battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

michaelc

Hi folks, Very excited to be putting together something to throw on our roof. We are planning a 7.4KW system using Outbacks Radian inverter. We have limited budget for this and it appears the Radian is reconfigurable so we can change things as we learn. The question I have is can we run the radian and not have batteries or charge controllers......just yet. We want to do the grid tie thing but initially just have PV panels and inverter using/selling back power. Later we would add a couple of 80 amp charge controllers and 800AH of batteries (if I remember a rule I read 1AH for every KW) I am new to all of this, and just cannot find any info on the plus or minus from running the radian without batteries, not even sure it is possible. We a being told 2 sunnyboys (a 3W and 4KW) hooked up to two strings of 14 panels would be better, then spend another 4K to AC couple later if we ant to be up when grid goes down. I really like the outback, and the outback charge controllers...because it has so many modes and options such as gen start etc. Any and all comments welcome. Mike

BB.

Re: battery-less Outback Radian

Mike welcome to the forum and the Alice through the Looking Glass world of AC inverters.

What used to be a (relatively) simple subject has been turned into a maze of options because of electrical engineers and marketeers.

There are two basic classes of AC inverters... The Grid Tied units that take power from the solar panels and "inject" that into your home's electrical panels and help reduce your billed power (save money in areas with high electric power costs). And Off Grid units which take power from a battery bank and generate a separate AC power--Generally used for off grid homes and emergency backup power.

To make things a bit more complex. There are "hybrid AC Inverters" with battery banks that can work both as a GT inverter and pump "excess" charging current back into the grid, and if the grid fails, the inverter flips over to AC off grid mode and supplies power to local AC loads from the battery bank (and solar panels).

And even more complex, SMA has created a pure GT AC inverter (no batteries) that during the middle of a sunny day can supply ~1,200 watts to an auxiliary AC power outlet that can be used for emergency power during the middle of a sunny day. When the sun is not in the middle of the sky (or when clouds pass overhead), the aux AC power "goes away".

The Radian, I believe, is the typical Hybrid AC inverter. It needs a battery bank to provide AC power--Either to the grid or for emergency backup/off grid power operation.

By the way, the rule of thumb for designing a off grid/hybrid AC power system is to have ~100 AH @ 48 volts minimum per 1kW of AC loads and/or solar array. The battery bank has to be large enough to "buffer" the AC loads and DC ripple current when operating in Grid Tied mode.

It can be difficult/costly to "grow" a solar power system... If you are doing this for emergency/backup power, then I would do things in this order (as money becomes available)--assuming the end point is a hybrid AC system capable of GT and OG operation:

1. AC Generator + Fuel supply for emergency operation (Naturl Gas and Propane are great fuels for long term operation/storage. Diesel is nice but smelly and gasoline is available everywhere--but both can have issues if stored more than ~a few months to a year).
2. AC Hybrid Inverter + Battery Bank (full size battery bank). Recharge from AC power/Genset during power outages
3. Build out solar array (you can add solar panels in several stages).

On the battery bank, you can start with "cheap" batteries and learn how to operate your system and figure out how many batteries you really need... And when the first set "goes bad" in ~3-5 years (or you "murder" them with poor maintenance and/or oops by leaving loads on when you go on vacation), you can then replace with your "dream set".

In general, batteries are the weak point of off grid/hybrid power systems. They are easy to damage (over/under charging, running dead when somebody leaves too many loads on, poor maintenance, well pump runs water into a broken pipe, etc.) and age even when operated correctly (3-5 years for "cheap batteries", perhaps 10-15+ years for expensive batteries).

And, with Grid Tied systems, your utility needs to allow GT solar systems (not all do)--And some utilities are overhauling their rate plans to "punish" GT solar folks and even those customers that work hard on conservation...

Old days of $4.50 per month connection fee and $0.20 per kWH rates are being replaced with $40-$100 per month connection charges and $0.05 per hour load rates (or even $0.025 per kWH paid for GT solar generated power)...

In general, solar GT power can be "break even" or even save money. Off Grid/Hybrid solar will never save money unless you do not have (cost effective) grid power available. Of course, emergency power can be worth every dime if you are hit by storm/earthquake and our out of power for weeks to months at a time.

But remember, in major metropolitan areas, the cities are shutting down municipal water because they don't have power for pumping and/or sewer backups/flooding because of lack of lift pumps/sewage treatment during power emergencies. Figuring out your emergency plans can be a nightmare.

-Bill

Blackcherry04

Re: battery-less Outback Radian

Bill, make this answer a " Sticky " A excellent explanation to a complex subject !!!!

BB.

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

BC04, thank you very much for the kind words.

I will make this thread a sticky, for now, and see if it helps others.

-Bill

mtdoc

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

I agree. Excellent explanation Bill!

