Thanks, I understand where youre coming from.


Fred

As a follow up, the GirdTie inverters don't wait for zero volts, there is a narrow window in voltage and frequency that is allowed by the UL spec.

Its ~264-211vac , +- 0.5hz ... doesn't take much to trip a unit offline and why the almost never will sync to a generator.

And there are units that do automatic transfer as you want, a Xantrex SW4048 or a Outback GTFX3048 ... but ANY inverter that will be a stand alone unit need battery storage on the input. So the Solar -> Battery is handled by a seperate unit called a charge controller.

As for the fuel thing, generators pig thru gas, 2 years ago in Florida when I had 4 hurricanes pass in 2 months, there were lines 8 hours long of people TRYING to get gas. Now a propane genny would make sense, but since I HAVE the panels, my addtional cost is just the Charger and Inverter ( about 1600.00 as I designed the charger and got it for "free" ). Battery bank was 1200.00 for 205 ah AGM's at battery USA, which just happens to be based in Lakeland 10 kWhr of storage

For this cost, lets say 4K, I have unlimited generation ablility while other are panic for gas ... and I have seen it more than once, and once is enough to know who gives a sh&t what it costs, I'M NOT going to be one of the people inline!

Hence the the constant refrain of "when can we get a 200-600 VDC simple, reasonable cost, don't care too much about the efficiency or extra function battery charger as a mate to the Xantrex GT family inverters"...

It would even be cool if the Xantrex GT could have an alternative DC output in the 50-125 VDC range so that an off-the-shelf MPPT charge controller could be used for emergencies.

-Bill

OK, I'll bite. Lets say SGT makes your dream box, its a black box that is parrallel to the GT's PV inputs, it reduces the PV voltage by 4 to 1 and similary boost the current so an off the shelf MX/SC/WX-60 can do its job

Whats the price in efficiency you'll tolerate and what's the market cost one would pony up to buy one? what do you expect its amps/watts can handle ?

Assume that there is a reason that 60 amps (or so) output is picked for a reason in Brand Other charge controllers...

4:1 voltage drop / 1:4 current...

200-550 vdc working voltage input

200vdc/4 * 60 amp output = 50 vdc * 60a = 3kW
550vdc/4 * 60 amp output = 137.5 vdc * 60a = 8.25 kW

Then there is my system running at ~300-320 VDC peak (of course, we all know that "my" system is the average system out there and the new product should work perfect with "my" system.

320/4 * 60 amp = 80 vdc * 60a = 4.8 kW

My system is an ~3 kW STC system, so 60 amp is way over the available power... perhaps even cutting this to 30 amp maximum output would be perfectly OK (assuming that people with larger arrays could parallel 4:1 converters).

We look at a "Brand Other" Mx-60 runs around $500-$650 each.

That is approaching ~$1.00 per watt at 12 vdc (assuming I remember everything correctly in that this is 60 amp * 12 vdc = 720 watts), but only ~$0.25 per watt for a 48 vdc battery bank. Obviously, when first introduced can charge more than as the product gets more competition.

Since the output power is highly dependent on the input voltage--picking a price point like $1.00 list, and $0.50 wholesale/volume buys does not make sense...

And looking at the pricing for the Mx-60... Pick 24 vdc battery bank. 24v*60=1,440 watts. Makes list price around $0.50 per watt. The solar panels are ~$5.00 per watt, so the "piece of equipment" is around 10% of the panel price.

Going back to my 320 volt / 4 @ 30 amps--that would be 2,400 watts or $12,000 list for panels. 10% of that would be $1,200 or $0.50 per watt...

$1,200---I would guess would be the high end price for a 30 amp output unit... Perhaps a smaller sized 4:1 converter unit, say 15 amps @ $600, would be a better price point for entry level converter.

The Honda eu2000i (1,600 Watt continuous rating) Internet price is around $900 (or a bit less) delivered. $1,200 for 2,400 Watts using solar power that would otherwise be wasted seems like a good price point.

Now, the prices I listed above are assuming a minimum function stand-a-lone unit. But, because it does something that nothing else does--I would think it could get some attention in the market. If it could be listed for 1/2 of the above price--(say 1/2 the price of a Mx-60 controller)--it would become very interesting to many more folks.

Now, whether this unit should be a stand-a-lone unit or combined as an optional input module for a Xantrex Solar Charge controller--something that marketing could work out.

