Renewable Energy: Solar Flashcards
How big part of the UK renewable energy sources comes from solar energy?
9 GW out of 30 GW
However in Scotland does solar power not contribute a sizeable part
What is a problem with the energy the sun radiats?
The amount of energy coming from the sum
is vast, far more than we actually need. The issue is the energy density
is low and how to convert it efficiently into forms that are useful .
How are solar energy levels in the UK?
4-5kWh/m2 day in the summer to 0.6kWh/m2 day in the winter.
An average household in the UK uses 6 kWh/day electrical energy.
How does seasonal changes effect solar energy?
Seasonal changes are due to the tilt in the taxis which the earth rotates about results in the seasonal variations in solar energt recevied at any one location on earth.
This influecne in the design of devices and ensure that they receive the maximum amountof energy throughtout the year they need to tilt as well.
How the solar radiation reaches the earth surface effects what?
If the radiation is direct beam radiation as would occur in a
cloudless day then you can focus this with mirrors and lenses. However, clouds
result in scattering and a diffuse form of radiation that is has no directional
characteristics. On average, in northern Europe 50 % of the radiation is diffuse
over a year. On clear days 90% of the light is direct sic ether will still be some
scattering from atmospheric particles .
What are the 2 main technologies used to harvest solar energy?
- Direct conversion to electricty using photovoltaic panels
- Using the solar energy as a direct heating process ie solar thermal power.
Explain solar thermal power
When heating there are a
number of variants for power generation, including the heating of fluids which can then be used in standard power cycle or heating to produce thermal air currents that can be used directly in an air turbine.
To achieve high temperature and therefore high thermal efficiencies solar thermal power needs to concentrate direct radiation from a large area onto to a smaller area. This is also called Concentrated solar power (CSP) and is quantified using a concentration ratio ( CR)
One of the largest solar thermal power plants is in the Mojave Deserts in
California. A steam power plant it has a capacity of 350MW using mirrors
covering 6.5km2. The thermal efficiency is 15% and has a capacity factor
between 25-50%
Explain solar thermal heating
The sun heats cold water.
Common in the UK but can directly integrated into domestic heating systems, usually when a system needs to be updated. Back up systems need to be available to supplement
or replace heating when there is no solar radiation available.
Explain Photovoltaic system
It directly convert solar radiation into electricity using photoelectric effect. So far the most efficient process have been achived using semiconductor materials like silicon.
Two silicon layers each altered to create either a postivte or negative state generate a magnetic field when sandwiched together. When the surface is exposed to thermal radiation the photo electric effect produces free electrons which travel across the field to produce a current and power.
A 10x10 cm cell for a photovoltaic system can produce how much voltage and amp?
0.5 Volts
3 Amp
Approximatley 1.5 Watts
Systems are about 10-20% efficient
Why are PV systems popular?
Because the government incentives through feed in tariffs.
The government make the electrical utility companies pay the PV owner for the electricity that is generated (and used ). They also
need to pay for any electricity that is exported into the grid. This results in the possibility that the system will pay for itself in
about 10 years.
What types of renewable energy are the government incentives through feed in tarrifs?
Solar PV
Wind power
Hydro
Micro combined heat and power
What is the cost of renewable energy?
The renewable energy are often precived as low cost because the cost of fuel is free.
When all the cost are accounted:
- The cost of the equipment
- The operating cost
- Financing
- Availability of generation (capacity factor)
All this leads to that renewable electricity generation is usually higher than other methods.
However, this is continuously changing as technology improves
and manufacturing costs reduce.
