System to energise electrical loads with alternating current in a photovoltaic plant, the photovoltaic plant comprising a main DC power line, a photovoltaic generator comprising a photovoltaic circuit that is made up of one or more photovoltaic strings connected in parallel to the main DC power line and is able to generate a first direct current and a direct DC voltage and a main AC power line connected to an electric distribution network, said system comprising: • a converter apparatus configured to be connected to the main AC power line and to the main DC power line and configured to convert an alternating current circulating in the main AC power line into a second direct current, and to feed the latter into the photovoltaic circuit through the main DC power line, if the DC voltage generated by the photovoltaic generator is lesser than a pre-set limit, so as to energise the photovoltaic generator, and • a DC/AC secondary converter configured to be connected at the input to a secondary DC power line which is connected to the connectors of a photovoltaic module of the photovoltaic generator, or of a circuit formed by a plurality of said photovoltaic modules connected to one another in series, and at the output to at least one electrical load, said DC/AC secondary converter being configured to convert a direct current circulating in the secondary DC power line into an alternating supply current, and to feed the latter into the at least one electrical load so as to energise it, wherein said converter apparatus comprises a main AC/DC converter configured to be connected at the input to the main AC power line and at the output to the main DC power line and configured to generate and feed said second direct current into the photovoltaic circuit through the main DC power line so as to energise the photovoltaic generator, wherein said converter apparatus comprises a DC/AC inverter configured to be connected at the input to the main DC power line and at the output to the main AC power line and configured to convert a direct current circulating in the main DC power line into an AC alternating current and to feed the latter into the main AC power line, and wherein said converter apparatus is configured to supply the main DC power line with a direct voltage which has a value Vref lesser or equal to said pre-set limit, characterized by the value Vref being lesser than a first threshold corresponding to the minimal input voltage to the DC/AC inverter required for its operation. • a converter apparatus configured to be connected to the main AC power line and to the main DC power line and configured to convert an alternating current circulating in the main AC power line into a second direct current, and to feed the latter into the photovoltaic circuit through the main DC power line, if the DC voltage generated by the photovoltaic generator is lesser than a pre-set limit, so as to energise the photovoltaic generator, and • a DC/AC secondary converter configured to be connected at the input to a secondary DC power line which is connected to the connectors of a photovoltaic module of the photovoltaic generator, or of a circuit formed by a plurality of said photovoltaic modules connected to one another in series, and at the output to at least one electrical load, said DC/AC secondary converter being configured to convert a direct current circulating in the secondary DC power line into an alternating supply current, and to feed the latter into the at least one electrical load so as to energise it,