Sustainable energy
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Solar for the grid Solar panels harness the sun's power to
generate electricity and provide clean power for homes, communities and
businesses
Why
solar is super
Solar
photovoltaic (PV) modules generate electricity from sunlight, which can be fed
into the mains electricity supply of a building or sold to the public
electricity grid. Reducing the need for fossil fuel generation, the growing
grid-connected solar PV sector across the globe is helping create jobs,
enabling families and businesses to save money, and cut greenhouse emissions.
Key
facts
·
The typical cost of a solar installation is
between £1,250 and £2,000 per kWp for smaller systems, cheaper oer kWp for
larger systems, but this cost is falling rapidly
·
There is rapid market growth, 28% during 2015
·
It generates 1% of global electricity
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Related Winners, news and
opinion
How grid-connected PV
systems are used
Most
grid-connected PV systems are installed on the roof or walls of a building.
This does not take up land that could be used for other purposes like
agriculture. Ideally the PV faces towards the equator but the exact direction
is not critical. However, it is important to make sure that there is minimal
shading of the PV. If the PV electricity production exceeds building demand
then the excess can be exported to the grid, and vice versa.
A
typical grid connected system rated at 1 kWp has an area of between 5 and 6 m2.
If the PV system is installed during construction or refurbishment, it can
sometimes be used as part of the building fabric, such as a roof or
wall-cladding. Ashden Award winner Solarcentury has integrated PV arrays into a
wide range of buildings.
Thornhill
primary school installed solar panels on their new building
Where
space and sun are available, large stand-alone PV arrays can be built and
connected to the public grid. In 2016, several solar farms in excess of 500 MWp
were in operation around the world, with many more planned.
Until
recently, grid-connected systems have not usually included batteries for
storage, because the mains grid can accept or provide power as needed. However,
if rechargeable batteries are included, a grid-connected PV system can be used
as a standalone ac supply in the event of a power cut, to allow essential loads
to keep working. Ashden winner Deng solar provided a 9.2 kWp grid backup system
for the central courts in Accra ,
Ghana USA
Solarcentury
won an Ashden Award in 2007
Benefits
By
reducing the need for fossil-fuel generation, grid-connected PV cuts greenhouse
gas emissions (and other air pollution), because no emissions are produced
during PV operation.
In
the past there has been concern about the greenhouse gases emitted (‘embodied’)
in the manufacture of PV systems, particularly in the production of ultra-pure
semiconductors. With current production techniques, these embodied greenhouse
gases are saved within 0.7 to 2 years of use of grid-connected operation,
depending on the amount of sunlight.
PV
is the easiest renewable electricity source to incorporate into buildings. The
electricity is supplied at the point of use, thus avoiding the losses which
occur in electricity distribution (these average 7% in the UK
Because
of this, it is a valuable way to raise awareness of electricity supply and use,
and helps highlight the potential for renewable energy. Several schools that
have won Ashden Awards like Home Farm Primary School
and Sir George Monoux
College
How it works
PV
modules use semiconductor materials (usually silicon) to generate dc
electricity from sunlight. A large area is needed to collect as much sunlight
as possible, so the semiconductor is either made into thin, flat, crystalline
cells, or deposited as a very thin continuous layer onto a support material,
usually glass. The cells are wired together and sealed into a weatherproof
module, with electrical connectors added. Modern modules for grid connection
usually have between 48 and 72 cells and produce dc voltages of typically 25 to
40 volts, with a rated output (see below) of between 150 and 300 Wp.
By 2030 PV could supply
13% of global electricity
According
to stats from 2016
In
order to supply energy into a mains electricity system, the dc output from the
module must be converted to ac at the correct voltage and frequency. An
electronic inverter is used to do this. Generally, a number of PV modules are
connected in series to provide a higher dc voltage to the inverter input, and
sometimes several of these ‘series strings’ are connected in parallel, so that
a single inverter can be used for 50 or more modules.
Modern
inverters are very efficient (typically 97%), and use electronic control
systems to ensure that the PV array keeps working at its optimum voltage. They
also incorporate safety systems as required in the country of use.
Ashden winner Deng solar provided a 9.2 kWp
grid backup system for the central courts in Accra , Ghana
Output
PV
modules are specified by their ‘watt-peak’ (Wp) rating, which is the power
generated at a solar radiation level of 1000 W/m2, equivalent to bright sun in
the tropics, and a temperature of 25C. In practice, the actual power produced
is affected by the weather, the angle of the sun relative to the panel, the
temperature of the panel and whether the panel is free from dust and bird
droppings. Even when conditions are not ideal, solar PV still produces a useful
power output.
Cost
The
capital cost of grid-connected PV varies between countries. As a guide, for the
UK in 2016 the typical installed cost for a domestic system was £1,250-£2,000
per kWp, while a large solar farm cost around £1,100 per kWp. In Africa, the
typical cost for a large-scale project was around $1,400 per kWp in 2016, while
in the USA
Translating
these installed costs to the cost of electricity depends on a number of
factors, most important being the location and orientation of the panels –
sunnier locations will result in higher generation, as will having the panels
angled towards the sun (i.e. facing south in the northern hemisphere).
In
the past, the cost of electricity from solar PV has been higher than the
consumer price for grid electricity, and substantially higher than the cost of
fossil-fuel generation, so a number of governments offered subsidies to support
the industry. However, by 2016 the levelised cost of electricity from solar PV
had dropped below the consumer price in several countries, and this trend is
expected to continue.
The
Aryavart Gramin Bank in India
has provided PV grid backup systems for its rural branches
The future
The
future The price of PV modules has decreased rapidly in the past, although the
rate of decrease has been slower since 2012. For crystalline cells, new ways of
processing silicon and increased volume manufacture are driving down prices.
The market share of thin film PV is growing rapidly as materials which have
been proved in the laboratory go into volume production, and these promise even
greater price reductions. The future potential for price reduction greater for
the ‘balance of system’ than for PV modules or inverters, and these costs already
dominate the overall system cost.
Because
of the decreasing prices, the rapid growth in the market for grid-connected PV
is expected to continue even if government support is reduced. The market is
beginning to take off in regions where electricity from PV is cheaper than
consumer grid prices. This is already the case in sunny regions, and will
become more widespread as prices fall. Roadmaps produced in 2016 suggest that
by 2030 PV could be supplying about 13% of global electricity.
