Category Archives: Sonar-Collecttors

Evaluation of Galleries

Direct sunlight enters to several spaces in the three museums. In two of these museums direct sunlight penetrates in galleries where artwork is displayed, that is the case of the Modern Art Museum and the Amon Carter Museum.

The museums were evaluated through site visits to the museums at different times of the year, interviews with curators and facility managers, photometric measurements (with and without electric lighting), photographic documentation of sunlight penetration using fish-eye photography with the SunPath program (Reference 4), and computer simulations using the ECOTECT and Desktop RADIANCE software to analyse the patterns of sunlight penetration and to calculate illuminance and luminance levels throughout the year. The following section describes the evaluation of each museum.

The Modern Art Museum

Large spans of glass illuminate the main entry lobby (north and south-facing), and the sculpture galleries (east-facing), both are two-story high spaces. Most of the galleries in the first floor are windowless and are mainly illuminated by electric light sources. The subtle transition between the highly illuminated east-facing galleries and darker windowless central galleries is successfully achieved through intermediate galleries and passages. Most of the galleries in the central area of the second floor use toplighting as the main source of illumination in combination with halogen lamps. The illuminance levels in these central galleries are well controlled through a series of internal and external louvers that intercepts most incoming direct and diffuse light rays. Light levels in these galleries do not exceed the 200-lux recommended for oil paintings. Along the west side of the second floor are located seven galleries that are illuminated mainly by side light windows with white interior screens (see Figure 2-right).

Sunlight penetration was observed throughout the year along the west-facing galleries, located on the second floor (see yellow areas of Figure 2-right). Illuminance value measured over an oil painting was between 2,000 and 4,000 lux (Figure 5), which are 10 to 20 times higher than the maximum recommended illuminance of 200 lux for oil paintings, as stated in the “IES Recommended Practice for Museum” (Reference 5).

Figure 6 is a fish-eye photo taken from an oil painting’s viewpoint with a sun path diagram, and shows the number of hours the painting is receiving direct sun on its surface. This painting is exposed to direct sunlight mainly during the late afternoon hours between 4:00 and 6:30 PM between the equinox and summer solstice. Many of these west-facing galleries cannot be used to exhibit light susceptible artwork. Several of these galleries had
remained empty since the opening of the museum, and few of them only display sculptures made of metal.

Figure 5: Direct sun over oil painting, at the Modern Art Museum’s west gallery, March 5, 2004, 6:30 PM.

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Figure 6: Fish eye photo taken from painting’s viewpoint with sun path diagram, at the Modern Art Museum’s west gallery.

The landscape

Of the 20.000 sq meters of hilly landscape, the location for the house was chosen in the middle of the south slope so that the top of the hill would protect it from cold winter winds. At the same time the view of the Farfa river Valley from the house would not be in anyway obstructed (Figure 3).

2. The design of the house

The house project was developed according to the following principles:

1. Advantage of the local renewable energy resources should be taken such as sun, vegetation, breezes and winds through bioclimatic strategies and solar technologies for

Fia.4 — Perspective of the house

heating and cooling naturally the building.

2. Traditional as well as innovative technologies are to be used so as to disseminate similar solutions in the area;

3. Technological and morphological solutions that could be applied in existing constructions are recommended;

4. Building materials with low environmental impact are to be used.

The house shape draws its inspiration from local architectural traditional buildings: very compact structures broken by terraces facing the valley (Figure 4). For administrative limitation required by the Regional Competition “Zero Emission Residential Buildings”4, the house was divided into two compact volumes (volume A and B) and organized around a Mediterranean patio with an olive tree in the centre (Figure 5). The olive tree is the most common tree of the area.

A

Volume A

A

PIANTA DEL PIANO TERRA

Fig. 5 — Floor plan of the house

A terrace facing south and covered by a light canopy of deciduous climbing plants, essential to control solar radiation in the summer, links the two volumes. This solution allows taking advantage of the surrounding microclimate of the house, particularly during the summer.

A terrace, a garage, a technical room and a storage room are built under the terrace with a portion of their south wall above the ground. The solar thermal and photovoltaic technologies are integrated on this wall. This solution while respecting the natural land slopes minimizes the terrain movement (Figure 6).

