Fun with Powerwall 2 stats...

[Hungry Mile]

Thanks Vostok for starting this discussion, and to Hairyman and others for the contributions. It's really informative.

I too use Powershop, but AGL for gas. But I don't have a battery.

We run a home based business and so we have additional energy costs to the point that we average around 15 kWh per day of imports despite running 6.95 kW of solar panels. I just can't make a battery stack up financially yet. While I'd love to add a battery to further remove coal from the mix, the added expense in removing gas for heating is also unjustifiable.

Now that I'm getting a car with a 75 kW battery, that will change things up! I plan to install a Zappi so I can ensure I'm charging from solar exclusively as I'm exporting more energy than I can use during the solar day.
I'm guessing that means the household battery is further away.
Then again, I don't need to drive every day, and mostly, not far. So I'll still be exporting buckets full of sunshine. Maybe a battery is therefore still worth it?
Just semi publicly ruminating , but if anyone wants to chip in with their two bob's worth, I won't mind!

 

[Hairyman]

After reading Vostok’s reply earlier I have changed to Origin for my gas. I pay $1 per week to offset the carbon from the gas. Their pricing tiers are a little more expensive for the first 1855MJ, but cheaper after that. Likely a bit cheaper overall. The carbon offset was the main attraction for me. No one else seems to offer it.

 

[sberinger]

No battery here
Just huge solar 21.6KW
generated 116KWh today even with bad smoke
I export so much it covers what I use from the grid
even get a refund

 

[Anubis]

No battery here
Just huge solar 21.6KW
generated 116KWh today even with bad smoke
I export so much it covers what I use from the grid
even get a refund

Wow, you have a lot of roof space. That would be around 72 panels.
Is your system on PVOutput?
I have 7.2KW and am very happy with the 40KWh generated on most days.

 

[Vostok]

No battery here. Just huge solar 21.6KW. generated 116KWh today even with bad smoke. I export so much it covers what I use from the grid. even get a refund

Yikes... That is a big solar array. You must have 3 phase power (I’ve heard the limit in NSW is 10 kW per phase). Your system is 3.7x mine. The most solar I have ever generated in a day is 36 kWh.

In recent days, the smoke over Sydney has reduced my solar output by about 5%.

I have heard of people with big solar arrays say their bill is in credit, but do they ever actually pay out the cash, or does the credit keep going up and up and up... ?

 

[Anubis]

I have heard of people with big solar arrays say their bill is in credit, but do they ever actually pay out the cash, or does the credit keep going up and up and up... ?

I get a credit each quarter ($140 in winter quarter). I have my electricity and gas with AGL. I just ask them to move my credit over to the gas account each quarter.

 

[BirdOfPrey]

I have heard of people with big solar arrays say their bill is in credit, but do they ever actually pay out the cash, or does the credit keep going up and up and up... ?

I can confirm Origin pays out the credits via bank transfer.
Just need to find this option, the link for credit transfer is hidden deeply in mobile app FAQ section

 

[sberinger]

I have heard of people with big solar arrays say their bill is in credit, but do they ever actually pay out the cash, or does the credit keep going up and up and up... ?

Yes I get the cash back to nominated bank account each quarter

Most I have generated in a day was 150KW last year
Most I have generated this year was 136KW on 13th Nov

Got a new project
Building granny flat on investment property with 30KW system
Then charging tenant for electricity

 

[Vostok]

I get a credit each quarter ($140 in winter quarter). I have my electricity and gas with AGL. I just ask them to move my credit over to the gas account each quarter.

Now that is a smart idea which I’ve never considered before, and a good argument for having gas and electricity with the same retailer.

 

[Vostok]

I have a different tariff regime. It is available to anyone with an electric car. It gives me a 9.02c/kWh rate from 0000-0400.

I modded my spreadsheet to enable it to have four different ToU tariffs and whacked in the Powershop tariffs including the EV one.

It reduced the cost, but only by $18 for this 4 month period. The breakdown is below:

So it seems having a better FIT of 20c does a lot more to reduce the bill than having an extra-cheap overnight tariff.

 

[Hairyman]

I modded my spreadsheet to enable it to have four different ToU tariffs and whacked in the Powershop tariffs including the EV one.

It reduced the cost, but only by $18 for this 4 month period. The breakdown is below:

View attachment 480678

So it seems having a better FIT of 20c does a lot more to reduce the bill than having an extra-cheap overnight tariff.

Excellent information to have. I seem to be getting a lot out of their discounts for prebuying my power. I’ll run some more numbers for myself. It also looks like the next point if differentiation for the power companies will be FiT

 

[JayTee]

I was $200 in credit for the first 6 months of having a 8kw solar system but was only consuming about 20kw per day.

I then bought the S 75D and as I drive about 100km daily, our consumption went to about 40kw per day.
To keep things in credit I was tossing up between paying 14k for a powerwall with a 15 year payback or paying 9k for an aditional 7.4kw of solar with about 5 year payback.

We have 3 phase power and in NSW you can actually go up to a 30kw system if you want and can fit it. Because our house is a largish single level house with a big north facing roof, I decided on the extra solar option and couldn't be happier.

Averaging 90kw a day generated with a best of 107kw. Most days send 50kw+ to the grid.

