System for an off-grid cottage

C

Colin62

Executive Member
Joined
Apr 23, 2008
Messages
8,275
Reaction score
878
Location
Mistbelt, KZN
A friend is building a cottage, which will be off grid. They’re looking for a system that will keeps lights and so on going. The biggest drain is likely to be the fridge and washing machine. Stove and geyser will be gas, and while they’re not technical and won’t be watching the battery charge levels or fine tuning settings, they are tolerant of running out of power and happy to adjust to only doing laundry when it’s sunny.

Essentially a very entry level system, where price is more important than performance. Probably 3kW is enough, probably about 3kWh battery capacity (I’ve convinced them that Lifepo is worth the premium). A couple of panels to keep things charged.

How important is it to stick to 48v on the battery side? Or doesn’t it matter?
 
Colin62 said:
A friend is building a cottage, which will be off grid. They’re looking for a system that will keeps lights and so on going. The biggest drain is likely to be the fridge and washing machine. Stove and geyser will be gas, and while they’re not technical and won’t be watching the battery charge levels or fine tuning settings, they are tolerant of running out of power and happy to adjust to only doing laundry when it’s sunny.

Essentially a very entry level system, where price is more important than performance. Probably 3kW is enough, probably about 3kWh battery capacity (I’ve convinced them that Lifepo is worth the premium). A couple of panels to keep things charged.

How important is it to stick to 48v on the battery side? Or doesn’t it matter?
Click to expand...
It is important because both the fridge and washing machine have motors which will draw huge amounts of current from the battery at lower voltages when they start up.
 
The fridge will be a constant draw, but the washing machine i wouldn't really worry about. Run that daytime and you're ok.

Make sure to find an A+++ fridge at minimum. A lot of the stuff we get in SA is illegal to sell in Europe as it doesn't pass the efficiency laws.

Keep to 48v as thats what most systems are at, so upgrading later will be easier.

What other equipment will be powered on overnight?

TV? Laptops? Other equipment? Lighting can basically ignore unless you have halogens. Replace all lighting with decent LED, and forget about the draw.

Take a look at my goingsolar.co.za site i have a few posts on efficiency etc.
Not sure gas for geyser is the best route, but each to his own.

Panels are cheap. Inverters relatively cheap. Battery less so.

Size panels for winter usage, so that worst case scenario, you will be able to charge the batteries enough, or forego using power if not. Might be worth having a gennie if you can't forgo for the handful of days a year you can't get enough power for the day.
 
Why?

Average Vacuum cleaner < 2KW, and you'll use it for 10-15min max daytime.
I wouldn't recommend that on a cloudy winter day, but otherwise its irrelevant in terms of draw and power usage.

I say that as someone who's been offgrid with a 3KW inverter for > 10 years now.


Pegasus said:
They’re going to miss having a vacuum cleaner
Click to expand...
 
Pegasus said:
They’re going to miss having a vacuum cleaner.
Click to expand...
When I said cottage, I tried to convey that it is small. A broom and a mop will probably manage very well, but as noted above, it’s only a few minutes a week, and as long as the sun is shining, no sweat.
 
Standard upright sized 220v fridge draws around 120 Watts of power. Each time the fridge switches on the motor surges the power and this can be up to 1000 Watts for a brief second.
Make sure your fridge is running of pure sine wave AC electricity. Not modified sinewave.

48v is better as there is generally less conversion loss going 48v-->220v than say 24v-->220v which will be double the amps, and double the thickness cables, etc.

Double up on your battery capacity as this will last 3 times longer than had you not doubled up. Reason is most people will deplete their battery array to say 50% for example and this will only give you 500 life cycles. This is only an example, dont quote my figures.
Whereas if you double the battery capacity you might only deplete to 75% battery life remaining. (As an example)
Now instead of getting 500x2=1000 life cycles out of your batteries you will instead get 1500 or even 2000 life cycles.
Because you were looking after your batteries and not depleting them alot each day.

I would also look into getting a Dual MPPT charging system for the solar panels. This way you have solar panels on 1 input and add a small wind generator on the other input. Very handy to be generating power at night now and through winter when it is stormy and you have no sunlight
 
Pineapple Smurf said:
Standard upright sized 220v fridge draws around 120 Watts of power. Each time the fridge switches on the motor surges the power and this can be up to 1000 Watts for a brief second.
Make sure your fridge is running of pure sine wave AC electricity. Not modified sinewave.

48v is better as there is generally less conversion loss going 48v-->220v than say 24v-->220v which will be double the amps, and double the thickness cables, etc.

Double up on your battery capacity as this will last 3 times longer than had you not doubled up. Reason is most people will deplete their battery array to say 50% for example and this will only give you 500 life cycles. This is only an example, dont quote my figures.
Whereas if you double the battery capacity you might only deplete to 75% battery life remaining. (As an example)
Now instead of getting 500x2=1000 life cycles out of your batteries you will instead get 1500 or even 2000 life cycles.
Because you were looking after your batteries and not depleting them alot each day.

I would also look into getting a Dual MPPT charging system for the solar panels. This way you have solar panels on 1 input and add a small wind generator on the other input. Very handy to be generating power at night now and through winter when it is stormy and you have no sunlight
Click to expand...
Any links for suggestions on wind generators? it's something I have never thought about.
 
