Energy production: fossil and renewable energy sources

[GRI - 203-2],

With the goal of increasing generation of renewable energy, in line with the development plan outlined in the Industrial Plan, in 2021 Acea acquired a further 4 MW in the photovoltaic segment and installed 16 MW, thus reaching 72.5 MW in total.


Through Acea Produzione, the PV Companies127 and Acea Am- biente, the Group generates electricity primarily from renewable sources. The majority of production is provided by hydroelectric plants and another significant portion, also partially renewable, from waste-to-energy plants utilising paper-mill waste and Solid Recovered Fuel (SRF).

Acea Produzione is equipped with plants for generation from re- newables, both hydroelectric and photovoltaic, and fossil fuels (ther- moelectric), with the latter primarily through the high-efficiency co-generation plant of the Tor di Valle power plant, which had greater availability during the year. At this power plant, activity was also completed for construction of the third co-generation unit, composed of a 9.5 MWe internal-combustion engine, with an increase in installed power from 19 MW in 2020 to 28.5 MW in 2021.

The power park includes:

  • seven hydroelectric power stations located in the Latium and Abruzzo regions for a total of 122 MW,
  • 2 thermoelectric power stations located within the Municipal- ity of Rome area: Montemartini (78.3 MW)128 and Tor Di Valle (28.5 MW), for 8 MWe total available installed capacity,
  • one photovoltaic park, for a total of 5 MWp.

The generation of energy from waste-to-energy processing is as- signed to Acea Ambiente, taking place at two plants located in San Vittore del Lazio and Terni, and both with percentages of biodegrad- able material (renewable source) varying between 40% and 50%. The total gross electrical power currently available is approximately 58 MWe.

In addition, Acea Ambiente produces electricity using biogas derived from the anaerobic digestion process at the Orvieto Technol- ogy Hub and the composting plants of Aprilia and Monterotondo Marittimo.

Table no. 48 – Installed power of the electric power stations of Acea Produzione

hydroelectric power stations thermoelectric power stations
A. Volta di Castel Madama (Rome) power station - gross power 9.4 MW Tor di Valle power station: high-efficiency cogeneration (CAR) section (*) (Rome) methane fuel - gross power 28.5 MW
G. Ferraris di Mandela (Rome) power station - gross power 8.5 MW Montemartini power station (Rome) diesel fuel - gross power 78.3 MW
Salisano power station (Rieti) - gross power 24.6 MW  
G. Marconi di Orte power station (Viterbo) - gross power 20.0 MW  
Sant’Angelo power station (Chieti) - gross power 58.4 MW  
Cecchina power station (Rome) - gross power 0.4 MW  
Madonna del Rosario power station (Rome) - gross power 0.4 MW  
totale generale: potenza lorda 229 MW

(*) The CAR plant in Tor di Valle provides district-heating service in the area south of Rome.

The installed capacities of the Group, which overall amount to approximately 346 MW129, are presented in Chart no. 51, distinguished by energy source.

Chart no. 51 – Installed electrical power of the Group broken down by energy source (MW) (2021)

Chart 51


In 2021 overall gross generation of electricity increased by 10%, rising from 916 GWh in 2020 to 1,009 GWh in 2021. This increase is due to several factors: greater rainfall in the year influenced hy- droelectric generation (up 15%), the new photovoltaic component (+5% energy generated) and the waste-to-energy sector (+3%). This latter increase was due to Terni plant experiencing a lower number of shutdowns, making it more efficient in terms of energy usage compared to the previous year. The production of biogas also increased, above all thanks to the Aprilia plant, now running at full capacity. For further details, see the Environmental Accounts.

The share of electricity generated by renewable sources, about 698 GWh, is predominant, corresponding to approximately 69% of the total, with the following contributions:

  • 7 GWh from hydroelectric power,
  • 5 GWh from waste-to-energy,
  • 4 GWh from biogas (Orvieto, Aprilia and Monterotondo Marittimo plants)
  • 6 GWh from solar panels (see Chart no. 52 and Table no. 49)130.

After completion of upgrading and actions to increase efficiency in 2021 the only revamping that took place involved the Sant’An- gelo power plant, with the goal of optimising use of available water resources, with the same specifications in terms of installed power and authorised by concession.

In addition, Acea Produzione and Acea Ato 2, are collaborating on a particularly important project rooted in the development of synergies between the businesses managed by the Group. The project involves installation of an additional two 1.5-MWe internal combus- tion engines at the Tor di Valle High Efficiency Cogeneration Plant (CAR), which will be powered by the biogas from the adjacent Acea Ato 2 Roma Sud treatment plant. The Tor di Valle plant will in turn provide the treatment plant with thermal energy to heat the sludge in the digesters131 (see info. box for details). Construction of a 267.3 kWp photovoltaic plant has been authorised at the same power station. The worksite, launched in November 2020, was closed in 2021 and the plant is currently operational.


Since 2017, the Roma Sud treatment plant has been powered with electricity from the Tor di Valle power station (managed by Acea Produzione), with alternative power from the MV grid. Acea Ato 2 and Acea Produzione are working to increase synergy between these two plants with the transfer of biogas produced by anaerobic digestion section of the treatment plant to the power plant, for it to be used in the generation of electricity and thermal energy, as well as transferring thermal energy from the power plant to the digesters of the treatment plant to support the anaerobic digestion process.

