.
- 4) This diffraction effect makes it possible for radio signals to be received even if the receiver isn't in line of the sight of the transmitter.
- 5) The radio waves used for TV and FM radio transmissions have very short wavelengths (10cm - 10 m). To get reception, you must be in direct sight of the transmitter - the signal doesn't bend around hills or travel far through buildings.
- 6) Short-wave radio signals (wavelengths of about 10 m -100 m) can, like long-wave, be received at long distances from the transmitter. That's because they are reflected from the inosphere - an electrically charged layer of the Earth's upper atmosphere.
- 7) Medium-wave signals can also reflect from the inosphere, depending on atmospheric conditions and the time of day.
- 1) Communication to and from satellites (including satellite TV signals and satellite phones) uses microwaves. But you need to use microwaves which can pass easily through the Earth's watery atmosphere. Radio waves can't do this.
- 2) For satellite TV, the signal from a transmitter is transmitted into space...
- 3) ...where it's picked up by the satellite's receiver dish orbiting thousands of kilometers above the Earth. The satellite transmits the signal back down to Earth in a different direction...
- 4) ...where it's received by a satellite dish on the ground.
- 5) Mobile phone calls also travel as microwaves between your phone and the nearest transmitter. Some wavelengths of microwaves are absorbed by water molecules and heat them up. If the water in question happens to be in your cells, you might start to cook - so some people think using your mobile a lot (especially next to your head), or living near a mast, could damage your health.
- 6) And microwaves are used by remote-sensing satellites - to 'see' through the clouds and monitor oil spills, track the movement of icebergs, see how much rainforest has been chopped down and so on.
1) Infrared waves are used in lots of wireless remote controllers.
2) Remote controls work by emitting different patterns of infrared waves to send different comands to an appliance, e.g. a TV.
3) Optical fibres (e.g. those used in phone lines) can carry data over long distances very quickly. They use both infrared waves and visible light. The signal is carried as pulses of light or infrared radiation and is reflected off the sides of a very narrow core from one end of the fibre to the other.
1) Cameras use a lens to focus visible light onto a light-sensitive film or electronic sensor.
2) The lens aperture controls how much light enters the camera (like the pupil in an eye).
3) The shutter speed determines how long the film or sensor is exposed to light.
4) By varying the aperture and shutter speed (and also the sensitivity of the film or the sensor), a photographer can capture as much or as little light as they want in their photograph.
1) Sound waves are caused by vibrating objects. These mechanical vibrations are passed through the surrounding medium as a series of compressions. They're a type of longitudinal wave.
2) Sometimes the sound will eventually travel through someone's ear and reach their eardrum, at which point the person might hear it.
3) Sound generally travels faster in solids than in liquids, and faster in liquids than in gases.
4) Sound can't travel in space, because it's mostly a vacuum (there are no particles).
1) Sound waves will be reflected by hard flat surfaces.
2) This is very noticeable in an empty room. A big empty room sounds completely different once you've put carpet, curtains and a bit of furniture in it. That'sbecause these things absorb the sound quickly and stop it echoing around the room. Echoes are just reflected sound waves.
3) You hear a delay between the original sound and the echo because the echoed sound waves have to travel further, and so take longer to reach your ears.
4) Sound waves will also refract (change direction) as they enter different media. As they enter denser material, they speed up.
However, since sound waves are always spreading out so much, the change in direction is hard to spot under normal circumstances.
Frequency and Pitch
High frequency sound waves sound high pitched like a squeaking mouse.
Low frequency sound waves sound low pitched like a mooing cow.
Frequency is the number of complete vibrations each second - so a wave that has a frequency of 100 Hz vibrates 100 times each second.
Common units are kHz (1000 Hz) and MHz (1000000 Hz).
High frequency (or high pitch) also means shorter wave length.
The loudness of a sound depends on the amplitude of the sound wave. The bigger the amplitude, the louder the sound.
As big as the universe already is, it appears to be getting even bigger.
All its galaxies seem to be moving away from each other.
There is good evidence for this.
1) Different chemical elements absorb different frequencies of light.
2) Each element produces a specific pattern of dark lines at the frequencies it absorbs in the visible light spectrum.
3) When we look at light from distan galaxies we can see the same patterns but at slightly lower frequencies than they should be - they're shifted towards the red end of the spectrum. This is called red-shift.
4) It's the same effect as the vrrroomm from a racing car - the engine sounds lower-pitched wgen the car's gone past you and is moving away from you. This is called the doppler effect.
The Doppler Effect
1) When something that emits waves moves towards you or away from you, the wavelengths and frequencies of the waves seem different - compared to when the source of the waves is stationary.
2) The frequency of a source moving towards you will seem higher and its wavelengths will seem shorter.
3) The frequency of a source moving away from you will seem lower and its wavelenth will seem longer.
4) The Doppler effect happens to both longitudinal waves (e.g. sounds) and transerve waves (e.g. light and microwaves).
The further away a galaxy is, the greater the red-shift.
1) Measurements of the red-shift suggest that all galaxies are moving away from us very quickly - and it's the same result whichever direction you look in.
2) More distant galaxies have greater red-shifts than nearer ones.
3) This means that more distant galaxies are moving away from us faster than nearer ones.
4) This provides evidence that the whole universe is expanding.
Right now, distant galaxies are moving away from us - the further away a galaxy is from us, the faster they're moving. But something must have got them going. That 'something' was probably a big explosion - so they call it the Big Bang.
- 1) According to this theory, all the matter and energy in the universe must have been compressed into a very small space. Then it exploded from that single 'point' and started expanding.
- 2) The expansion is still going on. We can use the current rate of expansion of the universe tp estimate its age. Our best guess is that the Big Bang happened about 14 billion years ago.
- 3) The Big Bang isn't the only game in town. The 'Steady State' theory says that the universe has always existed as it is now, and it always will do. It's based on the idea that the universe appears pretty much the same everywhere. This theory explains the apparent expansion by suggesting that the matter is being created in the spaces as the universe expands. But there are some big problems with this theory.
- 4) The discovery of the cosmic microwave background radiation (CMBR) some years later was strong evidence that the Big Bang was the more likely explanation of the two.
Uniform Microwave Radiation
1) Scientists have detected low frequency electromagnetic radiation coming from all parts of the universe.
2) This radiation is largely in the microwave part of the EM spectrum. It's known as the cosmic microwave background radiation (CMBR).
3) The Big Bang theory is the only theory that can expalin the CMBR.
4) Just after the Big Bang while the universe was still extremely hot, everything in the universe emitted very high frequency radiation. As the universe expanded it has cooled, and this radiation has dropped in frequency and isnow seen as microwave radiation.
Big Bang Theory Limitations
1) Today nearly all astronomers agree there was a Big Bang. However, there are some who still believe in the Steady State theory. Some of these say the evidence just points one way. Others maybe don't want to change their mind - that would mean admitting they were wrong in the first place.
2) The Big Bang Theory isn't perfect. As it stands, it's not the whole explanation of the universe - there are observations that the theory can't yet explain. E.g. for complicated reasons that you don't need to know, the Big Bang theory predicts that the universe's expansion should be slowing down - but as far as we can tel it's actually speeding up.
3) The Big Bang explains the universe's expansion well, but it isn't an explanation for what actually caused the explosion in the first place, or what the conditions were like before the explosion (or if there was a 'before').
4) It seems most likely the Big Bang theory will be adapted in some way to account for its weaknesses rather than just dumped - it explains so much so well that scientists will need a lot of persuading to drop it altogether.