Backup down under

[wattmatters]

Today's project was setting up a second instance of Solar Assistant dedicated to monitoring our server rack batteries. We have 1 x Jakiper and 2 x generic 100 Ah 51.2 V server rack units. They all use the same PACE BMS, or at least close enough.

I had a spare Raspberry Pi 4 after I had migrated my Home Assistant onto a mini PC, so thought I'd give it a go.

A little trial and error on using the right battery connections and dip switch settings but have it working now:



I already had a Jakiper supplied cable for connecting to the Raspberry Pi USB, so that removed all the hassle of trying to figure that part out.

Here are the two dashboards side by side:



Why a second instance?

Well my system battery is a hybrid LiFePO₄ (3 x 100Ah server rack units ~15 kWh) + a bank of sealed lead acid backup batteries (~20 kWh).

I have a Victron Smart Shunt monitoring the whole hybrid battery and that is the source of truth for the whole system.

Unfortunately Solar Assistant does not (at least not yet) enable monitoring of two different types of battery data inputs. So I could have chosen to just monitor the server rack battery, or the Victron shunt, but not both.

This way I can now see both and it will be good to have the server rack battery data constantly monitored and recorded.

If you look at the snapshot above, can see at that moment (it updates every second) there was 2942 W going into the whole battery according to the Victron shunt while the combined battery BMS reports charging at 2895 W. While there may be some accuracy differences between them, that is about expected as the balance would be residual current going into the sealed lead acid.

Also note the SOC differences:
Whole battery showing 84%
LiFePO₄ showing 57%

Since the whole battery SOC is based on 35 kWh, 84% means there is 16% of 35 kWh = 5.6 kWh to fully charged.
LiFePO₄ at 57% means 43% of 15 kWh = 6.45 kWh to fully charged.

Obviously there is a discrepancy there but that is probably down to a few things, once of them being the PACE BMS SOC is probably wrong and needs a recalibration.

I will now have a much better view on the state of charge of the LiFePO₄ during regular daily cycling and see how the energy supply is shared between the LiFePO₄ and SLA at difference states of charge.

Next up is setting up the MQTT link with Home Assistant.

 

[wattmatters]

And after a bit of mucking about I managed to get the MQTT connection working with Home Assistant. Mine is not straightforward as I use an MQTT bridge in Home Assistant (which enables multiple MQTT sources).

Anyway, it's working:




So now the fun starts with dashboards, some relevant automations, creation of some custom template sensors (e.g. to track cell voltage ∆) and charts to monitor the total pack vs LiFePO₄ charge and discharge behaviour.

 

[wattmatters]

Gradually getting some dashboard dials for the individual battery and cell data:

 

[wattmatters]

This month was the second anniversary of installing our off-grid LiFePO₄ batteries to supplement the existing 20 kWh sealed lead acid battery bank and also the upgraded 8 kW off-grid inverter which replaced the 4 kW unit I was using for grid outage coverage and to run the pool pump with a 2.2 kW off-grid PV array.

I started with 10 kWh, and in May 2023 I added an extra 5 kWh of LiFePO₄.

In that time the battery throughput has been:

DC Charge: _____________ 7,373.1 kWh
DC Discharge: __________ 7,094.0 kWh
Discharge:Charge ratio ____ 96.2 %
Charge Source:
_ Off-grid PV: _________ 4,959.7 kWh (67.3%)
_ Other*: ______________ 2,413.4 kWh
.
* Other is mostly excess grid-tied PV, with some grid import during free energy periods.

This is the daily discharge:

And the average daily discharge by month, split into TOU periods:

The DC discharge:charge ratio is lower than typical for LiFePO₄ (99+%) but that's because this is a hybrid battery operating along with a bank of sealed lead acid, which most of the time is kept at float so it consumes energy just being there.

The hybrid battery operation has itself been an interesting exercise, is uncommon, not generally recommended but has been quite successful and has actually provided a nice buffer for the LiFePO₄ when state of charge gets low. In essence the LiFePO₄ never get down to 0% SOC, usually bottom out at ~8-10% which is handy for their longer term health. At low SOC the SLA takes up the slack, cycling the top 5% of its capacity which is also good for their long term health.

Has it been worth it?

In short, yes. Financial benefit wasn't the big driver, it was more a hobby but it still needed to be financially rational. IOW if the numbers were going to be crap then I wouldn't have bothered.

