The sun shines only at night


What happens when the sun goes down? The infernal question is no more.

Engie has been notified by the Power Authority of Guam that it was the lowest bidder and has won a contract to construct two solar power plants totaling 50 MWdc with approximately 300 megawatt-hours of energy storage. Significantly, the system is designed to deliver 100% of the electricity after the sun goes down. Engie noted that it will now begin work on the details of the twenty year power purchase agreement (PPA).

Engie says that the Samsung SDI batteries which it has chosen for the energy storage solution will be able to deliver electricity for up to seven hours. The 300 MWh and 50 MWdc values weren’t coupled with the energy storage inverter capacity or AC solar sizing. If the project were to deliver the full 300 MWh of electricity over the course of seven hours, the minimum size of the energy storage inverter would be just over 42 MW. If the solar inverter (MWac) were similarly sized, it’d be a DC:AC ratio of 1.16.

The projects are expected to come online in July 2022, and will delivery 85 GWh/year of electricity – a 19.4% DC capacity factor.

A 500 page project procurement requirement document (pdf) was made available for review in late 2018. The projects were proposed to be built in the specific locations noted in the above image, and connecting to a new substation being built.

The qualitative scoring system used to judge bids is located here (xls). Higher accuracy images of the sites are located here (pdf).

Phase II of the program (pdf) ended with two 25 year PPAs being signed with Hanwha Energy Corporation for 30 MW solar projects that will deliver roughly 144 GWh/year of electricity in total for 6.245¢/kWh and 6.599¢/kWh.

While there are plenty of solar+storage projects that run sites 24-7-365, this project is significant in that its among the largest energy storage systems announced globally, and the solar power is to be delivered 100% at night. Eventually, Guam Public Utility Commission will post the power purchase agreement (prior signed documents are on the website) and its prices, on their website.

With that, we will be given a new pricing perspective to consider in our models – what does 100% delivered at night solar power cost? The large majority of our solar pricing is daytime priced electricity – delivered 100% at time of generation. Recently, the Eland project in Los Angeles (above image) gave us some insight into our new pricing considerations. In that project, we saw solar electricity pricing of 1.997¢ delivered at time of generation, add 1.3¢/kWh for 200 MW / 800 MWh worth of energy storage, and another 0.667¢/kWh when we expanded to 300 MW / 1,200 MWh to deliver the excess electricity during the evening peak period.

A lot of unknowns still, but we’re inching close to 24-7 solar.

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