Efficient energy storage needed to reduce use of fossil fuels

Storage is often a challenge in our daily lives and it holds true for energy too.

With all of the commonly cited problems of using fossil fuels, more people are starting to look at how to store energy from other sources.

One of the oldest of all energy sources, wood, used in stoves for heat and cooking, is still used by a large portion of the world’s population, sometimes by first making charcoal.

More recent technologies include wood fibre in compressed form such as pellets. Biomass can also include other grasses, field crop residues and algae.

Burning biomass releases carbon dioxide, as does fossil fuel. However, the replacement plantings will absorb carbon dioxide, so in principle, the use of biomass is climate neutral.

However, scarce heating resources in developing countries often result in deforestation and soil erosion.

Biofuel, which can be thought of as biomass in liquid form, has become popular recently. It has the same benefit as fossil fuel in terms of its ability to be stored and used in a different time and place. It can also replace gasoline and diesel.

However, biofuel is controversial because its production takes fossil fuel to produce. As well, it removes food crops from production, which can make food more expensive.

Water is another natural source of energy storage. Water wheels that powered grain mills were one of its first uses, and dams would store water to provide for continuous use.

Hydroelectric dams now serve a similar purpose. Stored water is kinetic energy. Power is produced when water is released to the electrical turbines. Production is proportional to the amount of water and the distance it falls.

However, dams can also have environmental impacts because they flood land and disrupt ecosystems.

Water gives up energy when it forms ice and re-absorbs it when it melts. Ice was used to preserve food be-fore electric refrigeration.

In its most crude form, a hole in the ground was partly filled with water, which froze in the winter.

As warmer weather arrived, the ice was maintained by covering it with early insulation, such as wood chips and straw. Food was lowered into the hole to stay cool and retrieved when needed. This was effective well into summer.

Urban residents had ice boxes, which were cabinets that contained regularly delivered blocks of ice.

Unless climate change is extremely dramatic, winter regions will always have ice-making capability.

Ice storage technology has been updated for milder climates. Ireland’s Dundalk Institute of Technology uses intermittent wind power to freeze water in storage tanks, which allows the ice to run the chillers to cool one of its buildings.

Water towers store water but also energy. Water is constantly pumped into a high tower for future availability, which could be described as a sort of water battery. The reserve capacity allows more rapid drawdown at strong pressure when day-time demand is high because of the height of the reservoir. This saves the need for large pumps and more costly day-time electricity.

Off-grid solar photovoltaic systems use lead-acid batteries similar to those used in automotives to store electrical energy from wind turbines and solar systems. Energy is captured in the batteries when the wind blows and the sun shines and is stored for later use when the wind stops and the sunlight disappears.

Electric and hybrid vehicles use lithium-ion batteries that can be charged overnight when power rates are lower or in daylight from solar sources.

Major electrical facilities in countries such as Germany and the United States are starting to use battery storage on a larger scale. It helps with peak power consumption because battery-stored energy can be re-leased into the grid quickly: faster than any other source.

This kind of storage helps develop intermittent renewable energy sources such as wind and solar.

In a way, the electrical grid facilitates storage. Supplying renewable energy forms such as wind and solar energy to the grid means other energy sources can be withheld from the grid, such as slowing down a hydro-electric source or shutting off gas-fired power generators.

Fuel cell technology was introduced 20 years ago, but it is developing slowly.

Fuel, usually hydrogen, is stored in a cell with electrodes. Electrical current and water are produced when oxygen is introduced. The cells can be transported, which means they can be used in vehicles. Conventional or renewable energy can be used to produce the hydrogen by separating hydrogen and oxygen from water (H2O).

Compressed air storage is in its infancy. It uses energy from generating stations at night, when they are generally under-used (most often burning coal). Compressed air is stored in salt caverns or large storage pipes, where it is later used to operate a turbine in hours of high power consumption.

Solar thermal systems extract energy during sunlight hours using solar thermal collectors and store that heat in tanks containing water. The energy is used to heat domestic water or provide heat to a building space at some time in the near future.

Geo-thermal heating systems can store excess energy (heat) in the ground during summer. Some of it can be retrieved, albeit only at the start of the long heating season.

For the cold north, the holy grail of energy storage is to “sock away” summer heat to use through the winter.

No economical solution is in sight, but the desire to reduce dependence on fossil fuel is driving research, so perhaps long-term storage problem will be solved in the future.

Will Oddie is a renewable energy, sustainable building consultant with a lifetime interest in energy conservation. To contact Oddie, send e-mail to energyfield@producer.com.

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