Can you get used panels cheaply?
I just bought 20x 250W panels for $40 ea. Went through and tested them all and not a lazy let alone dud one amoungst them. Crunching the numbers, The ROI on the panels alone will be about 6 months on what they save me on power costs. Add in the DIY racking ( which I have the steel for already sitting around) and wiring ( have to buy most of that) and It might be 9 months. The inverters I already have which I picked up from the tip so it's a very sound investment.
Made 15Kwh yesterday with most of them lying flat on the grass in the back yard. Wanted to test them and I figured I may as well have them doing something till I get them on the roof.
15Kwh day x.30C Kwh = $4.50 day. x90 days for the billing period, $405.00
Other panels I have sitting on some scaffolding to put them at the correct tilt are producing 4x their KW rating so If these do the same, which they should because they are newer and better quality panels, that would be 20kwh/ day or $540 quarter saved.
Just ot to keep an eye on the power meter I'm spinning backwards. Don't want the next meter reading to be under what the last one was, they may tend to question that. Another month and the air will be running a fair bit so I'll make credit while I can.
You should be able to look up the solar ratings for your area to get an idea of the return you will get. IE, here it's 4X the Kw rating which is what I am getting here in spring. Summer may be a bit higher and winter lower. If you know the returns your panels should produce and how much extra power you want, you can size quite effectively.
That said, the new way of doing normal installs now because the utilitiys are limiting the amount of power you can install ( IE, limiting their revenue losses) is to oversize the array on the inverter by 33%. The idea of this is that that panels are never 100% efficent so by oversizing, you get longer at full output on the inverter. They don't care if say they are a 5Kw unit and you put 6.5 kw of panels on them and the panels produce 6Kw, the inverter just clips the excess current and runs full output. As I have my inverters well over paneled as well, I find I have made 3Kw before the whole array is even in full unshadowed sunlight at 9am. Just mucking round like this has shown me it's not the max output you want to worry about, it's the " Shoulder", the first 2 hours of the morning and last 2 hours in the evening. The full sun isn't where the gains are, it's the ramp up and ramp down you want to cater for.
I'm thinking of turning 50% of the panels away from perfect orientation and see how that goes. I think they will be fine in the middday sun but possibly may pick up a bit more morning and night. Or they may just average out the same which is what I think but nothing tested, no knowledge gained.
i'd definitely recommend looking for used panels. I'd also suggest don't go below 250W either. Smaller ones may be cheaper to buy but the installation costs make them end up costing more. Here I worked on .20C a watt for what I'd pay. Gives you a comparison between different size panels for the output cost but again, be aware the smaller the panel, the more you'll need and the more framing, wiring etc which is the exy part.
I managed to get below the .20C/watt but other places will be cheaper and others more.
Work out what you want to pay in your area and stick to that.