The sun shines, but not always… - EE Publishers · Energize RE: Renewable Energy Supplement -...
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Energize RE: Renewable Energy Supplement - June 2015 - Page 51 Private RE Systems The sun shines, but not always… by Cleverson Takiguchi, S&C Electric Solar power development in Africa has until now been predominantly concentrated in the North African region, largely due to its export potential. With encouraging recent examples in the south, east and the west, solar energy has gained more and more participation in the generation mix in Africa. Solar potential stretches far beyond the Sahara desert as almost all of Africa’s countries receive sufficient sunlight to efficiently and economically generate solar energy, estimated at an impressive 2 MWh/m 2 annually and that on average, most subsaharan nations receive 325 days of sunlight annually. Despite massive potential, the region has witnessed little progress in terms of solar power deployment due to limited government and private-player investment potential. In South Africa great strides were made through the renewable energy independent power producer procurement programme (REIPPPP) which by the 3rd round has accumulated over 1500 MW of PV and over 400 MW of CSP. Additionally, in South Africa, NERSA (National Regulator) is working on a draft for the connection of small-scale embedded generation which among others includes roof-top solar. As one could expect with benefits comes challenges, especially with solar energy which is an intermittent renewable energy source. Utilities will start to see issues in terms of grid stability especially for the distributed (or embedded) generation which is located at what is called the “edge of the grid”. Such impacts get amplified as solar energy increases in terms of total generation to meet demand. Variable output from solar generation produces local voltage swings that can impact power quality for customers, including voltage excursions beyond accepted power quality standards. This output variation may also contribute to distribution feeder-level voltage swings, which can occur in a matter of seconds. Traditional distribution voltage regulation equipment typically is not suited to respond to such rapid, highly variable fluctuations. The inverters of PV plants can be oversized to perform voltage- Var control but that means additional cost for the developers without a proper regulatory framework to reward them in some cases. Background Around 25 years ago, we were asking “Would it be possible to feed entire residential, commercial and, possibly, industrial areas only with power from the sun?” Nowadays, the question has changed: nobody is discussing if “it will be possible”, but “when it will be feasible”. The solar PV utility scale facilities make it possible to get the generation near the consumer, in any place where the sun shines, whether it is a remote island or at top of a mountain range. It is not a matter of “can we do?” anymore. The problem that emerged is that the variability of the generation source, created unpredictability for planning of the electric system. Additionally, PV produces only during times when the sun is shining, which changes the paradigm of a dispatchable energy supply reservoir the utilities are used to. All this makes solar (and wind) power, despite being abundant, not unreliable from the utility point of view. Within this context, bulk energy storage starts to play a prominent role. Pumped hydro, compressed air (CAES), super capacitors and flywheels are technologies that received some attention from government funding and R&D departments but one technology in particularly has shown to be more economically feasible and in most of the cases, has added technical advantages: Batteries. Bulk energy storage Solar PV generation is starting to embrace battery based energy storage. With different battery technologies and chemistries available, engineers can evaluate which one will be the better suited for a particular application in that specific geographic area, adding more technical and commercial benefits for the customer or utility. Not surprisingly, battery based energy storage is currently widely used on Solar PV utility scale generation. Due to the intermittent nature of solar power generation, cloud shadows and/or air dust can have an undesirable impact on the grid. In addition to providing benefits of smoothing intermittent PV output, the energy storage can bring many benefits: energy backup (provide stored energy to an industrial facility, to improve reliability), energy arbitrage (store energy in a time when prices are low, and supply or use it when prices are high) or energy supply (store in a time when have plenty energy, and supply it when energy is lacking), as showed on Fig. 2. The storage systems can provide a series of technical benefits that will make them a necessity when connecting solar or other intermittent generation sources at weaker/remote locations on the existing electric grid worldwide. The flexibility of use of battery based energy storage is extensive. From stored electricity for short periods of time to give a quick injection of energy to deal with the grid’s fluctuations; to storing the energy for several hours for dispatch at a more beneficial time such as to meet peak demand. Except for a few mature technologies, many approaches in energy storage are considered expensive, but what is the most expensive energy? Simple, it is the energy you don’t have! Battery technology Several start-ups, public utilities, private agents and governments are investing Fig. 1: Storage system acting as energy supply.
Transcript of The sun shines, but not always… - EE Publishers · Energize RE: Renewable Energy Supplement -...
Energize RE: Renewable Energy Supplement - June 2015 - Page 51
Private RE Systems
The sun shines, but not always… by Cleverson Takiguchi, S&C Electric
Solar power development in Africa has until now been predominantly concentrated in the North African region, largely due to its export potential. With encouraging recent examples in the south, east and the west, solar energy has gained more and more participation in the generation mix in Africa.
