Table 2.

Summary of economical, reliability and environmental indices for HRES

S.No.	Indicators	Description	Formulae	References
Economical indices
1	Annualized cost of the system (ACS)/Total annual cost (TAC)	It is defined as the summation of annualized capital system cost, annualized operational and maintenance costs, and the annualized replacement cost.	$ACS=C_{\mathit{acap}}+C_{\mathit{arep}}+C_{\mathit{amain}}$ $C_{\mathit{acap}}$: the annual capital cost of the system. $C_{\mathit{arep}}$: the annual replacement cost of the system. $C_{\mathit{amain}}$: is annual maintenance cost of the system.	[42]
2	Net present cost (NPC)/Net present value (NPV)	It demonstrates the ratio of annual aggregate cost of the system to the yearly power Net Present Cost (NPC) conveyed by the system. It is complete estimation of cost including starting cost, replacement expense and upkeep cost of system.	$NPC=TAC/CRF$ with $CRF=\frac{i{(1+i)}^y}{{(1+i)}^y-1}$ CRF: the capital recovery factor. i: the interest rate. y: the lifespan of the system.	[39]
3	Life cycle cost (LCC)	It is defined as the sum of the NPVs for all the total amount of the system costs such as capital costs, operation and maintenance costs, replacement costs.	$LCC=C_{\mathit{cap}}+C_{O\&M}+R_{\mathit{npv}}-S_{\mathit{npv}}$ $C_{\mathit{cap}}$: the capital costs. $C_{O\&M}$: the net present value of operation and maintenance costs. $R_{\mathit{npv}}$: the net present value of replacement costs. $S_{\mathit{npv}}$: the net present value of salvage value.	[39]
4	Levelized cost of energy (LCOE)	It is the ratio of the ACS to the total electricity generated by the system.	$LCOE=TAC/E_{\mathit{tot}}$ $E_{\mathit{tot}}$: the total annual energy generated by the system.	[24]
Reliability indices
1	Loss of power supply probability (LPSP)	It is defined as the percentage of power supply that it is not able to satisfy the load demand. It indicates the reliability of power supply to load.	$LPSP={\sum }_{t=1}^{8760}ES(t)/{\sum }_{t=1}^{8760}LD(t)$ ES(t): the power shortage at t hour (kWh). LD(t): the load demand at t hour (kWh).	[43]
2	Expected energy not supplied (EENS)	It is the expected energy which is not provided to the load under the condition when the load exceeds the available generation capacity.	$EENS={\sum }_{t=1}^{8760}{E}_{\mathit{unserved}}(t)/{\sum }_{t=0}^{8760}LD(t)$ $E_{\mathit{unserved}}(t)$: the amount of energy that will not be served at t hour of the year (kWh).	[42]
3	Deficiency of power supply probability (DPSP)	It is defined as the ratio of all (DPS(t)) values to the sum of the load demand for a given period, and it represents the possibility of an insufficient power supply situation when the hybrid system cannot meet the load demand.	$DPSP={\sum }_{t=1}^{T}DPS(t)/{\sum }_{t=1}^{T}LD(t)$ DPS: (power supply fault) is a condition that occurs when the main power generation components and/or backup units of the HRES cannot meet the load demand.7	[27]
4	Loss of load expected (LOLE)	It represents the expected number of hours in a year when the load exceeds the available electric generation capacity (h/year).	$LOLE={\sum }_{t=1}^{8760}{\sum }_{i\in S}^{}{P}_i\times Ti$ S: the total loss of load states of the system. $P_i$: the probability of the system encountering state i. T i: the time of a load exceeds the production capacity (hour).	[32]
5	Level of autonomy (LA)	It is the time ratio which expressed the percentage of load covered based on the operational time of the system.	$LA=1+T_{\mathit{Lns}}{T}_{\mathit{Operation}}$ $T_{\mathit{Lns}}$: the total time load not supplied. $T_{\mathit{Operation}}$: the total operation hour of the system.	[42]
Environmental indices
1	Total CO2 Emissions/Fuel emissions (E)	It evaluates the carbon dioxide emissions in a period of time.	$E={\sum }_{t\in T}^{}{\sum }_{n\in N}^{}{E}_{n}g{n}_{\mathit{nt}}$ $E_n$: the amount of CO2 emission generated by the unit of type n in time period t (ton/MWh). gn nt: the sum of the energy generated by the non-renewable generating n units in time period t (MWh).	[44]
2	Embodied Energy (EE)	It refers to the energy that a hybrid energy system does not consume during its use. It involves the production of components that consume non-renewable primary energy. In short, it is the energy required for all activities related to the production process.	$P{V}_{\mathit{EE}}=3379\times A_{\mathit{pv}}$ ; $WT\mathit{EE}=28.342\times A_{\mathit{wt}}^{2}2361.3\times A_{\mathit{wt}}$ ; $Ba{t}_{\mathit{EE}}=60\times C_n$ $P{V}_{\mathit{EE}}$, $W{t}_{\mathit{EE}}$, $Ba{t}_{\mathit{EE}}$: the primary embodied energy of PV panels, wind turbines and batteries respectively (MJ). $A_{\mathit{pv}}$:is the surface area of PV panel ($m_2$); $A_{\mathit{wt}}$: is the swept area of wind turbines ($m_2$); $C_n$ is the nominal capacity of batteries (Ah).	[45]