LIGHT FARM

Light-farm prototype(Hcpv Version)
 & me with a  Fresnel Magnifie

(Facade Light Harvesting)

Lightfarm is a system that utilizes building facade and rooftop for collecting and concentrating light rays which then is used for heating and power generation by HCPV photovoltaic cells. This kind of PV has an efficiency of 40% and is suitable for concentrated light up to 500 to 1000 times the intensity of sun rays.
In this case, instead of using conventional photovoltaic of 12 to 19% efficiency, we would concentrate light by building façade using the thin plastic Fresnel lenses accompanied by a glass layer, and then utilize a few sq. centimeters of HCPV to generate electricity for the household.
Photovoltaic cells would provide electricity with an efficiency of 40%, and the 60% formerly waste of energy is transmitted to heat-sinks for water and space heating purposes.

Household energy consumption in a year in temperate places equals 20000 KWH averaging a medium power consumption of 2280 watts. Every Square meter of sunlight contains 1000 to 1350 watts. It means that just 2 meters of constant sunlight energy would provide a household with sufficient energy. But unfortunately, neither are sun rays available constantly nor are our harvesting devices that efficient yet. Considering 5 hours of average daily sunshine with medium intensity of 900 watts, with photovoltaic cells of 17% efficiency, an area of 75 meters of photovoltaic cells would provide a house with its energy requirement.

 MAIN FEATURES OF THE SYSTEM

HCPV modules on Building facade

HCPV modules on Building facade

-Power generation with high efficiency (40% Cell / 25% Module efficiency)

-Heat generation even in cold but sunny winter days: The main advantage of this system is the capacity to harvest sun Heat even in winter days as the concentration let us collect the whole energy of the sunlight in a small area and overcome the problem of current thermal systems which is equity of sunlight absorption and ambient loss due to very low temperature of the ambient in winter.

-Integration with building’s façade and rooftops: Integration of system with buildings could be considered an advantage in 2 aspects. First of all, it could be a substitution for façade decoration which means a very considerable cut in building construction expenses, the second advantage is aesthetical aspects which in some cases the normal PV panels don’t match with the building's architectural design.

-Active tracking system: (Deployment of active solar sensor and driver which makes the design very easy to install without complicated prior regulations.

Very low energy consumption of actuators due to high static load capacity and short traveling strike and low duty cycle, deployment of conventional and economical sensors and actuators in the market with some minor changes)

-Aesthetical aspects: Glass facades are still very trendy and fashionable, Many new modern buildings are still being designed with glass façade and this trend is increasing every day, but LightFarm is not just a Normal Glass façade, there are features which makes it far more attractive than a conventional Glass façade…

Optical Art can change the face of the new buildings forever; Remembering the fact that Fresnel Lenses are some sort of magnifier, this can demonstrate the new approach to beautification and personalization of the building’s façade base on the choice of the building's owner. It’s enough to put a small design motif around the focal point of the lens, this small piece of art would be magnified by the lens and turn into the view of the building when someone is looking.

-Economical viability.

Reliable research institutes suggest that CPV would replace the conventional PV panels in near future, due to high efficiency and lower price per/watt energy generation, which could compete with fossil energy.

In specific the lightFarm project promises a real competitive alternative to fossil energy as the system has been designed for integrity with buildings where the end-users need them.

The LIGHTFARM design consists of 4 main parts which all of them have been deployed economically:

- Structure: the structure would be made of steel or aluminum profiles.

-Lenses/Primary optics: are Made of PMMA polymer sheets and they get shaped by an economic process.

 PMMA material costs less than

2 euro/Kg which is very economic and the process of manufacturing could also be very economic in case of a high volume of production. 

Insulation of module

Triple junction high efficiency solar cell

SOE/ HCPV cell / heat-sink 

- HCPV cells: Each HCPV cell Assembly consists of a square shape HCPV Cell of 10x10mm and it substitutes an area of 300x300 mm photovoltaic cell. It means that the area has been reduced to 1/900 of the original area while the price of the cell has just increased a few times more than conventional PV.

Each HCPV cell assembly consists of HCPV cell+ substrate and heat transfer diode+ secondary optic, would cost around 25 Euro (less than 250 Euro/sq meter) in mass production.

Considering the prices of the main components of the system and also the fact that the expenses of this system would not add to the expenses. it would replace a normal facade system and it doesn’t require extra funds compared to a normal glass facade.

All in One solution:

Light-farm is the optimum solution for areas that don’t have so many cloudy days in a year compared to sunny days; as the system efficiency drops dramatically in case of cloudy and rainy weather.

