My DIY battery storage system

[fechter]

Nice work!

Around here, they now have time-of-use metering, so electricity used during peak hours is more expensive than late at night.
If you charged a big bank of batteries at night when it was cheap, then used a synchronous inverter to push it back when it was expensive, maybe you could actually make money on the difference.

I'm sure they have some way to prevent this.

[jonescg]

If you could charge a 280 volt DC battery by day, and connect it to a grid-tie inverter, it would theoretically current limit to the maximum power output of the inverter (2 or 4 kW) until the battery was flat. I suspect you would need to limit the battery side current to 20 A or whatever the input current limit is...

If you had a time of use meter, it would effectively earn you money at night. I believe however that the 'smart meters' can only count energy pushed onto the grid during daylight hours, and in the evening when the power is expensive, it denies you the opportunity.

[fechter]

They have several variations of the rate plans, but most have the peak hours during the daytime when usage is the highest.

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I didn't find the one for solar grid-tie systems where you can credit back your account. No matter how much you push into the grid, they won't pay you, but you can earn credit for consumption.

It's in their best interest if a lot of people pushed power back into the grid during peak hours as this lessens the load on the infrastructure.

[whereswally606]

Jonescg,

Why would you try to earn money at night? Even If they could/would pay you, they would only pay you less or nothing due to the surplus in the grid at those times. I can imagine if you have more solar than your inverter could actually take (i.e. a poorly designed grid system) then this is a kind of way to buffer the excess into the batteries. I guess in OZ there is a good surplus of sun, nice problem to have.

Powerwalls (Tesla, other brands or DIY) I thought are ways of the producer using all the electricity they generate rather than having to export it and lose it to the grid. I just had a UK time of use (economy 7 meter) installed, i.e. a non-smart meter. This is because my wife and I bought a 2011 leaf to replace her old diesel golf estate.

Even though I had an old meter which could run backwards (which should have been replaced by the DNO when we notified them after we installed the grid tied solar). Charging at night at half the price nets us more in savings than the meter ever would turning backwards. Is currently about 90:150 ratio day to night since installing so it should pay for itself in a very short time.

As a side note I have realised last night that our internet connectivity to the adsl is probably being broke by the EMI being produced when the nissan leaf is getting charged. I think this because last night I lost connection at 12.30am when the car was set to come on timed charge. After getting the economy 7 meter installed the internet dropped out less in the day. This is to say, we stopped charging the car at any time and almost exclusively charge it at night now. Going to test using a battery to run the modem to see whether I can use the internet at night when charging the car. I don't know whether the interference is coming down the power cables or the copper of the adsl or just through the air. I am fairly convinced the leaf is faulting the modem. The battery will hopefully isolate one potential source of the EMI if it is coming through the ac power wires.

Anyway, love what you are doing here, I am hopefully this year going to build a bms from a chap called Greg Fordyce and use my Scooter lifepo4 as a DIY storage solution, but more cause I intend to use it to convert and 2nd gen prius to plugin and need a reliable battery.

Selling 2 of my Emax 110s and keeping the 90s, I want the space back and realise I have too many projects and too little cash flow to juggle it all.

[jonescg]

Sorry, by "at night" I meant, from 5 pm to 11 pm. It would mean being a total miser yourself, which most folks aren't going to do. Or live as a shift worker....

I plan on using this battery as a test-pack for when we own our own home and go full-legit with solar. Right now it makes no difference whether I store by day or not, but it will be a good proof-of-concept. Anyone with an EV can charge this battery during sunshine hours and plug in to the battery inverter at 5.30 pm to dump 6-9 kWh into the car. The BMS will prevent it from draining flat.

[jonescg]

On Sunday a good friend came around with an old PIP4048 inverter/charger. Finally I can put my battery to use!

This inverter/charger is designed to take DC from solar panels (no more than 120 VDC) and charge a 48 volt battery. It also has an inverter which allows it to provide up to 4 kVA of power AND it has a built-in battery charger from mains. In effect this is an off-grid inverter with grid (or generator) backup. Nothing is exported with this inverter.

Since the charger was optimised for lead acid I'm not sure about using it to charge the battery - not that it matters as I bought myself a new 25 amp, 48 V lithium charger.

With the inverter hooked up to the battery it was spitting out a nice 230 VAC, to which I charged the scooter and my friend's iMiEV. It took about 2.7 kWh based on the in-line AC energy meter.

