INTEGRATED SYSTEM FOR THE CULTIVATION OF ALGAE OR PLANTS AND THE PRODUCTION OF ELECTRIC ENERGY

Abstract

An integrated process for the cultivation of algae or plants and the contemporaneous production of electric energy using a system in which a luminescent solar concentrator having a photovoltaic cell positioned on an outer side thereof is interposed between a cultivation area and a radiation source, totally or partially covering the cultivation area. The electric energy recovered from the photovoltaic cell is used in the cultivation of the algae or plants.

Claims

1. An integrated process for the contemporaneous cultivation of plants and the production of electric energy from the same radiation source, the process comprising: cultivating the plants by exposing them to said radiation source in a cultivation area comprising at least one luminescent solar concentrator comprising at least one photovoltaic cell positioned on at least one outer side thereof, said at least one luminescent solar concentrator being interposed between said cultivation area and said radiation source so as to totally or partially cover said cultivation area, to thereby obtain the plants and the electric energy; recovering the plants from the cultivation area; and recovering the electric energy from the at least one photovoltaic cell; wherein: the cultivation area is a greenhouse; and the electric energy recovered from the at least one photovoltaic cell is used in the cultivation of the plants, wherein the luminescent solar concentrator comprises at least one photoluminescent compound having an absorption range within the range of solar irradiation, capable of activating photosynthesis at a photosynthetically active radiations (PARs) of 400 nm to 700 nm and an emission range capable of activating the photovoltaic cell, wherein said emission range is superimposable with respect to a maximum quantum efficiency area of the photovoltaic cell, wherein the luminescent solar concentrator further comprises a matrix made of transparent material selected from: transparent polymers and transparent glass, and wherein the at least one photoluminescent compound is present in or on the matrix of transparent material in an amount ranging from 0.1 g per surface unit to 5 g per surface unit, said surface unit referring to a surface of the matrix expressed as m.sup.2, wherein said process obtains the plants and the electric energy without negatively interfering with the growth of the plants.

2. An integrated process for the contemporaneous cultivation of algae and the production of electric energy from the same radiation source, the process comprising: cultivating at least one alga by exposing it to said radiation source in the presence of an aqueous culture medium in a cultivation area comprising at least one luminescent solar concentrator comprising at least one photovoltaic cell positioned on at least one outer side thereof, said at least one luminescent solar concentrator being interposed between said cultivation area and said radiation source so as to totally or partially cover said cultivation area, to thereby obtain an aqueous suspension of algal biomass and the electric energy; recovering the algal biomass from the aqueous suspension of the algal biomass; and recovering the electric energy from the at least one photovoltaic cell; wherein: the cultivation area is selected from open ponds, photoreactors, photobioreactors and combinations thereof; and the electric energy recovered from the at least one photovoltaic cell is used in the cultivation of the algae, wherein the luminescent solar concentrator comprises at least one photoluminescent compound having an absorption range within the range of solar irradiation, capable of activating photosynthesis at a photosynthetically active radiations (PARs) of 400 nm to 700 nm and an emission range capable of activating the photovoltaic cell, wherein said emission range is superimposable with respect to a maximum quantum efficiency area of the photovoltaic cell, wherein the luminescent solar concentrator further comprises a matrix made of transparent material selected from transparent polymers and transparent glass, and wherein the at least one photoluminescent compound is present in or on the matrix of transparent material in an amount ranging from 0.1 g per surface unit to 5 g per surface unit, said surface unit referring to a surface of the matrix expressed as m.sup.2, wherein said process obtains the aqueous suspension of algal biomass and the electric energy without negatively interfering with the growth of the at least one alga.

3. The integrated process according to claim 1, wherein solar light is the radiation source.

4. The integrated process according to claim 1, wherein the luminescent solar concentrator is an integral part of the cultivation area.

5. The integrated process according to claim 1, wherein the luminescent solar concentrator forms at least partially or totally the roof or at partially or totally the walls of the greenhouse.

6. The integrated process according to claim 1, wherein the photoluminescent compound is selected from: acene compounds; benzothiadiazole compounds; benzoheterodiazole compounds disubstituted with benzodithiophene groups; naphthoheterodiazole compounds disubstituted with benzodithiophene groups; naphthothiadiazole compounds disubstituted with thiophene groups; and perylene compounds.

