Is it possible/practical to build a system to grow?

[ianganderton]

So the forum sees quite a lot of posts from folks wanting to build a system bit by bit as to suit either their growing need or as they have the finances

But

I’ve seen lots of advice around how it makes a significant positive difference if resources like solar panels or battery cells are matched and this only seems possible if they are purchased at the same time because they degrade.

What design strategies, tips and tricks for components like batteries and panels would you suggest for building a growing system or do you think the disadvantages significantly outweigh the advantages?

 

[Hedges]

I have 17 year old panels and recent ones. For a series string, generally should be same model to match current exactly. Parallel strings, I mix completely different brands but all strings are equivalent to 24, nominally 12V (some 12, 24V, some 8, 36V). Their IV curves probably differ a bit, and I haven't determined what percentage reduction that might represent. Fairly little, I think. Voc is within a few percent.

Batteries obviously have to perform very similarly if they are to share current/voltage. A system which managed them separately would be needed to mix them. I've seem some inverters which take up to three separate batteries.

Some difference between on and off grid. On grid (or AC coupled off-grid), you can add inverters with their own PV panels, and they all work on the same AC line. Similarly DC coupling can be added in modules the size of one SCC. To just add panels, back to the "same Voc" idea.

If you buy something cheap/used, you can dispose or repurpose it later. For instance a small inverter for a few $hundred might get used in your car/truck later if you buy a low frequency 5 kW to 10 kW unit for home.

I originally planned to have my Sunny Boy SWR2500U work with the Sunny Island battery inverter some day. But, they don't have the right parameters or respond properly to signals. They cost me $0.80/watt back then, but I've picked up newer ones down to $0.08/watt.
Batteries I went as small as I could get away with, figuring they wear out just from age.

The other advice I've always heard regarding batteries is, you will kill your first set. So don't spend too much on them.

 

[svetz]

Microinverters solve all panel issues, AC batteries solve all mismatched battery aging problems.
Of course, they bring other issues too (e.g., Incrementally Adding AC Batteries).

 

[toms]

I think for an off grid house it makes sense to run complete systems to expand.

I have one main system, a system for my bore pump and airconditioning, and a system for my workshop.

I could have expanded the original system, but would have needed to parallel inverters and charge controllers in any case.