The short answer to michaelc's question is no - you cannot run a Radian without batteries.

BB.

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

I don't do "short answers". :p

-Bill "it must be genetic" B.

BB.

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

And to add a bit more complexity...

Many (few, some, most?) Off Grid AC sine wave inverters are capable of being "back fed" power and actually capable of recharging their battery bank directly.

However--Many (and older) AC sine wave OG inverters do not have any way of regulating the battery state of charge and can be "over charged" unless other methods of power control are employed (turn off GT inverter when battery bank is full, add "dump/shunt" loads and controller to bleed off excess charging current, etc.).

SMA, Schneider/Xantrex, and Magnum (at a minimum, Outback too?) have some newer OG Inverters that do have methods of controller battery charge when "AC Coupled" to a GT inverter (providing charging current). Usually this is done by varying the AC frequency (i.e., move from 60 Hz to 59/61 Hz and "knock" the GT inverter off line).

SMA (Sunny Island series) has a really interesting method of varying the frequency to "throttle" the GT inverter (when configured for "micro grid"). Unfortunately, in the US/Canada, SMA solutions tend to be really pricey.

The choice between solar array -> solar charge controller -> battery bank vs solar array -> GT inverter -> AC sine wave inverter -> battery bank...

I am not sure what is the "best answer"... I would tend towards the traditional DC Solar Charge Controller and not bother with the GT AC Coupled solution unless there are some extenuating circumstances.

In any case, I would highly suggest doing a paper design with several solutions and figure out the cost / benefit ratios for your needs. There are few black & white answers in solar design (or engineering). Everything is trade offs.

-Bill

michaelc

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

BB. wrote: »

And to add a bit more complexity...

Many (few, some, most?) Off Grid AC sine wave inverters are capable of being "back fed" power and actually capable of recharging their battery bank directly.

However--Many (and older) AC sine wave OG inverters do not have any way of regulating the battery state of charge and can be "over charged" unless other methods of power control are employed (turn off GT inverter when battery bank is full, add "dump/shunt" loads and controller to bleed off excess charging current, etc.).

SMA, Schneider/Xantrex, and Midnite (at a minimum, Outback?) have some newer OG Inverters that do have methods of controller battery charge when "AC Coupled" to a GT inverter (providing charging current). Usually this is done by varying the AC frequency (i.e., move from 60 Hz to 59/61 Hz and "knock" the GT inverter off line).

SMA (Sunny Island series) has a really interesting method of varying the frequency to "throttle" the GT inverter (when configured for "micro grid"). Unfortunately, in the US/Canada, SMA solutions tend to be really pricey.

The choice between solar array -> solar charge controller -> battery bank vs solar array -> GT inverter -> AC sine wave inverter -> battery bank...

I am not sure what is the "best answer"... I would tend towards the traditional DC Solar Charge Controller and not bother with the GT AC Coupled solution unless there are some extenuating circumstances.

In any case, I would highly suggest doing a paper design with several solutions and figure out the cost / benefit ratios for your needs. There are few black & white answers in solar design (or engineering). Everything is trade offs.

-Bill

WOW, THANK YOU so much for the wisdom and answering the question that is probably on the minds of many new folk. I have even more questions now but making the thread a sticky is a really good thing. I still have a lot to peruse in this forum, but am blown away with the quick and informative response. Mike

michaelc

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

Thanks again Bill and all. I absolutely will go with your suggestions. I have 2 gen sets and wired in a switch to isolate us when power goes out and generator is on. I would like to cut the manual switch out and use the second AC input on the Radian for the generator which is cool. Good call on the experimental batteries for initial operations until I figure it out. I put a 225 watt panel on our RV with a Blue Sky MPPT controller and figured I would leave the defaults alone and felt smug that my 2 6V golf cart batts would be taken care of.......wrong. Took some playing around with charge settings and fresh batts to get to a happy place, but now I love our little RV system.

I can utilize the Costco energizer 6V golf cart batteries. I figured 8 of them should work according to rule of the thumb provided here, not really looking to power the house from them, but as you indicated just acting as a buffer. Would the two 80 amp outback charge charge controllers be too much? I read somewhere the midnight classics would work with outback Radian. I will do a search on the forum for input also. Mike

Cariboocoot

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

michaelc wrote: »

I can utilize the Costco energizer 6V golf cart batteries. I figured 8 of them should work according to rule of the thumb provided here, not really looking to power the house from them, but as you indicated just acting as a buffer. Would the two 80 amp outback charge charge controllers be too much? I read somewhere the midnight classics would work with outback Radian. I will do a search on the forum for input also. Mike

If you're going to power a Radian you will need eight 6 Volt batteries minimum as they run on 48 Volts.

At that minimal level (220 Amp hours @ 48 Volts) you'd need about 1400 Watts of panel for full solar charging and an MPPT controller capable of handling 30 Amps @ 48 Volts such as the Rogue 3048.

