NEW DELHI: Sales of renewable energy certificates declined over 22 per cent to 1.25 crore units this fiscal on IEX and PXIL as compered to 1.61 crore in 2017-18, mainly due to lower inventory (supply), according to official data.In March, sales of RECs or green certificates declined by over 51 per cent to 11.78 lakh from 24.26 lakh in the same month last year.Indian Energy Exchange (IEX) and Power Exchange of India (PXIL) are the two power bourses in the country, which are engaged in trading of RECs and electricity.The trading of renewable energy certificates (RECs) is conducted on the last Wednesday of every month.Under the renewable purchase obligation (RPO), bulk purchasers like discoms, open access consumers and capacitive users are required to buy certain proportion of renewable energy or RECs. They can buy RECs from renewable energy producers to meet the RPO norms.The proportion of renewable energy for utilities are fixed by the central and state electricity regulatory commissions.An official said that the IEX saw a total trade of 9.34 lakh in March compared to 20.79 lakh in the same month last year.The data shows that in 2018-19, the RECs sales dropped 4 per cent to 89.55 lakh as against 93.29 lakh in the previous fiscal, largely due to the lower REC inventory.The official said that both non-solar and solar RECs continued to see low supply situation with buy bids exceeding the sell offer.Similarly on the PXIL, 36.53 lakh RECs were sold this fiscal compared to 68.55 lakh in 2017-18. In March, 2.44 lakh RECs were traded on the exchange as against 3.47 lakh in same month last year.The REC mechanism is a market based instrument to promote renewable sources of energy and development of market in electricity. It provides an alternative voluntary route to a generator to sell his electricity from renewable sources just like conventional electricity and offer the green attribute (RECs) separately to obligated entities to fulfill their RPO.