6 — A-A Section Summer ventilation behaviour

The organization of the rooms follows bioclimatic principles so that the main rooms face

Only project of 95 sq meters houses will be financed.

south while the service spaces face north. The most important transparent surfaces face south so as to take advantage of sun radiation in winter as well as the beautiful panorama in all seasons (Figure 7). All rooms are daylighted.

The two volumes have windows in the four facades, in order to allow natural cross ventilation (Figure 6). Moreover, since part of the house is very high, openings in the upper part of the volume are designed in order to promote the “stack effect” during the summer when there is no wind.

Construction Issues

An awareness of green building issues included the construction processes. In an effort to reduce wastage, minimise materials and a consciousness of cradle-to-grave costs, the following were implemented —

• with a significant amount of the building deconstructed prior to rebuilding, as much as possible of the existing structure was retained, including most of the western wall and a large section of the roofing structure. Where window openings were retained, existing window assemblies, where possible, were reglazed and painted to match new
windows, whilst other openings and the main stair were also retained as part of the new scheme;

wherever possible, demolition and packaging materials were separated for recycling, taking advantage of the services of the Council’s extensive Recycling Depot. This included separation of glass, concrete, timber, bricks and rubble, as well as paper and plastic packaging. These were then forwarded on as part of Council’s recycling program, such as rubble reused for fill, and timber sold off for use by local builders. A substantial amount of the original fitout was also sold off and removed for use by other builders and collectors;

asbestos was found on site within the original fixout, and removed with full OH&S compliance, and contained within a ‘tented’ area during demolition prior to removal for off-site burial;

implementation of Ultra-floor slab system reduced construction time as well as the amount of concrete and steel employed (and therefore costs and impact). The ribbed system, as wella s reducing concrete volume, also therefore allowed extra head room due to the thinner ability of slabs between floors. This was highly beneficial given the restriction of the existing poor height differences between floors; new voids on the upper level were a result of a design decision to reduce the contact between old and new slabs at first floor level, with ‘bridges’ connecting the slabs across at several locations. Minimal connection ensured less opportunity for movement and minimal cracking potential between the different slab qualities and ages. This also made construction easier, and was cost effective due to the reduced need for merging of the two slabs and therefore less concrete, as well as the added benefit of increased daylight penetration to the lower level;

Product Selection

Where possible, within the limitations of budget and the Council’s adaptability to change,

products were selected for their reduced impact on the environment as well as enhanced

health benefits. These included —

• external walls (all new walls, as well as existing walls made accessible during construction), were insulated with wool bulk insulation (R3.5 ceiling, R2 walls) in lieu of fibreglass, given the latter’s unresolved health issues;

• HDPE (High Density Polyethylene) was used instead of PVC for all drainage and plumbing, again in light of the relevant unresolved health issues of the chlorine content of standard PVC fittings;

• natural linoleum use for flooring in lieu of vinyl which normally contains PVC;

• timber selected only from plantation grown supply, without use of rainforest or imported timbers;

• the new Council Chamber furniture was locally crafted from old bridge timbers from the original Cowra Bridge;

Additionally, local and/or Australian-made products were given preference to imported

products and materials.

Ray tracing results

The results of penetration for specular materials are depicted in Fig. 1. In all of them it is clearly shown that most of the absorption takes place in the first 5 to 20 mm of the duct, advancing an apparent lack of “volumetricity”. Parameters like reflectivity, pitch and view angle are influencing the profile of absorption and cumulated energy through the channel.

Fig. 1. Plots summarizing the profiles of absorbed energy through the specular channel for different values of view angle, channel pitch and reflectivity.

Specular reflectance model shows the maximum penetrability achievable within channels. Therefore a high reflectance material is strongly recommended since the flux distribution within duct is in these cases smoother. However in all cases higher incident flux values are reached within the first millimetres of the duct what will lead to the higher material temperature values closer to the channel entrance. This fact is by itself contrary to the volumetric philosophy.

Obviously the increment of channel pitch leads to a better penetration of photons, but this increment cannot be indefinite since we may presume that cumulated energy decreases because of higher radiation losses. View angles below 30° seem to be more adequate for volumetric receivers as well. High reflectivity materials lead to a change of penetration

profile and then a peak is registered a few mm inside the channel. On the contrary, when low reflectivities are used the maximum absorption is obtained at the front edge.

