Page 317 - A Comprehensive Guide to Solar Energy Systems

322 A COMPrEhENSIVE GUIdE TO SOlAr ENErGy SySTEMS

15.2 Why We Need to Integrate Solar Power
into National Grids

Over the past century the world has become reliant on fossil fuel for most of its
electricity. This has led to a build-up of CO 2 atmospheric pollution that has seen the
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levels of CO 2 rise from 250 parts per million (250 molecules per 10 molecules) in the
1800s to 413 ppm as measured at Mauna loa Observatory on April 26, 2017 [8]. Fos-
sil fuel burning power-stations are responsible for at least 25% of this CO 2 pollution.
This increase in CO 2 is largely responsible for our present climate change and global
warming [1].
Although the amount of energy reaching the surface of the Earth is enormous it is, at
the same time, relatively dilute in that even in the hottest tropical areas the energy from
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the sun is of the order of 1000 W m . Photovoltaic technology is one way of exploiting the
sun’s energy to produce electricity and of reducing our reliance on fossil fuel.
The development of photovoltaic cells over the past 30 years has led to a dramatic re-
duction in its costs and today electricity produced from PV panels is possibly cheaper per
watt than fossil fuel [9]. This reduction in costs, combined with the introduction of specific
policies supporting renewable generation development, has led to a huge growth in solar
PV capacity in the United Kingdom which is set to continue. In the United Kingdom the
solar PV capacity has increased from 9.3 GW in February 2016 to 11.7 GW in February 2017.
It is expected that the growth will continue at a rate of 150 MW per month over the next
12 months, rising to 13.5 GW in February 2018 [10].
The growth in both the number of solar PV installations and their combined capacity is
unprecedented in UK energy supply. Solar PV is now highly significant in the energy mix
and its characteristics influence the way energy supply markets behave and how the net-
works used to deliver it perform.
The first feature most people would think of when asked about how much electric-
ity a solar panel will generate is its dependency on the sun. Solar PV output varies as the
sun comes and goes. Ideally, electricity companies need a steady production of electric-
ity, which should exactly match their clients’ demand. Most traditional power plants are
designed to provide a steady base-load of energy and are equipped to ramp up or down to
meet consumers’ needs as they vary steadily throughout the day. yet solar PV output var-
ies. does this really matter though?
The physical balancing of the available energy from nuclear, gas-fired and coal-pow-
ered electricity generation, and including solar PV (and also wind) with the demand is
a knife-edge process. To start, let’s look at how electricity demand varies in the United
Kingdom and focus on summer months. This is taken from reference [6].
The hourly variation over a day is shown in Fig. 15.1 (taken from Fig. 2.3 of page 21 of
reference [6]). The peak electricity demand in summer ranges from 39 GW in early April
to 33 GW in mid-May. This is reasonably constant until mid-August when the demand
rises again.