The rapid expansion of photovoltaic (PV) power plants in deserts and Gobi areas worldwide has significantly impacted ecosystems. Though greening trends are documented, their origin (PV plants or climate change) remains unknown. This study investigates the greening of the Talatan Gobi, China's largest PV base, using long-term Net Primary Productivity (NPP) and Normalized Difference Vegetation Index (NDVI) data. To disentangle PV development effects from climate change, we integrated slope analysis, Mann-Kendall trend test, correlation and Granger causality analysis, NPP component decomposition, and difference-in-difference (DID) framework. From 2012 to 2020, PV installations increased by 142.14 km2, while over 79.5% of the area showing greening. Both NPPa and NDVI rose significantly from 2002 to 2020. Correlation and causality results identified PV area and precipitation as key drivers of NPPa (R = 0.423, 0.461) and NDVI (R = 0.833, 0.741). Decomposition of NPP into climate-driven and human-induced components revealed shifting contributions over time and across land cover types. DID analysis demonstrated significant positive effects on NPPa and NDVI within 1-2 years, due to improved microclimate under panels. These findings provide robust, multi-method evidence that both climate change and PV development drive greening in the Talatan Gobi, with PV infrastructure playing an increasingly important ecological role in desert ecosystems.