Bi-Facial panels to help flatten production difference between winter and summer

[pgrovetom]

In California with the new NEM 3.0 export power value, is it possible when sizing a system to use all or some bi-facial panels with some kind of reflective ground cover to bring summer and winter export closer. My current system for years has broken even ( >$10k/yr usage cost) in part because NEM2.0 essentially lets me use PG&E as a battery or storage and I buy it back at night or on poor days. I'm now looking into a new system for a friend and wondering about how winter versus summer production and storage effect a system sizing and therefore lots of potential cost.

But in looking at the new California NEM3.0 export values, it looks like using a Hybrid Inverter with batteries matched to or above my home needs creates a problem of over-sizing the production and storage to make it work out during the winter months when losing PG&E as a 1:1 storage across a day and the year.

In my old system, I build up credits ( storage) during summer months that offsets my much lower production in winter. But a system that gets such lousy credit value for summer excess, seems like it will have a problem during the winter months. I live in Northern California in Sonoma County a and get good sun and reasonable rain/cloudy days. But the low angle of the sun in the sky and my summer optimized tilt just makes things worse in the winter. So it seems at first glance that any method that brings winter and summer production closer should help with system panel and battery sizing. I say that because each summer day I would store my large excess and use it at night from batteries till the solar power comes up and does a charge cycle the next day. So on a simplistic first order, it would seem the solar and battery sizing would be driven by daily and battery storage ( not PG&E credits). But my production on my existing system drops off by about 50% from summer to winter.

That suggests the sizing should be based on winter production and usage so as not to need 50% of your power from PG&E in winter months. If that is correct than it seems that using bi-facial panels with a lower winter tilt ( ground mount) and some kind of light reflective ground cover should help lean the production towards winter trying to bring them closer. Hopefully that brings winter up and summer production down. Since PG&E is paying so little for export ( except during some summer hours), It seems the low summer credit implies a system optimization leaned more toward winter would be good. My current system is optimized for maximum yearly power and summer optimization tilt but that only works because I'm on NEM 2.0 and PG&E is acting like a long term battery to use summer credits toward my large winter deficit.

Since batteries have no longer term storage benefit like PG&E, they only help flatten the day and not the winter summer problem

I'd curious of peoples thoughts on how California NEM 3.0 is effecting system sizing and the summer/winter problem.

So does this make sense?

 

[Brucey]

It would seem with a nem 3 setup that you would want to design for maximum winter production. Because it’s no longer your yearly output but your winter output that’s critical, to get your batteries recharged. And then other seasons you’ll have an excess.

 

[Koyaanisqatsi]

I'm in the same boat as you, more or less. I live in Atascadero. NEM 3 is causing me to (almost!) disregard any kind of Net-Metering agreement and just design my system large enough to use as little grid power as possible under all circumstances. I'll have to eat some excess/lost power when the batteries are charged and I'm not using as much power as the PV arrays are producing. (And actually, it will just be free energy time. Crank the HVAC down to freezing! And turn up the volume on the home theater!) I might do net-metering if it seems like a good way to go, once we're all set up. That should at least kill the cost of the grid-connection minumum fees.

I am setting up three 8-panel pergola-mounted bi-facial arrays that are close to the house and patio landscaping. We will be painting the house white or a very light color in the medium future. And all the landscaping is already light-colored rock. So we will have a lot of ambient light behind and under the panels, if all goes well. I'm also trying to determine ahead of time whether it makes sense to angle one array for summer sun, and the other two for winter sun, or just optimize for spring/fall across the board, or ???...

For sizing things, it's looking like we use between 20 and 30kWh per day on a typical summer day with not too much heat (say, less than 90degF). We sometimes break 40kWh/day on really hot summer days or really cold winter nights. So I'm going after 30-45kWh of battery storage with the hope that it will hold us for more than a single night. And the only grid power will come through a EG4 Chargeverter (100A/48V charger).

To be clear, we are under-spec'ing the PV with the intention of adding to it after we get some real-world data. And I also expect to add batteries for winter days, to keep grid consumption to a minimum.

 

[doctron]

Make battery size 45 to 50kwh. Make it yourself.

 

[GRMRC]

In California with the new NEM 3.0 export power value, is it possible when sizing a system to use all or some bi-facial panels with some kind of reflective ground cover to bring summer and winter export closer. My current system for years has broken even ( >$10k/yr usage cost) in part because NEM2.0 essentially lets me use PG&E as a battery or storage and I buy it back at night or on poor days. I'm now looking into a new system for a friend and wondering about how winter versus summer production and storage effect a system sizing and therefore lots of potential cost.

But in looking at the new California NEM3.0 export values, it looks like using a Hybrid Inverter with batteries matched to or above my home needs creates a problem of over-sizing the production and storage to make it work out during the winter months when losing PG&E as a 1:1 storage across a day and the year.

In my old system, I build up credits ( storage) during summer months that offsets my much lower production in winter. But a system that gets such lousy credit value for summer excess, seems like it will have a problem during the winter months. I live in Northern California in Sonoma County a and get good sun and reasonable rain/cloudy days. But the low angle of the sun in the sky and my summer optimized tilt just makes things worse in the winter. So it seems at first glance that any method that brings winter and summer production closer should help with system panel and battery sizing. I say that because each summer day I would store my large excess and use it at night from batteries till the solar power comes up and does a charge cycle the next day. So on a simplistic first order, it would seem the solar and battery sizing would be driven by daily and battery storage ( not PG&E credits). But my production on my existing system drops off by about 50% from summer to winter.

That suggests the sizing should be based on winter production and usage so as not to need 50% of your power from PG&E in winter months. If that is correct than it seems that using bi-facial panels with a lower winter tilt ( ground mount) and some kind of light reflective ground cover should help lean the production towards winter trying to bring them closer. Hopefully that brings winter up and summer production down. Since PG&E is paying so little for export ( except during some summer hours), It seems the low summer credit implies a system optimization leaned more toward winter would be good. My current system is optimized for maximum yearly power and summer optimization tilt but that only works because I'm on NEM 2.0 and PG&E is acting like a long term battery to use summer credits toward my large winter deficit.

Since batteries have no longer term storage benefit like PG&E, they only help flatten the day and not the winter summer problem

I'd curious of peoples thoughts on how California NEM 3.0 is effecting system sizing and the summer/winter problem.

So does this make sense?

Another way to think about. If you have a system that COULD export 12 months of the year even though you don’t want to means you have the option to reduce your grid usage quite substantially.