A common problem is to forecast the aggregate of several time periods of data, using a model fitted to the disaggregated data. For example, you may have monthly data but wish to forecast the total for the next year. Or you may have weekly data, and want to forecast the total for the next four weeks. If the point forecasts are means, then adding them up will give a good estimate of the total. But prediction intervals are more tricky due to the correlations between forecast errors.
Electricity is produced by a variety of generating units, each with different lead times and costs to be readied for service, and production costs once brought online. Because electricity is a commodity that cannot be easily stored, generation should match consumption at any given time; therefore, the cost of generating electricity has a direct relationship to electricity demand, typically referred to as electricity load. An accurate load forecast enables generators to optimize the mix of generating units that can serve the expected load while minimizing the production costs. This holds true for generators in both regulated and deregulated markets. In several deregulated markets, the electricity market operator is in charge of dispatching the available generation units according to the market's expected load and individual units' offered generation costs.
Forecasts of how much oil and gas could be produced by the UK offshore industry have been revised upwards. The industry regulator now believes 11.9 billion barrels will be extracted by 2050, up from an estimate of 8 billion four years ago. So far 43 billion barrels of oil or its gas equivalent have been extracted from UK waters. The new prediction is driven by lower production costs, technical advances and 30 new fields coming on stream. Estimates of oil and gas potential have been part of the debate about the financial situation facing Scotland should it become independent.