Solar PV quotes - could you sense-check and advise on Sofar vs Growatt

arty688

1961Nick said:

My experience of a 3.7kWh inverter, a 4kWp array & a SSE orientation is that the output flatlines indicating the inverter has reached it's peak.

I accept that a SE orientation is less ideal than the SSE I have, but the OP is located much further south & that should offset some of the difference.

I really do think 3.6kWh is too small for a 5kWp array. If 1.2 is the ideal ratio (?), then that suggests at least 4.1kWh.

Am I being cynical for thinking that a 3.6kWh inverter makes DNO approval simpler & this could be the reason for it's inclusion in the quote?

Yes my bad maths thought it was a 4.6kw array.

Also every KWh you lose that you would of used is worth about 6KWh you export.

Out of interest  what Optimisers have to do with it ?

tomkaier

1961Nick said:

The sofar is a good basic workhorse. It communicates with the Solarman app & provides very comprehensive data at 5 minute intervals for everything except the SOC which is virtually a live feed. The downside is that it's one way communication & you have to program the inverter using the front panel. That's ok for Octopus Go but clearly impractical for Agile.

Ah yes very good point, I had read that before and that certainly put me off the choice of a Sofar inverter. Only programmable at the actual device is a big no-no, IMHO. 

Screwdriva

I would caution against Chinese inverters. Yes, they're cheaper but the catch always comes later in the product's life.

Here is Growatt's warranty policy

https://www.ginverter.com/list-19.html

2nd_time_buyer

The optimisers ensure all the panels are outputting the same voltage, so that only the power varies. This means the inverter is also always operating at the same voltage. If you look at the Solaredge power efficiency curves the efficiency is still high even down to very low power outputs.

arty688

2nd_time_buyer said:

The optimisers ensure all the panels are outputting the same voltage, so that only the power varies. This means the inverter is also always operating at the same voltage. If you look at the Solaredge power efficiency curves the efficiency is still high even down to very low power outputs.

Still not sure what that has to do with inverter sizing ?

2nd_time_buyer

arty688 said:

2nd_time_buyer said:

The optimisers ensure all the panels are outputting the same voltage, so that only the power varies. This means the inverter is also always operating at the same voltage. If you look at the Solaredge power efficiency curves the efficiency is still high even down to very low power outputs.

Still not sure what that has to do with inverter sizing ?

Well the reason given for undersizing the inverter is that the efficiency is better at lower power outputs. However, with optimisers this effect is much less.

arty688

So

2 x 10 400w panels one optimised one not.

ideal conditions both set producing 4kw on a 3.6kw inverter so being clipped 

all but 1 panels go into complete shade

optimised one are know producing 400w more effiently on a 3.6kw inverter than a 4kw inverter ?(or not I have no real idea)
non optimised producing nothing.

Still no idea what that has to do with inverter efficiency ? System efficiency yes 

2nd_time_buyer

The difference is more at sunrise and sunset. 

The total power output from the panels will be low in both cases (even if all the panels receive the same light). However, the optimsed system is more efficient at low power levels. In part this is because the optimisers work by ensuring the same high voltage across panels regardless of conditions - only the current varies. With a non optimised system the voltage will vary depending on conditions. Since the inverter will typically have a minimum voltage requirement for the inverter to even start up (typically around 100v), and even if this is met the efficiency will be lower until the optimum voltage is met, effectively you would have lower efficiency in low-light conditions.

To be honest, I am not 100% certain of all the above as the data is not readily accessible from the manufacturers.

arty688

Had a quick look and Solaredge says having smaller inverter than panels gives you better low light efficiency . as inverters work more efficiently the closer thay are to the max output.

2nd_time_buyer

arty688 said:

Had a quick look and Solaredge says having smaller inverter than panels gives you better low light efficiency . as inverters work more efficiently the closer thay are to the max output.

Yes, that is the case for all inverters which is what I was trying to say above (badly). However, what I am suggesting is that the effect is smaller with an inverter with optimised panels for the reason(s) given above. Which would mean that the usual reason to oversize is less valid.