For places with more than a yearly average sun of 250 watts sun, an expansion of 25 sq meters of Fresnel lenses would supply the household with the required energy of the house. But the system also generates and harvests HEAT…

25 meters of sunshine contains 25000 Watts of energy, 15000 Watts ( 25000- 25000x40%) would convert to HEAT of which roughly 10000W is the amount that could be harvested through heat sinks.

10 KW of HEAT is a considerable figure and the first question which would rise afterward is: What to do With the HEAT harvested?

Building Designed specifically for integration with lightfarm project (Designer: Nasser Taghavi)

Saving the HEAT

Special Heat-sink designed specifically
 for water circulation in light-Farm

As far as I am aware of, Light Farm is the first project that proposes the integration of HCPV solar in building’s facade and this brings a huge advantage to the project compared to its precedents, previously to get rid of heat was considered as an expense for solar power plants out of the city while in this project the heat would be directly used in building for water and space heating. Yet there should be a proper system to save the HEAT for the use through the day and night.

The Fact is that the efficiency of converting HEAT to any other form of energy is so low, thermocouples can convert a maximum of 10 percent of energy to electricity and other methods are not also so efficient.

LIGHT-FARM instead proposes an easy and practical solution to save the HEAT. The solution is “Paraffin wax”

Paraffin wax is mostly found as a white, odourless, tasteless, waxy solid, with a typical melting point between about 46 and 68 °C (115 and 154 °F) and this specific melting point is exactly what makes an attractive solution of paraffin wax to save the HEAT. The question remains: How?

The algorithm of saving heat is like this:

-Sun rays hit the HCPV cells and convert to 40% electricity+ 60% Heat.

- The HEAT produced (10 KW for 25 Sq. meters) would be transmitted to the water(or any other thermal fluid) inside the heat-sink through the aluminium fins.

Water Tank enclosed by Paraffin wax

- a thermostat would turn on the pump as the temperature of the heat-sink exceeds 45° and cold thermal fluid would be circulated in heat-sinks and water tank.

- There would be a water tank of 400 Liters for each family to save the hot water, The pump circulates the water(or thermal fluid) inside the heat-sinks and the tank( in case of using thermal fluids, the heat would be transmitted to the water inside the tank through a radiator “heat exchanger”)

-The Heat capacity of water is Cp= 4.18 J/(g•K) so the temperature increases by around 20° each hour

- The maximum efficiency of the HCPV cells would be achieved at 25° centigrade, increasing the temperature would decrease the efficiency (1% for every 20° increment), and to avoid damages to the cell, it is better to keep the cell temperature less than 80° so there must be a way to control increasing of temperature.

- The tank would be enclosed by a volume of 400 kg of Paraffin wax with a melting point of 65°. So the water temperature would increase linearly until it reaches the melting point of the paraffin wax around the water tank. At this point, there wouldn’t be any change in the temperature until the whole mass of paraffin is melted. And this requires a lot of energy,

enthalpy of fusion, also known as the heat of fusion or specific melting heat of Paraffin equals 220 J/g and it means that the fusion of one gram of Paraffin requires 220 joules of energy.

400 kg of wax would require 220 x 400 x 1000 Joules of energy to melt and it requires 2 hours and a half for the harvested Heat to melt this amount of Paraffin.

The good thing about this solution is the sheer amount of the saved heat for using during the night and also maintaining the temperature on the melting point of the paraffin which is 65°.

The low price of paraffin (2 euro/kg) guaranties an economical solution out of this method.

Winter facade light harvest:

(Linear version)

CPV modules as colorful glass facade

CPV modules as colorful glass facade

To reduce the complexity of the project and to make it more viable there is the possibility to use linear Fresnel lenses, in this case, the tracking would be applicable just in one direction and the choice of tracking direction would be south-north tracking since there is just little changes in the angle of sun rays in south-north direction(almost 1° every 8 days), this means that the tracking could also be done manually on a weekly basis. 

Inspirations for Optical solar facade

Advantages:

-Less technical complexity,

-Aesthetics.

-Compatible with a vertical facade

-Winter solution( this configuration is more adaptable for winter days since the sun is not anymore at its zenith and sunbeams have an inclined angle. therefore the linear method is more adaptable for vertical glass facade.

Disadvantages:
Linear Fresnel lenses don’t have a high rate of concentration and for this reason, it is not economical to use HCPV cells, instead, we have to use CPV cells designed for low concentration of 10 to 40 suns intensity and the efficiency of CPV cells are less than HCPV(around 28%)

Optical art: 

First experiment with linear module...

