Whole house power backup

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SirHumphreyAppleby

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#316012 8-Sep-2024 13:38

Browsing at the Auckland Home Show on Friday, I found a 10kWh battery for under $3.5k. While I can't attest to its quality, this does seem significantly less than batteries were when we had our solar system installed in 2020.

We opted not to have a battery installed at the time as we use most of the power we generate - a decision I still stand by. We have, however, also been looking at getting a new UPS (never buying APC again) and adding a generator. With a base load of <0.6kW, a 10kWh battery should be sufficient to get us through all but the longest power outages (17 hours in 2018, 2-3 hours is more typical).

Given our inverter does not have a battery input, and we don't actually want to use the battery storage every day (at least not all of it), preferring to keep it as backup power, can anyone advise what hardware we'd need to install?

Several years ago I came across Victron inverters and they seem to have dual AC inputs with battery charging with a UPS mode, so I expect I would need something like that, particularly if I also wanted the potential to add a generator in the future (in the form of an input socket for now).

Quinny

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#3280691 10-Sep-2024 15:37

I have a whole-house backup via solar and a Tesla Battery. I would ask for the peak load of the unit (it may only be tiny, ie can't turn much on bar lights and freezer). While I paid a lot, we use a lot (20-25 kWh a day), and now I am on Good Nights with Contact; the Tesla algorithm sends around 20 kWh to the grid daily, which could double come summer. Last month's power bill was $6.36, with 579 kWh used. It comes down to what you use when, appliance efficiency, how much you can time shift, what the battery can store, and what you can run on the battery at once (peak load Tesla is 5-7). The new Powerwall 3 does not need an inverter and is retrofittable. The PW2 needs an inverter.

Why do you want the backup? Are power cuts common? My system predicts that I will likely have power (urban), so using it is more important. If the power cuts right now, I have 63% on a cloudy day, with 17.5 out to the grid, rather than keeping it all for a once-in-1-4-year power cut.

wellygary

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#3280694 10-Sep-2024 15:47

Quinny:

It comes down to what you use when, appliance efficiency, how much you can time shift, what the battery can store, and what you can run on the battery at once (peak load Tesla is 5-7).

Pretty much this,

The OP needs to check what the max draw on that battery is, 10Kwh is great but if you can't pull more than 1KW out then what use is having a "whole house" backup,

600W base load sounds like a fridge/freezer and a bunch of LED lights/background devices?

So the assumption that your water/space heating are non electrical,

How many panels do you have?

SirHumphreyAppleby

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#3280698 10-Sep-2024 16:12

Quinny:

Why do you want the backup? Are power cuts common? My system predicts that I will likely have power (urban), so using it is more important. If the power cuts right now, I have 63% on a cloudy day, with 17.5 out to the grid, rather than keeping it all for a once-in-1-4-year power cut.

Keeping computer systems up and running is the primary requirement. Unfortunately, not everything is central and it's a bit of a pain making sure everything comes back online and is operating as expected. Fridges and freezers are the other consideration, but they can be off for quite a long time before we'd be too concerned about those.

We use most of the power we generate, even in summer as the pool heating (pumped water onto roof) takes quite a bit. It's also somewhat self-adjusting as when it's sunny, the pool is heating.

wellygary:

The OP needs to check what the max draw on that battery is, 10Kwh is great but if you can't pull more than 1KW out then what use is having a "whole house" backup,

600W base load sounds like a fridge/freezer and a bunch of LED lights/background devices?

So the assumption that your water/space heating are non electrical,

How many panels do you have?

That particular battery has a maximum sustained output of 100A. The lower end of its operating voltage is 43.2V, so I guess it can support up to 4.3kW.

The 600W base load is based on Solar Analytics reporting, which shows between 0.5-0.56kW over night. That would include three freezers (peak startup current unknown), a few essential computers not much else. Water heating is electric, but is on a timer and never on over night. I'd be wanting to cut off water heating (and the pool) when the supply was out, unless a generator was plugged in.

Currently we have 18 panels and a ~5kW inverter.

pdh

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#3280737 10-Sep-2024 17:42

Last year, I put in a 'part-of-house' UPS - built around Victron kit.
Extremely nice gear.
(I'm a retired control systems engineer).

Forcing reason was our very poor mains reliability (eg: 7 outages this Jan - Okura, Auckland fringe) and post-Covid work-from-home Zoom contracting.

