Adding battery storage to your existing solar array

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Adding battery storage to your existing solar array

Post by jonescg » Mon, 10 Sep 2018, 16:35

Of the 95 people who bought the AVASS battery cells, there's probably a good ten who are wondering whether or not they're bitten off more than they can chew. Chances are, they already have a solar system which is grid connected, and the batteries were an affordable way of capturing some of that energy. But it is a DIY project and there are lots of things to do before the 16 cells sitting in your garage will be working for you.

But it's not too difficult - hang in there! This thread is about adding a 48 volt battery to an existing grid-tied solar array.

Most homes with PV installed are simply exporting to the grid while the sun shines, and you're getting paid 7 to 13 cents for every kWh exported. Any electricity consumption during the day is a dollar not spent, so that's good. The reality is, very few grid-tied solar inverters will have provision for adding a 48 volt battery. So what do you do?

There are two options. A quick and inexpensive yet slightly less efficient one, and a more expensive complicated one which DC couples the battery.

The quick and easy one is to buy an AC coupled, grid-tied battery inverter. There are a few options out there - Goodwe SBP, Selectronic SP Pro, SMA, Victron and Enphase spring to mind, but there are others. Expect to pay between $1100 and $2000 for such an inverter, plus installation.

Most solar homes have something like this:
Grid tied PV house.png
Grid tied PV house.png (12.24 KiB) Viewed 165 times
Adding a battery isn't practical using the existing inverter, but you can add an AC coupled inverter like this:
AC Coupled home with battery.png
AC Coupled home with battery.png (15.77 KiB) Viewed 165 times
It measures the AC from the grid and the AC from the solar inverter and decides where to send the energy - if it's sunny and the household loads are low, charge the battery. If the sun has set, the battery provides the energy to run the home via the battery inverter. If the loads exceed what the inverter is capable of, the grid can step in to make up the shortfall. Finally, when the battery is fully discharged, the grid takes over completely until sunrise.

The more expensive and complicated option is to replace your grid-tie inverter with a hybrid inverter with DC coupling. The Goodwe ES series, Victron, SMA and BYD hybrid inverters are all viable options. Expect to pay between $2000 and $3000 for the inverter, plus installation. There may be some roof time too.

Some of these inverters will operate on a specific PV input voltage, meaning the solar panels on the roof might need to be re-configured into a new series-parallel arrangement - MPP Solar have a range of inverters that have a MPPT voltage of 150 V max, so the panels would need to be configured into multiples of 3 in series.
DC Coupled home with battery.png
DC Coupled home with battery.png (15.42 KiB) Viewed 165 times
But the first thing anyone must do is get their battery build into a nice cabinet close to the inverter(s) and set up with a contactor, current sensor, isolation breaker and fuse. And a good BMS! We have plenty of experience to share details on that front.
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Re: Adding battery storage to your existing solar array

Post by Gobopolice » Tue, 11 Sep 2018, 13:24

great to see this thread started, I am 1 of those 95 people and I am a Noob to all of this.
I have 32 of the 220amp hour Brighsun batterys. Going to wire them up as 16S2P 48v.
Bought a nice hydraulic crimper and serious wire cutters, Lugs are on order , any day now to arrive.
I have just collected my Goodwe 5000SBP and have ordered the Zeva BMS with 200amp shunt and LCD screen.
I have started welding together my Battery Dolly yesterday. Putting it on 4 x 200kg rated wheels !

Just waiting on Richard to start setting his system up which is the same as what I have :lol:
As Im not sure how the Goodwe will comunicate to the Zeva BMS, cross that bridge later.

I have an existing solar setup of 22 x Jinko panels 265w in 2 strings of 11 each paralell into 1 mppt input in a Fronius 5kw inverter.

Exciting times :shock:

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