Tell me why my system sucks. Off-grid PNW build.

[Patrick H]

I am building a house this summer and will be putting in solar. Here's what I have planned so far, I'd love input on quality of parts and if you think it makes sense or if I should change something.

Solar System
24 x 400w bifacial Canadian Solar Mono Panels - $207 each - $4,968 total
10 x 100ah (2 of the 5 battery kits) - $8,449 each - $16,898 total
Sol Ark 15k (recommend other all in one set ups?) - $7,925
Fuses, cables, etc - Haven't looked at these yet
Rack mount - Haven't looked at these yet

My situation
The house I'm building will be off grid. My house is at 48 degrees latitude and gets and average of 2.5 hrs winter sun per day. I will be rack mounting these, and we get a lot of snow there so the bifacial panels should do well there.

I will be powering:

• My house, which will be using a lot of passive principles like making use of the natural light with a big southern exposure, big windows etc which should help reduce energy consumption
• Shop/garage - will need to power lights there but not very much. Occasional use of power tools, charging batteries etc.
• Possibly a well pump, or that may on a separate system - that will depend on where the well is drilled, that has not been finalized yet.
• House heating will not be on solar, I'll be doing a rocket mass heater for that.

That's about it. Unfortunately I don't know exactly what my energy usage will be with things like an electric water heater etc but I'm trying to size this to be big enough to handle everything within reason. This system would have a max PV output of 12,480 watts when accounting for the backside of the bifacial panels, and a 50kW battery system to give me a few days of back up. I want as little reliance on a generator as possible - I'd rather put money into a better solar system instead.

Side note - someone recommended a CO2 water heater which is much more efficient with solar - any thoughts or experiences?

All input appreciated on the system and also recs on where to buy. Thanks

 

[dcg9381]

We have no idea how well this is going to work, too much variation (on the usage side). Nothing wrong with what you're planning. My thoughts:

10 x 100ah (2 of the 5 battery kits) - $8,449 each - $16,898 total

What's the total capacity here? Or a reference to the kit. Is this the 50kWh total?

You're sun constrained so two things will be critical:

• Being able to clear snow off your panels
• Being able to change tilt / orientation between summer and winter use (makes an efficiency difference)

Your inverter can do about 12KW continuous, so that's about 60A at 240V. Of the things you've mentioned a well pump is probably the highest draw, but that's likely to be under 15A.

People can give you advice on "oversizing" your panels. You can't oversize peak voltage, but I see recommendations of some oversizing - and I know I could get by with that on my own PV system.

I am absolutely convinced that you will need a backup power source. Likely an inverter generator - or something else that can help you "bridge the gap" while you figure out how much power you actually need. Not all inverters play nice with generators (although inverter generators may not have that issue). That does not mean a "huge generator" - I'm talking about something in the 3-5KW range that can bridge the gap if you get into trouble or have a week of overcast. Under $1k. Portable.

What is the availability of propane for fuel? It can power do heat, water, and provide fuel for a generator.

"C02 water heater" is more commonly known as a heat pump water heater. They're probably the most efficient in areas where temperatures or more moderate - perhaps if you can keep it in a basement or other area above freezing. They often have resistive heat as a back up heat source. We have one in Michigan, but my preference for small cabins in terms of simplicity, cost, and operation is a simple <$500 tankless propane heater. Whatever you get, it'll need to be winterized.

 

[BentleyJ]

Something is off with the math. Not sure where the 12,400W PV output number came from but 24 panels at 400W each is 9,600W. Edit, I assume the bifacial panels will produce more than a conventional panel but 12,400W vs. 9,600W is bit optimistic. If you are getting only 2.5 solar hours per day in the winter that would be 24kWh per day when the sun is out in good conditions. Any other situation solar production is going to be less. I'm thinking you may want to increase the size of your solar array but difficult to confirm with certainty without a daily usage estimate which is not available at this time.

