Off-Grid Rooftop Solar System: Definition, and How it Works

Off-grid rooftop solar systems refer to photovoltaic (PV) systems that are not connected to the electric grid. Unlike on-grid systems, which rely on utility electricity as a backup, off-grid solar systems are completely independent of the grid, instead relying on solar batteries to store excess energy for later use

One of the benefits of off-grid systems is that they foster energy independence, meaning homeowners generate their own energy without relying on external sources. Homeowners with off-grid solar don’t have to pay electricity bills because they rely on their own standalone electricity reserve. This provides the added advantage of protection from national power outages.

Off-grid solar systems are a great option for remote properties unreachable from the electric grid via power lines. Off-grid solar systems allow the owner to power their home sustainably, using energy drawn from the sun via solar panels instead of buying energy from utility companies that exploit fossil fuels to generate electricity. Traditional brick-and-mortar buildings are not the only candidates for off-grid solar. Other common applications of off-grid solar systems include sheds, cabins, boats, and RVs.

There are some drawbacks of off-grid solar systems. First and foremost, they’re expensive, with higher upfront costs than grid-tied systems. An off-grid solar system sometimes costs up to $100,000, and almost half of the total system cost usually goes toward solar battery storage. Another issue is that off-grid solar systems have finite energy storage, meaning that once the stored electricity has been used, there is no way to generate more without sufficient sunlight. For this reason, off-grid residences need to be located in areas of sufficient sunlight. Some off-grid systems incorporate a backup generator to serve as a backup energy source.

One of the important things to consider when installing an off-grid system is sizing the system correctly. Consider the average hours of sunlight in your area and how much energy the batteries need to store based on the loads (lights, appliances, etc) to avoid being caught out without power.

What is an Off-Grid Rooftop Solar System?

An off-grid rooftop solar system is a self-sustaining photovoltaic (PV) system that allows a home or building to generate and store its own electricity with 100% independence from the utility grid. Off-grid systems are designed to provide electricity to homes, cabins, or other buildings located in remote areas. They typically consist of solar panels, a charge controller, an inverter, and solar batteries.

Off-grid systems are remarkable in that they represent the forefront of sustainability by allowing a household to achieve total energy independence. Unlike hybrid and on-grid solar systems, which partially rely on the grid as a backup, off-grid systems are entirely self-sufficient and use only renewable energy. The grid, or utility grid, refers to the interconnected system of transmission lines, wires, and infrastructure that delivers power to the majority of US households. By severing reliance on this form of electricity, off-grid solar systems provide complete independence from external sources and eliminate reliance on energy generated by fossil fuels.

Utilizing an off-grid solar system eliminates the need for a relationship with a utility company, as well as the monthly electricity bills that most American homeowners face. With this comes some risk, as there is no form of backup supply if the amount of solar energy stored runs out. For this reason, it’s essential that the off-grid system is correctly sized when it’s installed to make sure that it will provide a sufficient supply of energy even in periods of lower sunlight. Some solar setups include a backup generator to rely on in case of prolonged periods of low sunlight or unusually high energy demand.

The defining component of an off-grid solar system is its battery storage. Off-grid systems typically require more battery storage than hybrid systems, as they can’t switch to grid power like a hybrid system if sunlight is limited. Solar batteries are notoriously expensive, especially considering they usually need to be replaced every 5-15 years.

Whilst the idea of off-grid living is desirable for many, the cost is prohibitively expensive in some cases. Installing an off-grid system is not only more costly than an on-grid or hybrid system, it’s also more complex. Off-grid systems require careful planning to ensure they meet the energy demands of the household, especially during periods of low sunlight. Additionally, maintenance of off-grid systems is more intensive, as homeowners must regularly monitor battery levels and system performance to ensure everything is operating efficiently.

How does an Off-Grid Rooftop Solar System work?

An off-grid solar system is a self-sustaining power system. Off-grid systems work by using solar panels to generate electricity from sunlight, storing the electricity in batteries, and using that stored energy as the primary source of energy for a house or building. Off-grid systems operate entirely independently of the main electricity grid.

