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Grid Management – Re-Balancing Power Generation

renewable energy

Power sector in India has witnessed tremendous growth in its energy demand, generation capacity, transmission and distribution networks. Renewable energy generation in India has been steadily on rise. With 175GW target of clean energy, it became necessary to have a grid that was highly adaptive (in terms of supply and demand). A good electric supply is one of the key infrastructure requirements to support overall development; hence, the opportunities for building smart grids in India are immense. The fluctuating nature of renewable energy, be it solar or wind, is a problem for any grid in the world. As of March 31, 2017, renewable energy sources accounted for 17.5 percent of all power generated in India. The country’s total installed power generation capacity was 326,848.54 MW with renewables accounting for 57,260.23 MW. The solar sector is witnessing installations at a rapid pace and had the largest gain in share with 5.5GW of installations in FY 2016-17. Solar accounts for 12,288.83 MW of the total installed capacity which represents 3.76 percent of the overall power generation. The installed capacity of solar has almost doubled from 6,762.85 MW in the previous financial year. Solar recorded the largest increase with its share rising from 2.24 percent at the end of FY 2015-16 to 3.76 percent as of March 31, 2017, an increase of 1.52 percent.

According to the recently released India Solar Market Update, it is predicted that 2017 solar installations will reach approximately 10 GW, a 130 percent increase year-over-year compared to 4.3 GW installed in 2016 as India becomes one of the top solar markets in the world after China and the United States. The concern comes as India pushes for an ambitious 100GW solar power installation by 2022. As more variable power generation sources are added into the grid, the more difficult this balancing becomes. This is where India’s massive power grid system needs rebalancing to deal with the fluctuating/ erratic nature of power generated from renewable energy flowing into the system and keep supply in sync with demand. It is time that power sector stakeholders in India should start discussing the issues around grid management and initiate steps to find potential solutions.

GRID MANAGEMENT: ISSUES AND CHALLENGES

Renewable energy sources are intermittent in nature hence; it is therefore a challenging task to integrate renewable energy resources into the power grid. Challenges and issues associated with the grid integration of various renewable energy sources particularly solar photovoltaic can be broadly classified into technical and non-technical:

Technical Issues:

Power Quality

  • Harmonics
  • Frequency and voltage fluctuation Power Fluctuation
  • Small time power fluctuations
  • Long time or seasonal power fluctuations
  • Storage
  • Protection issues
  • Optimal placement of RES
  • Islanding

Non- Technical Issues:

  • Due to scarcity of technical skilled workers.
  • Less availability of transmission line to accommodate RES.
  • RES technologies are excluded from the competition which discourages the installation of new power plant for reserve purpose.

Grid Integration Spans a Variety of Issues, Including:

New Renewable Energy Generation Power system planners can secure and sustain investment in new variable Renewable energy generation by aligning targets and incentives with grid integration considerations. Long-term, aspirational renewable energy targets establish a vision that can drive innovation in the policies and system operations that support clean energy. Also critical are “grid-aware” incentives (e.g., rewarding wind and solar generators that incorporate technologies that contribute to grid stability), which both motivate investment in renewable energy and mitigate negative impacts of integrating these resources to the grid.

Grid Management

As planners consider scaling up variable Renewable energy generation, the inherent variability of wind and solar resources complicates evaluations of whether a system with significant variable Renewable energy has adequate supply to meet long-term electricity demand. A variety of approaches exist for estimating the capacity value of variable Renewable energy, as well as techniques that enable utilities and power system operators to use wind and solar to reliably meet electricity demand.

Integrating distributed photovoltaic (PV) solar power results in unique benefits and challenges compared to the integration of utility-scale wind and solar power. Significant localized growth in PV can raise concerns such as voltage violations and reverse power flow in low-voltage distribution systems. However, various studies have shown that positive impacts (e.g., reduced line losses and avoided generation costs) can also result from distributed PV. Updating interconnection standards, procedures, and distribution planning methodologies to better reflect the characteristics of distributed PV can help realize these benefits and delay or even prevent the need for grid reinforcement.

New Transmission

Scaling up variable RE generation requires grid expansion and upgrades so that power systems can access high-quality solar and wind resources which are often remote from existing transmission networks. A well-crafted combination of policies, rules, and procedures (designed, for example, through an “RE Zones” approach) encourages investment in large-scale transmission expansion. These measures not only improve the utilization of variable RE, but also potentially defer the need for network refurbishment.

