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National Renewable Energy Laboratory (NREL) Study and Analysis

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Study Objectives:

An NREL study was completed to estimate the energy savings of the Bosch DC microgrid over conventional AC systems. The study examined the system performance of the DC microgrid for several key metrics, including annual grid energy, system energy efficiency, and PV utilization fraction, for several commercial building types under a variety of operating schedules in locations across the United States. NREL analyzed the energy performance of both uni-directional (basic) and bi-directional (advanced) versions of the Bosch DC microgrid in high bay LED lighting applications for several typical scenarios.

NREL Results:

  • The Bosch DC microgrid uses generated PV energy 6%–8% more efficiently than traditional AC systems.
  • The improvement in PV utilization was slightly higher in cloudy climates because the DC microgrid reduces—or, in the unidirectional case, eliminates—inverter operation at inefficient part-load ratios.
  • The DC microgrid used grid electricity slightly more efficiently than the baseline AC case.
  • The DC microgrid resulted in lower site energy intensity compared to AC baseline (greatest in hot-humid climates).

NREL Link: NRELStudy

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Center for Advanced Life Cycle Engineering (calce) Reliability Benefits and Validations

In a recent CALCE study comparing the reliability of lighting electronics, capacitors were found to be the weakest link. However, the study determined that the capacitors typically used in DC lighting are at least 2 times more reliable than the large, electrolytic capacitors typically required for the rectification stage in conventional AC lighting.

  • Longer life for DC loads due to less frequent failures from power electronics
  • Centralization of power conversion from AC-DC at the power server rather than each individual load
  • Lower operations and maintenance and replacement costs over the life of the system.
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