low voltage grid tie inverter

[clarsondd]

i was looking to see what grid tie inverters there are and it seemed like all the usually manufacturers' (sunny boy, outback, xantrex, fronius) products have a cut in voltage of about 180v. And, it would require like 15 pv panels to get to such a high (relative to a 12v pv panel) voltage.

this seems to put a real high up front cost to doing pv power.  ie a 125 watt pv panel @ $4 per watt is $500, times 15 panels = $7500 add $2500 for a grid tie inverter and your at $10000.  that is before wiring, disconnects, and labor.

what i was wondering is there more of a "starter" grid tie inverter.  something that would have a cut in voltage around 48v.  something that could be done with 4 panels on the low end and handle 8 panels on the high end.  above 8 panels you would have to upgrade/replace or double up.

there are inverters with 48v input and output 220v.  it doesn't seem like it would be that hard to add grid tie functionality.  or maybe there is a grid synchronizer, something that would take a generic 220 ac input and synchronize/tie in with the grid.

i suppose there is some prohibitive factor on why there isn't. such as testing, certification, industry compliance, liability and profit margin.

but i think there would be a lot more people (such as myself) that would be interested in doing pv if they could start out with a $5000 up front cost. 4 panels @ $500 = 2000, add $1000 for a grid tie inverter and you still have $2000 for labor, etc.  That probably is a bit on the low side, but still much better then $20000 - $25000 using a grid tie inverter that requires 200v dc to operate.

maybe i just don't know enough about what products are available.

what is available out there to efficiently grid tie 4 pv panels?

[boB]

I know that this is coming up eventually.  The Exceltech unit was supposed to be one of these and the old OK4U that was sold by Trace Engineering a few years ago is still being sold I think in Europe. (not UL1741 listed in the US so not here anymore)

BTW, which OutBack PV inverter were you referring to ??

Thanks,

boB

[Volvo farmer]

There's another way to solve this.

Kaneka is making a 60W thin film panel that is 67V  nominal. Four of those puts you over 180V and would cost about $1200.

Now why anyone would want to grid-tie 240W of solar is beyond me, unless the government is paying you to do it. Electricity savings would be on the order of 20 cents a day in most situations.

[boB]

Hi Volvo...   I can't see why anybody would want to buy an SUV to drive around town that gets 10 MPG either, but it must just "feel good" to do it !!

b{:)B

[clarsondd]

bob,

by "I know that this is coming up eventually", did you mean that is something that companies have thought about producing.  and if so do you know how long before they might available to the public?

>> which OutBack PV inverter were you referring to ??

not really sure.  I spent a few hours visiting several manufactures websites and they all had specs around 200v dc minimum input.  some were a little lower, some a little higher.  but none anywhere near 48v.  So, i thought i'd ask for some insight on the subject before doing more snipe hunting.

I know i was at xantrex, fronius, and sma website for sure.  maybe i was, maybe i wasn't looking at outbacks.  don't remember for sure.

[boB]

>>not really sure.  I spent a few hours visiting several manufactures websites and they >>all had specs around 200v dc minimum input.  some were a little lower, some a little >>higher.

Ahhh... OK.   Actually, if you're not looking for batteryLESS grid tie, OutBack and Xantrex both have inverters that sell back to grid from 48 Volts, and OutBack also has the 24 Volt GFX units.  You need a separate charge controller though.  They're not in one unit as they are in a Xantrex GT or Sunnyboy or PV powered etc...

Would soemething like that work ??  You don't need a huge battery bank either.

Xantrex used to have the SunTie that operated directly from a 48 V PV array but that didn't work too well.

boB

[electronbaby]

you can certainly use the Outback inverters to grid tie at 48v or 24v for that matter. Some efficiency will be lost to battery charging, but its certainly doable. Sharp made the Sunvista, which has a cut in of 110vdc and had 3 independent PPT inputs. I dont thing this inverter is still in production however. For the most versatility, I would go with the outback stuff personally. Im in the process of changing out all my equipment for outback currently.  The STXR Trace inverter was awesome for the niche it filled. It did have reliability problems however. Im not to familiar with the exceltech stuff.

