Distributed Generation Impacts on the Island of Lanai in Hawaii
Client: National Renewable Energy Laboratory
National Renewable Energy Laboratory (“NREL”) contracted Pterra to conduct an island-wide system-level integration study to determine the impact of additional photovoltaic (“PV”) systems of varying size and locations being installed on Lanai over the next few years.
Pterra conducted several technical studies including power flow, short circuit, protection coordination, angular and voltage stability, frequency regulation, system operation and limitations, harmonics and power quality, transient overvoltage and ground-fault overvoltage. Each of these studies provided a unique look at the levels of PV penetration that may lead to undesirable reliability impacts and costly system reinforcements.
The key finding of the study is the critical impact on frequency response of new PV generation. The study system is shown in Figure 1. The existing electrical supply comes from: L7, L8 and CHP – conventional diesel units, and LSRPV – PV units. The existing PV includes a battery to provide support during low-frequency conditions. The generators provide power to a peak load of about 4,200 kilo-watts, with a day-time minimum of 2,300 kilo-watts. An additional 800 kilo-watts of new PV was considered for the study.
Figure 1. Existing Generator Locations
With the new PV in service, the option to operate with fewer diesel units is available. However, this dispatch mode results in a reduced spinning reserve. The study simulations show that the system voltages collapse after applying a contingency. The voltage plot is shown in Figure 2.
The result of the analysis is an operating requirement to continue to operate an extra diesel unit for spinning reserve purposes. This had an immediate consequence on the economic benefit of the new PV, as the non-power related costs of the extra diesel unit offset the savings from use of solar energy.
The other technical tests did not identify any other constraints on the 800 kilo-watts of new PV.