200A Main Service Panel - 10kw Grid Tied System?

[Solar_Duc]

Any help is appreciated, let me know if more information is needed.

I want to install a residential 10kw grid tied system using a single SolarEdge SE11400H-US with no batteries. I have a main service panel w/ meter rated at 200 amps and 100 amp sub-panel inside the garage. My understanding is that the 120% rule will allow me 240 amps, then subtract the panel capacity 200 amps for a total of max 40 amps for solar.

How can install a 10kw system with a 200 amp panel without de-rating the panel?

The inverter’s maximum output at 208v is 48.5 amps per the spec sheet. This seems right for any 10kw system: 10,000kw / 208 v = 48.08 amps. The breaker needs to be oversized so: 1.25 x 48.5 = 60.625 => 65 amp breaker. If I were to de-rate the main breaker to 175A this would allow me 65A for Solar PV. Is this the only way to get a 10kw system with a 200A panel?

If I have to de-rate the panel, my current loads are listed below, can I get away with de-rating to 175A? I’m assuming a line side tap is not an option although I haven’t checked with my local building department or utility.

It seems 200A is the standard larger size panel for residential, I see that there are PV ready 225A panels. Is this the only way to get a 10kw systems?

Main Service Panel: GE P-0210, 200 amp max, 40 poles max, branch breakers 90 amp max using CU cable.

Main Service Panel Loads:
100A - House sub-panel
30A - AC
30A - exterior circuit (old hot tub circuit repurposed for powering landscape lights and sprinkler controller this could go away if needed)
60A - Spa (wired sized for 60A, but spa actually only needs 50A)

 

[JCSchwarb]

Any help is appreciated, let me know if more information is needed.

I want to install a residential 10kw grid tied system using a single SolarEdge SE11400H-US with no batteries. I have a main service panel w/ meter rated at 200 amps and 100 amp sub-panel inside the garage. My understanding is that the 120% rule will allow me 240 amps, then subtract the panel capacity 200 amps for a total of max 40 amps for solar.

How can install a 10kw system with a 200 amp panel without de-rating the panel?

The inverter’s maximum output at 208v is 48.5 amps per the spec sheet. This seems right for any 10kw system: 10,000kw / 208 v = 48.08 amps. The breaker needs to be oversized so: 1.25 x 48.5 = 60.625 => 65 amp breaker. If I were to de-rate the main breaker to 175A this would allow me 65A for Solar PV. Is this the only way to get a 10kw system with a 200A panel?

If I have to de-rate the panel, my current loads are listed below, can I get away with de-rating to 175A? I’m assuming a line side tap is not an option although I haven’t checked with my local building department or utility.

It seems 200A is the standard larger size panel for residential, I see that there are PV ready 225A panels. Is this the only way to get a 10kw systems?

Main Service Panel: GE P-0210, 200 amp max, 40 poles max, branch breakers 90 amp max using CU cable.

Main Service Panel Loads:
100A - House sub-panel
30A - AC
30A - exterior circuit (old hot tub circuit repurposed for powering landscape lights and sprinkler controller this could go away if needed)
60A - Spa (wired sized for 60A, but spa actually only needs 50A)

Hi Solar_Duc - Congrats on starting the solar design process. A lot of good details provided here. First I have to ask how you derived your opening concept to go grid tied. The grid tied inverters are often 2-3x more expensive than AIO, essentially the trade space provides free batteries for the difference. Having grid tie without batteries provides no power when the grid is down. The final straw for us was the power company says that any grid tied system over 10 kW requires a $1M insurance policy. That is way more than any minuscule amount they would pay us which is 1/2 the commercial rate. The payback on what they pay us would never offset the costs. That’s why so many systems in Florida are smaller than 10 kW. Home owners don’t even know why this is the recommended size, lol.

