9.6 Our Energy Future

We have some important choices to make in the next few decades because we have no option but to stop using fossil fuels as an energy source very soon, and we have to decide what mix of other energy sources, or other strategies, can be used to fill the gap. Some of our alternatives—wind and solar—are attractive because they are already cost effective, and are becoming more cost effective every year, but they are only available to us when the wind is blowing or the sun is shining. Wave and tidal, are more reliably available, but their development has been slow, even though the potential is significant. Large-scale hydro is attractive because it is readily dispatchable, so can be used to fill the gaps in the wind and solar supply, but there are environmental, social and practical limits to the amount that can be developed. Geothermal is an obvious choice in some regions. Nuclear fission is a reliable source of energy, but it has a bad reputation due to some serious past accidents and because of significant issues with disposal of nuclear waste. Nuclear fusion is still decades away, so is not going to be a candidate to replace fossil-fuels.

It is evident that we need to keep working on all of these options. That includes rapidly expanding solar and wind (and tidal and wave), and then ensuring that we have enough dispatchable energy (e.g., hydro) or continuous energy (e.g., nuclear) to fill the gaps. There are some other strategies that will be important to make it work, as follows.

1. 1. We—especially those of us in North America—can start by using much less energy, and that means driving less and flying less, living in smaller homes that are more energy-efficient, taking advantage of passive solar heating (and shading in hot seasons), and buying much less of the manufactured stuff that we don’t need.
   2. As shown on Figure 9.6.1, energy demand varies significantly from season to season and also from hour to hour within any day. In warm climates like California the electricity demand is lower in the winter than in the summer (mostly because of air conditioning). It is lowest in the middle of the night (1 am to 6 am) and highest in the evening (6 pm to 10 pm). There is also an afternoon low, but only in winter. In colder climates, where heating is needed through the winter, and where air conditioning is not widely used, the demand is typically higher in the cold part of the year. Electricity providers have to be very nimble to make sure that they can meet the demand at any time, but not generate more than what is needed. In the example shown for northern California, the demand ranges from a low of 7,900 MW on a Saturday afternoon in February, to a high of 15,400 MW on a Monday evening in July. Based only on this limited data, we can see that Pacific Gas and Electric (PG&E) has to be able to produce at least 16,000 MW for this market, but typically needs to produce less than 13,000 MW, and often less than 10,000 MW. If the demand curve could be smoothed out PG&E (and other utilities) could get by with less generating capacity overall and especially less peaking capacity, much of which is currently met with fossil fuel sources. Utilities can lower the peaks by charging more in the evenings (as PG&E does), and electricity users can play an important role by reducing their demand at peak times. For example, they could cook evening meals before 6 pm, or turn the a/c off between 7 and 9 and spend time outdoors on summer evenings, or not charge electric cars until after 10 pm. For most people, these types of changes would not represent a reduction in quality of life, just a change in habits.
      

      

   3. Another way to even out demand, and also maximize the benefit of sources such as solar and wind, is to store energy for short periods. An example of this is the Hornsdale wind farm in Southern Australia. When electricity production exceeds demand the energy is stored in a 100 MWh Li-ion battery (the world’s largest). That stored energy is used when demand exceeds production. Some of the presently available energy-storage options are listed in Table 9.6.1. It should be noted that these options can provide for storage of energy for a few hours to a few days, and so can help to smooth out daily changes in demand, but that they do not have the capacity for longer-term storage so as to smooth out seasonal changes in demand.
      While the options in Table 9.6.1 are described as “utility-scale”, lithium-ion batteries can be used for household-scale energy storage to help individuals avoid peak-time electricity rates, and even smooth the curve a little. The Tesla Powerwall has software that allows the user to store energy during low-tariff periods and discharge energy during high-tariff periods, and therefore provides an opportunity to save money and help reduce utility peaks.

      Table 9.6.1 Utility-scale energy storage options
      Data from the Environmental and Energy Study Institute (EESI)

      Type of Storage	Efficiency	Lifetime or Number of Cycles	Limitations
      Pumped hydro	70-85%	Many decades	Topography and land needed
      Compressed air	40-70%	A few decades	Low efficiency
      Molten salt	80-90%	A few decades	Heat source needed
      Li-ion battery	85-95%	1,000-10,000 cycles	Expensive at present, limited cycles
      Flow battery	60-85%	12,000-14,000 cycles
      Hydrogen	25-45%	A few decades	Low efficiency

   4. Another way to smooth peaks in electricity demand and in supply is to share electricity over wide areas. This way, for example, solar electricity produced in the afternoon in western and central North America could be used to help supply the peak evening demands of eastern North America. This type of sharing would involve the construction of super grids with efficient high voltage direct current transmission (which suffer energy losses of less than 2% per 1000 km). One example of this type of connection is the Québec–New England transmission line which has a capacity of 2250 MW and brings hydro power from northern Québec to the eastern USA. Another is the Pacific DC Intertie that brings 3100 MW of power from the Pacific Northwest to southern California.

Media Attributions

• Figure 9.6.1 Steven Earle, CC BY 4.0, based on public domain data from U.S. Energy Information Administration (Feb. 2021) https://www.eia.gov/todayinenergy
• Table 9.6.1 Steven Earle, from data provided by Environmental and Energy Study Institute (EESI), CC BY 4.0, https://www.eesi.org/papers/view/energy-storage-2019