Off-Grid Solar Systems

We are experts at providing complete solutions for your off-grid solar setup.

GEM Energy has over 35 years of in-house experience in designing off-grid solar systems.

We work directly with leading manufacturers like Exide, SMA, Selectronic, OutBack Power, Imark, and AERL. Our off-grid solar projects range in size from residential setups, regional properties, remote and automated systems to large-scale solar power setups. Our engineers have worked with Origin mining to develop easy to deploy standalone power stations which serve as monitoring bases in remote locations.

Designing off-grid solar systems requires a high level of skill and knowledge as well as a good understanding of the client’s requirements. Every project is unique, so our systems are custom-designed to suit each customer’s needs. By getting it right from the start, GEM Energy can guarantee that each system will perform perfectly.

As battery systems are starting to gain more traction in Australia, there are many new suppliers entering the market claiming they can do off-grid solar system design. However, seeing some of the systems GEM Energy has quoted against, we are amazed by the lack of correct understanding of off-grid solar.

Incorrectly designed solar power systems can lead to all sorts of problems for the end user and the installer. Many systems have simply been put together with ‘kits’ or off-the-shelf components, without the correct use of necessary formulas and values needed to design a well-performing off-grid system. The unfortunate thing is that by the time these mistakes become apparent, the system has been installed.

To give you a better understanding of how off-grid solar systems work we have explained a few things below. This will also help you when comparing our quote with quotes from other companies.

What are off-grid solar systems?

Off-grid solar systems, also known as stand-alone solar systems, provide grid like electricity in areas where grid power is either unavailable or directly replacing expensive or unreliable grid power. Off-grid solar systems consist of roof- or ground-mounted solar panels, a battery bank to store energy, an integrated backup diesel generator and an Inverter and/or Charger to act as an interface between the different inputs.

The system size is infinitely variable, GEM Energy has designed set ups that supply energy to run a fridge and TV, to supplying a complete island or remote community with electricity. GEM Energy also designs leading-edge off-grid Solar Irrigation Systems for pumping water.

In larger systems there is often a diesel generator integrated to assist in periods of higher than usual demand or to act as a backup for extended periods of bad weather. Other renewable sources like wind and hydro can also be integrated if the environment allows for this.

Compared to older off-grid systems, modern off-grid technology is very easy to maintain, fully automated and can be monitored and controlled online. A further benefit of modern off-grid systems is the quality of the power they produce. This power quality is often better than the average grid electricity and will extend the lifespan of your appliances and machinery.

Remote and automated systems

Remote and automated off-grid solar systems are what we call ‘genuine hybrid systems.’ They truly are a mix of different technologies, designed to be maintenance free, automatically switching on pumps or backup generators when needed.

Off-grid setup with Batteries

Off-grid solar systems – autonomy

Looking at the design of an off-grid system from a professional point of view, it is recommended to have at least 1.5 – 2 days autonomy in your battery bank. This is IF there is a backup generator present. Without a generator the “autonomy” time is recommended to be increased to 2-3 days.

The autonomy time is the daily usage times and means that with low or no sunlight during bad weather, you will have enough power to run all your appliances as normal, without the generator needing to come on.

To calculate the size of the battery bank you take your daily kWh usage and multiply it by the amount of days you would like to have autonomy. For example, if you use 10kWh per day and would like 2 days autonomy, you would need to have a battery bank which has 20kWh of usable storage.


Modern Gel and AGM batteries are efficient and maintenance free which means there is no topping up with water or acid. Lithium-ion batteries now offer a new, high-performance, yet more expensive energy storage alternative that is quickly gaining traction around the globe.

The usable storage of your battery bank is the amount of kWh you can take out of your batteries to a set point of discharge. The depth of discharge (DOD) is the major factor which determines how many years your batteries will last before they slowly start to store less and less power. The recommended DOD state is between 30%-40% which means we are only taking out 30%-40% of the total energy stored in the batteries.

By using Sonnenschein A602 batteries for example, you get at least 4500-5500 life cycles without degradation. After this the battery will start to slowly store less power. It does not stop working from one day to the other, rather it is a gradual decline in capacity.  Depending on the exact usage, we have seen this type of battery stay in good conditions for 15+ years. For applications where we expect high discharge and fast charge rates we usually recommend the American Absolyte battery. These heavy duty AGM batteries are maintenance free. Their life span is marginally shorter than that of the Gel Sonnenschein batteries but they have other features that make up for this. One of these feature is the mounting rack the batteries are supplied in which saves floor space.

Using a high-quality battery management unit and charger like the Selectronic will increase the life cycles and overall health of the battery bank. To reach a better return on investment (ROI), at least in the short term, on request we can design systems which will take up to 50% out of the batteries.

The “C” rating

Another thing we would like to explain in regards to the battery bank is the so called “C” rating. The C rating is the total storage capacity in Amps of a battery. Most batteries are labelled and sold with a C100 rating. However, the C100 rating only applies if the batteries are getting discharged over a period of 100 hours. In an off-grid scenario this would not be the reality and the correct rating would be a C10 rating (discharge rate over 10 hours).

