Solar Quotes for the North West

Spies

Reed_Richards said:

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.    

I'm not sure I want to pursue this quote if he isn't being 100% truthful.

Reed_Richards

Spies said:

I'm not sure I want to pursue this quote if he isn't being 100% truthful.

Fair enough but I imagine only a small fraction of solar installations would potentially benefit from a dual MPPT inverter so installing one may be a bit outside his comfort zone.

Spies

Reed_Richards said:

Spies said:

I'm not sure I want to pursue this quote if he isn't being 100% truthful.

Fair enough but I imagine only a small fraction of solar installations would potentially benefit from a dual MPPT inverter so installing one may be a bit outside his comfort zone.

He has spec'd a dual string inverter, isn't that dual MPTT by design?

Martyn1981

Spies said:

Reed_Richards said:

Spies said:

I'm not sure I want to pursue this quote if he isn't being 100% truthful.

Fair enough but I imagine only a small fraction of solar installations would potentially benefit from a dual MPPT inverter so installing one may be a bit outside his comfort zone.

He has spec'd a dual string inverter, isn't that dual MPTT by design?

Nope. As you add more panels to a string the voltage rises (panel voltage x no. of panels), so for larger installs to stay within the voltage max of the inverter, they'll have more strings, so for instance, 16 panels on one string will have double the voltage (half the amperage) of two strings of 8 panels. So it's entirely common to have a single MPPT inverter with 2 strings .....

.... BUT ..... those two strings have to match otherwise the string generating less power at any given point in time will drag down the other string. So you need to match panels, no. of panels, orientation, pitch.

If the strings don't match, or if you expect to get more shading on one string, then they need their own MPPT. Nothing unusual about dual MPPT inverters, and these can themselves have multiple strings, so perhaps two MPPT's with one string each, or one having two strings, or both having two strings, depending on the inverter chosen.

So ....... if you are having panels on two different orientation, then each string has to have its own MPPT, and to be honest, I'd be utterly shocked if this isn't the case. Have you been given the make and model of the inverter, as it's dead easy to look at the spec sheet for it (famous last words)?

Spies

I think he is being deliberately vague, I will have to press him for a full breakdown of what I'm actually getting.

It does look like its a single MPTT though, probably doing it that way to keep cost down.

Martyn1981

Spies said:

I think he is being deliberately vague, I will have to press him for a full breakdown of what I'm actually getting.

It does look like its a single MPTT though, probably doing it that way to keep cost down.

But please don't worry, and I hope I haven't caused you any undue confusion or concern. There's a good chance that at this stage quotes will be a tad vague as the installer won't want to 'waste' too much time checking availability of specific kit as you might not proceed. I'm sure you'll get a more detailed breakdown if you move forward.

Again, sorry if this seems overcomplicated, it's not really, it's just that we all pick up bits and bobs of information over the years, and in your case, it's best just to warn you about the need to make sure the inverter is suitable as you have some extra factors to bear in mind, such as the two orientations, and the fact that 4 panels is quite a small number, so the inverter will have to have a relatively low voltage range, and MPPT min voltage, to make sure it works best, for you.

These inverters exist, and we can check it all with you as you proceed, so don't get too worried ...... lots of virtual hands to hold on here, as we've all been through it.

Spies

I can't find a 'single MPTT inverter' that supports different string lengths so I'm still very confused by it all.

Wouldn't it be really inefficient if the strings weren't balanced?

Martyn1981

Spies said:

I can't find a 'single MPTT inverter' that supports different string lengths so I'm still very confused by it all.

Wouldn't it be really inefficient if the strings weren't balanced?

Yep, very inefficient, so for a single MPPT inverter that allows more than one string, the strings need to match. But just to recap, I'd still strongly suspect that the dual string inverter the installer will choose, will be a dual MPPT model. Just worth checking, that's all.

Purely as an example, here's a datasheet for some Solis Inverters which have dual MPPT and a low start up voltage, and low MPPT min voltage.

[But you wouldn't want to use these Solis inverters, even the 4kW dual string model.]





Silly story - It's many years ago now, but a poster on here said that they seemed to be getting about 5% less generation than they expected / compared to other systems nearby and asked for advice. At first we explained that that difference is small enough to possibly be down to just different set ups, but then I noticed that they had 17 panels, and I checked the specs on the inverter they had listed in their outsig, and it said it was a single MPPT, with two strings. Obviously, 17 can't be subdivided by two (or any number other than 1 and itself), so I asked if there were two strings and if they were 8 and 9 panels, and there were. So the 9 panel string was effectively acting as 8 panels, so that the MPPT could find a common point of generation for the two strings. If I recall correctly, the installer wasn't happy, but agreed to change the inverter to a dual MPPT model after the poster insisted.

Spies

Got quoted by E.ON tonight, 3.3kw for £5800, another company was around the same price for 3.6kw.

The one that quoted £4500 for 3.6kw are ignoring my emails to provide me with a list of components, so I'm stuck at square one.

Are there any large national installers I should try? 

JKenH

Spies said:

Got quoted by E.ON tonight, 3.3kw for £5800, another company was around the same price for 3.6kw.

The one that quoted £4500 for 3.6kw are ignoring my emails to provide me with a list of components, so I'm stuck at square one.

Are there any large national installers I should try? 

I was after extending my solar array and adding a battery and got a couple of quotes without a problem. When I enquired (by email) if we could modify the proposal to better meet my requirements, neither installer could be bothered to reply. My experience generally is that telephone contact elicits a better response than email which can be quite time consuming for suppliers to deal with.