Building service and building service energy modelling

E E E

radiation. If PV generation is higher than load: – = (energy injection).

P c i

E E E

If PV generation is lower than load: – = (energy withdrawl from the

c p w

public grid). Energy is self-consumed if there is simultaneous generation and load.

E E E E

= min( , ). is not measured by meter M1: the more the self-

S c c p Sc

consumption, the less is the energy exchanged with grid (both Ew and Ei).

The energy withdrawal is associated to our electricity bill, so it is paid with a certain

cost which is the bill cost (€/kWh). Costs are related to the complex structure of the

power system, including the following main activities: Generation, transmission,

distribution and sales (wholesale and retail). Bill cost includes Energy cost around 50%

of the bill cost, Electricity tariff that is the money needed to renumerate the

transmission system operators and distribution system operators activity and Taxes

(VAT + excises).

Energy cost is related to the demand and electricity generation. Demand and

electricity generation meet on the electricity (wholesale) market. Usually, buyers and

sellers pay the same market price. In Italy, for giving all the buyers the same

opportunities, there are two different prices: Sale price - Zonal price (Pz) and Purchase

price - National unique price (PUN: Prezzo unico Nazionale) which is the weighted

average of the Zonal prices. In the bill, energy costs include purchase price (PUN),

retailer’s margin and ancillary services costs. For the energy that we withdraw we pay

the overall bill cost, on the energy that we inject we receive only the Zonal energy

price which is more or less 50% of the total bill cost.

The transmission and distribution systems are natural monopolies. A part of the

electricity tarif remunerates the Transmission System Operator and the Distribution

System Operators -> network costs. Often, part of the tariff covers the power systems

costs not directly related to the grid and its operation (e.g., the costs of incentives to

renewables and to energy efficiency, the cost of R&D on networks) -> general system

charges (these can also be in the general fiscality). This means that is more

convenient to self-consume the electricity produced. Generally speaking, a prosumer

wants to increase its energy self-production: which means Less withdrawal from the

grid and means Lower injection.

Electrification is the way to decarbonize

This convenient to self-consumer electricity goes together with the concept of

electrification of thermal and mobility energy demand. Now a days the electricity

consumption (15-20%) and Natural gas is the most used energy source for ambient

and water heating in residential buildings and Energy consumption for transport and

mobility is not part of domestic demand. In the future the goals are to have at least

40% of the Electric vehicle charging being part of the domestic bill and have Heating

electrified through heat pumps, boilers and induction stoves. EV shift the convenience

towards domestic charging, thanks to PV and reduced tariff. Domestic charging will be

the most diffused one, with exception in urban areas. AC slow charging can be

performed at home with the installation of a wallbox (3-7 kW charging power, 400km

autonomy in 8 to 4 hours charging). For high power charging (>50kW) (less time) you

have: to pay more and to pay the energy and the charging service.

Gross metering and net meetering

Historically, gross metering is applied: the electricity

tariff is applied to the whole withdrawal (Ew) from

the grid. Until there were no prosumers (domestic PV

producers), the electricity was only flowing from the

grid, to the user. In case of a PV system, there is

need of a bidirectional metering accounting

separately of injected energy (Ei) and withdrawn

energy (Ew) ( Injected energy is remunerated at Pz

and Withdrawn energy is paid at bill cost (Cbill). A scheme is usually proposed by the

regulation, to sell Ei to a single-buyer (state buyer), that sells the injection of a

portfolio of small plants on the wholesale market, this is usually called dedicated

withdrawal in Italy (the state buys our energy at a fixed price somehow related to the

market price, so that we don’t have to worry about the selling of this energy). I order

to favour the installation of PV system it was applied a scheme called net metering

scheme alternative to dedicated withdrawal. In a net metering scheme, a consumer

pays the electricity tariff on the netted-out energy consumed from the grid. In this

situation, the grid can be imagined as a “virtual storage”, where the electricity that is

injected in a certain moment of time, can be withdrawn in a next period without costs.

The volume of energy for applicating the tariff is estimated as the difference between

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−E

E

the energy injected and withdrawn : Ei is remunerated at Pz and Ew is paid

w i

at the purchase price (PUN) until its volume is equal to Ei, while the excess is paid at

the bill cost (Cbill). Net metering represents an implicit support for RES.

Energy communities and collective self-consumption

Net metering does not give any price signal towards increasing self-consumption. Self-

consumption has many advantages on the side of network utilization: Addresses the

correct sizing of production plants, Decreases the network use at low/medium voltage,

Increases the acceptability of RES installation. The EU decided to support self-

consumption initiatives by defining “energy communities” and “jointly acting self-

consumers”. These initiatives consider, beside the Esc, the “shared energy”, meaning

the amount of energy that is produced by one user and simultaneously consumed by

another user in the same community. This corresponds, for each time period, to the