Hybrid Pumped Hydro Storage Energy Solutions towards Wind ...

Hybrid Pumped Hydro Storage

Energy Solutions towards Wind

and PV Integration

Prof Helena M. Ramos

INTRODUCTION

The growing energy crisis and the excessive consumption of resources are raising concerns about

finding new alternative energy sources, enabling new production methods and/or making existing

ones more efficient

Methane (CH4-waste sector), nitrous

oxide (N2O-agricultural sector) and

halogenated compounds, namely

chlorofluorocarbons,

hydrofluorocarbons and

perfluorocarbons (F gases), in

addition to carbon dioxide (CO2-

energy sector) are the main causes

of increasing environmental

awareness and increased levels of

greenhouse gases.

Compared to 1990, the European Union intends to reduce its internal emissions by 80 % by 2050.

Regarding this, it appears that a reduction in CO2 emissions of around 70 % between 1990 and

2050 is likely to occur in the energy and industrial processes sector

INTRODUCTION

At the beginning of this century, Europe made huge investments in renewable energy. Advanced

EEA data (EEA 2017) show that, on average, the share of renewable sources in final energy

consumption has increased by 6.7 % per year since 2005 (slightly slowed in the last 2 years)

The objective of the EU is to

achieve the target of 20% use

of renewable energy in 2020.

The proportion is estimated to

be 17 % in 2016, so it is within

the plan

INTRODUCTIONSweden is undoubtedly the most

prominent of the 28 Member

States (with a 54 % share),

followed by Finland and Latvia (40

and 38 %). Portugal is ranked

seventh (28 %), contributing

positively to the European average

Portugal is one of the 9 EU

countries with significant

greenhouse gas emission

reductions (more than 10% from

2005 to 2015)

■ Nowadays we seek to rationalize water and energy consumption and produce non-

pollutant energy by implementing clean, hybrid, cost-effective solutions based on

renewable energy sources to meet the environmental issues of sustainability (e.g.

minimization of CO2 emissions).

■ Moreover, many countries usually import most of the energy they need, suffering the

consequences of the increased consumption, on the price and on the availability

fossil resources, as well as they have to face the issue of greenhouse gases.

■ Accordingly, it is necessary to develop integrated studies on water and energy

(WATER – ENERGY nexus) in order to implement innovative clean solutions through

effective strategic analyses.

■ Contemporary societies are characterized by an extreme dependence on water and

energy.

Main objectives

■ Water consumption has been growing at more than twice the rate of the population growth in the last century.It is estimated that the global population of nine billion people are consuming about 60% of available freshwater WWAP (2018). Water extraction are expected to increase by 50% by 2025 in developing countries, and 18% in developed countries.

■ In 2025, 1 800 million of people will be living in countries or regions with absolute water scarcity, and two thirds of the world population might be under conditions of water shortage.

In 2010

■ New paradigm: the increased consumption has been responded with

increased supply, which has led in some countries, unsustainable

levels of water and energy consumption, production of pollutants with

the well known reflex to the climate change problem.

Hydropower and Pumped storage

have a huge advantage of start-up and energy injection in the grid rapidly,

lesser than three minutes, while thermal plants require a minimum of

eight hours to start generating energy, being highly polluting

ENERGY PRODUCTION FROM RENEWABLE SOURCES

Regarding the production of energy from

renewable sources, Portugal exhibits enormous

potential: hydro, wind, bioenergy, solar, tides

and waves

At present, the first four are the most widely

used and contribute the most to the vast

majority of renewable energy produced

Solar

Bioenergy

Wind

Hydro

Fossil Cogeneration

Natural Gas

Coal

The use of RES

Wind and solar supporting pumped

hydropower storage solutions

New cases of Pumped Hydropower Storage in Portugal

However, they still lack some competitiveness because of their intermittency, and therefore there is

a need to resort to fossil energies

Despite the gradual increase in electricity production from renewable sources, it is a fact that 2017

brought a setback as it was marked by the presence of extreme drought conditions, reflected in

hydroelectric productivity, which decreased by just over 1/3 of 2016 production

As a result, only 44.3% (22 956 GWh) of mainland Portugal's total electricity consumption (51 839

GWh) comes from renewable sources

In the opposite direction was the production of fossil source, which supplemented with 31 567 GWh.

This reversal resulted in an increase of more than 25% in carbon dioxide emissions compared to the

previous year, which amounted to approximately 15 x 10^6 tonnes of CO22


In any case, the variation in the production of renewable energy throughout the year can be

analyzed, i.e., although it is always different during homologous periods, it presents the same

annual patterns

Hydropower production was the

highest in the first quarter, and

in the summer months it was

three to four times lower. Wind

energy production is more

regular, but it also has the

same pattern as hydro (with

higher production in winter and

lower production in summer)


