Concentrated Solar Power Storage in South Africa

CSP Storage: South Africa provides insight into the current and future prospects of storage technology, as well as assessing the dispatchability potential for the South African market. In addition, it contains exclusive extracts from the CSP Today business intelligence reports.

The guide has been published in conjunction with the exciting launch of CSP Today South Africa 2014, taking place on 8-9 April in Cape Town. The must attend event for CSP developers and EPC groups who are looking to identify the opportunities and reduce CSP costs in South Africa.

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8-9 April, Cape Town

CSP Storage: South Africa

For more details on CSP Today South Africa 2014 please visit: www.csptoday.com/southafrica

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CSP Today South Africa 2014

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Overview

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CSP TODAY | CSP Storage: South Africa | www.csptoday.com/southafrica • 2

CONTENTS

CSP with Storage: Benefi ts and Challenges in South Africa

Introduction: South Africa’s Energy Mix .......3

A Brief History of CSP in South Africa .....3

Introduction: Thermal Energy Storage ........4

Thermal Energy Storage in South Africa ....4

CSP Storage Technologies

Introduction: Thermal Energy Storage technologies .................................................7

Molten Salt ...................................................7

Phase Change Materials (PCM) ................7

Concrete ........................................................7

Solid TES materials cont. ..........................8

Saturated Steam ..........................................8

Thermochemical storage ...........................9

Graphite .........................................................9

Ammonia and hydrogen .............................9

Compressed air energy storage ..............10

With South Africa providing one of the most exciting CSP markets in the world, industry focus has now turned towards understanding the intricacies of the country’s energy mix.

One of the key features of CSP technology is the potential to utilize storage and provide a truly dispatchable renewable energy supply. With energy stability and supply a critical issue for South Africa, the opportunity exists for CSP to play a leading role.

This is why CSP Today have created this guide, that outlines the drivers for storage in South Africa, as well as the drivers for this technology in South Africa.



CSP with Thermal Energy Storage (TES): Benefi ts and Challenges in South Africa

Introduction: South Africa’s Energy MixSouth Africa’s energy supply is currently characterized by insecurity and extreme uncertainty. There is simply insuffi cient power supply to meet demand. In winter months the national grid gets dangerously close to the brink of shutdown, a situation which continually threatens to destabilize commerce and industry, and compromise foreign investment.

Government, authorities and the media constantly remind the country’s people about the ever prevailing and distinct prospect of a recurrence of rolling power blackouts, with which the country was beset in the later months of 2007. South Africa’s State-owned utility, Eskom, is faced with ever increasing challenges, which could make the threat of blackouts a reality again.

Just as crucial as reliable energy supply is the need for South Africa to comply with worldwide legislation to reduce its global carbon footprint, move away from Eskom’s coal-fi red plants and contribute to the global effort to tackle climate change.

Renewable energy meets a broad array of needs, not just much needed reliable, consistent electricity supply, but also a way to possibly bring down the recent increases in power tariffs in South Africa going forward. The rising costs of energy are demonstrated by Eskom’s request for a 16% per annum tariff increase for fi ve years. This request was rejected by the National Energy Regulator of South Africa (NERSA), which granted an 8% average increase per annum over this period.

Yet renewable energy in its totality has certain restrictions – the key issue being its intermittency, as it is guided by the times that the sun is shining and the wind is blowing. It is right here that Concentrated Solar Power (CSP) stands out from the crowd. It is CSP which offers the unique characteristic, Thermal Energy Storage (TES), which overcomes intermittency. The ability to store energy enables CSP power stations to supply electricity even when there is no sun. CSP can therefore supply electricity during the evening peak time, when demand is highest. In doing so it avoids the intermittency problems encountered by PV and wind, and many renewable energy industry players advocate CSP as an integral part of the energy mix in South Africa for years to come.

A Brief History of CSP in South AfricaIn March 2011 South Africa’s Department of Energy (DOE) fi nalised details of the Integrated Resource Plan (IRP), a 20-year blueprint that showed the government’s commitment to energy from renewable sources.

The IRP indicated that renewable energy will make up a substantial 42% of all new electricity generation (totalling 17,800MW) from 2010-2030, and gave strong backing to Wind, Solar Photovoltaic’s (PV) and CSP within this new energy mix.

Under the IRP the DOE committed to produce 8400MW from solar PV, 8400MW from wind and 1000MW from CSP through the Renewable Energy Independent Power Producer Programme (REIPPP). In August 2011 the fi rst request for proposals for renewable projects was opened by the government



allocating 200MW to CSP in this initial stage, leaving 800MW available for future rounds.

