On-Grid Solar System
On-grid or grid-tie solar systems are by far the most common and widely used by homes and businesses. These systems are connected to the public electricity grid and do not require battery storage. Any solar power that you generate from an on-grid system (which is not used directly in your home) is exported onto the electricity grid and you usually get paid a feed-in-tariff (FiT) for the energy that you export. Unlike hybrid systems, grid-tie solar systems are not able to function or generate electricity during a blackout or power outage due to safety reasons; since blackouts usually occur when the electricity grid is damaged. If the solar inverter was still feeding electricity into a damaged grid it would risk the safety of the people repairing the fault/s in the network. However most hybrid solar systems with battery storage are able to automatically isolate from the grid (known as islanding) and continue to operate during a blackout. Batteries are able to be added to an on-grid solar system at a later stage if required.
In an on-grid system, this is what happens after electricity reaches the switchboard: The meter. Excess solar energy runs through the meter, which calculates how much power you are either exporting or importing (purchasing). Metering systems work differently in many states and countries around the world. In this description it is assumed that the meter is only measuring the electricity being exported to the grid, as is the case in most of Australia. In some states, meters measure all solar electricity produced by your system, and therefore your electricity will run through your meter before reaching the switchboard and not after it. In some areas (currently in California), the meter measures both production and export, and the consumer is charged (or credited) for net electricity used over a month or year period.
The electricity grid.
Electricity that is sent to the grid from your solar system can then be used by other consumers on the grid (your neighbours). When your solar system is not operating, or you are using more electricity than your system is producing, you will start importing or consuming electricity from the grid.
Off-Grid Solar System
An off-grid system is not connected to the electricity grid and therefore requires battery storage. An off-grid solar system must be designed appropriately so that it will generate enough power throughout the year and have enough battery capacity to meet the home’s requirements, even in the depths of winter when there is less sunlight. The high cost of batteries and inverters means off-grid systems are much more expensive than on-grid systems and so are usually only needed in more remote areas that are far from any electricity grid. However battery costs are reducing rapidly, so there is now a growing market for off-grid solar battery systems even in cities and towns.
The battery bank. In an off-grid system there is no public electricity grid. Once solar power is used by the appliances in your property, any excess power will be sent to your battery bank. Once the battery bank is full it will stop receiving power from the solar system. When your solar system is not working (night time or cloudy days), your appliances will draw power from the batteries.
Backup Generator. For times of the year when the batteries are low on charge and the weather is very cloudy you will generally need a backup power source, such as a backup generator or gen-set. The size of the gen-set (measured in kVA) should to be adequate to supply your house and charge the batteries at the same time.
Hybrid Solar System
Due to the decreasing cost of battery storage, systems that are already connected to the electricity grid can start taking advantage of battery storage as well. This means being able to store solar energy that is generated during the day and using it at night. When the stored energy is depleted, the grid is there as a back up, allowing consumers to have the best of both worlds. Hybrid systems are also able to charge the batteries using cheap off-peak electricity (usually after midnight to 6am).
The battery bank. In hybrid system once solar power is used by the appliances in your property, any excess power will be sent to your battery bank. Once the battery bank is full, it will stop receiving power from the solar system.
The meter and electricity grid. Depending on how your hybrid system is set up and whether your utility allows it, once your batteries are fully charged excess solar power not required by your appliances can be exported to the grid via your meter. When your solar system is not in use, and if you have drained the usable power in your batteries your appliances will then start drawing power from the grid.
Simplified layout of a hybrid solar system
Difference between On-Grid and Off-Grid Solar Installation
Solar Power systems can be categorized into two types – Off-grid solar system and on-grid/grid-tie solar system. But, why is the grid there in the first place? Also, which one should you choose between the two? Read on to learn the major differences between the on-grid installation and off-grid installation.
On-grid systems are those solar power systems that produce energy only when the utility power grid is there. In order to work, these systems need a connection to the grid. In case you overproduce power, the on-grid solar systems send the additional power back to the grid, which helps you save it for later use. On-grid systems are also dubbed grid-tie or integrated systems.
On the other hand, off-grid solar power systems are those that help you store the solar energy in batteries in case the power grid fails or the grid is not available. To balance the grid power during sunlight, power is provided by hybrid systems. These systems also send excessive power to the grid so you could use it later.
On-grid solar systems generally need solar panels along with a proper mounting system; solar cables and MC4 connectors; grid tied solar inverter and monitor; AC and DC safety isolator switches; and grounding earth cables and clamps.
Off-grid solar systems usually require solar panels with an appropriate solar mounting system; off grid solar inverter; solar cables and MC4 connectors; solar power controller and batteries; AC and DC safety isolator switches; and grounding earth cables and clamps.
Advantages and Disadvantages
On-grid solar power systems offer several advantages such as:
Utility is a 100% efficient battery, which has the potential to absorb all the additional energy.
You need not to bring any change in your lifestyle or conserve electricity.
It provides you a backup of a stand-alone unit.
Disadvantages of on-grid systems:
These provide less incentive to conserve These are battery-less systems, which provide you no backup.
Advantages of off-grid systems:
These are less expensive, even when compared to availing a utility line stretched to a property. However, there will be ongoing expenses.
These systems are good in terms of expandability.
These systems help you make efficient use of electricity, which benefits the environment.
Disadvantages of off-grid systems:
These require regular maintenance and troubleshooting.
Batteries of off-grid systems have less tangible cost, which means energy waste.
Benefits of Grid-Tied and Off-Grid Solar Power Systems
Solar power offers many benefits to home and property owners, most notably a reduction in electricity costs and usage. However, there are other benefits that are dependent on the type of system you choose, and it is important to weigh the pros and cons of grid-tied solar power systems and off-grid systems, in order to select the solar power option that is right for you.
Grid-tied solar power systems are the most common type of solar electric system in the United States. This type of system is attached, or “tied” to the existing electrical grid. Electricity that is generated by the solar array flows freely back to the grid, and to the utility company. The household or commercial property that benefits from the system is credited for the electricity generated by the solar panels. As long as the solar array generates more electricity than the household consumes, the electricity will be free. If the household or business consumes more electricity than is generated, it will be billed for only the excess consumption.
Grid-Tied Solar PV Systems
The features of a solar power system that are exclusive to grid tied installations include the possibility to earn, sell, and generate revenue from Solar Renewable Energy Credits (SRECs). In this case, the utility company will pay you for the electricity your home generates. In instances where the solar array is not generating enough electricity to power the home, the electrical grid will supply electricity whenever needed. This is great news for home owners who may not have enough sun exposure or spaces on their property for all of the panels required to power their home, because they can still discount their current electricity rates, and reduce their environmental impact.
Off-Grid Solar PV Systems
An off-grid system has several different features as well. This type of solar electric system is not connected to the electrical grid. Instead, it relies on batteries to store the electricity generated by the solar panels for use when the system is not generating enough to sustain household functions, for example, at night. Because it is completely separate from the electrical grid, the power will remain on for the household or building even in the event of a widespread power outage; in a grid-tied scenario, the solar power system must shut off during a power outage for safety reasons. However, it is important to consider the space required to store the batteries, as well the added expense to purchase them. Additionally, off-grid systems cannot take advantage of SRECs, because the electricity never flows back to the utility grid.
When choosing a solar power system, it is important to decide which benefits are the most important to you. If going off the grid, and want to remain powered on even when the rest of the neighborhood is enduring a power outage, an off-grid system may be the right solution for you. Otherwise, a grid-tied system may be the best choice. A qualified solar analyst will be able to discuss your particular needs, and find a solution that is tailored for your home.