Generally, stand-alone (off-grid) and smaller grid fallback PV systems run at low voltages, typically between 12 and 48 volts. This is because batteries are low-voltage units and so building a stand-alone system at a low voltage is a simple, flexible and safe approach.
Grid-tie PV systems tend to be larger installations, often generating several kilowatts of electricity each hour. As the electricity is required as a high-voltage supply, it is more efficient to connect multiple solar panels together to produce a high voltage circuit, rather than use an inverter to step up the voltage. This high-voltage DC power is then converted into an AC current by a suitable grid-tie inverter.
Grid-tie systems either link multiple solar panels together to produce a solar array voltage of several hundred volts before running to the inverter, or have a small inverter connected to each solar panel to create a high-voltage AC supply from each panel. The benefit of this high voltage is efficiency. There is less power loss running high-voltage, low-current electricity through cables from the solar array.
- For smaller stand-alone battery-based systems, low-voltage is the best solution, as the battery banks tend to work better as low-voltage energy stores.
- For grid-tie systems where the energy is not being stored in a battery bank, the highervoltage systems are the best solution.
- For grid-tie with battery storage, most systems create a hybrid with high-voltage power generation from the solar panels and a low or medium-voltage battery system. Neither approach is inherently ‘better’, it all depends on the type of system you are designing.
- Solar can be used in many ways and for many applications.
- Stand-alone systems, also known as off-grid solar systems, are the simplest and easiest to understand. They tend to be comparatively small systems, providing power where no other power source is easily available.
- With a grid-tie, your solar energy system generates electricity that is then used normally. Any excess electricity production is exported onto the grid.
- Grid-tie with power backup (also known as grid-interactive) provides you with the benefits of a grid-tie system with the added benefit that power remains available even if electricity to your area is cut off.
- Grid fallback systems often have more in common with stand-alone systems than grid-tie systems. In design, they are very similar to stand-alone PV systems, with an inverter running from a bank of batteries and an automatic transfer switch to switch power between the solar energy system and the grid power supply.
- Grid-tie systems have a different design to stand-alone systems. They tend to be high-voltage systems, whereas stand-alone systems run at much lower voltages.