3.8. Fluctuations and storage http://www.ck12.org
Figure 26.11:Okinawa pumped-storage power plant, whose lower reservoir is the ocean. Energy stored: 0.2 GWh.
Photo by courtesy of J-Power. http://www.ieahydro.org.
By building more pumped storage systems, it looks as if we could increase our maximum energy store from 30 GWh
to 100 GWh or perhaps 400 GWh. Achieving the full 1200 GWh that we were hoping for looks tough, however.
Fortunately there is another solution.
Demand management using electric vehicles
To recap our requirements: we’d like to be able to store or do without about 1200 GWh, which is 20 kWh per person;
and to cope with swings in supply of up to 33 GW – that’s 0.5 kW per person. These numbers are delightfully similar
in size to the energy and power requirements of electric cars. The electric cars we saw in Chapter Better transport
had energy stores of between 9 kWh and 53 kWh. A national fleet of 30 million electric cars would store an energy
similar to 20 kWh per person! Typical battery chargers draw a power of 2 or 3 kW. So simultaneously switching on
30 million battery chargers would create a change in demand of about 60 GW! The average power required to power
all the nation’s transport, if it were all electric, is roughly 40 or 50 GW. There’s therefore a close match between the
adoption of electric cars proposed in Chapter Better transport and the creation of roughly 33 GW of wind capacity,
delivering 10 GW of power on average.
Here’s one way this match could be exploited: electric cars could be plugged in to smart chargers, at home or at
work. These smart chargers would be aware both of the value of electricity, and of the car user’s requirements (for
example, “my car must be fully charged by 7am on Monday morning”). The charger would sensibly satisfy the
user’s requirements by guzzling electricity whenever the wind blows, and switching off when the wind drops, or
when other forms of demand increase. These smart chargers would provide a useful service in balancing to the grid,
a service which could be rewarded financially.
We could have an especially robust solution if the cars’ batteries were exchangeable. Imagine popping in to a filling
station and slotting in a set of fresh batteries in exchange for your exhausted batteries. The filling station would be
responsible for recharging the batteries; they could do this at the perfect times, turning up and down their chargers
so that total supply and demand were always kept in balance. Using exchangeable batteries is an especially robust
solution because there could be millions of spare batteries in the filling stations’ storerooms. These spare batteries
would provide an extra buffer to help us get through wind lulls. Some people say, “Horrors! How could I trust the
filling station to look after my batteries for me? What if they gave me a duff one?” Well, you could equally well ask
today “What if the filling station gave me petrol laced with water?” Myself, I’d much rather use a vehicle maintained
by a professional than by a muppet like me!
Let’s recap our options. We can balance fluctuating demand and fluctuating supply by switching on and off
powergenerators(waste incinerators and hydroelectric stations, for example); bystoringenergy somewhere and
regenerating it when it’s needed; or by switchingdemandoff and on.
The most promising of these options, in terms of scale, is switching on and off the power demand of electric-vehicle