I would like a battery to make our grid imports zero but it dosent make sense yet to me financially with our usage. Ill hang in there until PW3 is available or until a possible govt subsidy like SA has.

 

[JayTee]

No battery here
Just huge solar 21.6KW
generated 116KWh today even with bad smoke
I export so much it covers what I use from the grid
even get a refund

Interested to know which energy provider you are with? Most of them have a 10kw export limit. Do you export limit your invertor or feed it all in?

 

[Vostok]

We have 3 phase power and in NSW you can actually go up to a 30kw system if you want and can fit it. Because our house is a largish single level house with a big north facing roof, I decided on the extra solar option and couldn't be happier. Averaging 90kw a day generated with a best of 107kw. Most days send 50kw+ to the grid.

I almost can't conceive of that much solar PV... jeepers! Living in the inner city with small roofs really does constrain one's solar production. Makes my system look positively quaint in comparison. I'll be very interested to see how much impact Model 3 has when I get it. The LEAF increased our household consumption by about 10%, if Model 3 does likewise we'll still generate more solar overall than power that we consume (solar+grid), but it will get very close.

 

[Vostok]

Here's the first of my "what if" analyses. With my s/sheet, I can work out the exact effect of making changes to my install. I can scale the size of the solar array and battery up and down to test economic sensitivities. The most obvious one is to scale the battery down to 0 (i.e. no battery scenario) and then scale the solar down to 0 (run purely on the grid). The results are below, showing what my power bill would have been for the 4 months for all the different rateplans I've pulled in:

(note, many of these rateplans are not applicable if you don't have solar, so the comparisons are somewhat abstract in many cases, but the conclusions still hold).

Overall, solar is saving us (based on the 4 months of data) up to $2500 per year, for a payback time in the best case of 5.7 years (using straight line calculations - note this assumes that grid prices increase at exactly the rate of inflation). You might think that is not very good, but our installation used the most expensive high efficiency panels available, as well as being a very difficult install (2 storey house with roof pitch 40° requiring the house to be scaffolded). So it's at the bad end of the scale, and payback would be quicker with a bigger roof that could fit more, but significantly cheaper, panels to get the same output.

The two rateplans with the highest FIT have the shortest payback times.

It's then interesting to look at the payback time for the whole system including the battery - best case is around 10 years which I think is very good given the high cost of our install. The battery represented almost exactly half the cost of our system, but it doesn't double the payback time - it adds about 40% because of increased self-consumption (but somewhat ironically, at the loss of quite a lot of FIT).

Without a battery we would have exported over 2 MWh to the grid, which would have generated about $250 more FIT. But the flipside is increased peak and shoulder grid usage. Peak ToU consumption without a battery more than doubles from 9% to 20% of grid use. And you pay a lot more for that than what you lose in reduced FIT.

My final comment is that doing a straight division to estimate payback time effectively assumes that the entire system has zero capital value at the end, which of course it doesn't. Strictly speaking, you only have to pay back the depreciation of the asset up to that point, not its full capital cost. Anyone want to have a go at creating a depreciation schedule for a PV array + battery?

 

[sberinger]

Interested to know which energy provider you are with? Most of them have a 10kw export limit. Do you export limit your invertor or feed it all in?

Hi Jay
I am with Energy Australia
no export limit
12.5c FIT
22.2c per KW fixed rate

all plans with 20c FIT seem to be limited to 10KW installed system

 

[JayTee]

Hi Jay
I am with Energy Australia
no export limit
12.5c FIT
22.2c per KW fixed rate

all plans with 20c FIT seem to be limited to 10KW installed system

Pretty sure energy australia have a 10kw export limit, like most providers it is buried deep in their terms and conditions.
Whether they enforce this rule is another matter.
From their T&C document:

Im currently with EA as well on the same plan from when I had the 8kw system before the size upgrade. Havent had my first bill yet with the bigger system so was just planning to wait and see before deciding to switch providers or not

 

[sberinger]

Pretty sure energy australia have a 10kw export limit, like most providers it is buried deep in their terms and conditions.
Whether they enforce this rule is another matter.
From their T&C document:
View attachment 481131

Im currently with EA as well on the same plan from when I had the 8kw system before the size upgrade. Havent had my first bill yet with the bigger system so was just planning to wait and see before deciding to switch providers or not

OK hope they don't enforce it
I have my system for 18 months now with no restriction
I think EA employee's don;t know their own T&C
because I asked several different people if there was a limit before I got my system installed

 

[Vostok]

Pretty sure energy australia have a 10kw export limit, like most providers it is buried deep in their terms and conditions. Whether they enforce this rule is another matter.

I’m pretty sure in NSW the limit is 10kW per phase, so if you have 3 phase power one could install a 30 kW PV array. Your solar installer has to do the permitting with the energy distributor, I really doubt they would not enforce the rule and allow connection if it didn’t comply.

 

[JayTee]

I’m pretty sure in NSW the limit is 10kW per phase, so if you have 3 phase power one could install a 30 kW PV array. Your solar installer has to do the permitting with the energy distributor, I really doubt they would not enforce the rule and allow connection if it didn’t comply.

It is 10kw per phase allowable system size installation so 30kw for 3 phase.

However, most energy retailers limit the FIT (feed in tariff) to 10kw systems.

Alot of people who have bigger sytems like 15kw export limit the invertor to get around this rule.