Category Archives: Power Usage

Off-grid

I’ve “almost” completed my house in Noordhoek, and its completely offgrid power-wise.

Currently I have 6 x 300W panels, 2 x 220Ah GEL Lead Acid batteries, an FM80, and a Victron 3KW Multiplus running, which gives me about 2KW of usable battery +- in 16 hr period, or in easier to understand terms – about 125W / hr of usage outside of daytime.

Panels come in from the roof, in 2 strings of 3 panels each.
The FM80 can support 150V / 64A input max, so I have to put 3 panels max per string for safety reasons.
36V x 3 @ 8A x2 / 108V /8A per string.
For a 108V / 16A into the FM80.

This then comes out of the FM80 to a 24V battery bank.
The FM80 charges the in the early mornings, and keeps it topped up during the day if necessary.
The 24V battery bank is connected to a Victron Multiplus 3000/24, which then provides AC out to the house.

Batteries are 24v / 220Ah (5280W total capacity). 12v / 220Ah in series to double the voltage to 24v.
Usable capacity is 2600W overnight assuming a 50% discharge.
Overnight I actually use less than 1KW or so, so I discharge to about 80% overnight from a full battery.
Thats a 20% daily DoD, which should give me a decent lifetime.

This isn’t much!
Obviously the limiting factor here is storage (batteries), as the panels can generate far more than is needed to recharge the batteries or run the house.

What does my house need anyway in terms of power?

Lighting
Lighting is all filament LED, so is minimal
Kitchen = 5 x 3W
Bedroom = 1 x 8W
Bathroom = 3 x 3W

32W inside with all the interior lighting turned on.

Water
Hot water is provided by a solar geyser.
I’m not planning on supplementing the hot water with electricity to heat in winter unless I need to shunt excess power out from the solar panels at the inverter, so thats zero usage.

Fridge
Despite the complete lack of information on most websites regarding power usage for Fridge / Freezers, I’ve decided on this model – Bosch KGW36XL30

It claims to use 227 KWhr/year, so thats about 620W /day (or 25W / hr), which is quite reasonable.

Its R7,000 though, so not cheap!

Useful site for checking KW ratings here – http://www.shopmania.co.za, as most of the manufacturer sites are useless.

Cooking
Gas oven / hob setup, so zero power usage (SMEG 60cm unit).
Electric Kettles, and toasters are a no-no, as they suck too much juice.

Washing
Washing machine should use about 1-2KW a wash, so can only be run daytime when there is sun.

Entertainment
LED TV should be fine, as they’re about 50-70W on average.

Not much headroom for other electronics, but its sufficient for the basics. When I make more money, I can ship over the Lithium batteries 🙂