A method of storing energy

A method of storing energy

A method of converting a fuel into electricity (in relation to renewable energy the fuel is hydrogen).

Methods of using the Earth's heat to generate electricity.

Substances such as molten salt can be used to store and retrieve energy in the form of heat.

Hydrogen can provide a way of storing and moving energy around.

A method of storing energy

A method of generating electricity. Solar PV panels convert energy from sunlight directly into electricity.

A method of generating electricity. Solar thermal power stations convert solar radiation (visible and infra-red) into heat and then use the heat to generate electricity (alternatively the heat can be used in industrial processes).

A method of generating electricity. Wind turbines convert energy in wind directly into electricity.

There are two main types of geothermal energy generation:

• Volcanic heat: Geothermal energy can readily be generated from heat close to the Earth's surface in volcanic areas. This is a mature and proven technology.
• Hot rocks at depth: Rocks at great depths all over the world are hot enough to boil water and produce steam which can then drive turbines and generate electricity. The depths of the hot rocks varies, but outside of volcanic areas they are at least several kilometres below the surface. As of 2020 the technical difficulties have defeated efforts to economically use deep hot rocks for energy production.

Sheep enjoying the shade beneath solar panels Solar panels could be used wisely to work in with other land uses (see Solar Integration), like this, or they could be used with little or no concern for the local environment. Image credit Vicki Phelps via ABC

• A mature technology, although one in which the cost is continuing to decline substantialy.
• The materials used: glass, steel, aluminium, silicon, are common and readily recycled (although whether they are being recycled is another question).
• Solar PV farms are covering a lot of ground. The question of how the big areas of land beneath the panels should be handled is an important one. There is great scope for using partial shade provided by solar panels to advantage in growing a number of crops (see Scientific American) or the solar installations could be combined with grazing. However, some installations are being placed directly onto the ground and this could lead to serious soil, land and environmental damage.
• Aesthetics is a very personal matter, but I find it hard to imagine anyone seeing a solar farm as attractive; at best they might be made to be inconspicuous by where they are built and by using trees and shrubs as screens.

• A relatively underdeveloped technology that, at the time of writing, seems to have 'lost the race' with solar PV. The massive scale of solar PV production has reduced its cost to the point at which solar thermal cannot compete.
• The heat produced by solar thermal power stations can be stored for use in generating power later; an advantage over solar PV.
• The sustainability of the technology in terms of life expectancy and recyclability of materials is impossible to quantify because of the undeveloped state of the technology.

• A mature technology, although one in which the cost is continuing to decline significantly.
• Unlike solar farms, wind turbines take up very little space on the ground, farming goes on as before the building of the installations.
• Aesthetics is 'in the eye of the beholder'. Some see wind farms as ugly, others, especially those who accept the urgent need to change from fossil fuels to renewable energy, see wind turbines as graceful and a wind farm as an enhancement to a rural scene.

Recylability of batteries is a critical question in regard to their environmental sustainability. Lead-acid batteries are readily and routinely recycled, lithium-ion batteries are a very different matter, while some of the materials can be recovered, the process is expensive, far from all the materials are being recovered, and the lack of purity in the recovered material is problematic.

• Batteries are an efficient way of storing electricity in the short term (minutes, hours)
• They have proven valuable for providing what are called 'grid ancillary services', this is, maintaining stability in an electricity supply system.
• Battery life depends very much on the number of charging/discharging cycles in a given time. While the battery of an electric vehicle is not likely to be charged and discharged more than once a day, a battery used to help stabilise a power grid might undergo many charge/discharge cycles in a single day, although each might only use a small fraction of the battery's capacity. This question is discussed in more depth elsewhere on this page.
• Lithium-ion batteries are, at the time of writing, the dominant technology. They can, to some extent, be recycled, but as of the time of writing it has generally been cheaper to make batteries out of newly mined raw materials rather than recycling. This is not an environment-friendly situation. (More on this at fleetcarma: How Electric Vehicle Batteries Are Reused or Recycled.) Perhaps other battery technology, that is more readily recycled, may be developed?
• Mining of the cobalt commonly used (together with lithium, nickel, manganese and graphite) in making lithium batteries is linked with human rights abuses, including child labour and slavery.

There are several ways in which compressed air is used to store energy. At the time of writing it is very much a developing field of technology. (For one example, see Energy Matters, Five alternatives to grid-scale lithium-ion batteries.)