By December 2011 the Department of Energy had received 53 bids across all the different technologies, awarding 28 projects to independent power producers made up of 632MW of PV, 150MW of CSP and 634MW of Wind.

The two CSP tenders were awarded to Abengoa, a leading Spanish multinational renewable energy developer, that included the 50MW Khi Solar One plant and the 100 MW KaXu Solar One plant.

The bidding for window II of the REIPPP closed on 5 March 2012 with a total of 79 bids received. The total capacity of bids amounted to 3,255MW, far exceeding the cap that was set at 1,275MW across all technologies. The CSP allocation for window II was a maximum of 50MW (the capacity remaining from the 200MW assigned to CSP in the initial request for proposals).

On 21 May 2012 this 50MW was allocated to a consortium led by ACWA Power International, the Saudi Water and Power giant, and the South African energy company Solafrica to develop the Bokpoort CSP Power Plant.

In September 2012 the DOE announced delays to Round III of the REIPPP due to the diffi culty in advancing Round I and II projects to fi nancial close. The deadline for window I projects was initially scheduled for 20 June 2012, but was pushed back to October that year. Window II also faced delays, achieving the fi nancial close milestone on 9 May 2013, over 5 months later than the initial 13 December deadline.

200 MW was allocated to CSP for the third window of the REIPPPP. Originally scheduled to take place on 7 May 2013, Round III of the REIPPPP closed on 19 August, and the industry will learn who the preferred bidders are on 29 October.

Introduction: Thermal Energy Storage (TES) The incorporation of energy storage into CSP plants gives solar thermal technologies a unique advantage over other renewable energy technologies and in particular over solar PV at a time when the latter is able to deliver highly-attractive LCOE values. Thermal energy storage is nowadays essential to CSP plants to produce price-competitive energy through dispatchability.

Although, the initial investment costs are increased when implementing a TES system, the overall LCOE of the plant is reduced, making the CSP plant more

economically and technically attractive.

The integration of TES is not only driven by the reduction of LCOE and technology improvements, but also by emerging solar policies: Governments around the world have realized the relevance of CSP with TES as a potential ingredient to their future electrical energy portfolio. With fl uctuating capacity, inherent to most renewable energy technologies, addressing grid stability will become capital. In addition to the allocation of capacity for the development of CSP plants, many governments have also included mandatory use of TES for this reason.

Thermal Energy Storage in South AfricaTo encourage CSP with storage to generate energy during peak time, the South African Department of Energy (DoE) recently introduced an incentive in the form of a Time of Day (TOD) tariff.

A base tariff applies during the day and a higher tariff will be applied for supplying energy during peak time. According to the initial proposal, a bidder supplying energy during the peak time between 17h00 and 21h00 would get 240% of the base tariff, while there is no payment for supplying energy at night. Recently the peak period was extended from 16h30 to 21h30 and the tariff increased to 270% of the base tariff.

What has the reaction been from industry players to the new TOD tariff?

California-based global solar power developer, SolarReserve, provider of utility scale CSP with thermal energy storage (TES), sees the TOD tariff in a very positive light. In a recent interview with CSP



Today, Stephen Mullennix, Solar Reserve’s Senior Vice President of Asset Management, emphasized that “Utility scale energy storage is critical for South Africa in order to maintain stability in the grid, and to match energy supply with energy demand”.

Mullennix went on to explain that “the TOD tariff recognizes the intrinsic value of storage for shifting generation in order to meet demand. SolarReserve believes that South Africa will capture more signifi cant value by offering a TOD tariff, than by procuring intermittent energy”.

“The tariff enables a CSP plant with utility scale storage to be built instead of both an intermittent renewable supply, as well as a backup fossil supply. This derives greater value for all parties from the signifi cant capital investment needed to bring the plant online. In addition it brings economic stability to the operating period for all parties compared to the volatile fuel pricing markets such as coal.”

Marc Immerman, a Director of Solafrica, who recently commenced construction at its 50MW Bokpoort project in the Northern Cape, says: “The TOD tariff structure should result in a more sustainable procurement for CSP in South Africa given the morning and evening peak electrical demand in South Africa. As CSP is the only renewable technology able to store energy, this inherent value is now effectively recognized by the South African Department of Energy.”