Since wind speed and water

inflows have average year-

round variations with a high

correlation, production is

expected to be simultaneous

In contrast, in the summer

months, solar energy

production is at its peak

In this way, it is possible to

complement the production of

energy throughout the year with

the other two sources


There is a correlation between energy consumption and production from renewable sources, the

higher the output. The relationship between the energy source and the selling price of electricity

also exists in terms of costs, i.e. the greater the representativeness of the renewable energy source,

the lower the market price

A certain increase

in energy

consumption could

be a sign of a

recovery in the

economy


Correlation of the market price and the

renewable production

DemandRenewable energy production Market price

Specific emissions of the electric sector in Portugal 1999-2030

The penetration of Renewable

Energy Sources (RES) in existing

power systems, namely wind,

showed a considerable growth

since 2000, not only in terms of

installed capacity, but also the

total electricity share


In small and isolated systems,

without interconnections, the impact

of RES tends to be higher than in

interconnected power systems,

where the RES variability effect can

be smoothed


Due to the growing awareness

about environment, climate

changes, pollution and waste

footprint, clean and renewable

sources of energy are being

encouraged and used globally.


With these growing trends of using

intermittent renewable sources of

energy, there will be a greater need

to make flexible the modern energy

production and distribution

systems

For instances a rate of 56 % incorporation of renewable energy sources (RES) into electricity

generation was recorded in 2019, equivalent to 27.3 TWh of electricity generation, out of a total of

48.8 TWh in Portugal. The remaining 44 % represented fossil fuels, corresponding to 21.4 TWh

In electricity generation, there was a

3.1% increase in renewables

representation compared to 2018.

In fact, hydroelectric generation was

reduced due to a shortage of water

resources during the summer, which

was filled during the winter


The use of self-consumption devices (e.g. photovoltaic panels) is a factor in the development of a

number of clean technologies and the promotion of more active consumer behaviour, which is

also increasingly facilitated by the design of more efficient control appliances and systems


Although renewable sources of energy are practically inexhaustible and environmentally friendly, as

they depend on atmospheric conditions, they are also unpredictable and have variable availability

This often creates an imbalance

between energy demand and supply, but

the full potential of the use of renewable

energy can not be eliminated. This

imbalance may occur when there is a

shortage of energy sources, as is in

times of drought, when dams are losing

their capacity due to a lack of rainfall

and, consequently, without sufficient

storage for hydropower generation

BALANCE BETWEEN ENERGY SUPPLY AND DEMAND

Visualization of 30 days of superimposed power demand time series data (red), wind energy generation

data (blue), and solar insolation data (yellow). Average values are in color-highlighted black lines

But the opposite may also be the case, i.e., there are times when supply is greater than demand, so

all that unused excess energy is either exported or wasted


Three possible strategies to ensure a balance between energy supply and demand are as follows:

1) Limiting the generation of

renewable energy sources (avoiding

the waste of these resources) and

increasing the generation of

thermoelectric power. This solution is

not sustainable and does not fulfill the

objective of making energy production

more efficient


3) Store the surplus of electricity

produced to be used later in higher

consumption periods. This is the most

effective way to control the variation in

supply / demand.


2) Exporting the surplus to

neighboring countries is a solution

that depends on the external

absorption capacity, although it has

already been done;

incompatibility

PUMPED HYDRO STORAGE systems (PHS)

The introduction of PHS in the

Madeira Island (Socorridos)

Portugal, or in Canary Islands,

Spain, concludes that this type of

energy storage contributes

positively to the increase in wind

energy penetration

Pumped Hydro Storage systems (PHS) are one of the well-known and studied types of energy

storage that can be introduced with success in small/large and/or isolated systems, showing a

positive outcome in terms of increased wind energy absorption, while maintaining the economic

feasibility of the investment project.

In classical type of system, low cost electric power (electricity in off-peak time) is used to run

the pumps to raise the water from the lower reservoir to the upper one.

During the periods of high power demand, the stored water is released through hydro turbines

to produce power. Reversible turbine-generator groups act as pump or turbine modes, when

necessary

During peak

times, water is

released from

upper

reservoirs,

generating

energy as it runs

through turbines

to the lower

reservoir

PUMPED HYDRO STORAGE TECHNOLOGIES

Case Study: Multiple Purpose Socorridos System

The Multiple Purpose Socorridos System started operating in

1995 under its initial configuration:

• 16 km long string of hydro tunnels and canals, allowing the transfer of water

collected on the higher altitude and more raining northern side of the island, to

the southern side of the island

• Loading chamber in Covão with a maximum capacity of just 7 500 m3

• Hydroelectric station with three Pelton turbines with 8 MW of capacity and a

flow of 2 m3/s each

• Connection to the Stª Quitéria mini hydropower station, equipped with a single

Pelton turbine with a nominal flow of 1 m3/s


Initial Configuration: only Hydropower Station


Current Configuration: plus with Pumping Station

Operation in turbine mode

In pump mode

- the load diagram is further smoothed out with increased RES penetration possibility, of up to 30%

of the electricity production share, and reduced need for spinning reserves.

- this results in the avoidance of 100 ktonnes of fuel oil importing, which corresponds to a 4 M€

savings per year, and to an avoided emission of 300 ktonnes of CO2.

