Solar multi-generation in the Mediterranean area, the experience
of the STS-MED project
Alaric C. Montenon1, Filippo Paredes2, Alberto Giaconia3, N. Fylaktos1, Silvana Di Bono2,
Costas N. Papanicolas1 and Fabio Montagnino2
1 The Cyprus Institute, Aglantzia (Cyprus)
2 Consorzio ARCA, Palermo (Italy)
3 ENEA Casaccia Research Center, Rome (Italy)
A solar multi-generation approach has been implemented through four demonstrative plants in Italy, Cyprus,
Jordan and Egypt based upon solar concentrating collectors. Different design options have been developed,
including technologies that have been adapted and downsized from the utility scale of CSP plants, with the
aim to be integrated at building, settlement and community scale. Demo plants have been conceived as living
labs in order to support the further development of the technologies in a real-life environment, supporting the
local smart specialization strategies in collaboration with SMEs, local stakeholders and citizens.
Keywords: multi-generation, solar thermal, CSP, storage, concentrating solar collectors, solar cooling,
building integration, smart specialization, living labs
Global space cooling energy consumption increased by 60% between 2000 and 2010, reaching 4% of global
consumption (OECD/IEA Report 2013), meanwhile the production of heat accounts for more than 50% of
global final energy consumption (OECD/IEA Report 2014). The seasonal switch among the winter demand
of heat and the summer demand of cold is already a characteristic of the solar belt regions, including the
Mediterranean area. Therefore, specific efforts are needed in piloting innovative approaches to cover the
complex mix of heat, electricity, cold and other energy driven services by an optimized harvest, storage and
conversion of the solar radiation. As a matter of fact, seasonal demand can be holistically managed at a
settlement level by multi-generative solar concentration systems; the collection of high quality solar
radiation, mostly available in summer periods, can feed a solar cooling system in the hot days, while the
same collectors can cover the moderate heat demand in winter-time. Electricity can be generated from small
turbines or integrated PV panels. Residual heat can be used to drive other services, as the purification of
brackish, waste water or sea water desalination. Since November 2012, such a challenge is undertaken
through the Small scale Thermal Solar district units for Mediterranean communities (STS-Med) project,
supported by the ENPI- CBCMED program, with the construction of 4 pilot plants:
x in Palermo, Italy, led by Consorzio ARCA - coordinator of STS-Med - in the campus of the
University of Palermo, in partnership with the Italian National Agency for New Technologies,
Energy and Sustainable Economic Development (ENEA) for the Thermal Energy Storage (TES)
x in Aglantzia, Cyprus, led by the Cyprus Institute (CyI), in the campus of the institute,
x in Markaz Belbes, Egypt, at Sekem Hospital, led by Academy of Scientific Research and
Technology (ASRT) and built by Elsewedy Electric,
x in Irbid, Jordan, led by Al Balqa Applied University (ALBUN) and built by Millennium Energy
The 4 plants demonstrate that a smart integration and optimization of both commercially available and
innovative solar technologies can open a way towards the goal of “zero energy” communities in the
Mediterranean region (Rashad et al. 2015 and Kiwan et al. 2016).
© 2016. The Authors. Published by International Solar Energy Society
Selection and/or peer review under responsibility of Scientific Committee
doi:10.18086/eurosun.2016.05.06 Available at http://proceedings.ises.org
Figure 1. Novel Technologies Laboratory (left), rooftop of the University College in Irbid (right)
The buildings concerned self-produce the energy they need through sustainable systems, integrated at a
settlement level, with a significant reduction of CO2 emissions and consumption especially in seasonal peak.
The design of each demo site has been adapted accordingly with the result of specific energy audits and the
availability of either ground or roof space for the collectors. Local communities have been involved in
awareness activities and local SMEs have been invited to take part into educational activities during the
preparatory and erection phases.
