2.1. Renewable Energy Community Roadmap
A roadmap can be intended as a plan of informed steps to increase awareness on how successfully run a project and define long-term strategies. The roadmap itself can be specified through milestones, i.e., particular goals to be targeted to reach the final objective. From a general perspective, the main elements of a roadmap are:
a goal, i.e., the final objective;
activities, i.e., actions put in place by stakeholders to achieve intermediate targets;
milestones, i.e., tangible outputs fundamental to achieve the goal;
timeline, i.e., the temporal occurrence of activities.
The roadmap developed in this study takes inspiration from the Plan-Do-Check-Act scheme, a management structure intensively used to control processes or products and ensure their continuous improvement. According to this, the different steps of the roadmap, including milestones and intermediate activities, should be continuously monitored and revised. This allows for a dynamic roadmap, created to continuously support REC members and stakeholders. With reference to the Italian normative, the above-mentioned steps of the roadmap have been elaborated according to
Figure 1. In the roadmap, a year has been identified as the temporal horizon. In this timeframe, the different activities take place in a sequential way. It is worth noting that, although specifically built to help members of future RECs in Italy, its grounding steps can be easily applied to other European countries.
Step 1: PLAN
The first aspect to be considered is the identification of the local context in which the REC is planned to rise, starting with a study of the demographics as well as environmental, economic, and social drivers. In fact, RECs should not only target the environmental and economic conveniences, but also include the social attention to people living in slums or in a condition of energy poverty, as also suggested by the SDG7. Usually, there is always a member or a group of members taking the lead for this stage: in Italy, due also to the incentives dedicated to small/medium municipalities, it is common that local authorities or mayors seize the initiative and begin a consultation process for the engagement of citizens into the forthcoming REC. The starting point consists of the organization of dedicated meetings involving possible stakeholders, such as citizens associations, groups of consumers, retailers, and/or PV owners. The meetings have to set the basis for a common and shared vision of the REC: it is of utmost importance to gain awareness on the normative context as well as to focus on environmental concerns, expected economic revenues, and concrete actions to address energy poverty of residents. The milestone for this activity consists of a dissemination campaign, aiming at communicating to all citizens the advantages deriving from participating to a REC and raising awareness of the importance of single contributions for a sustainable transition. The subsequent step relies on the definition of a working plan to develop the strategy to be followed. The milestone for this last activity is the elaboration and writing of the call for participation that will be publicly diffused within the territory. From a temporal viewpoint, these activities may cover around two months.
Step 2: DO
Three main activities can be identified in this stage: the call for action, a development stage, and the effective REC constitution. The call for participation is made available through publication in the municipality website and through any official networks. The timeframe for participation can be arbitrarily set, but 3–4 weeks may be recommended. The publication of the call is the milestone for this activity. At the end of the call, the development phase I should (i) evaluate the geographical and technical potential of interested participants, who responded to the call, as well as verify the accomplishment of all normative aspects; and (ii) model the virtual and physical self-consumption rates among the future members of the REC. The two milestones for this activity are the energy mapping and the technical and operational design. The last activity in the “do” stage is the constitution of the REC, whose milestone consists of the juridical recognition from the GSE. The “do” stage is the most critical for an effective and reliable design of the community and is characterized by a higher duration, usually around 6 months.
A core activity in this stage consists of the identification of the electrical loads of the participants of the community. Energy audits may be conducted to determine energy profiles and critically identify which buildings consume the most and what energy efficiency measures could be applied to save costs and energy. The audit should also focus on possible variations in future energy needs, as well as energy efficiency improvements able to reduce the energy demand. In case of difficulties in pursuing energy audits, there are methods available in the literature able to derive hourly consumption profiles for typical households from a few aggregated measures [
39,
40,
41]. Data on energy demands should then be coupled with the choice of the renewable-based systems most suited for the local area in which the REC will be constituted. It is worth noting that the selection of a renewable system is not only dependent on the geographical location, it is also determined by economic and policy barriers. PV systems are likely the most suitable candidate as renewable production system for Italian cities. Indeed, from a spatial perspective, cities are usually densely populated, and rooftop areas represent a significant amount of free space, in conjunction with the high solar potential and with the attractiveness of the investment, making the PV technology sufficiently mature and competitive. Stakeholders involved in the evaluation of the solar production potential of RECs may benefit from free data portals and solar maps, such as SolarGIS [
42] or PVWatts Calculator [
43]. Subsequently, the technological and economic viability of the REC should be analyzed. This includes the consideration of auxiliary systems (batteries), infrastructure and equipment, costs, feed-in tariff, and subsidies. The steps explained so far belong to the operational stage of the REC constitution. However, under development phase I, it is also fundamental to determine how the geographical, technical, and normative constraints can be translated into the modelling of energy interactions at the community level. To have a better understanding of how RECs operate according to the Italian normative,
Figure 2 serves as reference.