Being off-grid means 100% reliance on your own equipment. While the Sol-Ark is a good product and will most likely do the job, everything is basically in one box. That said, If I were designing the system I would seriously consider the advantages of stacking a couple of smaller inverters and maybe even using separate charge controllers so there is no single point of failure. While the initial installation is more difficult with separate components there is a redundancy factor. One item can be repaired or replaced while the remainder of the system is operating although with diminished capacity. Take a look at the Schneider XW Pro, 2 inverters, 2 charge controllers and a PDP would be a very good, reliable system.

 

[Patrick H]

We have no idea how well this is going to work, too much variation (on the usage side). Nothing wrong with what you're planning. My thoughts:


What's the total capacity here? Or a reference to the kit. Is this the 50kWh total?

You're sun constrained so two things will be critical:

• Being able to clear snow off your panels
• Being able to change tilt / orientation between summer and winter use (makes an efficiency difference)

Your inverter can do about 12KW continuous, so that's about 60A at 240V. Of the things you've mentioned a well pump is probably the highest draw, but that's likely to be under 15A.

People can give you advice on "oversizing" your panels. You can't oversize peak voltage, but I see recommendations of some oversizing - and I know I could get by with that on my own PV system.

I am absolutely convinced that you will need a backup power source. Likely an inverter generator - or something else that can help you "bridge the gap" while you figure out how much power you actually need. Not all inverters play nice with generators (although inverter generators may not have that issue). That does not mean a "huge generator" - I'm talking about something in the 3-5KW range that can bridge the gap if you get into trouble or have a week of overcast. Under $1k. Portable.

What is the availability of propane for fuel? It can power do heat, water, and provide fuel for a generator.

"C02 water heater" is more commonly known as a heat pump water heater. They're probably the most efficient in areas where temperatures or more moderate - perhaps if you can keep it in a basement or other area above freezing. They often have resistive heat as a back up heat source. We have one in Michigan, but my preference for small cabins in terms of simplicity, cost, and operation is a simple <$500 tankless propane heater. Whatever you get, it'll need to be winterized.

The 50kWh is the battery system. 10 x 100ah batteries (5,120w each) is roughly 50kWh.

I have a small generator, but I have no intention of running a whole house generator to get through each winter. I understand this means cutting energy usage in the winter, which I'm fine with. Like I said I don't see the point of spending 10-15k on a whole house generator that relies on fossil fuels which are increasingly at risk of becoming more expensive and limited as time goes on. I think we are aligned on that, as my portable generator is about what you described.

Assuming the heat pump water heater isn't enormous, I should have room in the utility room I'm designing which will be well insulated and heated.

 

[Patrick H]

Something is off with the math. Not sure where the 12,400W PV output number came from but 24 panels at 400W each is 9,600W. Edit, I assume the bifacial panels will produce more than a conventional panel but 12,400W vs. 9,600W is bit optimistic. If you are getting only 2.5 solar hours per day in the winter that would be 24kWh per day when the sun is out in good conditions. Any other situation solar production is going to be less. I'm thinking you may want to increase the size of your solar array but difficult to confirm with certainty without a daily usage estimate which is not available at this time.

Being off-grid means 100% reliance on your own equipment. While the Sol-Ark is a good product and will most likely do the job, everything is basically in one box. That said, If I were designing the system I would seriously consider the advantages of stacking a couple of smaller inverters and maybe even using separate charge controllers so there is no single point of failure. While the initial installation is more difficult with separate components there is a redundancy factor. One item can be repaired or replaced while the remainder of the system is operating although with diminished capacity. Take a look at the Schneider XW Pro, 2 inverters, 2 charge controllers and a PDP would be a very good, reliable system.

The panels are 400W on the front, 120W on the back = 520W total. Obviously that's under optimal conditions etc. but the 520 x 24 is the 12,400W PV.