In Italy, the collectors are installed in a field nearby the building and the plant is generating electricity by an
existing ORC (Organic Rankine Cycle) and heat/cold with the help of an absorption chiller integrated on the
HVAC system. The case-study in Cyprus is located in the premises of the Cyprus Institute in Aglanzia
(district of Nicosia), Cyprus. The objective of the plant is to support the heating, cooling and hot water
system of the Novel Technologies Laboratory (NTL, Figure 1, left) by reducing the use of the existing
electric heat-pumps. NTL was designed to be a “near to zero energy” building (Papanicolas 2015 et al.) by a
specific selection of the materials and orientation of the windows and walls, which minimize the energy
demand for air-conditioning. A 14.5 kW peak power photovoltaic generator covers a part of its electricity
consumption. In Jordan the collector is installed on the roof of one of the buildings at University College in
Irbid (Figure 1, right). As for the Cypriot plant, the system is installed on the roof a public building (Figure 2,
right). The objective of the plant is to provide heating and cooling to classrooms of the university and hot
water in case of over-production. A small steam turbine can be activated to generate electricity. The pilot
plant in Egypt is located in Belbes to support Sekem medical center HVAC, at 60 km from Cairo city center
as the crow flies. The collector is installed on plain field next to the hospital. A small ORC turbine is
generating electricity balancing the seasonal demand of cold.
2. Solar collectors
As shown in Figure 2 and Figure 3, solar fields in Cyprus, Egypt and Italy are based on North-South aligned
Linear Fresnel Collectors (LFC) or Linear Fresnel Reflectors (LFR). The installed LFRs, specifically
designed for integration in built environments, have been developed by Idea (Vasta 2013 et al.), an Italian
company affiliated to Consorzio ARCA. In Jordan the plant relies on a Parabolic Tough Collector (PTC,
Figure 3) manufactured by the Italian company Soltigua. The characteristics of the collectors are detailed in
Table 1. Platforms are located at different latitudes, from 30°25'05.5"N in Egypt to 38°06'01.0"N in Italy.
Figure 2. LFR at Palermo, Italy (left) and Nicosia, Cyprus (right)
Figure 3. PTC at Irbid, Jordan (left) and LFR at Egypt Markaz Belbes (right)
Table 1. Characteristics of the solar fields
Aglantzia, on the
roof of a s
next to the NTL
Palermo, on the
ground at ARCA
Irbid, roof a
building of the
Average DNI per year
Type of collector
LFR - Idea
LFR - Idea
PTC - Soltigua
Global aperture area
Thermal oil, Heat
Transfer Fluid (HTF)
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Peak thermal power
32 m 52 m
84 m (3 x 28 m
(outlet) 170°C 140°C 280°C 240°C
All the collectors are working with thermal oil as heat transfer fluid (HTF) at different temperature: from
140°C to 280°C. The total thermal peak power of the plants is 460kW. The platform in Palermo is the main
contributor with 190kW with 3 identical LFC parallel loops. Figure 4 shows a simplified layout of the solar
plant installed in Sicily.
Figure 4. Layout of the field at ARCA (Sicily)
Figure 5. DNI and thermal power on the 6th of September 2016 (Italy)
The thermal power and DNI on the 6th of September 2016 are shown in Figure 5. A peak of 160kW was
achieved at 12.30PM. In Cyprus 70kW peak power is installed. On the 26th of July 2016, the Fresnel
collector was commissioned. Thermal power and DNI are show in Figure 6. The output power reached 68.7
kW with a DNI of 800 W.m-2 at 12.52PM.
Figure 6. DNI and thermal power on the 26th of July 2016 (Cyprus)
The peak power installed in Egypt is 115kW and 85kW in Jordan. All the 4 for plants are equipped with a
vacuum receiver and with the association of a secondary reflector for the LFRs in Cyprus, Egypt and Italy
with estimated 90% optical efficiency. DNI is the highest in Jordan with 2377kWh.m-2 per year. DNI in
Cyprus is 2142kWh.m-2 per year and in Egypt 1958kWh.m-2 (Source: SolarGis Imaps, Beták et al. 2012).
