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Residential Battery Systems and the Best Time to Invest A case study of Hawaii

Battery storage is a complementary technology to intermittent renewable energy sources. In particular, it pairs well with solar photovoltaic (PV) systems to capture excess solar generation during daylight hours and to draw energy from it when needed. Technological advancements and rapidly declining costs have made batteries more economically feasible for households, especially in the state of Hawai‘i, which faces the highest cost of electricity in the U.S. With the sunset of net energy metering (NEM) in 2015, and technical limitations from interconnecting additional PV systems capable of exporting energy to the grid, non-exportable PV systems are increasingly a viable option for residential customers in Hawai‘i. This paper analyzes whether the installation of a PV plus battery system is economically compensatory for households on Oahu, with the power grid as a back-up option. Given the importance of state and federal tax incentives in reducing capital costs, this paper compares household savings in the decision to invest now or later, given that the federal tax credit of 30% is set to decline in 2020 and expire by 2022. Installing a PV plus battery system in 2019 could increase net savings by 17-32% in Oahu compared to installing the same system in 2017.

Working Paper


Estimating the Opportunity for Load-Shifting in Hawaii: An Analysis of Proposed Residential Time-of-Use Rates

Hawaii’s largest electric utility, Hawaiian Electric Company (HECO) and its subsidiaries recently proposed a Time of Use (TOU) pricing scheme for residential rates. The TOU scheme has three tiers of prices: daytime, on-peak, and nighttime. The proposed rates have the highest cost during the on-peak period from 5pm to 10pm. For Oahu, the lowest cost is at nighttime, from 10pm to 9am. The difference between high and low rates is $0.33/kWh. For Maui and Hawaii Island, the lowest cost is during the daytime, 9am to 5pm. The difference between high and low rates are $0.35/kWh and $0.50/kWh, respectively. It is not stated whether the rates will be implemented as an opt-in, opt-out or mandatory program. This report summarizes literature on time varying pricing for residential rates to inform Hawaii’s electricity stakeholders, including ratepayers and policy-makers, of the potential impacts and considerations regarding the potential for TOU pricing in Hawaii.

Working Paper