As we know, calculating the value of batteries (and solar PV) is a dark art given the billing changes are affected by:
- a constantly changing tariff landscape (and they have changed a lot over the last two years!),
- consumption patterns which change due to having a battery,
- optimal tariff plan choice is different with than without a battery,
- prior consumption not being reflective of today's consumption patterns (and for us that has changed with the change in occupancy of our second dwelling).

So all I have done is to estimate the value of discharge energy at the time of consumption (allowing for DC to AC conversion losses) and taken away the value of any energy used to charge it, noting that more than 2/3rds of the energy comes from the off-grid PV which has no export value (as it cannot be exported to the grid). It is a somewhat flawed approach but that's what I have done.

So with that quite substantial caveat sprinkled with grains of salt, the batteries in their first two years have recovered 29.1% of their cost. For a home battery that's a pretty decent hit rate, even with the flawed approach.

Being an off-grid system has its advantages and disadvantages. The primary advantage is I can (within limits) do what I like, I need not be concerned with grid connection or export limits and it is substantially cheaper than a commercially installed grid-tied battery system.

The primary disadvantage is the output capacity means it is limited to the circuits it can cover. It does not supply power to some of our high power demand appliances, the most notable being our primary home's heating and cooling. If it was able to do that, then it would drain the battery quite quickly in winter and summer evenings but in doing so a far greater proportion of battery discharge would be during the peak tariff period, increasing the value of that discharge.

So it's definitely a trade off.

The whole project started back in 2020 as a way to automate our grid outage backup as we had added the cottage and my elderly mum had moved in. We were using a generator up / transfer switch systems until then but I wanted her to have energy security even if I was not about to start up the generator.

I started with the small off-grid inverter, a bank of pre-loved sealed lead acid batteries and later added some pre-loved PV to the garage roof so it was self-sufficient and pretty cheap. I then got it to look after running the pool pump since the off-grid PV had ample surplus most days to do that.

But then I experimented with communications, monitoring and control automations (which turned out to be quite powerful and flexible) and tested using it to run the property and it did a good job, but was clearly capacity constrained. Hence deciding to up the ante and try it out a new approach to home energy management. It's been a fun project and also triggered other stuff such as home automation.

And of course the original mission of providing grid outage coverage has been a great success. While I have detailed stats on our outages over many years, in this two year period alone we have had 29 grid power outages.

We will be moving from this home at some stage in the months ahead, so I'll be starting all over again with the home energy plans. We have been looking at some options and all the candidate homes will need energy system work. The off-grid system will come with me, so it may get redeployed, hard to say.

 

[wattmatters]

2024: We had 15 grid power outages this year (longer than 5-minutes) for a total of 14 hours and 15 minutes.

Off-grid system handled it all just fine. I used our car's vehicle to load system on a couple of occasions to help keep our home battery charged up.

Summary to date on our outages:

 

[wattmatters]

We will be moving from this home at some stage in the months ahead, so I'll be starting all over again with the home energy plans. We have been looking at some options and all the candidate homes will need energy system work. The off-grid system will come with me, so it may get redeployed, hard to say.

Well it's happening.

We have sold our home and bought another, move happens during second half of March.

I'll miss the view but not the heavy mowing and maintenance demands. It was a run down mess when we bought it, the new owners will get a well maintained and vastly improved property.



Our new place is in the same local area we are now but 15 km closer to the ocean. We will be a short walk to the beach we often take our dog for walks:



The new place has no solar PV and a single phase 240 V underground grid supply. It does have solar thermal systems for both hot water supply and for pool heating (the previous owners ran a business installing pool heating systems). No aircon or heating systems.

It has a 10 x 15 m shed which is the most likely location for PV to be installed once I do a bit of tree work:

A smaller ground mount system might be possible but would cost a lot more than using a roof (typically ground mount arrays are double the cost). The house has great roof for solar but the pool system has taken all the good solar real estate.

I have much to consider with energy systems for the new place. Unsure which direction I will head.

Watch this space...

 

[HardYakka]

Didn't see this tread until moments ago. We were on North Shore, Fairlight, then Jervis Bay, Vincentia. Had to leave to take care of a family farm in Oregon but will be returning.. Bermagui this time the opened the dual carriage way south from Wollongong past Berry and I've heard of a flyover south of Nowra now. South coast is growing too fast. They closed the golf club at Vincentia and are selling the property for houses..