- how the Socorridos System affects the daily load diagram, showing how wind penetration is maximized

due to pumping in low peak demand hours, and thermal generation is replaced by hydro production in

peak hours

Madeira pumped-hydro-storage system operation

1- Transformation in a reversible power station maximizes the hydropower production;

2- Allows overcoming the limitations imposed by the water scarcity;

3- Allows a greater penetration of clean and renewable energies (such as the wind and solar energies).

Movie

Currently are under construction several hydro-schemes in around 130

countries, and many others in design, adaptation and rehabilitation.

International overview

Hydropower Potential

~ Continents

Theoretical

Potential Installed Power

Production in

average year

To be installed (under

construction) Planned Power

(GWh/year) (MW) (GWh/year) (MW) (MW)

Africa > 2 461 967 23 482 97 519 5 222 27 868 - 91 723

Asia + Russia and Turkey > 19 716 941 401 626 1 514 198 125 736 205 156 - 340 453

Australia + Oceania ~ 657 984 13 370 37 138 67 420 - 2 768

Europe > 2 817 477 179 152 541 908 3 028 15 793 - 18 516

North America > 7 600 775 169 105 689 314 7 798 34 784 - 52 001

South America > 6 639 249 139 424 670 780 19 555 78 445 - 96 103

World > 39 894 392 > 926 159 > 3 550 856 > 161 406 362 466 - 601 565Based on: H&D (Hydropower and Dams) World Atlas, 2010; ICOLD – International Commision on Large Dams; ESHA – European Small Hydro Association; IWRA – International Water

Resources Association, IWA – International Water association; IWMI – International Water Management Institute; UNEP – United Nations Environment Programme; UNESCO-IHE – Institute

of Water Education; Water Aid.

World hydropower technical potential

The highest percentage of undeveloped potential is located in Africa (92%), followed by Asia (80%), and

Latin America (74%), even though this region is also characterized by two of the top ten hydropower

producers (in 2018)

Energy security (classic approach)

Base load – minimum level of consumption throughout the day

• Power plants that operate at low cost during the 24 hours

of the day throughout the year (coal or nuclear)

Intermediate load – predictable variation of consumption

throughout the day

• Power plants that are capable of working within minutes

with moderate costs (renewables and natural gas )

Peak load – sudden increase in consumption

• Highly flexible power plants that are capable to go to full

capacity within seconds (hydro)

Spinning reserves – power plants that are active and ready to be connected to the grid.

Pumped Hydro Storage

In PHS systems, energy is transformed into

potential energy that is stored in the form of

water level, by pumping water from a lower

reservoir to a higher level reservoir

In a traditional configuration PHS systems take

advantage of the difference between low and

high demand period of electricity prices to

generate its revenues

Hydropower systems

With the highest flexible technology for power generation. Hydro reservoirs provide built-in energy

storage, and the fast response time of hydropower enables to optimise electricity production across

grids and meeting sudden fluctuations in demands

Pumped Hydro Storage

System ImprovementsDouble Penstock

The use of a separate penstock for the pump and turbine increases the system’s flexibility and

reduces the time lag between storing and generating operation switch.

In isolated grids it allows for the storage of a highly variable energy source while at the same time

providing a stabilized energy for consumption.

Advantages:

- to store energy

- to firm variability of energy generated by

intermittent renewable sources

- to compensate the fluctuations of the loads

Construction of new

hydropower plants

+

Upgrade projects of

existing hydropower

plants

Portugal doubled the

installed capacity in few

years

Relevant Remarks

The high complementarity between renewable sources is the utmost advantage;

Pumping storage is an effective solution to address intermittent renewable energy

failures;

Hydraulic machines of Francis or PAT best suited for reversible hydroelectric systems

as they can also perform the power production and the pumping with good

efficiencies;

The use of the ocean as a lower reservoir saves the construction costs for the lower

reservoir.

New projects of pumped-storage systems in Portugal:

Baixo Sabor Power Plant:

- 4 reversible groups

- P = 171 MWCarvão-Ribeira:

-2 reversible groups

- P = 256 MWExamples of upgrade

Projects:

- Alqueva II

- Bemposta II

- Venda Nova III

In Portugal was increased in

pumped-storage hydropower

systems from 5 GW to 7 GW by

2020

Portugal currently leads in Europe, the countries

that will invest more in hydropower and solutions

with pumped storage (World Atlas, 2010)

Alto RabagãoThe opportunity lies in using the dam reservoir of hydroelectric facilities

Floating Solar Pannels

Converting solar energy into electricity through photovoltaic technology is an increasingly

cheap and efficient process. Portugal has one of the highest solar resource levels of

European countries, but using it means occupying very significant geographical areas.

The opportunity lies in using the dam reservoir of hydroelectric facilities. Thanks to this the

occupation of other areas of recognized utility (for agriculture, for example) can be avoided

and it's possible to make use of the connection to the already installed electrical network

that hydroelectric stations do not use constantly. Because there is more sunlight when there

is less rain and vice versa.

Recognizing this context and this opportunity, EDP opened, a floating solar photovoltaic

power plant at the dam reservoir of Rabagão river in Montalegre and the Alqueva Floating

Photovoltaic project.