Fig. 2. Plots summarizing the profiles of absorbed energy through the channel for different values of reflectivity at diffuse and specular models.

In the case of the specular model the channels work as light traps, and therefore the cumulative energy through the channels increases to reach the total value of 1. When this value is not reached within the graph this is because the depth of the represented channel is not big enough.

In the case of the diffuse model part of the incident radiation is lost through the channel aperture (Fig. 2). The channel itself is of course a light trap increasing significantly the apparent absorptivity of the channel from the material absorptivity values (Fig. 3). The cumulated energy through the channels reaches an asymptotic value representing the apparent absorptivity of the duct. The diffuse model shows that apparent reflectivity is more sensitive to viewangle parameter than pitch length (Fig. 3 y Fig. 4).

The real case will be neither the specular model nor the diffuse model but something in between.

Ray tracing provides clues on internal behaviour of light, but only with a thermal analysis we may quantify some of the effects. Because of that we decided to analyze the influence of the previous photon penetration profiles on heat transfer figures.

Fig. 3. Apparent absorptivity of the channel as a function of material absorptivity and pitch length for the diffuse model

Fig. 4. Apparent absorptivity of the channel as a function of viewangle and pitch length for the diffuse model.

Desiccant and evaporative cooling open cycles: standard and novel systems

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Standard desiccant systems are used to produce conditioned fresh air directly. Therefore, they can be used only if the air-conditioning system includes some equipment to remove the surplus internal loads by supplying conditioned ventilation air to the building. In the majority of cases this air-flow consists of ambient air, which needs to be cooled and dehumidified in order to meet the required supply air conditions. In desiccant cooling systems employing sorptive rotors, the components installed in the air-handling unit are activated according to the operation mode of the air-conditioning system.

These operation modes implement different physical processes for air treatment, depending on the load and the outdoor air conditions.

DEC systems are based on the physical principle of desiccant and evaporative cooling. Unsaturated air is able to take up water until a state of equilibrium, namely saturation has been achieved.

The evaporative cooling process uses the evaporation of liquid water to cool an air stream.

The lower the relative humidity of the air, the higher is the potential for evaporative cooling. In this type of air conditioning systems the dehumidification effect is used for two purposes: to enhance the combined evaporative cooling potential at given environmental conditions and to control the humidity of ventilation air. However, a standard desiccant cycle is not able to provide desired supply air temperature and humidity states under all conditions. Particularly in hot — Figure 1-Psychometric chart representing humid climates the desiccant cooling cycle has the standard DEC pr°cess path

limitations. Therefore in those cases employing

standard components such as a rotary dehumidifier, a combination of a desiccant cooling air handling unit with a cold backup system is needed. The ECOS provides a valuable option for air-conditioning applications in hot-humid climates without the need of a back-up system. Moreover the new concept can be implemented for small capacity plants (about 200 m3/h) overcoming a traditional restriction of standard DEC plants.

. Pre-selection of technologies

In the first planning phase of a solar assisted air conditioning system, the type of the building to be equipped with the air-conditioning system and the use of the building has to be closer analysed. High attention should be paid to architectural and technical measures which reduce the cooling load, e. g. by implementation of external shadings, night ventilation in combination with the thermal inertia of the building and by decreasing the internal loads as far as possible.

For further investigations, an annually load file should be prepared, containing at least hourly values of cooling and heating loads as well as humidification and dehumidification requirements. The load structure of a considered building area depends beside the physical properties of the building and the thermal and radiative gains on the usage of the building,

i. e. the frequency of occupation, occupation density and on the additional technical equipment in the rooms. The determination of a representative time series of loads is necessary since the correlation between solar radiation power and heating/cooling loads determines the energy demand from auxiliary sources as well as the utilisation of the solar thermal sub-system. Including these effects into the annual energy balance allows to assess primary energy savings, to choose appropriate sizes of the core components and thus to obtain reasonable economic figures of the planned installation. Several load calculation methods, e. g., according to the German standard VDI 2078 /1/, and building simulation programs like TRNSYS, ESP, etc., may be applied for this purpose.

A simplified decision scheme is presented in Figure 1 in order to support the pre-selection of air-conditioning technologies, which can be used in combination with solar thermal systems.

