Renewable energy sources
are variable, and ways have to be found to compensate for that. Fortunately
there are many, as my new book ‘Balancing Green Power: how to deal with
variable energy,’ tries to show. While no single grid balancing option will be
sufficient on its own, it suggests that, taken together, in an integrated and
widely interconnected approach, using a range of renewable sources, including
the non-variable options, effective balancing should be possible. Certainly the
range of approaches is quite large, including energy storage, flexible backup
plants, smart grid demand response and supergrid imports and exports.
However, some may have
problems. For example, in relation to balancing of
local surpluses and shortfalls across wide areas by interconnectors, it remains
unclear how much excess output will be available when needed for trade. Much will depend on prices and market structures, as well
on which renewables are developed and where they are located. Perversely, if
supergrids spread, countries may be tempted to reduce their renewable
over-capacity, and so have less to trade. It is also likely that there will be
large surpluses in the summer, when demand is less and solar at a maximum,
during which time few trades will be viable or needed, with some of the
renewable capacity being left idle.
Storage capacity will also be unused then, unless it is inter-seasonal
storage, and not much of that may exist.
Given that
renewable capacity may have to be set higher than would otherwise be needed to
meet demand, there will also be surplus production at other times, for example
when wind output is high and demand low. As critics have pointed out, in some
scenarios, assuming extensive renewable expansion, the surplus can be quite
large and would be very wasteful.
However, this misses the point that, not only can some curtailment be
avoided by supergrid exports, some of the excess can be stored directly, or
converted into valuable storable fuels, for later use, possibly in other
sectors e.g. heating and transport.
In addition to technical
and economic issues like these, which I look at in detail, there is also the
question of social and environmental impacts. Given
that the aim of balancing is to aid the development and use of clean, green
energy systems, it is fortunate that most of the balancing systems looked at in
the book seem to be environmentally unproblematic, with perhaps the exception
of pumped hydro storage. Some environmentalists have opposed large hydro
projects, though that has mainly concerned major new projects in remote areas
that might not be suited to pumped storage. Much of the current development
work concerns modifying and perhaps linking up existing, often smaller, hydro
projects, so that they can operate in pumped storage mode, although some new
medium-scale systems are also being developed.
Some energy
storage systems involve the use of toxic materials (e.g. in batteries), but
non-toxic versions are being developed. Hydrogen storage and transmission also has
risks, but so does the storage and transmission of most fuels, with hydrogen
arguably being one of the less risky options: it is lighter than air and so
disperses easily. Supergrid links may be invasive, but there are options for
overlaying them with existing grids, or putting some sections underground. That
is easier with HVDC than with conventional DC grids since, as the energy losses
in transmission are lower, there is less heat to dissipate, although going
underground would still add to the cost.
The use of
biomass, as a firm source of energy, and for production of biogas as a possible
energy storage medium, opens up some environmental issues. Some
environmentalist oppose the use of biomass for energy production on the basis
of land-use and ecological impacts: it depletes a crucial carbon sink, reduces
the area available for food production and can undermine local biodiversity.
However, biogas produced from farm and food wastes should not face these
problems, and avoids the release of methane into the atmosphere, in which case
it should be able to play a role in balancing variable renewables on a
sustainable basis. Some other forms of biomass may also be less of a problem,
short rotation coppicing of fast growing non-food crops for example, although
clearly careful regulation is needed, as with all types of renewable
system.
Although the
environmental and safety issues of the balancing options do not seem
insurmountable, in some cases, there might be negative public reactions to
deployment, as there have been in the case of renewable deployment generally.
On the supply side, some of the changes will be essentially invisible to the
public. Most utility-run storage facilities, pumped hydro apart, will look much
like any other plants. Similarly for most back-up plants and associated
biogas/syngas stores and Power to Gas conversion plants. As indicated above,
supergrid links may however be much less invisible, although, like hydro, they
would be remote from most people, and, with supergrids, there are options for
going underground in sensitive areas.
On the demand
side, there would be more intimate and widespread interactions. It is not clear
how consumers will react to smart grid demand management and time-of-use
pricing system and how much that will help limit peaks and avoid energy waste.
Most consumers are likely not to want to have to be bothered with energy
management, so automated systems may prove acceptable, as long as they see some
benefits. These benefits however may be longer term and not just economic and
there are data protection and privacy issues.
However, if the
new system can be seen to deliver energy reliably, without undue costs or
impacts, and without too much need for behavioural change, then it may be widely
supported. Then again, some consumers seem willing to voluntarily adopt new
energy systems, perhaps wishing to make personal contributions to energy
sustainability on behalf of future generations. The growth of the ‘prosumer’
self generation movement in many way challenges the technological and market
status quo, making old certainties redundant: a new system may be emerging. And
that will have to include new balancing systems.
‘Balancing Green
Power’, Institute of Physics Publications: http://iopscience.iop.org/book/978-0-7503-1230-1
