It’s easy to produce power when the sun is shining. The Achilles heel for residential solar system has always been “how can I best store the excess power I make during the day for use when the sun is not shining?”
The traditional method is the old faithful – lead acid/gel batteries, which still do have their place in the home/office. They are good at storing power where weight and space is not an issue.
Lead acid/gel do not cycle very well, and are sensitive to how far you run them down, thus their life is shortened by daily cycling beyond 50% in very warm or cold conditions.
Lithium based batteries are what we see used today in most portable devices, and can be scaled up to megawatt and above size (+1000kW).
They typically can be cycled about 4000 – 6000 times to 100% depth of discharge and are not as affected by temperature as much as lead acid/gel.
Within the Lithium based umbrella, there are various qualities and chemistry, including “Lithium Ion” “Lithium Iron Phosphate – LiFePo4” and “Lithium Titanate”, which is by far the best technology currently commercially available.
We typically use lead acid for load-shed proofing or back-up systems due to the low cycling needed and the lower cost. They may just have to “standby” for days before getting used.
For solar systems that are using the batteries every day to offset Eskom usage, we would suggest a good “Lithium Iron phosphate” which are also used by some of the larger telecommunications companies in Africa.
The Rolls Royce of storage is the Lithium Titanate units from the same supplier.
They can be cycled over 20 000 times to 100% depth of discharge and can withstand temperatures of -25 degrees Celsius to +80 degrees Celsius.
So, in summary, we will take all of the above into account when suggesting the size and type of storage according to your needs.
This is just a brief summary, the conversation about charge and discharge rates and energy density of the various technologies can be discussed in a separate forum.
(Copyright) John Airth (2020)
