Battery storage: What am I buying, apples or oranges?

There’s plenty of sizzle but what exactly is the sausage?

With the explosion of domestic battery storage products on offer, early adopters are generally savvy with the technical aspects of this new technology and know what questions to ask.

But Ma and Pa Kettle, who will make up the clear majority of battery storage owners in the future, have no simple means of comparing product offers and can’t be assured that their investment will meet their expectations.

This week this writer is in Madrid, Spain, on behalf of Australia, helping form the international umbrella standard on Electrical Energy Storage Systems, the standard that will endeavour to cover all forms of electrical energy storage whether it is electro-chemical, hydro or any other method.

One of the significant points for discussion, and one which has crept up like a Vietcong guerilla, is the means by which energy storage devices, most specifically those with degrading accumulation like chemical batteries are “rated”.

Currently, early adopters are relying on the “sizzle” put forth by the storage suppliers and in many cases availing themselves of the excellent reference site put together by Finn Peacock from Solar Quotes.

Like the rush of domestic PV installations which eager or crooked sales people over sold, leaving the installer to take the flak from dissatisfied customers, battery storage risks the same reputation in the absence of a uniform rating system for particularly domestic storage.

It’s all very well to place a nameplate that says your battery storage system is rated at say 10 kilowatt hours, but what does that mean to a person spending around $10000.00, what is the customer’s reasonable expectation and how can this be readily defined and policed?

If we use the Tesla Powerwall 2 as an example, their warranty has settled on the headline capacity of 13.5 kWh. The warranty states that the units will continue to operate at a minimum 70% of this initial capacity after ten years of daily cycling. It must be assumed that the system will continue to operate after that time but at an undefined capacity.

It is reasonable for the suppliers to limit warrantied values and performance to a period that reasonably reflects the purchase cost. In the case of battery storage, 10 years seems more than a reasonable period where the customer may take recourse on the supplier, should the product fail to meet the customers well informed expectations.

These expectations are the issue; how do manufacturers clearly articulate the performance and longevity characteristics of battery storage in a way that can be simply compared with the competition?

It has been suggested that the correct way of rating the storage of a battery storage system is to under state and over deliver. In this case, the Tesla would have a rating of 13.5 x 70%, so should therefore be sold as a 9.5kWh system, with a uniform industry reference period of ten years.

For solar PV modules, this works because the modules are uniform in their componentry, construction and usage, battery storage is a totally different story:; chemistry, cycling and environment all vary greatly, so to simplify the selection process for consumers is a great challenge.

Currently most electrical appliances, and motor vehicles have a simplified rating system which is a score with a minor amount of technical clarification.

This is simple enough for ordinary consumer to readily compare purchases, having assumed that all variables have been assessed according to a uniform standard to produce the result and that these results are enforceable by consumer laws.

As Finn Peacock has deduced, currently the only real measure of value of a battery storage system is the amortised cost of each KWh absorbed and delivered by the units.

Unfortunately, in the standards world cost cannot be used to determine performance as it is a moving target. So how do we collate all of the variables of a battery storage unit and simplify this to a simple system which allows a customer to compare apples with apples?  Watch this space.

Rob Campbell is Managing Director of Vulcan Energy.