Solar energy Flashcards
1
Q
Example of solar
A
Environment building- ‘day lighting’ designed narrowly, max distance from window to max sunlight
- natural sunlight to heat builiding
- cooling system: 2 windows, hot air rises so heat escapes also window above all doors allows heat to escape into corridor
- automatic windows open to let hot air out through terminal chimney
- so operates without energy input& fancy technology
- highlights importance of good design
2
Q
What are the 2 ways to harvest heat from the sun?
A
- solar thermal energy
- photovoltaics
3
Q
Energy from the sun
A
- energy is formed by thermonuclear fusion reactions occurring in the sun
- sun is undertaking a thermonuclear fusion reaction
- colliding at rate of 4 million tonnes a second
- hydrogen nuclei creates helium
- energy that governs that is speed of light E=mc2
- 3.9 x 1026 W (emitting at this rate)
- Tiny mass lost = BIG energy emitted
- Radiates energy from a surface temp of ~5500˚C
- 4H protons -> He
- E = mc2
4
Q
Energy from the sun
A
- large amount of energy coming to sun, we don’t get all of that, 30% of incoming solar energy is immediately radiated back into space.
- other 70% comes onto earth gets absorbed into landmass, oceans, seas and is remitted away from earth.
- in balance if we weren’t going through climate change, the 2 would cancel eachother out, what total amount of energy coming in what equal would goes out
- diffused solar energy is blue sky, clouds still get solar energy but blocks come in
5
Q
Earths energy budget
A
- incoming solar energy 100% (direct solar energy)
- absorbed by land and oceans 51%
- absorbed by atmosphere 16%
- absorbed by clouds 3%
- reflected by atmosphere 6%
- reflected by clouds 20%
-reflected from the earths surface 4% - radiation absorbed by atmosphere 15%
- radiation directly to space from earth 6%
- ## radiated to space from clouds and atmosphere 64%
6
Q
Greenhouse effect
A
- look at diagram
- incoming wave length are short, going from UV, through visible spectrum and out into the near infared spectrum
- when earth radiates back out its at a much longer wave length so this is far infared red radiation being emitted by earth and the basis for green effects, greenhosue gases will absorb at that far wave length energy did so essentially act like a blanket rather than letting incoming wave lengths in and the longer wave length to go back
- we have these gases acting like a blanket around the earth acting as a radiated energy is being loss to space to get a net warming effect.
7
Q
Energy from the sun is not evenly distributed
A
- Net solar power input across the globe is >10,000 times our current rate of use of fossil fuels and nuclear fuel
- have lots of solar panel so in theory could supply all energy demand with solar but there are 2 issues
1) DISTRIBUTION- is variable so higher amounts of radiation received at the equator.
2) PATTERN- pattern of solar radiation compared to energy usage - so if you’re in the UK we have a seasonal distribution so peak usage will be in in the winter, a time the least amount of solar energy is received - you need energy for cooling in the summer and energy to heat in the winter.
8
Q
How do we use solar energy?
A
Thermal energy
-As it sounds, we use the heat of the sun to do ‘work’
Photovoltaics
-We use a converter (a PV cell) to convert light energy from the sun into electricity
- sun heats things up and then we use that heat to do something useful.
9
Q
Residential space & water heating and commercial lighting are biggest uses
A
- big draws are in heating for space and also residential hot water & solar energy is a good way of reducing these demands
- BUT in the UK can’t take away all space heating but like the environment building, we can put measures in place to reduce the pressure on the grid on gas heating from other sources
- EG. commercial lighting has a higher primary energy usage than residential lighting.
10
Q
Thermal Energy
A
- Low temperature work:
- Passive heating and lighting
- Sun passes through glass, is trapped inside, hot air can’t escape = useful technique ( why design is imperative).
11
Q
Thermal Energy
A
Low temperature work:
- ‘Active’ heating
- Solar water heaters in temperate climes
- Uses a pump, incorporates storage, and a non-solar -backup so can adjust for supply inconstancy
- In some countries, up to 90% of water heating
- typically found on roofs, captures suns solar energy, heating up a water system that passes through an exchange mechanism into a water tank and heats up domestic hot water system.
- in this case you would need a pump.
- In UK, frost damages the tans, so tanks are held inside the building
- But in warmer locations , tanks are set up above thermal units, so this gets rid of need of a pump and can just use hot water to naturally circulate its way through the tank.
- look at pic
12
Q
The Flat Plate Collector
A
- qDEL= qABS - qLOSS
(look at diagram) - not complex and efficient in tapping off energy from the sun.
- efficient in terms of cost
- low maintenance, essentially all you need is a bock with a sheet of glass, glass allows suns radiation to pass through.
- process of transminisity- how much energy will get through ( as naturally some will reflect off) - try to maximise this, then hits a black surface as black absorbs energy and transfers into pipes of fluid running through
- insulating blocks at the back to capture heat and stop it being re-emitted (trying to avoid too many loses through the glass)
- can fill plain of glass with argon rather than air (as it is low conducting) or use a vacuum to prevent heat loss across barrier.
13
Q
Solar window Orientation
A
- moves from technology and the focus is more upon design.
- depending on the county you’re in, you can use the direction of the building , the simple solar gain through a window as one way to tap into solar energy.
- if a country is cold in the winter & warm in the summer you can maximise over hang to gain solar energy in the winter when sun is lower in the sky & protect solar gain in the summer.
14
Q
Spectrally- selective glass
A
- where technology comes in, is to maximise performance of glass. EG. use partly natural properties of glass & trying to enhance properties to change its transmitivity (amount of light it lets in) and amount of sunlight that goes back out.
- in this example, glass has been coated to allow visible light to pass through it (short- wave length)
- near infrared (allows excessive heating in summer to be reflected and for infrared ( given back to atmosphere ) is prevented from escaping - so lets the useful energy into the system and the bad out.
- look at pic!!!!!!!!!
15
Q
Passive solar heating types
A
- look at diagram
- technology we’ve know for a long time to maximise suns energy for heating.
- design techniques we can use, focus on the nature of the glass (what it lets in) and thermal mass needs to be considered.
- if a building is made up of concrete, it absorbs heat and neutralises energy, once the sun stops heating through the window, concrete allows energy to be released gradually over time so buildings cool down.
- so thermal mass (amount of stuff in a building) is important for solar heating.