Appreciate the input on not putting all my eggs in one basket. I will keep that in mind. And I will check out the XW Pro, thanks for the suggestion

 

[dcg9381]

The 50kWh is the battery system. 10 x 100ah batteries (5,120w each) is roughly 50kWh.

I have a small generator, but I have no intention of running a whole house generator to get through each winter. I understand this means cutting energy usage in the winter, which I'm fine with. Like I said I don't see the point of spending 10-15k on a whole house generator that relies on fossil fuels which are increasingly at risk of becoming more expensive and limited as time goes on. I think we are aligned on that, as my portable generator is about what you described.

Assuming the heat pump water heater isn't enormous, I should have room in the utility room I'm designing which will be well insulated and heated.

Thanks on the battery size, that gives me some idea of scale of total capacity.
I'm not telling you to run a whole house generator. I'm telling you this from experience - I would not EVER attempt to do what you're doing (especially where you are thinking about doing it) without a back up plan. Having a 3-5KW generator is that backup plan. Personally, I'd have two of them.

I get the "fossil fuels" deal, but I'm asking you about what "sustainable" fuel you have access to in the area. Electrical is great, but it's very "expensive" as a raw heat source for resistive heat.

Put a heat pump water heater into heated space and that's fine.. Especially in an area like a basement where most of the temperature control is essentially geothermal. Put it into heated space and it's going to work to cool that space. That's something to consider. And again, heat pump water heaters are $2k+ or so...It looks like only recommended for 40F or above. Put it in the house and you're kinda fighting your heating with cooling. It could be fine if you're heating with pellets/wood. Just depends. I like tankless propane (because I can get propane easily and it's portable) and it's electrical draw is exceptionally low.

I agree with others on the single inverter. What's at risk is potentially a total freeze up and massive damage to your home. You need at least one and perhaps more than one fall back.

 

[Patrick H]

Thanks on the battery size, that gives me some idea of scale of total capacity.
I'm not telling you to run a whole house generator. I'm telling you this from experience - I would not EVER attempt to do what you're doing (especially where you are thinking about doing it) without a back up plan. Having a 3-5KW generator is that backup plan. Personally, I'd have two of them.

I get the "fossil fuels" deal, but I'm asking you about what "sustainable" fuel you have access to in the area. Electrical is great, but it's very "expensive" as a raw heat source for resistive heat.

Put a heat pump water heater into heated space and that's fine.. Especially in an area like a basement where most of the temperature control is essentially geothermal. Put it into heated space and it's going to work to cool that space. That's something to consider. And again, heat pump water heaters are $2k+ or so...It looks like only recommended for 40F or above. Put it in the house and you're kinda fighting your heating with cooling. It could be fine if you're heating with pellets/wood. Just depends. I like tankless propane (because I can get propane easily and it's portable) and it's electrical draw is exceptionally low.

I agree with others on the single inverter. What's at risk is potentially a total freeze up and massive damage to your home. You need at least one and perhaps more than one fall back.

Right on, thanks. For space heating I'll be doing a rocket mass heater, which is an extremely efficient wood-burning system - so no draw from my solar for that. I would also like to preheat my water in the winter by running it through the thermal mass of my rocket mass heater, that's something I'll be exploring more.

 

[LBART]

Do you have a link about the rocket mass heater you are considering? At first look I see some that look poorly designed DIY contraptions.

 

[ElectricIslander]

We are off grid in the Canadian PNW, on a small island and manage to get through winters on a small amount of generator power.

