So now I have a solar PV system how do I make the most of it???

don0301 · 23 February 2012 at 12:16PM

sly_dog_jonah wrote: »

Is it one of these Fronius IG 40?

http://www.fronius.com/cps/rde/xchg/SID-525A48E3-D9D9606B/fronius_international/hs.xsl/83_382_ENG_HTML.htm

I'm also hoping that the summer combine the best angle of the sun with the longest days to maximise daily output. Our slightly east of south orientation means we'll never match an equivalent system thats due South though. But our pre-midday peak means I can get the washing machine on and clothes hung out earlier in the day

Feb's turned into a bit of an overcast let down in cider country, but with a bit of luck we'll get to PVGIS estimate+25% (running about 4% behind at the moment) in the next 5 days. Time for a sun dance.

Fronius IG Plus 35 V

I do, apparently, live in the driest part of the country.

grahamc2003 · 23 February 2012 at 12:19PM

I'm not sure it's such a good idea underspeccing the inverter. My sb1700 manual states not to exceed 1890W dc or else there a danger of explosions. Max input voltage is 400V - I assume that's an open circuit voltage. If the dc is getting near the limit, the yellow light flashes 4 times at 1 second intervals - if you see that then you have to disconnect things quickly to avoid inverter damage and the possibility of explosions.

'Overvoltage on the DC side canb even cause dangerous explosions of the Sunnyboy input capacitors and explosions of the electrolytes coming from the exploded capacitors'

don0301 · 23 February 2012 at 1:00PM

grahamc2003 wrote: »

I'm not sure it's such a good idea underspeccing the inverter. My sb1700 manual states not to exceed 1890W dc or else there a danger of explosions. Max input voltage is 400V - I assume that's an open circuit voltage. If the dc is getting near the limit, the yellow light flashes 4 times at 1 second intervals - if you see that then you have to disconnect things quickly to avoid inverter damage and the possibility of explosions.

'Overvoltage on the DC side canb even cause dangerous explosions of the Sunnyboy input capacitors and explosions of the electrolytes coming from the exploded capacitors'

rofl

You can plug a 100kWp array into a 4kWp inverter, and guess what? It wont blow up. Instead, it will just draw up to and no more than the current it needs to deliver its maximum output power, and no more. You've wasted one hell of a lot of the capabilities of your 100kWPk array, however! Where has the other 96kW "gone?" The answer is nowhere - it wasn't even generated. Any more than a 12V 100Ahr battery generates masses of power, when only a squity little lamp is strapped across it. (before anyone splits hairs, this is assuming that the source and load are all voltage matched - it IS possible to blow up an inverter by presenting it with two high an array voltage, but well designed systems should never achieve this).

your getting mixed up again graham

sly_dog_jonah · 23 February 2012 at 1:43PM

don0301 wrote: »

I think the inverter goes up to 3680W, might be wrong

don0301 wrote: »

Fronius IG Plus 35 V

http://www.fronius.com/cps/rde/xchg/SID-2C19F1B9-A00CA98B/fronius_international/hs.xsl/83_13017_ENG_HTML.htm Fronius IG Plus 35 V-1:OUTPUT DATA
AC nominal output at cos φ=1 3500 W

So it look's like you've already hit your maximum instantaneous output a month before the optimal sun elevation.

My sundance worked, my SoloPV briefly showed >3.6kW when the sun peeked out just after noon. Couldn't get a photo in time before it dropped to 3.33kW though.

larkim · 23 February 2012 at 2:10PM

don0301 wrote: »

It's only a bit of fun, cheer up

Sorry, I was feeling very grumpy this morning!!

Matt

grahamc2003 · 23 February 2012 at 2:17PM

The following comes from Chapter 2 - Safety Information Page 9 of the Sunnyboy sb1700 Installation manual.....

'Overvoltage on the DC side can even cause dangerous explosions of the Sunnyboy input capacitors and explosions of the electrolytes coming from the exploded capacitors'

Not sure why anybody would ROFL at that, or think that anyone can misunderstand the message.

zeupater · 23 February 2012 at 2:31PM

grahamc2003 wrote: »

The following comes from Chapter 2 - Safety Information Page 9 of the Sunnyboy sb1700 Installation manual.....

'Overvoltage on the DC side can even cause dangerous explosions of the Sunnyboy input capacitors and explosions of the electrolytes coming from the exploded capacitors'

Not sure why anybody would ROFL at that, or think that anyone can misunderstand the message.

Hi Graham

This is where people become a little confused between Volts & Watts and why most inverters have the ability to connect multiple parallel strings in order to limit the voltage entering on the DC side ....

