How much energy you need is purely dependent on your energy usage. Thanks Einstein.
Well- most of us don’t know exactly how to calculate that energy usage, and it is critical when you begin considering the size of your power system, and particularly if you are having battery backup, the size of your batter backup system.
To make this calculation, there are few things to consider. How many appliances will be running simultaneously? Will there be time for your batteries to recharge between using high energy appliances? Do you have it in your budget to buy some lower wattage versions of the same appliances? Are you willing to replace your incandescent bulbs with much lower fluorescent bulbs? Are there passive systems (i.e. sunroofs to open for cooling, passive solar heating, southern facing windows etc.) that you can utilize more effectively to reduce the amount of energy you use?
Once you’ve thought these things through, calulate based on the following notion. List each electrical device you will use. List their wattage, hours of daily use, and days used per week. Multiply that all together for each appliance and add your usage together. This will give you an overall picture of your weekly power needs.
From there, determine the size of your generating needs. Do this based on how much power you will need boht in the winter and summer (less important if you’re using micro-hydro, but very important if you’re using solar). Then determine the size of the battery bank. Doing this with complete accuracy requires more calculation than I’m prepared to provide now. However, a good rule of thumb is to base it on the number of days of stored battery power you will need multiplied by your average daily usage.
Energy Usage
In order to calculate your daily energy usage, it is useful to know the wattages used by various appliances. A brief list follows.
| Appliance | Continuous Watts Used |
| Desktop Computer | 90 |
| Laptop Computer | 24 |
| Average Computer Monitor | 50 |
| Microwave | 1400 |
| Coffee Maker | 900 |
| Toaster | 750 |
| Blender | 350 |
| Mixer | 120 |
| Television | 50-200 |
| Stereo | 25 |
| Vacuum | 600 |
| Clothes Dryer | 300 |
| Iron | 1200 |
| Dishwasher | 740 |
| Clothes Washer | 150 |
| Room Air Conditioner | 1000 |
| Central Air Conditioner | 2000-5000 |
| Large Fan | 10-50 |
| Water Heater | 500 |
| Evaporative Cooler | 400 |
| Space Heater | 1500 |
| Incandescent Bulb | Wattage Listed on Bulb |
| Fluorescent Lighting | ~1/3 Equivalent of Incandescent |