Increased System Flexibility

Accessing sources of operational flexibility becomes increasingly important in systems with significant grid-connected solar and wind energy. System operating procedures and market practices, especially the implementation of forecasting, faster scheduling, ancillary services, and grid codes and power purchase agreements are often among the least-cost options for unlocking significant flexibility without significant investments in new physical infrastructure. Another important institutional flexibility option is operational coordination between balancing authority areas, which enables sharing of resources through reserve sharing, coordinated scheduling, and/or consolidated operation.

Other sources of flexibility include flexible conventional generation and transmission networks. Additionally, demand response and storage are emerging as tools for increasing flexibility at very high penetrations of variable RE.

Options for procuring flexibility vary based on the regulatory context. For vertically integrated utilities, contractual or policy mechanisms provide the primary basis for encouraging the uptake of flexibility measures. In contrast, partially- or whollyrestructured power markets motivate flexibility through incentives and market design mechanisms, such as sub-hourly dispatch, ancillary services markets and price-responsive demand.

Planning for a High RE Future

In any power system, planning activities include assessing long-range demand and evaluating options for expanding capacity and transmission. With the introduction of significant variable RE generation, power systems planning increasingly focuses on evaluating options for increasing flexibility across the power system.

Grid integration studies help establish the flexibility requirements and build confidence among investors and operators that the power system can be operated reliably at increased variable RE levels. A grid integration study simulates the operation of the power system under various scenarios, identifies potential constraints to reliability, and evaluates the cost of actions to alleviate those constraints. Robust grid integration studies are based on significant stakeholder input, along with a broad set of foundational data.

Although grid integration studies usually include production cost simulations to model unit commitment and economic dispatch, determining the system-wide costs of integrating solar and wind power is much more challenging. The full costs and value of variable Renewable energy assets to the power system depend on dynamic and complex interactions among these generators and a system’s loads, reserves, thermal generators, and transmission networks. Grid integration studies illuminate the obstacles and opportunities that wind and solar integration could pose to a power system helping to dispel grid integration myths and misperceptions that inhibit large-scale deployment. These studies also lay the foundation for prioritizing and sequencing grid integration investments.

THE CHALLENGES OF TODAY’S EVOLVING ELECTRICITY GRID

Today’s power system must deal with a number of stressors that power system engineers of 100 years ago would have never conceived of. Three major trends are pushing for a change in how the electricity grid is managed, giving utilities and system operators plenty of new challenges to solve to maintain reliability.

Renewable generation is intermittent and difficult to control – The sun doesn’t always shine and the wind doesn’t always blow when customers need electricity. Instead of a centralized location like traditional generation, solar panels and wind turbines are being installed at distributed locations across the grid. Although they are a lowcost source of clean and renewable energy, these resources may inject power into the grid at times and locations that can create difficulty for grid operators. Problems can arise, such as random changes in voltage on distribution feeders, issues with fault detection and unwanted generation capacity which all affect the reliability and sustainability of the grid.

clean and renewable energy

Energy-consuming equipment is changing with the advent of new technologies – Older electrical equipment such as incandescent lights, heaters and motors were designed to react to changes in voltage and/or frequency. In fact, Conservation Voltage Reduction (CVR) is based on this concept. By reducing system voltage, the electricity demand from these devices will be reduced as well. Newer electronic devices do not respond to changes in system voltage or frequency, and they now dominate many homes; they include computers, lights (LEDs and CFLs), TVs, entertainment systems, etc. In addition to not responding to changes in grid voltage or frequency, these devices consume power in unusual patterns (called harmonics), which can affect the delivery of power and cause increased losses, equipment failure and a few worst-case scenarios, building fires.

power system

New protection systems and technologies have enabled the modern power grid to deliver more power than has ever been possible – For example, new wire technology has enabled existing wires to handle higher electrical currents for short periods of time; this can increase losses by more than 4 times the norm. While convenient and beneficial for today’s grid, these types of technologies have played a role in increased overall system losses from 5 to 7 percent to 9 to 12 percent.

ADDRESSING THE ISSUES OF MODERN POWER SYSTEM

The way that utilities and electricity system operators think about managing the grid has already begun to change. Instead of traditionally viewing grid management as one-directional and black and white (generation = controllable, demand = random and uncontrollable), grid operators are implementing demand management programs, which engage electricity customers to shift their electricity usage, improve their energy efficiency, enhance the reliability of the power system and sometimes offer cost savings or other incentives for participation.

The next level of grid management involves taking this important step even further. With the use of new technology, utilities are now able to view the demand side as a single, controllable resource that can respond to the real-time needs of the electricity grid. The right intelligent demand management technology can help grid operators implement this type of control without impact to their customers’ operations.

