Where Does Energy Come From? - The Renaissance of Renewable Energy - page 37

Heat Storage
Since heat is the vibration of scattered and unordered molecules, storing it is a bit like
herding cats; its natural tendency, consistent with the second principle of thermodynamics,
is to disperse. There are two main approaches to storing heat. The first involves strategies
such as insulation and passive-house technologies to retain heat or minimise its loss
in buildings. The second approach involves storing concentrated heat for later use as a
primary energy source. It is this second approach that concerns us here. We will deal with
insulation when we talk about energy efficiency.
Heat is a by-product of every energy conversion. The main challenge in terms of energy
efficiency is to retain and utilize this heat. A number of methods have been developed to
either store heat for short periods or to distribute it quickly to local homes and offices. The
most effective method of storing heat is that used by some concentrated solar power (CSP)
plants. During the day part of the concentrated solar heat is used to melt salts, which are
then stored at temperatures of up to 300 degrees Celsius in insulated tanks. At night or on
cloudy days, this stored heat can then be used to drive steam turbines, thereby ensuring
around-the-clock electricity generation.
Hydrogen
Like Coleridge's ancient mariner, lost at sea and lamenting the presence of “water, water,
everywhere, nor any drop to drink” (Coleridge 1857 , 13), we find ourselves surrounded
by a profusion of the perfect fuel source, but not in a form we can use. Water, one of the
most common substances on Earth, contains two atoms of hydrogen and one of oxygen in
each molecule. On Earth, hydrogen is therefore mostly associated with water, as its name
suggests (from the Greek hydro , meaning water, and genes , meaning creator). Beyond our
planet, hydrogen gas is greatly abundant, fuelling our sun and comprising an estimated
three-quarters of the entire mass of the universe.
Hydrogen seems like the answer to all of our energy problems: it burns extremely well
in a clean reaction, releasing only water vapour 1 ; it can be used in fuel cells to produce
electricity; and perhaps in the future we will be able to use it in nuclear fusion reactors. As
if that weren't enough, hydrogen is very easy to produce through electrolysis: an electrical
current is passed through water, breaking the bonds of the water molecule and releasing
hydrogen and oxygen.
Though the world's first internal combustion engine, developed in 1804 by the
Franco-SwissinventorFrançoisIsaacdeRivaz,usedhydrogen,thiswassoonabandonedas
an automotive fuel in favour of petrol and diesel. Since then, hydrogen engines have been
confined either to the experimental sections of auto shows or to the aerospace industry (the