Backup down under

[crossy]

I built a 3-way ATS that automagically selects between Grid, Inverter EPS output and our auto-start genset.

Normal operation is grid as we have an on-grid hybrid inverter, if the grid goes off, we transfer to the inverter EPS output and if that goes overload (it's limited to 3kW) or the batteries die the genset starts and takes the load.

All done with relay logic and mechanically-interlocked (for safety) contactors. No microcontrollers etc. etc. just a couple of commercial under/over voltage devices to determine what's on and what's not.

It just works with barely a blip of the lights except when the genset has to start.

 

[wattmatters]

I built a 3-way ATS that automagically selects between Grid, Inverter EPS output and our auto-start genset.

Nice.

As I have a permanently charged backup supply of 20 kWh of SLA batteries I do get plenty of time to do the manual swap over to generator if needed.

Also I can choose for the generator to either feed the off-grid generator (so it can recharge the battery / power loads), or just feed the house directly (replacing the off-grid system supply). Indeed at the moment my old off-grid inverter is still there and powered on, I could also use that. I don't intend for it to remain that way, but I guess it is another option. Actually it could be used solely to recharge the battery. Hmmm...

 

[koobs]

Which is what I now have. A few circuits are not covered by it - the ducted aircon, oven, large split AC....

...

I think powering the aircon would be the biggest priority in this weather!
Yes a transfer switch is on the eventual to do list. Currently if the grid goes down its only a few wires to swap over and ill be back up in 5min.
Blackouts are very rare here though. Maybe once every few years.

QLD grid under some strain today. Big peak demand event.

Yea huge aircon demand I bet. Crazy hot and humid today. Hasn't gotten any better for the night.

 

[wattmatters]

I think powering the aircon would be the biggest priority in this weather!

It's a balancing act. What is essential vs what you can reasonably cover while operating on backup.

In a grid outage you are reliant on your own supply, so it has to have both the power output capacity to manage the load's demand and the energy capacity to last for the duration of the outage, and you typically won't know how long that will be, although you can make a rough guess based on when it occurred and why (if you can find out).

Our ducted AC draws 3-4 kW, the oven of course can draw the same, and the other (old) split AC is not far behind, and naturally the resistive element hot water system is also a large power draw. Which is why I have decided that during grid outages these specific appliances won't be powered.

While my inverter could power the ducted AC, the energy draw means backup likely wouldn't last long. Because of the area it covers and the poor thermal properties of the house it sucks a lot of energy. For instance, yesterday the ducted AC alone accounted for 51.6 kWh out of a total consumption of 76.6 kWh. That's not an easy backup task. Remove that and the hot water system and we are looking at a much more manageable outage coverage challenge.

The two outbuildings do have full power cover during outages (and both have split AC), although really it's only the granny flat which I wanted to enable AC to be used during grid outages, not so important for the mancave. The split AC in the granny flat is a pretty low power draw and I wanted to ensure my elderly mum would be comfortable even during an outage on a hot day. Sadly, my mum passed away in early January, but we did have occasions when exactly this happened and I told her to keep on using the cooler and I was very glad she could.

We expect to do some renovation to our home, and part of that is to convert one end of the house into our master suite with a smaller living area. That's where the old AC unit currently resides and my plan is for that to be replaced with more efficient reverse cycle split AC and I will provide the option for that to be powered during outages. It should draw much less power, and require far less energy to keep a smaller space cool/warm.

 

[koobs]

The old AC systems are terribly inefficient. I've got 2 small 2kw AC split systems, one on each end of the house. In this weather, the AC in the bedroom easily keeps the room frosty enough for sleeping and uses only about 600w continuously. The old ducted system used to use about 5kw and did a worse job.

I think having good solar and battery has definitely made us less energy conservative. Aircon running 24/7 as long as someone is home now!

 

[wattmatters]

Unfortunately the home's design doesn't lend itself to use of individual split systems. The ducted unit is a 10 kW rated unit and not that old (5-6 years as we had it installed). The other older split is an 8 kW unit and was pre-existing, no idea of age - it really cranks out the cool but the real problem is this home leaks heat badly. For much of the year the weather is mild and so it's no big deal. February is however the month of high humidity.

For now I don't plan to grow battery (and PV) capacity just to cover night time use during these less comfortable times of year. I'll accept the grid hit for that.

This is the ducted AC power demand over the past few days:



During the day the solar PV usually covers it but to cover the evenings would require about an extra 20 kWh of battery, and the PV capacity to reliably fill it.