Building

Figure 1: Simplified decision scheme of thermally driven air-conditioning systems. It is assumed that both, indoor temperature and humidity are to be controlled. The starting point is the assessment of the cooling loads and of the required air exchange rates. If the installation of a centralized air handling unit is feasible, the following basic decision is, whether or not the hygienic air change rate is sufficient to cover the cooling loads (latent + sensible). This will be typically the case in rooms with high ventilation rates, as required e. g. in lecture rooms. Next, the tightness of the building shell has to be considered for the decision, whether a supply/return air system makes sense or not. Depending on these building and load oriented tasks, the decision on the distribution medium is made: either a pure chilled water system, a pure air system or combined solutions are possible. Finally, the technology (third column) has to be selected. In case a chilled water supply is necessary, the lowest required temperature level of the chilled water is determined by the question

Distribution medium

whether air dehumidification is realised by cooling the air below the dew point (conventional technique) or whether air dehumidification is realised by a desiccant process. In the latter case, the temperature of the chilled water may be higher since it has to cover sensible loads only. In extreme climates with high ambient air humidities, special configurations of the desiccant cooling cycle are required, when this technology will be employed.

Short cuts: DEC = Desiccant Cooling system, AHU = Air Handling Unit.

The scheme presented in Figure 1 can help to approach to the most appropriate technical

solution but does not cover the following questions:

— Necessity of a backup system for the cold/heat production or to allow solar autonomous operation of the solar assisted air-conditioning system;

— Type of the thermally driven chiller, e. g., absorption chiller or adsorption chiller;

— Flexibility in comfort conditions, e. g., to allow certain deviations from the desired air states;

— Economical issues;

— Availability of water for humidifiers in an air-handling unit or for cooling towers;

— Comfort habits for room installations: fan coils have lowest investment cost, but allow dehumidification only when connected to a drainage system; chilled ceilings and other gravity cooling systems require high investment cost, but provide high comfort.

Additional constraints may arise from an architectural / planning point of view or from

economic considerations:

— possibility to install the required air ducts in existing buildings

— question how the desired technical solution fits to the technical infrastructure of an exis­ting building (e. g., if a cold water distribution system already exists this might lead to such a system because of economical considerations even if fig. 1 leads to a pure air system)

— available area to install the required solar collector field

— available space for technical equipment (e. g. thermally driven chillers, buffer storage, desiccant air handling unit)

Discussion

From the results it is clear that low luminance ratios (of no more than 1:20) and a gradual decrease in luminance values can only be obtained when a. the material absorbs a certain amount (but not all) of the incoming light, b. the material reflects some of the incoming light onto the wall. This conclusion, however, is not complete. The conclusion should be written in terms of reduced transmission: low luminance ratios (of no more than 1:20) and a gradual decrease in luminance values can only be obtained when a. the material reduces the amount of the incoming light by absorption or reflection and b. the material reflects some of the incoming light onto the wall.

Figure 4: Effect of the size of the anidolic element on the luminance distribution on the wall

By substituting absorption with transmission, the origin of the main difference between the anidolic element described in earlier work and the materials described in this paper is clarified. This anidolic element was designed for optimal luminance ratios between the wall and the window. That this is indeed the case, has already been shown by van der Voorden et al. [3]. Besides increasing the luminance ratios between the inner facade and the window, the anidolic element can also influence the size of the luminance ratio by applying a smaller or larger anidolic element, see figure 4. A larger element will receive more light and distribute thus more light onto the inner facade.

However, the anidolic element takes up a lot of space, especially the larger ones which have the lower luminance ratios. The size of the element perpendicular to the window is about half the size of the opening along the wall. And the anidolic element in its optimal position is situated in such a way that the end of the element is in the same position as the beginning of the wall next to the window. This means that the occupant of the building can still see the sky directly when the person’s main view is not perpendicular to the window but under a slight angle. In such a situation the visual comfort is immensely decreased. An overlap of the other materials like net curtain and screen in front of the window, prevent the occupant’s direct view of the sky. An overlap of the anidolic element with the wall can create a dark line on the wall next to the window when the focus line of the anidolic element is shifted due to a horizontal shift along the window of the element. If not the
element is moved sideways, but the length of the element is increased, then the bright focus line is obscured by the longer element, thus increasing the low luminance ratios. An overlap of the other materials like net curtain and screen + 1 cm, achieves a larger amount of light on the wall compared with the material which does not overlap, due to the diffuse property of the material and its possible internal reflections.

