Off Grid for small Cabin

[pbennison]

We recently bought a cabin in northern NY with no grid power. I got an estimate to run grid power but it was three times the cost of the cabin. The cabin is small with a wood stove, propane heater, propane refrigerator and I plan to install LED lights. My plan is to have an off grid solar generator system with backup gas generator. I ran the power consumption calculator and estimated that I will use approximately 2000WH/Day. I have added a factor of 25% for a total of 2500WH/Day. I have spent the past couple months researching on forums like this and below is my first stab at a couple options. I would appreciate any and all advice. Plan would be to use the cabin during the spring, summer and fall. If needed I would disassemble and break down for winter.

Thank you...


2500WH/Day
2 Days Autonomy

Option 1
48V
4 250W Solar Panels
30A/48V Controller
3000w Inverter/Charger

Option 2
24V
4 250W Solar Panels
50A/24V Controller
3000w Inverter/Charger

 

[snoobler]

So you need 5kW of usable capacity for 2 days.

That's 10kW of FLA/AGM/GEL or 6.25kWh of LFP

With 1kW of solar, you need 2.5 hours of sun per day.

Simulating a 1kW system with 15% losses and panels mounted at 45°:



Looks like your worst case is in Dec, 82/31 = 2.6kWh/day average

Do you actually have items that will require 3kW of power? Your inverter power is dictated by your largest load, and/or your largest combined load. Do you want the convenience of being able to run everything at once, or are you cool with limiting high power items single use.

This matters because inverters have an idle draw - power they pull even when no loads are present. It's usually listed in their specs, but about 7.5W/kW of power is a good rule of thumb. A 3kW inverter may pull about 22.5W. Over a 24 hour period, that's another 0.54kWh, i.e., 20% of your total. If your biggest load is a microwave, and you don't plan to run high power devices, a 2kW would suffice. If you can live with a small 700W microwave, a 1500W inverter will do.

24 vs 48V is essentially at your preference.

 

[evilroy]

Take a peek over at the Small Cabin Forum / Off Grid, lotsa good info for you there too.

 

[Hedges]

Does the roof have sun exposure and available area?
I would double the PV array. It's cheap, as little as $200 for the 1kW you listed.
If you go with 10 kW AGM battery, 2kW PV should be OK charge rate 0.2C (but check specs of the model you consider.)
Estimate $2500 for the battery.
AGM means never having to worry about cold, so long as you have a reasonable low-voltage disconnect so never drain it completely.

 

[Delmar]

What exactly do you plan to power? You only listed LED lights. Please show your calculations.

Attempting to find DC items will save the losses from the inverter, and affect your decision on the battery voltage. My office runs from 12V with lights, fans and USB ports for charging portable items.

You can keep the inverter switched off, and only turn on when powering large items.

 

[Luthj]

My only addition to snooblers excellent post, is that if you plan to use lead, I would add another 10-15% to the PV array. Lead has lower charge efficiency, and needs enough excess PV output to allow extended absorb on sunny days. Extended partial SOC cycling is detrimental to lead lifespan.

Did you include standby power consumption in your calculations? Inverters and other gear can add 10-30% your total numbers with their quiescent/standby consumption.

 

[evilroy]

Bottom line based on 9 years off grid living or was that ten.....lost track....whatever you think you need power wise....double it, unless you want a giant money pit adopt an attitude that Electricity is not your friend, look for any and all ways around it, don't be afraid to experiment and create your own solutions, in the end it is much simpler and cheaper than you might think once you look at what you really need and what you think you need, snoop on forums and online stores for ideas....a lot of products can be re purposed, get you brain working, there is no set way to do it because some people just want an off the shelf solution and some of us constantly say that's nice but there has to be a better way, most importantly have fun doing it.

 

[MichaelK]

I'll do the numbers for lead-acid
2500Wh/day X 2 days X 2X for only 50% depletion = 10,000Wh, or 10.0kWh of power (5kWh at 50% depletion).

At 24V you'd need 10,000Wh/24V = 418Ah battery, a Trojan L-16 would match this. Four L-16s would be about 350$ X 4 = 1400$
At 48V you'd need 10,000Wh/48V = 208Ah battery, a Costco 210Ah golf-cart battery would match this. Eight Costco batteries would be 138$ X 8 = 1104$.