■ Alto Rabagão

■ A pioneering project at the European level, the floating photovoltaic solar power plant at the

Rabagão river basin, in Montalegre, tests the cooperation between solar energy and hydro,

as well as the environmental and economic advantages of this new technology.

■ With 840 solar panels occupying an area of 2500 square meters, the platform, which

results from a partnership between EDP Produção, EDP Renewables and EDP Comercial,

has an installed capacity of approximately 220 kWp and an estimated annual production of

around 300 MWh.

■ EDP has invested 450.000 euros to move forward with the installation of this pilot unit,

which will help in assessing the implications, advantages and disadvantages of the

installation on floating platforms of the photovoltaic conversion panels and their exploitation

together with the hydroelectric production. It is also intended to prove that this solution has

clear environmental benefits in the water body, and because it reuses existing installations,

avoiding the construction of new transport lines.

https://youtu.be/bFevGbcHq8M

https://www.edpr.com/

https://edp.pt/

https://youtu.be/bFevGbcHq8M

Alqueva Dam:

- Guadiana river

- started operating in 2004

Objectives:

- electricity supply;

- public water supply;

- irrigation of 115 000 ha of agricultural land;

- implementation of leisure and tourism

infrastructures.

2 reversible groups with Francis turbines

P= 256 MW

Improvements in the

wind and solar

energy sectors

Upgrade Project+ 2 reversible groups

+ 256 MW

Alqueva II

https://youtu.be/_EEtXr73N5U

https://youtu.be/_EEtXr73N5U

Upgrade Project Alqueva II

Regulation of the

grid:

- Hours of low

demand and low

electricity price

- Hours of high

demand and high

electricity price

PUMP

TURBINE

Upgrade Project Alqueva II

Simulating the operation Pedrógão-Alqueva:

-Average level in Alqueva ~ 147m

-Level in Pedrógão ~ 82,5 m

(half of the capacity)

- H = 64,5 m

- Qt = 192 m3/s

- Qp = 162 m3/s

Daily cycle: 5 hours – turbine

6 hours – pump

Qt/Qp= 1,19

Optimization: opportunity in energy tariff

= maximum profitability

= minimum level of energy price

Pure reversibility cycle:

Qt x Tt = Qp x Tp

Qt: turbine discharge

Qp: pump discharge

Tt: Time of operation of turbine

Tp: Time of operation of pump

Pumped-Storage using Seawater Pumped-Storage Power Stations

Seawater Pumped-Storage:

- 1st Seawater Pumped-Storage Power Station: Okinawa, Japão (1999)

- Lower reservoir = SEA

- Volume of the reservoir and volume of water unlimited

Some cares:

- Corrosion

- Adhesion of marine organisms

Remarks about Pumped-storage and hydro solutions

53

- improves energy efficiency

- generates clean energy:

-withou CO2 emissions

-without harming the environment

-allowing to overcome the scarcity of resources

(reutilization of the same hydrological source)

-without contributing to global warming

Renewable energies (subject of particular relevance in developed and developing countries)

Need of a good and competitive option to store energy generated by intermittent sources:

Pumped-Storage:Without storage, the energy

produced, may be wasted,

if not needed.

SMART PUMPED HYDRO SYSTEMS (PHS) – integrated solution

It also contributes to fossil fuel

savings, without jeopardizing the

reliability of the electrical system

and maintaining end-user

satisfaction indexes for electricity

The challenge of using renewable sources such as hydro, wind and solar power is their variability,

intermittency, unpredictability, and dependence on the weather

Combining renewable energy resources is the best way to overcome energy shortcoming, which not

only provides more reliable power systems increasing the storage capacity but also leads to the

reduction in climate change effects

Through proper

management of both

resources, it is possible

to guarantee a uniform

power supply to the grid

PUMPED HYDRO SYSTEMS (PHS)

Renewable-based technologies can make water-energy accessible for domestic, industry and

agricultural purposes, improving supply security while decoupling growth in energy from fossil fuels

RENEWABLE ENERGY TECHNOLOGIES

Renewable energy technologies offer opportunities to address trade-offs and to leverage on

synergies between sectors enhancing the water and energy nexus

However, connecting renewable power plants to the grid can cause dynamic controlling problems if

the electricity network is not prepared for handling such variations due to the intermittency of

renewable sources availability

Problem

Therefore, a continuous and reliable power supply is hardly possible without energy storage. Using

an energy storage system, the surplus energy can be stored when the power generation exceeds

the demand and then be released to cover the rest hour periods when the net load exists, providing

a robust flexible back-up for intermittent renewable sources

Solution

This has the advantage in

increasing the system flexibility

and reliability, decreasing the

variability of renewable sources

availability, since the variable

power output can be levelled

out due to a complementary

nature between renewable

resources through their

integration in the hydropower by

a pumped storage solution


The problem of designing a PHS system is complex and, although it could be done on an iterative

procedure, by defining several possible scenarios and comparing the technical and economical

results, this would be a time-consuming approach, possibly not leading to the optimal results.

