chhamilton
New Member
- Joined
- May 31, 2022
- Messages
- 1
I recently finished building a new home in the Laurentians, in Quebec, Canada. I was originally planning to go fully off-grid, but when I sized out a system for that it was pretty expensive. In the end I decided to be on-grid, with a whole home generator for backup power, with gas for cooking and wood for backup heat, and with plans to put in some solar at some point. Having just gone through a 1 week power outage I'm thinking I might do that sooner rather than later.
The generator is a 19kW / 80A generator, and it is sufficient to run all the major circuits in the house. I can overload it if I go around the house turning everything on, but it's generally not a problem. The problem is that it's noisy and expensive, and *most* of the time it is completely overkill. Because of this I keep it in manual mode and only turn it on and off as needed.
I'm thinking that I'd like to install solar for a few basic necessities:
- the fridge (so I don't lose a fridge full of food again)
- the water pump (so I can use water without the generator needing to be on)
- basic electronics (Starlink internet, HomeAssistant RaspberryPi, television)
- lighting circuits
- a single 15A wall outlet for charging phones/laptops
Looking at peak load I'm hitting about 12 kW (with well pump surge 39A @ 240V = 7kW and fridge surge 13A @ 120V = 1.5kW being a good chunk of that). Looking at max continuous load I'm looking at 4kW. It looks like a 6kW inverter should do the job, assuming it has at least 2x surge capacity.
Looking at average power usage while inhabited (2-3 days per week) I'm calculating about 11kWh. This drops to about 8kWh when I'm not around (no lights, no water, no television). Call it 9kWh/day on average. If I was looking for full autonomy for that gear I'd probably want 8kW of panels and about 30kWh of batteries.
The key thing is I'm not looking for full autonomy. I just want to reduce the generator usage, and when I use it I want it to be at capacity for as short a time period as possible. I'd like to keep the generator usage down to a couple hours every day or so (charge the batteries, keep the hot water hot, run the dishwasher, do a load of laundry, etc). Doing some simple modeling I arrive at 3kW of panels and 10kWh of storage as being reasonable. The panels will generate 4-8kWh of power in an average day, I'll consume 9kWh on average, drawing 1-5kWh of that from the batteries, and I'll get 2-5 days of autonomy before needing to help the batteries charge. At 100A (4.8kW) into the batteries they'd be charged with 2.5 hours of generator time.
Does all of that sound reasonable?
Now for the architecture.
Right now the entire main panel is on the generator. My plan would be to run a 20A 240V circuit off the main panel to the inverter-charger, and then have the inverter drive a 30A 240V split-phase panel. I'd move the various circuits to this panel. Those circuits would forever and always be running through the solar system, even when the grid is up and running. I could use a variety of automation smarts to drive turning the generator on and off when the batteries get too low, but if it's possible to have the inverter-charger drive this logic directly that's even easier (less work for me!)
The next step would actually be to do some shopping. Space is somewhat at a premium so I'd prefer a single split-phase inverter as opposed to pairing 2 single-phase inverters. Since I've got some large inductive loads it appears that I should be looking for beefy low frequency inverters. From what I can tell, it looks like the MPP LVX6048 would do the job? Any reason why not? Any alternatives?
For batteries I was looking at the 48V 100Ah Jakiper rackmount batteries. They seem well reviewed and the prices are good.
Solar will be roof mount. I have a flat roof, so I need to find some appropriate racks, ideally adjustable. Any recommendations?
Anything else I should be thinking about?
The generator is a 19kW / 80A generator, and it is sufficient to run all the major circuits in the house. I can overload it if I go around the house turning everything on, but it's generally not a problem. The problem is that it's noisy and expensive, and *most* of the time it is completely overkill. Because of this I keep it in manual mode and only turn it on and off as needed.
I'm thinking that I'd like to install solar for a few basic necessities:
- the fridge (so I don't lose a fridge full of food again)
- the water pump (so I can use water without the generator needing to be on)
- basic electronics (Starlink internet, HomeAssistant RaspberryPi, television)
- lighting circuits
- a single 15A wall outlet for charging phones/laptops
Looking at peak load I'm hitting about 12 kW (with well pump surge 39A @ 240V = 7kW and fridge surge 13A @ 120V = 1.5kW being a good chunk of that). Looking at max continuous load I'm looking at 4kW. It looks like a 6kW inverter should do the job, assuming it has at least 2x surge capacity.
Looking at average power usage while inhabited (2-3 days per week) I'm calculating about 11kWh. This drops to about 8kWh when I'm not around (no lights, no water, no television). Call it 9kWh/day on average. If I was looking for full autonomy for that gear I'd probably want 8kW of panels and about 30kWh of batteries.
The key thing is I'm not looking for full autonomy. I just want to reduce the generator usage, and when I use it I want it to be at capacity for as short a time period as possible. I'd like to keep the generator usage down to a couple hours every day or so (charge the batteries, keep the hot water hot, run the dishwasher, do a load of laundry, etc). Doing some simple modeling I arrive at 3kW of panels and 10kWh of storage as being reasonable. The panels will generate 4-8kWh of power in an average day, I'll consume 9kWh on average, drawing 1-5kWh of that from the batteries, and I'll get 2-5 days of autonomy before needing to help the batteries charge. At 100A (4.8kW) into the batteries they'd be charged with 2.5 hours of generator time.
Does all of that sound reasonable?
Now for the architecture.
Right now the entire main panel is on the generator. My plan would be to run a 20A 240V circuit off the main panel to the inverter-charger, and then have the inverter drive a 30A 240V split-phase panel. I'd move the various circuits to this panel. Those circuits would forever and always be running through the solar system, even when the grid is up and running. I could use a variety of automation smarts to drive turning the generator on and off when the batteries get too low, but if it's possible to have the inverter-charger drive this logic directly that's even easier (less work for me!)
The next step would actually be to do some shopping. Space is somewhat at a premium so I'd prefer a single split-phase inverter as opposed to pairing 2 single-phase inverters. Since I've got some large inductive loads it appears that I should be looking for beefy low frequency inverters. From what I can tell, it looks like the MPP LVX6048 would do the job? Any reason why not? Any alternatives?
For batteries I was looking at the 48V 100Ah Jakiper rackmount batteries. They seem well reviewed and the prices are good.
Solar will be roof mount. I have a flat roof, so I need to find some appropriate racks, ideally adjustable. Any recommendations?
Anything else I should be thinking about?