What is the bidirectional meter and how does it work?

What is the bidirectional meter?

The bidirectional meter is an advanced metering device that can record both the electricity taken from the grid and the electricity fed in. It has become particularly important with the spread of domestic renewable energy production systems, such as photovoltaic panels.

In more traditional circumstances, until the first smart meters, electricity grid users had a meter, jargonily called a ‘passive’ meter, connected to measure their consumption. With the one-way meter, the user could only verify the amount of energy consumed. However, thanks to the massive rollout with first- and second-generation electricity meters, the houses of all users now have a new meter capable of measuring both the energy withdrawn from the grid and the energy fed in, after it has been produced.

This is because, today, a user can also be a producer, as well as a user, of electricity, as the owner, for example, of a photovoltaic system. In this case, his electricity system changes radically, allowing him to sell the energy produced to the grid. Furthermore, it is not uncommon for a surplus of production to occur, in which part of the energy produced ends up in the public grid, giving rise to the so-called ‘energy exchange’. To manage this exchange, users must have an electricity meter capable of measuring the energy consumed and fed into the grid, i.e. a bidirectional meter.

How does the bidirectional meter work?

The operation of the bidirectional electricity meter is based on the following: 

• when users consume energy from the grid (e.g. at night or when consumption exceeds production), the meter records incoming energy;
• when the system produces more energy than is consumed (typically during the hours of sunshine for photovoltaics), the surplus is fed into the grid and the meter also registers the outgoing energy, in addition to the energy withdrawn.

Thus, the data stored in the meter follow two directions. In the first case, the measurements of Energy Withdrawn from the electric grid, i.e. consumption, are used for billing. On the other hand, the totals of Energy fed into the grid will also be transmitted to the GSE to calculate incentives.

It is possible to better understand the two scenarios through examples. Let us imagine that a photovoltaic system is installed in our houses, the possible scenarios are, of course, two:

• the production of electricity by the system is not sufficient to cover consumption. In this case, one has to resort to the electricity grid and the energy will be counted as withdrawn and included in the bill;
• electricity production exceeds consumption. In this second circumstance, the plant produces a large amount of electricity and the energy available is more than is needed. The excess is, of course, not consumed and is sold to the grid, accounted for as Energy Inputs. The energy sold to the grid will not be invoiced in the bill, but will be paid by the GSE to the producer, in this case our photovoltaic system owner.
  

What are the advantages of the bidirectional meter?

In addition to the measurement of energy withdrawn and consumed, the functions of the bidirectional meter are diverse and constitute significant advantages for those who use it to its full potential. In fact, the bidirectional meter: 

• allows the exchange of energy on site;
• allows both consumption and production to be accurately monitored;
• is fundamental for the correct calculation of energy balances;
• facilitates the management of biannual tariffs;
• it is essential for accessing incentives for renewable energy.

In Italy, the most widespread model is the latest generation digital meter, which in addition to bi-directionality offers smart functions such as:

• remote reading;
• real-time monitoring of consumption;
• remote management of various basic functions.