There is a big push everywhere to reduce our use of fossil fuels, replacing them with renewable energy sources, such as solar or wind power. This pressure, of course, is driven by climate change ideology and related concerns about a warming planet. The most eager folk hope that we will be "carbon neutral" by 2030, urged on by the United Nations and recent IPCC edicts and warnings. Regardless of how important you think the issue, the push for "clean energy" will doubtless continue unabated for a long time. Under the guise of "net zero", to stop emitting carbon dioxide from burning coal, oil and gas, many governments and industries are slowly installing more wind and solar power. Those both produce electric power, so there is also a push to switch vehicles and various industrial processes over to electricity.
The often unrecognized problem with wind and solar energy is that they are intermittent; the sun doesn't shine at night, the wind often does not blow, and clouds come by at random intervals. To make up for the times when renewable energy is unavailable, requires some form of backup energy storage medium; a system that can easily convert from electric grid power and back again in a controlled and practical fashion. Replacing all other electric power sources with wind and solar would require absurd levels of backup storage for many days, or even weeks -- to get us through a Canadian winter, for example.
To explain this better, consider a modest city of one million people, which typically requires 2 gigawatt (GW) of electric power on average, with likely variations between 1 and 3 GW. If all of that must come from wind and solar, the city would need at least 6 GW of solar and wind generating capacity to get an average around 2 GW, and a minimum of 30 GWh (gigawatt-hours) of backup storage just to make it through one windless night. That is equivalent to more than 500,000 electric car battery packs. Even then there would be a high probability of frequent outages. Maintaining a truly reliable grid solely with wind and solar power would increase these numbers further.
Of course by 2030 wind and solar will NOT provide all our electricity no matter how loud the alarmists shout and the green people dream. Nuclear energy will still be around, providing constant base generation (24/7), and with new technology, nuclear may be pressed into moderate, long-term growth, if governments can deflect or appease the anti-nuclear crowd. However, nuclear power cannot easily be dispatched; that is turned up and down at a moment's notice to match the instantaneous demand in the power grid. Nuclear takes days to start up or shut down properly and works best operating at a constant output power - hence the base supply.
Then there is hydroelectric power, which is somewhat or partially dispatchable, providing some limited "energy storage" by way of water reservoirs - not nearly enough, of course, to replace reliable and fully dispatchable fossil fuel plants, but some. And hydro-power cannot be expanded much since all the good sites are already in use. In addition to solar and wind, there may be other renewable energy sources that can run on stored energy; e.g. fuel cells and hydrogen, although I personally would not invest in that (see more below).
Dispatchable loads may also come into play: allowing your air conditioning or electric vehicle recharging to happen at the whim of the grid controllers, so as to shift their loads into times when power is abundant - all for a modest reduction in your cost per kWh. Mind you, industry and commercial enterprises have so far not been keen to accept brownouts in return for reduced rates, but some degree of "load shifting" should be palatable to most people if done well. In addition, there will continue to be modest improvements in process efficiencies: better insulated homes, tightened up industries, reducing energy and heat waste a bit. Together these may reduce or flatten peak loads through the day.
These changes, together with the inevitable residual natural-gas generating stations (which are very dispatchable), other traditional generating plants, and possibly newer power sources such as biogas, ethanol and biodiesel, would greatly reduce the amount of energy storage required as we move toward a more sustainable future. Nevertheless, huge investments in energy storage for electric power will have to be made if we want to continue adding wind and solar capacity while keeping our power grids reliable, as every consumer expects.
The obvious choice for electric energy storage is batteries. When grid power is plentiful, AC power is rectified to DC and used to charge electro-chemical battery cells. When extra power is needed, the batteries discharge through inverter circuits to feed AC power back into the grid. The current front-runner in this regard is rechargeable lithium batteries of varying internal chemistries and constructions. Encouraged by the growing EV market, lithium cells are slowly getting better and less expensive. They have a high round-trip efficiency (kWh returned to the grid vs. kWh required to recharge them) around 80%, are rapidly dispatchable in either mode, and have a decent usable life. Potential problems with limited materials resources can probably be worked around over time, and the cells can be recycled.
Large (gigawatt-hour - GWh) battery storage plants are currently in planning or under construction. They are intended to shift loads by a few hours at most, not by days or weeks, and even so, they will be expensive. Many such plants would be needed (terawatt storage!) to do away with fossil fuel generation altogether, so that is unlikely to occur by 2030.
There are other, often-hyped energy storage media possibilities, such as pumped water, compressed air, hydrogen, thermal storage, flywheels, artificial fuels, raised heavy weights, and so on. However, they all suffer from either low round-trip efficiency (e.g. hydrogen, air, thermal), capacity and scalability issues (pumped water, raised weights), or large capital costs (most of these). These technologies will find small, niche markets, but are unlikely to provide grid-wide backup power at the required level.
Combined with their low operating factor (less than 40% of the time storing and less than 40% releasing stored energy) means that any stored power supply is expensive on a dollars per delivered kWh basis (both capital and operating) compared to raw solar/wind or most traditional energy sources. As far as I am aware, no other energy storage technology can match batteries for high efficiency, flexibility, and response time. Yet even batteries can provide backup power at less than 33% utility (80% efficiency, combined with < 40% discharge time). Thus, if a battery plant and nuclear plant cost the same on a per kilowatt rating basis (I doubt if they do, but just suppose), then the long-term cost per delivered kWh of the battery plant would be at least three times that of the nuclear power plant, depending on other assumptions and variables.
Ultimately, of course, reality will have its way. Yes, we will get additional solar and wind energy, some large (but limited) battery storage plants, some percentage dispatchable loads, more nuclear, and slivers of additional hydro and other sources, but we will also keep many clean gas-fired turbine generators; and probably more than a few other carbon-based power plants will continue operating after 2030. Perhaps by then the "climate change" demands will become sufficiently subject to reason that the push for "net zero" will fade, diminish, or quite reasonably be pushed out a few decades more.
In the end, reality always wins, and we will continue to have a mix of energy sources and storage media going into the future.
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