Solar Power

Photothermal Panels

1. Explain what a photothermal solar panel is.

Using photothermal solar panels is a relatively new invention; however the concept of using the suns power to heat homes is not. For example the centauries ago south facing homes were built to increase the temperature in homes. They were built to maximise the heat in the homes especially in winter when the sun is low and the climate becomes harsher, and to avoid most of the solar radiation in the summer to keep the homes cooler.

The rooftop solar water heater was created based on the ideas that the ancient Romans used. The Romans found that by putting glass in windows the solar radiation is trapped in the room so the warm temperatures stay for a longer period of time. The rooftop solar water heater traps the suns rays in a glass collector which then heats up water located inside insulating glass pipes.

This water is then sent along pipes towards a heat exchanger. The heat exchanger is located in the hot water tank It is shaped like a coil, the boiling water moves along it heating up the cold water in the tank, which is then used to heat the home or provide hot water.

When the water comes out of the heat exchanger it is then passed along the pipes. This time the water is quicker to heat up, because it is still warm from the last cycle. There is usually a black insulating material covering these panels to protect it from the weather. New tubes have a glass outer case and a vacuum to take out the air in and around the pipes because heat is lost at a fast rate through the air.

2. Outline features of modern photothermal solar panels that make them highly effective at capturing the sun’s energy.

They are light and durable to they are not badly affected or damaged by the weather.

GEOGRAPHY AS LEVEL ENERGY ISSUES

Vacuums are being added to them to take out air surrounding the pipes so none of the heat produced is lost through the air.

No extra space on the ground is needed so they can be situated in rural and urban areas.

This technology is not 70% cheaper than it was in the 1970s

3. Why are these panels so unpopular in the UK? (there are a number of reasons)

These solar panels are only thought to work very effectively between the months of March and October.

Even during the summer months a home would only be able to provide 70% of its hot water need. This is excluding central heating.

4. What is a heliostat and how does it work?

A heliostat is an piece of machinery that is able to track the movement of the sun across the sky. They are used to position mirrors to reflect the suns rays continuously throughout the day

Concentrated Solar Power

1. What is the correct name for the mirrors that direct the sun’s rays towards the target?

Parabolic mirrors

2. Produce a mini case study of the impressive new power plant near Seville. (Location, how it works, output, future expansion).

Enough sunlight falls on the earth every minute to meet the world’s energy needs for a year. Seville has tapped into this renewable abundant energy resource. Building a power plant in the Andalusian countryside was a good location because the sun shines on this area for over 200 days a year. They built a large solar complex which has been operating since 2007. The large tower in the centre of the complex has been called the “Solar tower of power” and is 40 storeys high.

This tower collects the concentrated solar waves from 624 mirrors, and produces electricity for approximately 6000 homes. These mirrors are able to rotate to track

the suns movement across the sky, to maximise the amount of energy absorbed.

These concentrated rays are reflected towards one point of the tower called the receiver. They concentrate to heat up by about 1000 times to try and generate 500°c + to turn the water behind the receiver into steam.

Behind the receiver there are pipes full of water which are turned into steam. This steam then stored in a chamber like a boiler until it is ready to be used. It is then send along a series of pipes which turns a turbine and then a generator which produces electricity.

The success of the first plant encouraged engineers and scientists to construct another power station next to it to increase the amount of electricity that can be generated. This second tower is said to be able to produce twice as much power as the first.

The complete construction of the combined power plants it on course to be completed in 2013. The total cost of this project is €1,200 million, and should produce 300MW of electricity to power 180,000 homes. These power plants should reduce the amount of CO2 by 600,000 tonnes.

The original power plant generates 24.3GW/hr per year of clean energy. All of the heliostats cover a surface area of 120m². The hot water is stored in tanks that can reach temperatures of 250-255°c. If they used salt to store the heat the temperature would increase to about 600°c.

The second power plant will have 1000 sun tracking heliostats which will drive 120m² mirrors, which will send their concentrated rays to a tower 165 metres tall. This plant will produce 1.2MW of electricity from 154 silicon plate heliostats.

They are also testing another solar energy system, parabolic trough collectors. These work as the sun is concentrated onto mirrors which are shaped in a parabolic form so they are able to move into an upright position towards the sun.

The suns rays are then concentrated onto an absorbing pipe which contains synthetic oil. The absorbing pipe is found at the mirrors focal point. This oil is the heated up to temperature about 400°c. The oil is then pumped through a series of heat exchangers to produce steam.

This plant is designed to supply 25000 homes with electricity, and currently produces more electricity than the tower.

However researchers believe that in time the tower might prove to be the most efficient out of the two options.

Unfortunately both systems have the same fault. They are not designed to operate when the sun sets. To overcome this, scientists found a way to store the heat in water in the tank though the heat will only be stored for up to an hour.

Eventually they found that they could use salt to store the heat at temperatures reaching beyond 220°c. This will cause the salt to melt and become completely clear resembling water. The molten salt can be heated to a much higher than water without boiling so it is easier to store heat in.

With this plant in full operation they believe that it can provide 200,000 homes with electricity. And they are hoping that in the future they can build a power plant like this one large enough to produce between 700 and 800MW of electricity.

