Should an inverter be undersized for a panel array?

TomOnBoard

I'm being told that a 3kW panel array can be matched to a 2.5kW Inverter.

I understand that a 3kW array will seldom produce its full maximum output in Irish conditions, and that normal operation will probably produce much less most of the time. However, will the odd occasion when a full 3kW might be produced fcuk up the 2.5 inverter or is there normally a sufficient margin built in to deal with this?

Gumbo

TomOnBoard wrote: »

I'm being told that a 3kW panel array can be matched to a 2.5kW Inverter.

I understand that a 3kW array will seldom produce its full maximum output in Irish conditions, and that normal operation will probably produce much less most of the time. However, will the odd occasion when a full 3kW might be produced fcuk up the 2.5 inverter or is there normally a sufficient margin built in to deal with this?

Think again.
My 3kw system (10x300w panels) regularily produces up to 3.4kwh!

South facing roof in north dublin.

Condenser

TomOnBoard wrote: »

I'm being told that a 3kW panel array can be matched to a 2.5kW Inverter.

I understand that a 3kW array will seldom produce its full maximum output in Irish conditions, and that normal operation will probably produce much less most of the time. However, will the odd occasion when a full 3kW might be produced fcuk up the 2.5 inverter or is there normally a sufficient margin built in to deal with this?

You can underside by quite a bit. You're inverter needs a certain level of power to work optimally and it's better if you can achieve close to this in winter and low light conditions than having an oversized inverter underperforming.
If you ever plan on adding more you could always go for a larger inverter and only use one string connection as most decent inverters have two. In this case you won't lose out on performance.

quentingargan

MCS standard in UK suggests that the peak panel output can be 25% more than the inverter, though I would only push it that far if the roof has a less than ideal orientation.

Simulations usually show no significant loss if the inverter is under-sized by 10 to 15%.

As said earlier, inverter works more efficiently the closer it is to its rating.

gctest50

TomOnBoard wrote: »

I'm being told that a 3kW panel array can be matched to a 2.5kW Inverter. ......

If it burns your house down, I'm sure the insurance company would love to hear you had a 2.5 connected to your 3.0 panel


Anything ~ 50% load or above and the inverter will be as good as it can be

They are not good at 10% -- 20% load

air

gctest50 wrote: »

If it burns your house down, I'm sure the insurance company would love to hear you had a 2.5 connected to your 3.0 panel

This is total *ollocks.

It's standard practice and in fact once you keep within the DC voltage and current limits of your inverter you can generally connect as much as you like without risk of damage.

It's standard practice in the UK to install 4kW of PV to inverters with a peak output of 3.68kW as their standard domestic export limit is 16A.
I would say 90% of UK 4kW installs have this precise setup .

Having said all that, inverters are cheaper than ever, low load inefficiency is the main downside to not undersizing as has been mentioned.

Gumbo

On a side note to anyone considering PV, on the jobs I’m inspecting I’m insisting on an additional smoke detector in the space where the invertor in placed.

I done this in the attic eaves space on my own system. Most builders have no issue with it and it may just aid in the escape should anything go wrong.

TomOnBoard

kceire wrote: »

On a side note to anyone considering PV, on the jobs I’m inspecting I’m insisting on an additional smoke detector in the space where the invertor in placed.

I done this in the attic eaves space on my own system. Most builders have no issue with it and it may just aid in the escape should anything go wrong.

That seems sensible to me.

TomOnBoard

gctest50 wrote: »

If it burns your house down, I'm sure the insurance company would love to hear you had a 2.5 connected to your 3.0 panel

That seems very alarmist!

freddyuk

kceire wrote: »

Think again.
My 3kw system (10x300w panels) regularily produces up to 3.4kwh!

South facing roof in north dublin.

If you are "in the business" you should understand the difference between KW and kWh!!
I would hope your 10 x 300wp modules do produce more than 3.46kWh (kilowatt hours) on a good sunny day but the question is about "peak" power which is measured in KW (Kilowatts). So if they are producing 3.46kw for maybe 6 hours over the day you will produce 20.76 kWh over that day. Your peak power may be 3.46kw for brief periods especially during cloud spikes in cool breezy conditions.

quentingargan

gctest50 wrote: »

If it burns your house down, I'm sure the insurance company would love to hear you had a 2.5 connected to your 3.0 panel

Technically, under-sizing the inverter improves efficiency, and improved efficiency means less heat generation. I think it is being alarmist, though I do like the idea of a smoke alarm anywhere that you have power electronics and connections.

The most common potential fire hazard I have seen with solar PV is badly crimped MC4 connectors. If the spark doesn't have proper MC4 crimpers, you can't just squeeze this up with a pliers. I've seen melted connectors with soot above them, and damaged inverters as a result.

Gumbo

freddyuk wrote: »

If you are "in the business" you should understand the difference between KW and kWh!!
I would hope your 10 x 300wp modules do produce more than 3.46kWh (kilowatt hours) on a good sunny day but the question is about "peak" power which is measured in KW (Kilowatts). So if they are producing 3.46kw for maybe 6 hours over the day you will produce 20.76 kWh over that day. Your peak power may be 3.46kw for brief periods especially during cloud spikes in cool breezy conditions.

I am not in the business. I am a customer so I would also expect anyone in the business to know the difference.