Solar for Dummies.

jkforde

anyone know what the general efficiency difference is between June 21 full sun compared to Dec 21 full sun - aren't PV cells significantly more efficient when they're cooler?

graememk

https://www.boards.ie/discussion/comment/120021785#Comment_120021785

It's on the spec sheet how much it changes per degree.

Sun is low in the sky, more atmosphere to get through

redmagic68

https://www.boards.ie/discussion/comment/120022845#Comment_120022845

Which spec sheet?

graememk

https://www.boards.ie/discussion/comment/120023563#Comment_120023563

What's your panels?

I mean data sheet

LONGi-Data-Sheet-LR4-60-HPH-350-380M.pdf

Eg this is the longi one

Stc is 1000w/m2 25c cell temperature

For every degree above it, it loses 0.35%

Under it, it gains

unkel

That's interesting. So your 380W panel maxes out at 380W at 25C, it will gain or lose 0.00035*380 per 1C difference or 0.035*380W = 13.3W per 10C difference

So performance at temps:

-20C -> 440W

-10C -> 427W

0C -> 413W

+5C -> 407W

+10C -> 400W

+15C -> 394W

+20C -> 387W

+25C -> 380W

+30C -> 373W

+50C -> 346W

One of the reasons Ireland is so good for PV

graememk

https://www.boards.ie/discussion/comment/120023683#Comment_120023683

And that's why may and June is so good in Ireland, the months are sunny, but still not that hot and the days are long, vs July and August

unkel

Yes August is the warmest month, but not even in the top 3 for PV production in Ireland.

redmagic68

https://www.boards.ie/discussion/comment/120023641#Comment_120023641

https://www.boards.ie/discussion/comment/120022845#Comment_120022845

Apologies that’s temperature based. I thought you were talking about the relative strength of the sun in June compared to now say. Though there might have been a way to work out expected yields based on todays yield if there was a data sheet giving a numerical comparison for solar irradiance.

graememk

https://www.boards.ie/discussion/comment/120023960#Comment_120023960

That's a big ol "it's complicated"

Mainly because the sun is in a different position in the sky in regards to your panels.. regarding time of day.

For instance my panels are fairly flat, so I'd get a 10x output difference between now and June.

redmagic68

https://www.boards.ie/discussion/comment/120023991#Comment_120023991

I know that why I got all excited when I heard about a chart 😂. Though someone had come up with one that took into account the elevation of the sun, location and inclination of the panels by month. Still if your system is getting 10x of a flat install worst case scenario I should get at least 5 of a 38 degree pitch.

your flat panels are suffering now but will rock with a high sun I gain now with. Pitch but lose in the better months was my understanding of it.

graememk

https://www.boards.ie/discussion/comment/120024000#Comment_120024000

Yep on a perfect day I only get about 3-4kwh from 8kwp (split NE/SW)

I think the highest I got was 55kwh

redmagic68

https://www.boards.ie/discussion/comment/120024013#Comment_120024013

How many days annually do you reckon you get 20 kWh

DC999

https://www.boards.ie/discussion/comment/120024000#Comment_120024000

For me the best roof, is a full roof 😊. Best to use all the roof / space / garden you have (budget permitting of course). I used a flat extension roof to get 5 panels. Main roof fits 11 more. For me filling all the roof space was the goal.

bullit_dodger

https://www.boards.ie/discussion/comment/120024130#Comment_120024130

The question of comparing installations doesn't make much sense, on something like the number of days as it's too dependent on the slope and orienatation of the panels as much as it is on the amount of panels. Two identical (size wise) systems with different orientations will have different answers. However, on a general level......here's what my system did for 2022 (barring a few days at the start of the year along with the 10 days to go until the end of 2022)

Yellow dotted line is a 10pt moving average. As you can see I average 2-3Kwhr now in december, but come May-Aug I'm averaging 10x times that with 20Kwhr. Basically for everyone who recently has an installation put in March 1st is when it starts to kick into gear. Don't worry about Nov-Feb. Think of it as a "bonus" anything you get.

Gloomtastic!

Nicked this from the Interesting Maps thread in AH. Think the units are hours.

Sunshine in Ireland, county by county…..

slave1

That Offaly blue is weird

redmagic68

https://www.boards.ie/discussion/comment/120025321#Comment_120025321

Are you suggesting Offaly is weird 😂. Does seem strange though the sun just drops off a cliff

redmagic68

https://www.boards.ie/discussion/comment/120024857#Comment_120024857

Cool. I know what you mean by comparing systems was just trying to get a feel for how many days I could potentially get off grid. Yesterday we had 2 day time units to pay for but didn’t cook dinner, but still seemed great. Now I need a bigger battery screw The payback…..🫣😂

redmagic68

https://www.boards.ie/discussion/comment/120024823#Comment_120024823

Have 8.4kwp up there already. To go bigger we’d need a bigger inverter and one to take three strings as I’d could potentially get 4kwp to the south on a garage. It’s likely to be a waste however as I’d need 20kwh more in batteries to benefit from it, diy not a runner, or an ev parked at home during the day which isn’t possible while I’m working as I commute.