7. The integrated process according to claim 1, wherein said at least one photovoltaic cell is positioned only on the at least one outer side of the at least one luminescent solar concentrator.

8. The integrated process according to claim 2, wherein the photoluminescent compound is selected from: acene compounds; benzothiadiazole compounds; benzoheterodiazole compounds disubstituted with benzodithiophene groups; naphthoheterodiazole compounds disubstituted with benzodithiophene groups; naphthothiadiazole compounds disubstituted with thiophene groups; and perylene compounds.

9. The integrated process according to claim 2, wherein said at least one photovoltaic cell is positioned only on the at least one outer side of the at least one luminescent solar concentrator.

10. The integrated process according to claim 1, wherein solar light is the radiation source, the luminescent solar concentrator is an integral part of the cultivation area, the luminescent solar concentrator forms at least partially or totally the roof or at partially or totally the walls of the greenhouse, and wherein the photoluminescent compound is selected from: acene compounds; benzothiadiazole compounds; benzoheterodiazole compounds disubstituted with benzodithiophene groups; naphthoheterodiazole compounds disubstituted with benzodithiophene groups; naphthothiadiazole compounds disubstituted with thiophene groups; and perylene compounds.

11. The integrated process according to claim 2, wherein the photoluminescent compound is selected from: acene compounds; benzothiadiazole compounds; benzoheterodiazole compounds disubstituted with benzodithiophene groups; naphthoheterodiazole compounds disubstituted with benzodithiophene groups; naphthothiadiazole compounds disubstituted with thiophene groups; and perylene compounds, and wherein said process obtains the aqueous suspension of algal biomass and the electric energy without negatively interfering with the growth of the at least one alga.

12. The integrated process according to claim 7, wherein said process obtains the plants and the electric energy without negatively interfering with the growth of the plants.

13. The integrated process according to claim 12, wherein solar light is the radiation source, the luminescent solar concentrator is an integral part of the cultivation area, the luminescent solar concentrator forms at least partially or totally the roof or at partially or totally the walls of the greenhouse, and wherein the photoluminescent compound is selected from: acene compounds; benzothiadiazole compounds; benzoheterodiazole compounds disubstituted with benzodithiophene groups; naphthoheterodiazole compounds disubstituted with benzodithiophene groups; naphthothiadiazole compounds disubstituted with thiophene groups; and perylene compounds.

14. The integrated process according to claim 9, wherein said process obtains the aqueous suspension of algal biomass and the electric energy without negatively interfering with the growth of the at least one alga.

15. The integrated process according to claim 1, wherein the at least one photoluminescent compound is present in or on the matrix of transparent material in an amount ranging from 0.1 g per surface unit to 3 g per surface unit, said surface unit referring to a surface of the matrix expressed as m.sup.2, and said at least one photovoltaic cell is positioned only on the at least one outer side of the at least one luminescent solar concentrator.

16. The integrated process according to claim 2, wherein the at least one photoluminescent compound is present in or on the matrix of transparent material in an amount ranging from 0.1 g per surface unit to 3 g per surface unit, said surface unit referring to a surface of the matrix expressed as m.sup.2, and said at least one photovoltaic cell is positioned only on the at least one outer side of the at least one luminescent solar concentrator.

Description

EXAMPLE 1

[0085] Preparation of a Red Luminescent Solar Concentrator (LSC) with Photovoltaic Cells

[0086] 88 photovoltaic cells IXYS-KXOB22-12, each of said photovoltaic cells having a surface of 1.2 cm.sup.2, were positioned at the four outer sides of an Altuglas polymethylmethacrylate (PMMA) sheet (dimensions 5005006 mm), obtained by mass additivation of 100 ppm of Lumogen F Red 305 of Basf, and subsequent casting.

[0087] The photovoltaic performance of said photovoltaic cells was measured under standard lighting conditions (1.5 AM, 1000 W/m.sup.2) and the current-voltage characteristics were obtained by applying an external voltage to each of said cells and measuring the photocurrent generated with a digital multimeter Keithley 2602A (3 A DC, 10 A Pulse) obtaining the following result: [0088] maximum power (Pmax)=14.8 W/m.sup.2.