The key at your stage of construction is planning for energy conservation by making everything as efficient as possible:

• Low powered appliances (everything "inverter" is the magic word - fridge, washer, inverter motor driven propane drier)
• High quality, low power water pump
• Insulate, insulate, insulate - draft seal, draft seal, draft seal
• Model your energy use before selecting a solar system (download an Excel sheet of loads and count everything - in particular loads that are always on)
• Look carefully at inverter idle power usage (Sol-ark is not the best in this respect) consider Schneider - much less always on idle losses. Inverters and fridges/freezers can use up most of your power if not carefully selected (because they typically run all the time)
• Look carefully at battery idle power usage which is a constant drain on your stored energy (be careful with some batteries - check idle power of Fortress Eflex vs Fortress E-Vault vs Discover AES for instance). Make sure you understand the difference between open loop batteries (you are the computer keeping your battery bank on track) and closed loop batteries (software takes care of twiddling with your battery settings to keep everything going as it should)

Off grid is an entirely different focus and doubly or triply so in the PNW!

By the way, heat pumps with C02 as the working fluid are better for air to water use due to better efficiency at high output temperatures as required for domestic hot water heating or for in-floor radiant heating.

If you preheat your water, make sure that your water heater allows preheat - many do not (such as our Bosch flash heater since it can overheat if the incoming water is too hot).

We have an Rheem Heat Pump hot water heater in our city house that works really well and ditto for the Mitsubishi air to air heat pump we use for house heating but rely on a Bosch Propane flash heater for the off grid cabin. The cabin is heated by wood and a backup Williams wall heater (no power required).

We get by on about 3 KWhr to 4 KWhr a day with the inverter fridge, inverter washing machine, mostly drying clothes on the line and running a dishwasher every few days. Watch movies on a laptop, LTE WiFi hub for internet.

 

[Patrick H]

Do you have a link about the rocket mass heater you are considering? At first look I see some that look poorly designed DIY contraptions.

This is something you build, not buy, generally speaking. I have a book on how to design and build them, I haven't read it yet but will soon.

 

[LBART]

This is something you build, not buy, generally speaking. I have a book on how to design and build them, I haven't read it yet but will soon.

That is what it looked like in what I found. I am always curious on new ideas.

 

[Patrick H]

@BentleyJ @ElectricIslander I'm curious what your opinions are on a Victron system vs the Schneider, any thoughts there?

 

[BentleyJ]

I'm curious what your opinions are on a Victron system vs the Schneider, any thoughts there?

Unfortunately, I don't have any first hand experience with Victron so any personal opinions would be a result of incomplete info. That said, it seems like very few Forum members experience serious, unexplained problems such as random shut downs, voltage or amperage excursions outside of set points, communication issues, premature hardware failures Etc. Overall I believe the Victron Brand is top level. For US split phase installations it seems like their product offerings are limited or an autotransformer is needed.
I'm happy with the XW+ and if necessary would likely replace it with a XW Pro without second thought.

 

[SamDeleted]

Tell me why my system sucks.​

It so expensive!

Maybe I'm just tight fisted lol , $20k plus on a PV system seems like a LOT of money

 

[Patrick H]

Unfortunately, I don't have any first hand experience with Victron so any personal opinions would be a result of incomplete info. That said, it seems like very few Forum members experience serious, unexplained problems such as random shut downs, voltage or amperage excursions outside of set points, communication issues, premature hardware failures Etc. Overall I believe the Victron Brand is top level. For US split phase installations it seems like their product offerings are limited or an autotransformer is needed.
I'm happy with the XW+ and if necessary would likely replace it with a XW Pro without second thought.

Right on, thanks

 

[S610]

What is the availability of propane for fuel? It can power do heat, water, and provide fuel for a generator.

100% agree. An off-grid propane stove, generator, water heater etc...provides redundancy if the solar goes out. Also allows for propane heaters in a pinch. Best not to have all our eggs in one basket.

 

[Zack R]

Have you looked into geothermal heat pumps? Could be an option since you will already be excavating to build the house and presumably the septic drainfield.

I'd combine that with a nice wood stove (or two) for heating. Modern wood stoves burn clean and efficient compared to smoke dragons of the past. Perhaps not as efficient as a rocket mass heater but still around 80%, plus you don't have to build it and you get to enjoy the pretty fire (worth something in itself).