After we get through this Summer and this year's Winter I'll have a much better picture of how we are travelling with what we have.

If we do manage to get our renovations completed then I'll definitely consider adding more off-grid PV and storage and moving the new aircon to the off-grid system.

 

[wattmatters]

Couple of updates:

1. Did some basic maintenance of my Yamaha inverter generator.
As usual it starts first turn of the key without fuss. Ran the generator for about 15-minutes or so as it doesn't see much duty, then an oil change and put the starter battery on the trickle charger for the afternoon. I have a trickle charger plug permanently connected to the battery so I can easily plug it in whenever needed. I did that because the battery is inside the generator's casing, so no need to unscrew the access panel to get to the battery.

2. Added new Home Assistant automations to control the level of supplemental "grid" charging based on how much spare grid-tied PV output capacity there is. Put my first draft of the automations into play this afternoon. Seems to be working OK, may need some fine tuning.

I already had an automation which turned on or off supplemental "grid" charging based on:
- battery state of charge and how much energy would be required to reach 100% SOC
- off-grid PV solar output forecast for the rest of the day, IOW whether the small 2.22 kW off-grid PV array would have sufficient capacity to fully charge the battery by the end of the day
- whether there was enough spare PV capacity from the 11 kW grid-tied PV array to divert some of that to supplement the battery charging.

I do not import energy from the grid for charging the battery, unless I invoke "Storm Mode".

However I was not previously able to automate the level of supplemental charging. It was set at a fixed 10 A (about 500 W). This was due to a bug with the way Solar Assistant orders inverters and the different system parameters which are controllable for Inverter #1 and Inverter #2. My primary inverter was listed in SA as Inverter #2, and so additional parameter settings such as max grid charge current were not functional.

However yesterday I managed to get SA to reconfigure the inverters and have their logical position swapped and my primary inverter is now Inverter #1 in Solar Assistant. So now these additional parameter settings are accessible for automation.

So what happens now is if the the system decides supplemental "grid" charging is required, it will ramp up and down the level of charging based on how much excess grid-tied PV capacity there is. This can be done in 10 A (DC) steps, which is approximately 500 W each step up to 120 A (~ 6kW). There is also a 2 A (~100 W) option.



Here we can see the battery is at 89% SOC and requires another 3.3 kWh to be fully charged. The Off-grid PV Forecast is today's full day production estimate taken from the Solcast PV forecast integration. Behind the scenes it calculates how much the balance of day forecast is.

Grid Charge Req'd tells me whether the system thinks it need some supplemental energy to complete a full charge. The system monitors my grid-tied PV and because sufficient excess capacity is available it is providing supplemental charge power. In this case it's been set to 30 A (~1500 W) but the inverter only uses what it needs to remain within the overall 50 A current limit I have set for this battery.

Meanwhile the battery is charging at 2.55 kW, while the off-grid PV array is generating 1.4 kW.

It's good for days like today when it's on/off clouds/rain/sun and the small off-grid array would never fully charge the battery but the larger grid-tied array can definitely provide a decent boost.

 

[koobs]

Why bother charging supplemental from the grid at all? Does the inverter not just pull straight from grid if there is insufficient power left in the battery?

 

[wattmatters]

Why bother charging supplemental from the grid at all? Does the inverter not just pull straight from grid if there is insufficient power left in the battery?

Perhaps I didn't explain well enough, so I will hopefully make more sense this time.

I'm not charging from the grid at all. You may have noticed the quote marks when I wrote "grid".

I'm really (supplementally) charging from my grid-tied solar PV system.

When I use the system in this manner, I am diverting (grid-tied) PV energy to my off-grid battery, energy which would otherwise have been exported to the grid.

On a good solar day my small off-grid PV array has enough capacity to fill the battery on its own, so no supplemental charging is called for.

But on not so good solar days it does not. Meanwhile since my grid-tied PV array has five times the capacity of my off-grid PV array the grid-tied PV array quite often has ample spare capacity to help out.

So if the off-grid PV array can't get the job done, and if the grid-tied PV has spare capacity, then I use that spare capacity to help charge the battery.

But if the grid-tied PV array does not have spare capacity (either solar conditions are poor, or heavy loads are being used, or a bit of both) then I do not import energy from the grid to supplement battery charging. It just gets what it gets.

I have an automation to make a call as to whether supplemental charging is required, and it regularly updates this status throughout the day. If supplemental charging is required, then my other automations decide whether and when to begin and end any such supplemental charging, and how much power can be supplied without resulting in importing energy from the grid. It will then ramp up and down charging power according to available spare capacity.

