The latest white paper by Anie and Rse presents a detailed analysis of the financial viability of a storage system paired with a solar photovoltaic installation.
Installing a solar photovoltaic installation on a home rooftop is certainly an excellent solution for producing and consuming clean energy, but without a storage system it can be considered an incomplete choice. Storage technology is not widely understood, even though its uptake is growing, yet its installation can deliver both economic and environmental benefits.
With the white paper on electrochemical energy storage, now in its third edition following those of 2015 and 2017, the Anie federation, which represents electrical and electronics companies within Confindustria, and Rse, a research company in the electro-energy sector, have measured the advantages currently arising from the adoption of residential energy storage systems. Among the topics of greatest interest to us are the collective self-consumption scheme paired with storage systems and the aggregation of residential storage systems to provide dispatching services — a term referring to the balancing, at national level, of energy supply and demand flows.
It should also be noted that the latest data from the Gestore dei servizi energetici (Gse), a state-owned company that monitors the achievement of national targets set for renewable sources and energy efficiency, show that at the end of 2019, up from 2018, more than 880,000 installations were in place with a total capacity of approximately 21 gigawatts. The majority are small installations below 20 kilowatts. Over the same period, growth was also recorded for small-scale storage systems, whether residential or commercial, with a total of nearly 26,000 systems amounting to a cumulative capacity of 118 megawatts.
It is useful to set the scene and outline the current regulatory framework. The collective self-consumption scheme paired with a storage system in Italy is provided for by two pieces of legislation: the European directive Red II (2018/2001/EU), which promotes energy obtained from renewables, and Italian law 8/2020, through which the government established a regime of transitional rules to encourage the testing of pilot projects on collective self-consumption and energy communities.
End customers, the white paper specifies, may join together to become renewable energy self-consumers or establish renewable energy communities if:
To complete the picture, the Autorità di regolazione per energia reti e ambiente (Arera), through resolution 318/2020, defined the "Regulation of the economic settlements relating to electricity shared by a group of renewable energy self-consumers acting collectively in buildings and apartment blocks, or shared within a renewable energy community". In doing so, it regulated the economic terms linked to the valorisation of collective self-consumption.
To set the incentive tariff linked to the promotion of energy shared within schemes and energy communities, the Ministry of Economic Development issued the ministerial decree "Individuazione tariffa incentivante per impianti a fonti rinnovabili", published in the Gazzetta ufficiale on 16 November 2020.
The Anie and Rse analysis is highly technical and detailed; it is worth highlighting here that the saving is the result of the relationship between the size of the photovoltaic installation and the individual user's consumption, as a function of its output and net of the energy market selling price. The study presents the example of a small apartment block with eight units in climate zone D, equipped with a solar photovoltaic installation of maximum size equal to a scalable 20 kW — that is, one that allows for subsequent expansions of the battery pack. The study takes into account the normal annual degradation of the installation, namely the 1 per cent reduction in output (20 per cent in total over an assumed useful life of 20 years).
In the case examined, the estimated annual electricity draw amounts to:
The preferred storage system among the four considered is the 15 kW capacity lithium-ion one. It is the type most widely used today because it guarantees a number of charge and discharge cycles that makes purchasing a single device sufficient over the timeframe within which the return on investment is expected.
The authors of the research assessed the economic benefits and payback periods in two scenarios, namely assuming the 50 per cent tax deduction over ten years is or is not applied to the photovoltaic installation as well as to the storage system. In brief, in the presence of a 50 per cent tax deduction, the investment — whether for the photovoltaic installation alone or for the integrated battery system — can have a favourable effect on payback periods.
These could be reduced further through the apartment block's participation, in aggregated form, in ancillary services, including voltage regulation, as outlined in the Piano nazionale integrato per l'energia ed il clima (Pniec). Or indeed through the ability to combine some of the benefits provided for under collective self-consumption schemes with those arising from the Superbonus 110 per cent tax deduction, guaranteed by a comprehensive renovation of a building that achieves a performance improvement of at least two energy classes.
In this scheme the real advantage stems from the possibility of storing the energy produced. Furthermore, the presence of a battery spares users from having to change their behavioural habits and, at the same time, offers flexibility margins for the provision of services and for relieving congestion on the distribution network.
The second case of interest to us concerns the possibility for a group of small storage systems to participate in the dispatching services market, the instrument through which Terna, the national grid operator, procures the resources needed to manage and control the system — for example, to balance supply and demand for energy in real time. This scenario is provided for by the May 2017 resolution of Arera, 300/2017, when systems are aggregated virtually and form an installation with a minimum capacity of 1 MW. The resolution also introduces the figure of the balance service provider (BSP), or aggregator, whose role is to manage the resources and interface them with the market as a single unit.
In this second example, the aggregate comprises 1,245 users residing in Milan, all equipped with an installation of the same generating capacity. Using the established criteria, the annual benefit was found to vary from approximately €0.3 million to €0.6 million, assuming an electricity offer of 2 MW. These figures are unfortunately unattainable, at least for now, because Terna would have to accept all the energy offered by the aggregator.
The accepted share is, more realistically, capped at 10 per cent of the total. In that case, the overall annual earnings can nonetheless be described as considerable: between €30,000 and €60,000. More specifically, each participant's net return depends on the aggregator's revenue percentage and the method chosen to distribute the benefits. The latter will also need to cover the costs associated with the increased wear on the battery, caused precisely by participation in the dispatching services market.
In the future, it will be possible to benefit from this type of distributed device not only for grid balancing — that is, to ensure equilibrium between injections and withdrawals — but also to provide other types of services. Among these is secondary power reserve, which is the automatic function used to restore the gap between the national system's demand and production. Furthermore, they could become essential during periods of peak energy demand at regional and national level. Once a greater number of distributed storage systems are in place across the country, it will also be possible to provide services to the energy distributor, to resolve local grid congestion and to regulate voltage.
