Off Grid Solar Questions

[lbcrocks]

I'm new to solar power, but ultimately am planning on building my own house, and want it to be off grid. I'm in the research phase of the solar power system and have just a few questions. I'm planning for all of my typical "high draw" appliances (stove, dryer, water heater) to run off of propane, as to minimize the amount of electrical draw from appliances, but living in the south want to have an A/C and heater. I'm looking at a 4 zone ducted mini-split system for the house, but am finding it hard to figure out what wattage they use to size my solar system.

The system I'm thinking might be big enough, would consist of 15- 395 W Solar Panels, a 12K Growatt Hybrid Inverter, and 2- BigBattery.com Kong 15kW Batteries.

Also, with a PV array with 15- 395 watt panels, run as 3 in series, 5 parallel, would I need a combiner box to run that to my inverter?

Any information would be greatly appreciated.

 

[OffGridInTheCity]

I'm in zone 4 and use heat-pump for home but need your home's square feet to give guidance. I have a 4ton/forced-air whole house and it maxes out at 5000kwh. 12,000w inverter will likely be enough to run the mini-split you need.

15 x 395w panes = 6kw PV. I have a 13kw PV and need 40kwh for 80% DOD - so by extrapolation (as a ballpark) you'll need around a 20kwh battery bank to have enough storage to be able to consume all you produce. A smaller battery is OK, you'll just find that you top off earlier in the day and 'loose' some of your PV if it's too small - so leave room to expand.

My13kw PV produces 18,000kwh per year. You can use PVWatts https://pvwatts.nrel.gov/pvwatts.php to a good guide for your specific location/weather. I have 16.7% efficiency losses so I only get 15,000kwh/year useable out of the inverters with 18,000kwh coming in. So figure in 15% losses as a general guide - e.g. if you produce 8500kwh/year you'll have 7,225kwh of actual power available.

Solar is sooooooo cool! Best advice, leave room to expand everything! Panels, parallel a 2nd inverter, larger battery bank over time

 

[Kornbread]

Might want to research BigBattery.com. The wiring of the pv panels depends on the controller. Although, I have read some posts about their reliability, mini-splits can be very efficient. Much more efficient than my old geothermal heat pump.

 

[lbcrocks]

I'm in zone 4 and use heat-pump for home but need your home's square feet to give guidance. I have a 4ton/forced-air whole house and it maxes out at 5000kwh. 12,000w inverter will likely be enough to run the mini-split you need.

15 x 395w panes = 6kw PV. I have a 13kw PV and need 40kwh for 80% DOD - so by extrapolation (as a ballpark) you'll need around a 20kwh battery bank to have enough storage to be able to consume all you produce. A smaller battery is OK, you'll just find that you top off earlier in the day and 'loose' some of your PV if it's too small - so leave room to expand.

My13kw PV produces 18,000kwh per year. You can use PVWatts https://pvwatts.nrel.gov/pvwatts.php to a good guide for your specific location/weather. I have 16.7% efficiency losses so I only get 15,000kwh/year useable out of the inverters with 18,000kwh coming in. So figure in 15% losses as a general guide - e.g. if you produce 8500kwh/year you'll have 7,225kwh of actual power available.

Solar is sooooooo cool! Best advice, leave room to expand everything! Panels, parallel a 2nd inverter, larger battery bank over time

I'm looking at around 2400 sq. ft. barndominium. The mini split I'm looking at is 48k BTU @ 22.4 SEER rating.

I was basing my 15 panels off the fact the inverter has a max input of 7000 watts, so was aiming to keep the total wattage below that threshold, but with that calculator you posted, looks like I can bump that up to 21 panels with the expected losses for my area. I figured the battery bank would need to be in that ballpark, and that's why I want to go with the 30 kWh from the 2 Kongs, that and their price/kW. And according to bigbattery.com, I would be able to link 8 of them together down the road if I see fit. The roof size I am planning for, would be able to accommodate a total of 31 panels, so I would have room to expand there as well. I just don't know that the inverter has the ability to be paralleled or not. I'll have to look into that one.