DNI in Palermo is the lowest with 1703 kWh.m-2 per year. The solar fields were all completed in September
2016. Dimension of the mirrors of the 3 LFRs are identical: 0.32m x 2.000m. Cypriot LFR was the first to be
installed on the island (Montenon and Fylaktos 2016). It is composed of 288 mirrors with a reflective area of
184.32 m2, driven by 72 DC motors (4 mirrors per motor). In Egypt, the system is composed of 468 mirrors
and the reflective area is 299.52 m2, but driven by 13 DC motors (36 mirrors per motor). The Italian field is
hybrid: 2 LFC modules are configured as in Egypt and the third collector is configured according to the
Cypriot model. In this way it is possible to lead comparisons between the two strategies. On the one hand in
Cyprus the flexibility of the field is higher but requires more maintenance due to larger number of motors: if
one motor fails, the system will be only slightly impacted and can continuously operate with the rest of the
71 motors. On the other hand, the Egyptian collector relies on fewer motors, so requiring less maintenance,
but if one motor has to be changed a larger area of the solar field will be impacted; furthermore, tracking
angles of the motors is not independent and the whole field cannot be placed in flat position for cleaning
purpose for instance. In Cyprus and Italy, HTF loops are separated from the thermal storage medium.
Nonetheless, small buffers are installed in the HTF loops in order to stabilize the temperatures.
11 13 15 17 19
Thermal power (kW)
DNI Thermal power
Thermal power (kW)
DNI Thermal power
Figure 7. HTF Loop at CyI (Cyprus) : oil loop (left) and pressurized vessel (right)
As shown on the main layout (Figure 4), in Sicily, on the field installed at ARCA a buffer tank is also
integrated in the HTF loop with a total volume of 800L containing 500L of thermal oil (Paratherm NF)
pressurized with nitrogen at 3bar (for a thermal storage capacity of 22kWh). In Cyprus the thermal oil
(Duratherm 450) is stored temporarily in an 800L tank (containing 425L of oil), pressurized with nitrogen at
3bar (Figure 7). A 3kW electric heater is wrapped around the tank to pre-heat the oil in case of cold start-up.
The role of these tanks is also to stabilize the outlet temperature of the piping. Pre-heating the oil decreases
the viscosity of the HTF and increases the Reynolds number to maintain it above 10,000 (turbulent flow).
Based on experience, the solar absorber pipe bends at low ranges of the Reynolds number, due to thermal
gradients, and it may get in contact and break the external glazing pipe. As soon as the oil inside the
buffering tanks is heated to a satisfactory value, the inverter pump of the HTF loop starts. The control of the
platforms in Cyprus and Italy aims to correlate the output with the real time value of the DNI. To that end,
two pyrheliometers are installed on the respective sites (Figure 8).
Figure 8. Pyrheliometers at ARCA (left) and the Cyprus Institute (right)
3. Thermal storage
Thermal storage is a key element of the four platforms. It permits to buffer the production for some minutes
to several hours. Details of the thermal storage in use in the 4 platforms are exposed in Table 2. In the plants
built in Jordan and Egypt, the HTF is directly stored respectively at 240°C and 140°C. In both Cyprus and
Italy, a heat-exchanger transfers the heat from the oil to TES system. In Cyprus thermal storage is based on
water pressurized with nitrogen up to 146°C ensuring 2 hours of autonomy for cooling in summer or 4 hours
for heating in winter. The same nitrogen tank is used to pressurize the thermal oil (Figure 9). Storage with
water is a low cost technology and vessels are available on Cypriot market.
Table 2. Thermal storages
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Figure 9. Buffer of oil, expansion vessel, thermal storage tank (left to right) at CyI (left) and molten salts storage, oil storage
and expansion tank (left to right) at ARCA (right)
Safety relief-valves are installed on the tank in case of over-pressure. The developed TES integrated in the
pilot plant built in Sicily includes innovative features. Different options have been reviewed. TES systems
commonly applied in conventional CSP plants operate with “solar salts” (molten nitrates mixture
NaNO3/KNO3 60%/40% of weight distribution), in two-tanks heat storage system operating from 290°C
(cold tank) to 385°C (hot tank) when oils are used as HTF in the solar field (Lovegrove and Stein 2012). In
small CSP plants (lower than 1MW range) it is rather difficult to replicate such a complex scheme due to the
lower operative temperatures (280°C maximum in Sicily) and principally due to the need of expert personnel
to manage molten salts loops too. Therefore, an innovative TES system has been specifically developed in
STS-Med project. It is also based on molten salts, but the management of the TES is eased. This is lower
than the melting point “solar salts”, which is around 220°C (Serrano et al. 2013). Hence, the temperature
range is much more compatible with the above-mentioned small-medium CSP temperatures (up to 300°C).
