The use of solar energy in the copper mining processes: A comprehensive review

1. Introduction

Copper demand will continue growing in the long-term as the global population increases and shifts from rural to urban areas(Schipper et al., 2018). Big countries such as China, India, and many emerging countries will continue with increased urbanization, wealth, and a huge need for products such as cars, computers, household goods, and consumables. These activities require huge amounts of copper.

To obtain mineral commodities from copper ores, three basic processes are required namely extraction, material handling, and processing (Schlesinger et al., 2011). Energy consumption in each process varies according to the type of mineral. For copper ores, the processing accounts for 45% of the total energy requirements, extraction, and material handling 45%, and general and administrative costs (10%) (Curry et al., 2014).

Energy in the copper mining industry is needed in three forms namely: electricity, heat, and fuel. The share of each form of energy is 35% electricity, 26% Diesel-fuel, and 20% biomass-fuel. The cost of energy is currently high and represents about 25–30% of total operating costs (Cochilco, 2020). It is expected that copper mining in Chile will need an annual electricity demand of 39.5 TWh by 2025, which represents an increase of 60% (Cochilco, 2020). Consequently, a sharp increase in CO2 emissions is evident, if no decision will be taken shortly.

Besides, customers are increasingly aware of the carbon footprint of their supply chain (Fahr et al., 2016). Life cycle assessments, considering embodied energy and CO2 emissions, of the copper mining processes, have been carried out (Norgate and Haque, 2010) (Moreno-Leiva et al., 2017). The results showed that the crushing and grinding processes have the main contribution to the total CO2 emissions. Bardi (2014) highlighted the issue of mineral depletion with a special focus on the role of energy in the mining industry. His work concludes that energy is a fundamental factor in the mining industry.

Another important factor is given by the fact that the metal content of copper ores (i.e. grades) has been falling since higher-grade reserves are progressively depleted (Cochilco, 2020) (Chandia et al., 2016). For instance, between 2001 and 2012, copper ore grade has decreased from 1.25% to 0.84% (Cochilco, 2020). This results in a significant increase in energy demand. During the period 2001–2012, electricity demand increased by 71%, from 38, 000 to 65, 000 terra Joule while fuels demand increased by 62%, from 47, 000 to 76, 000 terra Joule (Chandia et al., 2016). Unfortunately, the production of copper has just increased by 15% in that period (Chandia et al., 2016). This means that energy demand is growing 6-times faster than copper production due to a constantly decreasing ore grade that carries bigger needs for energy. By 2025, the electricity share for concentration will increase from 50% to 62% of the total required electricity by the copper mining industry (Cochilco, 2020). Recently, Palacios Jose-Luis et al. (2019) revealed that the decline of the ore grade is becoming a serious issue. The authors have calculated the exergy required to extract and concentrate copper ore and concluded that the calculated value is of one order of magnitude greater than the one used as a reference so far.

When the target is replacing fossil fuel energy from the grid with solar energy, where the electricity is mainly Alternative Current (AC), the copper mining industry should consider Concentrating Solar Power (CSP) in its future energy mix (Chiloane, 2012). This is particularly true when the operation is located far away from the grid. When this scenario is evaluated for the Chilean copper concentrate plants, an important reduction of greenhouse gases is found when CSP and Solar Photovoltaic (PV) are used.

The fall in the prices of solar technologies combined with the attraction of Chile as the right place for investors led to the first Chilean solar application boom, which encourages the private sector to plan and build several solar power projects. In April 2020, the cumulative installed capacity of photovoltaic installations in Chile amounted to more than 2.7 GW. This represents an increase of 15.2% in comparison to the same month of the previous year, when the total installed solar PV capacity in the country reached 2.36 GW. Most of the solar projects are installed in the Atacama Desert where most of the copper mines are located. Indeed, the Atacama Desert receives the highest levels of radiation in the world, exceeding 2500 kWh/m2 for Global Horizontal Irradiation.

The use of solar energy to supply the copper mining processes should be capable of account for the variability in energy consumption associated with the variability in the mineral characteristics. The more important being the rock hardness, which has a direct impact on energy consumption in comminution. In the case of using PV energy, an interesting alternative is combining the PV plant with a Battery Energy Storage System (BESS) that would serve as a buffer between variable energy consumption and variable solar energy supply. The application of this alternative in northern Chile has been investigated in (Pamparana et al., 2019a) and (Pamparana et al., 2019b).

