1 inverter or 3?

[mpooley]

Hi I think they are index linked ---  http://www.decc.gov.uk/en/content/cms/news/pn10_010/pn10_010.aspx 
and tax free income too.

The return on a 3.96kwp is 9.46% and on 6.1kwp is 9.5%
the income would be approximately (working on SAP figures) £1,907.00 p/a + Money saved off Bill £330.00 so total of £2,326.00
My oil bill is £1350.00 p/a  unless i'm going daft i think that it pays my oil bill and my electrity bill for "free" and leaves me an "income" of approx £500.00

I know that if you want to do a proper comparison you have to compare it with the "loss" of the income from the bank but to be honest as I see it , as long as it is index linked I have a relative immunity from Oil price rises . That is very comforting to me in my retirement LOL.

Mike

[Patrick123]

Sorry to spoil the party, but if you're using 5000 kwh/year and £1350/year on oil, shouldn't you first be considering some energy-efficient lamps, isolation etc... ?

[Kombi]

I think the point of having 3 inverters is to maximise each string performance individually. Since you have 2 roofs and a "sticky bit" I assume each array will perform differently due to shading/orientation. So if you have one 6kW and one of your string is shaded then the whole system will be affected. With 3 inverters only one array is affected. You say that the installer has spent quite a bit of time designing the system so surely he is able to comment/justify his recommendation. As PV system, and the FIT, are valid for 25 years, I think it is important to seek the best performance possible. One solution might be more expensive upfront than others, but if it gives better performance over 25 years, then aren't you better off in the long term?

[RichardKB]

The other thing to think about is if the 6KW inverter fails you have zero output while it is being replaced/repaired, but with 3 seperate inverters then the chance of all 3 failing at the same time is rather remote.

Rich

[mpooley]

Sorry to spoil the party, but if you're using 5000 kwh/year and £1350/year on oil, shouldn't you first be considering some energy-efficient lamps, isolation etc... ?

mmh yeah never thought of that

I havn't got one old style bulb in the house - have very good insulation  and have done everything possible to cut down on my electricity use - so much so i'm beginning to think my meter is wrong.
But we have no gas here out in the sticks which means everything except the heating is electric and it is a blimmin big house! so what else do you want me to do?

[mpooley]

I think the point of having 3 inverters is to maximise each string performance individually. Since you have 2 roofs and a "sticky bit" I assume each array will perform differently due to shading/orientation. So if you have one 6kW and one of your string is shaded then the whole system will be affected. With 3 inverters only one array is affected. You say that the installer has spent quite a bit of time designing the system so surely he is able to comment/justify his recommendation. As PV system, and the FIT, are valid for 25 years, I think it is important to seek the best performance possible. One solution might be more expensive upfront than others, but if it gives better performance over 25 years, then aren't you better off in the long term?

Yes indeed i have no problem with that - just thought i'd ask on here before making a decision.

[mpooley]

The other thing to think about is if the 6KW inverter fails you have zero output while it is being replaced/repaired, but with 3 seperate inverters then the chance of all 3 failing at the same time is rather remote.

Rich

thats a good point .

Thanks

Mike

[Justme]

I must have missed the bit about linking to inflation as I was so happy to be getting 41p lol.

With your quoted 13kwh per day consumption & a 6kw array you will prob be exporting 80-90% of what you produce unless you can shift lots of use to sunny hours. Your projected savings of £330 look like nearly 50% used on site. I cant see that happening.

[mpooley]

I must have missed the bit about linking to inflation as I was so happy to be getting 41p lol.

With your quoted 13kwh per day consumption & a 6kw array you will prob be exporting 80-90% of what you produce unless you can shift lots of use to sunny hours. Your projected savings of £330 look like nearly 50% used on site. I cant see that happening.

It's true that is an approximation.
lets see I spend approx 10p per unit so £500.00 p/a say I export 75% annually - i'm assuming i'll be using more as a percentage of my own power in winter.
so say 3750kwh exported @ 3p - which means I import 3750 @ 10p so I pay 1250 x 10p and 3750 @ 7p which = £125.00 + £262.50 = £387.50  therefore  i will save £112.50

It's not a big enough difference to the calculation to be significant and it assumes i only generate 5000kwh and that i cant devise ways of using the leccy during the day.
I suppose I could use an immersion heater in summer instead of the oil boiler. Also I think a lot of our leccy is used by the cooker which will be during the day in summer plus possible electric car lol

I'm sure it will be ok 

Thanks

Mike

[Kombi]

Slightly off topic but you could consider going down the same route as me: rather than export any excess it will be used to charge a small battery bank which will power the lights and computer at night. Not necessarely the cheapest solution by far but at least I should be using virtually all what I produce and when we have a power cut (unfortunately more often than desired) I won't be in the dark, nor without heating.

[mpooley]

Slightly off topic but you could consider going down the same route as me: rather than export any excess it will be used to charge a small battery bank which will power the lights and computer at night. Not necessarely the cheapest solution by far but at least I should be using virtually all what I produce and when we have a power cut (unfortunately more often than desired) I won't be in the dark, nor without heating.

What I wanted originally was a battary bank so that I could charge it up  with my excess while still being grid tied but was informed that It would cost an extra £10,000.00
and i would need to replace it every few years?

Mike

[Justme]

£10k sounds a bit much, but yes it will be costly as you have such a large demand. Dont forget the big inverters too.

Our first bank (used forklift cells) cost about £150 & is still going strong providing 3kwh per day year round. We are increasing it & the replacement cost about £400 (but is more than twice the size) , but again is used forklift cells in a bank.

Even with a large enough bat bank you still wont be able to store all the power you could make & will still be importing LOTS in winter.