Batteries have less storage the faster they are discharged, hence it is important to apply the right “C” rating when doing calculations for usable storage.

Furthermore, it is common industry standard to allow for at least 10% conversion losses from AC (alternating current, used in households) to DC (direct current, produced by solar panels and transmitted by the grid) and DC back to AC.

Both the correct “C” rating and the conversion losses are often not factored into the off-grid system design by many solar companies. This might be because it makes the battery bank look smaller, reducing the maximum value of a proposal and therefore the more ambitious figure is used. Or it is simply because these companies do not have the knowledge of designing off-grid solar systems correctly.

This is essentially misleading information and can mean that you will see big price differences between systems. In the end it is you, the customer, who finds out the hard way if the company who sold the system knew what they were doing or just tried to make a quick sale.

AC/DC coupled systems

DC coupling

DC coupling – Image credit to homepower.com

Depending on how much research into off-grid solar systems you have done so far, you may or may not know the difference between AC coupled and DC coupled systems. In a DC coupled system the energy flows from the solar panels through an MPPT charge controller and then straight into the battery. An AC inverter is connected to the battery and, when needed, takes the stored power from the battery bank to supply 240v AC power.

In AC coupled systems we install an AC inverter (almost like a standard grid-connected inverter) which will turn the DC power from the solar panels directly into usable AC power. That way it will directly cover the electrical loads in the house or business without having to go through the batteries. This dramatically reduces the amount of usage on the batteries.

A bi-directional inverter or so called Inverter-Charger like the Selectronic SP-PRO is then used to charge and discharge the batteries. This bi-directional charger also controls the AC inverters and manages the entire off-grid system. Depending on the generator, it can also automatically start and stop the generator as needed.

An AC coupled system has the benefit of less conversion losses as power does not need to flow though the battery bank first. You would only need to draw power from the battery bank at night.

A DC coupled solar system minimizes conversion losses by flowing power straight into the batteries and charging them.

To get the best out of both methods we often design systems that have both, AC inverters and DC chargers. In those systems the DC side can fill up the batteries for night time usage with minimum losses, while the AC side covers your loads during the day with minimum losses. This method has been proven to be very efficient with gains of over 10%, and is one of GEM Energy’s key advantages over our competitors.

Off-grid solar systems – how it all works

Our preferred equipment for off-grid projectsSelectronic

For smaller systems up to 5kW we generally use OutBack Power equipment, a North American brand known for its reliability in harsh climates. For larger off-grid solar systems we tend to use the Australian made Selectronic products. Due to their rich features and outstanding efficiency, many of our off-grid systems include Imark MPPT Chargers or Shunt regulators, made in Melbourne, and AERL’s DC charger, designed and made in Brisbane. AERL have won multiple national awards for their DC Charger’s efficiency and we have seen firsthand the outstanding performance and quality of this component.

Installation and beyond

One of our dedicated in-house engineers will be allocated to design your project and be available for you seven days a week from the quoting process through to the handover of the system itself. The installation itself will be completed by one of our highly trained Electricians.  Our Electrician connects the Selectronic SP-PRO unit to the battery bank, your house (loads) as well as the generator. The SP-PRO will charge the batteries and take stored energy out of them if needed at night or even during the day when it is cloudy.

The load side of the SP-PRO is usually connected to your normal main switchboard which we can also supply and install if needed. The AC Solar inverters will then be connected to your main switchboard as they would be with any other grid connected solar system. The only difference is that the inverter and SP-PRO will talk to each other via an RS485 network cable. The SP-PRO will now know how much power you are currently using, how much it needs to charge the batteries and how much power is coming from the solar inverters. If your load is more than the solar panels can produce at the time, the SP-PRO unit will take the extra energy needed from the batteries, or turn on the generator if the batteries are too low.

If all your batteries are charged and the solar inverters producing more power than your loads are, then the SP-PRO will tell the solar inverter to produce less power. If this happens during the day you can see this on your in-home display and you can then turn on extra loads.

In general, our off-grid solar system are fully automated and can easily be monitored locally. Online monitoring is also possible but requires an ADSL or any other type of hard-wired internet connection.

GEM Energy’s standard process includes the close monitoring of your new solar system over the first 4-6 weeks so we can fine-tune it to your individual needs.


GEM Energy is a fully accredited Selectronic integrator which benefits all of our customers as their standard five-year warranty is automatically extended to seven years.

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What our customers say about us

We are mechanical engineers and were very fussy about the installation. GEM Energy’s team proved to be very professional and the workmanship excellent.
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Director, Down Under Property Investments

We have found the GEM Energy team to be very reliable and the work of a high standard.
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Gin Gin & Dry

…it wasn’t until we met with GEM Energy Australia that we were confident we were dealing with a compay that had the expertise to get the job done.
Phil Sellwood

CEO, Bundaberg YMCA