6. Conclusion

All above results were obtained in a black office with a white wall next to the window. In a grey or white office the luminance ratios are automatically lower due to the contribution of the internal reflections to the amount of light on the walls. For new buildings, it is therefore clear that the window posts must be painted as light as possible, as was already mentioned by [7]. For luminance ratios that are still too high a transition region in the window by adding a pattern to the edges of the windowpane will already improve the visual comfort. If the luminance ratio between the window and the wall is even higher, a translucent, diffuse material positioned in front of the window and in front of a part of the wall will improve the visual comfort. This overlap will also prevent the occupant of the building from viewing the sky directly when the person’s main view is not perpendicular to the window. A coloured material can be applied, but this has the adverse effect that the view outside becomes coloured as well.

The luminance ratios for the investigated materials are always lower than the ones that can be achieved with an anidolic element, whether it is perforated or not, due to the focussing power of the specular element. However, the anidolic element takes up more space, and does not increase visual comfort for every position in a room.

References

1. Velds, M, Assessment of lighting quality in office rooms with daylighting systems, Ph. D. Thesis, 2000, Technical University Delft

2. Bokel, R. M.J., Heijmans B. N., Pel M., Voorden M. van der, Proceedings of the International Building Physics Conference, 2000, Eindhoven, The Netherlands.

3. Voorden M. van der, M. B.C. Aries, R. M.J. Bokel, Development of a contrast-reducing anidolic shaped element, Proceedings of PLEA conference 2002 (Toulouse).

4. Dutch NEN-norm 3078

5. Moore, F. Concepts and practice of architectural daylighting, Van Nostand Reinhold Company Inc., New York. 1985.

6. Osterhaus, W. K.E., S. E. Selkowitz, Background and conceptual plan for conducting post occupance evaluations of interior luminous environments, Energy and Environment Division, Lawrence Berkeley Laboratory, Berkeley, USA, 1992

Photovoltaic properties

For monitoring the photovoltaic performance of the system, a separate prototype with a hybrid absorber with polycrystalline silicon cells and a reflector was constructed.

The optical efficiency g(a) is defined as the ratio between the performance of the concentrating module and a vertical module of the same area as the concentrating aperture. It was determined through outdoor measurements. The short circuit current Isc of the concentrator module was monitored as a function of the angle of incidence p in the meridian plane. The optical efficiency (figure 6), was then derived according to

[Eq. (3)]

^(a) =

Isc -1000

I1000 • • G ■ cos(fl)

where 11000 is the short circuit current of the bare module at an irradiance of 1000 W/m2 at normal incidence, Cg is the geometrical concentration of the concentrator system, p is the angle of incidence of beam irradiance, and G is the global intensity perpendicular to the sun.

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Figure 6: Optical efficiency RT(QT) of the Solar Window and the transmittance of the glazing f(Q).

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

The measurements were performed during high irradiance and with a diffuse fraction of around 10%. The concentrator accepts all irradiance for solar altitudes exceeding 15° in the meridian plane, which means that the diffuse optical performance of the concentrator will be similar to that of a module tilted 20° with a correction for reflectance losses. This further means that the optical acceptance of diffuse irradiance will be around 70% of the beam efficiency. For this reason, the global intensity can be used in Eq (3) without significantly increasing the error of the model.

The optical efficiencies are functions of the projected angle of incidence in the transversal plane (i. e. the north south vertical plane) and the transmission of the glazing is given as a function of the conventional angle of incidence. Ray tracing represents the theoretical optical efficiency of the system at 85% reflectance. The graph labeled Optical efficiency — Isc in figure 6 contains contributions from measurements with corrections from ray tracing. The difference between measured values and ray tracing at 15°<0T<60° is due to resistive losses in the cells when the reflector is effective. The cells on the prototype absorber did not cover the whole width of the absorber, which meant that for angles above 40° the reflected beam partly missed the cell. The angulars above 40° are instead generated by ray tracing. The transmission of the glazing has also been included in the graph as it was used in the calculations of the annual output.

