Off-Grid Solar


How to design the right Off-Grid solar system

The top priority we emphasize to our clients is:

When installing an off-grid solar system, the selection of components and the overall design play a crucial role.

In the absence of a backup grid, any power loss or malfunctioning parts could leave the property without power supply. Therefore, investing in quality and reliability is paramount, considering that the system will be powering your house for decades to come.

When installing an off-grid system, the focus should be on an appropriate solar system design. The off-grid space offers many options, including various sizes of solar panels, batteries, and inverters. A ‘one size fits all’ approach is not suitable, and systems should be tailor-made to meet the specific usage needs of each client. Additionally, incorporating modularity in the design allows for adaptability to changing requirements and facilitates the system’s expansion along with the client’s needs.

Essential Design Considerations: 

  1. Maximise power demand of the site.
  2. Average daily energy usage (kWh)
  3. Days of autonomy

Key Components: 

  1. AC-Coupled Inverters (solar)
  2. Off-Grid Inverter/Battery charger
  3. Battery Solution
  4. Solar Panels
  5. Solar Railing/Racking
  6. Generators

Essential Design Considerations (Terminology & Requirements)

Maximum power demand of the site

When designing an off-grid solar system, it’s crucial to consider the maximum electrical loads within your property to determine the appropriate off-grid inverter for your needs.

We recommend the Selectronic SP Pro482 inverters, boasting a 7.5kWh rating. This translates to a constant draw of 7,500 watts at 230 volts, equivalent to 31.73 amps, allowing for a 32amp main switch supply. These inverters provide a 30 second output of up to 18kW, enabling swift power adjustments and seamless generator integration without disrupting the system.

For households with higher current requirements, such as running large appliances like air conditioners and induction cooktops, we propose installing a second Selectronic inverter. This transforms the setup into either a single phase 50amp/63amp supply or a two phase 32amp supply. Additionally, for scenarios with substantial loads, a three phase supply can be achieved by incorporating three Selectronic inverters.

It’s important to note that the lower your maximum demand, the less stress your off-grid installation will experience. The Selectronic Power offers the advantage of future upgrades by adding another inverter, allowing for increased provisions. This flexibility is especially beneficial, as it eliminates the need to discard obsolete components when expanding the system.

We strongly recommend the use of energy efficient appliances throughout your property to minimise both maximum demand and average daily usage. This proactive approach contributes to the overall efficiency of your off-grid system.
For detailed specifications and additional information, please refer to the Selectronic brochure:

Average daily energy usage (kWh)

To determine your daily energy usage, we use a calculation tool that allows us to record the daily operation of your appliances, considering variations in usage during winter and summer (typically, power consumption is around 30% higher in winter). With each electrical appliance, we calculate both its power rating and the anticipated daily usage hours.

This process is collaborative, involving discussions with our clients to gather accurate information for calculating their specific daily energy consumption. It’s important to note that energy intensive appliances, particularly those involved in converting hot to cold or vice versa, such as heating and cooling systems, air conditioners, fridges, and freezers, contribute significantly to overall energy loads. The impact on energy consumption is directly relevant to the duration these appliances are in operation.

Here are some examples:

  • A hair dryer or kettle running at 2000 watts for 10 minutes represents a daily load of 0.4kWh.
  • Leaving a 15 watt light globe on all day results in a daily load of 0.36kWh.
  • Running a 200 watt plasma TV screen for 8 hours accumulates a daily load of 1.6kWh.
  • Operating a ducted air conditioning system at 4000 watts for 5 hours leads to a daily load of 20kWh.

Feel free to reach out to us to discuss these calculations. There are no right or wrong answers, rather, the goal is to tailor the solar and battery system to accommodate your specific daily usage. Generally, a higher daily usage may require a larger solar system and a correspondingly larger battery set to cover loads before resorting to generator assistance.

Days of autonomy

When designing a solar system, our goal is to strive for practicality, aiming to install solar panels and batteries capable of meeting your energy consumption needs throughout the entire day, 365 days a year. Achieving this in summer is relatively straightforward, as explained below.

Consider a 12kW solar system that, on a good day, can generate up to 50-60kWh. This allows the solar energy to cover all daytime loads (let’s say 10kWh), top up a 20kWh battery system, and still have the potential for additional usage, up to 30kWh if required. The surplus energy stored in the batteries is then utilised from sunset to sunrise, ensuring continuous power supply.

However, the challenge intensifies in winter. Using the same example, on a wet, cloudy day, a 12kW solar system may produce as low as 10-15kWh. While this still covers daytime loads, it limits the energy stored to only 5kWh. Overnight usage would deplete the batteries, leaving them 25-50% lower than the previous day.

What does this mean?
During the winter months, this system would last 2-3 days without reliance on the grid or the need to activate a generator for additional battery top up, avoiding any inconvenience. The longer this period, the more self sufficient the property becomes.

This duration is closely tied to the daily usage patterns, taking into account the property’s capacity to generate and store sufficient power to cover these loads. Achieving a balance ensures a resilient and sustainable energy solution throughout the changing seasons.