Professor Wikus van Niekerk, Director of the Centre for Renewable and Sustainable Energy Studies at Stellenbosch University, comments. “I think this incentive is exactly what the CSP projects in South Africa need in order to demonstrate the real value of the electricity that CSP can generate.

“The TOD tariff for CSP is a signifi cant breakthrough that acknowledges the contribution of thermal energy storage. This will now allow CSP to not only compete with the existing open cycle gas turbine (OCGT) peaking plants but will also augment the PV plants in the evening hours.”

Interestingly, as a result of the new tariff, some prospective bidders without storage who were planning to submit for Window 3 of the REIPPP program were forced to withdraw their bids.

“The new TOD tariff does not make fi nancial sense for a CSP project without storage, and will force all future CSP plants to have storage,” says Riaan Meyer, CEO of GeoSUN Africa, a spin-off of the Centre for Renewable and Sustainable Energy Studies (CRSES) at Stellenbosch University.

“I support the new TOD tariff since it will promote CSP with storage, but it was released only in early May this year, three and a half months before the bid submission of 19 August. This meant that CSP projects without storage planning to submit withdrew their bids. The developers I spoke to will resubmit in a next bid window projects with storage,” Meyer continues.



CSP Storage: South Africa was created by CSP Today using its latest business intelligence reports: the Parabolic Trough Report 2014: Cost, Performance and Thermal Storage and the Solar Tower Report 2014: Cost, Performance and Thermal Storage. This fi rst section contains extracts from these technology reports to explain the potential for CSP integration with storage.

CSP Storage Technologies

The thermal storage capability of a CSP plant is one of the main features facilitating the integration of CSP into the grid. The objective of TES is as follows:

Provide dispatchable energy, extending the operating hours beyond sunset when no solar radiation is available Avoid fl uctuations associated with the intermittent

solar resource Reduce dumped energy making the plant more

effi cient

The current TES technology employed in commercial operating plants consists of one or more pairs of tanks where molten salts are stored at two temperature levels, providing a temperature differential that is used to generate steam. The molten salts have a melting point in the range of 230-240°C, and TES in a parabolic trough plant consists of the following components:

Cold tank(s) where molten salts are stored at a temperature range of 290-300°C Hot tank(s) where molten salts are stored at a

temperature range of 380-390°C

Heat exchangers where the molten salts exchange thermal energy with the Heat Transfer Fluid (HTF). This feature is not required if the HTF is also molten salt Pumps to move the molten salt between the cold

and hot tank(s)

During the charge mode of the TES, some hot HTF mass fl ow leaving the solar fi eld is sent to the TES where it heats up the circulating molten salts from the cold tank(s) to the hot tank(s). As a consequence, the cold molten salt is heated up to 380-390°C and is stored in the hot tank(s) for later use. During the discharge mode of the TES, the operating principle is reversed and the molten salts stored in the hot tank(s) are sent to the cold tank(s), passing through the heat exchangers where they release thermal energy to heat up the HTF. (See Figure 1 for an overview of an oil HTF parabolic trough plant with TES).

Commonly in modern solar power tower plants molten salt is used as the heat transfer medium (HTF), and it is also used for TES. In this system molten salt, at 290°C, is pumped out of a “cold” storage tank to the external receiver on top of a tower where it is heated to 565°C and delivered to a “hot” storage tank. The hot salt is then

Figure 1: Oil HTF Parabolic Trough Schematic

-390°C -375°C380°C

290°C

Heat exchanger

Thermal energy storage

Steam generator

Steam turbine

Condenser

Solar fi eld

Source: Parabolic Trough Report 2014: Cost, Performance and Thermal Storage



extracted for the generation of 552°C/ 126bar steam in the steam generator. This principle of using the molten salt as both the HTF and TES is also being demonstrated in new parabolic trough plants, such as Enel’s Archimede plant in Sicily. These higher operating temperatures are favourable for increased thermal conversion effi ciency, and ultimately mean that more watt-hours are stored per unit of fl uid. (See Figure 2 for an overview of a molten salt HTF parabolic trough plant with TES).

An Overview: Thermal Energy Storage technologiesAlthough a wide range of energy storage solutions have been proposed, only molten salts and synthetic oils are seeing serious commercial use. However, current R&D efforts have led to a number of developments in energy storage, mainly spurred on by the possibilities of plants operating at higher temperatures. (See Figure 3 on the next page for an overview of Thermal Energy Storage technologies).

