Grid tied solar system.

[bcroe]

A conventional freezer or refrigerator compressor does have a significant starting
surge, and the SMA SPS does not really have surge capability.

If you have a soft starting inverter type compressor (not found in standard units) then you might get away with it. But rather than deliver max current and drop the voltage to match the SPS will simply shut down on overload.

That is a shame, because the top items I'd like to back are the fridge in summer, and the furnace blower
in winter. Both are motors with starting surges. Maybe the feature could be offered with a super cap on
the panel side for the surge, and a big surge capability in the DC to AC conversion. Bruce Roe

[posplayr]

EDIT: 7/13/2015: Rather than just remove this post, I will detail what is wrong with it in case someone is asking about something similar.

First the transfer switch in this diagram probably has no practical way of providing an interlock between GRID power and the internal (solar, generator) power sources and so it is in violation the NEC.


This is what I have been thinking about for a relatively low cost contingency stay alive system for 30-45 days.

The idea if for a Grid tied 10 Kilowatt system using SunnyBoy TL inverters and Secure Power Supply (SPS) 1500 watt outputs. I would split the 36 panel array into two separate 5 Kwatt systems of 2 each strings of 9.

In order to bolster the SPS surge capacity I would use 3KWatt UPSs with some LA 48V battery combination for the main part of the day.
There would be two SPS ports each with 1500 watts. I could back feed the breaker as if it was 240 although the phasing will be random. It would not matter it would still provide 120V loads just not any 240 V loads which would overwhelm the system anyway. It would be rated at 2x12=24 amps @ 120V

If all else fails and it is too hot then the 7Kw Generator can be kicked in for a few hours morning and evening.

After turning off the generator, and you turn in for the evening. The UPS would putter along on subsistence loads. Either size the batteries to keep the refrigerators going at nite or shut all down except for LED lighting.

When this setup is not in contingency mode the UPS batteries remain topped off as the are plugged into one of the house 120V outlets and are only plugged into the SPS 120V solar when in that mode.

[SunEagle]

This is what I have been thinking about for a relatively low cost contingency stay alive system for 30-45 days.

The idea if for a Grid tied 10 Kilowatt system using SunnyBoy TL inverters and Secure Power Supply (SPS) 1500 watt outputs. I would split the 36 panel array into two separate 5 Kwatt systems of 2 each strings of 9.

In order to bolster the SPS surge capacity I would use 3KWatt UPSs with some LA 48V battery combination for the main part of the day.
There would be two SPS ports each with 1500 watts. I could back feed the breaker as if it was 240 although the phasing will be random. It would not matter it would still provide 120V loads just not any 240 V loads which would overwhelm the system anyway. It would be rated at 2x12=24 amps @ 120V

If all else fails and it is too hot then the 7Kw Generator can be kicked in for a few hours morning and evening.

After turning off the generator, and you turn in for the evening. The UPS would putter along on subsistence loads. Either size the batteries to keep the refrigerators going at nite or shut all down except for LED lighting.

When this setup is not in contingency mode the UPS batteries remain topped off as the are plugged into one of the house 120V outlets and are only plugged into the SPS 120V solar when in that mode.

I would not rely on getting the full 3kw from SPS from 10AM to 6PM. Maybe if there are no clouds and it is Summer you might get that for 5 to 6 hours but not 8.

[bcroe]

I would not rely on getting the full 3kw from SPS from 10AM to 6PM. Maybe if there are no clouds and it is Summer you might get that for 5 to 6 hours but not 8.

Assuming you work out the other issues, I would expect your solar power availability to be centered around
solar noon. Only a couple hours are going to give max power. Since you have gone to so much trouble
already, you could widen that a lot by adding some east facing and west facing solar panels. This is the
power curve that provides here. Bruce Roe

[posplayr]

I would not rely on getting the full 3kw from SPS from 10AM to 6PM. Maybe if there are no clouds and it is Summer you might get that for 5 to 6 hours but not 8.