Therefore, it is important to have a more systematic approach


DESIGN OF A HYBRID SYSTEM

Undersized hybrid

system is more cost-

effective, but may

not be able to meet

the load demand and

viability studies

HYBRID SYSTEM

SIZED

Oversized hybrid

system satisfies the

load demand, it can be

an unnecessarily

expensive solution

Optimum size of the hybrid renewable

energy power system depends on several

simulations based on specific mathematical

models and system components management

towards the best solution

HYBRID AND PUMPED HYDRO STORAGE TECHNOLOGIES

Different energy resources can be combined building an integrated hybrid energy system that

complements the drawbacks existing in each individual energy solution

Therefore, the design goals for hybrid power systems are the minimization of power production

cost, purchasing energy from the grid (if it is connected), the reduction of emissions, the total life

cycle cost and increasing the reliability and flexibility of the power generation system

The pumped hydro storage can be seen

as the most promising technology to

increase renewable energy levels in

power systems

In some locations, the

solar and wind resources

have an anti-correlation,

complementing each

other and giving a

combined less variable

output than

independently

Hydro, wind, solar and pumped hydro storage (PHS), as hybrid power solutions, constitute a

realistic and feasible option to achieve high renewable levels, considering that their

components are properly sized


The distribution of daily-mean wind

(green) and solar PV (red) power output

each month, both scaled by their long-

term all-year average

PHS schemes currently provide the most commercially important means of large-scale grid

energy storage and improve the daily capacity factor of the generation system

Pumped hydropower energy

storage stores energy in the

form of potential energy

that is pumped from a

lower reservoir to a higher

one putting the water

source available to turbine

to fit the energy demand


The principle of PHS is to store electrical

energy by utilizing the potential energy of

water.

• In periods of low demand and high

availability of electrical energy the water

will be pumped and stored in an upper

reservoir/pond.

• On demand the energy can be released

respectively transformed into electrical

power within a short reaction time.

Therefore PHS can adjust the demand supply

to balance respectively, reducing the gap

between peak and off-peak hours, and playing

an important role of levelling other power

generation plants and stabilizing the power

grid.


Basically there are four types of PHS concepts which are distinguished by the water regime

Off-stream, this type consist of an upper and lower reservoirs

connected by a power waterway. Off-stream are PHS mainly

divided in single purpose (pure pumped storage) or multiple

purpose usage

Pump-back, reversible units installed at an on-

stream hydropower plant to firm up peaking capacity

during occasional periods of low flow


Diversion type or so called water transfer PHS divert water

from one river basin to another

Seawater, (the Okinawa Seawater demonstration

plant) by utilization of seawater for the lower

reservoir has been built in Japan


This system is equipped with a

photovoltaic (PV) system array, a wind

turbine, an energy storage system

(pumped-hydro storage), a control

station and an end-user (load)

A typical conceptual pumped hydro storage system with wind and solar

power options for transferring water from lower to upper reservoir:

This whole system can be isolated from

the grid, i.e., as a standalone system or

in a grid connection where the control

station can be the grid inertia capacity.

This is currently the most cost-effective

means of storing large amounts of

renewable energy, based on decisive

factors, such as, capital costs, suitable

topography and climate changes

challenges


The design criteria are mainly derived by the power market demands and actual site characteristics


To develop a PHS project the design criteria have to be transferred into a technical concept

There is no common approach to transfer

design criteria to develop a PHS project

It is a “puzzle” of engineering judgment

and knowledge transfer as well as

experience


The layout of the HPHS project will be developed based on the site existing

characteristics

Desirable site characteristics:

• Geological conditions should be suitable;

• Head is proposed to be as high as suitable;

• Length of the penstock should be not too

much long;

• Suitable size for sufficient power installation;

• Site should be located reasonable closely to

load centers or transmission corridors

HYBRID PUMPED HYDRO STORAGE

Machine types differ in their flexibility to participate in the reserve markets

and in their investment cost


Ternary set systems allow to significantly reduce transition time

compared to conventional reversible turbines. A ternary set consists

of a separate turbine and pump on a single shaft with an electric

machine that can operate as either a generator or a motor

The main available solution to realize variable speed operations are

doubly fed induction machines (DFIMs) and converter fed

synchronous machine (CFSM)

In the DFIM the stator is directly connected to the grid, while the

rotor windings are connected via a power electronic converter using

slip rings. Through frequency control of the rotor current, it is

possible to have variable-speed operation while the stator frequency

and voltage remain constant. In CFSM a synchronous machine is

connected to the grid via a full-rated converter. Therefore, the

frequency of the motor–generator can vary from the grid

Machine types differ in their flexibility to participate in the reserve markets

and in their investment cost


The power market demands determine the machine configuration and the

storage volume

• How much additional

pumped storage fits to

the energy market?

• How much flexibility is

required in today’s

market?

• Which machine type

should be applied?

• What is the market

optimal capacity and

storage reservoir size?


