1,25 kwp solar sytem for cabin plan

Jancho

New Member
Joined
Feb 21, 2022
Messages
9
Hello!
I'm planning to instal solar system for my new cabin. Location is Europe, Croatia.
Goal is to run the apliences during all seassons of the year (the cabin will be used mostly on weekends (2-3 days in a week).

The power consumers would be:
- inverter air conditioner or convector heaters (up to 1,5kw max power)
- 30-50l electrictric boiler for quick hot water showers (up to 1,5kw max power)
- mini refrigerator (110 kwh/annual)
- led TV
- water pump (600wh max power)
- lights
- other small apliences such as chargers, wifi modules and else

The cabin would have 20cm thick walls with very good insulation, total size of around 25sqm. I havent seen an exact plan that would match for my cabin so I decided to ask for help here.

I tought of having:
1) 4x330w panels (STC: 41 VOC, 10A)
2) 3VA/2,4kw/24V inverter + 40A MPPT regulator + 1KW Charger (found it on aliexpress for around 400 USD)
3) 2x12V/230Ah AGM battery
4) Backup generator 3kw for winter time
5) Wiring

All together would cost me around 2.500,00 USD.

What would you advise me to do differently or warn me about this system?
How would you build your system if you would install the similar one? Do you think the system would work for heating and quick hot water showers? Would my battery bank od 5,5kw total be enought or should I consider making it closer to 10kw? Would 40amp integrated charge regulator be enough or should I consider having a separate one (something im range of Victron 100/50). My budget is around 2.500 USD.

I might have forgot something so feel free to ask me. Thank you in front for advices and help. 🙂
 

Rednecktek

Photon Sorcerer
Joined
Sep 8, 2021
Messages
2,391
Location
On a boat usually.
- inverter air conditioner or convector heaters (up to 1,5kw max power)
- 30-50l electric boiler for quick hot water showers (up to 1,5kw max power)
Those are going to destroy your battery capacity. Just as a point of reference a bog standard 100Ah 12v LiFe battery can run ONE heater for about 35 minutes before it's dead. The general consensus with heating is "Anything But Solar" because of the power needs of electric heat.

For the math, 5.5Kw would run 1 heater for about 3.5 hours and your entire bank is dead. The water heater will draw a LOT of power when it gets the tank up to temp, then kick down into a lower power mode to keep it there. Either way it's using power almost 24/7.

Unfortunately for you (and us other folks on a budget) AGM batteries (and FLA and Gel) can only really be used to 50% capacity, so in reality you have 24v * 230Ah / 2 = 2.76Kwh, or about 1hr 45Min of a single heater.

If the batteries will stay above freezing, consider a 200Ah 24v LiFe battery or a couple of basic 200Ah 12v batteries in series for about 4,8Kwh. It'll cost you about the same as each AGM and double your Wh availability.

The panels are a good start but you'll probably only generate about 5.5Kwh a day assuming 6 hours of sun. That's your entire bank and leaves you nothing if you get cloudy weather or a rain storm or anything.

Is natural gas or propane available? How about diesel heaters? Wood stove? On demand water heater? Any of those would make your batteries MUCH happier.

Anything you can save on energy consumption is worth 5 times the cost of solar equipment (give or take). If you can find a way to drop those heaters and water heater I think you'll have a good start you can grow into later.

Just some thoughts.
 
Last edited:

12VoltInstalls

life passes by too quickly to not live in freedom
Joined
Jan 18, 2021
Messages
4,695
Location
Vermont
propane available?? Wood stove?
Wood stove would be best in my opinion, no electricity needs. Plus it gives cooking opportunities and can make a lot of heat fast if required.
A second being a propane RV furnace. 16000btu units run at 3A for the fan and ignition controllers. That’s way easier to supply than electric convection heaters.
 

Jancho

New Member
Joined
Feb 21, 2022
Messages
9
Firstly, thank you very much for the comment.
I might instal convectors instead of inverter air conditioner. Those will use around 500w. And taking into count that the cabin is well insulated, those might not use a lot of energy, maybe 1,5kw a day.

For the hot water, I tought of using flow heaters, but they are rated around 4kw. Even tho they will be used not more then 20-30 minutes a day, im not sure if batteries will be able to provide that much of power at once.

What about the solar water heaters, how they do in winter and how muvh would that system cost?

I got good deal for classic batteries (not AGM) but im sceptic about them. Even tho AGM are more expencier they are kinda more safer and maintenance free. I believe I will actually invest around 1.200 USD at the end to get the finnal power of over 10kW. Do you think I might have a good deal on LiFePo4 batteries, because I realy cant find any cheaper ones at the moment.

PS. I would actually use stove or fireplace but right now the cabin is not designed to have one. The next ones will for sure have it. 🙂

Let me know what you think about that.
 

12VoltInstalls

life passes by too quickly to not live in freedom
Joined
Jan 18, 2021
Messages
4,695
Location
Vermont
got good deal for classic batteries (not AGM) but im sceptic about them. Even tho AGM are more expencier they are kinda more safer and maintenance free
In my observation- I’ve never bought an AGM - AGMs are good for UPS/standby emergency power but I haven’t seen them last well in regular use. ‘Classic’ flooded lead acid do need their fluid level checked and replenished occasionally if needed but I think they last much longer. Just my opinion.

I have 8 cheap “marine” deep cycle batteries that have worked well for me over several years now. At this point they have crossed the break-even point for cost over time and are doing quite well in my circumstance. Mine are outside and I get well below freezing temps all winter (-28*F the lowest this season so far) and I don’t need to be concerned about charging them whereas LiFePo will be permanently damaged if charged below freezing. Plus, if something weird occurs and I need batteries quickly they are just a Walmart away.

LiFePo is often a better choice, however. It depends. If your batteries were super inexpensive and you can get more the ‘classic’ batteries are hard to argue against. If you are working with a ten- or fifteen-year plan and cash money isn’t a concern LiFePo should probably be evaluated. But it sounds like your current batteries are the best expense for you at the moment.
 

Jancho

New Member
Joined
Feb 21, 2022
Messages
9
Its around 1250 kwh. I have around 2,5 sunny hours a day during December and Yanuary and around 7 during summer time.
 

koppted

Solar Enthusiast
Joined
Sep 27, 2019
Messages
141
And if you have diesel as a ready supply, I've found diesel heaters to be way more efficient than RV heaters. And they're solar friendly 12v or 24v.
You link goes to a product that's no longer available. Do you have a diesel heater in particular that you use and would recommend?
 

Rednecktek

Photon Sorcerer
Joined
Sep 8, 2021
Messages
2,391
Location
On a boat usually.
You link goes to a product that's no longer available. Do you have a diesel heater in particular that you use and would recommend?
They're all clones of each other, so as long as you know what to look for they're pretty much all the same. I posted that one because I have purchased multiple of them and it was easy to find the page in my Orders history.

The 3 key things I've found that make a unit better or worse are:
1: White fuel line, NOT green. The green line is too soft and it has fuel delivery issues
2: LCD control panel, NOT knob. There is no troubleshooting, monitoring, or tuning you can do with the basic knob control.
3: Get the kit, NOT the pre-built-in-a-box. The pre-builds are actually harder to get piped up, offer less ducting flexibility, and are louder.

The links are for what NOT to look for. Pretty much any of the other kits with the white fuel line and LCD display are all the same thing, different sticker. If you end up going with one, feel free to ping me and I'll send you my step-by-step-with-pictures How-To for cleaning and servicing.
 
Top