Supplemental charging still costs a little bit of money as I am foregoing a grid feed-in credit (~AUD 7.6c/kWh). But our net tariffs are asymmetric and the energy is then used to offset consumption during the evening during peak (36c/kWh), late evening shoulder (28c/kWh) and overnight off-peak (18c/kWh) periods.

 

[wattmatters]

Here's a comparison showing battery charge/discharge power for last 48 hours (nearly) as well as the SOC, the Charger source priority and Max grid charge current settings:



Both days were challenging for solar production, with much passing cloud and some rain. Sun one minute, cloud/rain the next.

Today was worse than yesterday. Can see how the charging power went up and down like a yo-yo both days. Overnight discharge loads pretty typical.

At the top of the chart are two coloured bands.

The top one (purple/green) shows when the charger source priority was solar only (purple) or solar & utility simultaneously (green).

The lower mostly pink one shows the max grid charge current setting. Dark pink = 10 A, brown = 20 A, light pink = 30 A.

Zoomed in shows when these settings were changed by the automations:



The effect of the new automation (commenced early this afternoon) can be seen in the outline shape of the charging power peaks. On the second afternoon of the above chart - when the sun was out and there was spare capacity, the charging power was keep higher through the afternoon compared with the day before when the supplemental charge setting was fixed at 10 A.

Now I didn't get to a full charge by end of today (95%), but had the automation operated all day I suspect I may well have. SOC ended up higher than it otherwise would have been.

Now while these cloudy/rainy/sunny days are pretty challenging, I suspect the most useful aspect of this change will be during Winter when my small off-grid array will likely not have the capacity on even a good solar day to fully recharge the battery.

Eventually I will put up more off-grid solar PV which will negate much of this, but in the meantime I may as well make better use of the PV capacity I already have.

 

[wattmatters]

Not such a good solar day today, so the supplemental charging did its bit to help fill the battery. I also added a new 40 A supplemental charging step into the routine which did kick in a few times.



I didn't get a full battery by end of day (reached 89%, normal pattern is to cycle between 69% and 100%).

I estimate the supplemental charging routine added close to 4 kWh which otherwise would have been missed. That will definitely see us through the peak tariff period tonight.

 

[wattmatters]

Today's charging performance saw the supplemental charging automation do a good job.

First the battery power plot from today, can see the battery spent long periods flatlined at the max charge setting (50 A), which equates to ~ 2,650 W, but because there is a bit of parasitic draw from another inverter, then the effective peak charge rate is closer to 2,500 W.



Can see when the system decided to turn supplemental charging on (teal) and off (orange).

Then if I overlay on this chart the real power flow to/from the grid, where negative power = export to grid, positive = import from grid.



I have highlighted where, for very brief periods, I was importing energy from the grid. That's a result of my automations having some delay in their response to changes in the grid power flow - delays which are deliberate on my part - but is something I am working on refining. Getting the balance between speed of response and not over reacting to brief changes in loads or supply.

In the end it only represented 0.03 kWh of energy imports, which at weekday daytime rates cost about ~ half a US cent. Think I can take that hit.

The battery completed a full re-charge at around 3pm with 10.2 kWh of charging. Meanwhile the off-grid PV array only generated 6.6 kWh today, and under normal circumstances about 5.5 kWh of that would reach the battery.

 

[wattmatters]

Latest update:

My two year old clone PIP HS-4048 AIO inverter died. This was the one I replaced with the EASun 8kW unit, so it's no longer in service.

Plan is to remove it when I next get the chance and then attempt a repair. It'll be a while before I get a chance to do that but I'll share my experience.

Most likely some of the capacitors are cactus. It was cheap and a great learning tool. If I can revive it, then I have a few ideas on how I might use it.

And just for interest I check the cell voltages in my two server rack LiFePO₄ batteries when they were at 100% SOC:

4 March 2023

Battery	Min Cell Voltage	Max Cell Voltage	∇ Cell Voltage
Upper	3507mV	3543mV	36 mV
Lower	3508mV	3545mV	37mV

 

[wattmatters]

Some updates.

I had the main circuit board reorganised so now have a dedicated essential loads panel:





Then added an IotaWatt power/energy monitoring system:



Happily sitting side by side.



I will be getting my small off-grid AC distribution panel relocated to the space to the left of the IotaWatt housing. It has two output circuits, one primary to supply the home (32 A breaker) and one for some dedicated off-grid GPOs (20 A RCBO).

Still have a few more things to do....

