Sunny Boy 3000 US and 3 phase residential

m4v3rick

Hello,

I have an uncommon residential 3 phase installation on the way (L1,L2,L3,N coming from grid to a three pole breaker on the main distribution panel). Since this is a relatively small installation I thinking in the sunny boy 3000 (http://www.sma-america.com/en_US/products/grid-tied-inverters/sunny-boy/sunny-boy-3000-us-3800-us-4000-us.html) as it says it supports 208VAC, but I'm confused about how to handle L3 since it will only output L1, L2 and N..

Has anyone faced this? 3phase with sunny boy (or Fronius) that only output 2 phase? How should the load balancing be done? The utility has penalties if the lines are not balanced. Do I need a transformer and If I do, will it affect the generation?

Thanks!

BB.

Re: Sunny Boy 3000 US and 3 phase residential

What is it you are trying to do?

Just Grid Tied inverter feeding power into your mains (and back feeding the utility/turning the meter backwards when there is enough sun)?

Or are you trying for backup AC power when the utility fails (too)?

-Bill

m4v3rick

Re: Sunny Boy 3000 US and 3 phase residential

This will be a grid tied installation with a NET meter. No need to backup AC power

Cariboocoot

Re: Sunny Boy 3000 US and 3 phase residential

I believe SMA's support of 208 Volt 3-phase is that a Sunny Boy can be connected from L to N on 'Y' configuration. As such the best case is one per leg, providing all have array pointing in the same direction to try and keep the back-feed to the legs balanced. Although you can connect one to a single leg, which would be especially advantageous if that leg had more load on it during daylight hours.

If you want to be precise on the connection, contact SMA. No one knows their inverters better than they do!

3-phase is highly unusual for residential installs. Don't take it wrong but this is not a power source that should be dealt with by anyone not already experienced with it; it doesn't behave the way standard 240 VAC split-phase does.

BTW, there's really no such thing as "2-phase" power these days. We only have single, split, and 3-phase (probably some rare exception somewhere in the world, but not worth bothering about).

BB.

Re: Sunny Boy 3000 US and 3 phase residential

Then, basically you would connect the GT inverter as a "single phase" to feed back power... You only need all three phases back fed to the utility if you have a large solar array.

You need to talk to your utility and/or a knowledgeable local installer. Your utility probably has limits about how "unbalanced" your back feed can be (i.e., if one leg exceeds something like 3-10 kWatts, you then need to spread the power out to other phases).

This can simply be done by taking (for example) three times 3 kW GT inverters would give you 9 kWatts of back feed to the utility. (a typical GT inverter should be programmable for 208 vs 240 VAC output--another question to ask too... There can be issues over neutral connections and delta connected 3 phase power--vs 208 Wye three phase power).

And then, there may be other rules too... The GT inverters themselves (if single phase) do not care if it is 1, 2, or 3 phase connections. Each GT inverter only "sees" one phase and acts on that one phase. However, a utility may have a requirement that multi-phase generators (probably written for hospital/large building backup gensets) must turn off is one or more phases fail. So--There may be some additional requirements for shutting down all two or three GT inverters if there is a phase failure from the utility (this may be done by the GT inverters themselves, or could be done with an external 3 phase protection relay setup).

-Bill

m4v3rick

Re: Sunny Boy 3000 US and 3 phase residential

Thanks BB and Cariboocoot. I have done this before with the Enphase microinverters, we simply switch to the 208 vac cable and the microinverters "balance" between L1, L2 and L3, but with 15+ panels the single inverter is the best cost effective solution. However, unless I get three inverters (single phase) I might not feel comfortable (because of the possible "unbalanced" issue) and if I really need 3 sunny boys then we are back to microinverters

I will be contacting the utility today since I know they do have penalties when exceeding more than 10kW on one leg, but I'm not sure if this applies to back feeding too. I think I will contact SMA too just to be on the safe side. I have seen that their 10k+ GT inverters DO have 3 phase output (probably because they know it will be commercial).