Optical art makes an attractive solution out of a linear CPV facade.

Sustainable solutions don’t necessarily require to compromise the aesthetics of the buildings,

Not anymore.

Invisible Photovoltaic panel:

On the contrary to current black PV panels which in many cases don’t match with the design and gestalt of the buildings, Linear lightfarm delivers a versatile, integrated, and user-defined selection of DESIGN.

Animated gif( Click to enlarge)

LINEAR FRESNEL FACADE (winter solution)

Vertical facade light-harvesting has a considerable advantage in winter times compared to conventional solar thermal solutions. The fact is that in cold winter days with a sun that travels in an inclined plane in the sky, the amount of energy absorbed by the thermal collector surfaces is hardly more than the loss of the heat due to the very low temperature of surrounding ambient. with the concentration of sunlight, we change this balance and make it possible for the thermal collectors to receive more energy than what they lose by radiation and air convection.

About the prototype:

The realized prototype is an array of 4 modules; Each module harvests an area of 30x30 cm. The sunlight would then be concentrated into a 10x10 mm HCPV cell. To reduce the demand for accuracy, a prism-shaped secondary optic would lead the concentrated light into the cells.

The cells are placed on a heat sink which absorbs the heat from the cell and produces hot water.

All the modules are capable to turn in all directions and all of them are connected in a way that by moving one of them all the system moves together.

In this way by using an active sensor and a pair of linear actuator motors the modules track the sun’s position in the sky. There is a small gap between modules to let the modules turn freely without interference and also to avoid overlap of the shadow of one module on the active area of other modules. so in contrary to normal PV modules which at a different time of the day the solid angle (The solid angle, Ω, is the two-dimensional angle in three-dimensional space that an object subtends at a point. It is a measure of how large that object appears to an observer looking from that point) of the PV against the sun reduces as the sun gets away from its zenith; but in the Light-Farm prototype although there is a gap between the modules, the area of sunray harvested in whole the day remains the same, Thanks to a tracking system which makes the modules always face the sun, so the solid angle is always the same(for example a module of 30x30 cm always receives 30x30cm of sunray)

2-Axis solar tracker

Linear Actuator 

300Kg Dynamic Load

2-axis solar tracker would determines the sun position and the electronic driver would command 2 linear actuators in south-north & east-west directions.

The thermostat device reads the temperature of the Cell assembly Thanks to a thermocouple attached to the heat-sink. It gives the possibility to adjust the temperature in which the pump starts and stops to circulate the thermal fluid.

INPUT/OUTPUT

- Linear actuators consume the power in a periodic timing due to low duty cycle( during the whole day, they would be working just for few minutes and in most of the time they just bear static load without consuming any power)

At the moment both Actuators and sensor drivers are connected to an adaptor of a maximum of 22 Watts output and it works properly.

According to the figures and considering flaws in prototype accuracy, the overall efficiency of the system in harvesting sunlight is around 50% in the forms of electricity and Heat, Which promises a high-efficiency system by a proper industrial manufacturing system.

History of the project: (Former Concept)

The concept of the Lightfarm project occurred to me last year when I was trying to design a method to transfer sunlight into the internal rooms of large buildings for lighting purposes during the day.

The very first concept was to concentrate light by special parabolic or Fresnel modules into a collector,

The harnessed light could then be transferred into the buildings, using fiber optics,

The concept was novel but it was not justifiable as it was not at all economically viable to install those pieces of equipment just for few hours of natural light during the day. Contemplating the problem and noticing the sheer amount of the sunlight energy hitting the façade and rooftop every day, finally, I got to the point that the system should be shifted from light transferring into light harnessing: a system that concentrates sunlight and converts it to electricity and collectible heat. The completion of the design coincided with the announcement of Foundation Enterprise Hermes for the competition.

To present the project properly, I asked an old friend of mine (Nasser Taghavi) to help me with the design of a building suitable for integrating with lightfarm system, the result of this collaboration is the detached house with light collectors on the rooftop. The design showcase compatibility of HCPV solar on rooftops, yet there is more to be done in the Design of the different variations, especially the design of a building for Linear Facade Light-harvesting.

Possibility of collaboration:
This project is not yet fully formed and still needs a lot more research & development, that's why I humbly  invite all individuals, research institutions and companies  interested in this solar concept to contact me through linked-in or email:
 in particular I need to collaborate with companies active in CPV technology and architects who want to join in development of the system for realisation of the first project constructed based on the concept.