HTH
Z

Martyn1981 · 23 February 2012 at 2:49PM

grahamc2003 wrote: »

I'm not sure it's such a good idea underspeccing the inverter. My sb1700 manual states not to exceed 1890W dc or else there a danger of explosions. Max input voltage is 400V - I assume that's an open circuit voltage. If the dc is getting near the limit, the yellow light flashes 4 times at 1 second intervals - if you see that then you have to disconnect things quickly to avoid inverter damage and the possibility of explosions.

'Overvoltage on the DC side canb even cause dangerous explosions of the Sunnyboy input capacitors and explosions of the electrolytes coming from the exploded capacitors'

Holy Exploding Undersized Inverters Batman!

I think you're confusing the voltage that the whole set up is designed to deliver, and the wattage that the inverter can cope with.

Quick question, which is bigger 1,750 or 1,700? You may be surprised to find that you have an undersized inverter.

You may also be surprised to find that SMA are happy for a 2kWp array to run through the SB1700, however it needs to be set up as 2 strings to limit max voltage.

Long time ago I found this handy explanation, of the difference between what an array can generate, and what an inverter will process, if they have been set up correctly.

This concept of "overloading the inverter" crops up a lot. It shouldn't be an issue. A simple example will suffice.

Take your average 13 Amp 230V AC socket. It is rated to supply up to around 3kW. Now plug in a 100W light bulb. Does it blow up? No! the resistance of the light bulb is such that it will only draw a little under half an amp from a 230V supply. The socket may be capable of delivering another 12.5A safely, but the load simply doesn't call for it.

What happens if there is a prolonged fault, and your mains rises to 300V? Well, now it is outside the rating of the bulb, and in a short time, it will die. But that's from Over-voltage, not over current, or over power.

The same argument applies to your Inverter. it is designed to work safely within stated voltage limits, but you can safely hook a 2kW inverter up to a 4kW (capable) solar array, and the inverter wont suddenly blow up! All you've done is restricted the output of the SYSTEM to a half of what the panels could produce.

So, is fitting a slightly oversize array to a slightly undersized inverter just a waste of money? Not necessarily. Even your typical 4kWp system will spend relatively few hours of the day over relatively few months of the year generating more than maybe 80% of its potential peak output (your mileage may vary depending on panel type, age, orientation, weather, etc.). So some might argue that they can save more money by installing a cheaper 3kW inverter, and losing a little bit of peak power! But there are limits to this scenario. A much wider ratio of inverter to panel power capacities would suggest a non-optimal system.

MPPT tracking is all about finding the point on the source's V/I curve to extract the maximum power. But if the inverter isn't calling for the maximum potential power from the source (because it has already reached its design power, for example), then the system is no longer tracking MPPT. The inverter will probably let the source voltage drift a little higher, and simply draw a lower current, up to its designed (power) limit.

OK - so what about the reverse situation, of an undersized array? The potential output of the array will never be artificially restricted by the inverter in this case, but you've probably spent more on the inverter than you could have got away with. But then - a lower loaded inverter is probably going to be a happier and cooler inverter, so may last longer! Yes, some will point out that inverters are less efficient at lower powers, but check out the power-efficiency curves of most inverters these days, and you will find their efficiencies pretty flat from as little as 15% load, upwards.

Here's my bottom line. Inverters are (should be!) pretty bomb-!!!!!!, these days. They will protect themselves and regulate their maximum power output (and so their power draw from the source), with a view to maintaining the electronics at a safe operating current and temperature. Over-volting an inverter, like most pieces of electronics, can still kill it. But check out the max cold volts of your PV strings, and choose an inverter to suit. Don't get TOO hung up on trying to match inverter and panel peak powers 100% - there are many other considerations.

Hope this helps, and prevents any unnecessary panic!

Mart.

Martyn1981 · 23 February 2012 at 2:54PM

larkim wrote: »

Sorry, I was feeling very grumpy this morning!!

Matt

We all feel grumpy when we see Don's unseasonal highs!

I'm probably gonna regret saying this, but hopefully those are peaks, not sustained? Fingers crossed, but hey, I'm not jealous, honest, no I'm not (git)!

Mart.

EricMears · 23 February 2012 at 3:04PM

Find this rather astonishing :-

grahamc2003 wrote: »

If the dc is getting near the limit, the yellow light flashes 4 times at 1 second intervals - if you see that then you have to disconnect things quickly to avoid inverter damage and the possibility of explosions.

Along with (probably) a vast majority of solar panel owners, my inverter is tucked away in the attic in order to be as close as possible to panels (just like another page of the manual suggests). How on earth would I ever know if one of the status lights flashed four times - or even four hundred ?

I would hope that there is some sort of safety device to anticipate & prevent such damage to the inverter !

So now I have a solar PV system how do I make the most of it???

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