I might also ask around with another installers since this customer was told (by other installers) that a single SB3000 is capable of doing the work (they might not be aware of the 3 phase connection?).

Thanks!

BB.

Re: Sunny Boy 3000 US and 3 phase residential

m4v3rick wrote: »

Thanks BB and Cariboocoot. I have done this before with the Enphase microinverters, we simply switch to the 208 vac cable and the microinverters "balance" between L1, L2 and L3, but with 15+ panels the single inverter is the best cost effective solution. However, unless I get three inverters (single phase) I might not feel comfortable (because of the possible "unbalanced" issue) and if I really need 3 sunny boys then we are back to microinverters

I would guess that the Enphase wiring+Inverters don't balance between the phases--It is just the first inverter connects to Phase A, the second to Phase B, third to Phase C--Rinse, repeat.

You don't really need to worry about the unbalanced issues--It is for the utility to be concerned (as long as you meet all of the other requirements).

I will be contacting the utility today since I know they do have penalties when exceeding more than 10kW on one leg, but I'm not sure if this applies to back feeding too. I think I will contact SMA too just to be on the safe side. I have seen that their 10k+ GT inverters DO have 3 phase output (probably because they know it will be commercial).

I would be 99.99999% sure that the utility will apply the same 10kW unbalance limitations with solar GT as to the loads (even if it does not state so in their rate rules).

You could get into a situation where a failure (or simple unbalance) on your 3 phase loads with a single phase GT inverter installation:

Say you have 3x 5 kWH heaters, one on each leg. And one heater fails or cycles off. Now you have 5 kW load on two legs, and if you have an 8 kW GT inverter/array on the "off" heater leg--You have a 13 kW difference (8 kW to grid on one leg, and 5 kW to loads on other legs = 13 kW difference).

If the meter can report the "violation"--Then I would be very careful and I would tend towards a three phase GT inverter installation even for a smaller 5 kW array (it all depends on your loads and how they behave--If there are a lot of 3 phase loads, then a shutdown/failure will not cause unbalance. If the heavy loads are single phase, then power cycling can cause the unbalance when added to a single phase GT inverter)...

I might also ask around with another installers since this customer was told (by other installers) that a single SB3000 is capable of doing the work (they might not be aware of the 3 phase connection?).

Why SMA? What was the proposed size of the array (3x3 kW, 1x3kW or what)?

It is possible that a micro inverter (such as Enphase) may be your best solution for the 1-10 kW array. If your array will be >10 kW, then a larger 3 phase capable GT inverter or 3x single phase inverter (with three separate arrays) will be the better answer.

Interesting project and home (with 3 phase power in the US). I am not sure we can get 3 phase to a home legally (at least in the major cities--I wonder if code prohibits to prevent "home businesses").

-Bill

m4v3rick

Re: Sunny Boy 3000 US and 3 phase residential

BB. wrote: »

I would guess that the Enphase wiring+Inverters don't balance between the phases--It is just the first inverter connects to Phase A, the second to Phase B, third to Phase C--Rinse, repeat.
You don't really need to worry about the unbalanced issues--It is for the utility to be concerned (as long as you meet all of the other requirements).

Indeed this is the way they do it, the official explanation is "three phase cabling balances the phases by rotating conductor use from one microinverter to the next".

If the meter can report the "violation"--Then I would be very careful and I would tend towards a three phase GT inverter installation even for a smaller 5 kW array (it all depends on your loads and how they behave--If there are a lot of 3 phase loads, then a shutdown/failure will not cause unbalance. If the heavy loads are single phase, then power cycling can cause the unbalance when added to a single phase GT inverter)...

I am sure they can somehow spot the differences on the legs (since I have been warned on penalties about this). That's why I feel uncomfortable using just one inverter

Why SMA? What was the proposed size of the array (3x3 kW, 1x3kW or what)?

