What is the connection between buying a new car and installing 19.3kW of PV panels, and a almost 10kWh of battery storage on being off grid? It depends.
For more than 10 years I have intermittently looked at the cost-benefit of developing solar panel and battery storage technology. Noted that all the experts (Renew magazine and solarquotes.com.au ) agreed that on a cost-benefit basis solar panels and export of surplus power back to the grid is worth it. But battery storage for those grid-
connected is not.
But, after having six days without power many years ago. Judging that power retailers are less and less willing to have resources on standby case of massive power outages. I’m now determine to get a off-grid system capable of providing power in the event of a sustained grid-failure. With export to the grid a much less important consideration.
But every time after I read up on panels and batteries. I am particularly taken down with battery technology. So I took no action instead deciding to await further improvements in both.
Then I read issue 151 of Renew Magazine, and everything changed.
I read the article on page 96 in which you profile Dr Tony Vassallo. That reports he and his wife Sandy installing five Zenaji ‘Aeon’ Lithium Titanate batteries and read further about them online. Comparing them to the Tesla PowerWall (who claims as to Lifespan are reputedly not to be trustworthy) and the RedFlow Zinc Bromide batteries. Which up to then seemed to be the most credible solution on the market. I made myself a little table to compare principal features, as below.
But what really disappointed me about the RedFlow battery was that if the grid fails I would need two of their ZBM2 batteries to deliver the 5kW to 6kW power needed to run electric cooktop + electric oven + normal house load (say 600W to 1000W).
Further reading suggested that both the Tesla PowerWall and the RedFlow ZBM2 are tortuously SLOW to charge. Effectively requiring many hours of steady PV power to recover the batteries to full charge after being drained/discharged overnight. This restriction is not shared by the Zenaji batteries. (this has important advantages as I am now beginning to find out).
So I decided it was time to make the commitment. I started by contacting solar installers, asking for a fully off-grid capable system with 5 Zenaji batteries with the intention to fit several more once the per unit price drops over time.
The only installer in NSW that even knew about Zenaji batteries was 24Hour Solar Power based in Lismore. So that is
the company that I used.
I had read some articles from solarquotes.com.au recommending; high-efficiency panels as they suffer less from heat/light degradation over time, and connecting articles. To off-grid installations that suggests 7 to 10 kW of panels should match with battery storage of at least one days’ usage. Preferably more if you want to survive cloudy periods in Winter. But as I am on the grid (for the time being at least). I have decided to try a completely different approach of:
- 9.65 kWh battery storage (five x Zenaji) which is only half our daily usage; and
- 49 high-efficiency (395W) panels
- A simple adjustable timer switch on the 4800W existing hot water service. So that I can restrict its operation to between midday and 4pm; and
- A generator input for my existing generator (rated 3.2 kVA continuous).
Experience with Zenaji’s system
This system was installed on October 6, 2020, and on reasonably clear days the panels would carry the house load from just before 7am and fully charge the batteries before 9am, and after that it exports between 5kW and 10kW to the grid but at midday the Hot Water Service demand must be met for an hour or so before significant export resumes.
On reasonably clear days the system supplies all of our own 20kWh load and on average exports 40kWh to the grid. Now that we are into summer the export figure frequently exceeds 70kWh for the day. even when we run our ducted air-conditioning flat-out during daylight hours.
The results on very cloudy, totally overcast, days are the reason to put on so many panels. If heavy overcast and rain allows us to generate as little as 1000W. Although if we get a partial break in the cloud cover even for half an hour the large panel array matched with the ‘wide-throat’ of the Zenaji batteries sees their charge improve at an astonishing rate.
Without such break in the cloud cover however; at the end of daylight hours the batteries may be at less than 50% capacity so. Depending on what we are cooking for dinner, we have had to resort to the grid during the night. In the event this occurred during a time of grid-failure. This would use our 3.2kVA generator to gradually top-up the batteries with the benefit that at any time we have a load that exceeds the generator capacity; such as cooking, or the hot water service. We have no fear of over-loading the generator, as the demand will be easily met from the topped-up batteries.
Comparing a new battery storage with a new car
Now, all this cost $49,000, almost the price of a new car. My existing car is 22 years old and would cost $65,000 to replace. So in the last two years I spent $15,000 on new suspension, clutch, radiator and reconditioned gearbox and engine. For those of you who purchase a new fuel-efficient car every five years. Did you ever weigh up the environmental cost of creating all the aluminium, plastic and steel each time you buy a more ‘efficient’ vehicle? I hope to get another 400,000km out of the car over the next 22 years or until I can afford to replace it with a robot-driven electric car powered by my solar array.
With the $50,000 I saved by NOT buying a new car I have realized a decades-held dream and had installed a powerful PV + Battery system. I expect to last 20 years; so it does not matter whether it pays for itself in a traditional cost-benefit analysis. But watch this space; it is just possible that with a 20-year lifespan this system could be financially viable on its own merits.
After a smart-meter is fitted. It allows us to see that as we are exporting 25kWh to the grid for every kWh we consume; it made sense to change electricity retailers to one that provided a better feed-in tariff. So we changed suppliers and await our first account with interest.
On our estimates instead of paying the electricity company $2300 p.a. we should be receiving a similar amount from them instead. A $4000 p.a. reversal in fortunes over 20 years easily exceeds the cost of this installation. But let’s see what happens in the winter months after all.
Words and images with thanks from H&M Christiansen, Central Coast NSW
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