The Principles of Resource Efficiency - Thanatia: The Destiny of the Earth's Mineral Resources - page 476

according to temperature and the amount of energy exchanged. Design with
Pinch analysis (Linnhoff et al., 1982) and system integration.
Corollary 3: Development of renewable energies require extensive research in
grid automation and energy storage.
Reflection 1: Neither heat nor electricity can be mass stored, so they need
to be used as soon as they are produced. Heat is ine ciently transferred, as it
constantly loses temperature and diffuses. It is thus only an effective option whilst
distances remain short. Contrarily, electricity can be transmitted and distributed
long distances at the cost of resistance that decreases as voltage increases. Losses
in such systems typically range from between 6% and 8% of a country's electricity
production. Energy e cient measures from the supply side involve the use of direct
current (DC) transmission that decrease line losses by 25% whilst also improving
precision control. The use of power electronics known as Flexible AC Transmission
Systems, or FACTS, can enhance transmission capacity in AC lines by as much
as 20-40%. On the demand-side, given that electric motors are one of the major
electricity consumers, use of variable speed drives (VSD) can reduce consumption
by as much as 60% with respect to the more commonly used constant speed drive
motors 6
Reflection 2: Minimising mechanical, thermal and chemical gradients is key to
saving energy and achieving good e ciencies. Instead of using large gradients it is
much more effective to use cascades of smaller ones in which, each loss of an intensive
property is used to increase another one to a small degree. This has three conse-
quences: firstly, significant investment is required for control proficiency; secondly,
the systems need larger and more intricate devices (since a drop in pressure, tem-
perature or chemical potential requires additional stages in steam turbines, larger
surface areas in heat exchangers and bigger chambers in chemical reactors). The
following papers expand on the idea: Linnhoff et al. (1982); Kemp (2006); Wang
and Smith (1994).
Reflection 3: Research on energy storage is rapidly advancing and wide open.
Energy can be stored chemically (hydrogen, methane, biofuels, liquid nitrogen :::),
biologically (starch, glycogen), electrochemically (batteries, flow batteries), elec-
trically (capacitors, super-capacitors, superconducting magnetic storage), magnet-
ically (permanent magnets), mechanically (compressed air storage, pumped hydro
storage, flywheels, springs:::), and thermally (ice storage, molten salts, solar ponds,
hot rocks, eutectic systems:::). Any of which could take the forefront and become
an important part of future sustainable options, should the right funds and people
be diverted into such projects 7 (Denholm et al., 2012).
6 See for instance ABB Energy E ciency in the Power Grid. http : ==www:nema:org=Products=
Documents=TDEnergyEff:pdf: Accessed March 2013.
7 See for instance: http : ==www:sandia:gov=ess=index:html. Accessed June 2013.