Fossil fuels are the main sources that are being used to produce energy today. They are not only being depleted, but also polluting the environment, and affecting our economical stability. Solar hydrogen and fuel cell systems when integrated together represent a new approach that promises clean and friendly energy production.
Our project’s objective is to investigate powering residential homes with solar energy and hydrogen fuel cells systems combined using a scaled down model house. This model provided cost effective studies and analysis to estimate systems efficiency, size and capacity necessary to energize an average residential home. It is also very important to establish a reference point by building a small mockup that could eventually help constructing full scale homes, saving money and time.
The current system consists of solar panels that are connected to the household, and to an electrolyser. When the sun is shining, the solar panels produce electricity that is used to produce hydrogen and to provide energy to a residential home. The energy demanded by the household during the period of sunlight will be just a portion of the total energy needed to run the house twenty four hours per day, therefore, the remaining solar energy produced in this process will have to be stored for later demand. First, solar radiation hits the solar panels, and produces an electrical reaction in the solar cell itself. The solar cell is a p-n junction made out of silicon, which means that the material is divided into two different regions, the p material region and the n material region. The p material is an impurity that leads to a deficit of mobile electrons in the silicon. The n material is an impurity that leads to extra mobile electrons in the silicon. When joining these two materials together we end up with a neutral region at the interface with an electrical field. When a photon hits this junction and frees an electron, it sees the Electric field and moves toward positive charges. Current flows if there is a complete circuit. This current is utilized to meet the energy demand of a household, and to produce hydrogen.
Secondly, if the solar panels system had been designed to meet 100 percent demand of energy in the household, then the amount of energy produced by the solar panels will not be completely consumed during the period of sunlight, therefore the remaining energy will be used to produce hydrogen by electrolysis. This hydrogen will be stored in tanks to produce energy using fuel cells.
Thirdly, by providing energy from the solar panels to the electrolyzer, water can be dissociated into hydrogen and oxygen. One mole of water produces one mole of hydrogen and half mole of oxygen. The hydrogen produced in the process could be stored in tanks and be used after the sun set to supply a fuel cells system and produce energy for the remaining hours of the day .
Finally, the hydrogen gas is supply to the fuel cell system. The fuel cell system will produce energy on demand after the sun set. A fuel cell is an electrochemical device that converts chemical energy into electrical energy. Fuel cells consist of a polymer electrolyte membrane that is surrounded by electrodes, anode and cathode. The hydrogen is supplied to the anode and oxygen or air to the cathode.
This research paper focuses on calculating the amount of hydrogen needed by a regular household 24 hours per day against the amount of hydrogen that could be produced by the conversion of sunlight into electrical energy, and into hydrogen. Two solar modules of 15 watts output each was used. The power outputs of these two solar panels, with 0.22 square meters area each, were measured in sunlight to determine their output energy and efficiency. A Dynaload System with various electric loads was used to varying loads and currents on the solar panel from 0 A to 1.5 A. The output of these solar panels was measured three consecutives days every hour from 9:00 AM to 4:00 PM. After measuring their energy output, it was discovered that they reached a maximum power point of 15 watts at 15 volts and 1.0 amp. The efficiency of these solar panels is based on the fact that 100 percent efficiency is defined as 1 KW of solar radiation that 1 sq meter of earth intercepts in 1 Hour. If the solar panel has an area of 0.22 sq meter and 15 watts output, then its efficiency is about 7 percent.
In the current project, it was assumed that the average household requires more than 10,000 kWhr of energy per year. This house will use a PV system of 9.08 kW, which will need a roof area of about 1000 sf, and about 700 sf of floor plan area. The efficiency of this PV system is about 75 percent, which accounts for the inverter’s efficiency and wiring losses.
The scale for our small scale model house will be calculated based on the numbers from the full scale house. The 9 kW will be simulated by the 300 smaller version of our experiment of 30 watts PV system. The dimensions of the real household will be scaled down 100 times in a sample house that is 10 sf of roof area and 7 sf of floor plan area. Therefore, the amount of power needed to run this household is about 22,000 watts taking into consideration every appliance and electric light in the house. If the scale factor for energy analysis is 300, then the small model house will be running with about 75 watts of power requirements.