Since you are talking about a 3-phase 208V system, my knowledge is limited since in the USA these are used in commercial applications mostly. My first solar system was grid tied via a line/supply side fused disconnect. This was then connected to exist 4/0 aluminum feed from the grid. This kept our Amp rating the same which was 240V * 200amps or 48kW total. The solar inverter interacts with the grid to meet the on demand, supplying direct AC power, with supplemental grid, or extra backfeeding the grid. It does this through increased voltage and measured phase shifts that allows the backfeeding of the grid.

I am not sure about your power factors. I am used to derating values less than the maximum by 15-20%. Recommend doing an energy audit writing down all large draws such as fridges, freezers, HVAC, stoves/ovens, microwave, hot water, TVs, then do an average for lights. You need to figure out the 1) worst case when everything is on and 2) average worst case day. That will give you design parameters for 1) inverter and battery sizing and 2) PV solar size.

Hope this helps.

-Jay

 

[Solar_Duc]

Hi Solar_Duc - Congrats on starting the solar design process. A lot of good details provided here. First I have to ask how you derived your opening concept to go grid tied. The grid tied inverters are often 2-3x more expensive than AIO, essentially the trade space provides free batteries for the difference. Having grid tie without batteries provides no power when the grid is down. The final straw for us was the power company says that any grid tied system over 10 kW requires a $1M insurance policy. That is way more than any minuscule amount they would pay us which is 1/2 the commercial rate. The payback on what they pay us would never offset the costs. That’s why so many systems in Florida are smaller than 10 kW. Home owners don’t even know why this is the recommended size, lol.

Since you are talking about a 3-phase 208V system, my knowledge is limited since in the USA these are used in commercial applications mostly. My first solar system was grid tied via a line/supply side fused disconnect. This was then connected to exist 4/0 aluminum feed from the grid. This kept our Amp rating the same which was 240V * 200amps or 48kW total. The solar inverter interacts with the grid to meet the on demand, supplying direct AC power, with supplemental grid, or extra backfeeding the grid. It does this through increased voltage and measured phase shifts that allows the backfeeding of the grid.

I am not sure about your power factors. I am used to derating values less than the maximum by 15-20%. Recommend doing an energy audit writing down all large draws such as fridges, freezers, HVAC, stoves/ovens, microwave, hot water, TVs, then do an average for lights. You need to figure out the 1) worst case when everything is on and 2) average worst case day. That will give you design parameters for 1) inverter and battery sizing and 2) PV solar size.

Hope this helps.

-Jay

Jay, thanks!

I'm going grid tied since I want to sell back excess power generation, this is for my home not a commercial system. Looks like I confused the 208v and 220v, I was thinking 208 was 2 phase power without the neutral and 220 was 3 phase with a neutral. I am in the California Bay Area if that helps.

I have my useage from my utility company:
average monthly: 1,013 kWh
Max monthly: 1,292 kWh
Highest Daily: 62 kWh

For the breaker I assume I need to look at all the individual devices to find peak load.

Is my assumption about the panel correct, I need to derate to get a 10kW system?

 

[JCSchwarb]

Jay, thanks!

I'm going grid tied since I want to sell back excess power generation, this is for my home not a commercial system. Looks like I confused the 208v and 220v, I was thinking 208 was 2 phase power without the neutral and 220 was 3 phase with a neutral. I am in the California Bay Area if that helps.

I have my useage from my utility company:
average monthly: 1,013 kWh
Max monthly: 1,292 kWh
Highest Daily: 62 kWh

For the breaker I assume I need to look at all the individual devices to find peak load.

Is my assumption about the panel correct, I need to derate to get a 10kW system?

How much will the net metering pay you back? For us, it was way too low and would never offset our equipment and installation cost. The most important requirement for us was uninterrupted power. Without a battery system, no grid = no solar production. Grid tied systems are much more expensive. Plus are much more regulated. My company wants a $1M insurance policy to interconnect. Juice is not worth the squeeze.

10kW * 4 avg hours a day * 300 = 12000 kWh. / 12 = 1,000 kWh per month avg production
Avg monthly usage = 1,013 kWh
Note there are solar production apps to tighten up your estimate. Trees and shadows in the winter can also cause a huge hit to productivity from Oct - Mar so take a look at sun exposure to the area you are designing. Even some shade can cut production by nearly 70-90%. Conclusion is you will never offset the cost of your equipment to backfeed the grid.

