Minimum wattage for inverter?

[rickeolis]

I'd like to get into PV cheaper than buying a whole $20,000 system. (On-grid style) Can I start with a Xantrex or Outback inverter rated at 3 KW, and start out with enough panels to provide 1 KW, then add panels throughout the years up to 3 KW?

[AbyssUnderground]

Yes that will work but you will need to use batteries, not just solar. So you could infact use the full 3KW.

[TAH]

Why do you need batteries for a grid connect?

[altosack]

I would have to ask "what is your eventual plan for the system ?"

If you want to eventually have batteries and be autonomous from the grid, you will go with a different type of grid-tie inverter (Trace/Xantrex SW series or Outback GT). In this case, your inverter will be either 24V or 48V (I would recommend 48V), and you will need only (2) or (4) 12V nominal panels to get started (actually, you won't need any panels to get started, but you did say you wanted get into PV . This could be as little as 300W @ 48V (75W panels are the minimum size to get a good $/W)

If you have no intention of getting batteries, it's then better to go with a batteryless inverter such as Xantrex GT or SMA SunnyBoy (the market has exploded with these over the last 2 years; there are many others). In that case, the inverter has a minimum voltage rating that will tell you how many you need (I think it's usually about 150-200 V, but I don't work with batteryless systems and I'm not sure - download the manual from their website to find out). You can then add identical PV modules in series up to the maximum for the inverter, usually about 600V, IIRC. Make sure you get 24V nominal panels; the minimum number would be about 5 for 150V, or about 600W to start (120W is the smallest 24V panel with a good $/W).

My preference would be to go with a battery system; a 48V string of Trojan T105s is only about $500, much less than the extra panels you need to get started with a batteryless system, and when the grid goes down, you don't (at least for a little while). And (that's not all, behind door #3...) you can connect a nice homebuilt axial flux wind generator to dem dere batteries if you're so inclined.

Dave

[AbyssUnderground]

Sorry I missed that bit.

[rickeolis]

   Yeah, well, I want to remain on-grid simply for the fact that at any time I have sunlight, I'll be offsetting my grid costs. With the battery method, I would be using wattage to pump into the batteries, not the net-metering, which would not pay off as well.

   Just last night, I was reading in-depth on Xantrex's website and found a spec on the GT-3000 inverter stating that you must have at least 170 volts (or so???) to be able to turn the unit on. This is regardless of wattage apparently, so that answered my questions.

   So it looks like what AltoSack said in his post, that about 5 panels of at least 75 watts would be needed at first to make it work.

   I plan to eventually have enough panels to run over 3 KW, but it might take a few years of buying panels here and there to get to that point.

-Rick-