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

don0301

sly_dog_jonah wrote: »

I'm just pointing out that your inverter max power output is less than what the panels can output and you've hit the inverter's peak output a month before the 'optimal' solar radiation point for the panels.

Therefore for the next month until optimum sun elevation (and the following one after optimum) your panels will be capable of outputting more power than the inverter can output (in the best weather). Therefore for 4months of the year at least, your inverter will be constraining the peak output under optimum conditions. I just don't fully understand why anyone would deliberately cap the peak power output for the sake of a few £ saved on the inverter? Each to their own though.

Our inverter can output up to 3680W and the panels 3700W. Allowing a % or two for DC cable losses, our inverter should never constrain the potential output of the panels.

What was the cost saving of going for a cheaper inverter with a lower power output than the panel array can generate?

this has been explained already......

Martyn1981 wrote: »

.

sly_dog_jonah

don0301 wrote: »

this has been explained already......

Martyn was referring to peak output when the panels get hot, ie summer time.

Unless Essex has just moved sub-tropical I doubt the panels will reach a high temperature in Feb/March/April. I know some inverters can measure the panel temperature, maybe some systems on pvoutput would demonstrate the relationship between panel temperature and time of year?

don0301

sly_dog_jonah wrote: »

Martin was referring to peak output when the panels get hot, ie summer time.

Unless Essex has just moved sub-tropical I doubt the panels will reach a high temperature in Feb/March/April. I know some inverters can measure the panel temperature, maybe some systems on pvoutput would demonstrate the relationship between panel temperature and time of year?

try reading it again...

sly_dog_jonah

don0301 wrote: »

try reading it again...

I suggest you try reading it again.

Martyn refers to 'long good days' and panel performance at high temperature. This implies summertime performance in the UK.

Your array, by virtue of it's high pitch, has optimum performance in spring around March 27 you say (plus equivalent period in autumn) when ambient temperature and heat from the sun will be significantly less than in summertime.

Regarding switch on/off thresholds, how much would they vary if your inverter was 10% higher capacity?

Martyn1981

sly_dog_jonah wrote: »

I suggest you try reading it again.

Martyn refers to 'long good days' and panel performance at high temperature. This implies summertime performance in the UK.

Your array, by virtue of it's high pitch, has optimum performance in spring around March 27 you say (plus equivalent period in autumn) when ambient temperature and heat from the sun will be significantly less than in summertime.

Regarding switch on/off thresholds, how much would they vary if your inverter was 10% higher capacity?

Hiya Sly.

Didn't mean to start an argument, remember I'm in the dark as much as you. Just regurgitating information I've picked up here and there. I just have a strange memory, and these things stick.

Hope I never came across as saying undersizing is best, just explaining why the industry (as I've read comments) explains the potential benefits.

By panel temps, ambient will be important, but what I really meant (understood) was that when the panel is receiving maximum or near maximum solar radiation for processing, it will also get pretty damned hot, pretty damned fast from said sunlight. I'm working on the basis that panels can't hold max for very long, so the kWp of a system will not be sustained for more than a minute or so. Hopefully, someone with longer PV experience and a 'regular' inverter, can post what their maximum sustained output was. Was it more than 90%?

Really dredging the memory banks here, but remember reading one example I saw posted on another forum where someone (an installer I think) posted the results from some modelling software on a particular 4kWp install and various SMA inverters. I can't remember the exact numbers, I know they were all in the 3,700 or 3,800 range, but the percentages stuck. Here goes:

SB4000 100% (baseline)
SB3600 100.5%
SB3800 101%

So the 3800 loses some peak, but makes up for it with higher efficiency. The 3600 would be slightly more efficient but is losing more peak.

Obviously that example was for a specific install and specific panels. Also forgive my vagueness, but this is from memory, and at least 6 months ago (weird brain or what!).

So across a year the difference is significant enough to note, but in my opinion, not important enough to worry about. Personally, in that example all 3 inverters look perfectly reasonable, but given the choice, you may opt for a SB3800.

In short (too late!) for undersizing, it's not just about saving money on the inverter, it's also about maximising total average annual generation.

Any help?

Mart.

Edit: Short of 2 identical systems on neighbouring roofs, doubt anyone would be able to find 1% or 2% in the variables and roundings. So why worry!

Martyn1981

edwink wrote: »

Hello Mart

Just to update you regarding our installation. To cut a very long story short I have spoken with our installers. They are sending an electrician to change the inverter. They said I should have a Sunny Boy 1200 for the 6 panels on the main roof of the house and 2 stacker 500 inverters on the lower extension roof as there is shading on these panels. Just wondered what your opinion is on that set up before they get here in 2 days or so to change it all.

Look forward to hearing from you.

ED

Hiya Ed. Obviously I hope your system is fine, but kinda hope now it is actually wrong after I’ve scared you and caused so much trouble, if only to justify my intervention!

Been doing some more modelling for you! Well, that is to say, I had another go at Sunny Design, and the 6 panels into a SB1200 looks perfectly fine to me. However, as Zeup and Albyota said, the package doesn’t reference the panels you have, so I just tried it with a few different makes of 240Watt panels.

I assume that is ok (all panel makes and models will have their own voltages) as a guesstimate, but remember my chimp limp bangings on the keyboard are no substitute for knowledge and experience. Perhaps Z or Alb can comment. On the set up, not my chimp like characteristics!