So assuming gray days and avg production of 4 hours your system will not produce much extra for net metering. If you have the room I would build a 15 kWh system with 50 kWh battery back up. You would use grid power as supplemental. For proper system sizing you will need to know your maximum draw at any point in time. That will tell you how large of an inverter you will need.

American residential voltage is 120V split in-phase. Measuring from L1 to L2 will yield 240V or either leg to Neutral as 120V.

You will not need to derate your panel regardless of which system you go with.

 

[OzSolar]

The inverter’s maximum output at 208v is 48.5 amps per the spec sheet. This seems right for any 10kw system: 10,000kw / 208 v = 48.08 amps. The breaker needs to be oversized so: 1.25 x 48.5 = 60.625 => 65 amp breaker. If I were to de-rate the main breaker to 175A this would allow me 65A for Solar PV. Is this the only way to get a 10kw system with a 200A panel?

Why 208v? It sounds like you have a 240v house?

Yes, you have to derate or do a line side tap. You could also use 7600 watt inverter. 10,000 watts of PV is just right for that inverter. That's what I would do.

If you end up derating your panel you very likely can step down to a 150 amp main without any trouble. Normally much easier to find and cheaper.

 

[Solar_Duc]

Why 208v? It sounds like you have a 240v house?

Yes, you have to derate or do a line side tap. You could also use 7600 watt inverter. 10,000 watts of PV is just right for that inverter. That's what I would do.

If you end up derating your panel you very likely can step down to a 150 amp main without any trouble. Normally much easier to find and cheaper.

I do have 240v, I was confused looking at the spec sheet as I noted above my mistake... Thank you for the input on de-rating that is what I suspected I'd have to do, I'll look into the 150 amp mains and see if they are easier for me to source. I want the larger inverter for full capacity, I am planning to install 10kw and want that on my application to PG&E (local utility company) to get locked into their current rate plans for the next 20 years.

I looked into this further and did a load analysis on my main panel and it came up with 140 amps, so it looks like a 150 amp main breaker will be fine. Looking online the 150 amp is readily available.

Thank you!

 

[Solar_Duc]

How much will the net metering pay you back? For us, it was way too low and would never offset our equipment and installation cost. The most important requirement for us was uninterrupted power. Without a battery system, no grid = no solar production. Grid tied systems are much more expensive. Plus are much more regulated. My company wants a $1M insurance policy to interconnect. Juice is not worth the squeeze.

10kW * 4 avg hours a day * 300 = 12000 kWh. / 12 = 1,000 kWh per month avg production
Avg monthly usage = 1,013 kWh
Note there are solar production apps to tighten up your estimate. Trees and shadows in the winter can also cause a huge hit to productivity from Oct - Mar so take a look at sun exposure to the area you are designing. Even some shade can cut production by nearly 70-90%. Conclusion is you will never offset the cost of your equipment to backfeed the grid.

So assuming gray days and avg production of 4 hours your system will not produce much extra for net metering. If you have the room I would build a 15 kWh system with 50 kWh battery back up. You would use grid power as supplemental. For proper system sizing you will need to know your maximum draw at any point in time. That will tell you how large of an inverter you will need.

American residential voltage is 120V split in-phase. Measuring from L1 to L2 will yield 240V or either leg to Neutral as 120V.

You will not need to derate your panel regardless of which system you go with.

The payback is significant for me he here in California with the current Net Energy Metering (NEM) 2.0 rate plans that I want to get locked into, my payback period is about 5 years right now. If I wait until the new NEM 3.0 comes in to effect in April my payback period will be over double that as it incentivizes batteries.

Everything I'm reading shows that I will need to derate the panel, I would like to not have to.... What reasoning do you have that I could use as justification for my plan submittal with the city?