IMPROVING GRID INTEGRATION

To improve the grid integration, one has to improve planning and accounting for renewables (rather, for all generation), factoring in their burden on the rest of the grid such as transmission congestion. A few specifics for this are:

Power Evacuation Planning – The starting point requirement should be that if Renewable energy plants are being built (and they are growing in total wind/solar farm size to not just tens of MW but hundreds), there must be sufficient transmission capacity. This is often an intra-state issue for now.

Enable Inter-State RE – This effectively increases the balancing area, and isn’t so transmission burdensome when the favorable sites are near the border. The problem isn’t the regulations disallow it, just that the present rules for inter-state transmission require 15 minute firm schedules, something impractical for renewable power. The use of power exchanges for improved (non-realtime) balancing is also an option (subject to transmission constraints), but this begs the question why are these used so little today, even when prices are ostensibly low, only a few Rs./kWh? The reason isn’t technological but operational. Current financial settlement norms, while good for the exchanges’ risk profiles, make it tough for states to buy much power since they have enormous liquidity problems.

Improve Measurements, Predictions, and Analysis for RE Generation, Including Data Sharing – This could be through the proposed Renewable Energy Management Center(s) (REMC), which should also coordinate with state and regional load dispatch centers. Data sharing is especially important for wind power, which has much more granular variance than solar power, especially on a kilometer scale. REMCs need not be a large or complex institution – these could be envisaged as virtual centers in synergy with Load Despatch Centers.

Demand Best (reasonable) Predictions from Generators – CERC attempted to mandate wind generators to predict, day ahead, their output in 15 minute blocks with a tolerance of 30% (with some corrections allowed in 3 hour blocks), beyond which they would need to pay UI (unscheduled interchange) charges as per the current Availability Based Tariff (ABT) as a Renewable Regulatory Charge within the Renewable Regulatory Fund. There was opposition, and the proposal is currently on hold, pending validation (technically, predictions are asked for, but penalties not enforced). Improved predictions and nimble grid operations are better than of simply socializing the prediction variation costs.

Make Balancing a Proper Grid Requirement – While there is now a separate entity for Regional and National Load Despatch (POSOCO), India needs a completely independent Regional Transmission Operator (also called an Independent System Operator in some parts of the world). Such an RTO/ISO must also coordinate with state Load Despatch Centers, balancing their financial needs with grid operations. Importantly, all despatchers must be discouraged from a mindset of loadshedding as a balancing mechanism. One simple option (as a thought exercise for now), treat load shedding as having a cost, say, equal to the next available resource in terms of merit-order despatch. (In reality, load shedding’s cost may be far higher to society overall).

Strengthen the Grid – Even before we think about ancillary services, there need to be basic improvements to operations, including the use of Primary frequency control from generators with free-governor mode of operations, whereby deviations in frequency automatically signal the generator to increase/decrease output. No generator should be allowed to ignore or bypass control signals like some reportedly do today. In the future, frequency tightening can be achieved by the use of Automatic Generation Control (AGC) based on Area Control Errors (ACE) as signaled by an Area balancing authority.

Begin Ancillary Services in the Grid – These value grid support mechanisms beyond simple kilowatt-hour generation, such as the ability to ramp-up/ramp-down rapidly. Today, either the grid is left unstable or such services are provided by the suboptimal provider (coal plants aren’t designed for cycling production), without appropriate compensation.

Move Towards Robust RE Technology – Technologically, RE could provide more than simple kWh generation, such as reactive power, if it were incentivized to do so. In addition, India must plan for the ability of such generators to handle Low Voltage and Fault Ride Through capabilities, something China grappled with but ultimately enforced in recent years. The difficulty of a weak grid is exacerbated when Renewable energy generators cannot handle low voltages or faults; they trip, further weakening the rest of the grid.

Deploy Smart Grids to Make Demand More Dynamic and Grids Robust – This extends to storage solutions (which often finds value not in energy (kWh) arbitrage but also in providing ancillary services). Both of these are discussed in more detail in a separate chapter in this volume.

The century old grid is changing and the question becomes is this a managed transition? Renewables aren’t just inevitable; they should be supported and scaled up. Much more subtle than the challenge of meeting the peak is keeping the grid in balance. Advanced transmission infrastructure, updated grid integration and operation mechanisms are key to scaling-up solar to 100 GW by 2022. Combined with improved pricing, storage technologies and a Smart Grid, the policy push for generation investments in green power can be not just sustainable, but even help meet the broader goals of the Indian power sector, viz., access and affordability.

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