SMA Sunny boy + Sunny Island help?

[redline0316]

Semi-new to solar and looking for some advice! (Had a Sunpower grid-tie lease, but now looking to do something more complicated)

I would like to install a 10+kw sunny boy system + a sunny island setup for load shedding and power outages.

I've got 1,000 sq ft of non-shaded flat roof, which per the pvwatts page says 12kw using 15% efficiency panels. Should I put all of these panels on a single large sunny boy, or should I split them on to two inverters?

I've also allocated space for a pair of sunny islands + batteries, however, is it possible to program them to load shed on a grid tied system during say 12PM-9PM? During a power outage I would also need it to become an island for critical loads.

Thanks in advance!

[inetdog]

Semi-new to solar and looking for some advice! (Had a Sunpower grid-tie lease, but now looking to do something more complicated)

I would like to install a 10+kw sunny boy system + a sunny island setup for load shedding and power outages.

I've got 1,000 sq ft of non-shaded flat roof, which per the pvwatts page says 12kw using 15% efficiency panels. Should I put all of these panels on a single large sunny boy, or should I split them on to two inverters?

I've also allocated space for a pair of sunny islands + batteries, however, is it possible to program them to load shed on a grid tied system during say 12PM-9PM? During a power outage I would also need it to become an island for critical loads.

Thanks in advance!

One limitation that you have to keep in mind is that you CANNOT in general connect two different MPPT devices to one string of panels. They will compete for sensing the voltage versus current curve and will mess each others MPP determination up.
So you will either have to incorporate switching to move some panels back and forth between the input of the SB and the input of the SI or do a fixed allocation of some panels to one or the other.

A 12kW inverter is pretty large for residential use, but would probably be less expensive than two 6kW.
Do you have any partial shading issues which would require two or more MPPT inputs? You cannot, AFAIK, get more than two MPPT inputs on one SB.

The SI by itself cannot be connected to your AC system while the grid is also connected. If you want to be able to produce standalone AC and also supplement the grid from battery or sell power back to POCO from the same off grid inverter, you will need to use a hybrid inverter such as some from Xantrex, or simply turn off the SI and switch the panels to the SBs.

[redline0316]

One limitation that you have to keep in mind is that you CANNOT in general connect two different MPPT devices to one string of panels. They will compete for sensing the voltage versus current curve and will mess each others MPP determination up.
So you will either have to incorporate switching to move some panels back and forth between the input of the SB and the input of the SI or do a fixed allocation of some panels to one or the other.

A 12kW inverter is pretty large for residential use, but would probably be less expensive than two 6kW.
Do you have any partial shading issues which would require two or more MPPT inputs? You cannot, AFAIK, get more than two MPPT inputs on one SB.

The SI by itself cannot be connected to your AC system while the grid is also connected. If you want to be able to produce standalone AC and also supplement the grid from battery or sell power back to POCO from the same off grid inverter, you will need to use a hybrid inverter such as some from Xantrex, or simply turn off the SI and switch the panels to the SBs.

There's no partial shading issues, I was just wondering if there was any advantage to smaller strings, etc. Thinking of going with 48 panel arrangement (7 rows of 7 columns). I will have to tilt, so not sure how to best lay them out for ease of wiring.

I thought in the SI diagram below, it has a load shed relay...wouldn't that mean the SI could supplement the grid from battery?

[inetdog]

I thought in the SI diagram below, it has a load shed relay...wouldn't that mean the SI could supplement the grid from battery?

No, it just means that the SB can drop non-critical loads when it does not have enough output capacity (along with SB and WB) to keep the voltage up to the identified critical loads.

[sulfur]

One limitation that you have to keep in mind is that you CANNOT in general connect two different MPPT devices to one string of panels. They will compete for sensing the voltage versus current curve and will mess each others MPP determination up.
So you will either have to incorporate switching to move some panels back and forth between the input of the SB and the input of the SI or do a fixed allocation of some panels to one or the other.

A 12kW inverter is pretty large for residential use, but would probably be less expensive than two 6kW.
Do you have any partial shading issues which would require two or more MPPT inputs? You cannot, AFAIK, get more than two MPPT inputs on one SB.

The SI by itself cannot be connected to your AC system while the grid is also connected. If you want to be able to produce standalone AC and also supplement the grid from battery or sell power back to POCO from the same off grid inverter, you will need to use a hybrid inverter such as some from Xantrex, or simply turn off the SI and switch the panels to the SBs.

SMA has a good software available online for string sizing, try it out to figure what size inverter and panel quantities work best for your ideal size solar system. 12kw is very practical if you have a descent net metering program available and you use that much power, which is likely. Your proposed SI and SB setup is more efficient than hybrid system and less stressful to batteries, but is a little more expensive than some hybrids, I use similar setup. SI is a battery charger and 120VAC inverter that will make SB sense the grid is present when it is not. I would not recommend depleting battery power to sell back to grid in any system(but inet was correct that SI can not do this), the wear on batteries would likely cost more than the premium time of day kwh that folks are trying to save?

The SI is normally always connected to the grid, when grid is present, it is using it for its battery charger. The SI inverter will not turn on until the the grid goes down, then the SI begins to produce 120VAC and allows the SB to turn back on(if using step up transformer or 2 SI). There is no instance I know of when someone would "switch the panels to SBs", are you talking about solar panels or load breaker panels? Solar panels are always only feeding SB's?

I only use the SI in an off grid setup utilizing a 200 amp transfer switch, the benefit is that the SB power does not have to pass through the SI. Allows for larger solar system, but is not as automatic. This way SB can produce very efficient grid tied net metered power and SB can also run in off grid situation feeding house and charging SI batteries. SB disconnects itself when grid goes down and SI inverter can't touch grid due to transfer switch.