EXAMPLE 2

[0089] Preparation of a Yellow Luminescent Solar Concentrator (LSC) with Photovoltaic Cells

[0090] 88 photovoltaic cells IXYS-KXOB22-12, each of said photovoltaic cells having a surface of 1.2 cm.sup.2, were positioned at the four outer sides of an Altuglas polymethylmethacrylate (PMMA) sheet (dimensions 5005006 mm), obtained by the mass additivation of 100 ppm of 9,10-diphenylanthracene (DPA) and 100 ppm of 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DTB), and subsequent casting.

[0091] The photovoltaic performance of said photovoltaic cells was measured under standard lighting conditions (1.5 AM, 1000 W/m.sup.2) and the current-voltage characteristics were obtained by applying an external voltage to each of said cells and measuring the photocurrent generated with a digital multimeter Keithley 2602A (3A DC, 10A Pulse) obtaining the following result: [0092] maximum power (Pmax)=12.0 W/m.sup.2.

EXAMPLE 3

Cultivation of Strawberry

[0093] Two equivalent strawberry seedlings of the 4-season reflowering SELVA/Thelma and Louise type were taken and positioned, one exposed directly to solar radiation and the other through the red luminescent solar concentrator (LSC) obtained as described in Example 1.

[0094] During the exposure period (20 days), the average solar radiation, measured at 12.00 noon, proved to be 700 W/m.sup.2. On the first test day, a solar radiation of 1,000 W/m.sup.2 was registered at 12.00 noon. Of this solar radiation, the fraction ranging from 400 nm-700 nm defines the photosynthetically active fraction (Photosynthetically Active RadiationsP.A.R.s), which is equal to 400 W/m.sup.2, equivalent to 1840 E/m.sup.2/sec.

[0095] Under these conditions, the strawberry exposed directly to sunlight receives 1840 E/m.sup.2/sec, whereas the strawberry positioned under the above-mentioned red luminescent solar concentrator (LSC), receives 681 E/m.sup.2/sec.

[0096] The photosynthesis parameters of the two seedlings were also measured at the beginning of the exposure period and after 20 days. The results obtained are reported in FIGS. 1 and 2 in which, the photosynthesis yields [Yield-(%)] are reported in the ordinate, and the violet light intensities emitted at 440 nm, in E/m.sup.2/sec [Light intensity(E/m.sup.2/sec)], are reported in the abscissa. A MULTI-COLOR-PAM Multiple Excitation Wavelength Chlorophyll Fluorescence Analyzer of Walz was used for these measurements.

[0097] As can be deduced from the above FIGS. 1 and 2, the trends of the photosynthesis yield (Yield) for the two seedlings are superimposed both at the beginning and the end of the test, showing the same good vegetative state, with and without the red luminescent solar concentrator (LSC).

EXAMPLE 4

Preparation of the Algal Inoculum

[0098] The algal strain of the internal collection Nannochloropsis salina was used, which normally grows in seawater. The cultivation process adopted is described hereunder.

[0099] A 50 ml sample of culture of Nannochloropsis salina, having a concentration of dry algal biomass of 0.8 g/l, previously maintained at 85 C. in a solution at 10% of glycerine, was defrosted, leaving it at room temperature, and was then subjected to centrifugation to remove the supernatant, obtaining a cell paste.

[0100] The cell paste thus obtained was inoculated into a glass photobioreactor (FBR) having the following dimensions: 11 cm (length of base), 5.5 cm (width of base) and 18.5 cm (height), with a useful volume equal to 750 ml, open at the surface (not sterile), containing 350 ml of seawater to which nutrients had been added (culture medium indicated hereunder), obtaining an algal culture.

[0101] The culture medium used was the following: seawater (350 ml) having a conductivity equal to 50 mS/cm-55 mS/cm, to which only the nitrate, phosphate and iron (III) nutrients had been added in the following amounts:

NaNO.sub.3: 0.5 g/l;
KH.sub.2PO.sub.4: 0.045 g/l;

FeCl.SUB.3.: 0.006 g/l.

