Solar design planning - Northern California

[GarySaf]

Hello,

I’m planning Solar for my property and been reading through all the different posts and designs and hoping to get enough of a plan together to apply under Nem 2 (California - PGE) for a grid tie by the end of February 2023.

My biggest challenge in understanding / planning this out is the size of the property, annual usage and some unique install issues and hoping for some guidelines and where I might be completely off in my understanding and where things look realistic.

I have a home and barn and for 2022, my total PGE usage was 48000 kwh.

Planning for the next 3 years of usage there’s an upgrade our irrigation pump from 5hp - 10hp, an additional air conditioner for the barn and an added mini spilt for the home and at least 1EV, potentially 1 - 2 Electric UTV’s.
Realistically I think I should plan an additional 50% which would put my annual usage at 72000 kwh

Under the net metering agreement the usage for both meters would be aggregated, so essentially the grid tie would only be connected to the house and any surplus would offset the usage of both meters.

That particularly works really well as the barn would pretty much have to be dependent on grid power due to the irrigation and high usage at night.

So, here’s where my starting assumptions are - please correct where I’m seeming very off base or any different ideas.

Panels: 98 panels +/-
Presuming each panel produces an average approximately 2kwh per day (based on a few neighbors solar setup), to offset 72000 kwh annually, I would be looking at around 98 400w panels.
(72000 / 365 days / 2kwh per panel = 98)

Inverters:
Here’s my biggest confusion and I think the biggest cost concerns. Not tied to any brand but just seeing what others have successfully done, it seems I have a couple different directions.

1. If I went with something like the Sol Ark 15k’s, I not clear on whether I can get away with 2 or need 3?

2. If I went with the Schneider XW Pro Hybrid, it seems I need 4? 4 is also the max stacking capability it seems.

3. Any other inverter setup I should consider, as the expense is concerning especially on the Sol Ark's. Again, because of offsetting the barn usage, the grid tie is important, but perhaps I could lower the number of panels for now and later move some parts of the house on a separate off-grid system - Not sure if permitting on this would force me off Nem 2, but definitely a consideration to help keeps costs manageable.

Batteries:
For the moment, I haven’t even begun to consider batteries, as the whole project is already seeming quite expensive, but this would be the next step, when I have a handle on the panels, inverters and other costs.

Distance from panels to garage:
One of my other concerns is the wiring and costs for this as the panels would have to be 350 ft from the main meter.
There is 2 inch empty underground conduit laid out, but I wasn’t sure what I should consider specifically for the distance and how this might affect the overall plan.


So, that’s roughly where I’ve gotten - would appreciate any thoughts, ideas or suggestions.

Thanks, Gary

 

[JCSchwarb]

Hello,

I’m planning Solar for my property and been reading through all the different posts and designs and hoping to get enough of a plan together to apply under Nem 2 (California - PGE) for a grid tie by the end of February 2023.

My biggest challenge in understanding / planning this out is the size of the property, annual usage and some unique install issues and hoping for some guidelines and where I might be completely off in my understanding and where things look realistic.

I have a home and barn and for 2022, my total PGE usage was 48000 kwh.

Planning for the next 3 years of usage there’s an upgrade our irrigation pump from 5hp - 10hp, an additional air conditioner for the barn and an added mini spilt for the home and at least 1EV, potentially 1 - 2 Electric UTV’s.
Realistically I think I should plan an additional 50% which would put my annual usage at 72000 kwh

Under the net metering agreement the usage for both meters would be aggregated, so essentially the grid tie would only be connected to the house and any surplus would offset the usage of both meters.

That particularly works really well as the barn would pretty much have to be dependent on grid power due to the irrigation and high usage at night.

So, here’s where my starting assumptions are - please correct where I’m seeming very off base or any different ideas.