At 24V, you'd need a charge of 1/8th (0.125) of capacity, which would be 418Ah X 0.125 X 26V charging X 1.25fudgefactor = 1698W. Call it 1800W.
At 48V, you'd need a charge of 1/8th (0.125) of capacity, which would be 210Ah X 0.125 X 52V charging X 1.25fudgefactor = 1706W. Call it 1800W of panels

That would be six 300W panels. That could easily be mounted on a single rotating ground mount sunk in concrete. Because panels are now the cheapest component you buy for your system, I'd optimize the solar to charge the battery instead of optimizing the solar to balance your usage. I've never heard one single complaint that someone had too many panels.

 

[pbennison]

Well, it is getting warmer up here in NY and I plan to start purchasing some equipment. Below is my first stab at a list of equipment I am going to purchase, (thank you MichaelK!). I will build the prototype at my house for proof of concept then disassemble and bring to cabin.

- (6) 250W grid-tie panels - Santan Solar
- (8) 6V batteries - I have a friend in the battery business
- Epever 50A MPPT controller 12/24/36/48V - Amazon
- Schneider 4048 48V Sine Wave 120/240VAC split-phase inverter - Amazon
- Transfer Switch, Lugs, heat shrink, cables, etc.

My next step is to figure out the last item on the list, (Transfer Switch, Lugs, heat shrink, cables, etc.). Is there a site/can someone help me decide all the miscellaneous items that will be required.

 

[MichaelK]

My next step is to figure out the last item on the list, (Transfer Switch, Lugs, heat shrink, cables, etc.). Is there a site/can someone help me decide all the miscellaneous items and specifications of these items that will be required.

This is off-grid, right? If that is the case, you do not need a transfer switch. The Conext 4048 is designed with both AC-in and AC-out terminals, so you simply go to Home Depot and purchase a standard split-phase main panel like this one. https://www.homedepot.com/p/Siemens...Indoor-with-Copper-Bus-PN2020B1100C/312138640

The L1 terminal of AC-out is wired to the top terminal 1 of the panel, and L2 of AC-out to the right-hand terminal. The Neutral, N, goes to either of the vertical bussbars on either left or right. The ground connection on the AC-out terminal gets wired to the bussbar with the green screw. All the ground wires that come into the panel from outlets, recepticals, ect, get connected at the green bussbar.

For proper grounding, you may use multiple below-ground metal elements, like water-pipes, steel well casings, pounded ground rods, ect, that are all connected together. You also may have multiple above-ground grounding elements like light-fixtures, power sockets, ect all connected together. BUT, all the below-ground elements and all the above-ground elements may ONLY be connected and one and only one spot. That may be at the main panel pictured below, or inside the inverter housing. Follow the instructions in your installation manual.

In North America, you also need to bond Neutral to Ground, also at one and only one location. Again, this is either in the main panel, or in the inverter. Follow the instructions.
View attachment 44134
Lastly, you may connect a generator directly to the inverter, via the AC-in terminals. You wire a plug like this into the wall, and run a 4-wire 240VAC cable from the generator directly to the plug. The inverter will receive the power, and convert it into DC to charge the batteries.

Conntek DIY Wiring Generator/Industrial NEMA L14-30P 30 Amp 125/250-Volt 4-Prong Locking Power Inlet Box 80601-GYBX - The Home Depot

This is a 30 Amp 125/250-Volt L14-30 Power inlet box that is designed for outdoor use and can be hardwired directly to transfer switches or panels. This rain-tight, rustproof structure is perfect with

www.homedepot.com

 

[JoeHam]

And the 4048 has a transfer switch built in if you need to augment power with a generator.

 

[Hedges]

Well, it is getting warmer up here in NY and I plan to start purchasing some equipment. Below is my first stab at a list of equipment I am going to purchase, (thank you MichaelK!). I will build the prototype at my house for proof of concept then disassemble and bring to cabin.

- (6) 250W grid-tie panels - Santan Solar
- (8) 6V batteries - I have a friend in the battery business
- Epever 50A MPPT controller 12/24/36/48V - Amazon
- Schneider 4048 48V Sine Wave 120/240VAC split-phase inverter - Amazon
- Transfer Switch, Lugs, heat shrink, cables, etc.

My next step is to figure out the last item on the list, (Transfer Switch, Lugs, heat shrink, cables, etc.). Is there a site/can someone help me decide all the miscellaneous items that will be required.

$1500 for an inverter, and $300 for PV panels?
Pay a bit more for panels and you can get more efficient ones (more watts per unit area and per pound, save on mounting hardware and effort.)
Consider much larger array if you can fit them. For a 50A, 48v SCC, 2800W (STC) of panels might fully utilize it on a good day. 4000W of panels, in a couple different orientations, will keep SCC busy for more hours. (but make sure batteries can accept the current.)
Epever - I've seen a few threads on the forum describing issues, like it stops delivering power until reset. Consider others.

