All solar power systems work on the same basic principles. Solar panels first convert solar energy or sunlight into DC power using what is known as the photovoltaic (PV) effect. The DC power can then be stored in a battery or converted by a solar inverter into AC power which can be used to run appliances. Depending on the type of system, excess solar energy can either be fed into the electricity grid for credits*, or stored in batteries.
There are 3 different types of solar systems (1) on-grid, (2) off-grid and (3) hybrid.
1) On-grid: (aka Grid-tied or Grid Feed Systems)
On-grid solar systems are the most commonly used by businesses. Their purpose is to substitute as much utility power as possible with “free” solar power. They are also connected to the public electricity grid in such a way that any excess solar power generated can be exported to the electricity grid for credits or a feed-in-tariff (FiT). So, for safety reasons, these systems are designed not to be able to function or generate electricity during a blackout or load shedding. Blackouts usually occur when the electricity grid is damaged, and if the solar inverter was still feeding electricity into a damaged grid, it would risk the safety of the people working on the damaged grid.
So while the on-grid systems will significantly reduce your utility electricity bill, they won’t be of any assistance to you during blackouts or load shedding.
2) Off-grid: (aka Stand Alone Power Systems or SAPS)
Essentially an off-grid system doesn’t need to be connected to the utility electricity grid at all. They can be designed in such a way that they will generate enough power and have enough battery capacity to meet the premises’ requirements throughout the year. PV panels on the roof will provide all the power required and power stored in batteries will get you through the night.
Pure off-grid systems have usually only been found in more remote areas, lying far from the electricity grid. However, in recent years, with battery costs reducing rapidly, and with some off-grid inverters now accepting 3 different sources of power, there is a growing market for off-grid solar battery systems even in cities. These off-grid inverters can use the sun as it’s primary source of power, the batteries as it’s secondary power source, and the utility electricity grid as it’s third source of power.
In order to achieve this, the off-grid inverter is configured to accept the sun as it’s primary source of power, the batteries as it’s secondary power source and only if the batteries discharges down to a predetermined level, the inverter can then switch to a tertiary power source i.e. the utility electricity grid. As soon as the sun shines brightly enough again, the inverter will switch back to accepting it’s primary power source i.e. the sun.
These off-grid inverters can also be programmed to switch to the tertiary source, if the load ever exceeds the maximum output of the inverter. When set up in this way, the off-grid system now actually works as a hybrid system.
3) Hybrid:
Hybrid systems can be described as (1) grid-tied with battery storage, or (2) off-grid with utility back up. They combine solar and battery storage in one and are now available in many different forms and configurations. 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 backup, allowing consumers to have the best of both worlds.
*this depends on the ability of the utility and it’s infrastructure to support this feature, and whether or not the utility is prepared to give credits for this excess power.