They also signed a shareholder agreement.
Banks are expected to finance the majority of the project, which will cost an estimated AED1.2bn ($327m) to build.
Acwa submitted a world-record low bid to develop the project, of 5.85 cents a kilowatt hour (kWh). They were selected as preferred bidder in January 2015.
Dewa also doubled the capacityof the plant from 100MW to take advantage of the low tariff.
The project is the second phase of the Mohammed bin Rashid al-Maktoum Solar Park, which has a planned total capacity of 2,600MW.
Spains TSK is also participating in the consortium.