According to the centralized PV and storage configuration on the left, batteries are allowed to exchange electricity only with the power grid to which they are physically connected. Since the demand associated to this centralized member is always equal to zero, the only allowed distribution direction is outgoing, i.e., electricity is only released to the power grid and never drawn from it. The amount of electricity released to the power grid is recorded on an hourly basis by a centralized meter owned by the REC. This measurement will serve to compute the total electricity that is virtually shared among members by adding it to the electricity released by each member. This scheme is accounted for as virtual self-consumption, VSC, i.e., the condition for which electricity produced by the REC is virtually consumed by its members. For the distributed configuration, PVs and batteries are physically connected to the building; here the PV production is accounted for as physical self-consumed, a scheme called PSC by the normative. In addition, the PV system is connected to the power grid to release electricity in case of a surplus. In the distributed case, batteries are not allowed to exchange with the power grid. They can only be charged with electricity directly deriving from the PV discharged by electricity used by the building in which they are installed. In case of residual electrical demand, electricity is drawn from the power grid. For each distributed member, the meter measures released and drawn electricity.
The mathematical model serving for the development phase I is formulated with the aim of minimizing the Net Present Value, NPV, of the investment, as expressed in Equation (1):
The initial capital investment,
, is equal to the sum of the capital costs for installing PVs and storages, considering the installed nominal capacity:
The yearly cash flow is given as the difference between revenues
and maintenance and operating costs
:
Maintenance and operating costs can be formulated as:
The following constraints refer to the electrical capacities and associated flows. Electrical production for each member
of the REC can be formulated as:
with the following constraint on the minimum and maximum installed nominal capacity, regulated by the binary variable
to control the installation of PVs for different members:
The amount of electricity physically self-consumed, according to the PSC scheme in the Italian normative, is equal to the minimum between the electricity produced by a production technology and the electrical demand, for each member of the REC and at each time-step , as can be seen in Equation (8).
For future explanations, it is important to clearly distinguish the two cases that can occur:
→ all demands have been covered by the PV production and an electrical energy surplus occurs.
→ only a part of the total demand has been covered by the PV production and, consequently, additional electrical supply is needed to satisfy the remaining demand.
As a further specification, along with the
members of the REC, the model accounts for a “central node,” labelled as
. The fictitious member
is characterize by a nil demand, as expressed in Equation (9), and the PSC is consequently zero, as in Equation (10).
Equations (11) and (12) regulate the electricity balance at the single member level. These equations are strictly related to Equation (8) and two different cases may arise. In fact, in case (1), the left member of Equation (11) is equal to a positive electricity surplus that can either be used to charge the battery,
, or released, i.e., sold, to the power grid,
. Moreover, in this case, the left member of Equation (12) is equal to zero, forcing
and
to be zero as well. On the contrary, in case (2), the left members of Equations (11) and (12) are, respectively, equal to zero and to a positive value that represents the electricity deficit. The latter can be covered by the storage,
, or by the power grid,
. These equations hold also for the central node
. In particular, they force all produced electricity to be released to the power grid.
Moving from the single member to the community level, the total released,
, and drawn electricity,
, are calculated with the following two equations.
It is worth noting that Equation (14) also includes the amount of electricity discharged by the centralized storage, eventually installed at the central node
, to cover some excess demand of the community just before buying it from the power grid. The amount of electricity that is virtually shared under the VSC scheme at each time-step is computed as recommended by the Italian technical framework for RECs, Equation (15).
Finally, the exported and imported electricity represent the amount of electricity that is, respectively, released and drawn to and from the power grid net of the shared electricity. In particular, the latter is used to compute the actual emissions associated with the electricity production of the power grid.
This final part of the model presents all the equations related to the installation and operation of storage systems. Equation (18) controls whether a storage system is installed or not at a specific member while posing a limit on its maximum capacity.
The maximum charging and discharging electricity of all storage systems is limited by the energy to capacity ratio as in Equations (19) and (20).
