It has seemed that solar batteries aren’t worth the expense and effort, costing around $12,000 or so. Queensland’s Solar Battery Rebate came along last year and piqued a lot of interest in storage solutions, but is this $3,000 incentive enough to tip the balance?
What can batteries do for you?
Quite simply, they can store any power you generate during sunlight hours and discharge it at night. This might sound as if it’s saving you as much money as you’d spend on-grid power every night, but you have to remember that you could have sold all this excess power back to the grid. The real value of the excess power is your electricity rate minus the feed-in tariff that you’re missing out on.
A quick savings comparison
The average T11 rate for Queensland’s most popular electricity providers is $0.273 (I’ve tried to find 2019 prices, but even the companies’ own sites still have 2018 figures). When you subtract the average feed-in tariff figure from these providers, the average kWh coming from the battery is only worth $0.128, not $0.273. This is a significant difference.
This difference has a big effect on the payback period for the cost of the battery. Two very common batteries are the 13.5kW Tesla Powerwall and the 4.8kW Samsung.
The Tesla Powerwall
Even with a best-case scenario with no rainy or overcast days and daily full usage of the stored power, the household is only saving $1.73 per day (13.5 x $0.128). This is $630.72 each year, which means the $12,500 battery pays for itself after 19 years and ten months if there’s no rebate. Even with the rebate, the homeowner won’t see daylight (as it were) for 15 years, which is five years longer than the Powerwall’s warranty period.
The Samsung Solar Battery
Using the same workings, the Samsung battery, which costs $6,000, fares even worse. This battery only has a 4.8kWh capacity so without the rebate users are looking at a 26-year payback period. With the rebate, this is halved to 13 years, but this again is longer than the 10-year warranty. This battery can only offer a 3kWh continuous discharge, so might not cover a lot of night-time use.
These are also best-case scenarios with no rainy days, no holiday periods, no outages, and no degradation in either the battery or the panels. It looks like solar batteries are only worth it if the payback period is less than ten years.
Blended payback periods
If you’re looking to install panels and battery at the same time then you’ll have an average payback period of eight years, which is within the usual 10-year warranty. However, this payback is paid back primarily by the panels, not the battery. The battery might still be taking 15 years to pay back while the panels take just three. Average these figures out and you’re looking at eight years, which is great if you can afford both panels and battery. Just be aware that your battery isn’t going to pay for itself any time soon. It may, however, have other values for you.
Solar batteries are worthwhile in some circumstances
If you’re in an area with regular outages, then having your back-up battery can be invaluable. In fact, during an outage you wouldn’t be exporting your power back to the grid anyway, so you’re essentially getting your $0.273 for these periods.
It’s also important to many people to be able to maintain power – people who work from home or who have vulnerable relatives in the household, for example. In these circumstances, the monetary value is at most partly relevant – it’s keeping the lights on and the drinks cool that matters most, rebate or not.