 

[JCSchwarb]

The payback is significant for me he here in California with the current Net Energy Metering (NEM) 2.0 rate plans that I want to get locked into, my payback period is about 5 years right now. If I wait until the new NEM 3.0 comes in to effect in April my payback period will be over double that as it incentivizes batteries.

Everything I'm reading shows that I will need to derate the panel, I would like to not have to.... What reasoning do you have that I could use as justification for my plan submittal with the city?

I think we are talking past each other on why not to go grid tied. How much power do you expect to generate to make it worth it? I calculated likely averages in your area. I have had both systems and can tell you grid tied is not the best option from a value or power availability position.

Regarding the connection for grid tie: A Line-side tap, that does not require derating, also known as a supply-side interconnection, where the solar inverter output is tapped between the main service breaker and the electric meter. In this case, the 120% rule does not apply. This is because the main service breaker is the only overcurrent protection device needed to protect the busbar where there is a line-side tap. See drawing attached.

 

[OzSolar]

I looked into this further and did a load analysis on my main panel and it came up with 140 amps, so it looks like a 150 amp main breaker will be fine. Looking online the 150 amp is readily available.

Thank you!

You're welcome. Glad I could help.

 

[zanydroid]

I do have 240v, I was confused looking at the spec sheet as I noted above my mistake... Thank you for the input on de-rating that is what I suspected I'd have to do, I'll look into the 150 amp mains and see if they are easier for me to source. I want the larger inverter for full capacity, I am planning to install 10kw and want that on my application to PG&E (local utility company) to get locked into their current rate plans for the next 20 years.

I looked into this further and did a load analysis on my main panel and it came up with 140 amps, so it looks like a 150 amp main breaker will be fine. Looking online the 150 amp is readily available.

Thank you!

(I’m located in California, have a NEM2 system and currently designing a NEM2 expansion).

You should derate the panel and get NEM2 in. Then consider reconfiguring your MSP to get back to 200A if you need to. There are a bunch of legal ways to do this that involve either line side tap (would not recommend starting with this, PG&E needs to be involved), meter ring adapter to provide line side tap (also don’t recommend, PG&E needs to approve), solar ready bus bar (built in line side tap), increase to 225a busbar, refactor MSP into a distribution panel…

You basically have infinite time to sort that out but very finite time for NEM2

I have to respectfully disagree with the off grid recommendation. I would absolutely go grid tied. You need the permit anyway in California for off grid, and in many places this includes fire district check. There’s very little interconnection fee. System design is simpler than off grid with batteries. To get the proper savings of off grid with batteries you need to forgo UL9540 which is also not allowed in California.

 

[JCSchwarb]

(I’m located in California, have a NEM2 system and currently designing a NEM2 expansion).

You should derate the panel and get NEM2 in. Then consider reconfiguring your MSP to get back to 200A if you need to. There are a bunch of legal ways to do this that involve either line side tap (would not recommend starting with this, PG&E needs to be involved), meter ring adapter to provide line side tap (also don’t recommend, PG&E needs to approve), solar ready bus bar (built in line side tap), increase to 225a busbar, refactor MSP into a distribution panel…

You basically have infinite time to sort that out but very finite time for NEM2

I have to respectfully disagree with the off grid recommendation. I would absolutely go grid tied. You need the permit anyway in California for off grid, and in many places this includes fire district check. There’s very little interconnection fee. System design is simpler than off grid with batteries. To get the proper savings of off grid with batteries you need to forgo UL9540 which is also not allowed in California.

Come back and tell us how great grid tied is when the grid goes down for a week or more.

 

[zanydroid]

Come back and tell us how great grid tied is when the grid goes down for a week or more.

Outside of earthquakes (once every 30 year sort of disasters) the grid only goes down that long in public safety shutoff areas and in the mountain exurbs. And for those places I recommend grid tied grid forming storage batteries.

You want grid connected to get the boon of crediting surplus generation across seasons. With NEM2 we still get 1:1. For many zip codes in Northern California there is a significant surplus in summer and significant deficit in winter due to the climate. How would an off grid system ever compete with this kind of net metering accounting.

