Modular instead of centralized

pwilliz

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Mar 16, 2022
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Looking at the two ways of managing power there seems to be the centralized approach i.e. one or more large inverters, 48v battery bank and enough solar cells to provide the necessary voltage to charge the batteries (ok, I am deliberately excluding a bunch of detail).

But I am interested in the other more modular approach.

One solar panel, one micro-inverter and one or more cells just for that solar panel. Yes it may be more expensive once the system is fully scaled up, but initially at least the capital outlay is commensurate with the scale of the system. So starting with one panel, the panel battery absorbs extra energy that can dispensed via the microinverter as required. Its a modular package deal that could all be attached to the solar panel.

I can't seem to find such a configuration anywhere. In this modular style build, I would need the solar panel to battery to include overcharge protection to the cell(s) and an MPPT to charge the battery and then the micro-inverter takes that DC (solar/battery) and generates AC.

Am I dreaming? Thanks for any thoughts :)
 

jberger

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Jun 1, 2021
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The microinverters don't work that way, they need grid power to sync with and charge the batteries.
There is a level of simplicity and monitoring that makes microinverters very appealing, until you start looking at the limitations and costs.
There is a reason most of the market goes with strings of panels to larger inverters, it makes more sense for most implementations.
 

pwilliz

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Mar 16, 2022
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Thanks for posting. As I understand it, the enphase IQ8 is not grid tied.


Since the IQ8-60-2-US micro-inverter will operate on a min start voltage of 30 volt, then in theory you could provide 10-11 3.2 volt cells to drive the micro-inverter and the solar panel feeds the battery/micro-inverter input.

Solar panel -> battery(10 x 3.2v = 32v) -> micro-inverter -> A/C out (290V AC).
 

stienman

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Jan 6, 2021
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You'll need to roll your own, with a solar charge controller and a grid tie inverter. The solar charge controller is easy and cheap - lots of those are available. The grid tied inverter is less common, except for panel to AC microinverters.

Here's a 300-400W grid tie inverter:

There are likely others.

You will, of course, have to deal with the problems of exposure to the elements, and you'll have to work out a control system yourself if you want to tell these units what they should be doing under different circumstances, rather than letting them choose based solely on their input power/voltage.

I don't think it's a great idea overall, though. The inverters are as or more expensive than a direct panel to AC inverter, and adding battery backup to your grid is better in a shed or garage, rather than outside with the panels. An AC to DC battery charger, and a grid tied inverter are all that's needed indoors. Same effect, but better in a number of respects.
 

kundip

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Jun 27, 2021
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The microinverters don't work that way, they need grid power to sync with and charge the batteries.
There is a level of simplicity and monitoring that makes microinverters very appealing, until you start looking at the limitations and costs.
There is a reason most of the market goes with strings of panels to larger inverters, it makes more sense for most implementations.
True. But just for alternate view. The string panels are sized to inverter and you cannot adjust or add panels easily. With micro- inverters you can add panels easily without having to upgrade Envoy or MultiGate etc. If one panel or micro-inverter is giving trouble - nothing else is affected. You can replace either or both quickly. Also on my Envoy system I have 3 different models of Enphase micro-inverters. You can add or replace any model seamlessly. (Depending on sizing.)
 

GregTR

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Sep 16, 2022
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You kind of answered your own question: The self contained PV/Inverter/Battery solutions don't scale well and eventually will cost substantially more and be less efficient than a properly designed and built whole system. This is the reason why I am not a fan of Enphase in general, it might work fine for a smaller system but once you get into the 15 kW+ setup and large batteries they just become substantially more expensive than an alternative solution that does not require you to buy two micro inverters every time you want to add a panel and a bit more battery storage.

If you can't stomach/afford the outlay of a full system from the get go then you've got some options already listed above by others.
 

kundip

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You kind of answered your own question: The self contained PV/Inverter/Battery solutions don't scale well and eventually will cost substantially more and be less efficient than a properly designed and built whole system. This is the reason why I am not a fan of Enphase in general, it might work fine for a smaller system but once you get into the 15 kW+ setup and large batteries they just become substantially more expensive than an alternative solution that does not require you to buy two micro inverters every time you want to add a panel and a bit more battery storage.

If you can't stomach/afford the outlay of a full system from the get go then you've got some options already listed above by others.
I am sure you are right.
You kind of answered your own question: The self contained PV/Inverter/Battery solutions don't scale well and eventually will cost substantially more and be less efficient than a properly designed and built whole system. This is the reason why I am not a fan of Enphase in general, it might work fine for a smaller system but once you get into the 15 kW+ setup and large batteries they just become substantially more expensive than an alternative solution that does not require you to buy two micro inverters every time you want to add a panel and a bit more battery storage.

If you can't stomach/afford the outlay of a full system from the get go then you've got some options already listed above by others.
 

GregTR

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Sep 16, 2022
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True. But just for alternate view. The string panels are sized to inverter and you cannot adjust or add panels easily. With micro- inverters you can add panels easily without having to upgrade Envoy or MultiGate etc. If one panel or micro-inverter is giving trouble - nothing else is affected. You can replace either or both quickly. Also on my Envoy system I have 3 different models of Enphase micro-inverters. You can add or replace any model seamlessly. (Depending on sizing.)
And to play devil's advocate, by increasing the number of components you're greatly reducing the MTBF (Mean Time Between Failures). While a failure might not be as catastrophic as losing a string inverter, it's a lot of pain to climb to the roof, remove a panel or two, get under them to swap a micro inverter.
 

kundip

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Jun 27, 2021
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I am sure you are right. I have only produced 7,000 kilowatts so far this year. So I don't think I am ever ever going to get to 15,000+ kilowatts. It is definitely an area I don't understand.
My bill for this year, so far, is USD $481 we also have a daily supply charge here totalling USD $169 my total bill is USD $650 (258 days) or, total, USD $2.52 per day.
My total imported from grid is 2,400 kilowatts this year so far. The rest I have produced myself.
P.S. my micro- inverters are down at ground level. Not under panels. Photo shows a new bunch of micro- inverters (Sunny Boys) I am installing.
 

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