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I charged the battery up during the day, putting about 3 kWh worth of sunshine derived electricity in, and this afternoon, plugged the scooter in to charge. I was curious as to the watts out of the battery versus watts into the scooter - power cabinet battery clamped at 34 amps and 52 volts, while the scooter was accepting 26 amps at 55 volts. So about 80% conversion efficiency. I think there are more efficient ways of doing this Probably have to find myself a 48 to 48 DC/DC converter or something.

I took the FLIR camera home from work and had a look around. The mains power timer seems to have a bit of phantom draw.
The cells were warm, but only 29'C after a good hour's discharge at 34 amps.

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An example of why you should use 2.5 mm2 extension leads, not 1.0

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Very happy with it so far!

[jonescg]

I have moved house! Better than that, I've bought a house!

Really nice place in the Perth hills with a beautiful big workshop.

I've already put the rails up for solar on the shed roof.

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The shed has the best aspect to the north, albeit with a bit of shade in the morning. The house is an east-west roof, so either a split system or not at all. There's 6 mm2 cable (single phase) to the shed, so I can push at least 5 kW back through that circuit.

Will set a battery up eventually.

[EbikeAus]

Nice, what size is your shed?

I've recently moved and in the process of building a 6x8 or 9m shed.
I have a 48v LiFePo4 off grid system with batrium bms from my last place, can't wait to set it up again

When you can I'd recommend a new inverter those pips are notoriously inefficient.
I have an Aussie made Latronics but victron are good also

[jonescg]

11.5 m by 7.5 m and 4.2 m high at the peak I might even put a mezzanine on the eastern end for storing crap, and it creates a sort of clean space for electronics and battery fabrication.

The PIP inverter is just for short term inverting - I plan on installing a Goodwe 5048D-ES and connecting the battery up to that. My battery is good for a solid 7 kWh, maybe 8 kWh in summer. It would certainly manage our summer electricity needs just fine but heating a house in winter would probably push us closer to 20 units a night. I've got room to add 8 more panels to the 12 I already have, getting me up around 4 kW. This would generate about 9 kWh a day in winter, so better than nothing.

[jonescg]

Woah, thread revival!

I have finally got around to installing solar on the house, building a big arse LiFePO4 battery and soon, mounting a hybrid inverter on the wall.

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About 8 kW (peak) of solar in an east-west split - so probably a maximum of 6.5 kW and good production right up to sunset.

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Site of the new battery

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The battery cells are Brighsun 460 Ah LFP cells originally used in a bus project, but was parted out to AEVA members. We all bought 16 cell lots (48 V) for about $1100. CHeapest 20 kWh battery you'll ever find.

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Just a basic EV-Power NC loop BMS to open the contactor when any cell goes out of spec. The control board needs 12 V which is supplied by the 48 V to 12 V DC/DC converter. The converter itself is powered by the switched side of the contactor, so when it drops out, there's nothing on the battery.

The inverter will be installed shortly and the whole lot turned on at the end of the month.

[fechter]

Nice!

What are you going to use for an inverter?

I got some LiFePO4 cells from a dead Fisker pack I use for when the power goes out. It just saw some action the other day when we had a rolling blackout due to excess demand on the power grid. Having some solar to go with it would be real nice.

[jonescg]

It's a bit complicated, but I ended up getting a Goodwe GW5048D-ES single phase hybrid inverter. It has two MPPT PV inputs, takes a 48 V battery, and can push 5 kW AC out continuously.

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The problem is about one in three homes in Perth are wired up for three-phase (415 V phase to phase, 240 V phase to neutral). My house is one of these. The supply feed is 6 mm2 cable, so I'm good for about 22 kW in either direction.

However, three-phase hybrid inverters aren't common, and those which run on low voltage battery packs are even less common and are also more failure-prone. Moreover, our network provider (Western Power) has set a limit as to how much power you can push back during the day, and how much phase imbalance you are allowed. In my case, it's a maximum phase imbalance of 2.5 kW meaning a 5 kW inverter on one phase is not on. However, if you have a battery, they let you increase the amount of PV, increase the size of the inverter, and allow up to 3 kW of export on a single phase. SO yeah, it's messy. But the system is approved for 7.9 kW of solar, a 5 kW hybrid inverter one one of the phases and an allowance of up to 3 kW of export. The export will earn me 7 cents per kWh, or about 60c on a good day. The network connection fee is $1 per day.

My preferred system would be a 25 kW three-phase inverter with low voltage battery storage, but most seem to run 400-600 V DC batteries for this. Makes sense - lower losses in the conversion. But high voltage battery packs are a PITA.