The Radian does not care what charge controller is looking after its batteries. But it will only 'communicate' with Outback's FM series.

BB.

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

A Radian is a relatively, "huge", AC inverter... That is, at a minimum, an 8kWatt AC inverter. Using our "rules of thumbs" at 100 AH @ 48 volts per 1 kWatt of AC inverter output would give you a nominal 800 AH @ 48 volt battery bank.

Assuming ~200 AH @ 6 volt battery -- That would be a string of 8 batteries (48 volts) with four parallel strings--Or 32 golf cart batteries.

That is not a small system, and, normally I would be recommending larger AH capacity cells... At 3 cells per battery, that is 96 cells to check water levels/specific gravity every month.

Off grid power systems are expensive to scale up and require maintenance (replace batteries every ~5-8 years for mid-range batteries, AC inverter+charge controllers every ~10+ years, etc.)--Whether you use the system or just keep it on standby.

Much different for gensets--A large generator is not too expensive, and they hardly need maintenance/fuel unless they are running. And large gensets, when they are running can really suck down the fuel.

You really need to understand your power needs. Personally, if this is for emergency power, you probably only need to run a refrigerator, lights, a small water pump, and some electronics/cell chargers... A 3.3 kWH per day system with 1.2-1.5 kWatt AC inverter will run that stuff nicely. Battery wise:

3,300 WH * 1/24 volts * 1/0.85 inverter efficiency * 2 days of storage * 1/0.50 max discharge = 647 AH @ 24 volt battery bank

• 647 AH / 220 AH per battery string = 3 parallel strings
• 24 volt bank / 6 volt batteries = 4 batteries per string
• 3 parallel strings * 4 batteries per string = 12 golf cart batteries.

Or about 1/3rd the size battery bank as that required to run an 8 kW inverter at full output...

Of course, without knowing your loads (watts*hours per day), we still do not know if this will meet your needs--This is just a "generic" system design to support ~3.3 kWH per day from a battery bank.

Solar panel wise, there are two calculations to make... One is sizing the panel for the size of the battery bank. And the second for how many Watt*Hours per day you pull from the system and how many hours of sun per day you get in your area.

Quickly, for the above battery bank -- 660 AH @ 24 volts:

• 660 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,243 Watt array minimum
• 660 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,486 Watt array nominal
• 660 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 3,231 Watt array "cost effective maximum"

And assuming a reasonably sunny climate with a minimum of 4 hours of sun per day (for ~9 months of the year), to support a 3.3 kWH per day load.

• 3,300 WH * 1/0.52 end to end system efficiency * 1/4 hours of sun per day = 1,557 Watt array minimum based on 4 hours of sun per day

So, a 3.3 kWH per day system would require a solar array in the range of 1,557 Watts to 2,486 Watts nominal to ~3,231 Watts max (cost effective) array.

If you are still looking for a larger system--You can just multiply the above numbers to size the larger system (3.3kW * 3 to get a 10kWH per day system).

-Bill

michaelc

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

BB. wrote: »

A Radian is a relatively, "huge", AC inverter... That is, at a minimum, an 8kWatt AC inverter. Using our "rules of thumbs" at 100 AH @ 48 volts per 1 kWatt of AC inverter output would give you a nominal 800 AH @ 48 volt battery bank.

Assuming ~200 AH @ 6 volt battery -- That would be a string of 8 batteries (48 volts) with four parallel strings--Or 32 golf cart batteries.

That is not a small system, and, normally I would be recommending larger AH capacity cells... At 3 cells per battery, that is 96 cells to check water levels/specific gravity every month.

Off grid power systems are expensive to scale up and require maintenance (replace batteries every ~5-8 years for mid-range batteries, AC inverter+charge controllers every ~10+ years, etc.)--Whether you use the system or just keep it on standby.

Much different for gensets--A large generator is not too expensive, and they hardly need maintenance/fuel unless they are running. And large gensets, when they are running can really suck down the fuel.

You really need to understand your power needs. Personally, if this is for emergency power, you probably only need to run a refrigerator, lights, a small water pump, and some electronics/cell chargers... A 3.3 kWH per day system with 1.2-1.5 kWatt AC inverter will run that stuff nicely. Battery wise:

3,300 WH * 1/24 volts * 1/0.85 inverter efficiency * 2 days of storage * 1/0.50 max discharge = 647 AH @ 24 volt battery bank

• 647 AH / 220 AH per battery string = 3 parallel strings
• 24 volt bank / 6 volt batteries = 4 batteries per string
• 3 parallel strings * 4 batteries per string = 12 golf cart batteries.

Or about 1/3rd the size battery bank as that required to run an 8 kW inverter at full output...