Also, I gave the above as a maximum price, I would guess, the market will support for a one-of-a-kind product. If the manufactured price supports a lower list price--combining with other functions (such as a full fledged MPPT charge controller) may help keep margins up and lock the market to the one SGT unit.

Now, efficiency... 1st assumption is that this is a double conversion unit for emergency use--so that 0.93*0.93=86% is a guess at the approximate "best" efficiency one could get from this unit. It is possible that cost of copper wiring and the fact that I squared R wiring losses would be 1/16 of a low voltage controller may help some folks that have to place panels in the sun quite a distance from point of use.

If the list price is kept low, and this is assumed to be a generator replacement (auto-switch would be nice--may have to sync with GT LINK?), efficiency is not going to be the big seller...

And, as a "standby" battery charging system, if the efficiency is much less than 85%, then simply using a 120/240 VAC charger for battery maintenance (and maybe charging with that cheap emergency gas generator) would be more efficient anyway.

But, have to be careful of the added costs (Converter, Solar Charge Controller, possible AC Mains Battery Charger, possible backup-backup fuel driving generator)...

I will stop typing here... Anything of interest yet?

-Bill

I was thinking out loud of 3kw, as the voltage goes up the inductor has to increase accordingly, so while yes in theory you can get 8kw+, that wasn't my thought

All charger controllers are this way, the MX-60 is about 3kw, so you can't run it 60 amps at 70 volts for example.

The more functions in one box, the harder it is to make the product. Having a stand-alone DC converter has the appeal IMHO of just being a replacement for wires and switches... nothing more, and with copper costs, it could easily be 1-2K in wire and proper DC-switchings to re-create what I do in my garage

Efficiency would be pretty good, the GT5.0's input stage is about 25 amps for a 200-600V range and I believe its about ~98% efficient... thats still 100 watts of heat to deal with!

Now wether the market is big enough to fund the 7 figures to design, test, certify to UL/FCC a product is something a marketing guru would have to tell you ....

You could make this as an uncertified kit. Make it robust, make it safe, make a profit. This would not be a 24/7 item.
I would drag it out of it's box after the earthquake, yank the wires off the GT, and connect up my SGT Universal DC to 48V converter, attach my 330VDC PV array, and charge up the 4 Costco deepcycle batteries I've stored. When the batteries are full, I'll fire up my 48V - 120VAC inverter ( I know someone makes one! ) and run my fridge and freezer till nightfall, then use 2 CFL's to keep the house lit ( and attract looters ! )
When the grid comes back in a week or so, then I have to un-hook it all, but I'll have lived more comfortably that week.

unit blows up due to user abuse , starts fire an burns down house ... insurance company doesn't pay because the black box is not UL listed, owner sues "manufacture"

If your in a desperate need of power, no charge controller is needed, just hook the solar ( even potenional 300 vdc ) directly to the battery. Solar will run at the battery voltage until charged .. have to watch manually, but you will get some watts

It might only be a 100 watt charge from the 2kw array, but it will work just fine.

"Uncertified" commercial product--nobody, outside of China, would touch that with a 10 foot pole.

How about approaching the "cost" from a different angle... The 4:1 converter would have "roughly" the nominal current/power rating of a Xx-60 and 1/2 the price of the Xx-60.

Or reduce the current/power rating to achieve 1/2 of the Xx-60 price--and what would the 4:1 ratings be like?

Somebody already thinking of adding a Xx-60 controller and battery bank (and probably inverter too) to an existing GT populated Grid-Tie System, would not have a heart attack at that 4:1 price point (1/2 the MPPT charge controller cost). And it would get the vendor the sale of a Xx-60 and probably a sine wave inverter/charger/AC Transfer Switch too.

Just out of curiosity, would the system be stable if there was a GT inverter plus 4:1 converter + MPPT DC Charge Controller when attached to the same solar panels? Or would there need to be a cut over / transfer switch function (GT or 4:1. Sense current/function of GT Grid Tie with 4:1 and only switch on 4:1 when GT current/operation is off)...

-Bill

PS: At $300, it would be "cheaper" for me to buy the 4:1 than to hire an electrician with a ladder to rewire my existing solar panels and install the Low Voltage transfer system.

1) It's an Educational Kit. does not need certification. I'd buy one if it looked robust enough.

2) At $600, it's cheaper than getting an electrician the day after a earthquake or something takes the grid down. Pull out the box, hook up wires and all done. 1 hour, standing on the floor of the garage (if the garage is still standing)