We’re recently gone through the exercise of energy return ratios for photovoltaic (PV) energy generation, as we had yet another ‘expert engineer’ and ‘LEED data center expert’ claim that photovoltaic sources never paid back the amount of energy based on their production. Statements like this were common in the 1980’s, 90’s, and even early 2000’s. Although the quality and efficiency of early photovoltaic mass production releases were lacking, modern PV energy production returns far more energy than embodied in the production and use lifecycle of the system.
Currently the energy return on PV systems is between 6 months to two years. There is a lot of dependence of performance on the location, technology, and other factors such as weather. With the life expectancy of the systems to be 30 years or more, the ratio of energy return can be from 15-to-1 to over 60-to-1. This means that the energy captured via is 15 to 60 times more than the energy required to collect materials, manufacture, install, and maintain the systems.
The creation of PVs begins with the extraction of the raw materials, mining for elements such as quartz sand for silicon, copper, zinc, and aluminum for thin-film semiconductors and other resources needed. The process energy for each to be refined is included, such as the significant amount of energy for an arc furnace to reduce the quartz sand to metallurgical-grade silicon, which is then further purified into solar-grade silicon (at 99.9999% purity). Other types of PVs might require cadmium, indium, gallium, or tellurium which can come from zinc or copper smelters, mining, or other production processes followed by further purification for solar-grade purity.
All the raw materials and processes are included in the calculations no matter the component. Silica for the glass, copper or aluminum for conductors, and iron and zinc for the mounting and structural supports. Each does require a substantial amount of mining, transport, and production energy that cannot be ignored or minimized. Then the manufacturing of the solar cells, modules, electronics, and more added into the total energy for production. The installation, degradation, and maintenance are also factored into the total life cycle energy cost, which accounts for equipment defects and damage from any number of sources such as weather, vandalism, or loss of performance from lack of cleaning. The last portion is the eventual decommissioning, recycling, and disposal of all the components involved in with the PV, in a realistic manner considering that many components may not be acceptable for reuse or recycling.
The equation for the energy payback is all the above energy to create the PV along with installation and dismantling divided by the amount of energy generation. To obtain a ratio of 15:1, the amount of energy produced will need to be fifteen times greater than all of the energy involved to allow the PV to exist in a location for an amount of time. By dividing, the time then falls out to 2 years for a 15:1 ratio, 1 year for 30:1, and 6 months for 60:1.
Note that much of the electrical production numbers are taken in a conservative fashion, accounting for a higher-than-average amount of cloudy, storm, or other weather conditions that reduce the amount of solar irradiation over a given period. The calculations also allow for more losses through the electrical equipment, such as inverters and transformers, than is normally accepted by modern industry standards for buildings whether they are data centers or not. The reason is that most manufacturers would rather understate the performance by a modicum to have a greater chance of exceeding their calculations.
There are a number of studies with differing estimates and therefore numerous results, which is why such a large range is given here. There are divergent views on what is to be included in the calculations, how much to include in the degradation or losses, irradiation amounts, lifetime and more. Fortunately there are guidelines published by energy agencies to help get to a common understanding and comparison of the calculations across the industry, such as at the International Energy Agency (Solar PV – Analysis - IEA). It should be noted that none of the modern (post 2020) literature, studies, papers, or articles agree that PVs never pay off and to reject a modern PV project because of such outdated information should be refuted vehemently.