Of course, without knowing your loads (watts*hours per day), we still do not know if this will meet your needs--This is just a "generic" system design to support ~3.3 kWH per day from a battery bank.

Solar panel wise, there are two calculations to make... One is sizing the panel for the size of the battery bank. And the second for how many Watt*Hours per day you pull from the system and how many hours of sun per day you get in your area.

Quickly, for the above battery bank -- 660 AH @ 24 volts:

• 660 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,243 Watt array minimum
• 660 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,486 Watt array nominal
• 660 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 3,231 Watt array "cost effective maximum"

And assuming a reasonably sunny climate with a minimum of 4 hours of sun per day (for ~9 months of the year), to support a 3.3 kWH per day load.

• 3,300 WH * 1/0.52 end to end system efficiency * 1/4 hours of sun per day = 1,557 Watt array minimum based on 4 hours of sun per day

So, a 3.3 kWH per day system would require a solar array in the range of 1,557 Watts to 2,486 Watts nominal to ~3,231 Watts max (cost effective) array.

If you are still looking for a larger system--You can just multiply the above numbers to size the larger system (3.3kW * 3 to get a 10kWH per day system).

-Bill

Thanks, Our utilities offer a rebate of 1.50 a KW, up to a max of 10KW. They would like to see at least a 4KW system on the house that ties into their system. We use 847KW a month average. Seat of the pants guesstimate to reduce our electric bill and have a little to sell back to further reduce our utility bill was 6 to 8KW. We get at a min 4 hours a day of sun. My roof is obstruction free and one side faces east, the other side faces west. Was planning to use 28 solarworld 265 panels, 14 on one side of the roof and 14 on the other, mounted at the apex. I figured the Radian put into mini-grid mode would feed juice into the house and sell any unused to the utility. And if we were eating more juice than the panels put out, the inverter would tap the utility to augment. I think after reading expert testimony here on the forum, I need to rethink. Maybe the sunnyboy inverters would be a better choice to do accomplish the initial goal of eliminating the electric bill, if not the whole utility bill via credits from sell back. Our secondary goal would be to have critical loads powered in the event our utility died, or was ordered to shut off (we have 3 coal powered power plants and are self sustaining in Colorado Springs) and of course we have a couple of small generators. I will use the math in your post to calculate various scenerios. Looks like AWS has a ton of hardware to pick from at a reasonable price so that is good. Mike

Cariboocoot

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

If you do not need/want the ability of battery back-up power (for when the grid goes down) skip the Radian. Standard GT inverters such as SMA or Fronius or even Enphase micros will give you the same grid tie performance for a lot less money and maintenance.

solar_dave

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

And if your splitting the panels you would be better off with 2 separate Grid Tie inverters.

bill von novak

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

michaelc wrote: »

Hi folks, Very excited to be putting together something to throw on our roof. We are planning a 7.4KW system using Outbacks Radian inverter. We have limited budget for this and it appears the Radian is reconfigurable so we can change things as we learn. The question I have is can we run the radian and not have batteries or charge controllers

Not to detract from the other excellent answers, but for a much shorter answer - no.

If you really need frequent backup due to a very unreliable grid, go with a battery based system like the Radian or one of the many other hybrid inverters and spend the money/allocate the space for batteries. T105's (golf cart batteries) will work but are painful to work with - they're flooded and thus will tend to be messy and annoying to maintain. You might consider starting with AGM batteries which take less maintenance overall (but are a bit more fragile due to the inability to replenish electrolyte.)

If you need infrequent backup I'd go with at Sunnyboy with the SPS backup. Two Sunnyboys will give you 3000 watts of backup on days your power is out, which should be enough to run refrigerators, lights, charge flashlights for nighttime etc.

However if you have a few gensets that all may be academic - you have backup power when you really need it, even at night. At that point anything else isn't going to be very cost effective unless you have very frequent outages (say more than 10% of the time.) Of course, if you want to do it anyway and you have the money, go for it.

mark

Re: battery-less Outback Radian

Greetings,
this sticky drove me to join, as this is the best and closest explanation to what I am trying to accomplish. I abbreviated your post and a added some questions/ect in red and would appreciate it if you or anyone would expand upon them.
As a back ground - I am designing a system. I have the genset/fuel tie in taken care of. I also happened into a number of UPS units and a large reserve of smaller capacity batts to power them (think about 2+ days of usage on each ups) as opposed to a battery bank. They supply power to the appliances they are dedicated to and float a charge to the batts until needed. I am interested in putting a system in place that will generate power to supplement/replace/put power back in the grid during regular operation and if the grid drops, allow for the panels to feed the house and/or also float charge all my UPS systems via automatic transfer switch.

BB. wrote: »

To make things a bit more complex. There are "hybrid AC Inverters" with battery banks that can work both as a GT inverter and pump "excess" charging current back into the grid, and if the grid fails, the inverter flips over to AC off grid mode and supplies power to local AC loads from the battery bank (and solar panels).

