The Energy Balance
Earth gets all its energy from the Sun and loses energy into space if more energy is lost into space than is received from the Sun, the planet gets cooler. If it loses less energy than it receives, the planet will warm up. Have you noticed that it is often cooler when there are clouds in the sky? Some types of clouds act like giant sun umbrellas, shading the Earth and reflecting the sunlight that hits them. Other types of clouds act like a jacket, holding the heat in and preventing it from leaving the atmosphere.
Today, most clouds act more like a sun umbrella and help keep our climate cool. However, this could change if global warming affects the type of clouds, their thickness, and how much water or ice they contain. While it might be quite warm in the countryside on a summer day, it can get unbearably hot in a nearby city! That’s because the buildings and pavement in cities absorb oodles of sunlight, much more than the countryside. These cities are called “heat islands.” The countryside is also cooled by water evaporating from lakes and given off by the plants in forests and fields. Cities have fewer plants and bodies of water and so are not cooled very much by evaporation.
An energy balance of a region (or country) is a set of relationships accounting for all energy which is produced, transformed and consumed in a certain period.
This basic equation of an energy balance is: Source + import = export + variation of stock + use + loss
Consider a primary energy balance.
- Sources are the local (or national) primary energy sources, like coal, hydro, biomass, animate, etc.
- Imports are energy sources which come from outside the region (or country).
- Exports go to other regions (or countries).
- Variations of stock are reductions of stocks (like of forests, coal, etc.), and storage.
- Use can be specified sectoral, or by energy form, or by end-use, etc., as required.
- Losses are technical losses and administrative losses:
- Technical losses are due to conversions and transport or transmission
- Administrative losses are due to non-registered consumptions.
Energy balances can be aggregate, or very detailed, depending on their functions. They can also be elaborate, showing all sorts of structural relationships between energy production and consumption, and specifying various Intermediate forms of energy. An energy balance can also be set up for a village, a household, a farm, or an agricultural unit. It will show the inputs of energy in various forms, the end-use energy, and the losses. Specific for energy balances of agricultural systems is the fact that parts of the outputs of the system are, at the same time, energy Inputs into the system (agricultural residues, dung). Energy balances have to be built up from surveys of what is actually going on. This requires energy resource surveys, and energy consumption surveys, as well as more technical energy audits.
Section 12 goes into some aspects of energy auditing. Energy balances provide overviews, which serve as tools for analyzing current and projected energy positions. The overviews can him useful for purposes of resource management, or for indicating options in energy saving, or for policies of energy redistribution, etc. However, care must be taken not to single out energy from other economic goods. That means that an energy balance should not be taken as our ultimate guide for action. Energy data are to be translated into economic terms, for a further analysis of options for action. And, of course, socio-cultural and environmental aspects are equally important.
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