4kW grid tie planning advice

[solarsemi]

Hi All,

First time posting here. I am early in the process of planning a modest 4 kW system for my home in Toronto, Canada. I'm hoping to receive some reassurance on my understanding so far and collect input on what I have not considered so far. I'm hoping to design the system, source most/all of the equipment myself, coordinate some/all of the permitting and work with an electrician for the install.

Here are my notes so far:

• 100A service to the home. Panel is full. Considering a small sub-panel expansion to make room for a new back-feed breaker.
• I am pre-approved by Toronto Hydro for a 4kW system (I have not submitted the official net metering application, but no red flags after an initial review)
• My understanding is that a 4kW system should generate about 4-4.5 MWh which would meet our current needs
  • We have a gas furnace and gas stove. No EV right now
• I have about 250 sqft of flat roof with no obstructions. I haven't selected a specific panel model yet, but after some searching it seems realistic that 250 sqft can support 4kW of panels
• Planning on using a ballasted flat roof mounting system that supports 5-10 degrees of tilt, facing south. I know I'll need a structural engineer's assessment for this
• I have my eye on the Growatt MIN 3800TL-XH-US for the inverter and connecting it load-side
  • 3.8kW at 240V will produce 15.8A peak. This is compatible with using a 20A breaker which appears to be allowable by code for 100A service (rule 64-112 4) ...similar to the 120% rule in the US from what I can tell)
    • I've read through the ESA bulletins on PV systems, but am not experienced with code rules in general
• I am familiar with cold temp voltage derating for when assembling strings
• Longer term, I'd love to install a solar carport in the backyard. I have about 200 sqft back there which could maybe approach another 4kW array if I used bifacial panels.
• No battery storage planned at this time due to space contraints

Questions:

• Can anyone with Canadian electrical code experience comment on key considerations for a single line diagram? I'm a little unsure of what over-current protections are needed in addition to a back fed breaker
• Does anyone have suggestions for installers in the greater Toronto area or tips on Canadian vendors for sourcing equipment?
  • Specific flat roof mounting system recommendations?
  • Any other inverters out there comparable to the Growatt?
• Any reason to consider a service side interconnect? Load side seems less expensive and less complicated. I suppose the main benefit of service side would be not having to expand the panel.
• What else should I be considering while planning this system with respect to increased electrical loads in the future (heat pump, induction cooktop, EV charger all possible) and the option of being able to support a few more kW on a carport?

Thanks in advance

 

[JBertok]

With regard to the main service panel, the inverter is going to need a dedicated double-pole split-phase breaker. It should be possible to make room for that by moving some circuits to your new loads panel fed from the inverter and transfer switch/breakers. I don't think a service side tap would be necessary; those tend to be for string inverter installations and/or when a separate meter is required.

How you set this up is dependent on your expectations for the system. Will the Net-Metering agreement be a 1:1 compensation or is self-consumption incentivized by a reduced compensation? Are you looking to separate the loads in your house to critical and non-critical with respect to how they're handled during a utility outage?
Also, you mentioned growing the system in the not-so-distant future. It might be worth spec'ing out a larger inverter right from the beginning, installing a big enough load panel that most circuits in the house can be moved immediately to it, and then expanding the PV when you're ready. The permitting process for system capacity is centered around PV production, not the size of the inverter, so you should be able to oversize the inverter. Same in Canada as in the US far as I know. The Growatt inverters with the high-voltage batteries will be a limiting factor in how you can expand the system in the future because you're always going to have to stay within the limits of your inverter's MPPTs, unlike a 48V nominal system where you can mix and match any components at any time and expand the system almost endlessly. It's for that reason it might be worth it to go large from the start.

 

[solarsemi]

Good points, thank you.

You suggestion about over-sizing the inverter for future expansion is a logical one. I'll look into that further. There were some clauses in the code about how to properly derate a system with an over-sized inverter (program a lower output, affix new labelling, restrict access etc.) but maybe that is only applicable if there are panels capable of generating more than what the system was approved for.

The net metering AFAIK is 1:1 compensation. I think the utility pays the time of use rate. And any credits that are earned can be used over the subsequent 12 months.

I haven't read much about the Growatt batteries. On principle, battery storage would be great. But outages are rare in the city from my experience, and there is limited space in the house.

 

[JBertok]

If battery storage isn't in the plans, and your net metering is 1:1, it really mitigates the point of attaching a loads panel to the output side of the inverter.

It would be good to know if these inverters can function in the absence of utility power without a battery. I don't know the answer to that. If they can't, then the output side of it really has no practical purpose for your scenario. Similarly, if using it as basically a string inverter only, with no plan to implement battery backup, or steer self-consumption around optimizing time-of-use rates using that battery, then sizing for future anticipated growth isn't necessary either - at that point you just add another small inverter for the new system and they don't need to share anything.