Off grid systems are sized based on the energy demand of the appliances to be connected: systems are sized to meet the power and energy needs of the user. The system designer must therefore go through a load assessment process to understand the needs of the user.

Load assessment is critical. Undersized systems will not deliver what they are expected to deliver. Many systems have failed over the years not because the equipment has failed or the system was installed incorrectly, but because users believed they could get more energy from their system than what the system could deliver. The systems failed because the users were unaware of the power and energy limitations of their systems.The problem is that the user may not want to spend the time determining their realistic power and energy needs which is required to successfully complete a load assessment form. They just want to know: how much for a system to power their lights, fridges and and TV.

Load assessment consist in listing the appliances that will be connected and, record on the load assessment worksheet the quantity of each type of appliances, its wattage and the hours it will be in use every day. It is necessary to repeat the operation both for AC and DC loads. As a result from the load estimate, total AC watt and watt-hours is obtained, and, the same for DC loads.

Watt rating of equipment can be found on its name plate either directly or by multiplying the volt and amperes rating which are provided when the watts are not. Watt-hours are obtained by multiplying watt by usage time.

over sized systems will cost more than necessary.This step of the design process is the occasion for the designer to find out where energy is wasted and propose energy efficient alternatives. The goal of energy efficiency is to reduce energy consumption without affecting users comfort. It offers the possibility of reducing the size of the system and therefore its cost. Lower energy consumption comes with low consumption equipment or a smarter use.

At the end of the load assessment you should had have identified DC and AC loads; you should also have determined DC and AC appliances contribution to the load demand, this the total watt for each type of appliances the last you should determine is the energy demand for each type of appliances.