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What do you think of my grid tie, battery, PV design?
#1
Hello all,

I've been considering adding PV & battery to my home for the last 5 years and am finally putting pen to paper.  Below is the design of what I'd like to do.  This drawing is pretty high level and does not include a lot of details, but hopefully will be able to convey my thoughts.  I've got a tiny roof in the middle of a city, so PV system is limited and very small.

Some specific questions in yellow:

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#2
(11-01-2020, 12:41 AM)poldim Wrote: Hello all,

I've been considering adding PV & battery to my home for the last 5 years and am finally putting pen to paper.  Below is the design of what I'd like to do.  This drawing is pretty high level and does not include a lot of details, but hopefully will be able to convey my thoughts.  I've got a tiny roof in the middle of a city, so PV system is limited and very small.

Some specific questions in yellow:

PV array - Its common that you combine a designated set of panels for the PV input specs of a specific piece of equipment (Hybrid Inverter X).   Then a separate / second PV array for the 2nd piece of equipment, and so on.   If you have 2 sets of 'max' PV arrays in parallel, then they could exceed the equipment input capabilities of one of the Hybrid Inverters.   Maybe you have some special kind of tandem / smart / sharing Hybrid Inverters?  but otherwise its normal to keep them separate.

Battery Bank - I combine mine and have a single BMS (Batrium) that manages the overall battery bank.   Batteries don't how many charging sources there are or how many loads there are as long as the overall max charge/discharge don't exceed the battery bank design.    But there's no 'rule' that you can't have 2 separate battery banks - you would have 2 separate things to manage instead of 1 bigger one and the  charge/discharging may not be evenly distributed if that matters to you.
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#3
(11-01-2020, 01:06 AM)OffGridInTheCity Wrote:
(11-01-2020, 12:41 AM)poldim Wrote: Hello all,

I've been considering adding PV & battery to my home for the last 5 years and am finally putting pen to paper.  Below is the design of what I'd like to do.  This drawing is pretty high level and does not include a lot of details, but hopefully will be able to convey my thoughts.  I've got a tiny roof in the middle of a city, so PV system is limited and very small.

Some specific questions in yellow:

PV array - Its common that you combine a designated set of panels for the PV input specs of a specific piece of equipment (Hybrid Inverter X).   Then a separate / second PV array for the 2nd piece of equipment, and so on.   If you have 2 sets of 'max' PV arrays in parallel, then they could exceed the equipment input capabilities of one of the Hybrid Inverters.   Maybe you have some special kind of tandem / smart / sharing Hybrid Inverters?  but otherwise its normal to keep them separate.

Battery Bank - I combine mine and have a single BMS (Batrium) that manages the overall battery bank.   Batteries don't how many charging sources there are or how many loads there are as long as the overall max charge/discharge don't exceed the battery bank design.    But there's no 'rule' that you can't have 2 separate battery banks - you would have 2 separate things to manage instead of 1 bigger one and the  charge/discharging may not be evenly distributed if that matters to you.


Thanks, looking at MPP and Sol Ark. MPP appears to have a much lower limit per PV string of 150v while the Sol Ark is at 500v.

I think one of the benefits of two separate systems that I keep coming back to is redundancy. So if one battery goes down, or you take it down for maintenance, you still have the other one working. This would maintain all but the heaviest loads for me and would cover 90% of my use cases. In this situation, if only the one battery string is down but both inverters are still online, it should be able to support the 10kw load by pulling from the grid.
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#4
Mpp have up to 950VDC input depending on choice of inverter. I have strings of 450 and 600VDC nominal input.

Build it redundant but dont have 2 totally separate systems. Use a common battery bus is my sugestion and instead do so tyou can switch to grid if needed and also you can take out one battery string without issues.
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#5
Combined battery bus - both packs connected (via breakers or fuses)
Separate MPPT allow for different shading / angles / directions output variation between pannel groups
Dual hybrid should enable all loads to be serviced with no split, unless you need off-grid UPS style protection
Larger single inverters have higher idle loads, which can be very significant with an energy loss that over 15 years is more than the cost of the unit....

The 150V limit on some MPPT controllers seems to be a common level and I have nevery figured out why 150V and not 200V or something else. 150V is the wrong voltage level for newer panels around 300W and higher because the Voc in cold conditions pushes above this for 4 panels in series. 3 Panels in series is usually fine, but a bit more wiring.
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