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Solar backup power with Gridtie or MPPT???


Wetkit
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So I have been snooping around the interwebs and asking quotes from installers.

My ideal system would be a 5kva bi-directional invertor, 48V battery bank with a MPPT controller on the solar array.

 

Most of the installers is happy to quote me on the above, but all of them say my battries will not last. According to them the battries will cycle at least 3 times a day, reducing even the most decent battery to jelly in a year or less!!!

 

They reccomending I go 5kva bi-directional with battery bank, but to connect the solar array to a gridtie invertor.

Supposedly the battries will now only be used when Eksdom is down and the gridtie does not deliver enough power to keep everything running.

Thing is will the gridtie invertor be able to re-charge the battries backwards through the bi-directional invertor?

 

Now all of the above is sort of true, but are they, these installers, not trying to make more sales by pushing gridtie invertors?

 

Surely if your battries cycle 3 times a day, either your solar array is too small, your battery bank is too small, or both?

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  • 6 months later...

So I have been snooping around the interwebs and asking quotes from installers.

My ideal system would be a 5kva bi-directional invertor, 48V battery bank with a MPPT controller on the solar array.

 

Most of the installers is happy to quote me on the above, but all of them say my battries will not last. According to them the battries will cycle at least 3 times a day, reducing even the most decent battery to jelly in a year or less!!!

 

They reccomending I go 5kva bi-directional with battery bank, but to connect the solar array to a gridtie invertor.

Supposedly the battries will now only be used when Eksdom is down and the gridtie does not deliver enough power to keep everything running.

Thing is will the gridtie invertor be able to re-charge the battries backwards through the bi-directional invertor?

 

Now all of the above is sort of true, but are they, these installers, not trying to make more sales by pushing gridtie invertors?

 

Surely if your battries cycle 3 times a day, either your solar array is too small, your battery bank is too small, or both?

Yup, if they cycle 3 times a day, then either battery bank is too small (i.e. kwh), or the PV array is too small ;)

Calculate how many watt/kilowatt you need, for at least 15 hours, add say 20-30% to that and your battery bank shouldn't have to cycle 3 times per day. Then make sure you have enough PV Kw to recharge that bank within 5-6 hours. 

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