Quotes and install questions

Zarch · 3 August 2018 at 7:58PM

Okay, had a think and yes Pinnks, I agree. £700 is not worth it for just 286kWph extra, even with widely optimistic FIT/usage figures. Obviously unless I can negotiate a price on those 320 panels.

So the south-west ish (35 orientation) facing panels (Porch (26 degrees tilt), Main Roof (35 degrees) and Dormer (15 degrees)) come in around 3719kWh on PVGIS

and the east-ish (-29 orientation) facing Extension (29 degrees) around 764kWh PVGIS for the year.

So could a 5000 inverter be a waste of money too and the DNO to go with it?

The Extension has big shading issues from noon/1pm onwards. That install is really to get dawn to lunchtime generation only, then its in full shade.

So come the afternoon the only panels really working will be the SW facing stuff.

There will probably be a very short timeframe where both sets of panels are getting any/decent sun. Maybe a few hours tops in the summer.

So will there be enough power to properly drive a 5kWh inverter? Would a 3.68 be more efficient? I'm a bit lost on the technical reasons why here? :rotfl:

So what is the suggestion? Ask for a quote on the cheaper 300w panels again, but with a 3.68 inverter instead? A quick google suggests about £100 saving retail price 5.0 versus 3.68?

Suppose it depends if there are any other costs associated with the DNO application and connection to consider?

Thanks all. Loving the input. :T

pinnks · 3 August 2018 at 8:48PM

Good questions. Take a look at this https://www.dropbox.com/s/6igylwtwqv3gijk/Comparison.pdf?dl=0. It's a couple days during the recent super blue sky days to show my total production and that of each of my two systems.

Top row is total for each of two days; middle row is my larger WSW-facing system; bottom row is the SSE-facing smaller system.

So, bottom row - 45 degree roof with real shading issues from the chimney from about 13:30 and then from the ridge itself. In the morning you can see how generation ramps up as the sun comes up and the panels are in full sunlight. As I say, come 13:30 catastrophic. Should have gone SE but that boat has sailed!

Now middle row. 40 degrees with no shading to speak of. Gets borrowed light until the sun starts edge round to the west of south. Until then the graph is flat at a couple of hundred watts. Then the panels get sun and POW! Lovely bell curve until the sun goes down and no shading issues once the sun comes round.

So, take that as a guide for your roof areas and you might get some indication of what your production curves might look like.

If you add those theoretical curves together in your head (yeah, I know) then you will probably find your max production is not much more that 3.68kW even on the best days when you are maxing out on each panel.

One of the reasons I bit the bullet and had the second, small, system installed was that I was annoyed that I had no generation to speak of in the mornings. I had considered going large and all the things you are thinking of and because of the looming FiT reduction rushed my decision and gave upon the DNO. I was thinking 23 x 330W panels or 7.6kWp. Ended up with 21 x 250W panels at 5.125kWp. The irony is, doing it as two installs was probably slightly more expensive than taking the most expensive panels of the time and going large from the outset, but I'm no longer bitter and twisted as a result of learning with hindsight:rotfl:

Haha, here's the shading issue with my small system - forgot I posted this a couple of years ago abd just stumbled cross it https://www.dropbox.com/s/2k06xp8bjehyx32/More%20on%20the%20impact%20of%20shading.pdf?dl=0

gefnew · 3 August 2018 at 8:50PM

Hi all
Forget the idea of fits and look to the future of every thing electric.

Martyn1981 · 4 August 2018 at 7:26AM

pinnks wrote: »

One of the reasons I bit the bullet and had the second, small, system installed was that I was annoyed that I had no generation to speak of in the mornings. I had considered going large and all the things you are thinking of and because of the looming FiT reduction rushed my decision and gave upon the DNO. I was thinking 23 x 330W panels or 7.6kWp. Ended up with 21 x 250W panels at 5.125kWp. The irony is, doing it as two installs was probably slightly more expensive than taking the most expensive panels of the time and going large from the outset, but I'm no longer bitter and twisted as a result of learning with hindsight:rotfl:

That might be where my heart over head nagging voice is coming from, as I did exactly the same as you adding a proportionally very expensive small second system in order to get afternoon/evening generation.