I also tried the SB1700, but the package didn’t seem to want to comment. I took that as a bad sign (doubt it was a good one). I think the minimum voltage of the 6 panels I was substituting couldn’t quite reach the minimum needed for that inverter.

Heavily caveating my response, but I think the SB1200 looks good.

Next, the 4 panels. Didn’t want to say too much before, but I was having trouble finding any set up that liked those 4. 5 are ok, but 4 just a little low. Didn’t want to worry you.

Other than knowing about the idea of ‘stacking’ multiple small GTI (grid tie inverters), I have to put my hands up and say, ‘I don’t know!’

My brain says two 500Watt inverters and 4 240Watt panels sound like very similar totals, but I have absolutely no idea how good or bad this is. If I can find out more, I will of course let you know asap. Can anyone else out there help Ed, and educate me?

On the bright side, your installers do sound like they are happy to help and work on optimising the system, that can’t be a bad thing. Everyone makes mistakes, it’s what they do (or don’t do) to rectify the problem that identifies the keepers.

Hope I’m helping.

Edit: 6.10pm, found out a bit more about 'Steca' inverters, plus bits and bobs. PM sent. M.

Mart

electricgreenmachine

First I apologize if this has been covered already. I have read many pages of the very helpful posts but could not find this discussed.

I have read a lot in these posts about using the power you generate during the day as much as possible. eg use the washing machine during the day not at night. So that you use your generated electric and don't end up paying a lot at night by using the suppliers electric at 10 to 13p per unit.

This all sounded very sensible to me until we had our 3.9kw system installed and turned on this week....

What I noticed was that the original electricity meter that measures what we use from the supplier runs backwards when we generate more than we use!

So surely it does not matter (admittedly from a purely financial point of view) whether I use my washing machine etc when I am actually producing electricity or not. Because the meter reading will be exactly the same either way and therefore what I pay the supplier for my electric will be purely the electric that I did not produce. The meter will have deducted everything I don't use as we go along.

Have I missed something or are there different meters around? I can imagine a situation where a different type of meter might not run backwards and then my argument fails.

Are there two types of meter?
Do the people that have meters that will run backwards need to worry about using the power during the day?
- if not perhaps we should let them all know!

I hesitate to now hit the send button as I am sure you will all laugh hysterically at such a silly idea, but here goes ....

wuthton

electricgreenmachine wrote: »

First I apologize if this has been covered already. I have read many pages of the very helpful posts but could not find this discussed.

I have read a lot in these posts about using the power you generate during the day as much as possible. eg use the washing machine during the day not at night. So that you use your generated electric and don't end up paying a lot at night by using the suppliers electric at 10 to 13p per unit.

This all sounded very sensible to me until we had our 3.9kw system installed and turned on this week....

What I noticed was that the original electricity meter that measures what we use from the supplier runs backwards when we generate more than we use!

So surely it does not matter (admittedly from a purely financial point of view) whether I use my washing machine etc when I am actually producing electricity or not. Because the meter reading will be exactly the same either way and therefore what I pay the supplier for my electric will be purely the electric that I did not produce. The meter will have deducted everything I don't use as we go along.

Have I missed something or are there different meters around? I can imagine a situation where a different type of meter might not run backwards and then my argument fails.

Are there two types of meter?
Do the people that have meters that will run backwards need to worry about using the power during the day?
- if not perhaps we should let them all know!

I hesitate to now hit the send button as I am sure you will all laugh hysterically at such a silly idea, but here goes ....

Unfortunately you need to inform your electric supplier that your meter is running backwards, they will then fit a new one that doesn't.

If you get caught with your meter spinning backwards they will estimate your usage.

electricgreenmachine

wuthton wrote: »

Unfortunately you need to inform your electric supplier that your meter is running backwards, they will then fit a new one that doesn't.

If you get caught with your meter spinning backwards they will estimate your usage.

Good grief!
Many thanks for that. I had no idea. If I had not been reading these posts I would never have thought there was anything wrong.
I am amazed that the installers did not mention it.

Although I still don't understand why they need to estimate anything as it still goes the right way when we are using more than we produce. So it still shows exactly what we have used from the supplier.
I am still a bit confused. Surely this gives them a better idea than having to assume I export 50% of what I produce.

Cardew

electricgreenmachine wrote: »

Good grief!
Many thanks for that. I had no idea. If I had not been reading these posts I would never have thought there was anything wrong.
I am amazed that the installers did not mention it.

Although I still don't understand why they need to estimate anything as it still goes the right way when we are using more than we produce. So it still shows exactly what we have used from the supplier.
I am still a bit confused. Surely this gives them a better idea than having to assume I export 50% of what I produce.

It doesn't show 'what you have used from the supplier'

Let us take a hypothetical case where you only used small amounts of electricity in your house, say, 500kWh pa from the mains + what you used from the PV panels

Your panels generate, say, 3,500kWh pa.

This means that your meter will run back 3,000kWh each year and you would be refunded £300+ from whoever supplies your electricity.

You should be paying the electricity company for 500kWh of electricity.

If, as used to happen, someone used a device to 'wind back' their electricity meter, they would be convicted of stealing electricity if they were caught.

Well, in effect, that is exactly what you have got - a device to 'wind back' the meter. Albeit with no itent to steal.