Load evaluation

The load evaluation involves gathering information on loads which will serve as the basis for the rest of the system design process. Power ratings and usage estimates for necessary and potential loads are gathered into a table - one for direct current and one for alternating current. Usage will be estimated in this chart on a monthly basis so that it can be easily used in the load and solar resource comparison if necessary. The monthly total is typically calculated by estimating weekly usage and multiplying by 4 to get a monthly total. This process works well for loads that are used only occasionally, but it is necessary to be careful if a load is used for consecutive days, for example during all 5 business days of the week. These loads should be treated as operating 7 days out of the week as removing 2 days a week from will reduce the average energy requirement, but in reality the system will be required to store and generate the full energy requirement on most days.

When designing any system it is almost always necessary to explore various different designs with varying loads and usage patterns to arrive at the best balance between cost and budget.

Additional considerations

• The make, model, and power rating of any loads currently present at the site should be documented. Photos can be invaluable later on.
• If the system design is going to incorporate loads that have not yet been purchased, guidance should be provided about the value and importance of purchasing energy efficient loads.
• This process can be difficult in locations that do not currently have electricity or that have users that do not have experience with electricity beforehand. In these cases there is a tendency to over-estimate and under-estimate appliance usage depending on the individual. In these cases, more responsibility falls upon the person performing the load evaluation and the system designer to provide guidance and accurate estimates.
• Potential projects that do not currently have an electrical system will also require additional evaluation and design work to ensure that the building will have adequate outlets for (power receptacles) and lighting for the intended use of each room.

DC load evaluation

Typical direct current loads include lights, cell phones, radios, and DC refrigerators. If a system incorporates an inverter, it is important that its idle consumption is included in the DC load evaluation.