Off-Grid Electrical Sourcing Options Over the years, we (outdoorsmen) have become accustomed to the many creature comforts of modern life. Whether it’s watching TV or a movie, talking or texting on our cellphones and PDAs, or simply making a morning cup of coffee, all of these devices have one thing in common, they requireelectrical power. In off-grid situations, the challenge is; how do we generate, store, and make available electric power. This series of articles will provide the basic concepts required to provide a steady and reliable source of power no matter where the need is
Continuing on with our series on discussion of Electrical Sourcing, we will now discuss how to properly size your battery bank.
The first step is to calculate how much electricity you use each day. To do this, you must meticulously calculate amp usage consumed by each item and multiply it by the time the load is energized (AH – Amp Hours. The actual wattage consumed is listed on that item’s label. Some average examples are shown in the image on the left. Divide that amount by 120 to calculate the amperage consumed (at 120Vac). To calculate the AH consumed by the item being powered, multiply the item’s amp rating by the number of minutes it is being used (on) and divide that result by 60. Accumulate all of the amounts calculated for everything in a 24hour period to get a daily total.
Once you have that amount, the next step is to calculate the battery bank size typically required. To calculate the battery bank size typically required, multiply the total AH (Amp-Hours) calculated in the first step by 3.75 to estimate the battery bank size to install to satisfy the requirements for a single day. If you want the battery bank to last for two days, double that battery bank size, and so forth.
If your power consumption is not evenly spread between charge cycles, the battery bank may need to be increased by 50% or more.
Summary Example: On the following page, is an example of a worksheet you need create using the steps discussed above Green Line Items are inserted by the user as required and Red items are calculated automatically according to electrical formulas. After you have included all of your line items, the daily amperage consumption will be totaled and the required Battery Bank Sizing will be available. In this example parallel 48Vdc battery banks were used. Remember, depending on your demand levels, this amount may need to be increased by 50-100%.
In the next issue of CAM Okeechobee, we’ll discuss how to properly design, use, charge, and backup your battery bank.