The power market demands determine the machine configuration and the

storage volume


Transient analysis during pumping must be evaluated as characteristics differ

significantly from turbine mode

Hydraulic transient events are disturbances in the

water conduit cased during changes in the state

from flowing to non flow conditions and vice versa

Typical cases are:

• Turbine/Pump start up or shut down,

• Valve opening and closing (variation in cross-

sectional flow area),

• Changes in boundary conditions (e.g. adjustments

in the water level at reservoirs)

• Rapid changes in demand conditions,

• Changes in transmission conditions, and

• Pipe / tunnel filling or draining

The main design techniques are used to

mitigate transient conditions such as:

• Alteration of pipeline characteristics

• Improvement in valve, turbine and

pump control procedures, and

• Design and installation of surge

protection devices


Transient analysis

Special attention must be given to

the extremes: the maximum and

minimum energy heads, discharges,

power, maximum changes of load

from speed (full load rejection, to

partial or full load)

Pump / Turbines normal operating

conditions represent all 15 lines.

Normal modes of operation for hydro power plants


Transient analysis Normal modes of operation for hydro power plants

Colored lines 14 and 15 are cases

when control and protection system

trigger emergency shut-down at

overspeed and overflow

If not properly designed these 14 and

15 cases are sources of troubles and

accidents

The turbine over speed signal was

reached and emergency stop level

close the guide vanes which has been

enough to result in an accident


Transient analysis

An installation having unstable

characteristics, in a trial/error

corrector mode (PID) operation,

pump turbine excited penstock

resonance and resulted in

penstock rupture and casualties.

We can see the measured

pressure resonance in this

operation prior to penstock rupture


Transient analysis

Preliminary analyses and the engineer’s experience are useful for deciding whether additional

devices will be needed for diminishing the amplitudes of the pressure surges or preventing

pressure surges

Those devices might be surge tank(s), pressure regulator valves, air injection, governor controls,

or air chambers. If the system includes any of those devices, assume that the devices will

function correctly when making the analyses for the normal cases

Reducing the rate at which valves or wicket gates close also can diminish or prevent pressure

surges. Analyze the various cases to find which initial conditions, together with the various

transient conditions, result in the most extreme high or low pressures or the most extreme high or

low rotating speeds


https://youtu.be/yfZoq68x7lY

https://youtu.be/yfZoq68x7lY

Multi-criteria tool

An electrical generating system composed primarily

by wind and solar technologies, with pumped-storage

hydropower schemes, is defined, predicting how

much renewable power and storage capacity should

be installed to satisfy renewables-only generation

solutions

It explores the combined

production of hydro, solar and

wind, for the best challenge of

energy storage flexibility,

reliability and sustainability

Technique based on a multi-

criteria evaluation, for a

sustainable technical solution

based on renewable sources

integration

MULTI-CRITERIA TOOL

OPTIMAL DESIGN OF A HYBRID SYSTEM

The purposed mathematical model can predict how much wind, solar power and pumped hydro-

storage energy capacity should be installed to satisfy a hybrid renewable solution

As for solar energy although less

fluctuating, it only works during day light

hours. It offers more reliable power and

can be committed and managed, using

relatively smaller energy storage systems

to provide continuous and quality power

Wind is highly fluctuating meteorological

parameter changing every hour and

annually. Therefore, to connect wind power

with the grid and assure quality power

supply, large energy storage systems are

required

Pumped hydropower storage plants have several advantages:

(1) flexible start/stop and fast response speed,

(2) ability to track load variations and adapt to severe load changes,

(3) capacity to modulate the frequency and maintain voltage stability and

face climate change and reduce footprint effects on an integrated solution.

The optimal design of a hybrid solar–wind-

system supported by a pumped-based hydro

scheme can significantly enhance the technical

and economic performance for efficient energy

harnessing

The multi-variable techniques are also known

for their accuracy and simplicity when

encountering complicated optimization

problems

The main objective is to analyze the

capacity of such a system to be able to

store the excess of wind/solar energy, at

times when energy demand is lower, and

provide reserves in the form of hydropower

at times when consumption exceeds the

wind/solar production or, alternatively,

making the system self-sufficient

Multi-criteria tool


𝐸𝑖𝑡, 𝐸𝑖

𝑝depend on the tri-time tariff

Multi-criteria tool

Vi is for water volume at time (i)

Ei is for energy at time (i)

Di is the demand at time (i)

Hi is for hybrid power/energy available

at time (i)

Si is the solar energy at time (i)

Wi is for wind energy at time (i)