[0102] The above photobioreactor was illuminated from the outside with a fluorescent lamp characterized by a solar spectrum, (of the type OSRAM Dulux D/E, 26 W/840, Lumilux cool white, temperature (T)=4000 K, G24q-3), positioned, with respect to said photobioreactor, at such a distance so as to produce a light intensity measured on the outer surface equal to 250 E/m.sup.2/sec, in continuous, 24 hours a day. The light was supplied on only one side of the photobioreactor and the photosynthetically active radiations [Photosynthetically Active Radiations(P.A.R.s): 400 nm-700 nm] were measured with a QSL-2201 radiometer (Quantum Scalar RadiometerQSL) of Biospherical Instruments Inc., equipped with a scalar irradiance sensor.

[0103] Said algal culture was grown at a constant temperature, equal to 23 C., and the desired temperature was obtained with a thermostatic bath and an immersed coil, in the presence of carbon dioxide (CO.sub.2) diluted in nitrogen (N.sub.2), which was fed to said reactor by bubbling, with a flow which was such as to maintain the pH within the range of 6.5-7.5.

[0104] After about a week, the algal culture had reached a concentration of dry algal biomass of 0.5 g/l. Said inoculum was used for the subsequent cultivation tests.

EXAMPLE 5

[0105] Algal Cultivations with and without Luminescent Solar Concentrators (LSCs)

[0106] The algal cultivations were carried out in pairs in 750 ml photobioreactors (FBRs), the same as those used for the cultivation of the inoculum in Example 4, assessing the growth in light after the application of the red luminescent solar concentrator (LSC) obtained as described in Example 1 or of the yellow luminescent solar concentrator (LSC) obtained as described in Example 2, with respect to a reference put under the same growth conditions but without a luminescent solar concentrator (LSC). The algal cultivations were carried out batchwise, starting from the same culture medium used for the preparation of the inoculum as described in Example 4, and inoculating the photobioreactors (FBRs) so as to initially have 50 ppm of algal biomass.

[0107] The growth measurements were integrated by measurements of the photosynthesis capacity to allow a better characterization of the effect of light on the vegetative state of the microalgae.

[0108] The following luminescent solar concentrators (LSCs) were used for the purpose: [0109] yellow luminescent solar concentrator (LSC) which absorbs blue light (<500 nm) within the range of photosynthetically active radiations; [0110] red luminescent solar concentrator (LSC) which absorbs green light (500 nm<<600 nm) within the range of photosynthetically active radiations.

[0111] The following pairs of algal cultivations were carried out: [0112] K141 [without a red luminescent solar concentrator (LSC)] and K140 [with a red luminescent solar concentrator (LSC)]: with the same light intensity of 250 E/m.sup.2/s measured on the surface of the photobioreactor (FBR) (value typical of light limiting growth) and a temperature equal to 23 C.; in the case of red LSC, the light intensity of 250 E/m.sup.2/s, measured on the surface of the photobioreactor (FBR) was obtained by illuminating said red LSC with a light intensity of 712 E/m.sup.2/s; [0113] K143 [without a red luminescent solar concentrator (LSC)] and K142 [with a red luminescent solar concentrator (LSC)]: with the same light intensity emitted from the source, corresponding to 865 E/m.sup.2/s, measured on the surface of the photobioreactor (FBR) without a LSC and corresponding to 409 E/m.sup.2/s measured on the surface of the photobioreactor (FBR) after passing through said red LSC (value typical of photoinhibition) and a temperature equal to 23 C.; [0114] K145 [without a red luminescent solar concentrator (LSC)] and K144 [with a red luminescent solar concentrator (LSC)]: with the same light intensity emitted from the source, corresponding to 616 E/m.sup.2/s, measured on the surface of the photobioreactor (FBR) without a LSC and corresponding to 317 E/m.sup.2/s measured on the surface of the photobioreactor (FBR) after passing through said red LSC (value typical of light limiting growth) and a temperature equal to 31 C.; [0115] K131 [without a yellow luminescent solar concentrator (LSC)] and K130 [with a yellow luminescent solar concentrator (LSC)]: with the same light intensity of 250 E/m.sup.2/s measured on the surface of the photobioreactor (FBR), (value typical of light limiting growth) and a temperature equal to 23 C.

