System Design and Sizing

Data needed for system design

This refers to designing an 'Off-grid' system. Designing a grid-connected system requires a somewhat different approach. We first need to know:

Details of the load

• The type of equipment you need power for and what is the purpose of the equipment
• The system voltage

And for every piece of equipment:

• Its power rating or current
• The hours per day it must run
• Whether the use varies from day to day or month to month

If precise data is not available, some reasonable estimates should be made

Details of the site

• Location (latitude, longitude or name of the nearest town and how far)
• We have extensive weather data for the world, averaged over at least 10 years
• Note that single year data is not useful as it does not include year to year variations
• Details of any nearby objects that can cast shadows (or limit the area available for the photovoltaic modules) Any special 'microclimate' details (e.g. a site that experiences regular fog or mist)

Details of required reliability / lifetime etc

Often it is enough to know the type of system (telecom, navigation aid, domestic house, etc), but other important aspects are:

• How long between intended service visits?
• How long the system should continue to operate if it sends an alarm message that something is wrong?

Read on for system design choices...