"In the real world a
wind farm’s output often drops below 10 per cent of its rated “capacity”
for days at a time. Solar power disappears completely every night and
drops by 50 per cent or more during cloudy days. “Capacity” being a
largely meaningless figure for a wind or solar plant, about 3000
megawatts (MW) of wind and solar capacity is needed to replace a 1000 MW
conventional power station in terms of energy over time: and in fact,
as we shall see, the conventional power station or something very like
it will still be needed frequently once the wind and solar are online.
In
fact it's already common to see efficient combined-cycle gas turbines
replaced by open-cycle ones because they can be throttled up and down
easily to back up the rapidly changing output of wind and solar farms.
But open-cycle gas turbines burn about twice as much gas as combined
cycle gas turbines. Switching to high-emissions machinery as part of an
effort to reduce emissions is, frankly, madness!
Certain countries are helped because their power systems are supported by major inter-connectors
to adjacent regions that have surplus power available. The increasingly
troubled French nuclear fleet, which formerly had plenty of spare
energy on tap, for a long time helped to make renewables plans look
practical across Western Europe.
But
this situation is not sustainable in the long term. Under net-zero
plans, all nations will need to generate many times more electricity
than they now can, as the large majority of our energy use today is
delivered by burning fossil fuels directly. Neighbouring regions will be
unable to provide the backup power needed; emissions from open cycle
gas turbines (or new coal powerplants, as in the case of Germany at the
moment) will become unacceptable; more existing base load stations will
be forced to shut down by surges in renewables; more and more wind and
solar power will have to be expensively dumped when the sun is shining
and the wind is blowing.
Power prices will soar, making more or less everything more expensive, and there will be frequent blackouts.
None
of this is difficult to work out. Building even more renewables
capacity will not help: even ten or 100 times the nominally-necessary
“capacity” could never do the job on a cold, windless evening.
Only
one thing can save the day for the renewables plan. Reasonable cost,
large scale energy storage, sufficient to keep the lights on for several
days at a minimum, would solve the problem.
What are the options?
First
we need to consider the scale of the issue. Relatively simple
calculations show that that California would need over 200
megawatt-hours (MWh) of storage per installed MW of wind and solar
power. Germany could probably manage with 150 MWh per MW. Perhaps this
could be provided in the form of batteries?
The
current cost of battery storage is about US$600,000 per MWh. For every
MW of wind or solar power in California, $120 million would need to be
spent on storage. In Germany it would be $90 million. Wind farms cost
about $1.5 million per MW so the cost of battery storage would be
astronomical: 80 times greater than the cost of the wind farm! A major
additional constraint would be that such quantities of batteries are
simply not available. Not enough lithium and cobalt and other rare
minerals are being mined at the moment. If prices get high enough supply
will expand, but prices are already ridiculously, unfeasibly high.
Some
countries are gambling on hydro pumped storage. Here the idea is to use
electricity to pump water uphill into a high reservoir using surplus
renewables on sunny, windy days: then let it flow back down through
generating turbines as in a normal hydropower plant when it’s dark and
windless.
Many
pumped systems have been built in China, Japan and United States but
they have storage sufficient for only 6 to 10 hours operation. This is
tiny compared with the several days storage that is needed to back up
wind and solar power through routine sunless calm periods. Much larger
lakes at the top and bottom of the scheme are needed. There are very few
locations where two large lakes can be formed with one located 400-700 m
above the other and separated by less than 5-10 km horizontally. Such a
location must also have an adequate supply of make-up water to cope
with evaporation losses from the two lakes. Another problem is that at
least 25 per cent of the energy is lost while pumping and then
generating.
Hydro
pumped storage will seldom be a feasible option. It cannot solve the
problem on a national scale even in countries like the USA which have a
lot of mountains.
Carbon
capture and storage (CCS) for fossil fuel stations is also touted as
way of avoiding the problems of wind and solar power. But this is not a
technology, just a case of wishful thinking. In spite of many years of
work and enormous amounts of money spent, nobody has yet devised a
technology that can provide large scale, low cost CCS. Even if capture
worked and didn't consume most or all the energy generated, storing the
carbon dioxide is a huge problem because three tonnes of carbon dioxide
are produced for every tonne of coal burned.
Hydrogen
is another technology which is often suggested for energy storage: but
its problems are legion. At the moment hydrogen is made using natural
gas (so-called “blue” hydrogen).
This, however, will have to stop in a net-zero world as the process
emits large amounts of carbon: you might as well just burn the natural
gas. Proper emissions-free “green” hydrogen is made from water using
huge amounts of electrical energy, 60 per cent of which is lost in the
process. Storing and handling the hydrogen is extremely difficult
because hydrogen is a very small molecule and it leaks through almost
anything. At best this means that a lot of your stored hydrogen will be
gone by the time you want to use it: at worst it means devastating fires
and explosions. The extremely low density of hydrogen also means that
huge volumes of it would have to be stored and it would often have to be
stored and handled cryogenically, creating even more losses, costs and
risks.
The
conclusion is simple. Barring some sort of miracle, there is no
possibility that a suitable storage technology will be developed in the
needed time frame. The present policies of just forcing wind and solar
into the market and hoping for a miracle have been memorably and
correctly likened to “jumping out of an aeroplane without a parachute
and hoping that the parachute will be invented, delivered and strapped
on in mid air in time to save you before you hit the ground.”
Wind
and solar need to be backed up, close to 100 per cent, by some other
means of power generation. If that backup is provided by open-cycle gas
or worse, coal, net zero will never be achieved: nor anything very close
to it.
There
is one technology that can provide a cheap and reliable supply of
low-emissions electricity: nuclear power. Interest in nuclear power is
increasing as more and more people realise that it is safe and reliable.
If regulators and the public could be persuaded that modern stations
are inherently safe and that low levels of nuclear radiation are not
dangerous, nuclear power could provide all the low cost, low emissions
electricity the world needs for hundreds or thousands of years.
But if we had 100 per cent nuclear backup for solar and wind, we wouldn't need the wind and solar plants at all.
Wind and solar are, in fact, completely pointless.
Bryan
Leyland MSc, DistFEngNZ, FIMechE, FIEE(rtd) is a power systems engineer
with more than 60 years experience on projects around the world"