And even more complex, SMA has created a pure GT AC inverter (no batteries) that during the middle of a sunny day can supply ~1,200 watts to an auxiliary AC power outlet that can be used for emergency power during the middle of a sunny day. When the sun is not in the middle of the sky (or when clouds pass overhead), the aux AC power "goes away".
Can you provide the product name for this, I have spent about 30 minutes on their site to no avail. Thanks
It can be difficult/costly to "grow" a solar power system... If you are doing this for emergency/backup power, then I would do things in this order (as money becomes available)--assuming the end point is a hybrid AC system capable of GT and OG operation:

1. AC Hybrid Inverter .
2. Build out solar array (you can add solar panels in several stages).

And, with Grid Tied systems, your utility needs to allow GT solar systems (not all do)--And some utilities are overhauling their rate plans to "punish" GT solar folks and even those customers that work hard on conservation... I am in TX and dont think this is an issue, but will start looking...

Can you provide me with more information on automatic transfer panels that might allow me to power to the grid normally and switch to powering the house when the switch automatically flips and then back again when grid comes back up? (do I even have the concept correct?)
-Bill

Thanks in advance
Mark

BB.

Re: battery-less Outback Radian

Welcome to the Forum Mark,

This is what I know about the SMA backup AC power from a GT (battery less) AC inverter:

New SMA Inverters - Secure Power Supply

Transfer switches... There are manual switches which can be just a pair of circuit breakers with a "interlock" so only one can be turned on at a time.

There are manual transfer switches with manual selection on a "per branch circuit" application (if you have a small generator or AC inverter, only turn on those circuits you need at the time):

http://www.hardwarestore.com/transfer-switch-6-circuit-616871.aspx

And there are simple automatic transfer switches (basically, a relay that switches (with a relay) from grid power to backup generator (for example).

http://www.solar-electric.com/autrswandgea.html

You can AC inverters (really inverter-chargers) that can have several AC inputs (grid+Backup Generator) and will provide power to a "protected sub-panel". For example, when AC power fails, the inverter will disconnect from the grid and supply AC power to your loads... When the battery gets discharged, it will turn on the backup generator and share generator power with the loads and helping to recharge the battery bank.

There are quite a few inverter-charger systems with internal AC transfer switches (basically, a big UPS system with external battery bank and support for solar+backup generator power).

In general, if your AC power is reliable, it is usually cheaper and easier to go with a pure backup generator and use GT Solar to (hopefully) save money on your power bills.

If your AC power is unreliable, you can go with a full Hybrid AC inverter which can manage Grid Tied (feed power to grid)+Backup Genset+Solar... Will not "save you money" on your electric bills vs GT solar--But if you have long power outages (exceeding several weeks), it can be a very nice way to go.

-Bill

MarkC

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

Some hands on with the SMA Sunny Boy 4000 TL-US; The secure power supply (SPS) works well with my Club Car battery charger - 48 nominal volts (56 V actual during bulk) up to 15 amps. It appears the SPS will actually modulate and quickly click on/off (seconds) as clouds reduce the input wattage from the panels - strange but true. Tests of up to 1200-1300 watts with hair dryer work well. At 1800 watts, the SPS kicks off for the alloted minute or so. Of course, the more panels, the less likely to kick off during low light due to input watts, but I plan on testing with only 8 of my 280 monos some time in the future.

Question for BB;
Assuming grid failure and I have started a "Prius" type generator to power the off-grid sub-panel using a Smart UPS (6000 VA) with 240 volt split phase isolation transformer. What would happen if I fed the output of the SMA Sunny boy to the same sub-panel? (I am NOT going to haphazardly try this - purely hypothetical!!). Do you think the APC Smart UPS would "fool" the on-grid Sunny Boy into operating IF the 240 V load was assurred to be always above the Sunny Boy production? Do you think the APC Smart UPS/isolation transformer would stay on line or sense another power source and shut down? Again, just some musing about possibilities, but if there was a safe way to try this - hmmm - lots of possibilities with all the "bells and wistles" that both the SMA and the APC equipment have.

BB.

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

MarkC wrote: »

Question for BB;
Assuming grid failure and I have started a "Prius" type generator to power the off-grid sub-panel using a Smart UPS (6000 VA) with 240 volt split phase isolation transformer. What would happen if I fed the output of the SMA Sunny boy to the same sub-panel? (I am NOT going to haphazardly try this - purely hypothetical!!). Do you think the APC Smart UPS would "fool" the on-grid Sunny Boy into operating IF the 240 V load was assured to be always above the Sunny Boy production?