Solar potential stretches far beyond the Sahara desert as almost all of Africa’s countries receive sufficient sunlight to efficiently and economically generate solar energy, estimated at an impressive 2 MWh/m2 annually and that on average, most subsaharan nations receive 325 days of sunlight annually. Despite massive potential, the region has witnessed little progress in terms of solar power deployment due to limited government and private-player investment potential.
In South Africa great strides were made through the renewable energy independent power producer procurement programme (REIPPPP) which by the 3rd round has accumulated over 1500 MW of PV and over 400 MW of CSP. Additionally, in South Africa, NERSA (National Regulator) is working on a draft for the connection of small-scale embedded generation which among others includes roof-top solar.
As one could expect with benefits comes challenges, especially with solar energy which is an intermittent renewable energy source. Utilities will start to see issues in terms of grid stability especially for the distributed (or embedded) generation which is located at what is called the “edge of the grid”. Such impacts get amplified as solar energy increases in terms of total generation to meet demand. Variable output from solar generation produces local voltage swings that can impact power quality for customers, including voltage excursions beyond accepted power quality standards. This output variation may also contribute to distribution feeder-level voltage swings, which
can occur in a matter of seconds. Traditional distribution voltage regulation equipment typically is not suited to respond to such rapid, highly variable fluctuations. The inverters of PV plants can be oversized to perform voltage-Var control but that means additional cost for the developers without a proper regulatory framework to reward them in some cases.
Background
Around 25 years ago, we were asking “Would it be possible to feed entire residential, commercial and, possibly, industrial areas only with power from the sun?” Nowadays, the question has changed: nobody is discussing if “it will be possible”, but “when it will be feasible”. The solar PV utility scale facilities make it possible to get the generation near the consumer, in any place where the sun shines, whether it is a remote island or at top of a mountain range. It is not a matter of “can we do?” anymore.
The problem that emerged is that the variability of the generation source, created unpredictability for planning of the electric system. Additionally, PV produces only during times when the sun is shining, which changes the paradigm of a dispatchable energy supply reservoir the utilities are used to. All this makes solar (and wind) power, despite being abundant, not unreliable from the utility point of view.
Within this context, bulk energy storage starts to play a prominent role. Pumped hydro, compressed air (CAES), super capacitors and flywheels are technologies that received some at tent ion f rom government funding and R&D departments
but one technology in particularly has shown to be more economically feasible and in most of the cases, has added technical advantages: Batteries.
Bulk energy storage
Solar PV generation is starting to embrace battery based energy storage. With different battery technologies and chemistries available, engineers can evaluate which one will be the better suited for a particular application in that specific geographic area, adding more technical and commercial benefits for the customer or utility. Not surprisingly, battery based energy storage is currently widely used on Solar PV utility scale generation.
Due to the intermittent nature of solar power generation, cloud shadows and/or air dust can have an undesirable impact on the grid. In addition to providing benefits of smoothing intermittent PV output, the energy storage can bring many benefits: energy backup (provide stored energy to an industrial facility, to improve reliability), energy arbitrage (store energy in a time when prices are low, and supply or use it when prices are high) or energy supply (store in a time when have plenty energy, and supply it when energy is lacking), as showed on Fig. 2.
The storage systems can provide a series of technical benefits that will make them a necessity when connecting solar or other intermittent generation sources at weaker/remote locations on the existing electric grid worldwide.
The flexibility of use of battery based energy storage is extensive. From stored electricity for short periods of time to give a quick injection of energy to deal with the grid’s fluctuations; to storing the energy for several hours for dispatch at a more beneficial time such as to meet peak demand. Except for a few mature technologies, many approaches in energy storage are considered expensive, but what is the most expensive energy? Simple, it is the energy you don’t have!
Battery technology
Several start-ups, public utilities, private agents and governments are investing Fig. 1: Storage system acting as energy supply.
Energize RE: Renewable Energy Supplement - June 2015 - Page 52
Private RE Systems
in research and development of bulk energy storage systems, but by far, battery technologies and chemistries are attracting most of th is money, due i ts obvious advantages: non-geographical dependent, non-weather dependent, mobility, proven technology, flexibility, as well has a developed and mature market.
Besides, it fits a wide range of applications of grid’s ancillary services and other technical benefits. Batteries can be considered the most reliable and fast growing energy storage technology at the moment.
The battery based energy storage systems also complement the smart-grid concept. These systems will soon help the utilities to comply with a more severe power quality requirement from a increasingly demanding grid code. They will also reduce the impact of electric vehicles and additional solar-roof distributed generation entering the system and causing instability at a weak point of the grid at certain times of the day.
