Solar panel microinverters for island array

[Boron]

Hi Guys
Hope this is not a dumb question but AFAIK all the microinverters are of the grid-tie type and require connection to grid/main voltage so they can synchronize. Indeed if the mains trips then sync volts lost and the system shuts down (seems odd cant be right pls advise).
My planned system is to use panels with individual microinverters sending ac240V to my auxilliary Dis Board. I do not want to connect my system to the grid. Hence I believe its called an "Island " system.
I will have a manual (at the moment) c/o switch to power house base load eg my PC stuff (thru a UPS) and other non-surging loads. This can be configured base on operating experience eg Fridges, freezers etc.

My thoughts are that I need to provide a (alias 50hz mains volt reference to the microinverter grid but it wont ever allow export of power into in - blocking diodes - I thought a simple low power say 100VA UPS (sine wave) could do the job and this would be power from my main battery storage used to store excess power from panels.

Would this allow the microinverters to net together with their independant ac outputs?

OBTW I have realised that there is something called a "Smart Grid SG" system of microinverters which have wifi (up to 99units) back to a hub up to 5m distance line of sight and then to a PC App? These are ca £120 ea/panel + £50 for the hub unit? vs basic microinverter £50 ea

Anyone experience this stuff? is it OTT? or only for the Big Boys

My objective is to be able to monitor the performance and SOH of individual panels. It seems to me that the simple set of dc strings just hangs together and you hope for the best. Controlling individual panels with MPPT on board can give extra power efficiency AFAIK. Also one bad panel brings down a whole string without warning?

Your comments will be much appreciated as I am trying to understand this "Smart" system.



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[DIYrich]

With micro inverters, they "push" power into the system, whereas DC panels make the power available to be "taken" by the MPPT.

On an on or off grid DC PV system, the battery charger and inverter take what they want, and excess power is left at the panel.

On a grid connected system, excess AC PC power can be easily pushed to the grid.

In an off-grid system there is no place for excess AC PV power to go (batteries are full). So you need something to control production. Hence your ups idea only solves half the problem: sine wave for micro inverter to follow.

You still need to solve the excess power problem. Island controllers can control production by frequency shifting. They also maintain margin in the battery to dump short periods of excess production (waiting for micro inverter to respond to frequency shift).

 

[kommando]

I use a SMA Sunny Island which is a battery inverter and provides a standalone grid, it also controls all my PV inverters by increasing its grid frequency as the battery fills up. Easy to do on matching SMA PV inverters and now also, after changing the settings, a Solax inverter. You would need micro inverters that have this setting, ie a frequency adjust start and a frequency ramp. For the SI to do its magic this is for UK 51htz and 10% for each 0.1htz. I am not aware of any micro inverter with this setting.

 

[wpns]

While I can appreciate your desire to make an off grid system using grid-tie components, that really is not the purpose for which they are designed. Nothing’s impossible, but if you are wanting to make an off grid system, you should start with components that will work in that application.

 

[Boron]

With micro inverters, they "push" power into the system, whereas DC panels make the power available to be "taken" by the MPPT.

On an on or off grid DC PV system, the battery charger and inverter take what they want, and excess power is left at the panel.

On a grid connected system, excess AC PC power can be easily pushed to the grid.

In an off-grid system there is no place for excess AC PV power to go (batteries are full). So you need something to control production. Hence your ups idea only solves half the problem: sine wave for micro inverter to follow.

You still need to solve the excess power problem. Island controllers can control production by frequency shifting. They also maintain margin in the battery to dump short periods of excess production (waiting for micro inverter to respond to frequency shift).

Thanx for the heads up, that thought (what to do with excess ac in an island grid) occurred to me last night and fried my skull.
Its notable that ac systems havent been adopted on Solar Farms (neither has Panel Solar tracking. They seem to favour, med 500Vdc strings and branch inverters. Their panels probably have inbuilt MPPT (called dc optimisers?). I dont know if they have come up with a wireless panel monitor system yet?