Solar Quotes for the North West

QrizB

Spies said:

I got another quote this morning for 3.65kwp (10*365) from the same person
£4500 inc vat £1.23/kwp
Good?

Given the complications of your system, yes I would take that.

Does it include a dual-MPPT inverter (something like this)? Your two roofs will see quite different insolations (and probalby run at different voltages) so you want to make sure the inverter can track each string independently.

Which leads me to think you don't need ten identical panels. You could have 365s on the 4-panel roof where space is tight and 410s or 495s on the six-panel roof where you've got a little bit of room to stretch out?

Spies

QrizB said:

Spies said:

I got another quote this morning for 3.65kwp (10*365) from the same person
£4500 inc vat £1.23/kwp
Good?

Given the complications of your system, yes I would take that.

Does it include a dual-MPPT inverter (something like this)? Your two roofs will see quite different insolations (and probalby run at different voltages) so you want to make sure the inverter can track each string independently.

Which leads me to think you don't need ten identical panels. You could have 365s on the 4-panel roof where space is tight and 410s or 495s on the six-panel roof where you've got a little bit of room to stretch out?

The Jinko Tiger N-Type 395W Black Mono (1855x1029mm) are the largest panels that would fit inside the allowable area on the less complicated roof.

I think the 400w+ panels are slightly larger from what I've found.

QrizB

Ok, so 4x 365w on the awkward roof and 6x 395w on the simpler one is 3830 watts.

Split SSE and WSW you should get some power from dawn to dusk all year round, and a nice long hump during the middle of the day; nothing too peaky.

Sounds like a pretty good solution given your situation!

Spies

Been told I can't mix different types of panels.

Martyn1981

Spies said:

Been told I can't mix different types of panels.

Hiya. Is that the installer saying they won't mix them as part of the deal, or that it's not possible to mix them?
If the later, then that's simply wrong, they will have to use a dual MPPT inverter as the panels are split over two different orientations, so 'they' simply have to match the panels to the requirements of the MPPT and string, there's no need for the two rooves/strings to share common panels, that's the whole reason for dual MPPT inverters, so that two different arrays* can be managed by the single inverter.

*Differences could be the number of panels, amount of Wp, voltage, orientation, pitch, size and type of panels, and of course a  number of these differences, all at the same time.

Edit - Just for clarity, the panels on each string/roof will need to match each other, just not those on the other string/roof.

Spies

He just said that it's not possible to mix panel types, I did find this on Google which seemed to suggest that you cannot mix types even over 2 different strings.

https://powerforum.co.za/topic/5040-mixing-solar-panel-strings/

If that's not accurate then the only other reason might be he needs to buy 10 of one type to get the price needed, but I'd rather he told me that.

His quote consists of just an email at this stage with no specific list of parts, I've had to ask which inverter he planned on using.

What should I expect as a formal quote? 

Martyn1981

Just to confuse you more, you can have for instance 2 strings, but if they go into a single MPPT, then they need to match, or else the more powerful string will operate at the level of the less powerful one, in order to find a common power point to track.

That's why QrizB mentioned a dual MPPT inverter, so that the strings can differ from each other.

[Don't worry about this, but you can on larger systems also have two strings on each of the MPPT's too, in which case the strings on each MPPT would need to match each other, but not have to match the strings on the other MPPT ...... fun in't it?]

QrizB

Here, if these illustrations work they should help. If not, well my PowerPoint skills are basic rather than 1337 ! I've taken some panel voltages and currents from specs for panels similar to yours (not exactly the same so the numbers aren't quite right).

This first example shows how you could do it with two completely independent strings, each feeding its own inverter. Total output is 3600 watts. Because the strings run at quite different voltages you can't connect them directly together (136v and 210v would fight against one another, you'd end up with the panels underperforming at best, or even the smaller string being damaged).

However having two inverters is more expensive; you're having to duplicate quite a lot of components.

In a dual MPPT inverter you have two sets of input electronics but only one set of outputs, so you only duplicate the bits you need. You still have a maximum output of 3600 watts.

Hope this manes sense and apologies if it doesn't!

Spies

The difficulty here is I don't want to tell the installer is wrong at this point. 

Reed_Richards

Maximum Power Point Tracking, for anyone else who was wondering.  You could possibly tell the installer you have a mate who was banging on about a dual MPPT inverter and ask the installer what that means.