## Order Of Magnitude Estimates

In terms of energy consumption, production, supply, and demand, estimates are needed and an order of magnitude calculation will suffice. By order of magnitude, we mean an answer (one or at most two significant digits) to a power of 10.

EXAMPLE

How many seconds in a year? With a calculator it is easy.

365 days * 24 h/day * 60 min/h * 60 s/h = 31,536,000 s, an answer to five significant digits

When you round to one significant digit, this becomes 3 * 107 s. For two significant digits, the answer is 3.2 * 107 s.

Order of magnitude estimate: Round all input to one number with a power of 10, then multiply the numbers and add the powers of 10. So without a calculator, the above becomes:

4 * 102 * 2 * 101 * 6 * 101 * 6 * 101 = 4 * 2 * 6 * 6 * 105 = 288 * 105 = 3 * 102 * 105 = 3 * 107

If you have trouble with powers of ten, please consult the instructor.

## Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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