Choosing correct voltage inverter (grid-tied)

[jridley]

This has certainly been covered before, but I wasn't able to find it (poor searching skills probably).  I'm a newbie but have a decent electronics background.

If there's a good FAQ, feel free to just point me to it.

I'm going to be picking up a few things and putting in a very small experimental grid-tied solar installation just to figure out what I'm doing, and maybe next year put in a few kilowatts.

A friend and I are going to be picking up some panels (splitting shipping costs).  The ones we're looking at are 37v open circuit, 29 volts Vmp.

The inverters we're looking at are rated either 14-28 or 28-52 volts.

With the Vmp at 29 volts, I'm unsure which range of inverter to get.  I'm concerned that a 28-52 volt inverter might not get enough voltage to do anything on partially overcast days, but OTOH a 14-28 volt inverter might have more than it can handle with these panels.

I also wonder whether inverters are more efficient near the top end of their voltage range (IE 50 volts instead of 30 on a 28-52 volt inverter) which would argue towards putting panels in series.  If so, could a 28-52 volt inverter deal with two of these 29v Vmp panels in series?  Probably not, I'm guessing since that's way over voltage.

[joestue]

If the inverters are designed properly they would be most efficient in the center of the voltage range.
however, the efficiency curve is primarily load dependent, and if those grid tie inverters don't provide an efficiency curve in the manual then i wouldn't buy them.

got a link for them?

[jridley]

I'm looking at either a 300 or 1200 watt Power Jack inverter, depending on whether I decide to just buy one big enough for my initial test or enough for later on.

[removed]

I actually have one of the 300 watt ones that I bought along with some bare cells, before realizing that in order to build a 180 watt panel properly just the parts would cost me more than buying a completed Astronergy 230 watt panel, so those cells are just going to sit in the basement unless I find a free source for tempered glass.  Since I'm going to be buying a panel that's far more than the 18 volts I was planning on, I don't know if I can use it or not.

The panel I'm looking at is one of the Astronergy ones here

[removed]

(1) Please do NOT post links to commercial sites until you've established yourself here and (2) in most places there are regulations about connecting microgeneration to the grid, eg type-approved and installed by someone with appropriate certificates, and cheap stuff off ebay is rarely going to cut the mustard

[Mary B]

Those Power Jack inverters are NOT UL approved and may burn your house down. Stay well away from them.

[DamonHD]

Thanks, I missed out the UL magic word.  Rough equivalent here in the UK is G83/1-1 and CE.

Rgds

Damon

[Bruce S]

When I go looking for "approved" stuff , I look for the UL,CE, & TUV. that pretty much covers the planet.
Damon, thanks for catching those links, work got in the way again  .
Bruce S

[jridley]

OK, so no help here then, I guess.  I'll ask the seller.

[DamonHD]

As was said before, you'd need to see the published curves by the manufacturer, but unless certified (a) they are likely unreliable and (b) any connection you do may be unsafe and illegal.

The seller is likely to say what you want to hear; we'd like you to stay safe.

Rgds

Damon

[ghurd]

Cheap GTI are a waste of money and effort.  Plus dangerous.

Ignoring the illegal and dangerous aspects of it, very very few will last long enough to pay for themselves.
There are a ton of examples on U-tube.

Here is a story about cheap GTI,
http://ludens.cl/Electron/chinverter/chinverter.html

G-