To begin, solar panels are installed in a suitable location, such as a roof or ground mount, to capture sunlight and convert it into electricity. These solar panels are made up of photovoltaic cells that generate direct current (DC) electricity when exposed to sunlight.

Secondly, the DC electricity generated by the solar panels is sent to a charge controller, which regulates the amount of electricity flowing into the battery bank. The charge controller ensures that the batteries are charged safely and efficiently, preventing overcharging or damage to the batteries.

Next, the electricity stored in the battery bank is converted from DC to alternating current (AC) by an inverter. This conversion allows the electricity to be used by standard household appliances and electronics that require AC power.

Finally, the AC electricity from the inverter is distributed to the electrical loads in the building, providing power for lighting, appliances, and other devices. The battery bank stores excess electricity generated during the day for use at night or during periods of low sunlight, ensuring a continuous power supply.

What are the advantages of installing an Off-Grid Rooftop Solar System?

There are six main advantages of installing an off-grid rooftop solar system. The main advantage of installing an off-grid rooftop solar system is that it facilitates energy independence, meaning homeowners don’t need to rely on the utility grid. Other main advantages of off-grid solar include cost savings on electricity bills, protecting against power outages, avoiding utility rate increases, providing energy to rural locations and promoting renewable energy.

More information on the six main advantages of installing an off-grid solar system is listed below:

• Enables Energy Independence: Unlike most photovoltaic (PV) systems, off-grid solar systems are entirely disconnected from the utility grid. Off-grid solar allows homeowners to generate their own independent source of energy in the form of solar and store it for future use during power outages or low sunlight conditions.
• Saves on Electricity Bills: If a household is able to generate enough energy to meet its needs and have some leftovers to store in the solar battery, then it is energy independent. Energy independence eliminates electricity bills because the owners are able to power their homes completely using the energy they generate themselves and don’t have to buy any electricity from the grid.
• Protects Against Power Outages: Off-grid solar systems serve as protection from national power outages caused by bad weather, damaged equipment and grid maintenance, because households are able to use the electricity stored in the solar battery.
• Avoids Utility Rate Increases: The average price of electricity in the US (measured per kilowatt-hour) increased by nearly 13% between 2022 and 2024, according to the Federal Reserve of Economic Data. Installing an off-grid rooftop solar system allows owners to control how they source their energy and avoid utility rate increases in the process.
• Provides an Energy Source for Rural Areas: Rural and remote areas have limited access to the electric grid because they lack the infrastructure to connect to it, so off-grid solar systems are an alternative option to provide a consistent source of power. Solar panels installed on the roofs of buildings in remote areas are able to serve as part of a microgrid - a group of interconnected solar systems generating power independently from the grid - powering multiple households or businesses.
• Promotes Renewable Energy: Despite the ongoing climate crisis and calls from lobbyists to prioritize renewable energy, most utility companies in the US exploit fossil fuels like coal and petroleum to provide electricity to their customers. Installing an off-grid solar system allows owners to power their homes using 100% clean energy, in turn reducing their carbon emissions and doing their part for the environment.

What are the disadvantages of installing an Off-Grid Rooftop Solar System?

There are four main disadvantages of off-grid rooftop solar systems. The main disadvantage of off-grid solar systems is the high upfront cost, which is typically between $30,000 to $65,000 but sometimes goes as high as $100,000 depending on system size and storage requirements. As a rule of thumb, off-grid costs about double what an on-grid system typically costs, meaning it takes longer to recuperate the initial investment. Other main disadvantages of off-grid solar include finite energy storage, lack of backup power, and the limited lifespan of solar energy.

More information about the four main disadvantages of installing an off-grid rooftop solar system is listed below.

