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Re: My DIY battery storage system

Posted: Feb 08 2018 1:16pm
by 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.

Re: My DIY battery storage system

Posted: Feb 08 2018 9:11pm
by 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.

Re: My DIY battery storage system

Posted: Feb 09 2018 9:11am
by fechter
They have several variations of the rate plans, but most have the peak hours during the daytime when usage is the highest.
Time of use rate plan.JPG
Time of use rate plan.JPG (40.81 KiB) Viewed 2073 times
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.

Re: My DIY battery storage system

Posted: Feb 09 2018 10:23am
by whereswally606

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.

Re: My DIY battery storage system

Posted: Feb 09 2018 8:40pm
by 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.

Re: My DIY battery storage system

Posted: Feb 19 2018 7:06am
by 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.
PIP4048 inverting happily.jpg
PIP4048 inverting happily.jpg (194.21 KiB) Viewed 1987 times
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 :lol: 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.
FLIR0057.jpg (48.64 KiB) Viewed 1987 times
An example of why you should use 2.5 mm2 extension leads, not 1.0 :)
FLIR0059.jpg (51.9 KiB) Viewed 1987 times
Very happy with it so far!

Re: My DIY battery storage system

Posted: Oct 01 2018 7:54am
by 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.
ShedPVsml.jpg (233.83 KiB) Viewed 1533 times
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.

Re: My DIY battery storage system

Posted: Oct 01 2018 4:45pm
by 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 :D

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

Re: My DIY battery storage system

Posted: Oct 02 2018 2:06am
by jonescg
11.5 m by 7.5 m and 4.2 m high at the peak 8) 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.