Calculating Power and Energy Needs

It is absolutely necessary that you go through the tedious task of identifying what your power and energy needs are likely to be, and consider your tolerance for the worst case scenario. It is important to note that people use energy, not homes. Your tolerance for heat, your usage of water, your desired lighting levels, your usage of entertainment appliances, and the amount of convenience you demand are all behavioral issues that dramatically impact the size of solar energy system you need. In fact, the way occupants use electricity is just as important as the appliances, devices, and lighting that you select.

This calculation process involves using a worksheet to identify every power consuming appliance and device in your home and determining how long each will be consuming power. Remember, energy is power over time. We need to determine the maximum power consumption at any given instant and the energy needs over time. We can then take into consideration how much solar power generation is necessary to meet your needs and how much inverter power will need to be installed. The battery is sized with the solar and inverter ratings in mind, and is primarily determined based on how long you can go without recharging.

It is very common to realize that the initially proposed power and/or energy needs are unrealistic, and changes need to be made to either the home or expected behavior before the system is installed. It is also common for owners to forget or ignore the limitations that result from the initial calculations. They tend to add power loads to the home and get lazy with turning off lights and fans an unplugging laptops and chargers. Don’t fall into this trap, and be realistic when going through this exercise. Over-sizing things from the start may be advisable, especially batteries which are virtually impossible to upgrade once installed without buying a whole new battery system.

Off-Grid Energy Needs Calculation Worksheet
A simple spreadsheet can be used to calculate your total power and energy needs.

If you refuse to go through this step, be prepared to hand over $1 million and I’ll be happy to install a solar energy system that will meet your every expectation, whim, and desire. I’m joking, but I can’t stress enough how this step will both save you money and ensure your satisfaction with an off-grid experience. This process is usually done by your engineer, but they will need feedback on how you intend to use the home. Your solar dealer/consultant can also help. However, in the end it is your responsibility to live within the parameters of the system, and deal with the results if you choose to ignore them.

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