Panels: 98 panels +/-
Presuming each panel produces an average approximately 2kwh per day (based on a few neighbors solar setup), to offset 72000 kwh annually, I would be looking at around 98 400w panels.
(72000 / 365 days / 2kwh per panel = 98)

Inverters:
Here’s my biggest confusion and I think the biggest cost concerns. Not tied to any brand but just seeing what others have successfully done, it seems I have a couple different directions.

1. If I went with something like the Sol Ark 15k’s, I not clear on whether I can get away with 2 or need 3?

2. If I went with the Schneider XW Pro Hybrid, it seems I need 4? 4 is also the max stacking capability it seems.

3. Any other inverter setup I should consider, as the expense is concerning especially on the Sol Ark's. Again, because of offsetting the barn usage, the grid tie is important, but perhaps I could lower the number of panels for now and later move some parts of the house on a separate off-grid system - Not sure if permitting on this would force me off Nem 2, but definitely a consideration to help keeps costs manageable.

Batteries:
For the moment, I haven’t even begun to consider batteries, as the whole project is already seeming quite expensive, but this would be the next step, when I have a handle on the panels, inverters and other costs.

Distance from panels to garage:
One of my other concerns is the wiring and costs for this as the panels would have to be 350 ft from the main meter.
There is 2 inch empty underground conduit laid out, but I wasn’t sure what I should consider specifically for the distance and how this might affect the overall plan.


So, that’s roughly where I’ve gotten - would appreciate any thoughts, ideas or suggestions.

Thanks, Gary

Hi Gary from NoCal!

I started off like most designing around a grid tied system. Then I saw a few Will videos and started doing research on pros and cons of grid tied vs offgrid. My power company requires $1M liability above a 10kWh system. So when comparing types of systems, I discovered that high frequency inverters with battery backup to be the same price as a no-battery grid tied system. My second requirement was security and peace of mind. After doing net metering in SoCal, I learned it is best to not have any extra production left over, because the wholesale costs are far below aggregate costs of one’s system.

To get an accurate UV/lumens calculation, one needs to look at solar slant angles, tree shadows and average UV/lumens by season. After my installation of 60 panels, I discovered the oaks had to be drastically trimmed as partial shade greatly affects output.

If you design around security, then you will need your worst month to calculate Solar PV size and batteries. Then you will need to do a watts audit to determine your highest demand at a given time. This is how you will calculate the size of your inverters.

Your distances are fine with higher voltage strings. Consult a chart for AWG sizing at a given voltage string. Higher voltage reduces wiring diameter needed. My guess is 10 AWG stranded copper is sufficient, but check the lookup values.

Hope this gives you some ideas to think about.

-Jay

 

[400bird]

Are you looking for basic grid tie inverter?
Or do you want the battery/grid interactive/grid forming inverter so you can have power when the grid is down? This is where the price adds up quickly. Grid tie inverter (not battery backup) Could save you significant costs.

On the Schneider inverters, they connect to the battery only. You'd need charge controllers to connect the PV to battery. Charger controllers match your solar wattage, inverter matches you AC wattage, they don't need to be the same, you can match to your specific needs.

 

[Think About It]

Considering your requirements, I don't see any need for batteries.

Which structure will have panels? Garage/House or Both

I thought there were two meters. Which one is the main meter? House or Garage

I would do a PVWatts calculation first.

PVWatts

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations

pvwatts.nrel.gov

Sol-ARk is a great AIO inverter (I have one). But if you're not going to need batteries then you're spending a lot more money than you need to.

If you are using 72000KWh per year, that's a daily average of 197KWh. Assuming you're generating your power over 4 hours per day, that would be 49KWh, over 5 hours it would be 39KWh. Two Sol-Ark 15's would not do the job.

BTW, 197KWh is a lot of power. Do you really need that much?

 

[JCSchwarb]

Considering your requirements, I don't see any need for batteries.

Which structure will have panels? Garage/House or Both

I thought there were two meters. Which one is the main meter? House or Garage

I would do a PVWatts calculation first.

