Solar Panels
As mine sites realize the positive impact on the operating costs and affect that using renewable energy has on the environment, the more they will start using solar farms. Solar farms consist of many solar panels for collecting solar energy and converting it into electric power. The sun provides approximately 1,000 watts of power per square meter and the solar panel transforms that power into approximately 130W per square meter. The cost efficient solar panels are being sourced out of China at prices significantly lower than in the past.
This is not new technology. Edmond Becquerel first discovered the photovoltaic effect in 1839 by generating electricity from sunlight. Over 100 years later, researchers understood what this meant on an atomic level and discovered a way to develop a device that could provide the transformation of sun power to electric power.
Monocrystalline silicon solar panel
Monocrystalline silicon solar panels are of high quality and can produce 0.60 volts in an open circuit at 25°C. They can be connected in series to produce higher levels of voltages and in parallel to increase amperage. Solar panels are normally connected in series and therefore produce about 20 volts on a clear and sunny day. The operation to efficiency performance is indirectly proportional. That is when the operating temperature increases, and the panel efficiency decreases.
A maximum power point tracking (MPPT) device is used as an advanced charge controller. Its purpose is to track power by measuring the voltage and adjusting the current to get maximum power transfer with given light conditions.
Wind Energy
Wind turbines are strategically located in areas of high wind occurrences, such as near the coast, hilltops or in open plains. Wind turbines come in a variety of shapes and sizes, however, the most commonly used design is the windmill. On mine sites, wind does not constantly blow, so wind turbines are suggested to be paired with other renewable energy sources to maintain a constant supply of energy to a microgrid. The currently studied microgrid is the combination of wind farms, solar farms, and battery storage of their joined energy.
Wind turbines use wind to create electricity. Kinetic energy applies force to the turbine’s blades that spins a rotor. The rotor then turns a generator that produces the electricity.
The Australian Renewable Energy Agency (AREA, 2020) states that wind energy in Australia is the main source of renewable energy. AREA continues to state that wind energy can generate enough electricity to meet 7.1 per cent of the nation’s total electricity demand. Their figures show that at the end of 2018, there were 94 wind farms in Australia that delivered almost 6GW of wind generated electricity, making it the one of the lowest costing large scale renewables in Australia.
The most significant advantage of wind energy is that it’s a clean source of reliable energy that does not pollute the atmosphere with greenhouse gasses.
Batteries
Battery technology is used to store solar and wind energy in the form of electricity so the electricity can be used day or night or on overcast days when the energy sources are not in use. The lack of such steady supply of electricity is why there is a need for large energy storage systems (ESS). Energy storage systems require load levelling or grid storage batteries to provide a seamless flow of electricity.
Lithium Ion (Li-ion) Batteries
Lithium ion (Li-ion) batteries are preferred for their load levelling capabilities due to the small footprint, long life, and low maintenance. Even though lithium ion batteries are more expensive than lead batteries, Li-ion batteries do not suffer from sulfation like lead acid batteries when not fully charged periodically. This is a problem on a mine site where demand often exceeds supply. The benefits of Li-ion batteries are that they are light weight and easily transportable to remote locations. The drawback to Li-ion batteries is the high cost. The batteries best suited for ESS are lithium ion or redox flow batteries.
Vanadium Redox Flow Batteries
Vanadium Redox Flow batteries (VRB) are fuel cells designed to store electricity. The fuel cells contain an electrolyte (metallic salts) that gets pumped through a core that consists of a cathode and an anode that are separated by a membrane. Electricity is generated by an ionic exchange that occurs between the cathode and anode.
Industrial types of flow batteries consist of an electrolyte that is made of sulphuric acid with vanadium salts. Vanadium is often used as it keeps corrosion under control. Large scale flow batteries are capable of between 100KWh to 60MWh and can be used for frequency regulation. Vanadium batteries are excellent for storing energy for large power systems.
Battery Management Systems (BMS)
Wind turbines have an energy output between 1 – 10MW, averaging out around 5MW. Most wind farms contain several wind turbines that produce between 30-300MW and require battery management systems. Battery management systems (BMS) keep the batteries at 50% charge to absorb energy during windy days, whilst delivering on high load demands. Modern BMS can switch from charge to discharge in less than a second to stabilize the voltage on transmission lines.
Hybrid Microgrids
Hybrid microgrids are systems that can automate the management of power from different sources to maintain stable and resilient power supply. By using an energy storage system and with lower costs for wind and solar energy generation, the integration of hybrid microgrids to include renewable technologies enables cost-effective, reliable, efficient, and flexible power supply without access to major utility grids. Hybrid microgrids are ideal for applications with high power demand and where power supply is limited, especially in remote areas.
As shown in Figure 2, hybrid microgrid is consisted of distributed resources which are parallel connected. This arrangement allows the system to operate in both islanded and grid connected modes, which will reduce the operating costs significantly when compared to conventional energy generation systems.