[0116] The exponential growth phases, having a duration varying from 60 hours to 100 hours, were monitored for each pair of tests, carrying out one/two daily withdrawals of algal culture from each photobioreactor (FBR).

[0117] Each withdrawal was subjected to measurement of the optical density, at a wavelength equal to 610 nm, using a Hanna multiparameter photometer series 83099, in order to be able to follow the growth trend of the algal biomass.

[0118] The measurement of the optical density was correlated with the measurement of the concentration of algal biomass, calibrating the signal obtained with said optical density measurement with the measurement of the dry weight of algal biomass: the concentration of algal biomass was consequently recalculated from the direct measurement of the optical density.

[0119] The specific growth (), associated with the light and temperature of each exponential growth phase, was recalculated by interpolating the measurements of the concentration of algal biomass with time according to the following equation (I):

C.sub.(t)=C.sub.(t)*exp(*t)(I)

wherein: [0120] C.sub.(t)=concentration of algal biomass at time (t) of the withdrawal (expressed in hours) (g/m.sup.3); [0121] C.sub.(t)=concentration of algal biomass at time (t) at the beginning of the cultivation (expressed in hours) (g/m.sup.3); [0122] =specific growth (sec.sup.1)
obtaining the following results: [0123] K141 [without a red luminescent solar concentrator (LSC)]: =0.020 sec.sup.1; [0124] K140 [with a red luminescent solar concentrator (LSC)]: =0.020 sec.sup.1; [0125] K143 [without a red luminescent solar concentrator (LSC)]: =0.017 sec.sup.1; [0126] K142 [with a red luminescent solar concentrator (LSC)]: =0.019 sec.sup.1; [0127] K145 [without a red luminescent solar concentrator (LSC)]: =0.022 sec.sup.1; [0128] K144 [with a red luminescent solar concentrator (LSC)]: =0.026 sec.sup.1; [0129] K131 [without a yellow luminescent solar concentrator (LSC)]: =0.020 sec.sup.1; [0130] K130 [with a yellow luminescent solar concentrator (LSC)]: no growth is observed.

[0131] From the data indicated above, it can be deduced that there are no significant differences in behaviour with the same light energy which reaches the photobioreactor (FBR) within the spectrum useful for photosynthesis (red+blue). Green light has no effect, even if it is sent onto the cultivation, it is not used.

Photosynthesis Data

[0132] Fluorescence measurements were carried out with a WATER-PAM fluorometer of Heinz Walz GmbH and analysis using Phyto-Win Rapid Light Curve software of Phyto Win, plus recovery of the photosynthesis yield [Yield-(%)] by re-adaptation to the dark following the Phyto Win software protocol.

[0133] The protocol envisages the use of photosynthetically active light with an increasing intensity up to about 2500 E/m.sup.2/sec. Each step lasted 10 seconds, eight steps were programmed and at the end of each step, a saturation pulse of a few milliseconds was sent.

[0134] The sample to be analyzed was taken from the photobioreactor (FBR) and diluted with demineralized water in order to make it suitable for the measurement instrument (Water PAM) which requires a basic fluorescence of the sample within an established range.

[0135] With respect to the tests K143 [without a red luminescent solar concentrator (LSC)] and K142 [with a red luminescent solar concentrator (LSC)]: with the same light intensity emitted from the light source, corresponding to 865 E/m.sup.2/s, a value typical of photoinhibition, the characterization by means of Water PAM fluorometry shows tendentially higher non-photochemical quenching values (NPQ), for the test without a luminescent solar concentrator (LSC): this means that this culture has a greater tendency to protect itself from photoinhibition and disposes of the extra energy as heat, this available energy does not increase the photosynthesis yield.

[0136] With respect to the tests K145 [without a red luminescent solar concentrator (LSC)] and K144 [with a red luminescent solar concentrator (LSC)]: with the same light intensity emitted from the light source, corresponding to 616 E/m.sup.2/s, there are no significant differences in behaviour with the same light energy which reaches the photobioreactor (FBR) within the spectrum useful for photosynthesis (red+blue).