 

[lbcrocks]

Might want to research BigBattery.com. The wiring of the pv panels depends on the controller. Although, I have read some posts about their reliability, mini-splits can be very efficient. Much more efficient than my old geothermal heat pump.

I've done some research on big battery, and watched review from Will Prowse and others, and for the price per kW, from what I can tell, seems to be a pretty descent option.

I was considering geothermal, but then found the mini-split, and thought that it would be a better fit, plus the fact that I am a DIY person, it seems a lot more DIY friendly, up to the point of having the system charged.

 

[Bud Martin]

I would figure the panels for worst case weather condition, you can over panel the system, the system pull power from panels as needed up to the maximum power the system can deliver, panels do no push power into the system, but you do have to watch out that the PV panel Voltage will not exceed the max PV Input Voltage, that is how SCC gets damaged.

 

[lbcrocks]

I would figure the panels for worst case weather condition, you can over panel the system, the system pull power from panels as needed up to the maximum power the system can deliver, panels do no push power into the system, but you do have to watch out that the PV panel Voltage will not exceed the max PV Input Voltage, that is how SCC gets damaged.

Yeah, that's why i only have 3 in a series. The inverter has a VOC of 150v, and each panel has a VOC of 50.1 V.

 

[Kornbread]

I would figure the panels for worst case weather condition, you can over panel the system, the system pull power from panels as needed up to the maximum power the system can deliver, panels do no push power into the system, but you do have to watch out that the PV panel Voltage will not exceed the max PV Input Voltage, that is how SCC gets damaged.

Is this true for all controllers? I mention this because of this article Overpaneling which states that " ... Growatt tech support says the Max PV Array Power is a hard limit, so these controllers can not be over-paneled. ... " in regards to an spf3000tl. At 12k and 150v pv input, it sounds like the op has a GW spf12000t and the manual does list a max pv array of 7k. Food for thought.

 

[OffGridInTheCity]

I'm looking at around 2400 sq. ft. barndominium. The mini split I'm looking at is 48k BTU @ 22.4 SEER rating.

I have a 2600sq ft home and use a 4-ton, top end SEER (Lennox) forced air whole-house heat-pump. In Zone 4 we get down to 27-30F/-2C occasionally with 35F/2C as the norm thru Dec and Jan. I forced it to be heat-pump only and my highest winter months (Dec and Jan) were 1200-1400kwh/month over 2 years. But this was scheduling it to raise the temp at 6am when it was 30F outside. In an emergency (no-grid backup), waiting till noon with 40-50F outside, it should be significantly less power.

AC in hottest months tops out at 1000kwh/month for me.

Of course, you're insulation and situation will vary but I bet you'll be significantly less than my situation.

I was basing my 15 panels off the fact the inverter has a max input of 7000 watts, so was aiming to keep the total wattage below that threshold, but with that calculator you posted, looks like I can bump that up to 21 panels with the expected losses for my area. I figured the battery bank would need to be in that ballpark, and that's why I want to go with the 30 kWh from the 2 Kongs, that and their price/kW. And according to bigbattery.com, I would be able to link 8 of them together down the road if I see fit. The roof size I am planning for, would be able to accommodate a total of 31 panels, so I would have room to expand there as well. I just don't know that the inverter has the ability to be paralleled or not. I'll have to look into that one.

Fantastic - sounds like you're in the zone... and I look forward to following your progress if you report it

 

[12VoltInstalls]

Yeah, that's why i only have 3 in a series. The inverter has a VOC of 150v, and each panel has a VOC of 50.1 V.

My reading of this is that you would be over voltage max with three in series? Or…?

I hate when in inverter labels state VOC input- it’s hard to decide if that means 165 actual voltage in cold weather is ok or if that would be an uh-oh. “Max volts” isn’t an interpretive number: it’s max. Solar panels vary in temperature coefficient.