The integration of solar energy into the copper mining industry could tackle not only the reduction of greenhouse gases but also the scarcity of water. As of 2017, the water consumption in the copper industry was 54.5 m3/s (19% seawater, 81% continental water) (Cochilco, 2017). 67% of this amount is consumed by the concentration process (Cochilco, 2017). The need for seawater will continue to increase to meet the copper industry needs. It is expected that the share of seawater will continue to increase to reach 42.7% (an increase of 230% compared with the quantity of seawater that was consumed in 2018) (Cochilco, 2018). The use of solar energy for desalination and transport of water from the sea is a practical solution. Water might be transported at distances ranging from 100 to 200 km and an altitude difference of 1500+ meters. One interesting aspect of the solar-pumping is that it may be designed in such a way that it is adapted to the availability of solar energy, being more intensive during the day.

Indeed, it is possible to identify three levels of development for the integration of solar energy into the copper mining industry:

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The first one considers the solar energy system to assist current processes and operations.
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The second level considers changes in the current operations to suit the availability of solar resources.
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At the third level, new processes and operations are designed to fully utilize the solar potential.

The present work:

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reviews the solar technologies that can be integrated in the copper mining process.
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reviews the current and mature applications of solar energy into the copper mining processes
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sheds some light on some ideas of future developments for the integration of solar energy into the copper mining processes.

The next section provides an overview of copper ore processing. Section 3 describes the current commercial solar energy technologies. Section 4 provides an overview of the applications of solar energy in the Chilean copper mining industry. Some alternatives for solar-mining integration are presented in section 5. Section 6 identifies opportunities and challenges and some general conclusions are drawn in Section 7.

2. Review methodology

The review methodology used in this work is presented in Fig. 1. It aims to provide useful information for the readers in step-by-step method. After highlighting the energy issues of the copper mining industry, we provide an overview of the copper mining processes. Next, different solar technologies are described and highlighted. Indeed, knowledge about copper mining processes and solar technologies is mandatory to understand how solar energy can be used in the copper mining industry. The current and future applications of solar energy in the mining industry are then presented and discussed. We gave particular interest for some ideas for the future development of the integration of solar energy into the copper mining processes.

It is important to note that the review focuses on the case of Chile since it is the leader of copper production. Thus, the reviewed papers have been selected using SCOPUS and Google search engine. Only scientific papers that present important contribution to the use of solar energy in the copper mining processes are reported. Besides, the scientific published papers, technical reports that are published by public institutions such as Cochilco are considered to provide the most recent statistics.

3. Copper mineral processing plants

Copper ore is extracted from the mine and a first size reduction stage is used to transport the ore for further processing. Pyro-metallurgical and hydrometallurgical processes are used to treat copper ores. As Fig. 2 shows, in the pyro-metallurgy process, copper-sulfide ores are ground to liberate Cu-minerals. After that, it is concentrated by a flotation process. The concentrate having a ~30% Cu can be sold or sent to a copper smelter, where it is heated up to 1200 °C to produce blister copper, which is cast into anodes for electro-refining to produce copper cathode of 99.99% purity (Schlesinger et al., 2011).

The hydrometallurgy process treats copper ore by adding dilute sulphuric acid to form a weak solution of copper sulfate. The copper is then recovered by electrolysis and the electro-winning step is used to produce copper cathodes (Schlesinger et al., 2011).

Copper ores processing requires important amounts of electricity, heat, fuel, water, oxygen, and chemical agents among other services. Fig. 2 highlights the energy and water needs in the different stages of copper processing. The most intensive energy-consuming process is the grinding process. Low-grade heat (Temperatures <80 °C) is necessary for efficient copper refining. Besides, considerable water is consumed in the flotation and leaching stages. Fuels are required to power transportation and excavation activities. It is also used in the smelting stages as an auxiliary source of heat. Oxygen is used in the smelting-refinery stages to oxide the copper sulfides. Oxygen is also used in the pressure oxidation process of ore-sulfiles (Marsden et al., 2007). Leaching and flotation require chemical agents to enhance the concentration process (Schlesinger et al., 2011).

4. Solar technologies

This section provides an overview of solar technologies that are suitable for electricity generation and heat production.

