EG4 18KPV Design/Configuration Help for 16,000kWh PV, 400A service, new build, Net Zero Home in Vancouver, BC

[ElectricIslander]

Very nice diagrams that you made! I like drawing in .ppt and excel as well.

We have a rather energy frugal friend in Lynn Valley with 6 kW of roof panels. She offset her entire annual electrical consumption before she got a heat pump this year. She now still has a rather low hydro bill, even with the heat pump.

Unlike with net metering, which has a goal of offsetting annual use, we aren't so much concerned about annual generation. Our average daily household load as measured is around 4 kWhrs (fridge, lights, washing, computers etc.). This comes from a H2200 inverter generator at the moment, but we plan to rely on only solar as much as possible next year.

Since we are off-grid and have no net metering we have to design for winter low light conditions so as to have enough PV (7kW) and battery (30kWhr) to keep minimum systems alive (unavoidable loads such as fridge and inverter tare etc.) over 4 or 5 days of no real PV input during typical cloudy winters.

For that I modelled solar harvest with PVWatts vs an energy load spreadsheet that considered minimum, average and maximum loads. 7kW is the maximum amount of PV I can get on our south facing unshaded roof so that is pretty much set which determined PV sizing.

 

[ElectricIslander]

Hrm, quick question for the experts here/those of you who know far more than I, if the inverter can output 50A, what happens if you have 18kW of solar on an "ideal/lossless" sunny day and one is net metering? Is it having to shed some 25A of power? i.e. there is a "not-insubstantial-portion" that is not being fed back into the grid. Is that right?

Unlike for windturbines and hydrowheels, any excess PV power isn't "shed" as in having to dump 25A, it's simply not drawn from the panels by the charge controller circuitry. If you had batteries, that power could be going to charge them until they are full, then again once full, any excess is simply not used.

 

[NovicePV]

Very nice diagrams that you made! I like drawing in .ppt and excel as well.

We have a rather energy frugal friend in Lynn Valley with 6 kW of roof panels. She offset her entire annual electrical consumption before she got a heat pump this year. She now still has a rather low hydro bill, even with the heat pump.

Unlike with net metering, which has a goal of offsetting annual use, we aren't so much concerned about annual generation. Our average daily household load as measured is around 4 kWhrs (fridge, lights, washing, computers etc.). This comes from a H2200 inverter generator at the moment, but we plan to rely on only solar as much as possible next year.

Since we are off-grid and have no net metering we have to design for winter low light conditions so as to have enough PV (7kW) and battery (30kWhr) to keep minimum systems alive (unavoidable loads such as fridge and inverter tare etc.) over 4 or 5 days of no real PV input during typical cloudy winters.

For that I modelled solar harvest with PVWatts vs an energy load spreadsheet that considered minimum, average and maximum loads. 7kW is the maximum amount of PV I can get on our south facing unshaded roof so that is pretty much set which determined PV sizing.

Thanks. Skelion actually uses PVWatts Data/DB so you can indeed, just "skip it" and use the site directly. I happened to use Skelion because I had to model the house anyways (for everyone else to see since they couldn't quite see what I was imagining in my head) and I could quickly layout/try different panels to see what my energy generation might be.

Thanks!
Oliver

 

[ElectricIslander]

Thanks. Skelion actually uses PVWatts Data/DB so you can indeed, just "skip it" and use the site directly. I happened to use Skelion because I had to model the house anyways (for everyone else to see since they couldn't quite see what I was imagining in my head) and I could quickly layout/try different panels to see what my energy generation might be.

Thanks!
Oliver

Ahh, good to know that's what Skelion does, will have to investigate.

Re excess PV energy again: The reason you can overpanel a charge controller is exactly that, PV energy doesn't need to be pulled from the panels. If you don't pull out electrical current, that energy is just dissipated as heat in the panels (ie they get warmer in the sun ...)

- Graham (Engineering and Physics background)

 

[NovicePV]

Ahh, good to know that's what Skelion does, will have to investigate.

Re excess PV energy again: The reason you can overpanel a charge controller is exactly that, PV energy doesn't need to be pulled from the panels. If you don't pull out electrical current, that energy is just dissipated as heat in the panels (ie they get warmer in the sun ...)

- Graham (Engineering and Physics background)

Hah, it's funny because "I should know that" as an B. Eng. My defense is that I haven't had to do any of that for 20+ years. LOL.

Anyways, this matters toe because I'm artificially capping what I can put back into the grid which of course affects my "Net Zero" balance. That said, the fix should be easy enough: split up the strings between the paralleled 18kPV units. Right?

Thanks!

 

[ElectricIslander]

Thought you had the "Engineer's" touch with your drawing skills ..... I don't know much about on grid or how the 18PV software works, but in the Schneider on-grid modes you can set something like the grid export "breaker" value to limit the export current. Why is your cap on export "artificial"? Is that the panel size limitation or some BC Hydro limitation?

 

[NovicePV]

Well it would be limited by whatever can be converted by one Inverter if I'm not mistaken. So, although the PV array might theoretically generate 18,000W (which ignoring losses would convert to ~75A at 240VAC) a single 18KPV Inverter itself can only draw and convert ~50A @240VAC right? That means I can only output that amount to the grid from a single Inverter...I think?

In essence, I'm "losing" 25A@240V (6000VA or let's just say W) as heat then. Am I understanding all this incorrectly? (Assume I have zero batteries to charge, and zero load at the house).

Thanks!

 

[ElectricIslander]

Don't know much about the 18KPV Inverters, but you have two of them right? With half of the 18kW PV panels on each it shouldn't be a problem outputting all of the power (9 kW each, i.e. 37.5 A @ 240V) to the grid since the inverters are both synched. By the way, "Primary and Secondary" is the new PC way of saying "Master and Slave" to the grid.

 

[NovicePV]

Don't know much about the 18KPV Inverters, but you have two of them right? With half of the 18kW PV panels on each it shouldn't be a problem outputting all of the power (9 kW each, i.e. 37.5 A @ 240V) to the grid since the inverters are both synched. By the way, "Primary and Secondary" is the new PC way of saying "Master and Slave" to the grid.

Yes, that's what I am counting on indeed. Split up the strings between the 2xParalleled Inverter.

Re: Primary/Secondary, yes I'm aware. Someone (whether Sol-Ark or EG4 or LuxPower I can't remember) was using Master/Slave terminology so I switched to language in the docs because I had a conversation with a company who got all confused and didn't understand primary/secondary vs. docs. Yep...really dumb, I know. Sometimes it's just not worth the effort to correct/fight; case in point, disagreements with the City of Vancouver (most of the time).