PVWatts

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations

pvwatts.nrel.gov

Sol-ARk is a great AIO inverter (I have one). But if you're not going to need batteries then you're spending a lot more money than you need to.

If you are using 72000KWh per year, that's a daily average of 197KWh. Assuming you're generating your power over 4 hours per day, that would be 49KWh, over 5 hours it would be 39KWh. Two Sol-Ark 15's would not do the job.

BTW, 197KWh is a lot of power. Do you really need that much?

That’s not the right way to calculate the system size. You are assuming every day in the summer. Lots of big trees around there with shade in winter and lots of cloudy days so the PV system would be considerably bigger. Regarding the inverter size, that has to do with peak demand not average use.

 

[GarySaf]

Thank you all for your replies - being at the beginning stages, it just really helps think this out;
A few notes on the replies above:

Batteries: It would be great for the independence, but the biggest issues are that in the summer I run an irrigation pump (approx 6.5kw per hour) and air conditioning (another 3-5 kw per hour), so for 12-15 hours when there is 0 PV production, that would take an immense battery setup and I definitely need to start by seeing what minimum I can start with on a Grid tie.

197kwh per day is a lot, I agree, but it's just the way the usage is. I went over our electric usage and for last month for example it was an average of 230kwh per day. Some months are lower of course, but total usage has been pretty consistent at 48000 kwh annually, not including planned EV upgrades.

PV Watts: I just ran through a few simulations on the PvWatts, using roof mount in areas where I have 0 shading. With the elevation of the barn where they panels will go, there is absolutely no obstruction, no trees.
It looks like with the roof space I specified, I would go to a DC system size of 50kw to offset 72000kwh annually.

The panels go on the barn and the main meter that would grid tie goes to the house (350ft of 2" underground conduit already laid out)

Inverters:
Here's where I think my real confusion is.

Looking at my daily utility bill for the house, the highest continual load appears to be 5kwh
The biggest loads are air conditioners and I think need some allowance for well pump startup.
Not tied to any inverter at the moment but using the Sol Ark 15k as an example, it says a maximum ac coupled input of 19500kw - I don't know how to figure out the maximum number of panels per inverter.

If it's 19500kw max input, am I correct that this translates to 48 panels (19500kw / 400w)?
But of course, the panels are not producing 400w of power, so don't know how to figure that out.

Then, if the house only needs a max of 5kwh usage at any given time, then am I correct that 10kwh would be grid sell output?
I think i'm just not understanding the inverters quite yet and how much input & output with grid sell I need.

Thanks again for all the help.

 

[GarySaf]

Then you will need to do a watts audit to determine your highest demand at a given time. This is how you will calculate the size of your inverters.

Just rereading some of the replies above and checking my usage:
October was the lowest usage at 1,300kwh and January was the highest at 5,800kwh - The total yearly house usage was 33,000kwh and the barn meter usage as 15,000kwh.
The barn meter is only relevant in that I need to grid sell sufficient power to offset the barn usage from the house meter as PGE would aggregate the usage of both meters.

The house appears to have a highest demand of 5000w.
Above these figures, I just need to plan for some allowance to add things like an EV.

Space for panels with no shading is not an issue and I just need to for the moment plan the max to submit my application under Nem 2, but I realize I have a lot else to consider.

 

[Hedges]

Almost 200 kWh/day in January.
Maybe you can meet that with lots of PV, maybe not.
PV is considerably cheaper than fuel (if all PV power is used), but to generate 4x as much in winter with half (or less) the effective sun hours means oversizing PV 8x. Still cheaper than burning fuel, possibly by a factor of 5.

If you run a generator, would be nice to capture water-cooling heat followed by exhaust heat, and pipe that for use.
"CHP", combined heat and power.

You may be able to buy 100 kW of used panels for $25k, so not unreasonable.
Mounting hardware and labor will add up.
Batteries are what bites.

