## 1 Introduction  
Technology assessment of energy production technologies is often computed as financial cost. The US Department of Energy (DOE) and the National Renewable Energy Laboratory have been aggregating data on cost estimates for electricity generation in an online application, the Transparent Cost Database [1]. In this database, four main metrics exist to assess the cost of, especially, electricity generating infrastructure investment:  
* **overnight capital cost**--combines all the capital cost data without interest (as if built _overnight_[2], computed in $/W;* **fixed operating costs**--including such costs as salaries, general overheads, insurance, taxes [3], computed as $/W;
* **variable operating costs**--including such costs as purchase of consumables (particularly associated with the fuel cycle, e.g., natural gas) [3], computed as $/kWh and;
* **levelized cost of electricity** (LCOE)--total costs (including annualized capital and yearly operating) divided by total energy service production [1], computed as $/kWh.  
Life-cycle \"cost\" metrics are developed in other fields for energy generation technologies. The metrics presented are often variable or incommensurate. In the field of net energy analysis, the _energy return on investment_ (EROI) is often computed, which measures the ratio of the energy in a given amount of the extracted and delivered fuel to the total primary energy used in the supply chain (_i.e._, the energy that is directly and indirectly required to extract, refine and deliver the fuel)\" [4]. For photovoltaic (PV) technologies, the _energy payback time_ (EPBT) is often reported instead, which measures the time necessary for an energy technology to generate the equivalent amount of _primary_ energy used to produce it [5]. Within the field of life cycle assessment (LCA) a different set of metrics are reported, including the _cumulative energy demand_ (CED), defined as the amount of _primary_ energy consumed during the life-cycle of a product or a service [6], and the energy or greenhouse gas (GHG) intensity, defined as the ratio of the primary energy consumed, or CO2 emitted for the construction, operation, and decommissioning, per unit of output of electrical energy over the lifetime of the device [7].  
The author believes that the multitude of different metrics and their incommensurability with financial metrics may be a barrier to more widespread use of physical information for electricity supply planning. This paper will advance the benefits of the computation of metrics for physical \"costs\" associated with electricity production by electricity generation technologies which are analogous to those published as financial cost described above.  
A recent meta-analysis and harmonization project has been carried out by researchers at the National Renewable Energy Laboratory (NREL) and a number of other institutions to determine the distribution in greenhouse gases (GHG) emissions from a variety of electricity production technologies over their entire life-cycle. Methodological details are provided in Heath and Mann [8].  
This paper presents the results of a meta-analysis of the energy requirements of electricity generation via PV, concentrated solar power (CSP) and wind. The process involved a number of stages, including: initial literature search, literature screening, data collection, and commensuration of system boundaries and units.