I also have an EV I want to charge, so provided self consumption is optimised I should only be leaning on the grid for 4 months of the year, and coming out in front all other times.

[fechter]

Dang, that does sound messy. Things are a bit simpler in my area. Only single phase. A lot of grid tie inverters can't run your house when the grid goes down which sort of misses the point for me. Well, I don't have significant solar (yet) so I just charge my bank and let it sit around doing nothing most of the time. But sure is handy when I need it.

[nicobie]

I can't wait until I can use the battery in my Volt in conjunction with my grid tie solar. I figure that 's the best of both worlds. It looks like it will be awhile though.

[jonescg]

Pleased to report my home solar and battery storage system is up and running!

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When I picked up the 28 Canadian Solar 280 W panels at auction (brand new, just a discontinued line) I put all of them on the roof as two arrays of 14 in series (7.9 kW max). When the system was finally commissioned it worked great on a warm sunny day, but a cold front passed through the next day wreaking havoc on the inverter. Basically over-sizing the PV is great when they show output reduction with temperature, but on a cold cloudy day where the clouds part for 10 mins, you would see 7.2 kW smacking into the inverter causing it to drop out. Every time it did this the grid would step in to compensate and it was generally making a mess. So I climbed up and bypassed two panels on each array, bringing the maximum power down to a more manageable 6.8 kW. So far so good.

The battery has no CAN-Bus BMS supplying information to the inverter, so it's SOC estimates are as good as useless. But it's working

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It occasionally draws from the grid as a buffer, but never for longer than 20 seconds. It's export limited to 3 kW, which is fine as it dedicates PV power to the household loads and charging the battery, and when it's full by midday, exports at a modest rate.

[stirucherai]

Hi jonescg,

Planning to go for GOODWE GW5048D-ES and connect to a DIY battery. Can you share what parameters you had given in the PA Master app during the configuration to setup you DIY Battery.

Pressume we are using BMS of battery pack to handle the charge and discharge disconnect. Also as part of discharge we forced to use the BMS default for how much it can discharge.

THANKS A LOT

[jonescg]

Hi @stirucherai,

It's a solid inverter, and highly recommended for these applications. In the PVMaster app, I chose "User Defined". It reminds you that you're taking your own risks blah blah... But you can just ender the Ah and critically, set Vmax. The Float voltage is about 2 volts lower than this, and set the float time to about 30 min. I don't think these make any real difference, as once the battery is full it sort of drops down to about 54 volts and stays there till you put some loads on.

Goodwe must have done an Over-The-Air update of their inverters, as the Self-Defined battery setup is giving really solid SOC indications. No need for CAN communications, it just uses voltage and coulomb counting.

For the BMS I'm just using EV-Power cell top units for balance and LVC/HVC signal. https://www.ev-power.com.au/product/bms-cbm-lfp08fl/

That normally-closed signal goes open if a cell goes out of spec. I am using that signal to drive one of these BCU devices which opens the main contactor should a cell go too low: https://www.ev-power.com.au/product/bcu-micro-08b/

This powers the main Gigavac contactor. The 12 V supply for all of this comes from a 48 V to 12 V DC/DC converter which is powered from the switched side of the contactor - that way if the pack goes low and the contactor opens, the whole lot is disconnected and I need to manually reset it by switching the BCU off, then bridging the main terminals of the contactor (with a resistor, the capacitors give a bit of a spark) and quickly switching it back on. I rarely need to do this as the PV Master App is set up to limit discharge to 11% SOC and it simply draws from the grid after that, until sunrise. If the battery starts charging at sunrise and I switch the kettle on, it will again draw from the battery which causes the main contactor to open. So maybe 15% is a better number?

[ridethelightning]

I'm so jealous of the LFP bus cells you managed to score!

I'm about to start my solar storage battery journey. I have 16 280ah EVE cells in the post. Cost around 3k Aud shipped, hopefully not too much tax to pay on arrival

We already have 6kw or so of panels and grid tied inverter but its Fronius Primo, which is not compatible with batteries.
which the installer kept pretty quiet about.

I'm planning a 48v system, so far plan is to charge from mains during a sunny day using a few Eltek flatpacks set to 57.xx volts.

Just wondering if you can recommend a good BMS for the job, so far iv looked at ZEVA and some cheaper DALY and JBD. I'm hoping for something simple and reliable, good for 250A perhaps.

[jonescg]

ZEVA is great, and it does interface with most inverters too.
However Ian is winding down the business, so you might want to get onto it before the end of the month!

I'm just using a very simple BMS from EV-Power - so far it's working great.