Meanwhile the IotaWatt set up has taken a bit of work but all going OK now. Getting some good data on circuits I haven't been able to reliably monitor before.

e.g. here's my water heater smart PV diverter in action yesterday:



Gives a good sense of how power to the resistive element is varied through the day depending on how much excess solar PV is available.

 

[wattmatters]

I will be getting my small off-grid AC distribution panel relocated to the space to the left of the IotaWatt housing. It has two output circuits, one primary to supply the home (32 A breaker) and one for some dedicated off-grid GPOs (20 A RCBO).

Now have the slightly upgraded Off-Grid inverter AC distribution panel installed.

Sits to the left of the IoTaWatt and Essential Circuits panel.

It's not exactly a work of art but it's doing the job.

What's not visible are the upgraded AC input and output connections to/from the off-grid inverter. Those are now 32 A (230 V).

I've set it up so that power backup to the home can still be provided old-skool style with a regular generator.

Next up I will be re-doing the battery compartment.

 

[nezjnr]

Are you just connecting with a USB cable to your SA? Any stability problems?

I have 3 units and one of them keeps resettings it's USB, not sure if it's a raspberry pi issue, inverter, need to switch to serial.

Very clean and nice job though.
Like your MCCB enclosure, how much did it cost? I had a quick search and saw one for like $300.
I have a 13 MCCB's that i'm trying to work out and enclosure for.

 

[wattmatters]

Are you just connecting with a USB cable to your SA?

Yes. The USB cable/plug for that inverter is a little exposed though. I was thinking I might get one with a 90° bend to make the cable run a little neater.

Any stability problems?

No.

I do however connect my RPi via ethernet cable as I do have a bit of a flakey Wi-Fi at times. Done the same for my grid-tied inverter.

Like your MCCB enclosure, how much did it cost? I had a quick search and saw one for like $300.

That sounds about right. I'm not sure the exact cost as the sparky bought it. He told me they were not cheap. I've outlayed a bit too much on this latest set up but just wanted it done right. There are still a stack of circuits inside the MCB (the large enclosure above the new panels).

I have a 13 MCCB's that i'm trying to work out and enclosure for.

The ones I have are 12 pole, so that leaves you one short. The smaller one is six pole. Not cheap either.

 

[Hedges]

The ones I have are 12 pole, so that leaves you one short. The smaller one is six pole. Not cheap either.

Seems to me those breakers are the fat variety.
DIN breakers and fuses come in at least two widths, so for smaller wattage you should be able to fit more.

Midnight has up to about 60A AC breakers which are skinny. From Carling, I think.
But the models they carry may be "UL 1077 supplemental protectors", which are rated lower than "UL 489 breakers"
There is probably a similar distinction to your regulatory body, so be sure to select the correct models.

Category Products - MidNite Solar's

MidNite Solar Category Products.

www.midnitesolar.com

 

[nezjnr]

Yes. The USB cable/plug for that inverter is a little exposed though. I was thinking I might get one with a 90° bend to make the cable run a little neater.


No.

I do however connect my RPi via ethernet cable as I do have a bit of a flakey Wi-Fi at times. Done the same for my grid-tied inverter.


That sounds about right. I'm not sure the exact cost as the sparky bought it. He told me they were not cheap. I've outlayed a bit too much on this latest set up but just wanted it done right. There are still a stack of circuits inside the MCB (the large enclosure above the new panels).


The ones I have are 12 pole, so that leaves you one short. The smaller one is six pole. Not cheap either.

I'm wondering how to make my USB cables a little neater as well, I've got three units so need to try and do something with the current sharing cables, haven't really seen anyone manage to pull much of there.



MCCB is the breaker under your off-grid inverter for the battery disconnect. They are the next step up of Circuit breakers.



I want to get mine looking looking like yours with a nice case and conduit.

 

[nezjnr]

Seems to me those breakers are the fat variety.
DIN breakers and fuses come in at least two widths, so for smaller wattage you should be able to fit more.

Midnight has up to about 60A AC breakers which are skinny. From Carling, I think.
But the models they carry may be "UL 1077 supplemental protectors", which are rated lower than "UL 489 breakers"
There is probably a similar distinction to your regulatory body, so be sure to select the correct models.

Category Products - MidNite Solar's

MidNite Solar Category Products.

www.midnitesolar.com

They look like standard 18mm ones.
Anything over 63a will be 1.5 or double width for a single pole.

You can get 63a for $5 but 80a first I could find was a Hager for $100.
The breaker to my off grid is right next to my 2 GTI breakers, which was bad planning on my part as heat is making it trip since I have it under pretty high load.