Unless things change and Fit becomes something along the lines of you get to use the units you feed in (grid battery) when you need them or the tax changes and fit price improves I’ve pretty much maxed out what would be sensible too do I think.

graememk

https://www.boards.ie/discussion/comment/120025403#Comment_120025403

or a second inverter ;)

This is my graph of the year.

Basically From March to Sept. I'm usually above 20kwh.

The 64kwh spike is incorrect on the 17th july, something went wrong with my logging. It was actually 37 kwh.

cobham

As someone previously described, this is a 'sharp learning curve' and some months after installation, I must admit to still being overwhelmed by details and complexity. It would seem that our CT clamps (what is a CT clamp?) are wrongly installed so various readings contradict eg we are deemed to be exporting from solar to grid in middle of night etc. There was some problem getting the MyEngergi app installed/running. There is a central green leaf (0%) on main page with a house symbol, the Eddi and the Grid feeding off same. So no information display for the battery? and nothing for the solar panels? how do we get these set up or should we wait for CT situation to be sorted. Our installer had set our battery to charge up at 6 am even though we do not have a nightrate and it makes no sense to feed the battery from the grid at full cost. Is it an easy fix to go thru the settings on the inverter to fix this?

Here is hoping that the installer will reappear to sort these and other matters!! Meanwhile I am very grateful for all the information/advice on here so thank you all.

bullit_dodger

I'll answer your question about "what is a CT clamp".

It's basically a ferrite (iron) core "clamp" which encompasses a cable. Looks something like this. Doesn't actually break the cable, just wraps around it. The cable passes through the hole.

So when electricity is passed through the wire on the right in the picture above, a magnetic field is created. The CT clamp measures the "strength" of the magnetic field and from that, it can deduce what the current is flowing through the cable without actually having to break into the cable to measure it.

Without getting too technical, the direction of the flow is determined by the way the magnetic field is setup, and if you put the clamp on backwards (think of the 2nd picture above if you reversed the clamp so the notch was on the other side) then an "export" would be seen as an "import", or vice versa.

Anyone (with the requisite skills and experience) can reverse the clamp, however, if the supplier has agreed to come out, then let them do it. It's also a question of which specific wire that the clamp should be on - and that isn't always "obvious" to the lay person.

MOD: Edited to provide clarification that skills and experience are required.

unkel

@bullit_dodger - "Anyone (and I mean anyone) can reverse the clamp without electrical knowledge"

Not when the clamp is in the consumer unit. Sure anyone can do it but you are not allowed to do it and you should not do it. Thought I'd point that out, in case someone unqualified is going to do something that could kill them!

cobham

Thanks for that explanation and timely warning Unkel. I have had a look at fusebox and cannot see any such clamps so must be behind somewhere. I am happy to rewire a plug but have a very healthy respect for power of electricity. I am trying to convince installer that there is a problem. He did come back once and sorted out a misbehaving Eddi but I have no confidence that he has any electrical expertise. A qualified leccie did a days work but another chap came later to add an extra fuse as advised by electrician and system has not been right since.

bullit_dodger

https://www.boards.ie/discussion/comment/120047089#Comment_120047089

If the consumer unit is involved, your right unkel, but then I'd argue that it's not really a "clamp" in the strict sense of the word for me.

unkel

I think it's the most common location to put a clamp on the incomer? Either there or in the ESB box outside - you can change the clamp in there no problem of course 😀

bullit_dodger

https://www.boards.ie/discussion/comment/120047871#Comment_120047871

Mine are over in the outside box and I would have assumed that with the lack of space in most consumer units that's where the main clamps would be on the in/out cables for the house, but maybe I'm wrong?

taytobreath

reverse the cores to reverse the direction. Only qualified personnel should be doing this

unkel

https://www.boards.ie/discussion/comment/120048146#Comment_120048146

Maybe you don't have a zappi? I'd have thought anyone with a zappi or other smart EV charge point will have both the CT cable and the mains AC cable coming out of the charge point go straight into the house and into the consumer unit, cleanest possible install

bullit_dodger

https://www.boards.ie/discussion/comment/120048216#Comment_120048216

Don't have a Zappi, although I do have a Harvi located in the external box. I've also used the same place for a OWL in the past, along with more recently another monitoring CT clamp, although the brand escapes me at the moment (?) Most consumer boards I've ever seen in the republic are pretty tight for space - so it's a bit of speculation/assumptions on my side that installers would use the external box, though naturally nothing wrong with the consumer board if that's a runner - although we're probably going away from the question in hand.

Basically you (cobham) would be the best judge of your knowledge. "Have-a-go enthusiasm" is a good thing in general, but with leccie, as unkel correctly calls out, it can get you hurt.....or killed. Reversing a CT clamp for me is like 5 seconds and I don't even need a screwdriver..... because it is in the meter box, not the consumer unit.

MOD: Provide additional clarifications