<p>This paper utilizes the Hargreaves–Samani model to estimate solar radiation on the East Coast of Peninsular Malaysia, encompassing Kelantan, Terengganu, Pahang, and the southern state of Johor. The model estimates solar radiation based on daily maximum and minimum temperatures and provides a practical approach for regions with limited solar radiation data. This study aims to assess the solar energy potential in these areas for Photovoltaic (PV) power generation. The methodology involves applying the Hargreaves–Samani model to calculate the monthly solar radiation from maximum and minimum temperatures. Results reveal that Kelantan and Terengganu recorded (estimated) the highest solar radiation, reaching 6.47 kWh/m² and 6.22 kWh/m² in May, respectively. Meanwhile, Pahang and Johor followed closely with 5.62 kWh/m² values in September and October, respectively. In comparison, the highest solar radiation (measured) values were observed in Kelantan (7.43 kWh/m²), Terengganu (7.37 kWh/m²), Pahang (7.46 kWh/m²), and Johor (7.29 kWh/m²), which are much higher than the estimated values from the Hargreaves–Samani model. Notably, Kelantan has the highest average yearly plant output among the three types of solar cells, which are solar power plants. The study concludes that the East Coast of Peninsular Malaysia, especially during peak months, holds significant potential for PV power generation, with solar radiation values comparable to global solar-rich regions. The total measured output of solar energy from these states is 1,057.78 GWh, which meets 0.71% of Malaysia’s total electricity demand of 148.6 billion kWh in 2023, while the estimated output covers 0.73%.</p>