In theory, it seems like it should work. The Smart UPS is a Sine Wave unit. The Smart UPS is rated for "4200 Watts / 6000 VA" unit and the SMA configured for 4,000 Watts maximum--So that should be OK (running very near the Smart UPS maximum limit).

If you run the Smart UPS + SMA Sunny Boy directly together, and use it to power the L1/L2 on the APC. The APC probably has less than 4.2 kWatt rated output when running only 120 VAC single phase loads. But nothing unusual (the SMA should only be a 240 VAC single phase output as I recall).

There could be an issue with the Smart UPS--I have ran across some of the Computer UPS's from APC/etc. that require the center tap (neutral/earth) bond to turn on. Some can be manually turned on, but I am not sure what would happen with an outage.

Do you think the APC Smart UPS/isolation transformer would stay on line or sense another power source and shut down? Again, just some musing about possibilities, but if there was a safe way to try this - hmmm - lots of possibilities with all the "bells and whistles" that both the SMA and the APC equipment have.

It seems like it should work... Of course, there is the question about how the APC will function when back-fed energy from the SMA. Many Inverters appear to work OK (assuming you have taken care of how to prevent the battery bank from being overcharged by the SMA). In the end, you will probably just have to test it. Assuming that you can justify the cost of frying the APC (don't think it will fry--But you will have to do some experiments to see if the system is stable or not over various operating conditions).

Just guessing here--I do not have any specific knowledge about either product.

-Bill

MarkC

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

BB. wrote: »

If you run the Smart UPS + SMA Sunny Boy directly together, and use it to power the L1/L2 on the APC. The APC probably has less than 4.2 kWatt rated output when running only 120 VAC single phase loads. But nothing unusual (the SMA should only be a 240 VAC single phase output as I recall).

There could be an issue with the Smart UPS--I have ran across some of the Computer UPS's from APC/etc. that require the center tap (neutral/earth) bond to turn on. Some can be manually turned on, but I am not sure what would happen with an outage.

It seems like it should work... Of course, there is the question about how the APC will function when back-fed energy from the SMA. Many Inverters appear to work OK (assuming you have taken care of how to prevent the battery bank from being overcharged by the SMA). In the end, you will probably just have to test it. Assuming that you can justify the cost of frying the APC (don't think it will fry--But you will have to do some experiments to see if the system is stable or not over various operating conditions).

Just guessing here--I do not have any specific knowledge about either product.

-Bill

A slight clarification - The APC Smart UPS 6000 feeds a APC SURT 003 isolation transformer that has a center tap and therefor produces the 240 volt split phase to the sub-panel (off-grid only). The UPS 6000 makes 240 V single phase ( a configuration setting). This combination is my system "generator" for off-grid mode (with the Prius traction battery feeding the DC/AC inverter portion of the UPS 6000). The output of the SMA is also a split phase 240 with a neutral and ground and also feeds the same sub-panel in on-grid mode. Both systems units produce the 240 V split phase in their respective "mode".

So, if the outputs of both "systems" (only in off-grid mode of course) could be tied together (L1, L2, Grd, Neutral) and assurances that the SMA production would always be exceeded (by say a bulk battery charger), the result would be using both the "generator" and SMA Sunny Boy with all my PV panels in off grid mode.

Probably need a really good designer of both APC and SMA equipment to look into this or - as you say - risk frying the UPS 6000/SURT 003 or even maybe the SMA (likely it will just not work!).

Thanks for your opinion!
Mark

MarkC

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

An "unofficial" answer from SMA concerning feeding both a APC SURT 5000/6000/SURT003 (240 v split phase) AND the SMA sunny-boy into the same split phase sub-panel (off grid mode only);

Quote (sort of) "IF the 240 v spit phase wave forms/voltages are acceptable to the Sunny Boy, it will co-feed the subpanel with any other "grid" supplier of sufficient quality. However, if the solar panels/Sunny Boy exceeds the amperage requirements of the subpanel, it will try to "back-feed" the SURT/isolation transformer" (probably not good - hopefully one system or other would go down - likely both)

So assuming it is that "simple";
1. How to ensure power usage from the subpanel always exceeds the solar production? Bulk charger system that cuts off the Sunny Boy? Seems would work if loads where carefully assessed, battery storage quite large, likely careful phase load analysis also (240 v split phase bulk charger?).
2. Can the SURT system respond to constantly varying current supply from the Sunny Boy? Would it be similar to a highly variable load?- say switching an air conditioner off/on rapidly as an independent test run of the SURT?
3. On a late afternoon sun, the Sunny Boy production would be consistently low enough to set up a "dummy load" that would be mostly from the SURT system as a "test" of combined feed.

I understand this might be a risky proposition and such "tricking" on-grid inverters is very much frowned upon, but experience with these industrial type UPS's seems to open up new potentials - so to speak!

