How to Measure Whether Your Solar System CAN function Off-Grid or Not?

“We have seen many people on social media saying that they are installing a 5 kW inverter and 12/16 solar panels so that they can say goodbye to Eskom and, in many cases, I would say that they have been misled,” says Alan Straton from Straton Solar.

A 5 kW inverter will NOT support all the power required (if all appliances and motors were switched on at the same time) in a typical South African home.

A quick exercise to measure your peak power consumption on startup of every appliance, light and motor in your home will soon reveal the folly of a 5 kW system being relied on to power your entire home in an off-grid situation.

The simplest way to see if any system specified for your home will support you going off-grid is to measure the power rating of every appliance, geyser, stove, light and device plugged in to your home currently.

The next thing to note is the start up draw of each appliance or motor that you will require.

Then make assumptions based on the above:

1. What will you power draw be if every single one of your appliances, geysers, stoves, lights and devices were turned on at the same time
2. Then, add up what the number will be if you add the start up draw of each motor – for example a motor may be rated at 1 kW but it’s start up may be rated at 1.5 kW for a certain amount of time.
3. Use the start up draw from each of the above in point 1 above.

An example:

• 25 Lights rated at 15 watts each = 375 watts per hour
• 15 devices (computer, TV’s, chargers, bedside lights etc.) plugged in at 150 watts each = 2 250 watts per hour
• 1 Geyser at 1000 watts = 1000 watts per hour
• 1 Pool pump at 2000 watts = 2000 watts per hour (peak at 2 750 watts)
• 1 Water Tank pump at 500 watts = 500 watts per hour (peak at 750 watts)
• 2 fridges at 600 watts each = 120 watts per hour
• 1 Stove at 3000 watts = 300 watts per hour
• 1 Hairdryer at 2700 watts = 2 700 watts per hour.

Adding the above up = 10245 watts per hour or 10.245 kW per hour

The other way to see what you consume per hour is to take your monthly bill and see how many units (kWh) you are being billed for. A typical small home will consume around 1200 units per month or 1.66 kW per hour (as an aside – we know of homes consuming 5 kW per hour WHILST the owners are on vacation!).

Q. So why do we as installers look at the HIGHER figure of 10.245 kW and NOT the lower figure of 1.66 kW?

A. In order to protect you and your valuable inverter and load shedding equipment from being roasted in a surge when your entire home is switched on at once.

Often what happens is:

1. The cost to ensure that an entire homes power demand is met is pretty prohibitive for most homeowners
2. Most homeowners balk at installing a ‘backup’ for their solar panels and batteries in the form of a generator or wind turbine.

Frankly it makes better sense for homeowners in an urban environment to rather use the grid as a backup if anything does go pear shaped.

What to look out for when specifying an inverter and battery for your home:

1. Match your expected power draw to the inverter and battery rating
2. Make sure that your battery has sufficient capacity to outlast a 4 hour outage after being run down to a minimum of 40% of capacity
3. Make sure that your battery can be charged up relatively quickly after an outage
4. Check what the power peak is for your inverter and battery and the duration thereof.

If you DO NOT go the off-grid route then make sure that your installer divides your electrical distribution board into ‘essential’ and non-essential’ distribution boards to power your essentials which, in most cases, are to power the fridge, TV, Router, small lights, charge a laptop, alarm, electric gate, intercom and electric fence.

Video: How to Measure Whether Your Solar System CAN function Off-Grid or Not?

More Info on How to Measure Whether Your Solar System CAN function Off-Grid or Not? here: https://straton.co.za/solar.
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