Running Out of Backup Power

After a recent power outage affecting us for roughly than 24 hours. I had a thought, how many people have still ran out of power after having backup power installed.

I have roughly 7KWH usable battery power and ran my house for about 10 hours.
Sadly no solar so for the first time in months, my house was “shutdown” on friday.

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I think if you don’t have solar then most people will run out if the power is off long enough as most who have just batteries don’t invest in too many as it’s a waste if they just idle. We have always had a generator incase sun is down and batteries die. I guess we could run out of petrol then we would be in the dark in that case.

My situation is the same as yours. I have 7kWh of storage. I can stretch that to last around 15 hours, which means I am okay as long as there is sun the next day. If it is overcast, I’m a gonner.

This is where a small generator may in fact be a good investment. Trouble is, I have so much backup stuff. I even have a submersible pump so I can pull water from the swimming pool in extreme situations (because we’ve had a 24-hour outage recently that took the small 1000-liter backup tank to its limits).

Sure, I can put up more tanks, but that scales poorly and takes up a lot of space when I already have a big hole full of water in the ground (and enough separate drinking water). The same argument applies to energy, for the odd occasion when you do run out, it is probably okay to resort to internal combustion :slight_smile:

Due to not registering CoCT switched me off with out warning, me being an hardass just went on and ran off grid with 3-4 months between mid feb to mid early june.
In that time there was 3 very bad solar days i ran a 1kw gennie for a few hours, the later the year the more efficient we had to be, ie shorter showers, less high usage appliances and some days we had to gas cook water and use a retrofit camping shower with a 12v pump. Changed from 3kw to 2kw geyser element

Also check your fridge if it has a holiday mode, i went from 2.4kwh per day to 1.8, in winter its now down to 1.3kwh. I also installed temp probes to monitor and can switch off the fridge for 4 to 5 hours in the morning, on for an hour then off again and saved a few watts like that on bad days.

We where also with out water the other day for just over a day, removed the non return valve, closed the mains tap and enjoyed a hot shower, we have an RO anyways for drinking water. (Rain water tank and RO waste water, feeds toilets)

So my 2c, get a genny 2nd hand, or a few solar panels you can lay on the lawn for the next time, coct dont fly their drones every day!

4.2kw array, 19.2kwh agm, 5kw inverter


Redundancy of power sources is always a good idea, especially in a standalone system, that is why countries generally have a mix of solar, wind, coal/gas, hydro, storage etc.

For residential use a grid connection is generally the easiest option, but then as you rightly mentioned power outages and Eskom are quite fond of each other.

Wind usually goes well with solar, in places where there is wind, because when the sun isn’t shining, there is usually wind, it is a bit expensive still, but also developing quite rapidly.

As the other folks mentioned, generators are still the ‘best’ backup option for us Saffers, low initial cost, generally reliable and fuel readily available. The cost per kWh can get scary with generators and it is worthwhile to compare the efficiency of different variants/brands/sizes before purchase.

The nice thing about battery storage is that you can then use the generator at it’s most efficient running condition to charge up the batteries instead of relying on the generator revs to compensate for your varying loads.

Hi JAOG, this is not completely correct, the control loops used by a Hybrid inverter while connected to the Grid or generator is generally to slow to compensate for inrush currents and fluctuating loads, it will draw such from the Grid/generator first and move the loads over to batteries after a short “delay”. You do have all kinds of nice features like “Power Assist” and “Dynamic Current Limiting” with Victron that can lessen the effect, but in general the Gen will be affected by loads being switched “Off” or “On”. Most hybrid inverters will also “dump” current back into the Grid/Gen when a big load switches off, this will cause the load on the generator to drop and that normally causes the Gen to “over speed” a little and the AVR must take over and compensate. There are a few more factors to take into consideration for example, try not to run the gen with a load less than one 3rd of its capacity ext ext ext…

The effect of the above is more visible in smaller generators and might not affect bigger generators that much in smaller installations, but bigger generators in bigger installations might be affected in the same way.

Agreed, thank you for the extra info Jaco. Let me maybe expand and clarify on what I intended to say. In general it is more efficient to run a generator at a higher output for a shorter period of time rather than a lower output for a longer period of time. If you have battery storage you can then size the components appropriately to take advantage of this. For example, in general it would be more efficient to run a generator at 50 A for an hour to charge up your batteries rather than 5 A for 10 hours if you have no batteries.

I base this on large generators such as the specifications shown below (note mechanical power), but believe the same will be true for smaller generators with possible exceptions being inverter generators.

I hope this makes sense now.