Cariboocoot

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

Short form: do not try to back-feed AC to any inverter that was not designed for this purpose, whether or not it is battery-based. Trying to jerry-rig some sort of regulation to prevent over-current is likely to fail, costing the life of at least the back-fed inverter. Just don't do it. Unless you like throwing away money. There are inverters designed to function this way. Use one of those instead.

Caveat finis.

eaboujaoudeh

BB. wrote: »

Re: battery-less Outback Radian (GT/Off Grid/Hybdrid Inverter options explained)

A Radian is a relatively, "huge", AC inverter... That is, at a minimum, an 8kWatt AC inverter. Using our "rules of thumbs" at 100 AH @ 48 volts per 1 kWatt of AC inverter output would give you a nominal 800 AH @ 48 volt battery bank.

-Bill

So given this analysis, is it like dangerous to connect a large PV system to a small battery bank? or just unrecommended?

For example, can i use 3 GVFX's for a 9 kW array and connect them to only 8 T105s? I can assign the allowable DOD of the batteries to 50%. Suppose i don't care if the load stays on or not. Is there an inherent danger in the system?

Thanks
-Elie

BB.

There are several issues around batteries... They have to be large enough capacity to supply the needed current to the loads. Some rough numbers for flooded cell lead acid batteries:

• C/20 -- 20 Hour discharge rate for typical off grid cabin design (5 hours for 2x nights plus 50% maximum discharge)
• C/8 -- Typical maximum sustained discharge rate (higher discharging current rate can overheat battery, not sustain loads over battery aging, batteries become "less efficient" during discharge--more waste heat)
• C/5 -- Typical short term sustained maximum discharge (minutes to hour or so)
• C/2.5 -- Typical maximum surge current (seconds to minutes -- Like starting a well pump)

On charging, more or less, higher than C/8 (~13% rate of charge), batteries can tend to overheat... Should have a remote temperature sensor to monitor battery temperature and control charging voltage (hot batteries need lower Absorb voltage).

C/5 (~20-25% rate of charge) is possible... For flooded cell batteries, heavy charging current is for when they are deeper discharged (say less than ~80% or so State of Charge)--Lead acid batteries are very efficient at charging at lower states of charge and not very efficient at heavy current charging at high states of charge (80-90% less efficient, >90% very inefficient).

Then there is the "ripple current" from a single phase AC inverter... The DC input current is a 120 Hz Sine Squared wave forum. If the battery is too small, then there can be issues with "micro cycling" during solar charging (i.e., 120x per second there would be a charge and discharge cycle --- I.e., battery is >12.7 volts for 1/2 cycle and <12.7 volts for the other 1/2 cycle).

For example--A relatively conservative design for an 8x 6 volt @ 220 AH battery bank would be ~2.2 kWatts of AC inverter and ~2.2 kWatts of solar array:

5% to 13% rate of charge for solar panels, take 10% nominal:

• 220 AH * 58 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 1,657 Watt solar array nominal

And an C/8 discharge rate for AC power:

• 220 AH * 48 volts * 0.85 AC inverter eff * 1/8 hour discharge rate = 1,122 Watt AC load for ~4 hours (bit less) for a "nominal" design
• 220 AH * 48 volts * 0.85 AC inverter eff * 1/2.5 hour discharge rate = 3,590 Watt maximum surge

And an C/20 discharge rate for AC power (5 hours per night, for 2x nights, with 50% maximum discharge for C/20 discharge rate)::

• 220 AH * 48 volts * 0.85 AC inverter eff * 1/20 hour discharge rate = 449 Watt AC load for ~5 hours a night for 2 nights (no sun/charging during day)

Assume an AC inverter can surge roughly 2x it rated power:

• 3,590 Watt maximum surge / 2 surge derating = 1,795 Watt estimated maximum AC inverter

Note--These are just quick design rules to get us "in the ball park" for estimating system designs. You can change the load profile, change assumptions, change battery types, etc. to support your needs if not a typical off grid cabin (charge during the day, run loads ~5 hours at night).

So--your 8x T105 flooded cell battery bank would (reliably) sustain ~3,590 Watts maximum for seconds to minutes... 9 kWatts, probably not.

Now--If you changed to AGM batteries from Concorde rated for C*4 maximum rate of discharge, in theory you could sustain:

• 220 AH * 48 volts * 4 discharge rate * 0.85 inverter eff = 35,904 Watts for ~10 minutes (in theory--I would confirm with battery engineer before I built system)

Look at how much current a 9 kWatt DC bus system would have to supply:

• 9,000 Watts * 1/0.85 inverter eff * 1/42 volts battery cutoff = 252 Amps @ 48 VDC bus

That is a lot of current to expect from a 220 AH flooded cell battery (bank). I would guess the battery voltage would collapse pretty shortly after the AC load was applied (and possibly melt battery terminals, etc.). -- Again guessing--This is not my area of expertise/experience.

