Off Grid System Design


So, you need an off-grid power system, we can assist you in selecting products from your own design or for a small fee provide you with one that has a performance guarantee. The 6 key points are listed below.


1) Work out your daily load

This is a critical step and underestimating this will reduce the life of the some of the component. Many people try to skip this step. Don’t!

Planning on going off-grid without knowing how much power you need is like building a house and not knowing how many bricks you need. Use our load calculator and enter the appliances you will be powering with your solar power system. You’ve got to remember absolutely everything that will be powered by your system and don’t forget water and septic – seemingly little changes can make a big difference.


2) Calculate the amount of batteries you need and chemistry you want to use

Now that you know how much power you need, you need to work out

  • What battery voltage you require 12v,24v or 48v  
  • Do you need only enough storage for a day or two or do you need to have enough batteries to store 3 or 4 days, or more, worth of power?
  • Will you be storing the batteries in the shed or purpose built location?
  • Batteries are rated for storage at around 25 degrees Celsius. The colder the location, the bigger the battery bank you need
  • Do you have another power source, like a generator, wind turbine or micro hydro turbine that can be used when the sun doesn’t shine?
  • what percentage you want to be from renewable energy or fossil fuel. With a tendance to use small lithium batteries these day it puts a heavier reliance on external sources like generators.
  • How many years do you want the batteries to last?

Each of these answers affects the size, and cost, of your battery bank.


3) Calculate the number of solar panels needed for your location and time of year

Our off-grid calculator can assist in working out how many solar panels you’ll need for your solar system. After knowing how much energy you need to generate per day from the load calculator, you’ll need to find the peak sun hours (PSH) available in your location

The number of PSH is how many hours the available sun shining on your panels at an angle throughout the day equals sunlight, as if it were shining directly on your solar panels when they get the most power. As you know, the sun isn’t as bright at 8AM as it is at noon, so an hour of morning sun may be counted as half an hour, where the hour from noon to 1PM would be a full hour. And unless you live near the equator, you do not have the same number of hours of sunlight in the winter as you do in the summer.

You want to take the worst case scenario for your area, the season with the least amount of sunshine that you will be using the system. That way, you do not end up short on solar energy for part of the year. Ask us how you can use the extra energy in summer.


4) Select the type of solar charging

Two types of solar charging – AC and DC coupled charging, each has its benefits and you can give us a call to find out which one will best work for your situation.

 DC coupled uses a solar regulator/charge controller – available in pulse width modulated (PWM) and maximum power point tracking (MPPT)

AC coupled uses a tradition grid-tie solar inverter setup for off grid operation (not all grid-tie inverters can perform this task)


5) Select the battery inverter

Now that we have batteries, we need to make the power usable. If you are only running DC loads straight off your battery bank, you can skip this step. But, if you are powering any AC loads, you need to convert the direct current from the batteries into alternating current for your appliances. If you are using AC coupling a Bi-Directional inverter or inverter charger is required.

You also need to know how many watts total your inverter will need to power continuously and the surge required. Use you load profile from step one to help with this.

Inverter are designed for a specific voltage battery bank, like 12 volts, 24 volts or 48 volts, so you need to know what voltage battery bank you are going to have before you settle on the inverter. Keep this in mind if you think you may be growing your system in the future. If you plan on having a higher voltage battery bank later, be aware that the lower voltage inverter won’t work in the new bigger system. So, plan ahead and go with the higher voltage to begin with, or plan on changing out your inverter in the future.


6) Balance of system

There are a lot of other little components that make up a system that make it safe and compliant, including:

  • Solar array racking
  • Solar array isolators
  • Solar array combiner
  • Fuses and breakers for over current protection
  • Cable – solar, battery and sensor
  • Battery box
  • Battery management


Contact us if you need help. All our designs are signed off under Clean Energy Council requirements and will therefore meet STC application requirements, if installed by a registered installer.