There are a number of technologies that store energy in the form of heat. Most forms of energy can be converted into heat with very high efficiency, however converting heat into a more useful form of energy, such as electricity, is much less efficient.

There are a number of challenges and inefficiencies involved in the generation, storage and use of hydrogen. Hydrogen technology is developing. Costs are coming down, efficiencies are improving. It is likely that it will soon become economically viable to generate hydrogen whenever renewable energy is pushing the wholesale price of electricity down.

• Generation of hydrogen by electrolysis is inefficient, about 70% of the energy is lost in the process.
• Burning hydrogen to generate electricity is also inefficient, about 70% of the available energy in the hydrogen is lost in the process.
• Fuel-cell combustion of hydrogen is also of low efficiency.
• Hydrogen is challenging to store and transport. It takes up a lot of space even when stored under very high pressure, if it is in contact with iron it tends to combine with the iron to form brittle iron hydrides, it can only be liquified at extremely low temperatures.
• At the time of writing Alan Finkel, Australia's Chief Scientist, said that the cost of running a car on renewable hydrogen could be three times the cost of running one on petrol or diesel.
• Hydrogen can be combined with nitrogen to produce ammonia, which is much easier to store and transport. The hydrogen can later be extracted from the ammonia. Of course there are energy and cost penalties in both conversions.

I have written more on the challenges of hydrogen in relation to energy storage and the conversion of power to gas (P2G) in Australia elsewhere on these pages.

This is being used by UK company Highview Power. At the time of writing it is very much a developing field of technology. (For one example, see Energy Matters, Five alternatives to grid-scale lithium-ion batteries.

This is a very mature technology.

• The life time of a pumped hydro station should be many decades.
• All the parts of a pumped hydro installation are readily recyclable.
• While being able to generate at short notice, pumped hydro's response time is not as fast as that of batteries.

At the time of writing this is very much a developing field of technology.

• Heavy masses can be raised and lowered in disused mine shafts.
• Heavy masses can be raised and lowered on towers.
• Heavy masses can be raised and lowered on slopes along railways.

(For one example, see Energy Matters, Five alternatives to grid-scale lithium-ion batteries.)

The graph above suggests that the capacity of most Tesla car batteries degrade by about 6% after 120,000 kilometres of travelling (the equivalent of about 240 full discharge/recharge cycles) and then degrade hardly at all after that.

Since the greatest distance covered by any of the Teslas involved in the study was 200,000 kilometres extrapolating beyond that involves risk, but the trend line is very suggestive; perhaps the batteries will still have a high capacity at 500,000 kilometres (the equivalent of about 1000 full discharge/recharge cycles) or more? Only time and more research will tell.

I suppose a more demanding test of batteries will be in utility-scale batteries on the grid where they go through many charging and discharging cycles every day.

This graph records power going into utility-scale batteries (charging - light blue) and coming out of (discharging - dark blue) in the Australian state of South Australia. It shows that the batteries switched between charging and discharging many times during the day. There is no reason to believe that this day was atypical.

I believe there were two such batteries operating at the time, Hornsdale Power Reserve and the Dalrymple battery; several others had been proposed and approved.

How long will these batteries last? I suspect that individual cells or groups of cells will be replaced as they fail. The relevant information on the longevity of the components may never be made public.

Related pages

Related pages on external sites...

The spiralling environmental cost of our lithium battery addiction; Wired on Energy, by Amit Katwala, 2018/08/05.

Environmental Impacts of Renewable Energy Technologies; Union of Concerned Scientists.

How will future energy storage work? Five alternatives to grid-scale lithium-ion batteries; Energy Matters

1414 Degrees; a company that is developing molten salt heat storage technology in Australia. The technology is especially suitable in situations in which industrial heat, as well as electricity generation, is required.

Green energy: What it is and how it works, based in Texas, USA

Related pages on this site...

Battery or hydrogen vehicles?, sustainability

Batteries, Pumped Hydro, Transmission: renewable energy generation is variable, how can the intermittency problems be overcome?

Electric vehicles: some thoughts

End of coal

Hydrogen and energy

Killer coal

Power to gas (P2G) in Australia

Pumped hydro energy storage

Snowy 2 or not?

South Australia's success in adopting renewable energy

Sustainable energy and environment; concentrating mainly on wind and solar photovoltaic

Why use, or not use, nuclear power?

Wind power in Australia

Wind power problems, alleged problems and objections

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