3. Where else in the world can we find similar power plants?

Photovoltaic Cells

1. Explain what a photovoltaic solar panel is.

The word photovoltaic literally means light electricity. These cells are made from semiconductors such as

silicon. They work, as a photon (a particle of light) comes into

contact with the photovoltaic cell, which takes a fraction of the energy collected by the semiconductor. Photons energy is purely kinetic so it can be transferred to the semiconductor material. This energy causes electrons in the particles to become “knocked off”. Enabling them to flow freely. The photovoltaic cells use an electrical field, which forces the electrons to g in a specific direction, creating an electrical current.

This current has a voltage which leads to power. Power can be calculated by using the equation P=IV. To stop the photons being reflected off the silicon have an anti-reflective material attached to them. Thought only 15-25% of the energy is absorbed. The electricity created will flow along the systems in your house, and any excess will go onto the national grid.

A major problem with this is that you can’t store electricity so a large proportion of the solar energy is lost.

Amorphous cells are les efficient versions of these cells but they are cheaper so a large percentage of people use these. The alternative is to use crystalline cells which are very efficient but are very expensive.

Now scientists are trying to build integrated photovoltaic solar panels. These will be built into roofs, windows and possibly paint. This should drive down the cost of solar electricity even further, because you are not buying the panels and the infrastructure.

2. Why are these panels so unpopular in the UK? (there are a number of reasons)

These panels are so unpopular in the UK because they are very expensive. Costing 2-5 times the typical grid power. Though if you make more electricity than you need you can sell the excess energy to the national grid for a premium.

3. Why might these panels be more useful and more popular in LEDCs?

These solar panels may be more useful in LEDCs because they tend to be in areas with a hotter climate with more exposure to the sun. This map shows that the majority of Africa would be a good place to build solar panels. They are also more popular with these communities because they can create solar cookers either buy purchasing them or creating ne themselves cheaply.

4. These are arguably the greenest way of producing electricity – what evidence is there to support this?

Solar power systems provide an environmental friendly source of energy, and produce almost no emissions. Most of the emissions produced are produced during the construction of the power plant. Furthermore the plant consumes no other fuel other than the light from the sun so no fossil fuels are being used. The only problems are that these power plants take up a large amount of space. Though the difference I the sizes of this power plant and fossil fuel power plants is minimal because fossil fuel power plants take up a lot of space for mining and exploration to find the raw materials that they need to use.

5. Which country has invested heavily in photovoltaics?

Germany has started to use a lot of photovoltaic cells to provide electricity. They are being built along the sides of roads and on the top of buildings and on the tops of walls. Germanys PV capacity has risen from 100MW in 2000 to 4150MW in 2007.

Passive Solar Heating

1. Explain how this process works?

Glass allows light in but traps heat. This is known as the “Greenhouse effect”. Sunlight coming through a window can heat up any room. This is good in winter but bad in summer.

Poorly designed windows can cause more bad heat transfer on winter nights and summer days than the good solar ain that they allow in on sunny winter days. Thermal modelling is important.

The solution is to have “isolated solar gain” through a greenhouse/solarium/sunroom/conservatory. This will create a “buffer zone” between the interior and exterior glass (there will be a window on the outside of the solarium and one between the solarium and the living area itself.

The sun room is located on the equator side of the house. If you are in the Northern Hemisphere this room will face south, and if you are in the southern hemisphere it will face north.

Glass is maximised on the equator side to allow in the abundant day light in. Glass is minimised on the other side of the house.

A solarium can be integrated into a low-cost near-zero-energy home. We have known how to do this since the 1978 solar energy tax credits in America.

In a 1980 New England Salt Box home the south side is high to let in the abundant sunlight. The North side is lower to block cold winter wind.

Sunspace creativity can be used in both single and two storey homes. They can be used for tropical plants, or even a spa or swimming pool. The year round conditions are tropical. This heat can also be used to heat water in the room which will contribute to the thermal mass of the home

What scientists are trying to find solutions to is how to send the temperature trapped in the sunny south facing rooms to the north facing rooms. The solution that they feel is the best is to design the houses that it has a natural convectional air current flow path.

This is where warm air rises because of its decreasing density in the solarium and cold air falls in the north facing rooms. This creates a circular air flow path that will continuously transfer heat between rooms while the sun is shining. This is a self regulating temperature balancing system.

In hot humid climates a process called cooling with sunshine. This is where large roof vents are open and all air flow is upwards. The thermal buffer zone is kept cooler than outside air. The temperature of the Earth is used to cool and dehumidify the temperature at the base of the building.

What we have to remember is never use roof angle glass or skylights, because in the summer these create a solar furnace, and has uncontrollable harsh glare. And in winter air rises, leading to major heat loss at night

through the glass. Roof angle glass leaks and hail can smash it.

2. Why is it not suitable for everybody’s home?

This is not suitable for everyone’s home because if you have a large house the heat will take longer to heat all of the rooms and so the chances of the owners having to use electricity is very high.

The construction of the house will be affected, and after it is built the cost of cleaning the windows will be very high.

They are not very child friendly, because they might fall through them.

This table shows the different forms of collecting solar power.