• High Upfront Cost: Installing an off-grid solar system is an expensive endeavor, with much higher upfront costs than installing an on-grid solar system. Homeowners planning to install an off-grid solar system have to be comfortable making a large investment of around $30,000 to $65,000, which means the payback period is much longer. The payback period is the time it takes for the electricity generated from a solar system to offset the upfront costs of the investment.
• Limited Energy Storage: Off-grid solar systems have a finite amount of storage, which is determined by the size of the battery. This means there is a chance that homeowners will be caught without power if the amount of energy storage needed is underestimated or if there isn’t enough sunlight over time to sustain the loads.
• Lack of Backup Power: Hybrid solar systems switch between energy generated by solar panels, energy from solar batteries, and energy from the electric grid so the owner constantly has power. Off-grid solar systems have no backup, as they are unable to draw energy from the electric grid during periods of low sun, so owners are unable to use electricity until their own panels start producing power again.
• Limited Lifespan of Solar Batteries: Solar batteries have a shorter lifespan than the rest of the solar system, requiring replacement every 5 to 15 years. This means that homeowners have to make peace with the fact that batteries, which are the most expensive component of the system, need to be replaced multiple times over __.

What materials are needed to install an Off-Grid Rooftop Solar System?

Off-grid rooftop solar systems are less hassle to install than grid-tied solar systems because anyone with basic electrical knowledge and the right tools is able to do it, as opposed to a solar technician with specific licenses and certifications. The seven main materials needed to install an off-grid rooftop solar system include solar panels, a solar charge controller, a solar battery, a solar inverter, a mounting and racking system, junction boxes, and wiring.

1. Solar Panels

The solar panels are the most important part of the solar system, as they are responsible for converting sunlight into electricity. To choose the best solar panels for an off-grid rooftop solar system, consider the energy needs of the household, the amount of usable roof space, the amount of direct sunlight per day, and the portion of the overall budget to spend on the solar array. Note that the average cost of a 400W monocrystalline solar panel is $430, whereas 100W monocrystalline solar panels are available for less than $100, so it really depends on the scale of the off-grid system they are being bought for.

The steps to figure out how many solar panels are needed to meet the energy needs of an off-grid household are as follows. First, divide the household’s annual energy kilowatt-hours (kWh) by 12 to determine the monthly average. Then, divide the monthly electric usage (kWh) by the hours of peak sunlight every month. Next, multiply this figure by 1000 to convert the kilowatts to watts. Finally, divide the total figure by the wattage of the solar panels (400W, 300W, 200W, 100W) to arrive at the number of solar panels needed.

2. Solar Charge Controller

The solar charge controller is a crucial part of the solar system because it regulates the energy produced by the solar panels so the battery doesn’t become overcharged and potentially damaged. Think of the solar charge controller as a thermostat controlling the heat in a house; the solar charge controller monitors and adjusts the flow of electricity to ensure the battery is neither undercharged nor undercharged.

The average cost of a basic pulse width modulation (PWM) solar charge controller is between $15 and $40, but sophisticated maximum power point tracking (MPPT) models go for up to $2000 and beyond. Note that each battery must have its own solar charge controller, so the overall cost varies depending on the size of the solar system.

3. Solar Battery

The solar battery stores the excess electricity generated by the solar panels, so it is essential for the off-grid solar system to be able to sustain itself through periods of low sun. Solar batteries are essential for completely off-grid solar systems that rely on backup energy and partially off-grid solar systems in areas with unreliable access to the electric grid.

A decent solar battery costs between $4,000 and $23,000, depending on the manufacturer, type, power capacity, and installation fees. The total cost of solar battery storage is often equal to half of the price or more of the entire solar system.

4. Solar Inverter

The solar inverter converts the energy generated by the solar panels or stored in the battery in direct current (DC) form into usable alternating current (AC). Off-grid solar inverters differ from traditional inverters in that they are designed for standalone solar systems that aren’t connected to the electric grid. They serve as the ‘heart’ of the system, regulating the flow of energy between the panels, the battery, and the loads.

Off-grid solar inverters are typically more expensive than on-grid inverters. They include complex components, require sturdy materials to withstand harsh conditions, and have higher maintenance costs. An off-grid solar inverter costs anywhere between $3000 and $13,000, depending on how advanced it is.