Molten SaltAs of today, molten salt has been the only technology implemented for extended utility-scale parabolic trough and solar tower TES using a eutectic mixture of 60% sodium nitrate and 40% potassium nitrate.

Very few single-component salts exist which have melting point within the 300 to 500°C range, such as sodium and potassium nitrates. While single-component salts are more practical from an industrial perspective, the scarcity of such salts limits their application, and therefore, multi-component systems

are considered more practical for industrial applications.

To decrease the cost of molten salt TES systems, the energy storage density of the fl uid must either be increased, or the storage temperature must be raised. For the former to be achieved, new multi-component formulations can be devised, or additives used. Additives can also prevent solid freeze from occurring, and ensure the solid-state salt remains as slush.

Phase Change Materials (PCM)PCM, where a material stores and releases energy when changing between its solid, liquid or gaseous states, holds much promise. Current efforts to utilize phase change materials are geared to using tried-and-tested sodium and potassium nitrate eutectics and leveraging the latent heat required to melt the solid salt combination.

The world’s largest PCM pilot is in Carboneras, in the Almeria region of Spain and is intended to show whether PCM could become a viable alternative to molten salt as a thermal storage medium for CSP, although commercialization is likely to be several years away.

One challenge to address in PCM was the insulating properties of the solid salt in the heat exchanger pipes. Researchers say they were able to get around this problem by adding fi ns to the exchange tube, increasing the heat transfer surface area.

ConcreteThe German Aerospace Center (DLR) is exploring the performance, durability and cost of using solid, thermal

Figure 2: Molten Salt HTF Parabolic Trough Schematic

-550°C 535°C550°C

290°C

Auxiliary Heater

Thermal energy storage

Steam generator

Steam turbine

Condenser

Solar fi eld




energy storage media (high-temperature concrete or) in parabolic trough power plants using standard heat transfer media that passes through pipes located within the solid storage material. As previously stated, solid media provide considerable saving potential, but also have issues which include maintaining good contact between the concrete and piping, and lower to the heat transfer rates into and out of the solid medium.

At the Almeria Solar Platform in Southern Spain, Ciemat and DLR performed initial testing to demonstrate that both castable ceramics and high-temperature concrete are suitable as solid media for sensible heat storage systems. That said, the high-temperature concrete would be preferable for its lower costs, higher material strength, and easier handling as well as longevity.

The modularity of concrete also constitutes a strong incentive towards this material, also allowing for perhaps better integration with the solar fi eld and power cycle

Solid TES materialsOther solid materials have been proposed and utilized for TES, including rocks, pebbles, slag, sand and manufactured ceramic spheres. However, different minerals have varying thermal properties, so care must be taken in their selection.

Benefi ts: Locally available Reduce transport and purchase costs.

Cheap Applicable to Trough and Tower Heat up to 650°C Scalable

One challenge is that the casing containing the solid TES is relatively sophisticated as stones, for example, undergo thermal expansion, so very rigid walls are required. This means the walls themselves will be good thermal conductors, which could not only mean leakage of heat outside the system but would corrupt the heat stratifi cation of the thermal storage unit. To counter this, a thin layer of high-resistance concrete on the inside of the casing, surrounded by a more porous concrete for insulation of the system, then a microporous insulator layer, a foam glass layer and fi nally a concrete outer structure are required.

Saturated SteamFor storage, Direct Steam Generation (DSG) poses a limitation, as opposed to molten salts and oil HTFs, since a combination of sensible heat storage for preheating and superheating, as well as latent heat storage for evaporation, has to be used. This could, however, be achieved using PCMs, or two independent storage media. For sensible heat, the same storage media can be used as for other HTFs, but for latent heat, for example, sodium nitrate could be used, as proposed by DLR.

There is also another type of heat storage, called Ruths storage, which works as a steam accumulator using pressurized liquid water. Hot steam enters the

Thermal Energy Storage

Latent

Salts

Metal alloys

Sensible

Molten salt two tank

Packed bed thermocline

Concrete thermocline

Sand-shifting two tank

Thermochemical

Metal oxide

Sulfur cycles

Ammonia decomposition


Figure 3: Possible CSP Thermal Energy Storage Technologies



system and is then compressed, converting the steam into superheated liquid water. However, research has shown that this has a limited application for CSP as it is expensive.

Thermochemical storageThermochemical TES is a promising new type of TES, which permits more compact storage through greater energy storage densities.

Thermochemical storage is based on a reversible chemical reaction, which is energy demanding in one direction and energy yielding in the reverse direction.

