A new study of the potential for variable renewable
energy (VRE) in China says that it
is vast, nearly 20 TW, and that, far from adding to the problem of grid balancing,
as more of both wind and PV solar is
installed over a wider area, they were mutually supporting. There was a ‘complementarity between wind and solar in
China, reflected in more optimal return-volatility performance of wind &
solar portfolios, as compared to wind-only and solar-only portfolios’. And expanding both made it easier to deal
with their variability: ‘For the same total installed capacity, wind
& solar portfolios with unconstrained technology shares exhibit better
return-volatility performance than portfolios with constrained technology shares.
This suggests that existing scenarios in literature with pre-defined shares of different
VRE technologies might be sub-optimal to support power system operation’.
The authors of the paper are unhappy with the use
of the term ‘intermittency’. While they say it ‘fairly characterizes the output pattern per VRE installation, the collective
VRE output pattern is more important from the perspective of power system
operation. We argue that “intermittency” should not be used to characterize the
collective output pattern of well-diversified VRE assets spread over a large
geographical area’.
Their study suggests that, as more capacity of solar
and wind is added, a larger average
system output share is available as reliable fixed output. i.e. a larger amount
of the total capacity can be treated as 100% firm - as measured by the system
capacity factor (CF), which they say can reach up to 5.5%. That means that less
backup or storage capacity is needed to cover the periods when all wind and all
solar inputs are low.
Optimal Choices for China
However, trying
to maximize the CF may not be the optimal choice on cost grounds: it might be
better, in terms of the Levelised Cost of Energy, to accept lower CFs and
higher system output volatility, since ‘with increased portfolio volatility (and portfolio return), the LCOE of
wind and solar portfolios decreases’. That might mean less use of low
CF solar, but then it’s a trade off: if higher cost low-CF assets are replaced
by high-CF assets, overall LCOEs fall.
The analysis has some limitations - due to the
scarcity of reliable data, it does not use hourly modeling of supply and
demand, only scenario/portfolio approach, and it uses LOCEs not full system
costs. In addition, it’s focused just on solar and wind, whereas China also has
a very large hydro capacity (252 GW), some of which can be used for grid
balancing. So can biomass-fired plants and geothermal plants. So we are still
some way from identifying system optimals and back up needs.
The situation in China is perhaps unique. It is
vast, covering a range of climate zones and with its renewable resources also
varying geographically. However, there is a lot of it. The study puts the maximum capacity that can be
installed at 575-4909 GW for onshore wind, 559-932 GW for off shore wind and
12,936 GW for PV. It says the best resources (in terms of both high mean CF and
high potentials) are found in Inner-Mongolia for wind and North China for
solar. That means there will be a need for more/and upgraded grid systems to
bring power to centres of population which are mostly in the South East. But it
is working
on that, with 30,000 kilometers of new Ultra High Voltage Direct Current
links having been installed so far and plans for 90,000 km in all by 2020. That
will help with balancing.
The
current state of play is that China has nearly 730 GW of renewables in place,
more than than any other country. Weak
grids have been a problem, leading to curtailment (non use) of some of the
output from this capacity, but that is being addressed, including by the new
supergrid network, as above. IRENA says that curtailment levels at wind
farms dropped to 7% in 2018 from 13% in the previous year, while solar PV
plants it dropped to 3% from 5.8% over the same period. With PV and wind costs
falling, the funding/subsidy over-spend problems that had also emerged, and
slowed growth, may now be reduced, so expansion should continue. And that is
happening: by the end
of 2018, renewables were up 12% on the year before, and in
the first quarter of this year,
China added 5.2 GW of new PV solar and 4.78 GW of new wind capacity. As this new study shows, there is
plenty of room for more, without leading to major balancing problems. And the
impetus for expansion, so as to cut emissions, is certainly growing, as
awareness of likely worsening climate impact spreads.
Emission cuts
China has
pledged to cut emissions per unit of GDP by 60-65% of 2005 levels by 2030,
potentially putting it on course to peak by 2027 and it has committed to a peak
in CO2 emissions by 2030, with best efforts to peak earlier. If the renewables
programme can accelerate again, along with its other emission reduction
efforts, it might be able to do better than that that. It
has been claimed that PV
Solar is now
cheaper than grid electricity in cities across China. In 22% of them it was cheaper than
coal power. And it has also been claimed that emissions from urban
passenger transport could
peak as soon as 2020 due to the use of green fuels, EVs, and, crucially, a
shift to public transport
That’s the good news. The less good news is that coal use
is still expanding, more so than in many
other parts of the world,
with new
coal plants being planned to
meet the growing demand, even if at slower rate than before. Something has to
give, if emissions are to fall, and that hopefully will happen, given
the cost advantages of renewables and as the potential for demand reduction are
realized.
Emissions from China’s coal-fired plants had
been falling up to 2017,
according to a new study, and although they then
increased, that then began to flatten off, possibly due to revised operating
procedures- to reduce emissions, some of the older less efficient ones were
only run part time, just to meet peak demand. However, that may not help longer
term, as and when more plants come on line- even if they are more efficient
than the old ones.
Certainly China’s overall CO2 emissions from
fossil fuels and cement production grew by an estimated 4% in the first half of 2019. That may be because of a surge in real estate and
infrastructure construction that saw emissions from steel and cement expand
rapidly, in part due to the huge ‘Belt and Road’ overseas trade expansion programme, with
new links being built- a new Silk Road. The
progamme has also involved vast investment, including in energy projects, outside of China. But it has been claimed that solar
expansion across the region
might start to offset some of the impacts of that, and, within China, there are
hopes for an overall emission peak by 2022-
well ahead of schedule. We shall see…It could get
worse , with more coal use, although
some are hopeful that it will get
better soon. Moreover, although it may only be temporary,
one of the side effects of the Coronavirus, and the national travel lockdown,
has been a significant fall in oil use.
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