The proposed size of the array as 1x3kW ( probably even 16 modules, two strings of 8 ). It is a small installation, maybe you are right and the microinverters might be the best option for this.

This home is unusual but I have seen at least two like these this month! Thanks for all your guidance.

BB.

Re: Sunny Boy 3000 US and 3 phase residential

Just out of curiosity, is this a 3 phase 120/208 Wye or a 120/240 Delta connected home?

And what are the loads--Large heat pump installation?

By the way, in California, installing a "small" grid tied system on a home that has large monthly bills can actually increase the monthly charges...

Basically, here we have to change to Time of Use metering... And if the home uses large amounts of power on summer afternoons, the TOU billing plan can dramatically increase the bill if the solar system is not enough to "zero out" the daily summer billing cycle.

-Bill

m4v3rick

Re: Sunny Boy 3000 US and 3 phase residential

I am not 100% sure but I think this is a 208WYE (I saw 3pole breakers on the distribution panel, a major AC unit for the first floor and some 220v A/C units for the top floor). I am guessing the big AC unit requires the 208 WYE?

Also, I am not sure I'm getting your TOU billing plan? Here in Mexico city we only have a basic net metering plan, you pay for the kWh you use from the grid and the extra kWh you export back to the grid is "deducted" from the next month bill (possible up to 12 months), so I'm not following how this can increase the monthly charges.

Thanks!

BB.

Re: Sunny Boy 3000 US and 3 phase residential

For example... Summer TOU billing is between $0.30-$0.50 or more per kWH. While "flat rate" billing is around $0.13 to $0.35 per kWH.

So, if somebody has heavy summer A/C loads (heavy in our area is around >900 kWH per month at top rates)--They can pay almost 2x as much for summer afternoon electricity.

If they went to Grid Tied Solar, the utility forces (per state PUC) into a Time of Use plan. And if the solar array is smaller than the afternoon loads--The home owner can end up paying a higher rate per kWH ($0.35 vs $0.50 per kHW worst case) during hot summer (week day) afternoon.

This happened to quite a few people--They installed a "small" solar GT system to see how it worked--And then got hit with a higher utility bill because of the rate change.

Also, for business and government buildings, they also found that solar power can drive up their billing too... In California, we have a very complex commercial set of rate plans. More or less, 1/2 the bill is based on per kWH charges, and the 1/2 of the bill is based on the peak 15 minute power flow (loads or generation).

Usually, a solar GT power system is setup to supply a peak feed into the utility at ~4x the average load of the building. For commercial users, this 15 minute peak is used to set the "reservation charges" part of the bill--And can take that ~1/2 monthly fixed fee and double or quadruple it--Even if the per kWH billing is reduced to near zero (or even credits).

A couple of News Articles...

For larger commercial customers (and agricultural users), it takes utility bill engineer (not joking) to figure out all of the possible permutations/options and decide how much or even if solar will save or cost the customer money.

-Bill

m4v3rick

Re: Sunny Boy 3000 US and 3 phase residential

Wow.. this sounds really complex, here in Mexico we only have heavy load rates (it is called high consumption rate) it kicks in when you use more than 10,200kWh a year (it varies from state to state)... and you have to pay $0.3usd per kWh (vs the regular rate of $0.079 and even $0.04usd per kwh).

Also I have confirmed that this home is using a 208/230 major AC unit (208WYE I assume). Then we will go for the microinverters instead. Thanks!!

ggunn

Re: Sunny Boy 3000 US and 3 phase residential

m4v3rick wrote: »

Hello,

I have an uncommon residential 3 phase installation on the way (L1,L2,L3,N coming from grid to a three pole breaker on the main distribution panel). Since this is a relatively small installation I thinking in the sunny boy 3000 (http://www.sma-america.com/en_US/products/grid-tied-inverters/sunny-boy/sunny-boy-3000-us-3800-us-4000-us.html) as it says it supports 208VAC, but I'm confused about how to handle L3 since it will only output L1, L2 and N..