5. Mounting and Racking System

The mounting and racking system serves two purposes in an off-grid system. Firstly, it secures the solar panels to the roof and ensures the solar panels are pitched at the optimal angle for power production. Solar racking is installed parallel to the roof on angled roofs and at a steep angle on flat roofs to maximize sunlight.

The racking system for solar panels comprises mounts attached to the rafters, rails for panel attachment, and aluminum flashing to reinforce holes made in the surface of the roof during installation. Typically, a solar mounting and racking system accounts for 10% of the total system cost. However, for off-grid rooftop systems, costs vary based on the racking type, required equipment, and installation labor.

Installing solar racking is a somewhat precarious process because any penetrations made through the roof during the fitting need to be meticulously sealed to prevent leaks, and the rafters need to be thoroughly checked beforehand to ensure they are able to support the mount.

6. Junction Boxes

The junction box is an often overlooked but very important part of the off-grid solar system. It houses all of the electrical components on the solar panel and protects them against the elements. Effectively, the solar panel junction box consolidates all of the wires in the solar panel so they are organized, standardized across installations, and easy to navigate for maintenance. The junction box contains important components called ‘bypass diodes,’ which keep the power flowing in one direction, preventing it from being fed back to the panels.

Junction boxes cost between $70 and $150, excluding installation costs. The price varies depending on its size, material, and waterproofing. It is a worthwhile investment to buy a high-quality junction box because malfunctions prevent electricity from being generated and lead to a complete loss of production.

7. Wiring

The wiring in an off-grid solar system transports the energy from the solar panels to the loads (the devices they power). Most cables used in solar panel wiring have a core of conductive metal like copper or aluminum, insulation wrapped around it to protect the cable from the outside world, and a rubber sheath.

It is important to choose the right cabling for an off-grid solar system based on its resistance to moisture, sunlight, and high temperatures. Solar cabling needs to be matched to the voltage and the maximum current (amperage) that passes through the solar system.

Is it hard to install an Off-Grid Rooftop Solar System?

No, it is not necessarily “hard” to install an off-grid rooftop solar system, but there are some prerequisites involved. These include having basic electrical knowledge, access to the right materials and basic tools, and understanding how to correctly size the system. One of the most important parts of installing an off-grid rooftop solar system is related to wiring. The good news is that most modern equipment, including cables, comes with premade ports and connectors, which make it easy to wire the components in an off-grid solar system.

The most complicated facet of wiring required to install in an off-grid rooftop solar system is the cable running between the combiner box and the charge controller. The combiner box is the roof-mounted equivalent of the junction box in a ground-mounted solar system. Running wires from the combiner box to the charge controller (in adherence with the building code) is tricky because the components are located on opposite sides of the building - the combiner box is next to the solar panels, whereas the charge controller is next to the battery - with obstacles like vents and chimneys in the way.

How much does it cost to install an Off-Grid Rooftop Solar System?

The cost of installing an "off-grid" residential solar system ranges from $30,000 to $65,000, nearly double that of an on-grid system due to the need for expensive solar batteries. High battery costs are the main deterrent to off-grid living, as batteries typically need replacing every 5-15 years.

The total cost of an off-grid photovoltaic (PV) system varies heavily depending on different factors, such as your energy needs, whether you need to purchase additional land, and whether you DIY install or use a professional installer.

Off-grid cost depends primarily on energy usage requirements because less energy and cost are required for off-grid applications like powering a cabin or campervan compared to a house full of electrical appliances. For example, it’s possible to set up a smaller system with around 1200kW of solar panels for about $15,000-$20,000. This amount of power is fine if mitigating your energy needs in other ways, like using wood stoves for heating and limiting the use of high-energy appliances. On the other hand, to fully power a large house using only solar power sometimes costs as much as $100,000.

