I'm looking for the Solar Guppy Members thought on what they concider the importaint feature for a Grid Tie Inverter

Importance features of a grid tie inverter
I have had a grid tied system since May, 1998.
I have a lot of “most importantâ€￾ features.

1) I have an Omnion 2400 grid tied inverter. (324v DC strings)
They went out of business a few years ago so owner serviceability is crucial for me.
There are a number of labeled test points but I have had to do some “by guess and by gollyâ€￾ fixing as I NEVER got a schematic and a $40 diode popped twice.
This kinda negates the warrenty choice unless the company is around to honor it
(same for my panels but that isn’t the question)

2)Cost is obviously a factor but reliability and wave shape should be compared in this and should go with efficiency. IE. $ per real watts out. A lower cost lower efficiency in my eyes is worse that a higher efficiency higher priced one.
Give me higher efficiency even at a higher price

3) communications is critical to me. What do I care about “instantaneous power outâ€￾.
I bought an electric meter from Hialeah Electric so I can measure TOTAL output but a good COM port and software package, even if add on (see Maui software) or even a bunch of fields pumped out comma delimited or even just like Outback’s Mate daily totals.
I will still get another meter for my next system

Your first 4 choices are then pretty even

In addition, I have considered Xantrex, SunnyBoy and Outback inverters mainly for my upgrade system
I like SunnyBoy as large installed base and they will be around awhile BUT they got no battery options. Grid up, SunnyBoy up, grid down, SunnyBoy down.
Same as my Omnion.
Yes, my grid doesn’t go down often so I don’t need batteries often but I see more and more instability in the grid being up and I have a few electric items I would not like to lose so I am going to be going to an inverter that will run when the grid is down.
My power company seems to be doing ZERO maintenance of the lines and vegetation growing up through the local lines.

SO, I would like.
1) grid tied
2) higher efficiency even at higher initial cost
3) stable company that will be around awhile and not bought out, this implies a good warrenty
4) communications capabilities with COMPLETE info out
5) battery capability is also crucial as I hate throwing away a refridgerator full of food and my furnace blower heater not working in the winter.
I may think of a few more later
Robert Winfield
Rockville, Maryland, USA

The biggest problem I see with current setups is the massive degrade that occurs when even a small part of a panel is obscured. Shadows and bird droppings produce a degradation far in excess of the area obscured.

System design is complicated and restricted. Array size and inverter capacity have to be carefully matched. Panel types should all be the same size and orientation.

The solution is an inverter per cell. All MPPT logic and power conditioning should be done in a small module (chip?) associated with each cell. The output from these small inverters would be combined on a panel to produce a single output from the panel. All panels should be connected in parallel. Shading, etc., would only affect the output from the shaded area. Multiple orientations would be a no-brainer. Additions to the system could be done in single panel units, and they would not need to be size matched to the rest of the units.

The "central control unit" should just be part of the main circuit breaker box. Data reporting from each inverter/cell would be accumulated at the main box, and available by communications to the building automation system.

Given the above target, what would be the next increment from the current designs? I think that using multiple small inverters is a better design than a single large unit. Current technology is certainly capable of an inverter per panel, or at least per short string of panels. It should be possible to swap out a single inverter, just as we currently swap out a bad circuit breaker. Yanking a 90 pound monster off the wall and trucking it to a remote service center shouldn't be necessary.

No fans. The masses are not going to accept a noisy device. And the fan is certainly going to fail before the solar panels. The idea of a mechanical device working without service for 30 years is harder to believe than the idea of an inverter per cell.

For a model of how solar panels and inverters can evolve in the future, just look at hard disks and their controllers. In the early 1980s, there was a separate controller card for hard disks. These days the entire controller function has moved into the logic on the hard disk.

Consider the ubiquitous wall warts that take 90-240VAC, and convert it to a clean 5VDC. How much more difficult is it to take 0.3-0.6VDC and convert it to 120VAC? Well, actually, I guess it is difficult now. But only because wall warts are a mature technology, and the reverse direction is still in its early stages.

There have been attempts with micro inverters. For some reason all have failed. Trace offered a 100w grid tie microsine that was discontinued. Solarex experimented with an AC PV module. Sandia apparently patented "AC PV Building Blocks". SunSine offered a 300w and 275w AC panel which were are now discontinued. An interesting point is that the SunSine unit warranted the panel for 20 years but the attached inverter for only five.