 

[pbennison]

$1500 for an inverter, and $300 for PV panels?
Pay a bit more for panels and you can get more efficient ones (more watts per unit area and per pound, save on mounting hardware and effort.)
Consider much larger array if you can fit them. For a 50A, 48v SCC, 2800W (STC) of panels might fully utilize it on a good day. 4000W of panels, in a couple different orientations, will keep SCC busy for more hours. (but make sure batteries can accept the current.)
Epever - I've seen a few threads on the forum describing issues, like it stops delivering power until reset. Consider others.

Thank you....

Any recommendations to replace the Epever? I want to get one I can rely on.

 

[iamrich]

2500WH/Day
2 Days Autonomy

Option 1
48V
4 250W Solar Panels
30A/48V Controller
3000w Inverter/Charger

Option 2
24V
4 250W Solar Panels
50A/24V Controller
3000w Inverter/Charger

Option 3

24V
9 250w solar panels (Santan ~$650)
MPP LV2424 or Growatt 24/3000 ~$700-800
(8) 6V batteries - You have a friend in the battery business $?
Combiner box $150 with breakers
Wire $100 (12awg from the panels, 8awg from the combiner to the SCC, 2awg from batteries to SCC, fuse on the battery side, etc)
$250 for mounting on the roof (XR100 rails, hardware, etc. Probably two rows (4 and 5 panels). Hopefully your roof is at least 17'x12'

Not sure why you need split phase?

 

[pbennison]

Thank you....

Any recommendations to replace the Epever? I want to get one I can rely on.

Victron?

Victron MPPT

 

[pbennison]

Option 3

24V
9 250w solar panels (Santan ~$650)
MPP LV2424 or Growatt 24/3000 ~$700-800
(8) 6V batteries - You have a friend in the battery business $?
Combiner box $150 with breakers
Wire $100 (12awg from the panels, 8awg from the combiner to the SCC, 2awg from batteries to SCC, fuse on the battery side, etc)
$250 for mounting on the roof (XR100 rails, hardware, etc. Probably two rows (4 and 5 panels). Hopefully your roof is at least 17'x12'

Not sure why you need split phase?

Good point. Honestly, I am not sure why I did that.

 

[Hedges]

Victron?

Victron MPPT

Several additional models from Victron (also several Epever)

Charge Controllers | SanTan Solar

store.santansolar.com

The only SCC I'm running is one of these (for communication compatibility with my inverter), but not common in US market:

ENF Ltd.

Company profile for solar Component and installer manufacturer MSTE Solar GmbH – showing the company’s contact details and offerings.

www.enfsolar.com

A couple of well-known names:

Charge Controllers - OutBack Power Inc

OutBack Power, headquartered in Bellingham, Washington and is the leading designer and manufacturer of advanced power electronics for renewable energy, back-up power and mobile applications. The Company is also a member of The Alpha Technologies -- a global alliance of companies that share a...

outbackpower.com

Product Categories - MidNite Solar

Display's a list of product categories

www.midnitesolar.com

Will's page of suggested SCC

DIY Off Grid Solar Charge Controllers

Building a vehicle mounted solar power system? Let me help.

www.mobile-solarpower.com

 

[pbennison]

Update: I got a deal on 10 280W solar panels. Trying to slowly build out my system.

I am now confused about how to connect the panels. Parallel, Series, etc. I want to take my time and get this right. Looking for advice on next steps.

 

[Hedges]

I am now confused about how to connect the panels. Parallel, Series, etc. I want to take my time and get this right. Looking for advice on next steps.

Most important is that Voc (from number of panels in series) never exceeds max allowed input voltage of charge controller/inverter.
The voltage produced on a freezing day will be higher than what is on the label. Assume 1.2x Voc for a safe figure, or get temperature coefficient from data sheet and your location's record cold temperature for a more accurate value.

Start with spec for your panels and specs for your charge controller.

 

[pbennison]

Most important is that Voc (from number of panels in series) never exceeds max allowed input voltage of charge controller/inverter.
The voltage produced on a freezing day will be higher than what is on the label. Assume 1.2x Voc for a safe figure, or get temperature coefficient from data sheet and your location's record cold temperature for a more accurate value.

Start with spec for your panels and specs for your charge controller.

Ok, I have 8 of these and if I connect in series that gives me, 8*44.3*1.2 = Approx. 426V. The Epever I am looking at is Epever 50A MPPT controller 12/24/36/48V. It states a Max of 150V input. Can I assume that I could use 2 in series and 6 parallel? Sorry for the newbie questions....