pv logged production analysis ?

[KLD]

Zeus,

Please excuse my ignorance of how inverters work. What actually happens when the inverter starts limiting the output? Will it switch off completely, or will generation simply be capped?
I guess the 19% figure you extracted from StB's plot is a sum of the nine or ten "steps" at the highest power? If the inverter were to only cap the output, then you can't just throw all the 19% away. Instead, those times associated with the highest output figures would all pile onto the last level just below the cap, won't they? A bit more spreadsheet wizzardy, maybe?

Klaus

[billt]

The inverter will just limit the output. On my guestimations the loss for this hypothetical system would be 2.1MWhr out of 78MWhr over 25 years, or 2.7%. That is with the very pessimistic assumptions made by Zeus. In reality the loss would be a lot lower than that.

If you start compounding stuff you can get very alarming numbers, but they don't actually tell you anything!

[StBarnabas]

I have rum a GTI limiting analysis on the StBC data. Here is the result

[zeus]

Hi All

KLD, billt, StBarnabas you're correct ..... my figures were based on the inverter entering an error condition and cutting out at above max generation until in spec conditions reappeared. Running an inverter limit ceiling of 85% with no cutout reduces the generation by approx 1.8% which equates to a reduction through the same compounded calculations of around £1180 over the 25 years on a 3.96kWh system, which fully supports billt's figure of £1300 compounded ( to billt )

Thanks & Humble Regards
Z

[GavinA]

bear in mind that an SB3300 will (from memory) have an actual optimum (nominal) operating rating of more like 3kW, meaning that it's happiest operating below 3kW, but will peak at upto 3300W ok. It's not intended to actually run at 3300W for long periods though, and I'd think that running a 4.2kWp pv array through it would mean it would be running at 3300W a lot for long periods during the summer, which I'd expect would reduce the operating life of the inverter (although I've no data to back that up).

so maybe add another £2k onto the cost side for this set up to pay for the replacement inverter when this one breaks just out of the guarantee period

[zeus]

bear in mind that an SB3300 will (from memory) have an actual optimum (nominal) operating rating of more like 3kW, meaning that it's happiest operating below 3kW, but will peak at upto 3300W ok. It's not intended to actually run at 3300W for long periods though, and I'd think that running a 4.2kWp pv array through it would mean it would be running at 3300W a lot for long periods during the summer, which I'd expect would reduce the operating life of the inverter (although I've no data to back that up).

so maybe add another £2k onto the cost side for this set up to pay for the replacement inverter when this one breaks just out of the guarantee period

Hi GavinA

Spot on  .... the SB3300 datasheet suggests AC 3300W nominal/AC 3600VA(/W) max. I have contacted SB requesting a definitive statement on possible long term detrimental effects of running the inverter to produce around 20% above nominal with around 10% at maximum.

Regards
Z

[GavinA]

bear in mind that an SB3300 will (from memory) have an actual optimum (nominal) operating rating of more like 3kW, meaning that it's happiest operating below 3kW, but will peak at upto 3300W ok. It's not intended to actually run at 3300W for long periods though, and I'd think that running a 4.2kWp pv array through it would mean it would be running at 3300W a lot for long periods during the summer, which I'd expect would reduce the operating life of the inverter (although I've no data to back that up).

so maybe add another £2k onto the cost side for this set up to pay for the replacement inverter when this one breaks just out of the guarantee period

Hi GavinA

Spot on  .... the SB3300 datasheet suggests AC 3300W nominal/AC 3600VA(/W) max. I have contacted SB requesting a definitive statement on possible long term detrimental effects of running the inverter to produce around 20% above nominal with around 10% at maximum.

Regards
Z

I'd be very interested in SMA's response to that query if you get one.

[Laurence]

In these times of inverter shortages (of some brands, anyway), Any installer is going to favour the inverter he has in stock, probably over the ultimate inverter for the job! Try asking for an SB3800 and see what your supplier says... Lots of air sucked in between clenched teeth probably means he can't get his mits on the larger product...

What about inverter efficiencies? I realise that it is only the one measure (and only at one point on the power curve), but SB3300 = 94.4% (Euro rating), SB4000TL = 96.4% (Euro).  What is the cost penalty/premium of that extra 2% yield in your system?

Yes, I realise TL means no galvanic isolation, which in some circumstances can increase installation costs - many dimensions to this argument!