Questions for Solar Installation Sales Interview

QrizB

NoobSolar said:

Thanks for resolving that question for me, 2nd Time. The info on the quote only says this:

SolaX Power 1 x X1-3.6-T-D

3.68 kW Total Inverter Rating

Possibly something like this (there may be more than one model of Solax X1 3.6kW inverter):
https://theecosupermarket.co.uk/product/solax-power-x1-boost-3-6kw-single-phase-solar-inverter-dual-mppt/

Verdigris

3.68 kW Total Inverter Rating

That's the maximum you can export, on a domestic single phase supply, without getting a G99 connection.

Spies

It's my opinion that undersized inverters are only more efficient if their startup voltages are somewhat lower then the larger units. 

For example, the Solis 3kw has mppt trackers that work from 60v and the startup voltage for the inverter is only 70v.

This ensures you're generating more often on smaller arrays. 

Reed_Richards

Verdigris said:

3.68 kW Total Inverter Rating

That's the maximum you can export, on a domestic single phase supply, without getting a G99 connection.

If I understand this correctly, 3.68 kW is also the maximum you can get out of your solar panels, even if you could use more.  So in the middle of a sunny day in summer that's 1.1 of your 4.8 kW going to waste.  Conventional wisdom on this board is that smaller inverters are more efficient so if the sun goes behind a cloud and you get 3 kW of solar power that might be (say) 2.8 kW with a larger capacity inverter because these are supposedly less efficient (I don't know if my guessed differential is correct).  Nor do I know how you tell if this works out in your favour overall.

My inverter has a software setting to limit the exported power but can give me the full output from my panels.  I am satisfied with this arrangement.   

arty688

Also remember the panel output power rating is measured in lab conditions and not really achievable and is also temperature sensitive so the number of times you will be producing over 3.68kw is very small.

Reed_Richards

Here's a day (4th August) chosen completely at random



That's a fair amount of time when I'm getting (or potentially getting) more than 3.68 kW from nominally 4.8 kW worth of panels.

2nd_time_buyer

... despite undersizing inverters being the norm. I am now inclined to turn the question around and say "why wouldn't you get an inverter to match the panel output?"

If you can cap the power exported to the grid to 3.68kw (if necessary). The difference in cost between a 3.68kw and 5kw inverter is typically in the region of only £100. Intrinsically it feels better not to be running something close to capacity for long periods.

Spies

From my point of view, I'm never going to make full power because I'm on two different elevations, so a 3.3kw inverter with 4.125kw of panels would be enough and rarely clip.

NoobSolar

I accept (with gratitude) the point about the max export. I now am concerned only with one remaining issue. - isn't a 5 year guarantee rather short? The unit you sent the link to seems to be a 10-yr guarantee.

2nd_time_buyer

Perhaps double check that with them. I have not seen any inverters with a measley 5 year guarantee. Although, it must be said I have not scoured every corner of the market.