 

[wattmatters]

We were on North Shore, Fairlight

My dad was born there and as a kid I used to spend summer holidays there with nana & pa. My brother & I would take ourselves to Manly beach for the day. Was down that way last week, stayed over at a mate's place just up the road at Freshwater.

Place is more crowded than ever. Sydney is a development monster.

then Jervis Bay, Vincentia

We also used to go to the south coast a lot and in his later years my dad lived in Durras and Batehaven. Lots of family trips to the region.

 

[wattmatters]

Yesterday I pulled the plug on my DIY off-grid system.

We finally moved home and while we still have both places for a while we are now residing in the new place. I needed to bring over some our our networking equipment I decided to terminate the system's operation. I will be pulling it down/apart some time during the next week.

It served us well. I discharged ~10 MWh through the battery in 2 years 8 months.

It's now time to focus on the new place. I'll likely not go the DIY route as it's physically much more difficult for to do me that at our new place, so I have sent an RFQ briefing to a couple of good local installers. Will see what they come up with.

Not sure what I'll do with all the kit. I could make a portable trolley power station, perhaps power the shed using that.

Today's job though is moving the EV charge station to our new place.

My utility metering is being upgraded in early April to latest smart meters. I requested it as the electricity plans I can access are far more favourable. It would happen anyway as soon as we installed grid-tied solar PV.

 

[wattmatters]

Today I took the off-grid PV array from the garage roof. Next up will be inverter, then batteries and sundry other components.

 

[wattmatters]

Batteries and inverter removed, picked them up today to be stored in the new shed. Just some solar conduit and cable to clean up.

 

[wattmatters]

I just pulled the trigger on a new PV/battery system for our new home.

It won't however be DIY - am letting the professionals do their work. Using a Sigenergy system.

14.725 kW of PV (it was what we could get on the roof as the existing solar thermal systems do take up a lot of prime real estate), 24 kWh of battery capacity, 12 kW hybrid inverter and a gateway for full home backup, monitoring and smart control systems. We have a single phase (240 V) connection, 80 A breaker and will have a 5 kW grid export limit.

US$18.9k fully installed.

Expected roof layout, although that one landscape panel on the western array will be centred, not offset like that!


I do have some tree work to do mainly to keep branches away from the home/roofline but some shading will be a fact of life here.

We share the place with some locals:



They often laze and graze on the front lawn.

 

[Brucey]

Any juicy government rebates or all a thing of the past now?

 

[wattmatters]

Any juicy government rebates or all a thing of the past now?

There are two sets of market based certificates which apply in my case and are already included in the installed price. Neither are taxpayer/govt funded schemes, they are market based mechanisms to encourage a reduction in carbon emissions (which is what the PV does) and peak network demand (which is what the battery does).

As incentives go, they are pretty effective and well designed.

i. Federal small scale technology certificates (STCs) for the PV, which are bought by large polluters to offset carbon emissions (that's on a gradual reduction each year, ends 2030),

ii. NSW state govt peak demand reduction scheme (PDRS), also a tradable certificate purchased by large peak demand consumers on the grid, e.g. big industrial users and large wholesale electricity buyers such as electricity retailers (else they need to make a greater contribution to peak demand infrastructure costs).

In each case no DIY system would qualify (unless you happened to be an accredited installer yourself).

The STCs were worth ~US$2.8k and the PDRS worth ~US$2.0k. The rights are assigned to the installer who then sells them on their respective markets.

We are in the midst of a federal election campaign (election on 3 May) and it seems like all major parties and independents are supportive of some federal incentives to increase the uptake of home storage. What form that may take I've no idea. In any case I have no need to be waiting for incentive promise-ware, we are using ~A$12/day in power and I want to nullify that plus have the instant outage backup (we get lots of power outages in this area - hence the original intent of this thread).

 

[wattmatters]

Only two weeks into our new place and we had a power outage the other night.

Turned out to be a faulty mains breaker, or a bad terminal connection to the busbar. Either way, it melted:



I think it's been on the way out as I had been noticing some minor flickering of our LED lights over past couple of weeks. I thought perhaps our lights were needing replacement.



I had it and all the other RCBOs and breakers replaced. Start afresh. No more flickering lights.

 

[Brucey]

Only two weeks into our new place and we had a power outage the other night.

