# A Machine Learning Approach for Solar Power Technology Review and Patent Evolution Analysis
## 2 Literature Review
### Solar Power Cells and Energy Storage  
As technology matures and the product life cycle enters the growth stage, there is a fast, increasing demand for equipment and services. Renewable energy sources are a viable but expensive alternative with ongoing concerns about the efficiency, cost and implementation across widespread electrical grid infrastructures. Most renewable energy technologies are in the late introductory stage of the product life cycle and yet demand has not seen fast, growing demand. This type of market response is often called the Gompertz effect since significant capital investments have been made in non-renewable energy facilities that are not fully depreciated and can function for many more decades [6]. Renewable energy such as wind and solar power cannot produce power reliably with current technology since power production rates change with seasons, months, days, or even within a day. The marketplace requires large scale and affordable solutions to alleviate fluctuating output and provide methods to store excess production for later consumption [7]. Solar energy is one of the most common and popular sources of clean energy, and the requirement to have access to sunlight is a very simple requirement compared to other solutions. Direct solar radiation may have the greatest potential for large-scale utilization once viable energy storage technology is developed. [PERSON] [1] reviewed and discussed both the merits and limitations of solar energy technologies. A number of technical problems affecting renewable energy  
Figure 1: The research flowchart of the technology mining and analysis. research are also highlighted, along with beneficial interactions between regulation policy frameworks and future prospects. Concentrating solar power (CSP) plants generate solar thermal electricity without greenhouse gas emissions and is a key energy technology with a negative impact on climate change. A thermoelectric solar plant uses a set of units arranged in the following order [8]. The first unit in the sequence is a mirror designed to collect solar radiation and concentrate it at a focal point. The second unit, linked to the solar concentrator, is the receiver and the heat exchanger which circulates heat transfer fluid (such as molten salt or synthetic oil) to absorb the concentrated heat. The final unit consists of a second heat exchanger that transfers the accumulated thermal energy to another fluid (usually steam) which drives a turbine electric generator. To reduce the cost per area required by photovoltaic (PV) cells, solar concentrators rely on a set of mirrors or moving mechanical structures to direct the light to the concentrator as the sun moves. Solar concentrators have disadvantages since they need to track the sun's position and may be affected by overheating from the concentration of light and heat on the solar cells [9]. The advantages of using volume holographic optical elements [10] are appealing for lightweight and cheap solar concentrator applications and are expected to become an important advancement when integrated into solar panels. [PERSON] et al. [9] presented a review of holographic-based solar concentrators using different materials. The physical principles and main advantages and disadvantages, such as cool light concentration, selective wavelength concentration and the possibility to implement passive solar tracking are discussed. Different configurations and application strategies are also discussed in this study. Unlike solar PV technologies, CSP plants use steam turbines that match conventional electrical generating services. CSP plants can be equipped with fossil fuel systems to deliver additional energy or to produce electricity during the night or when clouds block the sun [11]. There are four types of CSP reflection mirrors: solar power towers, Fresnel reflectors, Sterling dishes and parabolic troughs. CSP can use molten salt to store heat, enabling the generation of electricity for several hours even without sunshine.