4.1. Solar photovoltaic

Among photovoltaic (PV) solar cell technologies are Monocrystalline, Polycrystalline, Amorphous, Cadmium Telluride Thin Film, Copper Indium Gallium Di-Selenide, Nano Crystal, Polymer, Dye-Sensitized, and Perovskite. As Fig. 3 illustrates, they can be arranged into three generations. In red is highlighted the most popular one in current Chilean PV plants.

The efficiency of solar cells depends on their technologies. For instance, the efficiency of amorphous Silicon modules is about 8.1%. Nanocrystal based solar cells can achieve 16.6%. The efficiency of Perovskite Solar Cells is about 20.9%. The predominant technology found in the Chilean PV plants is based on Si solar cells (Olfian et al., 2020).

Solar PV can be installed at both small and large scales. However, copper mining industry is attracted by large scale applications because of the size of its installations. A comprehensive review about the large scale applications of solar PV with applications of electrical energy storage is presented by (Lai et al., 2017).

4.2. Solar thermal

As depicted in Fig. 4, there are several solar thermal collectors including non-concentrating and concentrating collectors. In red, are highlighted the technologies currently used in the Chilean mining industry. The efficiency of typical flat plate collectors (FPC) ranges from 0.72 to 0.75 (Zurita et al., 2018). The Evacuated Tube Collectors (ETCs) offer better performance than the FPC during cold weather and their efficiencies range from 0.62 to 0.82 (Zurita et al., 2018). Compound Parabolic Collectors (CPCs) are relatively simple than Parabolic Trough Collectors (PTCs). Their operating temperature ranges from 60 °C to 240 °C and their efficiencies range from 0.58 to 0.72 (Zurita et al., 2018). The concentration ratio of the PTC and the LFC ranges from 30 to 100 and 20–45 respectively (Zurita et al., 2018). The optical efficiency of the Central Receiver System (CRS) depends on the location, the type and the size of the receiver, and the size and the layout of the heliostat field. For instance, the annual optical efficiency of the heliostat field of a 100MWe power plant, located in the north of Chile is 62.2% (Behar et al., 2020). In the beam down system (BDS) the receiver is located at the ground and a secondary reflector is used to re-orient the solar rays to the receiver aperture. Solar dish has excellent optical performance and can achieve a very high concentration ratio. For example, a 489 m2 Dish has achieved a peak flux of 14,100 suns and an average concentration of 2240 for 95% optical efficiency. Solar furnaces are point-focus systems, which can reach temperatures higher than 3000 °C (Goel et al., 2020).

4.3. Solar hybrid PV-thermal

Hybrid solar PV-Thermal (PV-T) technologies aim to reduce the costs by combining the advantages of both thermal and PV collectors. They might be arranged in two sets: coupled and uncoupled PV-T systems. Fig. 5 shows the different types of PV-T technologies.

In the coupled PV-T systems unused solar radiation by the PV cells is absorbed by the thermal absorber (Ju et al., 2017). The most competitive coupled PV-T system is known as Concentrating PV-T (CPV-T). In the CPV-T, solar cells are simultaneously used as a thermal receiver and a PV converter.

In the uncoupled PV-T system, the PV panels and the thermal collectors are separated from each other. PV-CSP plants are a good example of the uncoupled PV-T system. Flat plate collectors and PV panels, which are used for domestic applications, could also be considered as an uncoupled PV-T system.

5. Applications of solar energy in the Chilean copper mining industry

5.1. Applications of solar PV

Mining and mineral processing operations are energy-intensive, both thermal and electrical. In the case of electric powered-processes, it could be assumed that a large-scale photovoltaic energy penetration with traditional PV plants into electric grids feeding mining plants, is the straightforward solution towards a more sustainable copper mining industry. This is certainly a viable option, with available off-the-shelf PV technology. However, there are opportunities to think outside the box and embrace ways in which PV energy can be integrated into different processes more efficiently and cost-effectively. This section presents three examples of such applications.

5.1.1. PV electro-refineries

Among the copper production processes, electro-refining and electro-winning, both based on electrolysis, are one of the most energy-demanding stages of copper production, and therefore greatly contribute to the large carbon footprint of the copper mining industry. This is also true for other metal electrolysis-based production processes. Electrolysis, independent of the type of metal in question, requires high continuous currents (DC) operating at low voltages, as can be appreciated from Table 1.

