**2. Regulatory, project finance and technical perspective**

The renewable electricity demand is predicted to add up 20% more within the next 5 years. They can have the quickest development within the power sector, providing nearly 1/3rd of the requirement in 2023 [5]. Further, there is forecast to exceed 70% of world electricity produced, primarily by PV and followed by wind, hydropower, and bio-energy. Hydropower remains the biggest such supply, meeting 16% of the world electricity demand by 2023, followed by wind (6%), PV (4%), and bio-energy (3%). Energy storage for grid applications lacks a sufficient regulatory history.

Whereas active regulation of voltage was not permitted and the DERs had to trip on abnormal voltage or frequency, participation in voltage and frequency control was desirable due to a gradual increase of the percentage of DER in power system. This was resolved in 2003. The first amendment to this came after a decade (11 years) but the second one came just after 4 years of first [6]. This comes in line with the steeper increase of DER penetration than the previous decade. As the DER are geographically dispersed, the communication interface between DER and the main grid and in between the DERs has been an additional demand of the hour for smooth and reliable coordinated control.

Some of the distribution grid safety demands are (1) short trip times, (2) ridethrough with momentary cessation (3) voltage rise concerns (4) protection coordination (5) islanding concerns for the safety of workers. Bulk system reliability demands (1) long trip times (2) ride-through without momentary cessation (3) reactive power support.

**121**

*Grid-Connected Distributed Wind-Photovoltaic Energy Management: A Review*

**3. Weather-dependent variability of renewable resources**

correlation, (vi) cross-correlation and (vi) predictable pattern.

mitigates the variability of every single RES.

The wind energy and PV are expected to have a lion's share in the prospect of the power utility. So, the future energy source is pivoted on the in-depth realization of their variability. Resource variability is a multi-faceted notion expressed by a range of distinctive characteristics. Simultaneously, research to date tells that there is restricted knowledge about the variability of the future power system. The variable attribute of climatic fluctuations is the reason of inconsistency of the RES and creates uncertainty in the energy production on the range of seconds, hours and days even. It is estimated that clouds limit up to 70% of daylight hour solar energy potential. Grid sometimes deals with aggregation over massive areas and this

Presently a large variation is tackled via switching in fast-acting conventional sources depending on the climate forecasts on a minute-by-minute and hourly basis. Such variability can additionally be taken care by setting up large scale storage on the grid or; by the long-distance transmission of RE linking to larger pools of such generations in order to equalize regional surplus or shortfall nearby in future. Graabak et al. [9] have addressed the variability characteristics such as: (i) Distribution long term, (ii) distribution short term, (iii) step changes, (iv) autocorrelation, (v) spatial-

Increasing penetration of unconventional generation to grid is reducing system inertia which can degrade system frequency stability. So, active power output is modulated in response to frequency deviation (Default droop 0.05 p.u. frequency

Voltage benchmarks standard for voltage fluctuations is within ±5% at customer end. As a DER exports active power, voltage rises and the profile is disturbed and

Current grid standards massively need that low-power KW range single-phase PV systems supply at unity power factor with maximum power point tracking (MPPT), and detect fault and island from the grid in such situation [7]. However loss of these generations under grid faults gives rise to voltage flickers, power outages, and an unstable system. So grid code amendments for increased entry of PV systems in the distribution grid are expected. The standards have undergone a significant review for low-tension interconnection in many countries. Also, reactive power can be supported either by changing the tap setting of the transformer or by the PV inverters with advanced control strategies to maintain the grid voltage. Investments in RES for utility are normally assessed from regulatory, project finance, and technical perspectives. The regulatory requirement is satisfied by utility compliance as well as reduction of the associated cost. The budget estimate looks at the investment and benefits of the particular project. The technical assessment deeply goes through the safety concern of the specific technology involved and its operation. Besides these project specific assessments for RES, physical benefits of transmission and storage and the effect in the integrated picture of the grid is also important. It is therefore always recommended to go for an integrated approach for full exploitation of renewable generation and electricity storage with respect to transmission and distribution [8]. And this in line with the state utility cannot be undermined also. It is further recommended at all levels to increase its research and development (R&D) in basic electrochemistry to find out the materials and discover the electrochemical technology suitable for use in grid. Department of energy, of concerned countries, have been leading the R&D to deal with reliability, resilience, cyber security, and affordability issues from the grid modernization perspective.

*DOI: http://dx.doi.org/10.5772/intechopen.88923*

for 1 p.u. active power change).

quality is compromised.

Increasing penetration of unconventional generation to grid is reducing system inertia which can degrade system frequency stability. So, active power output is modulated in response to frequency deviation (Default droop 0.05 p.u. frequency for 1 p.u. active power change).

Voltage benchmarks standard for voltage fluctuations is within ±5% at customer end. As a DER exports active power, voltage rises and the profile is disturbed and quality is compromised.

Current grid standards massively need that low-power KW range single-phase PV systems supply at unity power factor with maximum power point tracking (MPPT), and detect fault and island from the grid in such situation [7]. However loss of these generations under grid faults gives rise to voltage flickers, power outages, and an unstable system. So grid code amendments for increased entry of PV systems in the distribution grid are expected. The standards have undergone a significant review for low-tension interconnection in many countries. Also, reactive power can be supported either by changing the tap setting of the transformer or by the PV inverters with advanced control strategies to maintain the grid voltage.

Investments in RES for utility are normally assessed from regulatory, project finance, and technical perspectives. The regulatory requirement is satisfied by utility compliance as well as reduction of the associated cost. The budget estimate looks at the investment and benefits of the particular project. The technical assessment deeply goes through the safety concern of the specific technology involved and its operation. Besides these project specific assessments for RES, physical benefits of transmission and storage and the effect in the integrated picture of the grid is also important. It is therefore always recommended to go for an integrated approach for full exploitation of renewable generation and electricity storage with respect to transmission and distribution [8]. And this in line with the state utility cannot be undermined also. It is further recommended at all levels to increase its research and development (R&D) in basic electrochemistry to find out the materials and discover the electrochemical technology suitable for use in grid. Department of energy, of concerned countries, have been leading the R&D to deal with reliability, resilience, cyber security, and affordability issues from the grid modernization perspective.
