What Size Solar System Do I Need

What Size Solar System Do I Need? The most often asked question. That all depends on what you want to run on the system and at what times of the day, and for how long you run each device.

Running a Fridge, TV and WiFi only requires a small solar inverter and a few solar panels to run during the day when the sun is shining, however at night the fridge will drain the battery at a steady rate, therefore the battery needs to have enough capacity to last the night.

That been said, most new Hybrid inverters do not require large batteries or batteries at all if that is your choice. A hybrid system can use the solar power while the Sun is shining and if you don’t have batteries, it will automatically switch to utility power to keep the devices running at night. This way you can run your heavy loads during the day and import a small amount of power from the grid for night time. If you want to go Off-Grid as much as possible, then you will require a battery bank for the evenings.

How much battery storage do I need for night time?

Lets say a fridge is 150W. This means it will use 150 watts per hour of electricity. If you have a 200w solar panel you can run the fridge for free during the day. However at night time (+-16 Hours depending on location, shadows etc) you will need 150w/Hr x 16Hrs night time = 2400w. That is a fair size battery just to run a fridge.

Other smaller devices use a lot less power and run for shorter times. A TV is +- 100w but you only use it for 8 Hrs at night. = 800w. A kettle is normally 2000w but you only use it for 5 minutes = 166w Each time you boil it. Twice a night – 333w. The same goes for an Iron 2000w but you might use it for 1 hr = 2000w

Now you add the total watts together to get a rough estimate of your battery requirements. In our example our total is 5533 Watts of power we require. This means we need 2 x 5kwh batteries or a 1 x 10kwh or bigger battery. Just to run those few devices.

Read More on Selecting your battery

How many solar panels do I need?

If you only want to charge your battery for night time then – battery capacity divided by the number of sun hours. eg : A 2700 watt lithium battery / 8 hrs (Sunshine) = 337.5 watts per hour we need. That means you need at least a 350 solar panel to charge the battery to full on a clear sunny day. If the weather is overcast or slightly cloudy the performance of the panels goes down dramatically, which means you will need more panels just in case. However you also need to consider self consumption so it is always better to have more panels.

For a 10kw inverter with 33kwh of battery power, charging from 20% would require 4kw+ solar panels to charger over an 8hr time period. So you would require at least 8 x 600w panels for the batteries and another 8 for your day time consumption. So +- 16 x 600w panels.

How much power do my appliances consume?

These figures are based on my own investigation based on consumption per hour

• Geyser 3000-4000w Watt
• Stove top 1500-1800w watt per plate
• Oven 3500-7000 Watt
• Deepfreezer 100 watt
• Fridge 100-150 watt
• Shop fridge 700 watt
• Iron 1200-2200 watt
• Kettle 1500 watt
• Washing machine 1500 watt
• Tumble dryer 1500-2500 watt
• Each LED light 8-20 watt
• Each normal light bulb 50-100 watt
• Laptop 80 watt
• Computer 250-350 watt
• Gaming computer 450-600 watt
• Each TV 100 watt
• WiFi / Fibre router 9 watt

Distribution Board DB Wiring

Advise

Do not cancel your utility account until you are confident about your solar system. There could be many rainy days which means you will need a very large battery bank or pull power from the utility.

Always have a Generator as backup