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My Experience with 9.9kW of Solar panels, Fronius inverter and a Tesla Powerwall 2 by Peter Sendy.
I thought it was time to report in on my experiences and thoughts on my solar system at home.
Our guys installed a 9.9kW solar system when I moved into my new house (well new to me) a few
years ago now. My house has an east /west split install with 3.6kW facing east and 6.3kW facing
west, you can actually see my install on our website on the front page it’s the one with the green
I have single phase power and I used the old 300-watt Canadian Solar panels (I was happy to use
some old stock panels we had in the warehouse; they are working great) with our favourite inverter
a Fronius Primo 8.2kW single phase inverter with a single phase Fronius Smart meter to control the
export limiting to 5000 watts instantaneous export to the grid and it provides the consumption data
or advanced monitoring.
So, my system has been running perfectly since we installed it, I have a credit with my electricity company
which is currently around $700, I plan on waiting until its $1,000 and ringing them up and getting
that paid to me. In effect I estimate my system is saving / making me around $2,700 per year in total,
We have recently become Tesla battery installers and we installed the Tesla Powerwall 2 and
Gateway 2 on my house in December last year, so we kind of used my house (and a few others) as a
bit of a test site / learning tool for our electricians to get used to installing them.
The install went smoothly with Tim and Jesse being the sparkys installing the system with old muggins here
being the goffa, it took us about 4 hours all up to do the install and we did learn a few things that
day that would make our installs a bit easier on everyone in the future. We have a fancy type of sack
truck that has a hydraulic lift / lower system which really helps for the installs as the battery is very
I suppose the first thing I really noticed once we had it all up and running is just how seamless the
whole process was. As a part of commissioning the system we needed to ring the Tesla installer
support team to register the install and set up the monitoring. That process was very quick and
simple and was done in a matter of minutes (well done tesla support team).
The next thing was how cool the Tesla app is, its exactly how this type of App should be ULTRA
SIMPLE it’s so basic but shows you everything you need to know on one screen, I love the Tesla app /
I haven’t had the battery on for a full 12 months yet and I suspect I will use it a lot more in winter
when I am running electric heating but that said I have had it on through this mild Summer and have
used the AC a bit at night but not very much as it’s been a mild summer. I only seem to be using
about 3kW/hrs to 4kW/hrs per night from the battery when not running heating or cooling but I
expect that will go to 8kW to 10kW in the middle of winter (it gets cold in Echunga)
One of the things I was happy to learn about the Tesla is that in the event of a grid outage (black out)
the Tesla kicks’ in to run the show (as expected) but if it happens during the day the solar can charge
the battery while its making power during daylight hours (that wasn't the case with the Powerwall 1),
The other thing is we can program it to have a reserve in case of blackout. So, we can either
let it use all its power at night or program it to keep a reserve in case of blackout, I think that’s cool.
My brother Andy recently had a Tesla put on his place in town, he has a large house with 6
people and he has used all his tesla battery power by about 9pm or 10pm every night, he may
end up putting another one on at some stage but he really would need to add more solar panels to
make sure the second battery gets charged.
So, to the numbers, and I should use current numbers to make it more applicable to those who read
this article. Right now, a 10.73kW system on single phase is around $7,800 total out of pocket cost
on a simple single story install (2 story houses cost more to install) and the Tesla Powerwall 2 is
$11,000 out of pocket when installed at the time we install the solar. So, you can have a 10kW solar
system and a Tesla Powerwall 2 for less than 20K all up installed out of pocket cost.
As I said earlier with just the solar, I am saving/making around $2,700 per year which on the solar
alone equates to a payback time of around 3 years, this is obviously an excellent return on
investment and the reason we are installing so much solar in South Australia.
When you add the Tesla into the mix it will save you some money but those who cycle through more
of their battery power each night will have better returns so in my case, I seem to be averaging
about 4kW/hrs (kW/hrs is the unit of measure for a unit of electricity, you are charged by the kW/hr
by your electricity company).
So how do you put a value on the kW/hr of electricity coming from your battery, good question even
if I do say so myself. Most people who I have talked to about batteries seem to get this bit very
wrong. Most people I speak to regarding batteries have done their numbers by calculating they will
use x amount of electricity every night and then valuing that at electricity at retail rates which varies
a bit but let’s say .38 cents per kW/hr, this is simply wrong.
The only way you can use a kW/hr from a battery is if you put a kW/hr of electricity generated by
your solar system into the battery during the daytime. This means you are not selling that kW/hr to
your electricity company at say (in my case) 12 cents per kW/hr, so the real value of the kW/hr of
electricity from the battery in my case is about 26 cents. So 4kW/hrs per night by 26 cents works out
to $379.60 per year.
Now if you take my brother Andy’s house as an example, where he uses all his battery almost every
night, let’s say he uses 12 kW/hrs everyday that’s works out to be 4,380 kW/hrs at 26 cents is
$1,138.80 in savings per year. (based on current figures).
The other thing that simply has to be factored into the battery equation is the functionality the
battery provides. The Tesla Powerwall 2 with gateway 2 gives you the ability to run your home when
there is a black out or grid outage (provided the grid outage happens when you have some charge
(kW/hrs) in the battery) so what is that worth to you?
We have many clients who have installed a Tesla battery as they put a value on the functionality the
battery provides, and I am in that boat. I really like that I can still operate almost as normal when the
grid goes out. That being said running of a battery is not the same as running off the grid as the
maximum draw in black out or off grid mode is 3300 watts or 3.3kW of power when there is no grid.
So, the moral of the story is people will have different scenarios at their house and its probably best
to ring up and we can talk through your scenario and this should help to clear up the pros and cons
of battery’s as it will apply to you. I am happy to talk through your solar and or battery requirements
and quote you up accordingly, you can call me on 8391 5334 or email me at