The good news here, however, is that both options are good sizes, so whatever the decision regrets should be small to none.

The more I think about it now, perhaps the gain is too small. If the panel jump was say 280Wp to 330Wp (for more money again of course) then that might justify the future proofing, but the £700 here might be better put aside as part of a battery install for the future, where that consumed leccy will make a bigger difference.

pinnks · 4 August 2018 at 9:10AM

Good point about putting money aside for batteries. I assume the inverters are all "battery ready" these days but if not it might be worth ensuring that whichever size and version is bought has that capability. Might there be other preparatory work that could be done now to make a battery essentially "plug and play" whenever that day comes? I am thinking here wiring, space preparation, isolators and the like....

gefnew · 4 August 2018 at 10:42AM

Hi all
Some general info with regards batts and solar.
maybe of interest on the way you can add at a later date.
https://www.solarguide.co.uk/solar-batteries#/
regards

EricMears · 4 August 2018 at 11:33AM

pinnks wrote: »

So, 286kWh expected increase in generation each year, so still about £15 extra FiT and £15 extra own consumption savings equals £30 more return each year, for a spend of £700. I think I know what I would do - haggle or ditch the more expensive one:beer:

A £30 return on £700 is still over 4% in the first year (and no doubt increasing in subsequent years). Whilst that's nowhere near the 13% I'm getting on our system, it's still a lot more than you'd get by leaving it in a savings account.

So if you have a spare £700, I'd vote for the bigger system

Zarch · 4 August 2018 at 11:35AM

Okay, so I had a poke around PV Output for East facing and SW facing systems around my area. I took a look at their best production days and scaled my potential 0.9kWh East panels and 4.2kWh SW panels onto their figures with a bit of maths.

I came up with the following graph.......

https://www.dropbox.com/s/mn2jww9uwrztfb2/Solar%20Guestimate.png?dl=0

So It looks like i'd never really bust the limit of a 3.68kWh inverter as the East and SW panels won't produce at the same time.

Is this a fair assumption and what you were getting at Pinnks?

So the question is, DNO aside. Is it better to drive a 3.68 inverter closer to max for more of the time, than have a 5.00 sat there hardly working for large parts of the day?

What's the best solution there?

pinnks · 4 August 2018 at 11:49AM

That is exactly what I was thinking and would suggest the smaller inverter running near max will do the job. General consensus seems to be to run inverters hard rather than coasting but I don't know whether that is fact or legend-based.

Eric makes a good point re investment return of 4%. The only difference of course between PV and bank savings is you can still spent the money in the bank. Pretty much comes down to personal choice I think - have you done your graph with the larger system to see how soon you get to about 2.5kW production in the mornings as that will be when you can run those leccy guzzlers like washing machine or dishwasher. Maybe that will help you decide?

Zarch · 4 August 2018 at 12:01PM

pinnks wrote: »

That is exactly what I was thinking and would suggest the smaller inverter running near max will do the job. General consensus seems to be to run inverters hard rather than coasting but I don't know whether that is fact or legend-based.

Eric makes a good point re investment return of 4%. The only difference of course between PV and bank savings is you can still spent the money in the bank. Pretty much comes down to personal choice I think - have you done your graph with the larger system to see how soon you get to about 2.5kW production in the mornings as that will be when you can run those leccy guzzlers like washing machine or dishwasher. Maybe that will help you decide?

I'm not sure 17 x 320w versus 17 x300w is going to make much of a dint in getting me to 2.5kWh quicker. Its approx 7% uplift 300 to 320.

So added that on to the graph.

https://www.dropbox.com/s/skslk7y5x3t89vk/Solar%20plus%207%25.png?dl=0

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