Technical design of mini-grid systems is relatively straight forward compared to other steps in the mini-grid development process.
Technical software exists allowing systems to be designed to meet existing and projected demand (see section on Demand Assessment). The key is to ensure that the design is carried out by technicians with skills and experience in the relevant technology in planning, installation, commissioning, operation and maintenance.
Power generation and distribution systems can deliver either AC or DC power. Nano-grids supplying DC power typically use small PV-battery systems without inverters, which reduces the cost but limits the viable area of coverage for each nano-grid. Renewable AC power mini-grids may use hydro, biomass, PV/PV-hybrid or wind systems to generate electricity. Both AC and DC systems need proper monitoring and control systems to collect data and manage the grid.
The guiding principles for technical design are that the mini-grids should be
Up-scalable (not necessarily for hydropower and DC mini-grids); and
To make the systems as safe as possible, they should at a minimum be designed to comply with electrical codes and standards in the relevant country.
This includes standards for frequency and voltage levels.
The systems are deemed 'adequate' if they deliver the pre-defined quality of service and quantity of electricity to customers according to the business model (see section on Quality of Electricity Services).
The systems are up-scalable if they can meet demand growth at reduced life-cycle cost and they are efficient if the electricity service is provided at the lowest cost possible.
Power generation systems are sized to meet demand.
Sizing also has to take account of constraints such as available renewable resources, available funding and environmental restrictions. These are usually defined in the environmental social and impact assessment or resource usage rights and may include limits on the use of water, biomass or diesel, or noise and emission restrictions.
The distribution grid systems will require site visits by the design team in order to tailor the design for local conditions (eg ground conditions, wind strength and lighting incidence).
Customer connections, indoor electrical installations and metering will also need to be considered by those designing the mini-grid system.
There are often local codes and standards for connections and indoor installations which need to be incorporated into any design.
The choice of metering technology will depend on the tariff and business model.
Case study of a government owned, privately operated, solar PV hybrid mini-grid in Senegal