MathProg is a special purpose programming language that allows to formulate mathematical optimization problems. Its syntax closely follows the mathematical notation, allowing for a close correspondence between mathematical description and code.

• SOforSG.mod (Storage Optimization for Smart Grid) is a minimal example of a linear optimization problem, dealing for dimensioning and operation of a lossless energy storage. Its goal is to minimize operational costs of the household for energy purchase. For brevity, the model is quite minimalistic.
• StockCutting.mod
• Try TODD online: Knapsack problems with variable size
• Try DHMNL online district heating network optimization problem (MILP) with fixed/variable investment cost tradeoff.
• More MathProg energy models on GitHub.

• ojdo.org GLPK online, solve (small) optimization models directly in the browser; my personal instance of cocoto's GLPK online, using glpk.js by hgourvest.
• Operations research with GNU Linear Programming Kit (PDF). Sottinen, Tommi (2009). ORMS1020 course notes. Department of Mathematics and Statistics, University of Vaasa, Finland.
• Modeling Language GNU MathProg (PDF) Language Reference, Draft Edition, for GLPK Version 4.34, December 2008.
• GLPK for Windows hosts binaries of GLPK.