Off grid geodesic domes power from scratch

[valleydomes]

Hi,
I'm constructing 3x 18foot diameter geodesic domes on my property and aiming to go fully off grid.

Each dome will have a heat pump, small microwave (700watts), small coffee maker (550watts) and bar fridge (800watts) , sink, shower and compost toilet. Water pump will be a separate submersible unit in a rain water tank system powered by it's own means and hot water supplied by propane on demand system.

24v vs 48v Battery System

If I go 48v, that would present the option of going with a 48v heat pump and not have the inverter take the hit on that allowing me to go with a lower wattage inverter. Downfall being an extra 1000$+ per heat pump for the dc model and having to order a 12000btu (https://ecosolaris.com/en/produit/off-grid-solar-ac-dc4812/) vs 9000btu (https://senville.ca/9000-btu-mini-split-air-conditioner-senl-09cd/) and being 12000btu vs 9000btu would also use more power than needed to heat/cool the space. Having written this, I think I just talked myself out of going 48v...

If I go with the 9000btu which is 782watts, rated current of 6.8amps, minimum 16amp breaker requirement then a 5kw should be more than enough to handle the above mentioned items with their inrush currents? (5000w/110v = ~45amp)

We don't plan on running the domes year round but only during the summer/fall season, I don't suspect the heat pump will need to be running 24/7, if I stay away from the 48v system and run 24v, then would a 24v 100Ah LiFe04 battery suffice or larger? If it wasn't enough I could always add another 100Ah in parallel but would like to have my order done as to avoid shipping charges and delays from China.

If running the 100Ah battery, one 375 watt panel should suffice to charge it during summer and 2x 375watt panels if going with the 200Ah battery?

Thank you to anyone who decided to have a read on this

 

[snoobler]

24/48V is moot at this point, particularly since you hint that you believe one or two 100Ah batteries might suffice for this.

You need to establish your energy use. Link #1 in my signature.

A 9000BTU mini-split heat pump running only 8 hours in a 24 hour period alone will consume 3.2kWh of energy. You'd need 3.2/.8/.85 = 4.7kWh of storage. That's 184Ah alone. Again, assuming it only runs 8hr/day, and you use no other power of any kind.

.8 is due to only using 80% of LFP capacity.
.85 is a conservative assumption of efficiency loss between DC-AC

3.76kW of energy/day would require 5 solar hours with 750W of panels. 5 solar hours, particularly in winter when you need the heat pumps is amazing solar - better than I get here in AZ.

You need to determine your winter solar hours for your location, panel orientation and tilt. Link #5 in my signature.

Once you know your need, and you know your available solar, you can design an effective system.

 

[MichaelK]

Oh, cool, a hippy commune? Will there be young, scantily clothed girls? I want to join!

But seriously, even before doing a power audit as snoobler indicates, one 375W panel is not going to do it. Off the top of my head, I'd say you'd need 4-6 of those panels for each unit to create a viable system. Maybe in the 5000-6000W range if you want to power all three units with a single system.

I would not recommend paying more for DC rated appliances. You are better off investing in a larger AC system that will run cheap off-the-shelf parts.

 

[mike95490]

and bar fridge (800watts) , sink, shower and compost toilet.

Bar fridges are notorious for sucking power, because of thin insulation. Get a meter (Kill-a-watt), and average it's use over a week. A mid-size energy star fridge will cost more, hold more and consume less power.

Water pressure comes from ?? powered by ??

Does the toilet have vent fans or urine boiler heater ? Factor those into your budget. Panels are cheap - go overboard and go 48V

 

[MichaelK]

Hi Mike, nice to see you here! This site needs input from real electrical engineers!

 

[Q-Dog]

My mini fridge uses about 2/3 the power of my full size fridge, only holds about 1/6 the contents of the larger fridge, and the freezer only has room for 2 ice trays. We only use it for drinks and it is not on our solar backup battery system. If I were going completely off grid I would replace it.

 

[Supervstech]

255Sqft
What is the exterior constructed of? What insulation? Will 9000Btuh handle it? Maybe... glass? No way...

 

[mike95490]

Hi Mike, nice to see you here! This site needs input from real electrical engineers!

I'm rapidly approaching the conclusion folks here only want confirmation they done right, and not education or how to do something safely or reliably .

 

[snoobler]

I'm rapidly approaching the conclusion folks here only want confirmation they done right, and not education or how to do something safely or reliably .

What leads you to that conclusion?

 

[mike95490]

What leads you to that conclusion?

A pileing on of responses about 4 AGM batteries in parallel being a poor idea, in/after post

Initial setup of battery bank vs. Pv:

Specifications: for Hansol 355 watt panels : 6 panels total. Rated Power: 355W Open circuit voltage (VOC): 47.8 V Max power voltage (VMP): 39.2 V Short circuit current (ISC): 9.65 A Max power current: 9.06 Maximum system voltage: 1000V UL Fuse Rating: 15 A IP68 Junction Box with...

diysolarforum.com

I co-moderate 2 other forums, and have plenty to keep me busy without having to deal with frat boys that can't read/understand a link that breaks out the math on parallel battery issues . http://www.smartgauge.co.uk/batt_con.html
And hammer crimpers seem to be just fine, nobody has issues. Lot's of high wattage 12V systems pushing dangerous amps through 2/O wire just waiting for a fire.

 

[snoobler]

Thank you for bringing that thread to my attention. I have taken steps to address inappropriate posts.