Page 320 - A Comprehensive Guide to Solar Energy Systems

Chapter 15 • Integration of PV Generated Electricity into National Grids 325

The curve is the amount of energy that the traditional power plants have to supply on
a typical day. The drop in the middle of the day is due to the amount of energy supplied by
utility and roof top PV power supplies. As a result of the increased PV power from roof top
systems and from solar farms from 2011 to 2016, this drop becomes more pronounced and
the steepness of the ‘neck’ becomes greater.
This curve could well represent related systems of combined base-load power and so-
lar PV power, anywhere in the world and you can see a similar effect in Figs. 15.2 and
15.3 earlier. during the day, when solar plants are most productive, demand for electricity
from traditional power plants plummets. In the evening, the need for traditional power
increases due to the combined effect of solar output decreasing and energy demand, in-
creasing. This results in a steep rise (duck’s neck) in demand, which must be met by the
other sources power supply.
These other sources must be available at the right time and able to ramp up at the
necessary rate. These could be the traditional power plants we’re used to, but it might be
prohibitively expensive to keep these open just to meet short steep rises in demand, in
which case, we would see flexibility provided in other ways.
This “flexibility” could be consumers switching off their own demand in response to
high prices or direct payments. Fast acting alternative sources of energy like batteries
could perform the same function. Where the need for flexibility is great enough and trans-
parent to those who might provide it, it’s likely that we’ll see investment in new facilities
and the energy industry will develop new ways of buying and selling this capability.
So, how do we know that grid operators can make use of this flexibility and keep the
lights on the way we’re used to? Operators have a good track record of this, and perhaps
the best example to refer to here is the solar eclipse in North America on Monday, August
21, 2017. The Californian system operator successfully negotiated a 5 GW drop off in solar
output, and its rapid return at an average rate of 0.15 GW per minute. The National Grid
has looked at how to cope in Great Britain when the same thing happens in 2026. Their re-
port is entitled “A preliminary study of how a solar eclipse due in 2026 will affect GB when
there is up to 26 GW of solar PV”.

15.5 Effect of Growth in Small Distributed Installations

Another issue for the grid-electricity generating industry is the wide distribution of solar PV
panels. PV works very well in small, distributed installations. Because they are small and nu-
merous, there is very limited justification to add remote metering and control facilities. roof
top units are usually in the kilowatt range and the utility scale units (solar farms) can be any-
thing from 10 MW to 200 MW and in the United Kingdom they are usually less than 20 MW.
Even for larger installations, the owner/operator may not want to control their output
as it makes sense to sell all of the available output. After all, it is free when the sun shines.
The resulting shortcoming is the lack of information (called visibility here) of small-
scale generators given to the grid operator who is responsible for ensuring that the right
energy balance is achieved second by second. At present visibility is defined in terms of