Also the “two-tanks” configuration is replaced by a single-tank system avoiding any external pumping of the
molten salts and the critical management of pipelines against freezing. In the developed TES at ARCA, all
the typical operations of a CSP plant of charging and discharging are achieved inside the single buffer tank
where given temperature gradients and molten salts circulation are easily determined. Therefore, besides
lower equipment volume and cost reduction potentials, the plant operator does not have to manage molten
salts flows. Thus, the developed TES is tailored for residential users and fits into the STS-Med requirements.
The developed TES system is represented in Figure 10. The operation concept is based on the properties of
unmixed molten salts in the tank to thermally stratify along the vertical axis, as an effect of their low thermal
conductivity and the density variability with temperature. Two heat exchangers are immersed in the zones
where the temperature is lower (bottom) and higher (top) to be operated during the charging and discharging
phases. In a conventional two-tanks TES systems with the high temperature tank at TS-high = 385°C (and the
low temperature tank at TS-low = 290°C) about 280 m3 of “solar salts” shall be loaded to store 20 MWh
thermal energy, to drive a steam Rankine cycle.
Figure 10. Optimized TES system developed for STS-Med: general scheme with explanatory working conditions (left) and
prototype drawings (right)
The same principle can be applied to a smaller TES system with maximum temperature of 300°C, combined
with an Organic Rankine Cycle. In the pilot plant in Sicily, TES is filled up with about 7 m3 of eutectic
ternary salt mixture (42%/15%/43% of weight distribution). Considering the reduction of the overall amount
of salt, the use of a single tank instead of two tanks and the avoidance of external molten salt pumps and
pipelines, the cost (€/kWh thermal) of this optimized heat storage system developed can compete with the
large scale CSP benchmark.
In the framework of the STS-Med project a small TES prototype of 0.96 m3 has been designed, built,
installed and successfully tested at ENEA-Casaccia research center (Rome) in order to validate the concept
before the installation in the pilot plant in Sicily. Loading, mixing, and melting procedures of the salts in the
TES have been studied. The experimental results and concept validation with the prototype enhanced the
design of an up-scaled TES for the demonstration plant in Palermo. Specifically, further optimizations and
improvements have been performed in a “new” version of the TES installed in the STS-Med pilot plant in
Sicily. This upgraded prototype is designed to work in a thermal range of 160-280°C. It is characterized by
an inner volume around 8.0m3 (1.8m diameter, 4m height) corresponding to effective heat capacity of about
400kWh (thermal). The charging/discharging thermal power averages 250/125 kW (thermal). The tank has
been insulated with a 20cm coating of rock wool.
4. Cooling, heating and hot water
Cooling is the central task of all the STS-Med platforms, due to climate considerations in the Mediterranean
areas concerned by the project. The 4 plants rely on absorption chillers (Figure 11) to provide chilled water
at 7°C. The global cooling capacity of the platforms averages 110.1kW. Chillers in Cyprus, Egypt and Italy
are LiBr (Lithium Bromide) based, while in Jordan it is ammonia based. In Cyprus, the model used is
YAZAKI WFC-SC10. It is water-fired at low temperature (88°C inlet, 83°C outlet). Its cooling capacity is
35kW with a COP (Coefficient of Performance) of 0.7.
Table 3. List of absorption chillers
LiBr – Single
LiBr – Single
LiBr – Double
Ammonia – Single
Figure 11. Absorption chiller and cooling tower at CyI (left) and at ARCA (right)
The heat is transferred to the absorption chiller from the thermal storage medium through a heat-exchanger
(pressurized-water and water). Then the heat is stored in a 500L tank of water. This stabilizes the inlet
temperature for the chiller. A cooling tower dissipates the heat from the absorber and condenser chambers
(Figure 11). In Egypt the same capacity chiller is used but the heat medium is thermal oil instead of water. In
Italy, the double effect absorption chiller is the most performant with a COP of 1 and it includes its own
cooling tower (Figure 12). The cooling capacity is 23kW. The Jordanian chiller is a Robur HT model with a
cooling capacity of 17.1kW at COP 0.6. Its working temperature is 240°C.