Has anyone faced this? 3phase with sunny boy (or Fronius) that only output 2 phase? How should the load balancing be done? The utility has penalties if the lines are not balanced. Do I need a transformer and If I do, will it affect the generation?

Thanks!

It's simple. Set the internal jumper to 208V and connect L1 and L2 to two phases of the service. I'm pretty sure you can use the neutral or not depending on the other jumper. It's in the manual or SMA tech support is 916 625 3552.

m4v3rick

Re: Sunny Boy 3000 US and 3 phase residential

Yes, I know the SunnyBoy can be set to 208V but I am not sure of connecting it just to L1 and L2, what happens to L3 then? How would this keep L3 balanced against L1 and L2?

BB.

Re: Sunny Boy 3000 US and 3 phase residential

One single phase inverter will only power one phase... You would need 3x single phase inverters to power all three phases (whether this is L1 to L2, or L1 to neutral, Delta or Wye).

Or, a single three phase inverter.

Note that if you have multiple single phase inverters, usually you will need one independent solar array per inverter. Normally, you cannot connect one array to multiple MPPT input type inverters (or solar charge controllers).

-Bill

Cariboocoot

Re: Sunny Boy 3000 US and 3 phase residential

There's a matter of percentage to be considered. Usually the output of a single 3kW inverter on one leg or two of a 3-phase system represents an insignificant imbalance to the whole so it isn't an issue if there's no feed on one or two others. This is especially true if the feed is to a leg with the majority of lower-power loads on it (although they usually try to spread them out as a matter of course).

m4v3rick

Re: Sunny Boy 3000 US and 3 phase residential

Ok this takes me back to square one again and I'm confused.. so the SB3000 says it has 1 Phase conductors and 2 connection phases ( L1 and L2 ) and it says that depending on the voltage and the phase angle between L1-N and L2-N, the inverter determines whether it is connected to a 208 V or 240 V power distribution grid. Also you say that the balance might be insignificant. Is this enough to avoid having unbalanced issues?

Here is the situation, I know at least L1 and L2 are being used by two 220V A/C units, you suggest just feeding those lines from the GT inverter?

Cariboocoot

Re: Sunny Boy 3000 US and 3 phase residential

Details again. Delta or 'Y' configuration? This is why the SMA can do either: Delta would be 240 VAC across two poles, 208 Volt should be 'Y'.

Running a 220 VAC motor from 208 Volts - transformer involved or letting the motor suffer? If it were two poles of a Delta config it would make more sense.

How unbalanced the legs are will be a matter of the service size vs. the loads applied. If there is already a "significantly greater" load on one leg than the others then adding the inverter to that leg will help even things up as far as the utility is concerned.

It has been a long time since I had to deal with any 3-phase systems, and they were all quite large services on the magnitude of 6-10 times what a typical household uses. As such 3kW on any leg of one of those systems would be like a single lamp to an average service; hardly noticeable.

m4v3rick

Re: Sunny Boy 3000 US and 3 phase residential

Well, they are using a major A/C unit 208-230/1/60 (Volts/Ph/Hz) so this should be a 'Y'. I will try to get more info.. but well it seems I might give a shot to the sunny boy inverter.

BB.

Re: Sunny Boy 3000 US and 3 phase residential

In your case, the A/C is single phase and can take either 208 vac (which is Wye) or 240 (which is Delta). Both are Line to Line voltages.

If the A/C was 120 VAC, then it would Line to Neutral (of some sort--there is more issues with 120 vac on Delta).

And, it really does not matter, from your point of view, if the SB is on the same Lx to Ly as the A/C or not... The billing/metering/power sharing is all fine.

From the power company and "balancing" point of view, if you were forced to do single phase, then putting the SB on the same phase of the heaviest load should help prevent getting too far out of balance (and costing the penalty).

