At community scale, the energy systems of individual buildings can be interconnected into a microgrid: a local network of generation, storage, and loads that operates either connected to or independent of the utility grid. Community microgrids offer significant advantages over individual off-grid systems: battery storage can be shared across multiple buildings (reducing total storage requirements), generation can be distributed across a larger area (improving total solar harvest), and critical loads can be prioritized during low-generation periods.

The design of a community microgrid requires careful attention to protection, control, and metering systems that are more complex than single-building off-grid systems. Shared governance structures must also be in place to manage shared energy resources equitably. When well-designed and managed, community microgrids provide greater energy security and lower cost per household than individual off-grid systems, while maintaining full independence from utility infrastructure.

Review Questions

1. What is a load analysis and why is it the essential starting point for off-grid energy system design? What information do you need for each electrical device to complete a load analysis?

2. How are peak sun hours used in sizing a solar PV array? If a site has 5 peak sun hours per day and a building needs 4 kWh per day of electricity (after system efficiency adjustments), approximately how large should the PV array be?

3. Compare lithium iron phosphate batteries and lead-acid batteries for off-grid storage. What are the key advantages of each technology?

4. What is the function of a charge controller in an off-grid solar system? Why are MPPT controllers preferred over PWM controllers?

5. What are the advantages of combining solar PV with wind generation in an off-grid system? What site conditions are necessary for wind turbines to be a viable contribution to the energy system?