NZ users: significant electricity price changes.

[brucehoult]

I just got notification my power prices are changing on Electric Kiwi "MoveMaster" in the Northpower (Whangarei) region from Sep 19 (one month from now).

I assume Electric Kiwi will have similar changes in other regions. And some of it will be happening with other retailers as well, in particular passing on increased daily prices from the local lines companies.

Let me know if you're having any changes!

So, what's new?

• Daily charge: $1.15 -> $1.60
• 7-9 AM, 5-9 PM weekdays: $0.6375/kWh -> $0.6036
• 11 PM - 7 AM: $0.3187 -> $0.1810
• All other times: $0.3825 -> $0.4527

That's actually a mixed bag. In the letter they estimate given my usage patterns in the last 12 months this will result in an increased bill of $0.10/day.

But I already have other plans :-)

$164/year more in fixed charges hurts a bit, it was about the same increase on August 1 a year ago, and will probably go to $2/day a year from now. If it gets to $3-$4 I'm going to be seriously considering going off-grid. $4/day is more than my total bill this year (since getting the Pecron E3600 and 6x 440W solar panels).

There's a slight reduction in peak rates, but thanks to the 6.1kWh battery I already use zero power in those times. Or, actually, it's 0.5% of my kWh on average, as I have a few small things not running from the system, mainly water pump and lighting in little-used rooms.

It's nice to finally have a real night rate. Before, the 9 AM - 5 PM price was only 20% more than night, meaning there was zero benefit in charging batteries at night to use during the day as the round trip loss of AC->DC->battery->DC->AC is probably right around 20%.

Now with 9-5 rates at 2.5x the night rate (and peak 3.33x) that's worth charging batteries for, maybe even buying more battery.

Charging before 5 PM to use in 5-9 PM is now less attractive ... peak will now be 1.33x day, until now it's been 1.67x day. That's still a win, but a much smaller one.

With my current 6kWh of battery this is going to make it much harder to know whether or how much to charge batteries at night, at least in summer. Until now I usually haven't used grid power at night at all in summer, or at least only to keep the battery at 20% if it drains that low at 5 AM or something (usually not), ready for the 7-9 AM peak time. Usually I then have no problems filling the battery, even by midday or 1 PM. But there can be bad weather in summer, and then I've been topping up with 38c power before 5 PM.

Now if it's going to be a bad day then I should top up at night, if possible, not in the afternoon. Until now with a 20% price difference that didn't make much difference and I could just (have my automation) be reactive in the late afternoon.

In winter it's easier. It's clear that I should now start the day at the 7 AM peak with battery charged to 100% and avoid using power between 7 AM and 9 PM as much as possible. Which on the bad days with less than 1kWh of solar production will be about ... until midday. Except what I should now be doing is not letting the battery drop below what I need for the 5-9 PM peak. Which is 90%-100% and 90% often isn't enough, so I've always been topping up to 100% before 5 PM in winter.

But the two hour morning peak is already using 40% of the battery in winter, starting from 60% charge held overnight

What I really need is to charge the battery to 140% at night, to use it in the 6 peak hours. Or even more than 140% to not use that new 45c (up from 38c) rate either. That math doesn't math. But even a fairly bad winter day gives me solar power for that missing 40% ... 2.4kWh. The average midwinter day gives me 5kWh.

So, ok, I should usually in winter be able to do at least no charging from the grid between 7 AM and 9 PM, even if I have to run the load from the grid most of the day.

Until now the main thing, both summer and winter, was just to have enough in the battery to get through the 7-9 AM peak: 20% (1.2kWh) in summer since no aircon is needed in the morning, 60% (3.6kWh) in winter. And then see how solar production went during the day, and top up or run on grid power before 5 PM as needed.

So now there will now be a premium on forecasting how much solar production there will be next day, before bed time, and set the overnight top-up accordingly.

I've run some calculations, based on my actual usage in each part of the day in the last year.

I've decided it's worth buying an EP3800-48V 75 Ah 3840 Wh battery to increase my total storage to almost exactly 10kWh. Calculations say that will have a 4 year payback, the same as my existing system (which is already 1 year in). So it's already ordered, looks to be in stock at pecron.co.nz and I assume will be here in a few days. Certainly before September 19 when the prices change!

I looked at generic batteries, primarily at Micromall.co.nz. This is the best fit they have, a 100 Ah 5000 Wh for NZ$1999.

https://www.micromall.co.nz/products/48v-512v-100ah-110ah-5kwh-lithium-battery-lifepo4-battery-deep-cycle-battery

It's 33% more capacity for 21% more price, so 10% more kWh per dollar. But it would need some hacking to connect it to the Pecron expansion port, won't show up with its pack voltage and individual cell voltages, temperature etc on the Pecron's UI or app. Not worth it.

Previously it didn't make sense to get more battery, because it wasn't worth charging at night to use in the daytime between 9-5. And in summer even though the some afternoon solar power was often going uncaptured I was still usually able to make it through the night. So the payback was almost nonexistant on the 40% of good days when I might be able to fill the extra battery ... it would only be useful if the next day was bad. My previous calculations said a $1600 EP3000-48V (60 Ah 3072 Wh) might save me $150 a year. Not worth it.

But now with topping up to 100% at night every day from (probably) mid April to mid September that's now going to be saving near to $450/year from the extra battery (which is now EP3800 not EP3000).

The winter/bad weather strategy will now be to have 100% charge (10kWh) at 7 AM and run on battery until dropping to around 5.5kWh left (55%) to save for 5-9 PM. That's around 11 AM with totally zero solar production, 1 PM with a normal "bad" day, or 3:30 to 4:30 with average 5-6 kWh winter solar production ... needing just an hour or so running on "shoulder" 45c power.

That should be realllly close to running without grid power between 7 AM and 9 PM on an average winter day.

Close enough that it's not worth buying two extra batteries now.

[brucehoult]

The extra battery ordered after hours on Wednesday arrived Friday morning, I waited until after it was dark, after the 5-9 PM peak (when I run from battery), and after the 9-10 PM Free Hour of Power (when I top up the battery) to disconnect everything and re-stack it on top of the new battery.



Charged to 100%, gave it a couple of hours while it took periodic 1000W or 2000W sips of power, then turned the grid power off at 3 AM and ... now I have 58% SoC at 5 PM after a low of 30% at 8:20-9:00 AM and a high of 73% at 2:20 PM. On a week day I'd now want to get to 9 PM on battery. On a Saturday it doesn't matter. But I think (with my customary 1.65kWh free top up at 9-10 PM .. can't pass that up) it's probably going to be midnight or later before it hits 0% to calibrate the new battery's empty point. After that it'll be in normal production use. Even now in late winter I can clearly run from 7 AM to 11 PM on only free power in reasonably weather. Soon 24/7 will be possible until mid Dec to mid Feb when sometimes my aircon use exceeds solar production.