Energy storage in a photovoltaic system: why is it convenient? How to integrate it into PV systems? Definitions and advantages (part 1)

Accumulation capacity integrated into the PV system

Energy storage for photovoltaic systems essentially consists of particular “batteries” that are designed to store the energy produced by a photovoltaic system and to make it available for use, such as during night time, whenever the system cannot produce sufficient energy for self-consumption. In addition, these batteries can store the self-produced surplus of energy  in “stand alone” systems supplying even places outside the national grid.

The advantages of an energy storage system

Using a storage system for your PV system provides numerous advantages:

  • it allows you to considerably reduce the impact on electricity costs (and more saving on your bills)
  • it makes the electricity usage self-sufficient
  • it can optimize electricity for privileged loads through specific devices.

Types of photovoltaic systems

There are two types of photovoltaic systems:

  • stand alone system (isolated)
  • grid connected system (systems connected to the utility grid).

Stand Alone system

Isolated systems (stand alone) are autonomous systems normally used to supply electricity to users that hardly can connect to the grid, as located in inaccessible areas, or users with very low energy consumption, making the connection to the national electricity network not very convenient in terms of costs.

stand alone system

stand alone system

An isolated system is characterized by the need to cover the entire energy demand of users, having as essential elements:

  • photovoltaic modules
  • a charge controller
  • storage systems (batteries)
  • inverters (transforming direct current into alternating current)

These systems are cost-effective in cases when the electricity grid is absent or difficult to reach. In the event of power failure, the stand-alone system grants the continuity of the electricity supply as well, especially thanks to its integrated storage system allowing the energy  produced to be stored and reused when the photovoltaic panels don’t work (for example at night time).

Grid Connected system

Grid connected PV systems are electricity generating PV power systems allowing to exchange energy with the national grid. The exchange can take place in two directions:

  1. if the production of the photovoltaic field exceeds the consumption for a certain period, the surplus is fed into the network.
  2. in the hours when the generator does not supply enough electricity to satisfy the users, the energy is taken from the grid.

Generally, in grid connected systems, there are two counters that measure the energy exchanged in the two directions and there is an inverter that transforms the direct current produced by the photovoltaic system into alternating current.

Many grid connected systems are not equipped with batteries because the distribution network compensates for the supply of electricity when the solar radiation is not available. Today, thanks to the lower costs of storage systems, batteries are installed in order to increase the consumption of self-produced energy, so to have more savings.

Accumulation capacity in a Grid Connected system

grid connected system with accumulation capacity

grid connected system with accumulation capacity

An integrated storage system which is grid-connected increases the deferred self-consumption, i.e.the possibility of accumulating the electricity produced by the batteries, and using it at a later time, for example in the evening when the photovoltaic system is not producing energy.

In grid connected systems with storage batteries, the consumption flows follows a specific order:

  1.  the user feds from the current produced, in the first place, by the photovoltaic panels;
  2.  the user draws on the energy previously stored in the storage system (batteries) if the system is not working at the moment of supply request.
  3.  the user takes the energy from the national electric supply service when the batteries are low.
    Differently from the stand-alone system, which can function as a continuity unit, grid connected systems  have a safety system that automatically deactivates  in case of absence of supply voltage.

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