Those considering going off-grid in the US often have to contend with the additional costs of purchasing land. Location plays a significant role in determining land value and, as such, the final cost of off-grid solar installation. For bare land with no utilities in an area with little competition, the cost is often around $1000-$2000 per acre of land. However, for land in prime real estate areas, the cost goes up to $20,000 and beyond for each acre of land. Remember to factor these considerations into your budget if you haven’t yet purchased a suitable location for living off-grid.

One way to significantly reduce the cost of going “off-grid” with solar is DIY installation. Typically, DIY off-grid solar installation usually costs at least 50% less compared to using a professional installer. By performing the steps involved yourself, from sourcing parts to installation, there are ample opportunities to significantly bring down the cost of your system. However, taking on the responsibility of installing an off-grid PV system comes with important caveats. Firstly, installing solar yourself is not permitted in some areas of the US, depending on local regulations. Secondly, off-grid systems often have complex installation requirements, meaning that careful planning and adherence to safety standards are essential.

What is the difference between On-Grid and Off-Grid Rooftop Solar System?

The main difference between on-grid and off-grid solar systems lies in their connection to the electrical grid. While on-grid systems are linked to the mains electricity supply, off-grid systems operate independently by storing excess energy in batteries for use when sunlight is not available. Other differences between on-grid and off-grid solar systems relate to cost, reliance on sunlight, and how they operate during a power outage.

On-grid solar systems are much cheaper than off-grid systems of an equivalent size, predominantly due to the high cost of solar battery storage. For example, in the case of a home that requires 45 kilowatts (kW) of power, the battery is likely to cost around $15,000-$20,000. For this reason, going 100% off-grid is still a fairly uncommon decision for American homeowners. One way to get around the costs of battery storage is to invest in a backup generator, which means less money will go towards paying for expensive solar batteries. For example, installing a generator for a home that needs 45kW of power makes it possible to reduce your storage needs to around 15kW, which costs more like $6000. When choosing batteries, remember that lithium ones have a higher Depth of Discharge (DoD), so they often work out cheaper in the long run than their less expensive lead-acid counterparts.

On-grid (aka grid-tied) rooftop solar systems are connected to the electric grid, so owners are able to rely on backup energy provided by a utility company during periods of low sun. This makes on-grid rooftop solar systems less risky because they allow homes to run off solar when there is sufficient sun but switch to grid power when needed. Off-grid systems, on the other hand, are entirely independent of the utility grid, meaning that there is no backup power if the stored electricity runs out. When the battery depletes completely and the panels generate insufficient solar, a backup generator would be required to continue to power the home. For this reason, going 100% off-grid is only recommended in areas of high and consistent sunlight.

Another major difference between on-grid and off-grid solar systems is how they behave during a power outage. On-grid systems actually shut down entirely during a power outage in order to protect utility workers who might be working on power lines. This is known as the anti-islanding feature, which prevents the solar system from feeding electricity back into the grid while it is being repaired. On the other hand, off-grid solar works perfectly for power outages and blackouts, allowing homeowners to access a private and independent energy supply from battery storage.

What is the difference between Grid-Tied and Off-Grid Rooftop Solar System?

The difference between grid-tied and off-grid rooftop solar systems is where they send excess energy. Grid-tied solar systems feed excess energy back to the grid, entitling the owner of the system to a deduction from their next electricity bill, whereas off-grid solar systems store any excess energy generated in solar batteries for later use. The process of selling solar energy back to the electric grid is called net metering, where owners of grid-tied solar systems are able to exchange surplus energy they generate for credits from their utility company correlating to the number of kilowatt-hours (kWh) they return to the grid.

Off-grid solar systems are a great choice for properties located in a country whose electric grid has frequent breakdowns and for buildings too far away from the electric grid to be connected to it. However, there is a middle ground that allows owners to reap the benefits of both grid-tied and off-grid solar systems, which is using a hybrid solar system (grid-tied with a battery). Hybrid solar systems constantly switch between using energy generated by the solar panels, energy stored in the battery, and energy from the electric grid so the owner is able to avoid paying to use electricity when it is most expensive, such as during peak demand hours.