Table 1. DC current and voltage range required for electrolysis of different metals (Schlesinger et al., 2011).

Metals	DC current range	DC voltage range
Aluminum	70–300 kA	500-1300 V
Copper	10–40 kA	160–200 V
Led	4–6 kA	50–150 V
Niquel	15–30 kA	100–600 V
Magnesium	100–120 kA	300–600 V
Zinc	20–80 kA	300–700 V

Usually, these voltages and currents are generated using large step-down transformers followed by high power rectifiers, which convert alternating current into a controlled continuous current that flows through the anodes to cathodes in very large electrolysis pools. Fig. 6 shows a simplified diagram of an electro-refining process, where a voltage source rectifier feeds 8 refining pool groups. Each group is divided into approximately 48 pools with their own set of anodes and cathodes immersed into an electrolytic solution. The series connection of the pools and direction of the DC-current is depicted in Fig. 6(b). This process generates through electrolysis, 99% pure cathodes from copper anodes.

Today, injecting PV energy into an existing electro-refining plant requires boosting the PV strings output voltage and then converting from DC to AC through a central inverter connected by transformers to the point of common coupling (PCC). Then, to feed the DC industrial process another transformation and AC-DC conversion are required, as is illustrated in Fig. 7(a). However, since both PV and electrolysis plants work inherently with DC currents at low voltages, it becomes more efficient to feed directly the PV energy to the Renewable Energy (ER) plant through a single DC-DC conversion stage, reducing the number of converter and transformer stages, as shown in Fig. 7(b).

The DC-DC converter technology required for this approach is not available currently in the markets but has been developed and experimentally validated (Collura et al., 2019). This solution, as shown in Fig. 6(a) is conceived for retrofitting existing ER plants, i.e. the existing grid connection using a step-down transformer and an AC-DC converter to feed the ER plant remains. Hence, the PV system only performs an offset of energy consumption during the day. Nevertheless, energy storage could further reduce the consumption from grid sources, up to powering through PV power the whole ER operation. An additional benefit is that electrolysis pools are very large in area, and have available roofs to install the PV plant, thus having only short distances for power distribution, further reducing the losses. Depending on the PV module efficiency and available solar resource at the ER plant, basic calculations show that around 50% of the necessary power can be accommodated in the roof. Also, if hybrid PV panels are considered the necessary supply of heat for heating the electrolyte can also be supplied.

To take advantage of solar PV power, Weichmann et al. (Wiechmann et al., 2018) proposed to increase the distance between the electrodes of the electrowinning process. By increasing the distance between the electrodes, the current density per electrode and its respective resistance increase, which provides the required heat to the electrolyte. The study showed that a facility of 240,000 tons of copper cathodes per year can save 35 million USD by using solar PV and increasing the distance between the electrodes in the electrowinning process. Besides, a cut of 37.5% in the CO2 emissions is expected. The same author (Wiechmann et al., 2020) also proposed to increase the electric current in the electrowinning processes to increase the use of solar PV technology during sunlight hours. To do so, they suggested the use of the Intercell Triple Current Source bars to overcome the faulty contacts, increase the short-circuit resistance, and operate with 50% lower dispersion during the sunlight hours.

5.1.2. Applications of PV in comminution

Comminution (crushing and grinding steps) represents an important share of the total energy consumption in a mineral processing plant. In Chile, for instance, comminution is responsible, on average, for almost 50% of the electrical energy consumption of the mining process, being the largest greenhouse emitter in the copper concentrate production (Norgate and Haque, 2010).

The energy consumption in comminution operations is affected by the ore hardness, which introduces variability to the consumption (Pamparana et al., 2019b). The challenge, therefore, is designing and implementing solar alternatives that allow both facing the energy consumption variability and an actual integration in a process that is intense in energy consumption. Although theoretically, it is possible to design a comminution plant that can operate based only on solar energy, an interesting hybrid alternative has been studied (Pamparana et al., 2019b), which combines energy from the grid with a photovoltaic plant and a BESS. The typical concept is illustrated in Fig. 8. The use of solar PV to supply or partially power comminution processes might be capable to account for the variability in energy consumption associated with the variability in the mineral characteristics. The more important being the rock hardness, which has a direct impact on energy consumption in comminution. The power system shown in Fig. 8 allows lowering and flattening the consumption from the grid (peak shaving), whereas a fraction of the total energy consumed by the process is solar PV. The penetration of solar PV can be increased if the comminution processes are modified to allow for Demand Side Management (DSM), which can be done by having more than one ores stockpile to allow deciding whether to feed hard or soft mineral to the comminution plant, depending on the energy availability in the (PV + BESS).