 

[JCSchwarb]

Outside of earthquakes (once every 30 year sort of disasters) the grid only goes down that long in public safety shutoff areas and in the mountain exurbs. And for those places I recommend grid tied grid forming storage batteries.

You want grid connected to get the boon of crediting surplus generation across seasons. With NEM2 we still get 1:1. For many zip codes in Northern California there is a significant surplus in summer and significant deficit in winter due to the climate. How would an off grid system ever compete with this kind of net metering accounting.

Because one can build a much larger off grid system with sufficient battery storage for the same price. We used to live in SoCal and every year huge fear of fire being cutoff and there were years of weeks without power. Many were sold grid tied and lied to about solar generation, self-sufficiency when the grid goes down.

 

[zanydroid]

Because one can build a much larger off grid system with sufficient battery storage for the same price. We used to live in SoCal and every year huge fear of fire being cutoff and there were years of weeks without power. Many were sold grid tied and lied to about solar generation, self-sufficiency when the grid goes down.

I don’t see how the math works out with an apples to apples comparison on equipment tier, DIY vs hired out, and permiting.

And solar salespeople misleading customers is a separate matter.

 

[JCSchwarb]

I don’t see how the math works out with an apples to apples comparison on equipment tier, DIY vs hired out, and permiting.

And solar salespeople misleading customers is a separate matter.

Mainly because grid tied inverters are 3-4x an AIO inverter. The savings pays for the batteries.

 

[zanydroid]

Mainly because grid tied inverters are 3-4x an AIO inverter. The savings pays for the batteries.

HM1500 plus balance of system is a little over $400 for 1500W AC output. That is fully 1741SA compliant as a grid tie microinverter.

Which AIO are you comparing to? Which UL9540 battery or ESS is to be in your solution?

 

[JCSchwarb]

HM1500 plus balance of system is a little over $400 for 1500W AC output. That is fully 1741SA compliant as a grid tie microinverter.

Which AIO are you comparing to? Which UL9540 battery or ESS is to be in your solution?

Please provide link to the code that requires this 9540. For such a small system, I would do a “temp” installation. Build a shed that houses your offgrid UPS.

 

[zanydroid]

I still don't see how you can squeeze an ESS of reasonable size when a 7kW grid tied system using those HM1500 will cost $2000 for the inverters

Code reference here.

https://up.codes/viewer/california/ca-residential-code-2022/chapter/3/building-planning#R328

Everything fire risk related in California gets extra scrutiny from insurers. Non-9540 ESS will probably be grounds for cancellation of homeowner policy if they spot it. My homeowner policy was very painful to issue due to a permitted but riskier roof type (wood shake), and after a few rounds of being hassled over it (once when i was renewing during a really bad fire season, once during an inspection audit) I just replaced it (was going to do so anyway for solar install). And I think the ESS would be perceived as a higher risk.

 

[JCSchwarb]

I still don't see how you can squeeze an ESS of reasonable size when a 7kW grid tied system using those HM1500 will cost $2000 for the inverters

Code reference here.

https://up.codes/viewer/california/ca-residential-code-2022/chapter/3/building-planning#R328

Everything fire risk related in California gets extra scrutiny from insurers. Non-9540 ESS will probably be grounds for cancellation of homeowner policy if they spot it. My homeowner policy was very painful to issue due to a permitted but riskier roof type (wood shake), and after a few rounds of being hassled over it (once when i was renewing during a really bad fire season, once during an inspection audit) I just replaced it (was going to do so anyway for solar install). And I think the ESS would be perceived as a higher risk.

R328.2 states repurposed car batteries can be installed in outside shed. The best practice is to have ESS separate from occupied space. Most don’t realize no flammable materials are to be stored in garages but they do and insurance has the ability to not pay. Build a fire proofed shed and install your offgrid battery UPS system there.

 

[zanydroid]

The set of projects that can take advantage of R328.2 is limited.

It's uncertain which AHJs will approve the repurposed batteries. If they ask for engineering that will inflate the project cost.

Also those are HV batteries, not as many DIYers will want to try to use those.