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How Can You Add Batteries To An Existing Solar System?

Battery storage capable solar PV systems require special wiring and some require 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 few years – so chances are very high that many people considering adding batteries to their solar power system do not have one. However, there are some batteries that can be added to a solar power system without requiring an additional inverter.

Most people (who use average/above-average levels of electricity in their homes) will also need to strongly consider upgrading their current solar power 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 some 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:

  • 7 x 300W panels (to bring his system size up to 5kW – well, just over): ~$1,500 + installation
  • Upgraded inverter – $1,500 + installation
  • Tesla Powerwall battery: $11,700 + installation

Total cost: $14,700 + installation

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, $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 many more years!

The worst part is – the Powerwall only has a warranty of ten years (as do most other solar battery manufacturers). So it might reach the end of its lifespan before he’s even recouped his 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 solar battery prices drop significantly. Until then, the best bang for buck is solar-only.

>> Next: “Battery ready” solar systems, and how to buy one >>

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