The strong increase in generation from Non-Programmable Renewable Energy Sources (NPRES) can lead to a greater need for resources for the regulation of the power system, while these can undergo a reduction due to the loss of market shares for thermoelectric generation. These resources are in fact traditionally supplied by relevant (i.e. with size 10 MVA at least) thermoelectric and hydroelectric plants (except run-of-river ones).

An estimate has therefore been made of the contribution that such plants have kept providing, with regards to the minimum half-band for primary frequency regulation, from 2015 to 2022. The increase in NPRES generators can also cause a reduction in mechanical inertia in the network; therefore, the mechanical inertia provided by online plants has also been estimated.

The analysis was conducted first by reconstructing, starting from public data, the characteristics of the generation park in terms of primary source, technology, installed power and average inertia constant of the Production Units (PUs), and then determining the PUs online or offline state in each hour of the year (and therefore the presence or absence of a contribution to primary regulation and inertia) on the basis of an estimate of the power level achieved as a result of participation in the electricity market chain (the Day-Ahead Market, the Intraday Market, the ex-ante Ancillary Service Market and the Balancing Market).

For the years 2015-2022, the estimates obtained for the minimum total Italian primary half-band (SB1) and the Italian total kinetic energy (EK) are, respectively, approximately in the 170-740 MW range and in the 65-230 GW·s range. For both the estimate SB1 and EK, the annual duration curves alternate increases and decreases until 2019-2020 and then they decrease. This behaviour is substantially consistent with the annual energy exchanges for ancillary services: until 2020 these exchanges had an increasing trend, with some fluctuations for downward services, and then a strong decrease, also linked to an incentive for the transmission system operator to reduce system costs.

Finally, the focus on 2022 by plant technology and market zone has highlighted, also in line with the composition and zonal distribution of the production mix, a strong contribution to SB1 and EK by natural gas combined cycles ( especially those in the North zone), coal-fired steam turbine plants (for SB1 especially those in Sardinia, for EK especially those in South and Centre-South), poundage and reservoir hydroelectric plants (especially in North in both cases). For EK, the contributions of pumped hydroelectric energy storage and run-of-river PUs in North are also worth mentioning.

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