Help and guidance please on solar energy

zeupater

Love_Solar wrote: »

Question one answer

They all have a 4 kW Solar PV system installed which generates 4000 KWh per year per house as they all face the same direction. The only difference is the family electrical consumption per year. They all pay the same price per kw and that is 11p per kw.

1st family use only 2000 kwh per year
Answer 34% of consumption 680 kwh @ 11 p = £74.80
2nd family use 4000 kwh per year
Answer 30% of consumption 1200 kwh @ 11p = £132.00
3rd family use 6000 kwh per year
Answer 28 % of consumption 1680 kwh @ 11p = £184.80
4th family use 8000 kwh per year
Answer 25 % of consumption 2000 kwh @ 11p = £220.00

What savings per family do you think they will make per year?
answer in red text

......

Hi

Really ??? .... that must take some pretty basic assumptions into account including equality of usage patterns and averaged daily generation, which in turn makes any 'Answer' no more than a nominal estimate and nowhere near definitive ....

Let's have a quick look at the above .... with not knowing the usage patterns for each individual household let's look at using 'extremes' logic ...

<Option 1> .... all usage for each household is base-load and the base-load is a truly constant (24Hrs) and generation is based on an average hourly figure over the year (12Hrs average light), so 4000kWh averages out at 913W (4000/365/12). Lets look at the usage options ...

2000kWh/year = 228W(2000/2/365/12) average load, therefore 685W(913-228) would be exported, which equates to a self consumption of 25%(228/913), alternatively with (4000/(2000/2))>1 then all daytime generation would be provided by pv, equating to 50% of consumption ...

4000kWh/year = 456W, export 457, SC=50%, >1 (All), also 50%of consumption
6000kWh/year = 685W, export 228, SC=75%, >1 (All), also 50%of consumption
8000kWh/year = 913W, export 000, SC=100%, =1 (All), still 50%of consumption

... so, if using averages the above is correct, however it just serves to illustrate why applying mathematical averages doesn't work ....

<Option 2> .... Of course, there's also the opposite end of an 'extremes' test where there's little(<100W) or no base-load during the day and the total demand is made up by electric cooking (~6kW), kettle (~3kW) and dishwasher (~2kW) followed by lighting (~200W) and TV (Plasma~300W) in the evening where no matter how large the array or usage the pv contribution would be extremely diluted by the pattern of consumption ....

As can be seen, what qualifies as an 'Answer' is merely pure guesswork. Our own experience is that coming from a position of already being extremely energy usage aware, installing pv resulted in a step-change on annual electricity import of around 1000kWh/year, which is in line with what many others who started from a similar position have experienced/reported .... I don't attribute the ~1500kWh/year of efficiency and usage improvements made over the years preceding the solar install, or the ~500kWh/year made since to pv simply because it's not related ...

The only way you could achieve any form of technical analysis is to have a reasonably sized sample group provide detailed generation data and a similar group (ideally the same source) provide detailed usage, most probably down to a 5/10minute resolution encompassing at least a couple of years. It would then be possible to model usage against generation with the option to easily analyse the effect of changing the installed capacity or using a different usage pattern .... of course, this would all need to be done for individual systems on individual patterns with only the resultants allowed to be averaged (eg. annual kWh/£) - as soon as the source data is averaged for onward analysis the entire exercise becomes meaningless ....

HTH
Z

Martyn1981

hethmar wrote: »

Head spinning

Don't worry about the side issue with Love Solar, it's an interesting discussion for us, but possibly too much information for you. Apologies for any confusion that may have caused.

With your roof it sounds like you can fit a decent amount of PV, around 3.5kWp without having to go to any complex lengths. So that's a great starting point. If you can squeeze the amount up towards the 4kWp FiT tariff boundary, all the better, but not the end of the world.

Price wise, you want to get as many quotes as you can. Hopefully you'll get under £6k and close to £5k for 4kWp, and possibly get under £5k for 3.5kWp(ish), but it will depend a bit on scaffolding for two rooves.

You don't need to rush too much at the moment. The current FiT rate is safe till 1/10/15, so long as the government doesn't make some shock announcement (keep those fingers crossed). There will most likely be a 3.5% reduction in the FiT in October, but that's not the end of the world, better to get a lower price and save more that way.

How are you doing at the moment? Any problems, questions, concerns? Are you getting more quotes, need suggestions?