Integrating solar generation
As solar photovoltaic power generation becomes more commonplace, the inherent intermittency of the solar resource poses one of the great challenges to those who would design and implement the next generation smart grid. Specifically, grid-tied solar power generation is a distributed resource whose output can change extremely rapidly, resulting in many issues for the distribution system operator with a large quantity of installed photovoltaic devices.
Bat ter y energy s torage sys tems are increasingly being used to help integrate solar power into the grid. These systems are capable of absorbing and delivering both real and reactive power with sub-cycle response times. With these capabilities, battery energy storage systems can mitigate issues with solar power generation such as ramp rate, frequency, and voltage issues. Beyond these applications focusing on system stability, energy storage control systems can also be integrated with energy markets to make the solar resource more economical.
Impact in distribution systems
As we get down into the distribution network we start to face additional problems which have not been experienced previously. Distribution utilities have been used to passive networks where power flow has been from the bulk supply point to the load. Now they are faced with a network that not only has power flow in both directions, but the power flow from renewable sources can be very
variable. Distributed energy storage systems, particularly when located in close proximity to renewable resources, are uniquely suited to address such challenges, including local and feeder-level voltage swings that occur far too rapidly to allow traditional distribution voltage regulation equipment to respond.
Weak distribution networks
When intermittent renewable energy resources comprise a significant amount of overall generation, distribution system problems such as voltage swings are more likely to arise. These disruptions are compounded on “weak distribution networks,” which have characteristically low fault levels. Voltage levels on networks with low fault levels may not be sufficient to support all loads.
Voltage stabilisation
Stabilisation of distribution system voltage is achieved by minimising the rate of change of Reactive power. This method uses distributed energy storage as a fast-acting, short-term resource that allows time for traditional voltage regulation equipment (including switched capacitors) to respond as steady state resources on the distribution controller. Each distributed storage unit can estimate and regulate voltage on the source side of its distribution transformer by modifying its flow of real power (watts).
Voltage profile improvement
Utilities can improve the voltage profile by co-locating renewable resources and distributed energy storage systems. When
Fig. 2: PV intermittency in a 4,6 MW power plant.
Fig. 3: Shows the use of community energy storage control the voltage profile [5].
Energize RE: Renewable Energy Supplement - June 2015 - Page 53
Private RE Systems
storage is co-located with renewable resources at distribution load points, less power needs to be supplied by traditional generation. Utilities no longer need to rely on distant traditional generation plants, which are much slower to respond than local storage, to attempt to push voltage levels back up at the far edges of the distribution system. By leveraging local battery storage, which reacts more swiftly, utilities can ensure that voltage drops are less severe and less likely to impact service. In addition most battery storage solutions also have the capability to control reactive power which can further improve the voltage control. This has the effect on better utilisation of resources. Less carbon footprint.
Reverse current flow mitigation
When energy storage is co-located with PV panels, it can prevent reverse current flow caused by excess generation during outages. Storage reliably mitigates reverse current flow by quickly consuming real power to charge its own battery. By consuming any excess power generated, battery storage prevents energising the transformer’s load side, thereby avoiding equipment damage and other potential safety problems.
Energy storage offers a key piece of the puzzle
The technology that has been demonstrating that it can significantly help with renewable integration is distributed energy storage.
Distr ibuted energy storage systems, particularly when located in close proximity to renewable resources, are well suited to
address the key challenges associated with renewable energy supplies. Variability in output from wind and solar energy generation can create local and feeder-level voltage swings that occur very rapidly. Distributed energy storage can provide fast response to help firm voltage levels and effectively fill in gaps created by large voltage swings and fluctuations. Co-locating storage and renewable energy resources gives utilities a particularly effective way to manage unwanted voltage changes, allowing them to maintain grid stability while also meeting power quality requirements.
Distributed energy storage systems also provide a dispatchable energy resource for utilities, giving them more control to ensure renewable energy supplies are available to meet demand. Renewable energy generated when demand is low is then stored to meet later demand. Distributed energy storage systems provide greater flexibility and faster response than using conventional generating plants for compensating for shortfalls in renewable generation output.
Energy storage can be economically deployed in smaller capacity sizes, too, which can help avoid the need to invest in establishing a new plant. Distributed energy storage also supports other grid functions such as peak shaving, which can provide further savings to utilities by reducing the need to maintain conventional generation, and maintaining grid capacity to meet peak demand.
Contact Cleverson Takiguchi, S&C Electric Europe, Tel 021 905-0366 [email protected]
Fig. 4: Shows the use of community energy storage to prevent reverse power flow on a feeder [5].
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