Renewable-based energy systems have the potential to vastly increase the use of land devoted to energy, thus drastically changing landscapes and habitats, since conventional, fossil-based energy systems use a very small proportion of earth's land surface. Land use affects ecosystems, biodiversity, and geochemical cycles. It also affects people's well-being due to effects on views, noise, recreation, and quality of life. This means strong and transparent metrics to assess land use for energy systems are needed. This review considers some of the most influential papers and metrics in this category, namely ecological footprint, land use intensity and power density, attempting to make them transparent in terms of data used and calculations performed. The literature frequently relies heavily on assessments that are decades old, many dating from the 1980's. The lack of transparency in the methods and even confusion in the units has led to the published metrics being applied incorrectly. Even within the same paper, the calculation is often performed several different ways, leading to errors and confusion on several orders of magnitude. An assessment of land use by major electricity production technologies and fuels as well as an explanation and guide to commonly used metrics is provided.