Benefi ts: Very high energy densities achievable Mitigates losses Extend dispatchability towards base-load power

generation

Unlike sensible and latent approaches to energy storage, thermochemical systems can retain their stored energy for almost unlimited time periods. If thermochemical energy storage can be proven at a reasonable scale within the few next years then commercial deployment might be possible sometime after 2020.

GraphiteGraphite can be heated to thousands of degrees, which could greatly increase the effi ciency of CSP compared to the 560-570ºC of molten salts. Furthermore, only a few suppliers can offer molten salt of the quality required by the industry, which has increased costs to

the point where the storage material is a signifi cant expense for operators. Graphite, on the other hand, is comparatively plentiful and cheap.

Benefi ts: High energy density High level of thermal inertia Good relationship between heat input and output Ease of working and shaping Relatively low cost and high availability

Weaknesses: It glows and oxidizes above 450°C. This can be

overcome by encasing the material in an oxygen-free environment It’s too heavy, limiting scalability, particularly with

power towers Large amounts of piping needed

Ammonia and hydrogenThese alternative fuels are carbon-free and can be produced from any energy source. CSP can produce hydrogen and ammonia and then use the fi nal product as a fuel either to generate electricity, or act as a replacement for gasoline or diesel to power vehicles.

For hydrogen, the heat generated by CSP could be used with a solid oxide electrolyzer cell to split water at temperatures up to 900°C with a higher effi ciency than conventional steam (alkaline) electrolysis at near-room temperature.

Ammonia, meanwhile, has been used periodically as a fuel for the last 60 years and it can be used in



current vehicle engines and fuel or gas power plants with only minor modifi cations. Unlike hydrogen, it can be distributed using existing gas and oil pipelines. It also has an energy density two to four times that of hydrogen.

Compressed air energy storageCompressed air energy storage (CAES) has many potential applications for energy storage beyond CSP, and is not a form of TES. Essentially, power is used to compress air, which is later released to drive a turbine. Compression heats the air, while decompression cools it, so heat exchangers and possibly heaters may be required to ensure temperatures stay within an acceptable range, which of course has a negative impact on the thermal effi ciency of the process.

In the only two operating commercially-viable, largescale CAES facilities, this adiabatic process is used to hold pressurized air in large underground

caverns. This places geographical constraints on the method. More fl exible approaches include those proposed by SustainX Energy Storage Solutions and LightSail Energy, which would store the compressed air in tanks, making it less location-dependent than existing geological systems. LightSail uses a fi ne water spray to capture the heat of compression, which is then used in the expansion phase of the process. The company claims that the roundtrip thermal effi ciency is 90%, scalable up to 100 kW. LightSail has attracted funding from backers such as Bill Gates and Peter Theil.

The SustainX system, meanwhile, compresses and expands the gas within hydraulic cylinders, which allows the controlled transfer of heat with the ambient surroundings during compression and expansion. The company has demonstrated thermal effi ciencies greater than 90% for both compression and expansion. According to the company, a US DoE-funded demonstration project is currently underway.

We hope that this guide to CSP storage potential for South Africa proved useful. With the market in South Africa gaining momentum, a pipeline of CSP projects is emerging - creating opportunities for companies to build a business in the region.

The guide was created in conjunction with the launch of CSP Today South Africa 2014, taking place next February in Johannesburg. The event will show you how to reduce CSP costs and risk through international experience and investor insight to prove your competitiveness.

For more information please visit: www.csptoday.com/southafrica

or contact Brandon Paramo: +44 20 7422 4302

[email protected]

+44 20 7422 4302

[email protected]

Published in August 2013, CSP Today’s latest business intelligence reports – the Parabolic Trough Report 2014: Cost, Performance and Thermal Storage and the Solar Tower Report 2014: Cost, Performance and Thermal Storage – respond to the most critical needs of CSP stakeholders, representing 5 months of research and culminating in high-quality data and analysis. At the core of these publications – which follow a mirrored structure for comparative purposes – is the desire to fi rstly determine the true cost attributes and performance outputs associated with each technology across 8 global markets based upon the latest industry validated and localised cost data, and secondly, use these techno-economic and inter-market benchmarking results to identify where the greatest cost reduction and performance optimization gains can both be made and are required.

For more information on these publications and to view our complete Business Intelligence Portfolio please visit www.csptoday.com/research

Technology

Concentrated Solar Power Storage in South Africa