 

[JCSchwarb]

Thank you all for your replies - being at the beginning stages, it just really helps think this out;
A few notes on the replies above:

Batteries: It would be great for the independence, but the biggest issues are that in the summer I run an irrigation pump (approx 6.5kw per hour) and air conditioning (another 3-5 kw per hour), so for 12-15 hours when there is 0 PV production, that would take an immense battery setup and I definitely need to start by seeing what minimum I can start with on a Grid tie.

197kwh per day is a lot, I agree, but it's just the way the usage is. I went over our electric usage and for last month for example it was an average of 230kwh per day. Some months are lower of course, but total usage has been pretty consistent at 48000 kwh annually, not including planned EV upgrades.

PV Watts: I just ran through a few simulations on the PvWatts, using roof mount in areas where I have 0 shading. With the elevation of the barn where they panels will go, there is absolutely no obstruction, no trees.
It looks like with the roof space I specified, I would go to a DC system size of 50kw to offset 72000kwh annually.

The panels go on the barn and the main meter that would grid tie goes to the house (350ft of 2" underground conduit already laid out)

Inverters:
Here's where I think my real confusion is.

Looking at my daily utility bill for the house, the highest continual load appears to be 5kwh
The biggest loads are air conditioners and I think need some allowance for well pump startup.
Not tied to any inverter at the moment but using the Sol Ark 15k as an example, it says a maximum ac coupled input of 19500kw - I don't know how to figure out the maximum number of panels per inverter.

If it's 19500kw max input, am I correct that this translates to 48 panels (19500kw / 400w)?
But of course, the panels are not producing 400w of power, so don't know how to figure that out.

Then, if the house only needs a max of 5kwh usage at any given time, then am I correct that 10kwh would be grid sell output?
I think i'm just not understanding the inverters quite yet and how much input & output with grid sell I need.

Thanks again for all the help.

Something is not adding up. Your pump and AC is around 10 kWh for every single hour? But your peak demand is 5 kWh. I don’t know of anyone one other than a grow house that consumes that much water and air conditioning over the entire day.

 

[GarySaf]

Peak demand on the house is around 5kwh.
The pump is on the barn meter, so it's not going to be tied to the solar - I mentioned the pump usage, just to explain that batteries are not feasible.
The house is huge with high ceilings - with 2 HVAC's running simultaneously, 5 kwh continually is pretty easy.

 

[Think About It]

That’s not the right way to calculate the system size. You are assuming every day in the summer. Lots of big trees around there with shade in winter and lots of cloudy days so the PV system would be considerably bigger. Regarding the inverter size, that has to do with peak demand not average use.

I respectfully disagree for this use case. If he is using 70,000KW per year, he only needs to produce 70,000KW per year regardless of his peak demand - because he is net-metered. However, the inverter needs to be sized to handle the peak PV generation or else power will get clipped.

He is going to have 2 meters, 1 net meter and one regular meter. The power company is going to aggregate them.

 

[Think About It]

PV Watts: I just ran through a few simulations on the PvWatts, using roof mount in areas where I have 0 shading. With the elevation of the barn where they panels will go, there is absolutely no obstruction, no trees.
It looks like with the roof space I specified, I would go to a DC system size of 50kw to offset 72000kwh annually.

Please post the PVWatts report. My guess is that you are going to need inverter(s) that can handle 40 to 50KW of PV. You're going to spend 2 to 3 times the price for Sol-Ark 15s. You don't need batteries so you don't need Sol-Arks.

 

[Hedges]

Do you have 3-phase?

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Or single phase?

 

[Danke]

Not tied to any inverter at the moment but using the Sol Ark 15k as an example, it says a maximum ac coupled input of 19500kw - I don't know how to figure out the maximum number of panels per inverter.

If it's 19500kw max input, am I correct that this translates to 48 panels (19500kw / 400w)?
But of course, the panels are not producing 400w of power, so don't know how to figure that out.

Then, if the house only needs a max of 5kwh usage at any given time, then am I correct that 10kwh would be grid sell output?
I think i'm just not understanding the inverters quite yet and how much input & output with grid sell I need.

