The record breaking summer temperatures of early 2013 has lead many climate sceptics to question their stance on Climate Change, it also saw energy retailers faced with extreme ‘peak events’ as many households, in an effort to escape temperature over 40 degrees, turned on their air conditioning units.
If lucky enough to have invested in a residential solar PV system, the cost of keeping cool may largely be avoided by households – with the exception of energy used at night after solar panels stop producing energy. However, in the future, residential solar battery storage solutions may allow home owners to keep cool all night without worrying about rising energy costs.
Residential solar power battery storage solutions
One of the main barriers to transitioning to a low-carbon, renewable economy is reliability of supply. Solar and wind power both suffer from similar issues, the strength of the wind varies or, with solar, we have an overcast day which reduces the energy produced. On a daily basis solar energy only produces energy until the sun goes down, and can only be utilised during this time – unless, of course, you have battery storage.
Adding battery storage to a solar PV system, at residential or commercial levels, ensures that supply remains reliable and uninterrupted. A suitable device, and an appropriately sized system, will allow a household to produce and store enough energy to meet their energy needs without resorting to grid connected power during the night.
The batteries available commercially at the present time are heavy and expensive, roughly doubling the cost of a solar PV system. However, advances are being made in battery technology including sulphur cathodes and zinc-air rechargeable batteries.
Zinc-air rechargeable batteries
Currently commercially available battery storage solutions are based on Lithium-ion technology which can store around 455 Wh.kg-1. The zinc-air technology theoretically has three times the energy capacity (1350Wh.kg-1), in part due to the lighter zinc metal but additionally oxygen is taken directly from the atmosphere when discharging. When the battery is recharged this oxygen is released.
Zinc has a number of benefits over other chemicals. It’s relatively non-reactive, well understood and, because of is extensive use in existing technologies, benefits from a well developed recycling network. However, despite zinc’s favourable properties and extensive research history researchers have struggled to make an efficient zinc-air rechargeable battery. The main issue has been the ‘oxygen reduction electrode’ and the control of the reactions that take place when the battery is charged and discharged.
In addition to this main issue, researchers have had to deal with a number of issues associated with the battery being open, which is essential for oxygen to enter and exit the cell.
Current research on rechargeable battery storage
The historical issues faced by researchers looking to develop a commercial zinc-air battery have largely been associated with the electrolyte (conductive solution) within the battery, in this instance a concentrated potassium hydroxide solution. Researchers at Deakin University will investigate the development of a new type of electrolyte, room temperature ionic liquids (RTIL), comprised of organic low melting ionic salts.
The development of this new ionic solution will prevent electrolyte loss though the air holes in the battery, as they contain no water and are extremely hard to boil or evaporate. RTIL’s have been used previously to coat zinc onto steel, this is applicable to battery technology as it prevents short-circuiting through multiple charge/discharge cycles. Finally, the majority of RTIL’s are stable in the air preventing the formation of carbonates or other precipitates that effect battery function.
A number of breakthroughs have been made already, in the next two years the research team hopes to develop the research to a point where full sized cells can be studied for cyclability and efficiency. The long term goals of the team are to develop cost effective battery technology that will allow households across Australia to make the most of all the energy their solar panels produce.
© 2013 Solar Choice Pty Ltd
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