Like many solar owners, I’ve been watching with great interest as more energy storage products become available in Australia. The introduction of all-in-one energy storage systems and hybrid inverters have helped bring prices down for households looking to add energy storage. But batteries aren’t yet cheap. Plus, if you are an existing solar owner, the options for retro-fitting storage to your set up is another expense again. So when a good friend told me that a local technology business was offering to give away some used lead acid AGM batteries “to a good home” I thought why not? This was a good opportunity to pull my sleeves up and see whether the economics would stack up if the biggest cost of energy storage – the battery – was removed. So I researched the batteries (Enersys 24 x 2V cells) and then went looking for a suitable battery inverter to retrofit to my existing SMA three-phase solar inverter.
Putting it all togetherI quickly discovered that there are many challenges to getting a suitable storage inverter including:
- support for my three phase home (most homes are single phase)
- good charging and discharge rates (to fill the battery quickly and cover higher powered loads respectively)
- support for low voltage batteries (both lead acid and lithium for upgradeability)
- compatible with Reposit Power (to gain income from demand response programs aka DRM)
- low cost
- a three phase energy meter to accurately monitor net import/export across all three phases
- 75A charging and 75A discharging (3.6kW)
- battery backup feature
- support for LV batteries both lead acid and a range of lithium batteries
- retail price of ~$1500
With the research done it was time to collect the batteries. We split the cost of hiring a small van between us, and in an afternoon we’d moved over two tonnes of batteries around the suburbs – and into our garages. There was no need to visit the gym on that day! I then had the storage system connected by a qualified solar installer. The total cost was a little over $3000 including the battery inverter, all cabling and labour. I also had the installer add a double powerpoint to provide a low-cost emergency battery backup solution rather than rewiring specific circuits in my house. Given the high reliability of the electricity supply to our Sydney suburban home – rewiring the house to provide battery backup wasn’t worth the cost.