The simulations, presented in (Pamparana et al., 2019b), showed that the system adjusts itself to process hard minerals during the sun hours, where there is more energy available, and soft minerals during the night where the system depends mainly on the grid and the energy stored in the BESS.

5.1.3. PV for water pumping

The copper mining industry consumes important quantities of water. As of 2017, the water consumption in the copper industry was 54.5 m3/s (Cochilco, 2017). The issue of water arises since several of the most important mining units are located in zones where the scarcity of water is limiting for the local development. In this scenario, most of the new mining projects are considering the use of seawater to supply their requirements. Hence, by 2029 it is expected a large increase in the use of seawater for copper mining in Chile (Cochilco, 2018) (see Table 2). However, this strategy involves important challenges in terms of cost and energy consumption, mainly due to the need of pumping water (Fig. 9) from the coast to the mine site (a distance that can be hundreds of kilometers).

Table 2. Estimated water consumption (m3/s) for the period 2020–2029 in the Chilean copper mining (Cochilco, 2018).

Year	2020	2021	2022	2023	2024	2025	2026	2027	2028	2029
Continental water	13.81	13.79	13.89	13.82	14.21	14.09	13.87	13.82	14.20	14.53
Sea water	6.18	6.81	8.14	8.75	9.43	9.68	9.96	10.33	10.69	10.83
Total	19.98	20.59	22.03	22.57	23.64	23.77	28.83	24.15	24.88	25.35

Therefore, as the most important copper mines in Chile are situated in regions with a high level of solar radiation, the use of solar PV appears as a suitable alternative to supply the pumping stations (Gopal et al., 2013). For water pumping applications, centrifugal pumps are widely used. Three-phase induction motors typically drive them. Thus, to drive a pump using solar PV, a three-phase power inverter must be connected between the solar panel array and the induction machine to convert the DC voltage produced by the PV system into AC voltage. Moreover, to optimize the energy capture, the converter should carry out a Maximum Power Point Tracking (MPPT) algorithm to extract the maximum power available from the PV system (Wareesri and Po-Ngam, 2016).

On the other hand, for regulating the water pressure of large pipelines (as in the case of the copper mining industry) it is common to use several pumps operating in parallel. Pumps are operated in parallel when two or more pumps are connected to a common discharge line and share the same suction conditions (Fig. 10). The parallel pump configuration allows for increasing the water flow rate in a pipeline for a certain operating head (Fig. 11).

In general, solar PV pumping systems have been extensively reported in the technical literature (Singh et al., 2018), (Jain et al., 2014), (Sekhar and Banakara, 2018), where the research efforts have been focused on studying different power converter topologies to supply the pumps and different control strategies to obtain a desirable dynamic behavior of the system.

One of the main challenges for the copper mining industry is the need to secure water for the different mining processes. It has been reported that apart from the obvious need to have copper and technical human resources, water is the crucial resource for keeping the production aims of the Chilean copper industry. The possibility of pumping seawater to the far located copper mines is technically feasible. Furthermore, the work reported in (Montorfano et al., 2016) provides an economic evaluation of using solar energy, by means of photovoltaic panels, to provide the needed energy to accomplish seawater pumping requirements.

5.2. Applications of solar thermal

5.2.1. Solar thermal to produce hot water for electro-refineries

The integration of solar thermal energy in electro-winning and electro-refining processes is quite promising. In Chuqicamata, there is a solar thermal plant of 540 MWhth/year. It has a thermal storage tank to store hot water at 95 °C. The plant supplies 54.000 MWh/yr, of heat energy, replacing 85% of the fossil fuel used in the electro-winning process, enabling Gabriela Mistral Division to avoid about 203.6 ton CO2/year (Ushak et al., 2014). Fig. 12 shows Codelco's Gabriela Mistral Division solar thermal plant, located in Sierra Gorda district, Atacama Region. The solar collectors are cleaned by a dry cleaning device and their tilt is seasonally adjusted. The indirect heating concept is used so that the system consists of two loops. The primary loop works at 85 °C/55 °C return flow, while the secondary loop at 80 °C/60 °C (Fahr et al., 2016). The secondary loop feeds the electrolytic copper winning.