Secondary reason was to protect the electronics in our Hue lights & Samsung fridges (new house).
Neither were liking the nasty power flickers - Hues were resetting and Fridges were going into loony mode.

So, in simple terms, my main switchboard feeds a secondary 24/7 board via an inverter/charger with internal changeover to inverted DC - in the event of a mains failure. This also gives complete isolation to protect the mythical linesmen ;-) Just a joke !!!

I can't yet justify any solar, but the 5 kWH battery (48V) and 3 KW inverter/charger give me almost 10 hours.
Indetectable changeovers and very clean power.

It runs 2 PCs & 4 monitors, two printers, all house lights, water pump, fridge, freezer, uwave & garage doors.
Average load is under 600 W.
If it looks like a long outage, I've plumbed in generator recharge &/or bypass.
If we're away, with PC's off/idle, the up-time doubles.

Our big heatpump for hot water / under-floor heating + other big loads (eg: wall-oven, tablesaw) are not on this 24/7 switchboard.

I chose to spend a little more $$ to get a battery from one of Victron's very short list of 'guaranteed-to-play-nicely' battery suppliers (Pylontech). The Victron eco-system had what I was looking for: good rep, good reliability, and very smart software. Seemed like an engineer's tech company. Hence the decision to stick with a battery approved by them. I wanted a system my wife could live with if I check out.

Independent Power in Albany did a fine job with advice, sales & support to my sparky (minimal required).
I did the install & DC wiring - with sanity-check from the sparky.

So things I had to think through:
- Fire risk from big Lithium in the connected garage - and fire regs for installing same.
- Really well engineered BMS (battery monitoring system) - it's in the Pylontech
- Generator connection, bypass, failure modes & power limits
(eg: mains re-charge is slightly software-limited to avoid killing generator with max rush into inverter/charger)
- Extendability
- Electrical safety (AC & DC)
- Support for & use by people less techie than I am
- What circuits it made sense to protect/keep alive
- Cost-effectiveness (about 6 K$ +GST)

SirHumphreyAppleby

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#3280739 10-Sep-2024 17:52

pdh:

Last year, I put in a 'part-of-house' UPS - built around Victron kit.
Extremely nice gear.
(I'm a retired control systems engineer).

Thanks for that detailed write-up. There's a lot to consider there, but the price seems perfectly reasonable given all you had done. I am also interested in having the option for a generator should I need one.

Are you able to tell me how much the Victron units cost and which model you installed? The Quattro with the dual AC input, or do you have a separate transfer switch for when the generator is connected?

Solar probably complicates things as ideally the backed up supply would be before the solar to supplement it, but unimportant loads would be disabled when running on backup. Probably no more complicated than a few contactors, but obviously it's all additional complexity.

dahc

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#3280805 10-Sep-2024 20:25

SirHumphreyAppleby:

Browsing at the Auckland Home Show on Friday, I found a 10kWh battery for under $3.5k. While I can't attest to its quality, this does seem significantly less than batteries were when we had our solar system installed in 2020.

I'm interested in taking a look. Who was the exhibitor showcasing these batteries?

pdh

341 posts

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#3280848 10-Sep-2024 23:48

SHApplby:

The 6K$ was the Victron & Battery & some cables.
A bit more for the bypass switches, breakers, odds & sods and sparky - as below.
Which included moving some circuits to the 24/7 sub-panel (kitchen & garage).
- About 600$ for sparky (mates rates).
- About 600$ for 60A switch (bypass BESS), DC breaker & electrical boxes
- About 400$ for steel mount & flameproof wall protection for battery.
- About 600$ for generator socket, mains/gen switch, 12m HD power cable (generator to socket) & sparky.
Above costs include GST.

I used a Victron 3KW MultiPlusII 48V + Cerbo GX (the brains & comms for Victron systems).
In October '23, the Cerbo was 'free' with the MPII - which was 1770$.
A Can-bus cable 28$ - lazy, but my small-wire soldering skills have decayed ;-)
A 5kWh Pylontech US5000B-48V - which was 4120$.
Set of Pylontech DC cables (2m, 21 mm2) to connect the battery 100$
These prices are +GST.

