Sunny Boy 3000 US and 3 phase residential

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

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

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

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

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

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