5.2.2. Solar thermal for leaching

Solar thermal technologies can be integrated into the current leaching process to heat the solution. Low-temperature solar collectors are cost-effective for direct and indirect heating of the solution with no modification in the existing process. Some examples of such a design can be found in (Murray et al., 2017). Because of falling ore grades, changes in the current process might be a good option to fully utilize the solar potential and to improve copper extraction. Clare Murray et al. (2017) proposed an interesting design. As illustrated in Fig. 13, the authors have proposed the integration of solar thermal energy into a bioleaching process to increase copper extraction rates. The proposed design consists of the heap, two ponds, and the solar thermal collector field. The author has simulated the performance of the system and indicated that the copper extraction effectiveness can achieve 85% for a heap area ratio of 1:1 and a 10 kg/h m2 solution flow rate. The economic assessment reveals that the most competitive design has a heap area of 50,000 m2, which corresponds to an extraction of 76%.

5.2.3. Uncoupled PV-CSP system for electricity generation

Among the most promising solar PV-T concept is PV-CSP technology, which has gained increasing attention worldwide. In the Atacama Desert, the first non-compact hybrid PV-central receiver plant in Latin America is now reaching its final construction phase. The plant is known as Cerro Dominador and has a capacity of 210 MW. It is located 60 km away from Calama at Maria Elena in the Atacama Desert, Chile. Cerro Dominador consists of a 100 MW PV plant and 110 MW CSP. The CSP sub-system consists of a 220-m high tower surrounded by more than 10,600 heliostats. A molten salt receiver is installed on the top of the tower to heat molten salt to a temperature of 565 °C. The salt can be then stored in a 17.5 h storage system, which allows generating energy 24 h a day. Fig. 14 shows pictures of the Cerro Dominador plant under-construction.

5.3. Summary of the operational and planned solar plants

The main projects with environmental approval in Chile are located in the North of the country and surpassing the GWp. Up to date, various PV megaprojects are in operation, such as El Romero Solar 196 MW, Luz del Norte 141 MW, Conejo 104 MW, Llanos de Llampo 100.6 MW, Terrae 160 MW, among others. Moreover, several solar thermal projects are in operation, such as Pampa execution Evita 32.2 MW, to supply heat in the company Mining Gabriela Mistral. Table 3 provides an overview of the current applications of solar energy in the mining industry.

Table 3. Solar projects in the copper mining industry.

Mining Company	Mine	Capacity (MW)	Solar technology	Mining process	Solar developer	Financing
Antofagasta Minerals	El Tesoro	10.5	Solar thermal (parabolic trough)	Electro-wining	Solarpack	PPA
Anglo American	Collahuasi	25	Solar PV	All-processes	Solarpack	PPA
Quiborax	El Aquila	2.3	Solar PV	All-processes	E-CL	PPA
Antofagasta Minerals	Chuquicamata	1	Solar PV –Diesel	All-processes	Solarpack	PPA
Codelco	Gabriela Mistral	32	Solar thermal (Flat plate collector)	Electro-wining	Sunmark	PPA
SCM	Minera Constanza	0.308	Solar thermal (Flat plat collector)	Electro-wining	–	–

Concerning the financing, the copper mining industry are commonly use three main business models for solar projects (Nasirov and Agostini, 2018).

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The first one is an industrial pooling model, under which a copper mining company signs a long-term power purchase agreement (PPA) with generation plants and the conditions of the contracts are freely defined by both parts. In this case, the mining company acts as an off-taker, merely contracting the purchase of energy and avoiding any investment.
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The second one is a self-generation model, in which case a copper mining firm develops, finances, and operates a solar plant on its own land.
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The third model is net metering, under which a grid-connected copper mining firm develops, finances, and operates a solar plant on its own land. However, in this case, the utility company purchases the excess capacity generated by the solar energy plant.

In addition to the above-cited operational plants, eight projects are under development, whereby seven projects of a total capacity of 2075 MW have environmental approval and one project of 400 MW is under environmental evaluation. CSP for power generation in Chile is dominated by solar towers (five projects of 1645 MW), followed by a parabolic trough (three projects of 730 MW). These eight projects will be equipped with thermal storage of at least 10 h of storage.