A simulation software, MINSUN (Chant and Hakansson 1985), estimated the annual output of electricity using the optical efficiencies at different angles of incidence. The model used to describe the incidence angle dependence of the system in MINSUN is defined by Eq. (4)

[Eq. (4)]

Пар, — RT (@T )fL (A )

RT describes the behaviour of the reflector as dependent of QT and fL the transmission of the window glass as dependent of 0, . QT is the projected angle of incidence in the transversal plane and в, is the conventional angle of incidence relative to the glass normal.

This model has previously been shown to describe the optical performance of an asymmetric compound parabolic reflector system such as this one well (Brogren et al, 2004).

The simulations show a 93% increase in electrical output for the concentrator module relative to the vertical reference module, which means that one square meter of this window annually would deliver 79 kWh of electric energy. The annual performance is 43% higher than that of an identical module tilted 20°.

The active area of the tested measured prototype covers only 87% of the total glazed area, which this has to be taken into consideration when an economical comparison is made with other systems. It is however possible to increase the active area of the window in a future full scale installation.

AUTOMATION OF SOLAR PLANTS

L. J. Yebra1, M. Berenguel2, M. Romero1, D. Martinez1, A. Valverde1

1L. J. Yebra, M. Romero, D. Martinez, A. Valverde, CIEMAT-Plataforma Solar de Almerla,
Apdo. 22, E 04200, Tabernas, Almerla, Spain, Phone: +34 950 387923, Fax: +34 950
365015, E-mail: luis. yebra@psa. es

2M. Berenguel, Universidad de Almerla. Departamento de Lenguajes y Computacion. Area de
Ingenierla de Sistemas y Automatica, Ctra. Sacramento s/n, La Canada, E 04120, Almerla,
Spain, Phone: +34 950 015683, Fax: +34 950 015129, E-mail: beren@ual. es

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This work overviews some of the main activities and research lines that are being carried out within the scope of the specific collaboration agreement between the Plataforma Solar de Almerla-CIEMAT (PSA-CIEMAT) and the Automatic Control, Electronics and Robotics research group of the Universidad de Almerla (TEP197) titled “Development of control systems and tools for thermosolar plants" and the projects financed by the MCYT DPI2001-2380-C02-02 and DPI2002-04375-C03. The research is directed by the need of improving the efficiency of the process through which the energy provided by the sun is totally or partially used as energy source, as far as diminishing the costs associated to the operation and maintenance of the installations that use this energy source. The final objective is to develop different automatic control systems and techniques aimed at improving the competitiveness of solar plants. The paper summarizes different objectives and automatic control approaches that are being implemented in different facilities at the PSA-CIEMAT: central receiver systems and solar furnace. For each one of these facilities, a systematic procedure is being followed, composed of several steps: (i) development of dynamic models using the newest modeling technologies (both for simulation and control purposes), (ii) development of fully automated data acquisition and control systems including software tools facilitating the analysis of data and the application of knowledge to the controlled plants and (iii) synthesis of advanced controllers using techniques successfully used in the process industry and development of new and optimized control algorithms for solar plants. These aspects are summarized in this work.

Specific energy of ice storage

A simple calculation shows the interesting result, that the cooling capacity in the ice storage is at similar level as in a lead battery based on both volume and weight.

One supplier of lead battery informs, that a 50 Ah, 12 Volts battery has the weight of 13,6 kg. The dimesions are 0.24*0.175*0.175 meters. The energy content of 50 Ah can be calculated as a specific energy content of 0.159 MJ/kg or 294 MJ/m3.

The cooling system will have a COP-value (coefficient of performance) of about 1.3 (Danfoss BD35F, CECOMAF-data for -15 °С, 2000 RPM). This will result in a specific cooling capacity of 0.206 MJ/kg or 382 MJ/m3. For the ice storage: the specific cooling capacity is identical to the melting heat of ice, which is 0.333 MJ/kg or 333 MJ/m3.

The conclusion is, that the specific cooling capacity of ice is 62 % higher compared to lead battery on basis of weight and 13 % smaller compared with lead battery based on volume. In reality, the ice storage outperforms the lead-acid battery, because the allowed daily cycling is less than the nominal 50 Ah, which corresponds to 100% depth of discharge.