Sizing a backup system

[Isetech]

How to size a backup system, I hear there are many methods used by the experts.

They will request your utility bill, take the monthly usage and divide it by the days in the months or just read the daily average. What is wrong with this method, where do I start?

Then there is the ones who leave a kwh meter or some type of recorder on site monitor for 7 or more days, in winter or summer, yip in most cases it does change.

You could just go with the one most commonly sold, because it will do the job.

Then of course there is the one you can afford.

A customer got a pile of quotes and asked me to assist with deciding which quote to accept, the quotes ranged from R110 000 - R275 000.

My first question - How much can you afford ?

Second question - no not where is your utility bill (because we already know that the average 3 bedroom house uses around 30 kwh per day) What is it you are trying to achieve?

Once you can answer these 2 questions, then you can start looking at what is to offer.

Are you just looking for a backup system to keep a few items like the router, alarm, CCTV and a few lights on, then a standard inverter like the axpert type inverter will do the job.

IF your budget is low , then maybe you should just look at small unit like the 24 VDC axpert FLA type batteries, if setup up right they should last around 3 years.

We find that most people leave the battery cutout voltage at 10.5, throw in a few stages of stage 6 load shedding and you replacing those batteries just as fast as the alarm and gate battery (which also set to cutout at 10.5 VDC, its dead) These systems where never designed for load shedding. They have a low charge rate and the 10.5 VDC and not designed to be cycled so often. Until the manufactures design the system for load shedding they just going to keep smiling with all the battery sales

The battery cutout is designed to protect the battery worse case scenario, its not the refence point to cycle the battery, if you keep dropping a lithium battery to o% DOD, you will also shorten the life cycles of the battery or destroy the lithium battery.

[Isetech]

Not all inverter are the same, like a UPS, you dont just install a UPS, you need to understand the application, they are not designed to backup your PC for hours, they are designed to give you enough time to shut down your PC (10 to 15 minutes) some have a comms cable and they can automatically safety shut down your PC.

The same with inverter, they have specific applications, some are just a backup unit, some have CT's to control the feed back, not all inverters are the same.

This is were the budget and application come in, do you want a system that is just going to increase your monthly electricity cost, because you dont have a means to charge the battery, or do you want a system which can link to solar panels to charge the battery on sunny days and cover the power consumption to keep it operating.

Then you get systems which can connect to solar panels and feedback power, this is where it you could blow money that you dont need to.

If you have no intention of installing solar panels, spending R10k more because it is a bidirectional inverter with a CT and all the bells and whistles just seems foolish.

A cheap axpert or Lux power is probably going to do the job.

If you want to spend large and save a few bucks, then having a smart inverter with a CT to control the feedback might be a better option.

Make sure that whatever system you install, has technical support, installers are a dime a dozen, they will come and go. Something to think about, Keith mentioned in his latest video that Sunsynk do NOT offer technical support end users. Make sure that if you install a Sunsynk unit you play nicely with them because they can also switch off your system remotely. If you having a dispute with your Sunsynk installer, make sure you unplug the wifi dongle otherwise you could be sitting with a heavy door stop

I dont know enough about Victron to comment on installer remote access and control. I think Victron unit customers control who can remotely access their system.