Types of Systems

There are three main types of solar electricity system to choose from: grid- interactive, hybrid solar and stand-alone power systems. Which one is right for your household?

Households need to choose the right system for their current needs, and think about how it can be adapted to include new technologies in years to come. The most popular option has been to supplement grid power and reduce electricity bills with a grid-interactive system, however hybrid systems that include batteries to store solar electricity are gaining appeal. The price of home energy storage is expected to drop further in the next few years with technology breakthroughs and improvements to battery chemistries, meaning solar households should be ‘battery-ready’.

Grid-interactive systems #

Most solar customers choose a grid-interactive system, also known as a grid-connect system. Any electricity produced by the solar PV system but not needed by the house at the time it is produced is simply fed into the mains grid. The home can still, of course, draw electricity from the grid when insufficient electricity is being generated by the solar panels. Note that in some areas, the energy utility may place a limit on how much you can export, or even prevent it altogether.

Grid-interactive systems have two main components, the solar panel array and a grid-interactive inverter, connecting into the household’s switchboard and electricity meter.

grid-inverter
Figure 1: Grid-interactive systems have two main components, the solar panel array and a grid-interactive inverter, connecting into the household’s switchboard and electricity meter.

Grid-interactive advantages #

  • Easy to operate and low maintenance
  • Most cost-effective option
  • Electricity companies pay consumers for the surplus energy fed back into the grid via a feed-in tariff

Grid-interactive drawbacks #

  • Grid-interactive systems will not work during a power blackout. Grid-interactive solar inverters will shut down for safety reasons if the grid fails to prevent electricity from being fed back into the grid during maintenance.
  • Solar feed-in tariffs can vary depending on which state you live in and which electricity supplier you use and are subject to change.

Hybrid Systems #

Hybrid solar is a typical grid interactive PV system with the addition of batteries and is the most rapidly developing system that we cover in this booklet. Solar electricity generated during the day can be stored in the battery for later use, such as in the evening when electricity tariffs are higher. Combining a battery with a grid-interactive system provides much more autonomy from the mains grid and allows you to charge your batteries on low-cost off-peak tariffs.

Figure 2: A DC-coupled hybrid system might be configured as above, where the solar panels charge the battery via a charge controller, otherwise known as a regulator.

There are two methods of ‘coupling’ generation sources to the battery bank—AC and DC coupling. Just like an inverter converts the DC electricity from solar panels into appliance-friendly AC, batteries also need an inverter to render their stored energy useable. If the batteries are DC-coupled, they can share the inverter with the solar panels, while if they are AC-coupled, they’ll require a separate inverter of their own (it may be built into the battery, in which case the battery is known as an “AC battery”).

An AC-coupled storage system is connected to the AC side of a solar PV system’s inverter, much like any grid-connected appliance. Depending on the specifics of the system, they can store energy from solar generation as well as the grid.

DC storage is either connected to the output of the solar PV panels (via a dedicated DC-DC converter or solar charge controller, depending on the system design) or to the DC connection on a special solar inverter called a hybrid inverter. DC-coupled storage systems may or may not be capable of storing grid power, depending on system design and configuration

Hybrid Advantages #

  • Significant reduction in power bills by using stored as well as direct solar electricity to run appliances.
  • Consumers gain further independence from the grid than with a standard grid-interactive system, but the grid is still there if needed.
  • Excess power can still be sold back to electricity retailers.

Hybrid Disadvantages #

  • More expensive than standard grid-interactive systems with longer payback times. This will improve in years to come.
  • The batteries tend not to offer as much energy bill savings as the solar panels.
  • Complex, with more components that can go wrong.
  • Require specialist expert design and installation.

Stand-alone power systems (SAPS) #

Solar panels can also be used in stand-alone power systems (commonly abbreviated to SAPS) to provide all of a home’s power needs, without any connection to the grid. To do this, stand-alone systems include batteries to store the energy produced by the solar panels for later use, for example, on cloudy days or at night. Standalone systems are generally used by homes without access to a grid connection in rural or remote areas, but are sometimes used to avoid electricity supply costs even where the mains grid is available.

Figure 3: A stand-alone system typically has the components above including batteries to store the energy produced by the solar panels.

SAPS Advantages #

  • May be the only option where mains electricity is not available.
  • Can be cheaper than connecting to the grid in more remote areas.
  • Negates the need to purchase electricity (and pay connection fees) from a retail supplier.
  • Off-grid solar systems can be designed to power single items only such as water pumps, large appliances and solar hot water systems.

SAPS Disadvantages #

  • Higher maintenance than other systems and relatively expensive.
  • More electrical components, so there’s more that can go wrong.
  • Require specialist expert design and installation.
  • Batteries require significant storage space such as an extra room or shed.
  • A significant amount of solar energy produced is lost i.e. not used, particularly during the sunnier months. This excess solar cannot be shared with other homes and businesses connected to the grid.