Battery sizing

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Battery sizing

Postby Poida2 » Wed Oct 17, 2018 5:45 pm

Hi
I'm a newbi on this forum, so the questions I ask may already be answered elsewhere.

I have PVI-5-OUTD AURORA 5kW inverter installed in 2012. Tasmania.
The FIT is about to expire, 29c/kWh down to a pathetic 6c/kWh, so I am wondering about installing batteries.
I have been told AC COUPLED batteries may be the answer (System too old for Tesla powerwall).

The 20 PV panels (rated at 245W ea) generate about 18kWh/ day (4.9 kW x 3.7hr sun/day) on average over the year.

At the moment the solar feeds the house first and excess power gets sent to the grid (when the sun shines).
In summer, 85% of the power generated goes to grid!
kWh exported/kWh total: Summer quarter 2190/2525, autumn: 1634/1716, winter: 547/723, spring: 1604/1831

1. Can the battery config be similar? feed the house first (residential power, tariff 31) then excess power be diverted to the batts?

Our average daily usage residential (pre solar) T31 was 6kWh, (post solar) 4kWh.

Our average daily usage hot water (T41) is 4.5kWh

Our average daily usage underfloor heating (T61) is 24 kWh.

2. Could the energy stored to the batts be diverted to two or more tariffs?

Eg to T31 AND T41 ?

3. Battery sizing to get to a "float state", what I understand to be 30% of charge left in batteries daily.

(I stand corrected on this calculation):

Assume Battery's: 6V, 350Ah ea
Assume 3 days of reserve power.
T31 usage = 4 KWh (after solar feeds the house first).
3 days x 4kwh =12kWh
12000Wh/6V=2000Ah, (ohms law)
2000/0.3 (assuming 30% discharge)= 6667Ah
6667 Ah/350Ah =19 bats.
It seems rather a lot....

4. What battery config is best. Series or parallel. I'm aware parallel doubles amps, voltage stays same, in series =double voltage, amps stay same.

5. Do I need a charge controller?

6. Any idea on cost? Obviously I would need an electrician to wire it in, but I may be able to do a lot of the legwork, procure the batteries...

Thanks in advance...
Poida2
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