It does get easier, and 6 months to a year after install, you'll be able to argue with installers too ...... if you feel the need!

It's your thread, just keep asking questions, no question is stupid, if you don't know something always ask. Only not asking is stupid.

Mart.

Paino7

Hi, have been quoted for 3kw system over 2 roofs (SE, SW) with some shading from chimney stacks. Estimated output 2,300kwh/year. CJ Solar recommended 9-3 split of 250w eternity gallium 833 with enphase microinverters and came to 6.8k. Absolute said put 10 x benq sunforte 330w panels on SE roof only with Goodwe 3600 Single Phase Inverter
and included iboost for 6.7k. I'm in Leicestershire. Any advice greatly appreciated!

tunnel

Can the roof that was going to have 3 panels on take anymore or is that it?
I'd be tempted to go for the split system for maximum return and better all day generation, maybe get 12 x benQ 330W panels with solaredge, one recent poster had this for £6500 which would be a good price still.

Martyn1981

Paino7 wrote: »

Hi, have been quoted for 3kw system over 2 roofs (SE, SW) with some shading from chimney stacks. Estimated output 2,300kwh/year.

Hiya and welcome.

If both rooves can take PV, then I'd definitely use both. A SE + SW system is almost ideal when it comes to a good generation curve through the day.

How many panels could each roof take?

Mart.

Paino7

Thanks that's good to hear. Sizing appears limited by 2 large chimney stacks on the SE and 1 on the SW elevation. Despite these the first guy reckoned a 9-3 split possible, but another company felt overall the shading likely 'significant' and reckoned might need to lower or remove stacks to make it viable at all. Waiting for a quote on removing the SW stack at least as it's not in use. With that out the way could maybe do an 8-5 and avoid most shade.

Other factor was efficiency and longevity of solaredge with optimisers vs microinverters - which cj solar felt would do a much better job with shading(but £8.2k vs £6.5k for 3.96kw - both 12 panels).

To further complicate things a guy I know who's actually in the trade felt 6.5k was a 'worryingly low' quote!!?

Any advice appreciated!

ely_ellis

Paino7 wrote: »

9-3 split of 250w eternity gallium 833 with enphase microinverters and came to 6.8k.

Hi,
Last month I had 16 x 250w 8.33 Eternity panels with Solaredge optimisers/inverter + iBoost for £5650. So your quote maybe a little high. This could be due to additional scafolding for split roof but then again it is only 12 panels.
Note that the Eternity panels are different from the Gallium panels, they are not the same thing and differ in size! Check which panels was offered, Eternity or Gallium?

Paino7

This is direct from the quotation"Our proposed split system of 12 panels of 250w Eternity Gallium 833 Mono-Crystalline Black is coupled with Enphase Micro-inverter technology for each panel to boost your performance at the great value price of £6808 fully inclusive of all installation" but you're right I can't find eternity gallium when I google!!?

The other company are quoting 12xbenq 330w panels with solaredge for 6.5k, which seems reasonable but maybe could save a bit by going for 250s and perhaps less power? We only spend £30 month on elec so maybe don't need 4kw system but depends of FIT returns too I guess....

ely_ellis

I am pretty much a newbie on here but you wouldn't beleive the amount of research and brain aching I have gone through. It put me in good stead as I could 'test' the various companies who came to quote me and if I knew more than them, they wouldn't stand a chance. With that in mind, if a company quotes you 2 different panels as one, then they don't know what they are selling.
Personaly I would go with the 12 benq 330w panels, if they were my only optiions, cheaper and 1kW more! Then again I would still shop around but at least you have a starting point for comparison.
The big boys on here will give you much more learned help I'm sure.

Martyn1981

Paino7 wrote: »

The other company are quoting 12xbenq 330w panels with solaredge for 6.5k, which seems reasonable but maybe could save a bit by going for 250s and perhaps less power? We only spend £30 month on elec so maybe don't need 4kw system but depends of FIT returns too I guess....

I have to agree with Martin (with an I) on all points, that £6.5k isn't bad given that those 330's are pretty expensive. And it's an excellent reference point from which you can shop and consider other options.

I've got Solaredge on my WNW system. One of my panels is jammed right up against the side of the chimney, which is to the south of the panels. They all work well, and I'd definitely look to max out the 4kWp if you are considering such a system as even the shaded panels do well ...... though not 'as well'.

Martyn (with a y)