As far as the GT Inverter is concerned, it just needs to be told that this is a 208 or 240 VAC nominal connection (for new AC GT inverters, there is a requirement that they monitor the "neutral" voltage and, if out of spec., then the GT inverter is supposed to shut down. Regarding 240 Delta, there is usually only one set of phase wires==such as L1 to L2==that have an associated neutral on 3 phase delta).

But, confirm all of this--I am getting a bit in the deep end regarding 3 phase power. There are sometimes regional and local differences in what is available/standard service from a utility--And sometimes they can do thing like open Delta service (two transformers on a three phase service). This is not something that can be defined over the Internet (by me ).

-Bill

inetdog

Re: Sunny Boy 3000 US and 3 phase residential

m4v3rick wrote: »

Yes, I know the SunnyBoy can be set to 208V but I am not sure of connecting it just to L1 and L2, what happens to L3 then? How would this keep L3 balanced against L1 and L2?

With a grid tied inverter you do not have to worry about balancing the phase current. That will be done by default by the load drawing more or less current from the utility connection to make up the difference in solar contribution. As others have said, the only questions are:
1. Does the utility care about the amount of unbalanced load this will create? and
2. Will the unbalance be so great that you will have a voltage difference problem even if the utility does not care?

m4v3rick

Re: Sunny Boy 3000 US and 3 phase residential

inetdog wrote: »

1. Does the utility care about the amount of unbalanced load this will create?

The utility maximum allowed difference is 5% on the phases (watts). I know they might have penalties if this is not followed but not really sure how they can spot them.

2. Will the unbalance be so great that you will have a voltage difference problem even if the utility does not care?

The planned output is a 3.75kWp so If I just feed L1 and L2 I would assume that L3 will continue dragging power from the grid while L1 and L2 are not (at least during sunlight), then creating a difference. But this is just what I think.

Also this arises another question. If I just feed L1 and L2 I assume I would just need a two pole breaker on the main distribution panel then or a 3 pole with just L1,L2 and N connected?

Thanks!

BB.

Re: Sunny Boy 3000 US and 3 phase residential

I just want make sure a couple of things are clear (I am not sure how much experience you have with three phase power)...

First, L1-L2 are not "two phases", but represent a single phase (think of three transformers connected either in a triangle "Delta" shape--with L1/L2/L3 at the three corners vs Y "Wye" shape with L1/L2/L3 at the point of each leg of the "Y" with a neutral connected to the center of the "Y"). The other two phases are L2-L3 and L3-L1 (if connecting across the hots):

http://en.wikipedia.org/wiki/Three-phase_electric_power

Note that 3 phase power is a very complex subject (simple single phase AC power is not a piece of cake either). I took some classes in power engineering many decades ago, and just learned enough to know that I know nothing about 3 phase power.

This even goes back as far as the Wars of Current between Edison and Tesla. Edison knew DC power and the electrical principles behind DC which are pretty straight forward. Tesla was a math wiz--Which provided him with great insight into how and why AC would be better for larger distribution systems and how to implement such a system.

There is a huge amount of history/engineering/science behind why utilities wire their systems the way they do (delta/wye/etc.)... Basically, for your system/needs, the power levels are "low enough" that the utility may not really "care" about your exact configuration.

But if your system grows--The will care a lot.

I am kind of curious... What is it that you folks wish to study? The load/GT Inverter interaction is pretty well worked out to the first approximation. And it sounds like your setup is not really setup to research the second level problems with Solar GT power (power factor issues, circulating currents, delta vs wye vs open delta, remote control of inverters by the utility (power, power factor, voltage, two way communications, etc.)...

-Bill

ggunn

Re: Sunny Boy 3000 US and 3 phase residential

m4v3rick wrote: »

Yes, I know the SunnyBoy can be set to 208V but I am not sure of connecting it just to L1 and L2, what happens to L3 then? How would this keep L3 balanced against L1 and L2?

With an inverter this small you most likely won't have to worry about balancing. A three phase 208V wye supply to a building is never really balanced anyway since most of the loads are on single phases. The balance (or lack of it) changes every time you turn something on or off.