According to a latest study, the existing fossil-fuel based power plants, vehicles and factories if utilized for their designed lifetime will warm the earth more than 1.5 degrees Celsius. However, to limit the warming to 1.5°C(Paris Accord), not only no new power plants using fossil-fuel be built in future, even some running infrastructure needs to be closed urgently. To meet this objective, green energy sources are considered a perfect choice for future requirements because of their plentiful nature and localized availability. This project proposes a model of hybrid energy system (HES) to fulfil the energy requirement of a diversified community. Simulation based project considers HES formed of photo-voltaic (PV), battery storage units and diesel generator connected with utility grid at distribution feeder level. The energy management system (EMS) prioritizes the utilization of energy sources like PV and power grid by considering the global warming effect. Battery banks are employed to supply power at night and overcome the intermittent behavior of PV systems by supplying the previously stored surplus PV energy. However, EMS will activate the power grid if PV and battery banks are unable to fulfill the community load demand at any time. This formation will help reduce the warming effect of earth created by burning of fossil fuels etc. This project uses data (solar radiation and ambient temperature) from NASA surface meteorology and solar energy database. All the simulations are performed in MATLAB software to prove its practicality. Due to cost effectiveness, the proposed system is practical and can be implemented quickly.

Location of case study:

The proposed HES is analyzed for the community situated in the city of Quetta, Pakistan (Lat: 30.15, Long: 67.05). Quetta is the capital of the Balochistan province that has the tremendous potential of indigenous energy resources like oil, gas, coal, wind and solar. High solar irradiance and moderate temperature of Quetta city make it ideal candidate for PV utilization.

Main Architecture of HES:

To realize the concept of HES, the following sub models are considered.

1) Photo-voltaic power model: This model is based on single diode model which takes the input data in form of irradiance (in W/m²), temperature (in °C), and other module parameters at standard test conditions (STC). Instantaneous PV power (PV_Power) of a single module for any value of G and T, of Quetta city is calculated as PV_Power = (VPV*IPV). However, this work utilizes perturb and observe (P&O) algorithm to track maximum power point (MPP) via employed converter. Accordingly, total PV power of charging station is found by multiplying total number of PV modules with PV_Power.

2) Charge estimation model: Estimation of charge plays important role during charging and discharging process of battery banks. Batteries are used to store surplus energy from PV and stabilize the voltage of a dc bus. During the operation of HES, SOC of batteries play vital role to control the charging and discharging process of battery banks.

3) Inverter model: Inverter model describes the efficiency of HES after power conversion from DC to AC.

4) Diesel generator model: Diesel generator (DG) are used as backup source in case of emergency condition when no other source is available to satisfy the load demand. DG can be used from zero to full load but EMS activates DG as a last option in order to reduce CO2 emissions.

5) Load demand model:Load demand is modeled to estimate the amount of random power demanded by the community. This model represents hourly load demand of community which is formed of different categories like residential and public facilities.

Conclusion:

This project proposed HES which utilizes PV, battery banks and diesel generator along with utility grid to provide uninterrupted supply of electricity. It suggests the PV as the main source for supplying electricity at day time when the sun is available and utilize battery banks during night intervals. However, this project does not overlook the importance of existing power plants due to the existing huge infrastructure, availability and reliability. For this reason, we have suggested grid tied HES. This formation will minimize the CO2 emissions coming from conventional sources of electricity like coal, oil and natural gas.

Future work:

This work can be extended to design electric vehicles (EV) which can be modeled and connected as DC load. EV's are considered to replace the existing vehicles engines because today's engine pose big threat to earth environment.