BLOG POSTS ARE PRELIMINARY MATERIALS CIRCULATED TO STIMULATE DISCUSSION AND CRITICAL COMMENT. THE VIEWS EXPRESSED ARE THOSE OF THE INDIVIDUAL AUTHORS. WHILE BLOG POSTS BENEFIT FROM ACTIVE UHERO DISCUSSION, THEY HAVE NOT UNDERGONE FORMAL ACADEMIC PEER REVIEW.
By Nori Tarui and Pratistha Gyawali
Introduction
The dashboard illustrates Hawaiʻi’s residential electricity usage based on the 2019 Residential Energy Use Survey, a residential appliance saturation survey conducted by Hawaiian Electric Company. UHERO applied the conditional demand analysis (CDA), which is a statistical method to estimate average annual consumption associated with each appliance based on survey responses about their appliance holdings and household characteristics combined with customer energy billing. For example, we can estimate the electricity usage for a split AC unit by comparing average consumption of households with different numbers of split AC that are similar otherwise. The study is conducted by UHERO in consultation with HECO. CDA makes it possible to break down the total household demand of electricity into component demand functions, each of which corresponds to a specific appliance.
Survey Design
The survey consists of questions on monthly energy usage, photovoltaic systems (PV) information, weather data along with the different types of appliance ownership and household socioeconomic status. It has 2,992 qualified responses from residential households on Oʻahu, Maui, Lanai, Molokai, and Hawaiʻi Islands (out of a 11,000 random sample from 324,137 study population of those residential customers with average usage between 100kWh per month and 2,000kWh per month).
On energy usage, the survey comprises data on the billed energy of households. The net energy is calculated by taking the difference between the energy that has been supplied by the Hawaiian Grid and the energy that Hawaii Electric has received from customers’ solar PV. An important aspect of the project is the inclusion of households with PV. The most important variable for the study, estimated actual energy is the net energy in addition to the estimated PV production energy, which is simulated by Hawaiian Electric based on the historical solar irradiance.
Family size, household head’s age, work status, educational background, household income etc. come under household socioeconomic status. The average temperature, average heat index and sum of the cooling degree days (CDD) are provided for the billing period for the seven weather stations across the islands. CDD is the number of degrees that a day’s average temperature is greater than 65 F and thus measures the demand for energy required to cool buildings.
In order to apply statistical analysis, the sample data is weighted in two steps. The first weight calculation is done by the survey respondents’ age in the various islands while the second weighting is by PV and non-PV systems.
Summary
The pie charts represent each appliance group’s share of the total household energy usage by household type. Here, the total energy represents gross energy consumption, which is the sum of net energy and PV production.
In the sample households across all islands served by Hawaiian Electric, refrigerators have the highest share of the total household energy, which is about 21.4 percent, followed by electric devices (18.6%) and water heating (17.9%). Across all sample households on Oʻahu, refrigerators still have the highest share of the total household energy usage (22.5%) followed by electric devices (20.9%). In Maui County, refrigerators and laundry are both the highest usage of total household energy, 23.4% and 23.3% respectively.
Substantial differences exist between the households with PV and those without PV. In both single-family and multifamily households (i.e., households living in multifamily housing such as apartments) without PV, refrigerators have the highest usage of total household energy. However, in single-family households with PV, water heating is associated with the highest energy (26.3%) compared to refrigerators (20.5%). The total energy share of laundry is also higher in single-family households with PV as compared to those without PV. Households without solar PV are more conservative in their energy usage as compared to the households with PV. The additional energy from the PV sources have enabled households to use energy more liberally.
In the case of sample households on Oʻahu,, water heating, laundry and refrigeration have a larger share in the total energy usage in single-family households with PV than in single-family households with PV. However, the share of usage of electric devices in single-family households without PV is higher than that of single-family households with PV. For multifamily households without PV, the share of energy usage by cooling equipment, i.e., AC and fans is the highest. This might be because of larger family size and possibly more limited air venting associated with apartments and condominium units.
If you click or tap each pie chart, you will see a table of annual average electricity usage by electric appliance. (Move your mouse over each bar and you will see the annual usage in kWh for each appliance.) The tables show in detail which appliances are associated with most energy usage. Electric water heater, AC, having multiple refrigerators, and having an electric vehicle are all associated with substantially high electricity usage relative to other appliances.
What explains the difference in the energy usage between households with and without PV? Is it because households with larger energy usage are more likely to install solar PV, or is it because residents change their behavior and consume more energy once PV is installed? The answer may be a mix of both. Further data will be necessary for us to investigate these questions. UHERO will continue working with Hawaiian Electric to study the household-level impacts of Hawaiʻi’s decarbonizing energy transition and what it means to the State’s economy.
The finding is based on a contract with a funding from Hawaiian Electric. All views expressed here are the authors’ and do not represent the opinions of Hawaiian Electric.