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Backup Solar power

Backup Solar Power Options 

Backup solar power comes in several forms and there are significantly different solutions on offer for commercial and industrial applications as well as domestic residences. Battery-based backup solar power systems are available for both commercial and residential applications and function much like generators without some of the drawbacks that come with generators. With Eskom looking less and less likely to be able to provide enough energy reliably for the foreseeable future, most South Africans, and local companies, are looking to install some form of backup power system.

Battery-based backup solar power systems are silent, do not produce toxic emissions and have very low running costs. They also produce clean power with very short handover (switching) times. The running costs are extremely low as the energy stored in the battery is usually produced by the sun at no cost aside from the initial capital cost of the system. Loads can be fed directly by solar power input or drawn from the battery during bad weather and at night.

Battery-based backup solar power systems are not the only systems available, and engineers have designed and tested numerous storage solutions for solar energy especially when large-capacity commercial and industrial energy storage is required.

Backup Solar Power and Chemical Batteries

The first true chemical battery was invented by Italian physicist Alessandro Volta in 1800 – his name is the source of the electrical terms, volt and voltage. A crude stack of alternating discs of copper and zinc separated by cloth soaked in salty water became the world’s first device that could store and release a charge through a chemical reaction. The most enduring chemical battery, the lead-acid battery, was invented in 1859 and is still starting internal combustion engines in cars today. It is also the oldest battery type that was capable of being recharged. Several alternative chemistries were developed for batteries that never really challenged the dominance of lead acid. The nickel-cadmium and nickel-metal hydrogen are examples that had some promising characteristics, but these batteries were very sensitive to being overcharged and prone to damage.

The quantum leap in battery chemistry came in 1980 when American physicist Professor John Goodenough invented a new type of lithium battery. Together with M. Stanley Whittingham and Akira Yoshino, Goodenough developed a battery in which lithium could migrate through the battery from the anode to the cathode as a lithium-ion. In a relatively short time, lithium-ion batteries have replaced lead-acid batteries in many applications including energy storage for backup solar power systems, although they were initially substantially more expensive. Global mass production and economies of scale have reduced the cost of lithium-ion batteries dramatically and they are now the go-to storage solution for both large-scale and residential backup solar power.

Pumped Water Energy Storage for Backup Solar Power

Pumped storage systems are a relatively cost-effective backup solar power solution that works better for large-scale projects. They are well-suited to utility-scale power storage. Eskom has several pumped storage schemes that do not use solar but use grid power during off-peak times to store energy in water for peak-time usage.

In these systems, whether solar or grid power is used, large volumes of water are pumped from a lower holding dam to an upper holding dam using solar or off-peak grid power. If there’s a sufficient height differential between the two dams, the water can be gravity-fed from the upper to the lower dam through a turbine to generate power when it’s required. The limitations of these systems are imposed by the fact that they require specific site conditions to be feasible. There must be enough water available and a substantial difference in elevation in a relatively short distance between the upper and lower dams. In a water-scarce country like South Africa, sites that are suited to pumped water energy storage are limited.

Backup Solar Power Using Liquid Air Energy Storage

Liquid air energy storage uses electrical power, from solar or another source, to cool air to the point that it liquefies. The liquified air is stored in insulated tanks until energy is required. It is then brought back to a gaseous state by exposure to ambient temperature air or waste heat from industrial processes, where the expanding gas is used to turn a turbine and generate electricity. These systems use off-the-shelf components and well-established technology. Liquid air energy storage is also referred to as ‘cryogenic energy storage’ as the liquified air phase produces very low temperatures.

The process is suited to large-scale, long-duration energy storage. A plant situation is not limited to a particular site so the systems can be located at the point of demand. Working fluid for the process can be liquefied air or liquid nitrogen. These systems perform similarly to pumped hydro schemes and can harness industrial low-grade waste heat from co-located processes. Plant size may range between 5MW to hundreds of Megawatts.

A UK-based energy group plans to raise £400 million to build the world’s first commercial-scale liquid air energy storage plant near Manchester by the end of 2024. The facility will be capable of storing 50 MW of energy and will be one of the biggest battery storage systems in Europe. The minimum projected output of 250 MWh is enough to power 50,000 homes for five hours.

Plant-operating power will come from excess energy generated by intermittent renewable energy sources such as wind, solar and marine power.

Compressed Air Energy Storage for Backup Solar Power

Energy storage systems for backup solar power using compressed air are another option better suited to large-scale storage. This type of storage can typically only take place at specific existing sites. Electrical energy is used to compress air at up to 700 kgf/m² and store it, often in disused mines or underground caverns.

When the electricity demand is high, the pressurised air is released to generate electricity through an expansion turbine generator. Excess electricity generated by intermittent renewable sources of energy such as wind and solar power can be used to compress and store the air in what is known as a ‘thermo-mechanical battery’.

Backup Solar Power Systems from the Power Solutions Experts

The complexity of solar power systems increases with scale. Systems that must form part of a larger power campus that includes grid interaction, wind turbines and generator integration are technically challenging. Small residential systems are relatively simple, but utility-scale systems require a high degree of skill and expertise to design, commission and optimise. PacB Power Solutions has a wealth of knowledge in complex large-scale genset integration, renewable energy and diverse power systems. We offer utility-scale industrial, commercial and residential solar solutions. Call PacB today for backup power you can rely on.