How much can I practically/legally DIY, and other newb questions

[AE-NMidlands]

31kg! I wondered whether they were aimed at the solar farm market, where you might well be using mechanical handling aids for installation. Also for that use the bigger panels would reduce installation time.
A

[openspaceman]

31kg! I wondered whether they were aimed at the solar farm market, where you might well be using mechanical handling aids for installation. Also for that use the bigger panels would reduce installation time.
A

I fitted these as I worked out the various permutations of sizes and three best fitted my available space, or so I thought, I hadn't allowed for the overhang of an eave of the gable end. This meant I have had to raise the frame's angle more than the plan to have them nearly horizontal. The upshot is they shade part of one pf my original panels till the early afternoon.

They were heavy but two of us hauled them up two storeys via a sloping "ladder" and manipulated them onto the framework without much drama.

[AE-NMidlands]

@AE-NMidlands, if two of your aspects can have the same number of panels, you can parallel up the two strings into the same MPPT input. So it may be possible to do three aspects on a twin MPPT inverter.

I think that to get the most on the roof(s) they will be different sizes, but I'll try to do some sums to see how long the extra shoulder-season generation might take to balance the cost of the extra inverter.

If looking at hybrid inverters then presumably you are looking at battery storage, in which case why not just one hybrid inverter and one array directly charging the battery via a charge controller? - unless Nowty's suggestion would be appropriate.

I don't really understand this, one array with a battery, the others not? or do you mean link all 3 roofs to work as one array?
I had imagined each of the E, S and W arrays working separately to get the most possible out of them as early and late in the year as possible. I see a reference to dual and even multi-MPPT inverters, claiming to be able to cope with 3 or more arrays.
Re the output options, I see that Bimble show https://www.bimblesolar.com/ongrid/hybr ... X1-FIT-5.0 as having a 5kW output... also a Solis one, so at that output I guess they don't need paralelling up - I don't imagine getting up to using 120 kWhr in a day!

[marshman]

Re the output options, I see that Bimble show https://www.bimblesolar.com/ongrid/hybr ... X1-FIT-5.0 as having a 5kW output... also a Solis one, so at that output I guess they don't need paralelling up - I don't imagine getting up to using 120 kWhr in a day!

Be very careful with inverter specs. Note the use of the term "max" 6kW. A Solis RHI 6kW Hybrid with a "max" 5kW charge / discharge from the batteries. It will only maintain the "full" 5kW charge into the batteries for 15 minutes, after that it drops to 3.6kW. This has been confirmed as the case by Solis.

Before purchase satisfy yourself of the max and also the continuous ratings and see if that matches you load profile.

[sharpener]

@AE-NMidlands, if two of your aspects can have the same number of panels, you can parallel up the two strings into the same MPPT input. So it may be possible to do three aspects on a twin MPPT inverter.

I think that to get the most on the roof(s) they will be different sizes, but I'll try to do some sums to see how long the extra shoulder-season generation might take to balance the cost of the extra inverter.

If looking at hybrid inverters then presumably you are looking at battery storage, in which case why not just one hybrid inverter and one array directly charging the battery via a charge controller? - unless Nowty's suggestion would be appropriate.

I don't really understand this, one array with a battery, the others not? or do you mean link all 3 roofs to work as one array?
I had imagined each of the E, S and W arrays working separately to get the most possible out of them as early and late in the year as possible. I see a reference to dual and even multi-MPPT inverters, claiming to be able to cope with 3 or more arrays.
Re the output options, I see that Bimble show https://www.bimblesolar.com/ongrid/hybr ... X1-FIT-5.0 as having a 5kW output... also a Solis one, so at that output I guess they don't need paralelling up - I don't imagine getting up to using 120 kWhr in a day!

I would have thought you could connect the E and W arrays to the one MPPT using blocking diodes. The higher voltage will then win so you need not have the same # of panels in the two arrays provided each is within the MPPT spec. If they are facing opposite directions you won't lose any appreciable output by doing this, when the sun is in the S they will both be at glancing incidence anyway.

Agree with @marshman, 5kW nom is a good size. In fact my DNO will only allow inverting up to 3.7 kW and that is still enough for all everyday purposes.

A 5kW continuous load is easy enough to emulate using an electric cooker, I have tried this, a 32 A cooker point will in fact supply over 7kW and my inverter will allow a total of 12kW with pass-through.