I chose not to buy a Victron touch screen - instead a 2m Cat6 cable from the Cerbo to my switch lets me control/inspect the system with my phone anywhere or PC in the house. Does all I want.
If I added solar, I might add a touch screen - just for bling ;-)
Note that the Cerbo would control the solar - via Can-bus - I'd just need a 48V MPPT controller, panels & wire.
I'm trying to justify a couple of solar panels and a small MPPT - just to make the system self-charging for extended outages if I were absent. Currently, after 20 hrs, someone would have to connect & fire up the genny.

I set the BESS up with 2 of 3-way 220V 60A switches between the main and 24/7 boards:
(1) (Mains) --- off --- (Gen) which feeds the
(2) (bypass to 24/7) --- off --- (Inverter/Charger/Battery to 24/7)
That way I have:
(a) no possibility of anything back-flowing into the grid.
(b) ability to function if anything goes belly-up.
(c) I can run the 24/7 five ways - from:
grid direct, genny direct, grid via MPII, genny via MPII, or battery via MPII (inverter).
Obviously, the normal operation is hands-free... grid via MPII, automatically failing over to Battery via MPII.

The Victron Quattro would have been smarter than the MPII - for the 2nd AC input (mains + generator).
But I'm not sure we can get smaller than a 5 KW version of Quattro.
What I did with the switches is at least as good as the Quattro - just messier.

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SirHumphreyAppleby

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#3280856 11-Sep-2024 06:35

dahc:

I'm interested in taking a look. Who was the exhibitor showcasing these batteries?

Micromall Solar (www.micromall.co.nz)

The battery: BTL-48V210

SirHumphreyAppleby

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#3280859 11-Sep-2024 07:26

@pdh Thanks again for the details. Might be best for me to e-mail Independent Power with my requirements and see what they recommend.

billgates

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#3280865 11-Sep-2024 07:52

@pdh did you get approval from your local lines company for the Victron MPII install and 'Islanding' setup you have done in case of a grid failure?

@SirHumphreyAppleby Victron Quattro is not certified to be grid connected in NZ. MPII up to 5kW units can be connected to the grid. Do you have the make and model of the 10kWh battery you saw at the home show. The C rating of the battery will determine what is the max output it can deliver continuously. Most manufacturers do not list it so you will need to calculate it based on what specs the manufacturer provides. You would hope that its atleast 0.2C at minimum which is 2kWh. Ideally its 0.5C which would mean 5kWh continuous output.

Do whatever you want to do man.

SirHumphreyAppleby

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#3280868 11-Sep-2024 08:03

billgates:

@SirHumphreyAppleby Victron Quattro is not certified to be grid connected in NZ. ... Do you have the make and model of the 10kWh battery you saw at the home show.

The battery is linked above

Does the Quattro II have certification? From what I've read, this addresses regulatory compliance issues with the earlier version, but not necessarily here.

billgates

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#3280877 11-Sep-2024 08:34

Thanks. That battery can pull 4.5kWh continuous power going by the specs provided which is impressive. I imagine the cells are not best quality A grade for the price, but specs are still good. None of the Quattro's are approved or meet the AS/NZS 4777.2:2020. Lines company will accommodate inverters and batteries not listed on the clean energy council's approved list but they need meet the required standards which the Quattro does not and Victron in NZ and AU is not pursuing it either. It's being used essentially now in off grid applications only here.

Do whatever you want to do man.

Ge0rge

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#3280880 11-Sep-2024 08:54

@billgates - Is it possible to connect a device not on the Clean Energy list through a contactor that would automatically physically isolate the unit from the grid in the event of a grid outage?

billgates

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#3280885 11-Sep-2024 09:37

@Ge0rge its best to ring your local lines provider and confirm with them in writing what they will and will not allow. Different lines company around NZ provide different level of flexibility for what they will allow you to do for a device. for eg if the device is setup as a UPS with battery, you do not need any approvals. But in one of the five cases of pdh, they mentioned the MPII is functioning as an inverter and not just UPS with a battery connected that provides backup power to another sub panel which does have a grid isolator switch setup, so it won't back feed to the grid. This is essentially islanding the house. This part should require approval from lines company, so I am interested to know if @pdh had to get approval.

As for your use case, which is similar to what I have described above, some of the lines company are happy for you to proceed with an inverter not on the approved list, if it has the AS/NZS 4777.2:2020 compliance built in or if you get lucky and they are ok for you to use a compliant device like the Tele grid NA003 to isolate the house from grid.

Do whatever you want to do man.