[clarsondd]

Volvo Farmer,

Thanks for the suggestion on the thin film panels.  

I had thought about something along those lines. ie. the output voltage of a panel is based on how the cells are wired together.  So, while i would never rewire a panel to have an output voltage of 48 volts, i had thought of possibility that 48v panels might be available even thought i had never heard of any.

>>Now why anyone would want to grid-tie 240W of solar is beyond me

i was thinking more along the lines of 4 125w panels for 500w, but i suppose they could be 60w or 200w panels.

i'll avoid debating the cost effectiveness of pv.  but if you do go with pv, the choices are are grid tied, off grid or a combination of the previous.  no matter which you choose, the panels are still going to produce the same 20 cents of electricity.

myself i'd prefer to avoid batteries and their maintainence.

[clarsondd]

thanks for the info,

from excel tech website faq, their inverters do not have grid inter-tie capabilities

[clarsondd]

thanks much for the info.

i had seen the xantrex gt series, but looking further i notice the xw products.  I guess that is what your refering.

I did go to outback site and viewed their products.

I would prefer not to have to use batteries.  but if the choices are 48v with batteries or 200v without batteries, there is only one where the input is 48v.

do you know the amphour rating required for the batteries?

[Volvo farmer]

High voltage panels are becoming more popular, because of the grid tie phenomenon. five or six years ago, they were almost unheard of.

I'm rather opinionated on this subject. I have solar because it was the most cost-effective way to have lights, internet, pressurized water and TV on this cheap piece of dirt I bought. Running a power line 1.5 miles to my location would have been triple the cost of a solar system.

Nowadays, everyone is out to save the world from the dreaded global warming, or chasing government subsidies, or under the impression that they are going to get free electricity for life from solar panels.

Don't get me wrong, I get an extremely good feeling being electrically independent (well, independent until I have to buy batteries again). But from my perspective, grid tying 500W of solar, without battery backup is a lose-lose proposition. If the grid goes down, you've got no power, just like everyone else around you. In addition, you have spent money on a thing which will probably not pay for itself for thirty years, so it is not a good economic decision either. So that leaves the only benefit of such a system being the warm feeling of saving the world because someone on the news said the world is in trouble.

[TomW]

VF;

Well said. Truly.

I do the RE as a hobby and in many ways it is better than a boat a classic car or some other toy that is simply a drain on resources. Otherwise I would feel like a fool because it will never amortize itself in my lifetime.

Sad but true. So few folks "get" that part it is not even funny.

TomW

[Ungrounded Lightning Rod]

I can tell you why:

It's because the Corporate Average Fleet Economy (CAFE) MPG requirements killed the station wagon.

So people who need to carry a family around and tote big items or large amounts of them from the shopping centers went up to the next cheapest thing:  The SUV.  (They are "trucks" and thus don't count toward the passenger car mileage average.)

Then the SUVs also get used for one-driver commutes because driving a gas hog is cheaper than buying a separate car optimized for commuting.

If the eco-wackos manage to extend the CAFE standards to SUVs it will kill the SUV.  So the people who actually need them will move up to the NEXT least expensive (and still more gas-guzzling) alternative - a van or truck.

(Meanwhile, killing the SUV will wreak havoc with the rural population, who actually NEED an off-road four-wheel-drive vehicle.)

Lawmaking usually leads to unintended consequences.

[Volvo farmer]

YES!

This thread is going off the rails, but maybe that's what we need around here lately.

I pick up my daughter from first grade a half dozen times this year, when she ain't riding the bus. What a trip. I was in my '86 Volvo 240 station wagon and looked straight across the ROOF line onto the BED line of a new 4 door F150 with FOUR DOORS.