Does any of this help answer your questions?

-Bill

RCinFLA

One other benefit of hybrid inverter:

Hybrid inverters synchronizes to AC grid or generator source.  Many have grid inputs and generator inputs.  Only one or other can be used at a time.

The additional benefit, which is great for generator option, is the hybrid inverter will manage the available generator power.  You can set the maximum current allowed to draw from the generator based on capabiliity of generator.

If your AC loads are less then gen capability then excess gen capabilility will be used to charge batteries if needed.  If your AC loads are greater then gen capability then short fall is made up by inverter/battery power.  The sum must be less then gen max plus inverter max power.

This allows a smaller generator to be supplimented which is a very useful feature.  A regular generator loaded less then about 25% of its rated power is less fuel efficient.  The inverter/battery power AC suppliment can make the difference for a heavy starting surge current, like pumps and air conditioners.

On negative side,  I am not a fan of using a hybrid inverter in place of PV GT inverter for normal grid power suppliment.  It is more stressful on batteries to use it in this manner, shortening their longevity.  You will likely lose money for more often battery replacement cost then you saved on utility electric cost.

If you want battery backup power and PV GT suppliment then get a battery based hybrid inverter that has AC coupling.  Use a regular PV GT inverter to do the day to day PV GT power supplimentation.  GT inverters are not that expensive.

jemsol

I have in trouble, I have banana and Cotton irrigation farm land which is pumped by 6 *120kw pumps at three sites two pump each. My input power
1. 250kw solar 300kw diesel generator with two 160kw Siemens hybrid VFD (DC + AC) input at all three Pump stations.
But mistakenly we bought 5*50kw GTI inverters for all three sites. We are off-grid no main power for the next 5 years. But I have to use these GTI..... Advice me how.
Could I connect the GTI to a VFD via AC input to fool GTI by using some of my solar string? and Some are via DC Port!
Please help me.

BB.

I am guessing you are somewhere in/around Ethopia?

I am certainly no expert in solar+large pumping projects... Guessing you are presently using 3 phase 160 kWatt VFDs (variable frequency drives). These are basically Variable frequency AC inverters. This drives a (large) 3 phase pump. The VFD provides both "soft start" (the inverter starts at "low frequency" and slowly brings the motor up to speed). And VFDs also let you run the pumps at less than maximum RPM (reduce water flow/reduced pressure).

In the last decade or so, VFDs have been interfaced with solar panels. Solar panels are connected to the power input of the VFD, and the VFD is programmed to run the pump as normal, plus monitor the solar input voltage/power--And can run the pump slower in the morning and faster around noontime in full sun.

Since I am not in the business... I really cannot give you suppliers' names and available systems. Where you purchased your VFDs would be a good place to start.

The difference between a standard AC input VFD like you have (AC 3 phase power in, VFD power out) vs solar (high voltage DC power in, VFD power out) is not that much different--And there are many places that market these devices (India, China, Europe) and I am sure they sell to Africa/Middle East, etc.

That would probably be your first step in researching the issue.

There could be a "helpful" option of connecting your GTI to the Diesel Genset AC output. The big question there is for your Genset Company/Designers/Engineers. In theory, GTI to Diesel AC output--The solar will "assist" the genset's AC output and can reduce fuel usage (always a good thing).

The problem is integrating the Solar GTI inverters with the Genset. It can be pretty easy to damage/smoke the genset alternator if the GTI output exceeds the Pump loading--Alternators don't really like power being fed back to them (GTI 150 kWatt, and pump 120 kWatt, 30 kWatt going back "into genset").

While almost anything can be done (from an engineering point of view)--It may not be cheap (lots of engineering, lots of control equipment, safety equipment, and such).

Anyway--From my perspective, I would look for Solar input VFDs and see if you can find what you need (for the right price). It could be your lowest cost/most efficient solution. However, you would have to have a pumping system that can manage variable speed pumps (i.e., lower RPM in morning/evening, full RPM middle of day, and impaired operations during cloudy weather).

Guessing in the region of Addis Ababa, a fixed solar array will see (hours of sun per day):

http://www.solarelectricityhandbook.com/solar-irradiance.html

Addis Ababa
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 81° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
7.18	7.11	6.43	6.08	6.32	5.87
Jul	Aug	Sep	Oct	Nov	Dec
5.08	4.95	5.56	6.68	7.19	7.27

That is an impressive amount of sun year round... Typically >3 hours of sun per day is "not bad". And >5 hours of sun per day is very nice to have.

-Bill

BB.

Locking thread. Jemsol, please keep your discussion here:

https://forum.solar-electric.com/discussion/357459/grid-tie-inverter-connection-to-vfd-ac-input-without-grid-voltage#latest

-Bill "moderator" B.