The amount of energy that the earth intercepts per day is 4.3 kWhr, which means that we have power of 1kW of effective sun light during 4.3 hours of the day. During this period of time, it was found that the solar panels will produce sufficient amount of energy required by an average household for the whole day. During these 4.3 hours, the house will consume only a small amount of energy, and the rest will be used to produce hydrogen by electrolysis. The amount of energy that the sample house will be consuming during the time of solar energy production is about 17Whrs, and the amount of energy produced by the sun is about 97Whrs, so the remaining 80Whrs will be used for electrolysis.
The hydrogen flow rate generated by electrolysis used in this project was measured at different levels of voltage and amperage. At 3 volts, 0.7 amps, this electrolyser produces 4.3 mL/min of hydrogen, and as the voltage increased the amperage increased as well, and therefore better hydrogen production rates were obtained. At 6 volts, and 1.6 amps, the hydrogen production rate was 12 mL/min. However, if we keep increasing the voltage even more, the hydrogen production rate would not increase as expected. In fact the voltage was increased to 9 and 12 volts, but the current leveled at 1.6 amps, and the hydrogen production rate remained at 12 mL/min. This means that the internal electric resistance inside the electrolyzer was increasing due to the higher flux of gases blanketing the electrode. This could be explained by the amount of hydrogen produced by the hydrogen electrode side of electrolyzer, builds up a wall layer of hydrogen gas against the electrode surface that increase electric resistance and does not allow any electric current increase or further escalation in hydrogen generation. The average hydrogen produced by this reversible fuel cell process was measured to read 10 mL/min at 9.6Whr. In the present work, data from a full scale electrolyzer was used as a reference point for the full scale house energy balance and hydrogen generation at the rate of 1 cubic meter of hydrogen at 5kWhr. In this case the amount of energy produced by the 9.08kW PV system will be around 29kWhr per day, and the amount of energy consumed during the period of solar energy production is about 5kWhr, which gives us a surplus of 24kWhr to be used for hydrogen production.
The amount of energy that could be used to produce hydrogen is about 80Whr per day in the sample/small scale model house. Two electrolyzers or fuel cells will be used in the reversible process to produce hydrogen at a rate of 20mL/min. These two hydrogen electrolyzers, therefore, will produce 0.01 cubic meters per day in 4.3 hours. The amount of energy that the sample house will need to run 24 hours period is 97Whrs. 17Whrs will be provided directly form the PV system, and 80Whrs will be required to run the house 19.7 hrs after the sun set. To produce this amount of energy, the hydrogen needed will be calculated from the fact that about 15L/min are needed to produce 1 kW of power. Therefore, the amount of hydrogen required to produce 80Whr is about 0.07 cubic meters.
In the full scale house, the approximate energy requirement is 29 kWhr per day that can be covered by a 9kW solar PV considering 75% transmission and system losses. The amount of energy consumed by the house during the 4.3 hours that the solar array is effective is about 5kWhr. The remaining 24kWhr will be used to produce hydrogen by electrolysis. The electrolyser that was used in these calculations produces 1 cubic meter of hydrogen while working at a rate of 5kWhr. Therefore, the amount of hydrogen that could be produce in this system is 4.8 cubic meters per day. Considering that 1kW of power generated by a fuel cell needs 15L/min, thus the house will need 21.09 cubic meters to run during the 19.7 hours remaining of the day. The energy demand required in a household could be supplied by solar energy; when the sun is shining the photovoltaic array gives free energy from a unique and endless source. In order to provide enough energy to a household, the PV system must be design to generate 100 percent of the energy demanded by this household. http://facts-about-solar-energy.com/facts-about-solar-energy.html http://www.containedenergy.com/CE-SolarSystemSizing.pdf http://www.siemenssolar.com/solar-panels.html
http://www.nrel.gov/gis/solar.html