Smart grids are integrated power systems designed to allow
energy supply and demand to be balanced efficiently, in part by the use of electronic
control and management systems. Some
of this involves new hardware: energy stores that can be called on when supply
is low and demand is high, or back-up plants queued up to meet demand peaks and
green energy supply lulls. But some may be just software. For example, variable
energy pricing signals sent to consumers may depress demand when supply is low
or demand high. This is sometimes called ‘demand response’, and one variant relies
on the ability of some domestic and retail systems (eg freezers) to cope happily for
a few hours without power, so that they can be set up to go offline when energy
demand is high or supply low.
The smart grid concept is seen as offering a new more flexible
approach to energy supply and use, enabling the wider use of variable
renewables and reducing the need for ‘always on’ base-load power.
There are many practical problems facing the development and
integration of such systems, as has already been found with the deployment of
the relatively simple smart meters in the UK. The much more complex smart grid
will no doubt require even more effort and adjustments, particularly in
relation to consumer reactions. For example, consumers may not be happy with
interactive load management systems that automatically isolate loads when
demand is high- even if that saves them money. It may be better to offer them
the choice of pre-setting cut off price levels, and also an over-ride option,
so that they can, for example, continue to charge their electric car or run a
washing machine even if the price of doing so at that time will be high. There
are also issues with the integration of storage into smart grid systems:
ideally they should store power when its cheap and use it when its expensive,
but, in the case of Vehicle to Grid storage systems, will electric car owners
be happy to find that power has been drained out of their batteries if they
want to drive somewhere at around peak demand time. Contractual limits have to be set and
consumer friendly interactive control systems developed. Unsurprisingly then, at
both the technical and social level, smart grid and demand response systems are
currently a big area of research: http://www.sciencedirect.com/science/article/pii/S1364032113007211
However, there is a larger problem. This sort of system can only
deal with relatively small and short-term supply shortfalls. As a review of smart grids posted on the Energy Matters web site concluded ‘no smart grid is smart enough to generate
electricity when the wind doesn’t blow and the sun doesn’t shine’. That seems
clear if there are long lulls, but its actually a bit of a simplification: it may
not be the case if the concept of smart grids is expanded.
It is true that demand management can only shift demand peaks by
a few hours or in the extreme (with some industrial-scale interruptible
contracts) a day or so. Similarly, storage system like batteries can only meet
lulls for a few hours or at best a day or so, whereas there can be long lulls
in wind and solar inputs, for several days or even a week or more, sometimes
across wide areas. However, studies have
suggested that it will be rare for whole
continents to be entirely becalmed and cloudy for long periods, so if they
are spread widely enough, long distance HVDC supergrid interconnectors can
often deal with lulls in some parts by trading power from where there is
surplus to where it is needed. For example, the weather systems differ across
Eastern and Western, and Northern and Southern Europe and North Africa. Of
course there may occasionally be times, depending on local supply and demand, when
there will be little current green
energy surplus to trade across the supergrid- and certainly, there can be low
wind inputs at times: http://tinypic.com/view.php?pic=dgnse0&s=8
That’s where large storage options like hydro reservoir pumped
storage and compressed air cavern storage can help (for a few days), pumped up
previously using surplus green power. They can supply power locally or via the
supergrid to where it is needed. Power can also be generated from stored
hydrogen or syngas, these stores being topped up ready for this using gas
produced in P2G mode using surplus electricity from renewables previously and
run into gas turbines when power is needed.
It’s easier to store gas than electricity (and it can be stored for long
times) and even better/more efficient to store heat- so flexible CHP /DH plants
with heat stores can also help: their power to heat output ratio can be
increased to meet power shortfalls and any heat still needed supplied from the
heat store, assuming it has been charged earlier when power demand was low. For
the moment, most CHP plants run on fossil gas, but gradually they can be
converted to run on biogas and low carbon synfuels/P2G, and solar and
geothermal heat can also be used to feed the heat stores. And heat stores can
store heat for long periods if necessary, even months.
This flexible combination of power, heat and gas storage, linked
up by supergrids and balanced as far as possible by demand management, expands
the smart grid concept, so that, (along maybe with inputs from non-weather
dependent renewable sources (hydro, tidal, geothermal, biomass) it should be
able to deal with most if not all eventualities. Though that will depend on the
economics: some say it will be expensive, others that it will avoid waste,
improve balancing and cut costs. The current system is certainly wasteful, and
adding variable renewables to it without system changes could be even more so-
with surplus output at periods of low demand having to be curtailed. Smart electrical
system flexibility can limit that and also some of the need for backup capacity. Going further, to include heat and gas
systems and stores in the mix, along with supergrid trading, should help even
more, though as yet the optimal mix is unclear.
For a review of advanced balancing options see:http://iopscience.iop.org/book/978-0-7503-1230-1 The Energy Matters post: http://euanmearns.com/how-smart-is-a-smart-grid/
