This research aimed to build a monitoring solar smart agricultural farm for cassava farm and using solar cells panel to harvest enough energy. The crops farm is usually far from the city and does not have electrical energy from the grid transmission line system, and it more expensive if we need to install it. With the rising demand for renewable energy in this recent year especially for solar energy. Monitoring solar smart agricultural farms by used solar energy management to enough water for cassava farms with low cost of the system is difficult. The purpose of this research we studied the watering and not watering of cassava. For watering, we used a monitoring solar smart agricultural farm to manage solar energy that harvests from sunlight by polysilicon solar cells about 8 panels for operating the water pump 2hp that enough for plant farm with low cost of the system. The factor that has affected the growth rate of cassava we used many sensors for detecting such as soil moisture senor time-domain reflectometry (TDR) at depth 10cm and 20cm, humidity sensor, and temperature sensor (DHT22). The factor that has affected to light-harvesting of the solar panel we used many sensors for detecting such as BGT-JYZ2 solar radiation sensor, current sensor, and voltage sensor by PZEM-017 reader communicate. The capacity of battery we use PZEM-017 reader communicate for monitoring of battery voltage for predict battery percent. All sensors have connected with Esp8266, and it will send the data to NETPIE cloud for keeping the data in the system and show on mobile phones in real-time. The demand for water for crops farm is maximum in May about 216,000L and few in April about 64,800L with water drop head about 5,400. The product of cassava that got from used this monitoring system provides storage root number average about 9 per plant, weigh average about 9 kg per plant. For not watering provide storage root number average of about 6 per plant with 4kg per plant. This system can increase the product and quality of cassava.