Well that is the stressing case, however you overlooked that this is Tucson and I would have a tracker with 45 degree tilt capability.

Further, perhaps the diagrams are confusing, but there is no reliance on the SPS. The Gen set provides for a flexible switch over capability.

[posplayr]

This is the PVwatts output. Based on a 50% probability I get 12 and 10.5 hours of 3K watt SPS daily for June and July respectively. We have had relatively cloudy monsoonal weather for most of July.

[SunEagle]

Well that is the stressing case, however you overlooked that this is Tucson and I would have a tracker with 45 degree tilt capability.

Further, perhaps the diagrams are confusing, but there is no reliance on the SPS. The Gen set provides for a flexible switch over capability.

I understand your design. The gen set is the main power source until the sun comes up to do it's job. And you are correct being in Tucson you have a much better chance of long cloudless days.

I just didn't want others the think that they could "always" get 8 full hours of the full 3kw output of those SPS inverters.

One last shortcoming of the SPS is that I do not believe it will automatically start to produce power if the grid goes down. I believe you have to manually initiate the sequence to go from grid production to emergency production and then back again.

[posplayr]

I understand your design. The gen set is the main power source until the sun comes up to do it's job. And you are correct being in Tucson you have a much better chance of long cloudless days.

I just didn't want others the think that they could "always" get 8 full hours of the full 3kw output of those SPS inverters.

One last shortcoming of the SPS is that I do not believe it will automatically start to produce power if the grid goes down. I believe you have to manually initiate the sequence to go from grid production to emergency production and then back again.

In Tucson , you don't need an alarm to tell you the AC is off even at 9:00 am. As stated this is contingency only.

Dec 8.5 hours

[inetdog]

Since the SPS is designed for off-grid operation, it is not designed to synchronize to any other power sources. I do not think that you can parallel two SPS to get increased output. More likely both of them would shut down.
Unlike the SunnyIsland line, there is no provision for linking or synchronizing the SB inverters, since they are assumed to be synchronized to the power grid.
For the same reason, the SPS will not play together with a generator, except through a transfer switch.

Your only option that I know of would be to put a dual conversion UPS on the output of the SPS and use that to cover the surge.

[inetdog]

One last shortcoming of the SPS is that I do not believe it will automatically start to produce power if the grid goes down. I believe you have to manually initiate the sequence to go from grid production to emergency production and then back again.

Absolutely right. The only autostart is that once SPS mode has been initiated, an overload will trip the SPS off but it will try to restart after an interval (I believe 5 minutes) on the assumption that the insolation may be better or the surge load may not be present. There is no limit to the number of such restarts.

Turning the SPS switch off sets the unit up to validate a grid input when one becomes available and then enter GTI operation.

But it would not be difficult to wire up a relay to auto-start the SPS after a short delay whenever the grid goes down.
Note that you will also need a transfer switch to move the protected load from the grid connection to the SPS connection. And for a compressor load, that interruption while the SPS is staring up is almost certain to trigger a restart under pressure rather than just a normal starting surge. The five minute dead time should allow the pressure to bleed down before the SPS restarts.

[posplayr]

EDIT 7/13/2015: Rather than just remove this post, I will detail what is wrong with it in case someone is asking about something similar.

First the transfer switch in this diagram probably has no practical way of providing an interlock between GRID power and the internal (solar, generator) power sources and so it is in violation the NEC.

The Grid Tied Inverter is of a special sort that with what is called "grid interactive" interface. What that means is that the GTI has to push current to the grid by just riding above grid voltage even through that grid voltage is moving up and down as the GTI meanders around with near and far load variations. This means that the GTI does not regulate on voltage but instead on current; it pushes as much current as the collected power from the solar and the grid voltage will allow.

If you hook this GTI up by faking it out that there is a Grid, you will have to do some fancy load balancing as the solar production and local "island" loads change during the day. If those loads and production are not balanced they would have only to go into battery storage and if the balance exceeds the charging capacity then the line voltage in the house will go up till you start getting shut downs or worse.

