In an Aug. 2 Renewable Energy World article, we reported “Achieving 100 Percent Residential Renewables in Hawaii with Solar+Multi-Storage” since April 2017, 500 hours off-grid and 220 hours grid-tied, using Tabuchi Electric hybrid solar inverter with single embedded battery (10 kWh) and an ROI of three years. The best month was September 2017 with 709.5 hours off grid and 10.5 hours grid tied using dual embedded battery (20 kWh), and grid tied was only used to recharge the multi-storage devices on rainy or cloudy days.

When the Sept. 20, 2017, Puerto Rico Hurricane Maria caused loss of centralized utility grid-tied power and created all the difficulties with delays to restore grid-tied power to everyone, the importance and severe need for achieving 100 percent renewable energy for single and multi-unit residential homes with island nano-grid (off-grid) operation became very clear. Because of our reported case study demonstration of island nano-grid operation using the Solar + Multi-Storage system, on Oct. 16, 2017, Tabuchi Electric donated 10 systems to be installed in Puerto Rico and the neighboring islands.

Many families are still without power and running water after seven months. Deaths related to hurricane Maria keep climbing and are estimated to be over 1,000 today due to generators running out of fuel overnight causing lifesaving equipment to lose power.

As of a few weeks ago, Tabuchi had installed about 40 of their systems throughout Puerto Rico — as shown in Fig.1 — with 50 percent initially installed for off-grid operation until grid-tied power could be restored. Today about 70 percent of Tabuchi Electric systems are grid-tied and only 30 percent remain off-grid. Fig.2 shows an example of an isolated remote family home installing the Solar + Multi-Storage system for off-grid operation.

Figure 1: Tabuchi 40+ Solar+Multi-Storage system installations in Puerto Rico.

This is one of the donated off-grid systems that went to a family in remote Maricao, Puerto Rico, whose house has been without power for 20 years since hurricane George struck in 1998. The electric power was never restored to their area, according to Tabuchi. Fig.3 is a photo of Edison Rivera standing in his living room with the light on for the first time powered by non-fossil fuel consuming generator since 1998.

So the Tabuchi system can perform as an off-grid distributed power supply which is resilient against natural disasters as currently being used by 30 percent of their installs in Puerto Rico. The other 70 percent with grid-tied are operating in a mode that limits battery discharge to 70 percent to keep 30 percent battery power in reserve because there are still many random grid power outages (blackouts) that can last a few hours to many hours. As an example, on April 12, Puerto Rico had a rather large blackout affecting 840,000 customers that lasted over four hours caused by a fallen tree. And on April 18, a fault on a transmission line caused a total island wide blackout for 21 hours.

Figure 2: Tabuchi Electric installation at an isolated remote (Rivera) family home with no grid-connection since hurricane George hit the island in 1998. Credit Tabuchi Electric.

Some larger families have also integrated and installed 2 Tabuchi systems side-by-side to achieve 30-kWh or 40-kWh battery storage and up to 14.8-kW total PV power generation during peak mid-day sunlight. With the new third-generation hybrid solar inverter with embedded battery and 240 Vac capabilities, all major household appliances cumulatively consuming no more than 4 kW power can be powered off-grid for true 24x7 island nano-grid mode of operation, as long as there is enough sunlight to charge the battery adequately. Details will be reported in several papers at the 7th World Conference on Photovoltaic Energy Conversion, June 11-15 at Waikoloa, Hawaii, and disclosed in U.S. patent pending: provisional application No. 62/629,587 “Method and System for 100 percent Renewable Energy Management with Multiple Storages.”

Figure 3: Edison Rivera with living room light on first time since 1998. Credit Tabuchi Electric.

On March 29, the updated economics of residential rooftop solar PV was reported in another Renewable Energy World article “Solar Surprises: Small-scale solar is a better deal than Big.” It demonstrated the local spending value of solar for residential compared to utility scale, reducing residential cost of electricity from 11¢/kWh to <2¢/kWh whereas the utility cost was at 4.5-9.0¢/kWh when the repurchase costs of DER (distributed energy resources) and delivery costs from large-scale solar farms were factored in. In this case study in Hawaii with state and federal tax credits the residential lifetime cost of electricity (L-COE) from rooftop solar is reduced from 8.9¢/kWh to 3.4¢/kWh. This is well below the energy costs of the following sources:

  • Kauai Island Utility Cooperative (KIUC) solar-PV farm electricity purchase price of 11.9¢/kWh
  • KIUC Tesla PV+battery farm energy purchase price of 13.9¢/kWh
  • KICU diesel fuel cost of 15.5¢/kWh
  • Hawaiian Electric (HECO) oil fuel costs of 12.5¢/kWh
  • Li-ion battery storage costs of 37.3¢/kWh or 14.3¢/kWh with tax credits as shown in Fig.4

Figure 4: Lifetime cost of electricity for Hawaii case study.

Compared to HECO current residential peak time-of-use rate of 35.2¢/kWh, supporting small-scale solar is truly economically more efficient than large-scale solar. Today the cost of system for rooftop solar PV in Hawaii is as low as $3.04/watt ($1.15/watt with tax credit); Li-ion battery storage is $0.82/watt ($0.31/watt with tax credit); and hot thermal storage is $0.39/watt ($0.15/watt with tax credit) for a L-COE of 17.9¢/kWh (6.8¢/kWh with tax credit).

We achieved a one year utility costs savings from HECO for 2017 of $4,201 reducing the electricity bill from $4,754/year to $553/year and a 3.2-year ROI. In summary, the Solar + Multi-Storage system allows residential Puerto Rico to operate in island nano-grid mode (off grid or grid tied) and will benefit from similar electricity cost savings as we achieved in Hawaii.


Authors

John Borland (see below), J.O.B. Technologies, Aiea, Hawaii

Takahiro Tanaka, Tabuchi Electric, San Jose, California

John Ogawa Borland received his BS and MS degrees from MIT completing his BS thesis research at Hughes Malibu Research Labs and MS thesis research at Nippon Telegraph and Telephone Musashino Labs in Japan. He has published over 140 technical and invited papers around the world in the areas of advanced semiconductor device manufacturing techniques and high efficiency c-Si solar cells and has been awarded 6 patents. Currently he is President of J.O.B. Technologies a strategic technical marketing consulting company he founded in 2003 providing service to the semiconductor device manufacturing, equipment and metrology companies in the area of advanced front end of line process technology with the current focus on 7nm and 5nm technology for next generation smartphones. He is a senior member of IEEE, the IEEE Hawaii section chair, the chairs of the Hawaii joint EDS/SSCS chapter and PES chapter, and on the advisory committee for the IEEE International Workshop on Junction Technology (2008-present). He is also a member of the Electrochemical Society (ECS) and co-organized several ECS technical conferences/symposiums.