augment solar (E & W), parts advice please.

QrizB

Apologies if any of what follows seems like teaching granny to suck eggs.

Bimble have a nice comparison page https://www.bimblesolar.com/panelcompare which gives you the dimensions, outputs and cost per watt for their panels. It's then your choice:

• If you have essentially unlimited space, buy the number of watts you need at the lowest price per watt.
• If you are restricted in space, try various arrangements of panels to fit.
• If runnign strings (see below) make sure all the panels on the string match.
  

Generally it's cheaper to run panels in strings rather than have one inverter per panel, but one per panel may provide more output (eg. if shading is an issue). If you have two aspects (East and West) you will probably need two separate strings so each array can work at its own peak efficiency, rather than having the performace of the "good" panels pulled down by the "poor" ones.

One single string is simple; one inverter. With two strings you could fit two inverters but it may be cheaper to buy a single inverter with two separate MPPT inputs. Beware of inverters with two inputs but only a single MPPT; these will essentially combine your two strings into a single one.

Make sure your inverter(s) are happy with the current and voltage of the string you build. Short strings often have low voltages which may be too low to work with some inverters. Long strings have the opposite problem. Higher output panels may have higher currents, which can also be a problem. (For example, 250 watt panels are typically 30V at 8A. A string of four panels will be 120V at 8A, but some inverters won't turn on with voltages below 150V.)

Your original query was about 1 or 2 panels, 300-600 watts, in each of two arrays. I know nothing of your current setup but the following might work:

• East: 2x 300w Canadian Solar panels - 65V, 9A
  
• West: 2x 300w Canadian Solar panels - 65V, 9A
• Inverter: 2x Growatt 750TL-X - MPPT range 50-500V, 13A
• Total cost £760 (£360 for panels, £400 for inverters), 63.3p per watt, plus wiring, switchgear, roof rails etc.
  

If you're going to all this effort, however, you might want to consider larger and/or more panels while keeping the same inverters. You could go for four 380-watt JA Solar panels for £540 (adding 320 watts for £180) or make each array three panels, 900w (adding 600 watts for £180). The first barely changes the cost per watt (now 61.8p) but the second brings it down a bit (52.2p).

Please note these are not full system costs; the balance of the system will bump those numbers up.

Heedtheadvice

Thanks both. Both useful posts.

Will get design head into gear and see what I come up with.

Probably only room for 2 panels E & W each without significant shading (at least on one of the panels which would stop generation with just a 2 panel string!)

 I guess second hand, if cheap enough, might be the way otherwise probably not worth it. Will get out ruler and calculator!!

Thanks

QrizB

Heedtheadvice said:

I guess second hand, if cheap enough, might be the way otherwise probably not worth it. Will get out ruler and calculator!

The best bargains second-hand are where someone's removed an array from their own roof for whatever reason. I've seen several 4kWp arrays sell on eBay for under £1000 complete with inverter, roof rails etc.

Buying from a reseller is less subject to the vagaries of auction sites and lets you have them delivered. 220-250 watt penels are around £60-£70 each (plus delivery) and you can pick up an inverter for £100 but double-check the specs to make sure it will work with your array.

Heedtheadvice

Thank you. A useful heads up!

Exiled_Tyke

QrizB said:

Apologies if any of what follows seems like teaching granny to suck eggs.

Bimble have a nice comparison page https://www.bimblesolar.com/panelcompare which gives you the dimensions, outputs and cost per watt for their panels. It's then your choice:

• If you have essentially unlimited space, buy the number of watts you need at the lowest price per watt.
• If you are restricted in space, try various arrangements of panels to fit.
• If runnign strings (see below) make sure all the panels on the string match.
  

Generally it's cheaper to run panels in strings rather than have one inverter per panel, but one per panel may provide more output (eg. if shading is an issue). If you have two aspects (East and West) you will probably need two separate strings so each array can work at its own peak efficiency, rather than having the performace of the "good" panels pulled down by the "poor" ones.

One single string is simple; one inverter. With two strings you could fit two inverters but it may be cheaper to buy a single inverter with two separate MPPT inputs. Beware of inverters with two inputs but only a single MPPT; these will essentially combine your two strings into a single one.

Make sure your inverter(s) are happy with the current and voltage of the string you build. Short strings often have low voltages which may be too low to work with some inverters. Long strings have the opposite problem. Higher output panels may have higher currents, which can also be a problem. (For example, 250 watt panels are typically 30V at 8A. A string of four panels will be 120V at 8A, but some inverters won't turn on with voltages below 150V.)

Your original query was about 1 or 2 panels, 300-600 watts, in each of two arrays. I know nothing of your current setup but the following might work:

• East: 2x 300w Canadian Solar panels - 65V, 9A
  
• West: 2x 300w Canadian Solar panels - 65V, 9A
• Inverter: 2x Growatt 750TL-X - MPPT range 50-500V, 13A
• Total cost £760 (£360 for panels, £400 for inverters), 63.3p per watt, plus wiring, switchgear, roof rails etc.
  

If you're going to all this effort, however, you might want to consider larger and/or more panels while keeping the same inverters. You could go for four 380-watt JA Solar panels for £540 (adding 320 watts for £180) or make each array three panels, 900w (adding 600 watts for £180). The first barely changes the cost per watt (now 61.8p) but the second brings it down a bit (52.2p).

Please note these are not full system costs; the balance of the system will bump those numbers up.

My small 'extension' is two  300w panels with one 500w micro inverter. (Could have gone with a 600w but not really necessary and there were supply issues). So it doesn't necessarily have to be one micro inverter per panel.