6. Further developments for the integration of solar energy to the copper mining industry

6.1. Solar thermal energy for drying the copper concentrate

It is worth noting that 45% of the copper in Chile is exported as a copper concentrate. Currently, some copper mining processing plants use the fossil-fuel dryer to reduce the humidity of the copper concentrate. It is possible to use concentrating solar power for drying copper concentrate since the operating temperature of the drying process is around 180 °C. Detailed technical studies on the design of a solar process for drying copper and iron concentrates in Chile are presented in (Behar et al., 2017a) and (Behar et al., 2017b). Fig. 15 highlights a typical solar copper concentrate drying process. A parabolic trough solar field (or linear Fresnel) can be used to heat a Heat Transfer Fluid (HTF) (such as oil or molten salt). The HTF is used to generate hot air. The hot air (or steam) is sent to a fluidized bed dryer to dry the copper concentrate.

6.2. Coupled hybrid PV-T system for electro-refineries

In the copper mining industry, electro-refining and electro-winning processes are good candidates for coupled PV-T technology. This technology can be deployed in the roof of the big “tank houses” the generated electricity can be used to drive the ventilation fans or in the process itself as illustrated in Fig. 16. Fig. 16 illustrates a proposed solar electro-winning process powered by a CPV-T system. Note that the electro-winning process needs water and electricity to produce high purity copper. A compound solar concentrator concentrates rays on small efficient solar cells (CPV) to produce electricity. The water is then pumped to extract the heat induced by the unexploited solar radiation and stored in the thermal energy storage tank. The electrolyte of the copper electro-winning process is heated indirectly. A water/electrolyte heat exchanger (HEX) is used to heat the electrolyte. The surplus electric energy is stored storage in the Direct Storage (DS) batteries. This results in a hybrid solar stand-alone concept thanks to the thermal (tank) and electric (batteries) energy storage.

6.3. Solar PV with gravity-based storage and hydraulic power for water pumping

One interesting aspect of the solar-pumping is that it may be designed in such a way that it is adapted to the availability of solar energy, being more intensive during the day, so that no electrical storage is needed. The Espejo de Tarapacá project is a good example of the combination of solar energy and pumped storage. The project is located in Iquique, Tarapacá. It comprises two units: a 300 MW hydroelectric seawater pumped storage unit and a 600 MW-AC solar PV unit. To store solar energy, water is pumped into a reservoir that encompasses a total land area of 375 ha and a storage capacity of 83 GWh, respectively. Fig. 17 shows the design of the Espejo de Tarapacá project. Such a design is an attractive solution, since most mines, in Chile, are located in the Atacama, a region with almost no rainfall. Indeed, the Atacama Desert is pre-destined for solar PV with gravity-based storage and hydraulic power generation, since the high altitude of 2000–4000 m above sea level leads to a huge altitude-difference. Besides, it is located near the equator between 18° and 25° southern latitude, leading to very little annual variation in irradiance, which results in stable annual production of electricity and water pumping.

6.4. Other alternatives

Solar energy can satisfy the mining industry in terms of heat, electricity, fuels, and water. In tailings, PV is an important candidate to improve tailings management and increase water recovery by up to 90%. It can be used to recirculate water from tailings dams to the copper concentrate plants. What is interesting is that PV plants can be installed in the idle tailings dam surface, which reduces the civil engineering costs of the project. This might tackle one of the hot spots of social opposition. Another alternative option for installing PV panels is the so-called PV-floating-cover system for water reservoirs, which might have a double objective: power generation and reduction of the water losses by evaporation.

The use of both PV and CSP to desalinate seawater before use in the copper mining processes is also possible. Besides, thermal energy from the CSP system could be directly used for heating ore before smelting or heating air for roasting. The use of solar energy (especially high-temperature CSP) to produce solar fuels is an attractive solution for the copper mining industry. Solar fuels can be used to meet the thermal requirements of the roasting and smelting processes. It can also be used to power vehicles (haul trucks, cranes …), which results in a significant reduction in carbon dioxide emissions and fossil fuel imports. The use of high-temperature CSP technology for the pyrolysis of waste tires to produce gas, oils, steel, and carbon black is another advanced application of solar energy into the mining industry.