[No]Should I design an inverter?

[NiHaoMike]

For the sake of noise and cost. I only intend to run my PC and monitors, which has maximum consumption of 450W combined when crunching numbers or running video games. For most of the time, the total system consumes less than 150W.

Since you're only running electronics, DC most likely is all you need. Assemble the DC/DC part of your design first and if it works, call it done!

[TerraHertz]

But for home power, it annoys me that the standard grid-tied no-battery solar panel installation inverters seem to all be designed to deliberately be impossible to adapt to stand-alone battery storage operation. And systems that are designed to run in isolation with batteries, don't seem to have provision for agile grid connect/disconnect.

Not true at all.  Outback Power, Schneider Electric, Magnum, SMA, and others all sell such inverters.

Others might find useful the result of an hour I've spent hunting up those companies and distributors and reading their advertising.
---------
http://www.outbackpower.com/
17825 59th Ave. NE, Suite B, Arlington, WA 98223 USA
OutBack Australia: Suite 2 32-34 Peter Brock Drive, Eastern Creek NSW 2766
Phone: +61 (2) 8599 6960
   They call it grid-tied partial state of charge (PSoC)


http://www.schneider-electric.com.au
  Urrgh. over-complex website, doesn't work even with firefox. Can't get to details of inverter systems.


http://www.magnum-dimensions.com/
http://www.magnum-dimensions.com/renewable-energy-products/
 NE USA only. Not much for international market. Can't find any grid-tie partial...


http://www.sma-australia.com.au/
Headquarters: Niestetal, Germany
Global presence: sales and service subsidiaries in 20 countries
Australian Authorised Distributors:

  RFI SOLAR Tel. 1300 000 734           http://rfisolar.com.au/
     99 Station Rd, Seven Hills  NSW 2147

  Sol Distribution  Tel. 1300 660 483   http://sol-distribution.com.au/
     Unit 14, 39 Herbert Street, St Leonards NSW 2065

  Solar Juice   Tel. +612 9725 1111     http://www.solarjuice.com.au/
     Unit 1, 10-12 Forsyth Close, Wetherill Park, 2164 NSW

  Solar + Solutions  Tel. 1300 255 410  http://solarsps.com.au/
     456 Lower Heidelberg Rd,  Heidelberg VIC 3084


More inverter manufacturers:
ABB
ZeverSolar Evershine TLC8000 - 3 Phase, Dual MPPT
Kstar
---------

Just starting a file. As for the original question of flexible grid connection, it seems now there are some. Still not many; most are still either grid-tied or independent. And good luck trying to find any technical details on _any_ commercial inverter.

I still say there's a need for an open-source project here.

[mtdoc]

But for home power, it annoys me that the standard grid-tied no-battery solar panel installation inverters seem to all be designed to deliberately be impossible to adapt to stand-alone battery storage operation. And systems that are designed to run in isolation with batteries, don't seem to have provision for agile grid connect/disconnect.

Not true at all.  Outback Power, Schneider Electric, Magnum, SMA, and others all sell such inverters.

Others might find useful the result of an hour I've spent hunting up those companies and distributors and reading their advertising.
---------
http://www.outbackpower.com/
17825 59th Ave. NE, Suite B, Arlington, WA 98223 USA
OutBack Australia: Suite 2 32-34 Peter Brock Drive, Eastern Creek NSW 2766
Phone: +61 (2) 8599 6960
   They call it grid-tied partial state of charge (PSoC)

The term normally used is "Grid Interactive" aka "Grid tie with battery backup"

I'm most familiar with Outback products.

Their Radian line is their flagship grid interactive capable inverter/charger. I suspect it can be adapted to non-North American power specs but I haven't investigated.

]Here is a listing of their all their North American market (60Hz) grid interactive units

The do have inverters for the international market - 50Hz etc. This page has some and I believe there are others available as well.  I'd call Outback Australia.

There is full documentation of specs and manuals for each inverter linked on that website. They also have an active user's forum

They make high quality inverters and have a reputation for excellent customer service - which I've had first hand experience with in the past.  This may have changed in recent years - since they were acquired by the "alpha group".

http://www.schneider-electric.com.au
  Urrgh. over-complex website, doesn't work even with firefox. Can't get to details of inverter systems.

Yeah - Schnieder bought Xantrex a few years ago and took over their inverter line.  Their venerable XW line was a top grid interactive capable inverter for years. Now updated and called the "Context XW"

You can find details here. Click on one and under the details tab is documentation.  I believe these can be programmed to international 50Hz output and voltages.

http://www.magnum-dimensions.com/
http://www.magnum-dimensions.com/renewable-energy-products/
 NE USA only. Not much for international market. Can't find any grid-tie partial...