Unfortunately I feel we are still in market infancy and the market is not yet ready for integration.

Currently you can build a system as small as three panels with a SMA 700w inverter and RWE panels. However with the 700w inverter being ~$2/w and a 2500w inverter being ~$1/w I don't see it being a viable solution. I considered and rejected it myself.

Based upon current technology I tend to favor a modular central inverter design along the lines of the APC Symmetra UPS. I'd like to see a chassis with bays for inverters modules. Each module should support parallel operation with other modules as well as independant operation for small sub arrays. All would be controlled with a single grid-tie interface per box and single management card for monitoring. Small boxes could be designed for roof mount with larger units being wall mount or floor standing.

For example start on grid with 1Kw and a grid-tie module. Add a second or third 1Kw module as needed and later go off grid with a battery charging module. Stack enough units side by side and do a commercial install.

Failed module, fine. The unit should run using the remaining modules to full capacity while you yank the bad module, fedex it back and shove in the replacement. This is routine on high end computer equipment.

Finally the inverter needs to store logged data. Why dedicate a PC to something a CF slot or occasional downloads over an ethernet port can do much more efficiently.

The advantage to the consumer is an convenient growth, easy maintenance and a future upgrade path.

The advantage to the manufacturer is fewer parts to test, certify and stock, and a path to future sales.

Sean


Pertinent links:

Philips AC PV Panel presentation
http://www.nesea.org/buildings/be/Solar ... veland.pdf

AC PV Building Blocks
http://www.nrel.gov/ncpv_prm/pdfs/33586036.pdf

Solarex System
http://www.nrel.gov/ncpv/pdfs/26084.pdf

SunSine 300
http://www.nrel.gov/ncpv/pdfs/26085.pdf
http://www.nooutage.com/sunsine3.htm
http://www.ascensiontech.com/sunsine/ge ... espec.html

APC Symmetra
http://www.apcc.com/products/family/index.cfm?id=189

I thought Rob's suggest about embedded inverters was the wave of the future, and have heard that a few manufacturers are already building these, until speacock pointed out these haven't caught on very well - perhaps it's a product before its time. I'd still like to see it, since there are several advantages to using distributed inverters.


Secondly, SMA is rumoured to begin shipment of a grid tie inverter with battery back-up possibly as early as end of this year. I haven't corroborated this as yet, so I'm not 100% sure, seeing that SMA knows very well the bulk of the market is with basic grid tie systems.

If we can't have powerline modems in the US, then Ethernet based communications will suffice, either wired or wireless (WiFi). Although I've read recently that powerline transmissions capabilities might go wide open soon (once again, not corroborated). Either way, the application runs on any platform (Java, script, etc) and can feed Excel (or StarOffice/OpenOffice) with inverter stats and info that can be further crunched with macros either home brewed or obtained for graphing and table presentation.

Most of the pictures of installations I see look like the engine room on a submarine. The equipment takes up too much wall space and often looks "nerdy" If that is what you want fine but very few of the people I know would be happy with their garage looking like that.

So I would like to see less hours to install a system that does not look like Star Wars or a Submarine. It should have an absolute minimum of switches, lights and meters exposed to the user. Everything should be in one box with a conduit in and a conduit out.

Actually, both the Fronius IG and Xantrex SunTie have the all-in-one feature. Three conduits, DC, AC and data (optional), one small LCD display.

Sean

Does the Suntie have a battery charger? Does the SW Plus series have all the disconnects in one box? I have not looked at the Fronius so I do not know. It just seems that the last time I looked the was nothing that was a simple offgrid/gridtie one box solution.

it would be hard to be a single box off-grid solution , as you need batteries for storage !

Suntie and Fronius are Single Box solutions for Gridtie

"it would be hard to be a single box off-grid solution , as you need batteries for storage ! "

You could use one of those high rpm storage systems outdoors and it could be a single box indoors and the storage outside. The same could be done with batteries I suppose. I guess my real point is that the SW series is a long way from a single box and yes I know your topic relates to gridtie.

What I end up doing for my customers is modifing the SW conduit boxes to fit the disconnects,regulators,and displays. I do not like doing that because it takes too much time and is not strictly to UL listing. Up here in the Sierra's everyone wants seemless back-up power so the Suntie is not an option.