The superscripts (p, t, res) are assigned

for pump, turbine and reservoir

If 𝑖 𝑖

Yes

Start

Input demand data of energy demand (D), wind (W) and solar (S) along the time

Use dimensionless values, depending on the arbitrated peak consumption and the installed wind and solar power (using peak factors ( ))

e.g.,Wind , Solar , , Storage ,

No

Calculate the wind/solar hybrid power/energy

available: 𝑖 𝑖 𝑖

No

𝐸𝑖𝑝

𝑖𝑝

𝐸𝑖𝑡

𝑖𝑡

No

No No

𝑖 𝑖= 𝐸𝑖𝑝

𝑖𝑝 𝐸𝑖

𝑝 𝑝

𝐸𝑖𝑡 𝑖 𝑖

𝑖𝑡 𝐸𝑖

𝑡 𝑡

YesYes

𝑖 𝑖

𝑖𝑡 𝑖

𝑝

𝑖 𝑖

𝑖𝑡 𝑖

𝑖 𝑖

𝑖𝑝

YesYes

𝑖𝑝 𝑝

𝑝 𝑝

𝑖𝑡 𝑡

𝑡 𝑡


𝑝 𝑖

𝑡 𝑖 𝑝 𝑖

Qtmax is the maximum turbine flow

is the maximum pumped flow Qpmax

is the maximum pumped volumeVpmax

Vtmax is the maximum turbine volume

Vpi is the pumped volume at time (i)

Vti is the turbine volume at time (i)

is the maximum pumped energyEpmax

Etmax is the maximum turbine energy

Epi is the pumped energy at time (i)

Eti is the turbine energy at time (i)


If 𝑖 𝑖

Yes

Start

Input demand data of energy demand (D), wind (W) and solar (S) along the time

Use dimensionless values, depending on the arbitrated peak consumption and the installed wind and solar power (using peak factors ( ))

e.g.,Wind , Solar , , Storage ,

No

Calculate the wind/solar hybrid power/energy

available: 𝑖 𝑖 𝑖

No

𝐸𝑖𝑝

𝑖𝑝

𝐸𝑖𝑡

𝑖𝑡

No

No No

𝑖 𝑖= 𝐸𝑖𝑝

𝑖𝑝 𝐸𝑖

𝑝 𝑝

𝐸𝑖𝑡 𝑖 𝑖

𝑖𝑡 𝐸𝑖

𝑡 𝑡

YesYes

𝑖 𝑖

𝑖𝑡 𝑖

𝑝

𝑖 𝑖

𝑖𝑡 𝑖

𝑖 𝑖

𝑖𝑝

YesYes

𝑖𝑝 𝑝

𝑝 𝑝

𝑖𝑡 𝑡

𝑡 𝑡


𝑝 𝑖

𝑡 𝑖 𝑝 𝑖

Multi-criteria tool

This model was

developed for a time

scale of one average

year, assuming hourly

variations, where

dimensional data

regarding variations in

electricity demand and

wind/solar energy

production


The proposed dispatch model selects the best combination of peak factors to reach the optimal

solution in terms of efficiency, energy exploitation, cost, and footprint

The peak factor is the ratio of the total flow to the average daily flow in a water system and is

important in the study of a water system to determine potential water consumption values

The pumping process is done during the empty hours (i.e., of lower demand) and the hydroelectric

generation through peak hours (i.e., for highest demand)

The consumption during the off-peak hours is satisfied exclusively by wind/solar, while in the

remaining period, the power generation is complemented by hydro, if insufficient wind/solar

production is verified

Excess wind/solar energy that is not used for consumption in the system is used for pumping. In this

way, it is possible to reduce the purchase costs of electricity from the grid


Operating Principles and Important Restrictions

𝑽𝒎𝒊𝒏𝒓𝒆𝒔 > 𝟎.𝟏𝟓𝑽𝒎𝒂𝒙

𝒓𝒆𝒔

𝑽𝒊𝒓𝒆𝒔 = 𝑽𝒊 𝟏

𝒓𝒆𝒔 + 𝑽𝒊𝒑 𝑽𝒊

𝒕

𝑽𝒊𝒑≥

𝑸𝒎𝒊𝒏𝒑

𝑸𝒎𝒂𝒙𝒑 𝑽𝒎𝒂𝒙

𝒑, 𝑽𝒊

𝒕 ≥𝑸𝒎𝒊𝒏

𝒕

𝑸𝒎𝒂𝒙𝒕

𝑽𝒎𝒂𝒙𝒕

∆𝑬𝒊 = 𝑯𝒊 𝑫𝒊

𝑰𝒇 𝑽𝒊𝒓𝒆𝒔 ≥ 𝑽𝒎𝒂𝒙

𝒓𝒆𝒔 → 𝑽𝒊𝒑

= 𝟎

𝑬𝒍𝒔𝒆 𝑽𝒊𝒑

= 𝑬𝒊𝒑𝜼𝒑 𝝆𝒈𝑯 × 𝟑𝟔𝟎𝟎

𝑰𝒇 𝑽𝒊𝒓𝒆𝒔 ≤ 𝑽𝒎𝒊𝒏

𝒓𝒆𝒔 → 𝑽𝒊𝒕 = 𝟎

𝑬𝒍𝒔𝒆 𝑽𝒊𝒕 = 𝑬𝒊

𝒕 𝝆𝒈𝑯𝜼𝒕 × 𝟑𝟔𝟎𝟎

𝑰𝒇 𝒕𝒊𝒎𝒆 = 𝒐𝒇𝒇𝒑𝒆𝒂𝒌 𝒑𝒆𝒓𝒊𝒐𝒅 → 𝑬𝒊𝒑

= 𝑷𝒖𝒎𝒑 𝒑𝒐𝒘𝒆𝒓 𝒊𝒏𝒔𝒕𝒂𝒍𝒍𝒆𝒅 , 𝑬𝒊𝒕 = 𝟎

𝑬𝒍𝒔𝒆 𝑬𝒊𝒑

= 𝟎 , 𝑬𝒊𝒕 = ∆𝑬𝒊

OPERATING CONDITIONS RESTRICTIONS CONSIDERED

𝑬𝒊𝒑 𝑷𝒖𝒎𝒑 𝒑𝒐𝒘𝒆𝒓 𝒅𝒆𝒇𝒊𝒏𝒆𝒅


As the pumping system works in the early hours of the day (0-7h) the system presents sufficient

