Power, Energy and the Loads List For your New System

Preparation for any off-grid electrical system, that is, one that isn’t attached to the local or national grid, starts with an assessment and calculation of your energy demands.

A loads list is just a list of all electrical loads that may be employed in the finished system. Everything from lights, to TV sets, to hairdryers, to cell telephone chargers must be included on your list.

You first need to determine the total amount of electricity required by all devices at any given moment, in Watts. You can get a more detailed breakdown  in this book How to Build a Solar Panel.

Power is an immediate measure of electric supply; it’s a rate, not a quantity. A 100 watt light doesn’t consume one hundred Watts, since the Watt isn’t a measure of quantity.

For quantities of electric energy, we use the Watt-hour, shortened Wh, and its Big Bro the kilowatt-hour ( kWh ) which is just one thousand Watt-hours. You could be acquainted with the kilowatt-hour from your electric power utilitybills; it is the energy unit your bill relies on. To finish a loads list, you’ll need to know the Wattage required by each electric device that may be used. The Wattage of light bulbs is simple to get: glance at the labels on the devices. Many devices use power differently at different times; an example is an electrical cooking range. The power needed to operate it and, therefore, how much energy it consumes over time, relies on how many burners are turned on, and to what settings, and whether the stove is on also.

In a similar way, a chiller doesn’t consume a steady quantity of energy but basically cycles off and on during the day. Typically a chiller “runs” about 13-15 hours per twenty-four hour day. The only real way to measure such devices’ energy consumption, is to trace them over time and work out a daily or monthly average. So how will we do that? There are straightforward power and energy meters available that will do this job for you. Such meters are often connected into a wall outlet and the device to be measured is then wired into the meter. Most meters of this kind measure power drawn by the device measured in Watts and energy consumed over time measured in Watt-hours or kWh.

To determine the electricity employed by the refrigerator, plug it into the meter and leave it plugged in for a week or a month. (The longer the period of time, the more correct the average will be). At the end of the period of time, read the display and divide that figure by days and hours. Knowing there are twenty-four hours in a day, you can then establish the median daily, weekly or monthly Wh or kWh energy consumption by easy mathematics. The value of a correct loads list for your off-grid system can’t be overstated. If you are off the grid, you may produce each Watt-hour you need. For instance, if we had substituted an equivalent incandescent light bulb to our CFL above, and left the incandescent on for a similar 66 hours and 40 mins, it might use over four kilowatt-hours of electricity four times the energy utilised by the CFL.

In making preparations for an off-grid electrical system, it totally pays to take the time to gauge or conscientiously guesstimate your intended loads. Not only will you make sure that you finish up with a replaceable energy system that meets your real needs, you’ll often discover ways to preserve energy which decreases the size of the system you will need. A smaller system is a less costly system and a loads list is the most significant tool to get you there.

If you need more help trying to find out how many solar panels you need to power your home or part of it, have a look at this book How to build a solar panel.


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