How Can You Add Batteries To An Existing Solar System?
Battery storage capable solar PV systems requires special wiring and a special inverter in order to interface with the batteries properly.
Inverters that can work with batteries have only been on the market for the last year or two - so chances are very high that almost everyone who is considering adding batteries to their solar PV system does not have one.
Most people (who use average/above-average levels of electricity in their homes) will also need to strongly consider upgrading their current system size if it's less than 4-5kW - we recommend this as a minimum system size so it can produce enough power on overcast days or in the winter to charge the batteries.
Let's use the example of Gary, who bought a 3kW solar system two years ago, uses the typical amount of electricity for an average Aussie home (about 16kWh/day, at a cost of 30c/kWh) and wants to add a Tesla Powerwall to his home. Gary will require the following:
8x250W panels (to bring his system size up to 5kW): ~$1,500
Battery-compatible inverter (such as a Fronius Symo Hybrid or SolarEdge system): $3,000
Tesla Powerwall battery pack: $10,000
Total cost: $13,500
Gary balks at this cost - he only pays $200/quarter for his electricity at the moment, with his 3kW system offsetting half of his electricity usage. Even if adding a Powerwall completely wiped out his electricity bill (unlikely), $800 worth of savings per year means that even after ten years, he's only saved $8,000 - the battery upgrade won't pay for itself for another 5 years!
The worst part is - the Powerwall only has a warranty of ten years. So it might reach the end of its lifespan before he's even recouped his $13,500 investment.
In conclusion? It's expensive, but you can add batteries to an existing solar system. Don't expect it to make any kind of financial sense until battery prices drop significantly over the next 5 years.