TheChamp said:
Any links for suggestions on wind generators? it's something I have never thought about.
Click to expand...
No, too expensive in RSA
Pity though

I would just get a 200 - 500 Watt as this will be more than enough for night time use running the fridge, tv, a few LED Lights etc
 
Something like this from Banggood
Its a Chinese thing

I bought an American one for over R6000 in 2000 and I see they now around R30 000. The Air 400 or something like that, I sold it many years ago to a friend. Stupid move

www.banggood.com

600W 12V/24V 3 Blades S2 Wind Turbines Generator Nylon Fiber Windmill with Controller

Only US$192.99, buy best 600w 12v/24v 3 blades s2 wind turbines generator nylon fiber windmill with controller sale online store at wholesale price.
www.banggood.com www.banggood.com
 
Washing machine has a heating element. It draws a lot of power, keep that in mind.
 
Pineapple Smurf said:
Something like this from Banggood
Its a Chinese thing

I bought an American one for over R6000 in 2000 and I see they now around R30 000. The Air 400 or something like that, I sold it many years ago to a friend. Stupid move

www.banggood.com

600W 12V/24V 3 Blades S2 Wind Turbines Generator Nylon Fiber Windmill with Controller

Only US$192.99, buy best 600w 12v/24v 3 blades s2 wind turbines generator nylon fiber windmill with controller sale online store at wholesale price.
www.banggood.com www.banggood.com
Click to expand...
Well, this is 400W: https://www.amazon.com/Pikasola-Gen...276a6&pd_rd_wg=elglj&pd_rd_i=B0897PHY5X&psc=1

Issue is in South Africa it's too niche, you need to import it as anything local is pretty much there to make money off of government or something, since can't think of anyone else who would pay 4-5x the worth of the item.
 
Sinbad said:
Washing machine has a heating element. It draws a lot of power, keep that in mind.
Click to expand...
Not Top Loaders like mine
They have a separate hot and cold water inlet
Ive never in my life used the hot water option, no need at all
 
TheChamp said:
Any links for suggestions on wind generators? it's something I have never thought about.
Click to expand...
I'm also on the lookout for anyone that can possibly help me with a wind solution, it really does seem rare in SA.

The most prominent brand I've come across so far is TESUP and their turbines + inverter solutions, but of course more expensive than it needs to be and the reviews from abroad aren't favouring it too much with regards to generated potential and suboptimal startup speeds required.

For my use case it seems like a no-brainer, the coastal winds are always moderate-to-high day and night, and it's usually quite cloudy for effective solar use, but the installers, suppliers and info sites outnumber the wind ones 100:1 understandably. I'll definitely let you know if I get in contact with something / someone though.
 
Going with a wind generator as backup makes sense but for this install won’t happen, budget is extremely tight, and if there’s no power, it’ll be just like Eskom. Its not like South Africans can’t handle a little blackout or two. We’re not Texans after all...
 
I can confirm that a 3kW inverter is more than enough to run a complete household. We run out farmhouse on one, and that includes borehole pumps, microwaves, vacuum etc. We're 3 plus a caretaker and his wife, all supplied by the one inverter.
All it takes is a bit of management and scheduling wrt the large loads.
We cook with gas, but have a microwave, air fryer, instant pot etc, so it's not like you can't have the gadgets:)
Our fridge is a large double door unit with ice maker - it was the best rating I could get 3 years back. Main TV is a 65 plasma, and we have 2 gamers in the house as well.
I'd put in as many panels as possible, and size the battery according to the average nightime draw. Having a generator available is also a huge advantage, as there's nothing worse than a week of heavy cloud and having to worry about SOC. Just a small cheapie for those few hrs once in a blue moon...
My battery is a diy 12kWh LifePO4 btw.
Cheers
 
igeorge said:
I can confirm that a 3kW inverter is more than enough to run a complete household. We run out farmhouse on one, and that includes borehole pumps, microwaves, vacuum etc. We're 3 plus a caretaker and his wife, all supplied by the one inverter.
All it takes is a bit of management and scheduling wrt the large loads.
We cook with gas, but have a microwave, air fryer, instant pot etc, so it's not like you can't have the gadgets:)
Our fridge is a large double door unit with ice maker - it was the best rating I could get 3 years back. Main TV is a 65 plasma, and we have 2 gamers in the house as well.
I'd put in as many panels as possible, and size the battery according to the average nightime draw. Having a generator available is also a huge advantage, as there's nothing worse than a week of heavy cloud and having to worry about SOC. Just a small cheapie for those few hrs once in a blue moon...
My battery is a diy 12kWh LifePO4 btw.
Cheers
Click to expand...
Thanks for chipping in with that. We’ve gone with a 5kW inverter - not much difference price wise between that and the 3kW ones, and gives a bit of future-proofing. The battery (4.8kWh) is going to be the weak link, because that’s the most expensive bit. My personal concern there is adding a battery later, but if there’s no money, there’s no money.

To save money (which is more important here than to have plenty of electricity), we’re going in a bit light with panels, fully planning to expand as funds allow.
 
Shot. Just bear in mind that you need to be able to have enough panels meet daily demand and charge the batteries. Just do the math and make sure that you aren't deficient in one area.
If you know your average consumption, your battery can be sized accordingly ie see you through the night. A rule of thumb re panels is that xkW of panel will give 5xkWh of production, so see how that matches to your expected consumption. Don't forget to add 20% for losses, to be safe.
Have fun:)
 
As an example, if your average nightly load is 300W, and you are happy to use 80% of your battery capacity, then in winter (14hr night) that implies a 14*.3/.8 battery, or 5.25kWh.
Just to recharge the battery will require ~1kW of panels, double that to supply the daytime load which will probably be higher? And then reserve for cloudy conditions. Heavy cloud can lead to only 20% PV production...
 
You must log in or register to reply here.
Back
Top
Sign up to the MyBroadband newsletter
X