Key Components (More information):

AC-Coupled Inverters (solar)

There are two main types of inverters utilised in off-grid installations, with the first being the AC couple solution. This particular inverter connects to the off-grid inverter/battery solution, generating an AC supply that transfers power from the solar panels to the house’s loads. Effectively harnessing the DC power from the solar panels, these inverters convert it into usable AC power for the household. In off-grid setups, any excess power generated by the solar system can be used to charge the onsite batteries, ensuring a reserve for periods of insufficient solar availability.

The quantity of solar panels you install directly influences the size of inverters needed, often requiring multiple inverters for off-grid installations. It’s essential to note that there are limited suppliers of inverters compatible with each off-grid inverter manufacturer, with some exclusively designed for use with their own products.

Our top recommendations for inverters are Fronius and ABB (Fimer), with a preference for Fronius. Fronius, an Austrian company established in 1945, is renowned as one of the world’s premier welding machine manufacturers. Transitioning to inverter technology in 1992, they introduced their first photovoltaic (solar) inverter in 1995. Fronius currently stands as a market leader in inverter technology, offering solutions for various requirements.

We specifically utilise the Selectronic certified GEN24 inverter from Fronius, which seamlessly communicates with the off-grid inverter, allowing for the smooth transition of data. Fronius also provides the flexibility to daisy chain multiple inverters throughout the site, monitoring and communicating with them as a unified system.

Key Benefits of Fronius:

  • Austrian-owned and manufactured.
  • Established and thriving since 1945.
  • Superior product range.
  • Scalability for system size.
  • Advanced communication abilities for monitoring.
  • Fronius Service Partners (FSP) for comprehensive after-sales support (Velocity Solar is an FSP).
  • Industry leadership in this space.

For more information on Fronius, visit their website:

Off-Grid Inverter/Battery Charger

The off-grid inverter and charger serve as the central intelligence of any off-grid installation playing a pivotal role in collecting power from various sources and efficiently distributing it as per specific requirements. Here’s an overview of its key functions:

  • Communication with AC Solar Inverters (e.g. Fronius): The inverter communicates with and receives power from AC solar inverters, adjusting its supply to match the power needed for both batteries and loads within the property.
  • Battery Interaction: The inverter sends and receives power from the attached battery, converting power between AC and DC to ensure usability. It also verifies technical data from the batteries to ensure safe operation and accurate distribution.
  • Connecting to AC Source 2 (Generator or Grid): The inverter connects to the client’s AC source 2, allowing the supply from generators to run loads, top up power as needed, and charger batteries.

The off-grid inverter/charger is a crucial component, often one of the more significant investments within the solar system. The system relies heavily on this component for effective functionality.

Our top recommendation is the Selectronic SP Pro series 2i. Selectronic, an Australian family-owned company established in 1964, has been a leader in delivering energy solutions for over 50 years. Their head office in Melbourne and now distributing internationally. The SP Pro, their flagship product, is the only multi-mode, bi-directional inverter charger manufactured in Australia, forming the core of every battery based energy system. Key benefits of Selectronic include:

  • Compatibility: Ability to communicate with multiple inverter and battery manufacturers.
  • Flexibility: Ability to connect multiple inverters for larger loads or create a 3 phase supply for off-grid applications.
  • Reliability: Bypass functionality ensures continuous operation even if the inverter stops working.
  • Convenience: Auto-start functionality for generators, eliminating the need for manual operation.
  • Remote Monitoring: Capability for remote site monitoring, troubleshooting, and parameter adjustments.
  • Technical Support: Exceptional technical support service.
  • Australian Made: Manufactured and owned in Australia.
  • Power Handling: Large overcurrent demand ability for short periods.

Having installed numerous off-grid systems, we find that Selectronic offers all the necessary features and more. Its reliability, coupled with robust support and design capabilities, makes it our number one choice.
For more information, visit Selectronic’s website:

Battery Solution

The battery market for off-grid installations has undergone significant changes over the past 10 years, particularly with the introduction of lithium options. Unlike traditional lead-acid solutions, lithium batteries offer increased flexibility in case of malfunctions or upgrades, and they require less maintenance to ensure proper functioning.

Modern lithium battery solutions are not only more compact for the same storage capacity but also feature safer technology and modular designs. These characteristics make lithium batteries an ideal choice for the future of off-grid solutions.

Batteries can be configured in various ways, allowing for flexibility in installation. They can be set up in separate 2 volt increments and combined to create 24, 48, and 120 volt battery solutions. Alternatively, a single 48 volt battery solution (most common) can be paralleled to increase storage capacity.

Our top recommendation is the Power Plus ECO range, designed and manufactured in Australia. Power Plus offers a comprehensive range of Battery Energy Storage Solutions (BESS) for various renewable energy projects. We specifically utilise the ECO Plus range for off-grid setups, providing the best value for your investment with suitable charge and discharge rates aligned with solar energy needs.

Having installed Power Plus batteries in our off-grid projects for five years, we have found that integrating them with Selectronic inverters is straightforward, offering seamless communication and ease of installation and expansion.