I don’t know if Sol-Ark changed what they said a year ago, but you can also AC couple in addition to DC for more power than that.

19,400W DC inverted to 15,000W AC and AC couple (ex. Micro-inverters) up to 19,200W input.

So output of 34,200W. At least that’s what I got from their webinar. The manual isn’t very clear though.

 

[Shimmy]

I would say qualifying for NEM2 is going to be a stretch with timing, unless you keep things really simple. When you do upgrades that will increase load, add a separate off-grid system (with battery).

I would really just look at a few string inverters around 15-20kW and ground-mounted panels if I was in your situation.

 

[Hedges]

We think qualifying for NEM2 is just submitting a form and some documents to PG&E.

 

[GarySaf]

If he is using 70,000KW per year, he only needs to produce 70,000KW per year regardless of his peak demand - because he is net-metered. However, the inverter needs to be sized to handle the peak PV generation or else power will get clipped.

He is going to have 2 meters, 1 net meter and one regular meter. The power company is going to aggregate them.

That's the best and simplest way I should have put it from the beginning - it's exactly right.
Current annual use is 48000kwh, sizing up by 50% would be 72000kwh, but I could easily go somewhere in between for now.

Please post the PVWatts report. My guess is that you are going to need inverter(s) that can handle 40 to 50KW of PV.

Your guess is exactly right. Attached it the PVWatts report based on a 40kW system size and produces 61,231 kwh. I think that's a good starting point, though I have enough unobstructed roof space to go larger in the future.

You're going to spend 2 to 3 times the price for Sol-Ark 15s. You don't need batteries so you don't need Sol-Arks.

I think the inverter part is really what i'm not understanding. What would you suggest for inverters as options?

Do you have 3-phase?
Or single phase?

Single phase.

I don’t know if Sol-Ark changed what they said a year ago, but you can also AC couple in addition to DC for more power than that.

19,400W DC inverted to 15,000W AC and AC couple (ex. Micro-inverters) up to 19,200W input.

So output of 34,200W.

Yes, I think the input numbers are right, but i'm not clear on output. I'll plan to call them on Monday.
But again, I really open to what inverters to use. I just don't know what the other options are.

We think qualifying for NEM2 is just submitting a form and some documents to PG&E.

That's right - submit by April (preferably March to correct any issues as needed) and 3 years to build and connect.
The system design has to be the max I'd want approved and the one line diagram has to document this, but can be changed as long as the size isn't increasing.
For Nem2, the main advantage is not having to immediately plan on batteries.

I would say qualifying for NEM2 is going to be a stretch with timing, unless you keep things really simple.

The panels part is easy, I just need to plan on something between 40-50 kW. It's the inverters and equipment in between the panels and meter that's hard for me to figure out.
I defaulted to the Sol Ark as it's all straight forward in one unit, but of course the cost is really high.

 

[Hedges]

Attached it the PVWatts report based on a 40kW system size and produces 61,231 kwh. I think that's a good starting point, though I have

I think the inverter part is really what i'm not understanding. What would you suggest for inverters as options?

Single phase.

String inverters.

Five of these is ~ 40kW, can be had for $1700 each.

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With multiple PV string orientations, could increase hours of production and Wh/day by 40%.

Another guy here used 3x Fronius for 45kW

I think string inverters and central inverters are the most efficient and cost effective. They are used from 2kW to 4MW. The larger ones are 3-phase and higher voltage, so string inverters from a top brand are what you would use. Rooftop requires RSD box per PV panel, but ground mount does not.

Using UL-1741-SA inverters, you could later put some (or all) downstream of a battery inverter that uses frequency shift when off grid to support AC coupling. Then that amount of PV is available to battery backup critical loads.

SolArk can use AC coupled GT PV to some extent, but think it needs greater amount of DC coupled PV.
Sunny Island
Skybox or Mojave
Schneider