Deleted

ABrass

Without a cost for the additional sizes of the array the question is meaningless. It also assumes a set power use and an infinite battery.

Hexane

70sbudgie said:

My inverter switches itself off if the panels output less than 20W, so I'm not really aware of it "idling". Is this not a common feature for PV inverters?

Yes mine does this too. And yes it is a common feature. Possibly those of us whose inverters share this common feature should just be skipping this thread as not relevant to them.

QrizB

If you DIY, you can buy a kilowatt of solar panel for under £450 (I paid about £250 last year, but that was for used panels). If that extra kilowatt saves you £50 a year, it will pay for itself in nine years.

ABrass

QrizB said:

If you DIY, you can buy a kilowatt of solar panel for under £450 (I paid about £250 last year, but that was for used panels). If that extra kilowatt saves you £50 a year, it will pay for itself in nine years.

I'm really tempted by another 4kW or so, this time solar edged or optimised  to deal with shading on that aspect. I'm very curious about the difficulty to add another system in.

I've run the numbers and if I can get it for less than £1 a Watt it'll be worthwhile. Which at the moment means DIY.

Do you have any links to any guides?

Reed_Richards

What would you be paying if you had no solar panels?

What is the maximum solar power the inverter inside your "generator" can handle?  Is there a point at which you have to add another generator in order to add more solar panels?

How much does the generator cost?

How much does 1 kWp of solar panels cost?

I am thinking that if your generator is "expensive" but your solar panels are "cheap" then it could be economic to add more solar panels even though the returns diminish.   

Solarchaser

Ok I understand your point, but basically i still pretty much disagree.
Or more accurately I disagree for me.

If your calculations work for you, grand, that's really all that matters right?

To try and find a middle ground I'd say this, as a very low electricity user, it's going to be a struggle for you to spend money to save on electricity,  and so for your tiny consumption,  investment on improvements would have to be small as you can only ever achieve a small return.
I'm hoping that's not controversial. 

Now me, as a user of around 5x as much energy as you, any extra solar I can get for a decent price is worth it.
I paid 2k for 22x300w panels in 2019

I already had 4kw of solar at that point and was buying 5800kwh/ year.
I added on an electric car which consumed another 1000kwh/ year
A year later I was buying 3600/ year so essentially saving 3000kwh/year
At your 33p/kwh that would have saved me £990/ year, and so nearly 4 years later it was definitely worth the 2k for those extra panels

You could argue about electricity pricing and these are rough figures and all that, bit my point is more generally that it's horses for courses, my higher usage makes good use of higher solar, your lower usage doesn't.
My 4kw system makes about 50kwh in December,  yeah its !!!!!!, makes about 200 in October and 150 November,  my other system does similar due to bigger array but worse orientation,  and so I have double the bill reduction in those 3 months,  each of those kwh my house will use, and eo I have to buy less.... you would perhaps not be able to use, because you are a low user.

So my rambling here is basically to say you will have a diminishing return because you can't use it, as you are a well below average user.
Average Joe would benefit from the extra in most months of the year.

ABrass

Your spreadsheet is probably the same as the one everyone else uses already. Except with the wrong units and ignoring SEG.

Reed_Richards

Deleted_User said:

So you add an extra KW. That allows you to produce enough energy for 8 months of the year. In my case this gave me over £100 of savings - I was no longer needing to buy energy in September and October. 

Yes, I get the point you are trying to make.  My point is that if it costs you say £1000 to add that extra kW of solar panels and it saves you £100 per year then you'll get your money back after 10 years and that's not at all bad.  But if you also have to buy a new generator to be able to add that extra 1 kW and the new generator costs say £3000 then the total cost of that extra 1 kW is £4000 and you only get your money back after 40 years (if your generator lasts that long).  Either way it's the same return of £100 per year but this has to be considered in the light of the cost of achieving it.  An extra saving of £10 per year might be worth it if it only cost you £100.    

Solarchaser

Yeah I understand what you are saying, I'm saying I disagree, loads of extra solar means it's lost to the grid in summer, agreed, but summer is also when you use the least amount of solar, when you really need it, is when you consume most, and so more solar in winter means more consumable solar.
My daily consumption in summer, probably 6-10kwh, and in winter more like 50kwh (though that's including water heating for hot water and heating)

Of course there are summer specific things you can use that extra solar for, like a kids paddling pool that you fill with hot water every other day.
Horses, for courses

ABrass

Getting £300 savings out of a 1kW system is a bit ambitious. It assumes virtually 100% self consumption. With a token system like 1kW you'll use a fair bit but that's really high.