Yeah, my bad. I'd thought Magnum had a grid interactive model. They do make good off grid inverters.

http://www.sma-australia.com.au/
Headquarters: Niestetal, Germany
Global presence: sales and service subsidiaries in 20 countries
Australian Authorised Distributors:

  RFI SOLAR Tel. 1300 000 734           http://rfisolar.com.au/
     99 Station Rd, Seven Hills  NSW 2147

  Sol Distribution  Tel. 1300 660 483   http://sol-distribution.com.au/
     Unit 14, 39 Herbert Street, St Leonards NSW 2065

  Solar Juice   Tel. +612 9725 1111     http://www.solarjuice.com.au/
     Unit 1, 10-12 Forsyth Close, Wetherill Park, 2164 NSW

  Solar + Solutions  Tel. 1300 255 410  http://solarsps.com.au/
     456 Lower Heidelberg Rd,  Heidelberg VIC 3084

The SMA Sunny Island it their grid interactive model. It is high quality.

More inverter manufacturers:
ABB
ZeverSolar Evershine TLC8000 - 3 Phase, Dual MPPT
Kstar
---------

I have no knowledge of any of those manufacturers.

One I forgot to mention is Victron Energy They are a Dutch company that do not market in the US much but they make high quality inverters - some of which are grid interactive I believe.

I still say there's a need for an open-source project here.

I agree - it would be great to have that as well.

[nctnico]

Why not just get a small generator set? An alternator in a car doesn't work very well at idle speeds.

For the sake of noise and cost. I only intend to run my PC and monitors, which has maximum consumption of 450W combined when crunching numbers or running video games. For most of the time, the total system consumes less than 150W.

Modern  small generators are very quiet.

[NiHaoMike]

Why not just get a small generator set? An alternator in a car doesn't work very well at idle speeds.

For the sake of noise and cost. I only intend to run my PC and monitors, which has maximum consumption of 450W combined when crunching numbers or running video games. For most of the time, the total system consumes less than 150W.

Modern  small generators are very quiet.

Is there one that would be efficient at just 150W load? Granted, leaving a car idling won't be efficient either, but that only needs to be run part time with the help of a deep cycle battery. (Or use some other source, such as solar panels, to charge it.) 100Ah class deep cycle batteries can be found for under $100 and with the 50% derating, will run 150W of load for 4 hours.

[mtdoc]

Is there one that would be efficient at just 150W load?

You'd want an inverter generator which will allow power output to be independent of engine RPM. They do cost more.

Honda EU generators are the standard. The smallest is 1000W.  Google EU1000.

Yamaha and other companies also make similar models.

[NiHaoMike]

I'd be surprised if it would be as efficient as an inverter running from a battery and running a generator part time to charge it. It's pretty difficult to make a very small engine efficient. Not to mention it would be yet another device to maintain.

Also, where in the US does the grid regularly go down for more than 4 hours (or even one hour) at a time? If a single deep cycle battery can cover most of the outages, it might not be worth the cost to improve the efficiency of the second level backup solution.

[TheSteve]

Honda EU1000i or EU2000i - both wonderful options. I ran my EU2000i on the weekend in Eco mode(powering 100 watt amateur radio transceiver) for 13 hours on 1.1 gallons of gas. The bonus with an EU2000i is you can run the fridge/freezer/microwave if needed during a longer outage.

Not as much fun as building your own inverter of course.

[NiHaoMike]

It turns out my 96% efficiency estimation is quite bold. The DC/DC stage shows quite high efficiency, as well as the output HEMTs. The problems lie in the LC tank. They consume more power than I thought if I insist to squeeze things into a small flat box. Low inductance simply does not cope with high efficiency.

That's more or less what I found when I worked on a 2kW inverter. A large portion of the idle losses are in the output inductor. (Same goes for many audio amplifiers.) One trick to reducing that loss is to period skip near the extreme duty cycles, lowering the effective switching frequency. Or just output a trapezoidal wave at low output power so there would be no switching over much of the waveform.

HVDC eliminates that loss. Not to mention significantly lowering cost and complexity at the expense of making it only work on electronic loads.

If you just want an off the shelf solution, here are more reviews than you could ever imagine existed:
https://www.youtube.com/user/knurlgnar24/videos
Keep in mind that if you want fancy features like V/Hz control, expect to spend a lot. But for the uses you listed, that would be irrelevant.

[rx8pilot]

Honda EU1000i or EU2000i - both wonderful options. I ran my EU2000i on the weekend in Eco mode(powering 100 watt amateur radio transceiver) for 13 hours on 1.1 gallons of gas. The bonus with an EU2000i is you can run the fridge/freezer/microwave if needed during a longer outage.

Not as much fun as building your own inverter of course.

I had a few of those for my business and loved them. Really fantastic for gas options.

[Pineapple Dan]

I did design my own inverter. Well technically just a H-bridge and connected to an old transformer. It is ridiculously simple and hack-ish but one can run some stuff off it

https://vimeo.com/manage/videos/523141818

Should be able to make the output more sine wave-like by software but haven't tried this yet

I doubt it will do 500W but I intend to design an improved version, I want something that I can pack in with a solar charge controller & batteries and be remote controlled, reset automatically after overload and so on. My shop-bought 1KW inverter will just give up and start beeping once the battery goes down or if it gets overloaded. With a home-made one it will be easier to work around those problems