Final Flashcards
what is the locational marginal price?
The locational marginal price (LMP) at some particular point in the grid measures the marginal cost
of delivering an additional unit of electric energy (i.e., a marginal MWh) to that location.
What does the electricity market clearing price represent at a given moment in time?
The market clearing price represents the price of one additional unit (MWh) of energy and is
therefore called the system marginal price.
The figure below shows the daily load demand for the same day in CAISO from 2011 to 2016. What is
the coined name for this infamous curve? What causes this to happen? Why is it concerning for grid
operators?
The curve in the figure is the Duck Curve. The duck curve is caused by increasingly high levels of solar
penetration driving down the mid-day summer demand profile for a grid system mixed with an evening
peak residential load that occurs after the sun has set in the evening.
The duck curve concerns grid operators because of the sharp rise in demand mixed with the loss of
solar-based generation. The system is required to ramp up costly gas-powered generation to match the
rising load. In addition, the variability of the curve poses a threat to the grid’s reliability, impacting
system reserves and making the system more vulnerable in the event of an unprecedented line fault or generator trip.
Why might Demand Response be a good countermeasure for the curve? Suggest two DR
services that would be the most effective in offsetting the evening peak in demand and explain your
choices.
The duck curve and similar phenomenon that stress the modern grid introduce discussion for
flexibility on both sides of the load balance equation. While flexible generation technologies are finding
a place in these situations, demand has remained rigid. Introducing flexibility by way of demand
response could mitigate the uncertainty associated with the duck curve and reduce overall system costs
by redistributing or shaving daily peak load. This would alleviate grid operators from calling on costly
thermal generation to ramp up to meet unpredictable peaks.
Energy shifting could be a good DR strategy for the duck curve by limiting a fraction of the expected
load from turning on until later in the evening. Even shifting the peak load by one hour would give
generation time to ramp up.
Capacity DR would also be a key player in combating the duck curve. Having a percentage of demand on
stand-by to ramp down during the evening peak would reduce the amount of required generation for
the power system.
Contingency, Flexibility and Regulation DR may be options for the duck curve, since these services
would be able to act as fast-responding reserve in the event of a tripped generator. This would in theory
free up other reserves to tackle the evening ramp of the duck curve.
List at least 5 different grid storage technologies that can be integrated in the power system. What
grid services can storage provide? Are each of the listed types of storage suitable for each type of grid
service application?
Energy storage technologies such as pumped hydro storage, hydro reservoirs, compressed air
energy storage, various types of batteries, flywheels, supercapacitors, thermal storage, etc., provide
several service applications: energy management, backup power, load leveling, frequency regulation,
voltage support, reduction of renewable energy curtailment, etc.
Energy storage systems will play a significant role in enhancing power system flexibility and enabling
high levels of reneable energy integration and overall grid modernization, serving as an effective
flexibility option to address issues of grid resiliency and reliability.
Energy storage technologies vary in terms of use, power capacity, and energy storage capacity. In other
words, not every type of storage is suitable for every type of application.
What is the difference between power and energy capacity applications of grid storage systems?
Power capacity applications reduce the need for generation and serve as an alternative generation-
load balance source, while energy capacity allows for energy consumption to be decoupled from
generation, i.e., shifting energy consumption over time.
What determines the adequate amount of grid storage to be integrated into the power system?
The current and planned mix of generation technologies,
• Flexibility in existing generation sources,
• Interconnections with neighboring power systems,
• The hourly, daily, and season profile of electricity demand,
• The hourly daily and seasonal profile of current and planned variable renewable energy.
The key characteristics of battery storage systems are:
- Rated power capacity
- Energy capacity
- Storage duration
- Cycle life/lifetime
- State of charge
- Round-trip efficiency
Why is power quality analysis important? List at least 3 relevant standards for power quality.
Power quality is a measure of the ability of electric utilities to provide electric power without
interruption and in accordance with established specifications. Delivered electric power should be of
“satisfactory” power quality, i.e., voltages are sinusoidal waveforms without distortion and without
variations in voltage magnitudes outside the allowed range. The electric utilities can only control the
quality of the voltage; they have no control over the currents that particular loads might draw.
Some of the power quality relevant standards are ANSI C84.1-2020, IEEE 1159-2019, IEEE 1250-2018,
IEEE 519-2014, etc.
What are power system harmonics?
Ideally, voltage and current waveforms are perfect sinusoids. However, because of the increased
presence of electroic and other non-linear loads, these waveforms quite often become distorted. This
deviation from a perfect sine wave can be represented by harmonics – sinusoidal components having a
frequency that is an integral multiple of the fundamental frequency.
What are negative impacts of harmonic currents and harmonic voltages, respectively?
Harmonic currents can cause several issues, such as electric equipment heating and failures,
industrial process problems, equipment malfunction, circuit breaker tripping, etc. Distribution
transformers are especially sensitive to current harmonics, which can cause overheating, increased
losses, even failures. Voltage distortion affects not only sensitive electronic loads but also electric
motors and capacitor banks.
What are the most common power quality issues?
The most common power quality issues are: • Harmonic current and voltage distortion • Undervoltage • Overvoltage • Voltage sag • Voltage swell • Transients • Flickers • Noise
What is THD?
THD is a measurement of the harmonic distortion present in a signal
What is the THD of a perfect sinusoidal voltage waveform?
A perfect sinusoid has no harmonics (𝐼𝐼ℎ = 0), therefore, the THD of a perfect sinusoidal voltage
waveform is equal to zero:
Why is load forecasting important for power system operators?
Load forecasting helps the power system operator make important planning and operational
decisions. It is the foundation for electric utility planning. To anticipate how much electricity consumers
will use at any given time – and the necessary reserves for emergencies – power system operators rely
on load forecasting.
How can load forecasting problems be classified?
Classification of load forecasting problems:
• Very short-term load forecasting (forecasting horizon ranging from a few minutes ahead to a
few hours ahead).
• Short-term load forecasting (one day to two weeks ahead forecasting).
• Medium-term load forecasting (two weeks to three years ahead forecasting).
• Long-term load forecasting (three to fifty years ahead forecasting).
What are the most commonly used forecasting accuracy metrics?
SE, MAE, RMSE, MAPE
Why is rate design so critical to the success of grid-edge technologies such as distributed solar,
residential energy storage, and electric vehicles?
Rate design is necessary for the success of grid-edge technologies like distributed solar, residential
energy storage, EVs, etc. because structured retail rates can alleviate stress to the grid brought on by
the rapid adoption of these new technologies by incentivizing consumers to operate these technologies
at times of historically low usage or when grid conditions are favorable to handle these loads.
Consider the maximum EV dmand case for the following daily load curve. If you were in charge of
your local utility, how would you design retail electricity rates to reduce the impact of electric vehicle
charging on evening peak loads? Would your solution be economically feasible for both the consumer
and the utility?
One possible response for the utility provider is to have time-of-use (TOU) rates in place to offset
charging from immediately occurring as people return home from work. The temporal arbitrage created
by the incentivized rate design would alleviate evening peak loads by shifting the demand by EV
charging to later in the evening and reducing the maximum evening peak load. This approach would
benefit the utility by reducing system upgrade costs to handle the additional peak load, while also
providing consumers with discounted rates to take advantage of late-night charging. However, in this
scenario, consumers would risk not having a fully charged EV for late-night emergencies.