The dynamic of the state of charge of storage systems is expressed by Equation (21), whilst Equation (22) is a time periodic constraint to plan the next period of storage. Equation (23) limits the minimum and maximum state of charge of the storage accounting for the depth of discharge,
, and depth of discharge,
, that can be found in the data sheet of each battery.
Finally, when a storage system is installed, the PSC of each distributed member is given by the sum of electricity coming from the PV and from the storage physically connected to the member, as expressed in Equation (24). As before, the PSC of the central node
is equal to zero, as expressed in Equation (25). In fact, even though electrical exchanges may occur within the community and with the power grid, no exchanges occur between the grid and any of the distributed storages installed in the REC.
2.2. Linearization Technique
At the moment, Equations (8) and (15) are non-linear relationships, thus adding nonconvexity to the model and making it a Mixed-Integer Non-linear Programming (MINLP) problem. To linearize these equations, piece-wise linear functions can be used [
44]. This can be done by introducing a new set of binary variables,
,
,
, and
, reported from Equations (26)–(30).
Similarly, Equation (15) is linearized using the binary variables defined from Equations (31)–(34).
Step 3: CHECK
This stage consists of the development phase II, focused on the definition of benchmarks to which the REC performances should be compared during the monitoring activity. As an added-value, these tailored metrics also help for cross-comparison to other RECs, or to evaluate the impact of new members. This step usually has a duration of around 3 months. The definition of REC makes it evident that the primary goal is to attain community benefits in economic, environmental, or social aspects. Two commonly used load matching indicators are the self-consumption ratio
and the self-sufficiency ratio
, addressing technical and energetic aspects. More in detail, these indicators may evaluate how well distributed production and demand are matched in time and magnitude.
indicates the amount of produced electricity that is self-consumed by all members, whereas
measures whether the REC’s needs are met by the production of PV panels, as expressed in Equations (35) and (36).
may also be interpreted as the degree of independence from the power grid. It is worth noting that the complementary to one
gives information about the amount of electricity released to the power grid, thus sold at the unit electricity price of the market. For the VSC scheme, the virtual self-sufficiency ratio
is defined in Equation (37); it measures the shared electricity over the total demand. Therefore, this indicator highlights to what extent the REC production is sufficient to meet the electrical needs of members under the VSC scheme, i.e., for the amount of electricity valorized and incentivized according to the Italian normative. The indicator
, called total self-consumption ratio, is built as a combination of the indicators
and
, as reported in Equation (38). It measures to what extent the REC satisfies the electrical demand with instant PSC. These differentiations are also helpful to evaluate the economic impact for REC members in relation to the total consumption. Indeed, under the definition of the normative, PSC can be considered as an avoided expense, VSC as revenues, as it is incentivized.
Environmental performances are evaluated considering the carbon dioxide emission index,
, calculated as the percentage of CO
2 emissions avoided thanks to the constitution of the REC, as expressed in Equation (39). In fact, when a REC is constituted, the electricity produced by renewable technologies and discharged by batteries reduces the amount of electricity imported from the grid,
. In this paper, a net-balancing approach to carbon dioxide emissions is chosen, and, therefore, electricity sharing under the VSC scheme is considered carbon-neutral. A national-specific standard emission factor
is associated with the electricity imported from the grid and used to calculate grid-related emissions, as in Equation (40).
To account for the social impact of the REC, the energy poverty help index
is calculated to account for the number of families in energy poverty conditions that can be financially helped thanks to the distribution of REC revenues. Therefore, the
indicator can be calculated as in Equation (41). The value of AED has been fixed equal to
, that is the reference for a typical Italian family according to the Italian National Institute of Statistics [
45].
Step 4: ACT
The fourth step of the roadmap consists of a review of the technical and juridical design of RECs. During this activity, actions may be taken with respect to the results obtained from the previous steps and, generally, from the experiences gained during the overall constitution process. Indeed, it is important to review the core activities of the other steps and identify eventual “bottlenecks” or criticisms to adjust the strategy trajectory and incorporate any lessons learned. In case any change is going to be adopted (such as new documents, model adjustments, or the introduction of new indicators), the PDCA cycle should start again and be revised according to the needs. A typical milestone of this step is the standardization of procedures, fundamental to guarantee the continuous improvement and operation of the REC and also to serve as example for other forthcoming RECs. The timeframe for this step is around 1 to 2 months.