Key Benefits and Features of Power Plus:

  • Complete solution, including an incorporated battery cabinet.
  • Modular scalability for storage size expansion without drawbacks.
  • Australian owned and made.
  • Strong technical support for sites.
  • Versatile options for designing systems to meet diverse requirements.

For more information, visit the Power Plus website:


Solar Panels

Solar (Photovoltaic) panels serve as the primary power generation component in a solar system, capturing the sun’s energy and converting it into Direct Current (DC) power. This DC power is then sent to the inverter, where it undergoes conversion into usable power for your home.

Solar panels vary in size and efficiency ratings, and it’s important to note that bigger doesn’t always mean better. For instance, a 400-watt panel with 17% efficiency is not necessarily superior to a 370-watt panel with 18% efficiency. Efficiency reflects how effectively a solar panel harnesses sunlight relative to its size. In some cases, a slightly smaller, more efficient panel can yield greater production over combined roof space. It’s advisable to consult with a solar designer to ensure proper system design.

Choosing a solar panel can be challenging due to the multitude of manufacturers and their varying features. When evaluating options, consider the history and reputation of the panel manufacturer. Established manufacturers with a track record since 2000 generally have proven reliability. Price also plays a significant role, with a wide range available in the market. While higher end panels may cost more, it’s essential to weigh the pros and cons for your specific needs.

The internet and reviews can provide valuable insights, and we recommend SolarQuotes as a reliable reference point for gathering additional information in this space:

Our recommendations for solar panel manufacturers are REC and Trina, catering to different needs and budgets.

  1. Trina:
    1. Established in 1997.
    2. One of the world’s largest panel manufacturers.
    3. Financially strong.
    4. Offers a large range of mid-range panels.
    5. Low fault rates and warranty concerns compared to the industry average.
    6. Reputable Chinese manufacturer with multiple global manufacturing plants.
    7. Direct contact with the support team in Australia.
    8. Widely stock by suppliers in Australia due to popularity.

Learn more about Trina:

  1. REC:
    1. Founded in 1996 in Norway, they are a Norwegian solar company with a manufacturing plant in Singapore.
    2. Industry leader with innovations like Hydro-junction technology.
    3. Lead free technology.
    4. Offers a warranty on both manufacturing and labour for 25 years.
    5. Lowest temperature coefficient on the market for better performance in high temperatures.
    6. Singapore owned and manufactured for the Australian market.
    7. One of the lowest fault rates in the panel manufacturing market.
    8. An industry leader in new technology.

Learn more about REC:

Solar Railing/Racking

When it comes to installing solar panels and their railing/racking, the differences offered a relatively minor, but some considerations are essential for optimal performance. Here are key factors to take into account:

  • Colour: Railing options typically come in silver or black. While this is primarily a cosmetic choice, an all-black solution can enhance the visual integration of panels and railing, creating a neater appearance. It’s worth noting that the cost of black railing components is slightly higher, around 10-20%, for those interested in this option.
  • Tilt Frames: Tilt frames play a crucial role, especially in off-grid installations, aiming to maximise postproduction during winter months. Since the sun is lower in the sky with fewer daylight hours in winter, tilting the panels towards the winter sun enhances production during periods of higher demand on the system. An ideal tilt angle is around 30-40%, providing an efficient compromise.

There are three distinct options for tilting panels:

  • Commercial Tilts Frame: Suitable for urban aesthetics, these frames place panels in a landscape profile. However, they are not ideal for off-grid installations as they tilt only to 15 degrees.
  • Tilt Legs: Upgrade stands from back and front feet, slightly less sturdy than A frames but suitable for larger tilting requirements.
  • A-Frame: Structurally robust, these frames provide greater stability on the roof, making them our preferred choice. While they are more expensive, their specifications for high wind loadings surpass other options. A limitation is that they tilt to a maximum of 45%, which may be insufficient if the roof is reverse tilted to the required orientation.

Our Recommendations: Radiant & Sunlock


Learn more about Radiant:

Learn more about Sunlock:


Fuel powered generators play a crucial role as a backup power source integrated into standalone systems. Their primary function is to supply power during periods of heightened demand or extended durations of insufficient renewable energy generation.

In the design of standalone systems, our goal is to minimize generator run time and the associated costs. Generators are not only expensive to purchase but also come with high operational costs, noise, pollution, and a historical reputation as a potential weak link in standalone power systems.

An essential feature of any generator is the implementation of auto start functionality. This feature enables the Selectronic inverter to have preset configurations for turning the generator on and off as needed, ensuring optimal system performance. Auto start functionality also allows for bypassing solar when necessary and avoiding operation during inconvenient times, such as between midnight and 7am in residential areas.

Here are a couple of recommendations for off-grid generators that could be utilised. It’s important to note that generators for off-grid installations can range in cost from $3,000 to $10,000, with an average midpoint of approximately $6,000, to $7,000.

Generator Store –

Genelite –

When determining the appropriate generator for your off-grid installation, key considerations include:

  1. Maximum demand of the site (power)
  2. Average daily usage (kWh)
  3. Days of autonomy

These factors help ensure that the selected generator meets the specific power requirements and provides reliable backup during periods of low renewable energy generation.

Get in contact with us today so we can book a time to do your free in-house consultation.

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