The only way to power your house (as an island) is if you have an inverter with some type of voltage control and a standard GTI just does not do that. There are solutions where you create a shunt regulator with some type of a shunt load so that you can pull the excess power available away from the line through this load. This will keep the voltage in check and you can run what ever you want but the shunt has to be sized for the largest excess you would expect to see between production over your demand.

The other figure in this thread is also nonNEC compliant as the transfer switch does not have a mutually exclusive interlock with the GRID, but SPS does provide a voltage regulated output that would not over drive you circuits; it would provide what ever current is demanded with compliant voltage levels assuming the solar production could support it.

A full output solar system for Grid tied disconnect contingency.

Modes of operation:

NORMAL GRID:TIE

• Transfer switch is off and Solar Invertor backfeeds the transfer switch==> Sub Panel==> Main Panel ==> Net Meter ; all loads supported

GRID DOWN MODES: 200A MAIN IS OFF

• No Solar: Transfer switch selects either UPS or Gen Set (SB10KTL Main thrown off to prevent potential backdriving Transfer switch).
• Solar:Transfer Switch selects UPS to Power the Transfer Switch SB10kTL Turns on after verifying "grid" power.

Note that the UPS is doing basically what it is designed for which is fast surge protection for starting loads. Battery sizing for extended amp-hr pure drain operation is optional and offset by the generator.

I dont know if anybody has done this. With pure double conversion (as opposed to line interactive), I don't see why it would not work.

[posplayr]

Since the SPS is designed for off-grid operation, it is not designed to synchronize to any other power sources. I do not think that you can parallel two SPS to get increased output. More likely both of them would shut down.
Unlike the SunnyIsland line, there is no provision for linking or synchronizing the SB inverters, since they are assumed to be synchronized to the power grid.
For the same reason, the SPS will not play together with a generator, except through a transfer switch.

Your only option that I know of would be to put a dual conversion UPS on the output of the SPS and use that to cover the surge.

The two SPS 10V outputs are isolated and at random relative angles(frequencies). Each serves a different leg of a 240 feed to serve 120V loads only. You could get lucky and the two legs are 120 deg apart but that would be as correct as a stopped clock.

I was reserving dual conversion for a full solar capability not SPS. See previous figure. Why does that not work? There is no sync problem

[posplayr]

Absolutely right. The only autostart is that once SPS mode has been initiated, an overload will trip the SPS off but it will try to restart after an interval (I believe 5 minutes) on the assumption that the insolation may be better or the surge load may not be present. There is no limit to the number of such restarts.

Turning the SPS switch off sets the unit up to validate a grid input when one becomes available and then enter GTI operation.

But it would not be difficult to wire up a relay to auto-start the SPS after a short delay whenever the grid goes down.
Note that you will also need a transfer switch to move the protected load from the grid connection to the SPS connection. And for a compressor load, that interruption while the SPS is staring up is almost certain to trigger a restart under pressure rather than just a normal starting surge. The five minute dead time should allow the pressure to bleed down before the SPS restarts.

I think with the contingency nature of this whole process, that the requirement for manual intervention is not such a burden. If it was normal operation, it is fully automatic grid tied. If the grid is down you have to manage your loads and power sources to get through the day. It still seems better than mothering a battery bank all the time and a lot cheaper.

[sensij]

What if the grid goes down when nobody is home, or everyone is asleep? Without an automatic shut-off on the main breaker, you'll be feeding power into the grid, creating a safety hazard.

[inetdog]

I was reserving dual conversion for a full solar capability not SPS. See previous figure. Why does that not work? There is no sync problem

When grid power is present, I do not see any reason to have the UPS except to ride through the transition from one source to another.
You could add one more manual transfer switch to allow the SPS to be used to help charge the battery of the dual conversion UPS when neither grid nor generator are available.

The conversion losses of the UPS in normal (not bypassed) operation are probably on the order of 5% or so, so that has to be taken into consideration when adding up the costs.