4.2. Heating and hot water
The absorption chillers in Egypt and Italy are also heating in winter with better COP than cooling. Heating
capacity is 48.3 kW in Sekem and 23 kW in Palermo (Figure 11). In Cyprus the absorption chiller is simply
by-passed to heat directly two water stratified tanks (2000L each). The heat is supplied to the Air Handling
Units (AHU) and the Fan Coil Units (FCU) for the offices of the NTL. In Jordan, the absorption chiller is
also by-passed in winter. If the available solar energy exceeds the cooling and electricity generation
demands, the excess heat is released to hot water network through shell and tubular heat-exchanger. The
heated water is then stored in a tank. If the excess heat exceeds the storage capacity, it is dissipated by dry
5. Electric power units
Platforms in Egypt and Italy (Figure 12) cogenerate with ORCs (Organic Rankine Cycles) fired with thermal
oil. They both have an electric capacity of 10 kW and gross efficiency of 10% (Table 4) and need a cooling
tower to dissipate the heat rejection. They produce electricity in parallel with heating or cooling. The ORC in
Egypt works with inlet temperatures of 125°C to 150°C. In Jordan the oil exchanges its heat with a steam
loop to operate a demonstrative steam turbine of 1.2kW of electric power (Figure 12).
Table 4. Power units in Egypt, Italy and Jordan
Figure 12. Steam turbine during the installation in Irbid (left) and ORC Rank turbine in Palermo with cooling tower (right)
Nowadays solar concentration platforms are designed to produce several thermal MW and generally for
electricity generation in desert places. STS-Med project demonstrated the possible application of solar
concentrating technologies within integrated multi-generative plants at small/middle scale in built
environment either on the ground (Egypt and Italy) either on roofs (Jordan and Cyprus). Production of heat
to directly drive absorption chillers through thermal energy storage permits to avoid the stage of
transformation to electricity. The residual heat can be used for electricity production with the help of ORCs.
Thus, the co-generation of heat and electricity reduces the global balance of the energy consumption of
buildings and not only the electric part. The thermal storage permits to shift the production at peak load with
good flexibility. In the plant built in Sicily an innovative thermal energy storage system based on the use of
molten salts and specifically tailored for small scale concentrating solar applications has been integrated. The
main limitation to downscale solar cooling is the lack of commercial small scale absorption chillers and
ORCs. At the same time COP of absorption chiller, even with double-effect, is still poor if compared to
electric heat-pumps. Efficiency of small ORC turbine is also poor and their application at the project scale
(5-10 kW) can be considered as demonstrative of larger (50-100kW) applications. In this scope, the 4 plants
have been conceived as living labs, introducing the technology mix into different real-life environments
acting as showcases for the respective local communities. Comparative studies of design options and
subsystems will permit to identify the best strategies for the overall optimization of both efficiency and cost;
at the same time the local academic and technical communities will have a joint and open access to the demo
facilities as platforms for future collaborations and developments.
The Small Scale Thermal Solar District Units for Mediterranean Communities (STS-MED) project was
financed by CrossBorder Cooperation initiative funded by the European Neighbourhood and Partnership
Instrument (ENPI). In its scope, the project aimed to raise 4 pilot solar plants for air-conditioning and
electricity generation in four different locations: Cyprus, Jordan, Egypt and Sicily. We would like to thank
the European Neighbourhood and Partnership Instrument, as well as the 14 partners in the project (Consorzio
ARCA, ENEA, Sicilian Region, CEEI, CEA, IASA, Egyptian new and Renewable energy ministry, ASRT,
Elsewedy Electric, Jordanian Ministry of Energy and Mineral Resources, ALBUN, Millenium Energy
Industries, Cyprus Chamber of Commerce and Industry and CyI).
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