Ingenieur Vol. 75 ingenieur July 2018-FA - Page 19

to further increase the contribution of RE to the power sector. LSS, NEM and Selfco limited to PV technology and Virtual Generators not allowed At present, all the above mechanisms are limited to PV on the customer’s own premises. Non-PV technologies are on a case by case basis, and so far, there have been no success stories although many developers of small industrial estates and housing estates are interested to have a RE contribution, both for commercial, as well as Corporate Social Responsibility (CSR) reasons. This is because there is no clear mechanism to allow for non-PV generation. Apart from that, virtual generators should also be allowed, i.e. the RE generation may be off-site but allowed to sell to a particular customer by using the utility’s network for a fee. Co-generation and New Enhanced Dispatch Arrangement Most consumers do not go for co-generation (co-gen) due to the prohibitive rates charged by the utility. Recently, the EC launched the New Enhanced Dispatch Arrangement (NEDA), aimed primarily at Independent Power Producers (IPPs) with expired PPAs and those with existing PPAs but willing to sell at a lower cost than the PPA price. Cogens are also allowed to participate in NEDA but need to follow the same mechanism as the big boys, i.e. day ahead dispatch schedules with spot prices offered by the Single Buyer. Cogens using waste heat and other forms of renewable energy should be offered more flexibility in terms of dispatch schedules and spot prices. TECHNICAL ISSUES AFFECTING INCREASE IN RE GENERATION The most important issues affecting the increase of RE generation, whether under FIT, LSS, NEM or other schemes, are the technical issues put forward by the utility to limit or stop RE generation. Some of the major issues are listed below. • Lack of Load and Voltage Rise This issue normally affects the biogas, small hydro or other RE plants connected at a remote end of the distribution network where the load is very small. This usually results in an increase in voltage when power is injected at this remote end, sometimes beyond the +5 % allowed for medium voltage systems. The utility has allowed operations at leading power factor (where the current leads the voltage) or use of a reactor (basically an inductive device) to absorb reactive power from the network and bring the voltage down. However, this arrangement is counter-productive for the utility as reactive power is produced by other generators and there are technical losses in the system due to the absorption of reactive power by the generator. Conductor sizes may need to be increased due to the reverse flow of reactive power. Based on technical and commercial considerations, the utility should not allow this kind o f arrangement. However, the utility should allow for power flow from one voltage level to a higher voltage level, as long as the voltage rise is within limits. For example, from low voltage (LV) to 11 kV, and also to higher voltages, including 132 kV. In many jurisdictions in Europe, the Indian sub-continent and China, there is no restriction in allowing power to flow upstream. The objection by the utility is normally based on two considerations: losses in the step-down transformers and protection issues. The losses are a non-issue since whatever losses incurred in the step-down transformer are made up by reduction of losses in the overall distribution network. Detailed discussions with protection experts in both Distribution and Transmission networks have also revealed that in normal circumstances, there are no protection issues; whatever issues may arise can easily be resolved through technical solutions which the RE developer would be only too glad to pay for. • High Fault Current at Main Utility Substation (Transmission/Distribution Interface) This is the bane of many RE developers. Even in urban and heavily populated areas, many potential RE generators have been stopped due to this reason, even those proposing pure self-consumption schemes. The 11 kV vacuum circuit breakers (VCBs) at the main substations are normally rated at 20 kA. When there is high generation from IPPs in the vicinity the fault current at the Main Substation increases. A number of substations with a 132/11 kV interface already 17