reserves to be able to assist intermittent renewable energy production failures during the remaining

period


𝑝depend on the tri-time tariff

The daily cycle for electricity supply, dictated by

the tri-time tariff applied in mainland Portugal

TARIF PERIOD WINTER SUMMER

WORKDAYS

Peak 5h/day 3h/day

Half-peak 12h/day 14h/day

Normal off-peak 3h/day 3h/day

Super off-peak 4h/day 4h/day

SATURDAYS

Half-peak 7h/day

Normal off-peak 13h/day

Super off-peak 4h/day

SUNDAYS Normal off-peak 20h/day

Super off-peak 4h/day

1

The pumped hydro storage (PHS) is the energy

storage solutions, consisting on a separated

pump/motor unit and a turbine/generator unit

to manage the other renewable sources inputs

to face the energy demand


The benefit in using medium-head pumped-storage plants is to shorten transmission lines from the

alternative energy sources to the hydro storage facility, thus minimizing grid overloading due to

energy transfer across a country

Moreover, it has the advantage of locating wind or solar farms in higher topographic zones

The proposed solution focuses on a

converter connected to a

motor/generator. The efficiency

considered can vary between 60%

and 80% for pump/turbine mode,

respectively


Guidelines

GUIDELINES

PHS solutions demonstrate that technically the pumped-storage hydropower system integrating other

renewable sources is an attractive energy solution

The dynamic contribution of individual sources follow different patterns, due to the stability of hydro by

pumping and random variability of other energy sources and the energy demand

Employing the three technologies in a complementary and balanced manner, the hybrid system could

generate and store electricity at low cost, facing climate changes and reducing the footprint of electricity in a

self-sufficient solution

A consistent multi-criteria framework can be developed to optimize the availability and storage of renewable

energy, selecting the best combination of peak factors to achieve the optimum solution in terms of efficiency,

energy use, costs and footprint

Important considerations are highlighted and summarized from this multi-variable process:

The optimization showed that in a hybrid solution, turbines and pumps can be used at the same time

depending on the intermittency, availability and optimized variables, which include different renewable

sources, the storage capacity and the load demand.

The pumping system can be supplied by intermittent renewable sources when available, and at the

same time, can be guaranteed a constant power production by hydraulic turbines.

The only one pipe for the P/T solution requires different hours for each operation or the use of separate

pipes, which can offer more operating flexibility, where one is kept running, the other is stopped or in

operation, depending on the sources’ availability, constancy or intermittency, type of storage or type of

grid connection.

Three sources can be combined considering different pump/turbine installations, wind/solar powers

and different water batteries as volume capacities.

GUIDELINES

After selecting the best installation power for P/T, different conditions must be tested, changing the

wind/solar powers and the water storage capacity.

The results obtained show the process of selecting the best scenario is not straightforward, depending

on the final goal. Therefore, this type of analysis unfolds in important points:

For a specific condition, from the point of view of reliability and flexibility, there is a better use of

hydropower, specifically to accommodate the largest shares of other intermittent renewable (solar and

wind) energies with a better bridge and compensation between these energy sources

In addition, other hypothesis may involve an increase in the installed wind power from an operational

point of view, but there is an increase in satisfactory consumption

For the conditions where storage capacity increases, this does not make a significant contribution to

the best operation of the system. As a result, the reservoir is oversized to meet the satisfied

consumption, i.e., there is a dependency not only on the maximum daily energy use of the system but

also on the hydropower system

GUIDELINES

Thus, surplus energy from renewables produced at times of low demand (e.g., solar power in summer) can

be stored and ready for release when demand rises;

With more advantages and greater economic viability also in terms of CO2 emissions. The selected hybrid

solution is less expensive, considering the powers installed, with a lower initial capital cost

Additionally, it can be concluded that replacing fossil fuels by renewable energies requires:

(i) RES installations (e.g., wind turbines) widely;

(ii) using a range of different intermittent energy sources, especially those that are partially

complementary (e.g., sunny weather often means light winds and vice versa);

(iii) matching with suitable management of energy sources in periods of high demand. Still, there is

clear evidence of how all these modern integrated techniques for complementarity between

renewable sources can significantly reduce electricity tariffs and increase the reliability of the

energy supply as main targets of hybrid-energy solutions.

GUIDELINES

Hybrid Pumped Hydro Storage Energy Solutions towards Wind ...

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