Turned out to be a faulty mains breaker, or a bad terminal connection to the busbar. Either way, it melted:

View attachment 291652

I think it's been on the way out as I had been noticing some minor flickering of our LED lights over past couple of weeks. I thought perhaps our lights were needing replacement.

View attachment 291653

I had it and all the other RCBOs and breakers replaced. Start afresh. No more flickering lights.

Maybe loose connection finally got melty hot? I guess good practice to double check tightness of all connections when buying a house.

 

[wattmatters]

Maybe loose connection finally got melty hot?

Quite probably. We had a new meter installed a few days ago, and while the installer would have had no reason to be touching the lower half of the main breaker, the movement inside the board may have just been enough to send a dodgy connection over the edge. Glad that's all it was.

 

[wattmatters]

Had my new grid-tied PV system installed this week. The battery will follow in the next month or so, once we have the federal rebate process nailed down. Good local professional crew.

I've gone with a Sigenergy system (in the US they are called Pointguard).

We are a single phase 240 V connection.

14.725 kW of PV (31 x Longi LR7-54HTH-475M panels + Clenergy mounting system)
12 kW inverter (Sigenergy Sigen EC 12.0 SP)
24 kWh of battery (Sigenergy SigenStor-12S-24 battery)
Gateway (Sigenergy HomeMax SP 12K)

Cost ~ US$14.8 k fully installed including all approvals, commissioning etc.

PV is split across three strings pretty much filling up the west, north and east facing roof space I have left. Existing solar thermal systems for water heating and pool heating take up a lot of the prime north facing roof. I had considered removing the water heater system and putting in a heat pump water heater but it's functioning well and it was an extra cost I really did not want to add to the project at this time. When the system dies, I'll deal with it then.

The battery will be a stack of three 8 kWh modules. Gateway manages all the grid isolation / backup circuits, smart load management and of course consumption / grid monitoring.

For now the inverter is temporarily wall mounted in the garage. That will change when the batteries go in, the inverter will then sit on top of the floor mounted battery stack and the wall mounting board will be removed.

Unfortunately we were unable to get a clean cable run down through the wall from the ceiling for a super clean install so we went with an external conduit cover. AC isolator as well (that's a requirement here when the inverter is more than 3 metres from the Gateway). Paint peel on wall was pre-existing, I need to repair that.



Gateway on side wall of garage:



Our main circuit board/utility meter is on the other side of that wall.


For now the bypass is deactivated since the battery is not yet installed. There are also ports which can accommodate another inverter input (AC coupled), backup generator and a smart port which can be configured for various options (e.g. to provide partial backup for selected circuits).

I have the whole home on backup port of the Gateway, with the exception of the EV charging. The water heater booster operates on a separately metered off-peak supply.

As yet I have not connected anything to the smart port - this can do various things, e.g. provide a controlled shutdown of circuit(s) during outages when battery SOC drops below a set threshold. I may add our yet to be installed ducted aircon system to this. That's going in soon.

Has a pretty nice management portal (this one is browser based, there's also a nice phone app):





Spent last couple of days working out a few things with it, and yesterday integrated with Home Assistant:



And with the HA integration I was also able to set up my car charging with excess solar PV.



Along with the home battery the car will be an important load for the PV - with our connection agreement we are limited to no more than 5 kW of export. So generation is curtailed to no more than household load + battery charging + 5 kW of export.

Export isn't worth much anyway at A1.4c/kWh (~US 0.9c/kWh).

I moved to a retail plan with super off-peak rates last week, 12-4 AM @ 5c/kWh (our regular tariff is ~36c/kWh). So for now that can cover any supplemental EV charging I don't do with excess solar PV, as well as cover night time heating/cooling use once that starts. Once the battery goes in then it can also be a supplemental source of cheap energy in case solar production is poor.

System is able to be integrated with virtual power plants, and I may consider moving to wholesale energy trading rather than use a regular retail plan. For now I just have to wait for the battery half of the system and begin to gather data on our consumption. I have a broad outline of that since we've moved here:



There's no heating or cooling energy demand in that as we haven't needed it (yet) and the place has none! Our ducted reverse cycle systems will be installed soon.

* With the emphatic return of our federal government last week it means there will be quite generous rebates for grid-tied battery installations which kick in from 1 July. You can buy/install before then but the battery system needs to remain un-commissioned until 1 July to be eligible.