Solar advice please (quote and options)

Rahulpdev

About to invest in solar and this thread is interesting and helpful! Looking at 10 panels on front and 14 on back. Also toying with 5 on garage as it gets great pm light. How best to think about inverter sizing? Thought bigger is better but comments here suggest smaller is more efficient which I don't follow why tbh. No shading so no need for optimisers so not sure what the SolarEdge price premium would deliver for me? (Point may be moot as not likely it's in budget.)

Screwdriva

Rahulpdev said:

Looking at 10 panels on front and 14 on back. Also toying with 5 on garage as it gets great pm light. How best to think about inverter sizing? Thought bigger is better but comments here suggest smaller is more efficient which I don't follow why tbh. No shading so no need for optimisers so not sure what the SolarEdge price premium would deliver for me? (Point may be moot as not likely it's in budget.)

When you say front/ back, is this East West or North/ South? Also, what is the direction of your garage? 

Alnat1

Rahulpdev said:

How best to think about inverter sizing? Thought bigger is better but comments here suggest smaller is more efficient which I don't follow why tbh. 

I'm not technically minded and this is how it was explained to me (making up numbers a bit to simplify)

The inverter will use some power itself, so a 3.6kw might use 36w all the time, a 5kw inverter 50w, an 8kw 80w etc. It doesn't seem much but on a poor day in winter there might only be 100w coming off the roof so you don't want an oversized inverter using most of it.

Most installers will recommend an inverter a bit smaller than the total size of your array. This means you'll keep more of your generation on poor days but your system might clip slightly in the middle of the day in high summer.

I would probably have been better with a 5kW inverter, as all my panels face same direction but I didn't know enough to question this before my installation. My guy probably couldn't be arsed with a G99 application and went for the easy G98 option.

Rahulpdev

Screwdriva said:

Rahulpdev said:

Looking at 10 panels on front and 14 on back. Also toying with 5 on garage as it gets great pm light. How best to think about inverter sizing? Thought bigger is better but comments here suggest smaller is more efficient which I don't follow why tbh. No shading so no need for optimisers so not sure what the SolarEdge price premium would deliver for me? (Point may be moot as not likely it's in budget.)

When you say front/ back, is this East West or North/ South? Also, what is the direction of your garage? 

Hi, front roof is SE (35°), rear is NW, garage is SW, perpendicular to house roof.

Screwdriva

Rahulpdev said:

Hi, front roof is SE (35°), rear is NW, garage is SW, perpendicular to house roof.

Definitely saturate the SE roof (did you mean 135 °?) with panels. I would skip the NW roof and cover the garage as well. This would effectively be a SE/SW combination which should perform very well. 

SolarEdge optimizers are an excellent tool to protect against panel degradation, shading, fire risk and lack of panel level information. 

Waywardmike

I'm not a huge advocate for paying extra for optimisers if they're not required, the thought of all that extra equipment on the roof that can go wrong coupled with the access difficulty doesn't seem worth it for me.

That being said, in your scenario I'd say they are worth it due to the multi aspect (3+).  Unless the intention is to have multiple inverters?  Maybe things have changed but triple mppt inverters were few and far between.

Martyn1981

Rahulpdev said:

Screwdriva said:

Rahulpdev said:

Looking at 10 panels on front and 14 on back. Also toying with 5 on garage as it gets great pm light. How best to think about inverter sizing? Thought bigger is better but comments here suggest smaller is more efficient which I don't follow why tbh. No shading so no need for optimisers so not sure what the SolarEdge price premium would deliver for me? (Point may be moot as not likely it's in budget.)

When you say front/ back, is this East West or North/ South? Also, what is the direction of your garage? 

Hi, front roof is SE (35°), rear is NW, garage is SW, perpendicular to house roof.

Hi, like Screwdriva, I'm also interested what 35d means. Not being petty, but I have a WNW install, countering an ESE roof install. It's absolutely fine, but of course less generation across the year, and pitifull in the winter when the sun rises in the SE and sets in the SW.

So, if you mean 35d off east, then that's OK(ish), mine is 25d off East (115d from N), so the WNW isn't 'too' bad at 295d. But if you mean the SE is 35d from south, then the NW roof at 325d is getting poorer and poorer.

Doesn't mean you shouldn't do it, as the cost of the additional work will be less* (per Wp install) than the SE & SW install, since they are already on site, scaffolding will increase, but shouldn't double, and the same inverter can be shared as the roofs won't peak at the same time.

So well worth getting prices with and without the NW to compare, then you (or us) can look to PVGIS and see how the value works out, or doesn't.

*Purely as an example, if a south roof install of 4kWp was £5k, and the installer's will put 4kWp on the north roof for a total of £7.5k, then the north roof cost is ~50% of the south. If generation is ~50% (of south), then it may be worth considering. Not as simple as this, but just trying to explain the rough idea.

Spies

I believe he is referring to roof pitch at 35d

Alnat1

Spies said:

I believe he is referring to roof pitch at 35d

That's what I had assumed too.

Rahulpdev

I can see now that my previous comment was very unclear, apologies all!

Based on PVGIS calcs (and how they represent azimuth) the SE roof is -35°, the NW roof is 145° and 61% output of SE, and the SW garage roof is 55° and 94% output of SE. 

First quote has came in from Boxt for JA Solar panels and Sunsynk inverter. £8k for SE roof plus garage, £11k i.e. 37.5% premium to add the NW roof.

(Yes, roof pitch is 35°)