In the future scenario, with creation of the thermal sludge drying plant, this synergy will be further developed with the possibility to provide thermal energy for the drying plant, utilising the residual heat from the electricity generation units already installed at the co-generation plant.

This will enable replacement of the methane gas used at the Tor di Valle power plant with biogas produced through anaerobic diges- tion of sludge, with zero environmental impacts, in terms of CO2 emissions, because it is derived from the breakdown of organic substances. Similarly, the same benefit will be seen for the treatment plant, which will utilise renewable thermal energy produced by the biogas of the power plant.

In 2021, a technical and economic feasibility study was launched to evaluate the environmental, economic and authorisation aspects of the works, in preparation for implementation.

A significant portion of the energy from waste-to-energy produc- tion, as already noted, is associated with the combustion of the bio- degradable fraction of waste used as a primary source. In particular, the renewable share of the fuel (SRF) entering the San Vittore del Lazio plant was 43.0% of the total of waste-to-energy production in 2021, while at the Terni plant this share was 43.4%. The percent- ages are in line with 2020 for both plants, but lower than years previous to the pandemic. In fact, a change in SRF composition was recorded, particularly for the San Vittore del Lazio plant, which is probably linked to the strict limitations applied in the restaurant industry and catering through canteens in schools and business, etc.

Chart no. 52 – Electricity produced subdivided by primary energy source (TJ) (2021)

Chart 52


Table no. 49 – Electricity produced (by primary energy source) (2019-2021)

primary energy source (TJ (GWh) (*)) 2019 2020 2021
electricity produced (by primary energy source)
diesel fuel







natural gas (cogeneration)







waste to energy (approximately 57% of the total in 2021)







total thermoelectric














waste to energy (approximately 43% of the total in 2021)














photovoltaic solar (**)







total renewables







general total







(*) 1 GWh = 3.6 TJ.
(**) Photovoltaic includes the production at the plants located on sites of the water area (Acea Ato 2 and Acea Ato 5) for a total of 1 GWh produced.


La Centrale termoelettrica di Tor di Valle ha generato circa 99 GWh di energia termica. Il calore generato è stato utilizzato per servire un bacino di 42.680 abitanti in zona sud di Roma (Mostacciano, Torrino e Mezzocammino), attraverso una rete di teleriscaldamento che serve una volumetria pari a 3.861.163 metri cubi132. Nell’ultimo biennio sono state sostituite 35 delle attuali 361 sottostazioni termiche afferenti alla rete del teleriscaldamento, per migliorare l’efficienza del processo e l’affidabilità del servizio all’utenza (si veda anche il paragrafo Strategia e Sostenibilità, Il Piano di Sostenibilità 2020-2024 e gli obiettivi operativi).

La Società Ecogena, certificata in qualità di ESCo (Società di Servizi Energetici) ai sensi della norma UNI CEI 11352:2014, sviluppa le iniziative di efficienza energetica per il Gruppo e ne rendiconta gli esiti al Gestore dei Servizi Energetici (GSE) per l’ottenimento dei Titoli di Efficienza Energetica (TEE).
Tra le attività affidate ad Ecogena sono incluse anche la progettazione e la realizzazione di impianti di cogenerazione e trigenerazione133 per la produzione, in modo combinato, di energia elettrica, calore e freddo.
Nel 2021, gli impianti cogenerativi gestiti, abbinati a reti di teleriscaldamento, per effetto della conclusione di due contratti riferiti agli impianti presenti nelle regioni Lazio e Umbria, sono passati ad una potenza elettrica complessiva di 1,9 MW (era di 4,9 MW nel 2020).
Per dettagli relativi alla produzione del triennio si veda la tabella n. 50.

Tabella n. 50 – La produzione di energia da impianti di Ecogena e i titoli di efficienza energetica TEE (2019-2021)

  2019 2020 2021
energy produced (TJ (GWh)







of which plants owned by Ecogena







of which plants owned by third parties







thermal energy







of which plants owned by Ecogena







of which plants owned by third parties







refrigeration energy (all owned plants)







Total EECs (all from plants owned by Ecogena) 954 943 443

NOTE: Other information on EECs is provided in the Energy savings section of the chapter The use of materials, energy and water.

127For the PV Companies included, see Disclosing sustainability: methodological note.
128The power station is operational only in the event of extraordinary energy demand, and operation can also be managed remotely from the control room at the Tor di Valle Power
129The photovoltaic plants of AdF and the Terni waste-to-energy plant are not included (as they are owned by AdF and Acea Ambiente, respectively): the former produced and self-consumed 12.5 MWh in 2021, while the latter produced 444.3 MWh of which 61% was consumed on site.
130The photovoltaic plants of AdF and the Terni waste-to-energy plant are not included (as they are owned by AdF and Acea Ambiente, respectively): the former produced and self-consumed 12.5 MWh in 2021, while the latter produced 444.3 MWh of which 61% was consumed on site.
131In January 2021, the request was submitted to the Ministry for the Environment (MATTM) for preliminary verification for application of an EIA.
132Data from August 2021.
133Cogeneration, i.e. the combined production of electrical and thermal energy, allows high efficiencies to be achieved, between 80 and 90%. Trigeneration, which is a special application of cogeneration, allows use of a part of the thermal energy recovered in order to produce cooling energy in the form of cooled water for air conditioning in rooms or for industrial processes