Clean Energy Facts

Understanding Renewable Energy and Wind Energy Integration

Maui Electric is deeply committed to integrating renewable energy on our grids. This includes wind power from large facilities, biomass energy from Hawaii's last working sugar plantation, hydroelectric power, and photovoltaic ("PV"), mainly customer-sited rooftop systems that create electricity for customer use and send the excess to the grid.

By the end of 2015, over 35 percent of the electricity Maui Electric delivered to our customers came from these renewable resources. We've come a long way and have already surpassed the 2020 Renewable Portfolio Standards goal of 30 percent of sales generated from renewable resources. We realize much remains to be done as Maui Electric continues to do what's right for our community to add even more clean energy in a safe and reliable way.

renewable graph maui
Maui Renewable Projects

PV has grown at a record pace in recent years on Maui and throughout Hawaii. The chart below shows the growth in the total number of customers with PV who are eligible to receive credit for any renewable energy they send to the grid, a program known as net energy metering (NEM). By the end of 2015, there was a 10 fold increase in the number of Maui customers participating in the NEM program in just five years. In fact, more customers installed and interconnected their PV systems to the Maui grid in 2015 than in any previous year.

Maui Electric Cumulative NEM

Hawaiian Electric, Maui Electric, and Hawaii Electric Light are among the top utilities in the nation for solar systems installed per customer. Today, 13% of Maui Electric customers have solar systems installed, more than 20 times the national average of 0.6%.

Wind power is also an important resource on Maui and a critical part of our efforts to reduce our use of imported oil.

The output from Maui's three wind facilities is variable, depending on changes in wind speed and direction (the chart below illustrates this). While our goal is to integrate as much wind energy on our grid as possible, we are also committed to keeping the lights on for our customers with safe, reliable service. To do that, two of the wind facilities utilize large battery storage systems and some Maui Electric firm power generating units are operated to compensate for the wind's variability and to supply the rest of the energy required to meet customer loads.

Effect of Wind Variability on Frequency

Electricity generation must match electricity demand (consumption by end users) at each moment. When the generation being supplied to the system exceeds the amount of electricity being used by customers (also referred to as an "excess energy" situation), Maui Electric first reduces output from some of its oil-fired generating units and may take some of its generating units off-line. However, to maintain reliable service, there are limits on how low the output of firm generators can be turned down and constraints on whether a unit can be taken off-line. After taking these steps, if there is still an excess energy situation, then the amount of generation from an as-available generator, like a wind facility, may need to be lowered, or "curtailed." The amount of curtailed energy is the difference from the available output from the wind facilities, and the amount of energy from the wind facilities that could be accepted.

In accordance with Hawaii Public Utilities Commission Decision & Order No. 31288 (D&O), Maui Electric is providing the following information:

  • the quantity of wind energy accepted per month
  • the quantity of wind energy curtailed per month
  • an estimate of the cost to customers of curtailment by calculating "the difference between the average cost of curtailed wind energy and the average monthly energy cost of MECO's fossil generation."

Maui Electric notes that calculating the actual cost of curtailment to customers is more complex than the calculation defined above. The electric grid could not provide continuous power to customers if firm generation was simply turned off to eliminate curtailment of wind energy. As-available (also known as "intermittent") resources such as wind do not provide all the ancillary services1 that help maintain the stability of the electric grid. In order to reliably integrate more wind energy and reduce wind curtailment, additional costs (such as the cost to modify generators or the transmission and distribution system) over and above the cost of purchasing more wind energy would also be incurred. These additional costs could be more than the potential savings from simply accepting more wind power (identified in the table as Estimated Cost of Curtailment).

The cost of curtailment is expected to increase in the later months of each year because contracts between Maui Electric and two of Maui's wind farms include tiered pricing. The tiered pricing results in Maui Electric purchasing energy at decreasing prices as the cumulative year-to-date quantity purchased exceeds each tier. Because the cost of curtailment calculation shown in the table below utilizes these reduced prices, once the total energy (accepted plus curtailed) reaches the various contractual tiers, the difference between the hypothetical cost of wind energy and the cost of fossil generation widens.

Savings realized by electric customers due to the purchase of wind energy have also been added to the table below. The methodology is consistent with the calculation of the cost of curtailment, and represents the difference between the actual cost to purchase the wind energy and the estimated cost to produce that energy using traditional fossil fuel based generation.2

2017
 WIND ENERGY ACCEPTED (GWh)EST SAVINGS FROM WIND ENERGY PURCHASED ($000)WIND ENERGY CURTAILED (GWh)ESTIMATED COST OF CURTAILMENT ($000)
Jan 14.6 -1,072 0.9 -103
YTD 14.6 -1,072 0.9 -103

Baseline (2013)
 WIND ENERGY ACCEPTED (GWh)EST SAVINGS FROM WIND ENERGY PURCHASED ($000)WIND ENERGY CURTAILED (GWh)ESTIMATED COST OF CURTAILMENT ($000)
Jan 11.3 694 5.8 89
Feb 22.3 1,536 14.8 193
Mar 10.7 510 3.5 18
Apr 10.8 559 1.2 29
May 15.0 743 3.5 23
Jun 30.9 1,788 7.3 -20
Jul 24.2 901 2.7 99
Aug 30.9 1,382 2.4 99
Sep 27.4 1,368 2.7 449
Oct 15.0 617 0.7 112
Nov 16.1 761 1.0 178
Dec 15.8 924 1.2 206
YTD 230.3 11,783 46.7 1,475


Note: Totals may differ from the sum of individual amounts due to rounding. To view complete monthly data beginning with 2013, please click here.

In addition to providing this information, the PUC required Maui Electric to submit a System Improvement and Curtailment Reduction Plan by September 3, 2013. That plan includes specific system improvement measures, estimated cost of the measures, impact of the measures on curtailed wind energy, and the net benefit, of implementing the measures. A copy of the plan can be found here. In August 2014, to comply with a PUC order, Maui Electric submitted a Power Supply Improvement plan ("PSIP"). A copy of the PSIP can be found here.


1Ancillary Services are those services provided by generating resources that help maintain the stability and power quality of the electric grid, including frequency and voltage regulation. Ancillary Services include the ability to commit; dispatch and control from moment to moment the output of a generating unit; the ability of a generator to provide reactive power to control voltages; the ability of the generator to follow load to help balance supply and demand to regulate frequency; the ability of a generator to provide operating reserves - upward reserve in the event of the sudden and unpredictable loss of output from another generator or downward reserve in the event of a loss of demand from the system (such as if distribution circuits unexpectedly trip out of service due to a motor vehicle accident); and the ability of a generator to provide supplemental service (the ability to start up and shut down as needed to serve demand in event other generation is not available). Although not defined as an ancillary service in most utility jurisdictions, in island electric systems such as Hawaii's a generating unit's ability to "ride through" an unstable condition on the electric grid without tripping off line is also an important characteristic necessary to help maintain the stability and power quality of the electric grid.

2The estimated savings from wind energy purchased by Maui Electric is calculated as the difference between monthly payments to the wind farms for wind energy delivered and the estimated average monthly cost of Maui Electric's fossil generation had that energy been produced by Maui Electric units. The same average fossil fuel cost used in the cost of curtailment calculation is applied to the wind energy accepted to arrive at the cost of fossil generation.