The price of intermittency
Jean Pierre Riou
English translation Bernard
Durand
Avertissement : cette série d'articles en anglais reprend des articles du Mont Champot en français afin d'étayer une publication ultérieure.
Cet avertissement explicatif sera rapidement supprimé.
As of 11/30/2016, 11,292MW wind turbines were
connected to the grid.
Almost all of these wind turbines are connected to the
distribution network, medium and low voltage (MV and LV between 20,000 and 230
volts) which is managed by ENEDIS (ex ERDF).
Some 637MW are however connected to the public
electricity transmission network (RPT), composed of very high and high voltage
lines (THT and HT between 400,000 and 63,000 volts) that RTE manages.
Transformer stations located at the interconnection
between these networks.
ENEDIS,
publishes its network data in real time: at http://www.enedis.fr/le-bilan-electrique-erdf
Which
indicates, in particular, wind production on its network:
Which,
logically, slightly lower than the RTE figures.
The large random variation in wind power, however,
prevents most of their production from being consumed locally, as appears from
the comparison of this production with the power delivered at the same time by
ENEDIS to the RTE network.
These two
variables are strictly correlated.
The more one considers wind energy on a local level,
the greater the amplitude of the variation in its power.
Thus, even on the scale of a territory like Ireland,
wind power can fall strictly to 0 ... and even to negative figures,
since the servitudes of the machines (extractors, hydraulic pumps, heating of the blades in cold regions ...) operate permanently. As illustrated by Irish wind turbines on October 20.
since the servitudes of the machines (extractors, hydraulic pumps, heating of the blades in cold regions ...) operate permanently. As illustrated by Irish wind turbines on October 20.
Their
power "curve" hardly took off from 0 MW that day, with even a foray
into negative values (minus 2 MW) at the end of the afternoon! It is because
of this great variability in its production that wind power is anything but
local energy and that it requires thousands of additional power lines to allow
its overproduction to be pushed back ever further, by making them go up to
lines of higher voltage. This is what highlights the Derdevet report , which analyzes the constraints to come for
energy transport networks.
The following graph illustrates this phenomenon at a
German transformer station. With the connection of photovoltaic power stations,
the dimensioning factor is no longer the peak of winter consumption, but the
peak of summer photovoltaic production for much higher power flows. And it is
no longer a question of routing current to local consumers (positive flow on
the graph),
but
to push it towards higher virus tension levels to spread it over all the
territories
This
report draws attention to the case of Germany alone, which requires, according
to the scenario envisaged, between 132,000 km and 280,000 km of new power lines
and between 43 GW and 130 GW of transformation capacity in order to allow
forcing back more and more these random surpluses towards higher voltage lines.
(p 45 of the report)
Currently, it is the safety margins that are reduced by network congestion due to the unexpected transit of these unwanted flows. In particular the German flows (not nominated, or loop flows) which reduce the available capacities of our lines by dumping their surplus wind turbines coming from the north to transport them towards the south of their territory.
Currently, it is the safety margins that are reduced by network congestion due to the unexpected transit of these unwanted flows. In particular the German flows (not nominated, or loop flows) which reduce the available capacities of our lines by dumping their surplus wind turbines coming from the north to transport them towards the south of their territory.
The appearance of loop flows such as those caused by the massive installation of wind turbines in the North of Germany, and the delay in the construction of high voltage lines towards the South, sometimes saturate the electrical networks of neighboring countries and weaken them (see figure). These countries are not paid for the services they render to Germany, the balance of transits being zero at their borders.
To avoid the risks of blackout, the Czech Republic has warned that it plans to be able to block any new influx of renewable electricity likely to cause a failure of its network thanks to the construction of a giant phase -shifting transformer setting the admissible incoming power, which was to be commissioned in 2017.Poland also plans to install such equipment at the border with Germany.
The need
to deploy protective means such as these phase-shifting transformers can be
taken as a demonstration that the presence of interconnection lines has not
always had a positive effect. These have various interests, which shows, if
this were still necessary, the need for appropriate technical and economic
studies in each case.
Transit flows in the neighboring countries of Germany
in 2011-2012 (MW)
Phase-shifting transformers
Transit volumes
Loop flows
The
advantages of this race towards ever more pooling of resources, needs, but also
of problems, seems very limited by an inescapable parameter: the absence of
benefit from a pooling of resources. The amplitude of variation of wind power
remains considerable, even at European level.
Source étude de Sauvons le Climat.
To cope with the "high pressure potatoes" which deprive Europe of wind, it remains necessary to keep all the dispatchable power stations, ie those which supply current when a button is turned. But conversely, increasing intermittent energies productions results in the big difficulty of getting rid of their random surpluses as soon as the wind blows, even if it means paying for it, as demonstrates the correlation between German wind production and the price of MWh, which shows negative values during wind records.
But if
these useless overproductions break prices on the MWh market, the various
compensations paid to producers (purchase prices, additional remuneration,
capacity mechanism, etc.) are added to the consumer's bill to the additional
costs of the restructuring of the network allowing it to repress intermittent
production. This explains the strict correlation between installed wind /
photovoltaic capacity per capita and the retail price of electricity, as shown
in the graph below.
Regarding the media bludgeoning on the virtues of renewable energies, it is disturbing not to find a word in the French press to salute the feat of the WEST reactor which has just obtained its 1st plasma in France, as part of the project ITER nuclear fusion industry. The silence is just as deafening on the entry into commercial operation of the Russian reactor of 4th generation "BN 800", crowned with the price of the best nuclear power plant in the world by the American press and ... which derives from the technology of Superphenix , arrested after its best year of operation for electoral reasons. Moreover this reactor offers considerable progress in the management of nuclear waste. So, is it so obvious that the energy of tomorrow will not be dispatchable that such a share of public money is injected in the creation of infrastructures whose sole purpose is to try to bear the effects of intermittence? In any event, these considerable additional costs must currently be taken into account when comparing the value of an intermittent MWh with that of a dispatchable MWh.
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