Tesla plans to power its Gigafactory in Nevada with a 70-megawatt solar farm, according to a company investor relations document obtained by Electrek. The document, which The Verge confirmed was genuine, was given to analysts at a tour of the Gigafactory last week. At the same time, Tesla announced that it had started production of battery cells at the facility.

The 70-megawatt solar array installation planned for the roof is the biggest news, and Tesla claims it will be seven times larger than the world’s next biggest rooftop solar installation. The plan is for the Gigafactory to not directly consume any fossil fuels, and for the solar installation to provide most of the power needed by the facility. Any excess power generated during the day will be stored by Tesla Powerpack power storage batteries for use at other times. It’s likely that the solar panels will be produced by SolarCity, which Tesla acquired late last year.

Tesla says having an all-electric facility will allow for greater efficiency and zero carbon emissions, and much of the building’s heating will be provided by waste heat from the battery manufacturing process. A closed-loop water system will recirculate 400,000 gallons of water, reducing fresh water usage by 80 percent compared with standard processes, the company says. An onsite battery reprocessing facility will also allow much of Tesla’s battery cells to be recycled into new cells on site.

When Phase 2 of the Gigafactory is completed, Tesla expects the facility to produce 35 GWh of battery cells and 50 GWh of battery packs each year (many battery cells are combined in a single battery pack). The yearly production of battery cells would amount to more than the worldwide production of all lithium-ion battery cells in 2013, and would be enough to provide power storage for 500,000 Model 3 cars.