[marshman]

__

[nowty]

I would have thought you could connect the E and W arrays to the one MPPT using blocking diodes. The higher voltage will then win so you need not have the same # of panels in the two arrays provided each is within the MPPT spec. If they are facing opposite directions you won't lose any appreciable output by doing this, when the sun is in the S they will both be at glancing incidence anyway.

Never tried that (yet), sounds plausible but you would need to have an inverter which does a global peak scan (shade management function) like my SMA Sunny Boys.

A more elegant way is to use different types of panel so you get a similar working voltage with a different numbers of panels.
https://camelot-forum.co.uk/phpBB3/view ... tore#p9562

[sharpener]

I would have thought you could connect the E and W arrays to the one MPPT using blocking diodes. The higher voltage will then win so you need not have the same # of panels in the two arrays provided each is within the MPPT spec. If they are facing opposite directions you won't lose any appreciable output by doing this, when the sun is in the S they will both be at glancing incidence anyway.

Never tried that (yet), sounds plausible but you would need to have an inverter which does a global peak scan (shade management function) like my SMA Sunny Boys.

A more elegant way is to use different types of panel so you get a similar working voltage with a different numbers of panels.
https://camelot-forum.co.uk/phpBB3/view ... tore#p9562

I don't think so, with the diodes the MPPT will only ever see the higher voltage array and will not know the other one is there, so you will not get multiple MPPs in the output characteristic (VI) curve.

Didn't think it was a good idea to parallel arrays on different aspects without diodes even if the same nom Vmpp. The array with less light will pull down the output voltage of the one with more. The diodes prevent this from happening.

[nowty]

I would have thought you could connect the E and W arrays to the one MPPT using blocking diodes. The higher voltage will then win so you need not have the same # of panels in the two arrays provided each is within the MPPT spec. If they are facing opposite directions you won't lose any appreciable output by doing this, when the sun is in the S they will both be at glancing incidence anyway.

Never tried that (yet), sounds plausible but you would need to have an inverter which does a global peak scan (shade management function) like my SMA Sunny Boys.

A more elegant way is to use different types of panel so you get a similar working voltage with a different numbers of panels.
https://camelot-forum.co.uk/phpBB3/view ... tore#p9562

I don't think so, with the diodes the MPPT will only ever see the higher voltage array and will not know the other one is there, so you will not get multiple MPPs in the output characteristic (VI) curve.

Didn't think it was a good idea to parallel arrays on different aspects without diodes even if the same nom Vmpp. The array with less light will pull down the output voltage of the one with more. The diodes prevent this from happening.

So, your first paragraph is totally correct, but what's the point of the lower voltage string then ?, it will sit there and do nothing, even in full sun as its voltage will still be lower than the shaded string. A shaded string still gives a similar voltage, just with less current. Thats why you need a global peak MPPT so it switches to the lower voltage peak as the sun moves around.

Your second paragraph is a common misconception, we had a massive argument about this many years ago on the old forum. An identical array with less light does not pull down the voltage, in fact a shaded string will still contribute a little to the one in sunlight. Yes it will still work with blocking diodes, but it just adds another point of failure for no benefit.

I've done many experiments with this over the years with different types of inverters.

[sharpener]

So, your first paragraph is totally correct, but what's the point of the lower voltage string then ?, it will sit there and do nothing, even in full sun as its voltage will still be lower than the shaded string.

The point is this: I would have thought you could connect the E and W arrays to the one MPPT. The arrays face in opposite directions so to first order only one is generating at a time.

Your second paragraph is a common misconception, we had a massive argument about this many years ago on the old forum. An identical array with less light does not pull down the voltage, in fact a shaded string will still contribute a little to the one in sunlight. Yes it will still work with blocking diodes, but it just adds another point of failure for no benefit.

I've done many experiments with this over the years with different types of inverters.

Thinking about this again a photodiode is reverse biased in normal operation. So if you just connect them in parallel the array in the sun will generate slightly more voltage so will bias the other one slightly more in the reverse direction and it will contribute less current than it would on its own, or none at all. Maybe you don't need the diodes after all.

If you can draw me the combined load line on the output curves of two typical panels connected in parallel, one in 5x the irradiance of the other it might help my understanding as to why there are multiple possible maxima. I will look at it myself when I have more free time.

In any case I thought any decent MPPT does a global search periodically, Victon certainly claim to. Of course there is a trade off because during the search the panels are by definition not at the optimum operating point.