Solar Panel Guide Discussion

oldskoo1

Actually just spotted that the top part of panels are indeed shaded at 8:20am. Its actually quite hard to spot but you can just see the shadow across the top 3 panels.

tunnel

As the install is ongoing oldskool would it be too much to drop the panels further down the roof or did you specifically ask for them to be placed there?
If the roof is nigh on true south that should eliminate any chance of shading

maravesi

Many thanks Mart and tunnel for your replies.

We are not just thinking about getting a good return but also want to be partially independent from the grid. However, we don't want to waste our money either so your views are very useful as it's easy to get bogged down in the numbers and loose sight of the best option...

I tried to put a photo, but apparently as a new user I'm not allowed to post links (i'm rubbish with techy things- i'll try to do it in a separate post). The front roof is 22 degrees off South. (presumably then the roof on the side is 22 deg off East!)

maravesi

Not managing the photo thing. Let's try this(with added spaces) http:// postimg.org/ image/ ek9nrsbib/

Btw, if it matters, we are very low energy users - about 1100kWh per year. And we have a smart meter.

tunnel

Hi Maravesi
Is it right to assume that 22 deg off south is to the west? hence your 22 deg off east is ESE?
If that's the case then using both rooves would certainly help bring down your already low usage. You would have a nice start up generation and with the SSW good generation into the evening


You'll see from both mine and Marts signatures that you don't necessarily need perfect south orientations so nothing to worry about there.


Post your rough location and you may get a few recommendations for local installers that will happily chat to you about utilising both rooves, not just installers that only install on near perfect rooves at highly inflated prices.


Just checked out your pic, looks like you're going to need a solaredge system or micro inverters to help with shade management from the chimney and the stenchpipe.

Martyn1981

oldskoo1 wrote: »

So my curiosity is, due to the lower light levels, is the entire array unshaded required to produce that 1kW of power at 7am? Or can a part shaded array still produce that 1kW, because it is capable of 4kW.

Hiya. I'll take a stab at this, whilst hoping (waiting) for a better answer.

First the good news, shading doesn't stop a panel working, but it reduces it's output. The bad news is that, that panel, can then act as a brake on the rest of the string which is trying to find a common power point to run at. Obviously, the only common point will be the lowest point. Bypass diodes can help with this.

By splitting systems into strings, you can lump all the common shading (morning, evening, chimney etc) onto the same string. Also for any sizeable system, like a 16 panel 4kWp one, multiple strings are needed anyway to work within the voltage limit of the inverter. So 2 strings means half the voltage (twice the amperage).

Could one of the strings be producing the power, yes. Or it may be producing the majority of the power, whilst the shaded string contributes some.

For maximum shading, consider my systems. In the morning the WNW is completely shaded. In the evening the ESE is completely shaded, but they still generate, from light reflected down from the sky, but it's a lot less than direct sunlight. Eg my 3.58 ESE may generate 400W when no direct sun, but this will drop off as the sky gets more clear. A perfect, and I mean perfect (6 times a year?) blue sky may mean not enough reflection to keep the inverter generating - the lovely sun from the west shining over the roof won't find a nice bit of white sky to bounce off, and hit the ESE roof.

In relatively bad weather, more grey sky than white sky, my systems may generate proportionally to size, irrespective of where the sun is in the sky (hiding in the sky behind the grey clouds).

Does that make any sense?

Your chimneys will cause some shading, but it'll be so little at the lowest generation times, that you'll probably not even notice it. In the winter the sun rises in the SE and sets in the SW, so there won't be any shading from the chimneys.

Mart.

maravesi

hi tunnel

thanks for the advice. yes, i think solaredge might be a good idea having read up a bit. Unfortunately it's 22deg to east, so ENE side roof would that mean it's not worthwhile using the side? I did ask the guy who came around and he said given we use very little there is no point...but a bigger system is cheaper by the unit than a smaller one so i think should be a better investment...

We are in Bristol, BS10. Would love to hear of some recommended installers and best-value-for-money systems. I've got so muddled up in all the different types/brands/outputs/sizes...:eek:

Btw, I've just been out to see if the tree in front casts any shade on the roof. It was 12.30pm and the shade only reaches the street in front of the house so should be fine.

Martyn1981

tunnel wrote: »

Hi Maravesi
Is it right to assume that 22 deg off south is to the west? hence your 22 deg off east is ESE?
If that's the case then using both rooves would certainly help bring down your already low usage. You would have a nice start up generation and with the SSW good generation into the evening

Just checked out your pic, looks like you're going to need a solaredge system or micro inverters to help with shade management from the chimney and the stenchpipe.

@ maravesi ...... what T says.

Putting panels on both the SSW and ESE rooves would work well. Though calculating panel fittings on a hipped roof is a right pain. Is that the right 22d or is it the other way?

Cost wise, if you can fit 4kWp on the two rooves, then it shouldn't cost much more than a single roof install. The scaffolders will charge more, but not twice as much.

But, as T says, you might want to consider a SolarEdge system (or micro-inverters) to deal with chimney shading. Perhaps you can move that soil pipe, but I think they have to be 900mm above nearest window ...... not sure.

Another advantage of SolarEdge is that you could run three rooves through it, something that ordinary inverters can't do. I mention this, as it might be more cost effective to use normal panels, which cost less, but fit less on the two sunny rooves, but top up using the NNE(?) roof. That might sound odd, but adding more panels doesn't cost that much more, and may balance out the lower generation from a 'poorer' roof.

If you want to consider more rooves, have a play with PVGIS, there's a walkthrough in section 5 of the PV FAQs. Just put in your location, leave system size at 1kWp and try out the three orientations, just to get comparable performance figures. If I've just baffled you, then confirm roof orientations, roof pitch too, and nearest city, and I'll post some numbers for you.

BTW fantastic low consumption, very impressed.

Mart.

maravesi

Hi Mart

Thanks! Roofs are the other way around - SSE and ENE (if abbreviations are wrong - the front is 22deg to the east so side is 22 deg to north).

I'll have a look at the links you've sent many thanks! Did you fit your own? I'm just thinking you are based in Cardiff -perhaps if you used a specific company they might be able to do Bristol too. Any recommendations?

tunnel

maravesi wrote: »

thanks for the advice. yes, i think solaredge might be a good idea having read up a bit. Unfortunately it's 22deg to east, so ENE side roof would that mean it's not worthwhile using the side? I did ask the guy who came around and he said given we use very little there is no point...but a bigger system is cheaper by the unit than a smaller one so i think should be a better investment...

Don't panic as all is not lost, there are panels out there like benQ 330W's, maybe price up for 7/8 on the SSE roof with the other 4/5 on the ENE...again with either solaredge or micros. That way you 'll be able to have a near 4kWp system. Going that way you'll keep your best generation to the better roof.
Aim for a price between £6k(very tight) to £7k(easily doable), you are paying a premium for higher wattage panels but at least you get to use the space you have to the best effect.