This CAFE thing is outa control. All communities are different, but I am seeing a huge plethora of 4wd, four door TRUCKS on the road. I can't even see my Volvo in the parking lot at my daughter's school, because it's full of Surburbans, Tahoes, F150s, Escalades, Etc.

Maybe it's different other places in the US but look around next time you park in the supermarket, how many four-door trucks do you see?  I see a bazillion of them here and they ain't hauling hay or plywood in the bed, they're idling outside the elementary school, waiting to pick up fifty pounds of third-grader.

[boB]

>>from excel tech website faq, their inverters do not have grid inter-tie capabilities

So they still don't have the grid-tie inverter on the the official list yet, huh??

They show a couple at some of the energy fairs though...  One of which is a PV module inverter of around 250 Watts or so.  There's another one that's bigger too but can't remember the Wattage.  I think these are still "in progress", but the small one WAS being advertised a couple of years ago.  It wasn't quite ready for prime time I guess.

boB

[boB]

>>from excel tech website faq, their inverters do not have grid inter-tie capabilities

So they still don't have the grid-tie inverter on the the official list yet, huh??

Gary, the president (I think he's the pres) has shown a couple at some of the energy fairs though...  One of which is a PV module inverter of around 250 Watts or so.  There's another one that's bigger too but can't remember the Wattage.  I think these are still "in progress", but the small one WAS being advertised about 3 years ago.  That little system wasn't quite ready for prime time yet I guess.

boB

[DamonHD]

Well VF, I'm doing it primarily for the the warm feeling inside, and because with my west-facing roof I simply couldn't generate even 10% of our requirements mid-winter if the grid went down.  And I like the idea of not 'wasting' any energy we happen not to use in summer.

But, for a bigger system I'd put in an auto-islanding system with battery backup (such as SMA's) to at least cover the lighting, freeze, CH pumps and maybe even the Internet connectivity!

Rgds

Damon

[wdyasq]

When looking at inverters for a grid-tie wind-turbine setup I found 'Power-One' brand. They offer an MPPT 'grid-tie'.

They have a 'grid-tie with battery charging option'. However, it is not certified for United States use nor do they plan on certifying it for US customers. To have a grid-tie turbine and battery backup one would need another $$$$$ inverter.

Using an example of 500kWh/month, and the high rate of ~$0.16kWh, one's bill is about $80 a month. About $18 of it here is one's meter charge. If one were to have a system that almost met their needs here and put back .... 150kWh in a good month it would barely pay the meter charge.

Just sizing to 'pay back the inverter' over a 5 year period one would need to sell (or save) about $250 a year back to the power company and recover the additional $18/month 'meter charge'. This works out to ~39/mo. or ~8kWh/day additional production. Working with that number and an extra magical 1kW of panels ($4000 + install) one can easily see there is no golden egg laying goose.... But, a 3oz liquid golden goose egg at todays prices would be worth about $55,000.

All of these numbers are for $0.16kWh costs, about as high as seen in the US (with fuel costs going very high it will go higher). I sized a project where diesel was being used  as the generator fuel and it seemed reasonable to use solar and wind if possible. I have not actually visited this site yet.

Ron

[ghurd]

What gets me is people with new F-250s want to use my Toyota to haul a ton of wood or mulch or something, so they don't scratch their new truck.

When the Trace MicroSine was available to me, maxed out it would not have put enough power back into the grid to pay for the inverter in its lifetime.

Not including the small items, like PVs.

This is not a great place for solar.

G-

[Garry]

I live in Northern Oklahoma and have 24 Kyocera 63 watt 12V panels on my roof feeding a Xantrex stxr 2500UPG inverter. The date of manufacture is April 30 2003 but I don't know when I installed it. The display shows 5867 KW Hrs. total energy sold to the grid. Today which is very sunny at 12:00 noon the panels were making about 1070 watts. This system is for sale as I am finally able to start on my big wind turbine.

Garry