Fuel cells OR Fool cells
Everyone would agree that sooner we end our dependence on fossil fuels and develop new energy sources the better. The advantages extend beyond the reduction of greenhouse gasses as the oil sources are ultimately going to run dry. The two technologies that come to play here are the hydrogen fuel cells technology and Lithium-Ion battery approach.
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Tesla gave new hopes to the industry with some exceptional work in the battery technology. As the demand for these vehicles skyrocketed the struggles of Tesla also increased as they were not able to meet the demands. The preorders of Tesla are still waiting in line and are expected to get the deliveries as late as 2020 according to a Bloomberg report. The production rate has finally gained pace and we are getting four thousand Teslas per week.
Another solution that was industries most favorite is the hydrogen fuel cell approach. Japan is contesting to become the worlds first hydrogen society with more than 160 hydrogen stations and 40,000 FCV which is expected to grow to 900 hydrogen stations and about 1 million FCV.
The hydrogen seems to be excelling ahead with an energy density of 40,000 Wh/Kg compared to 278 Wh/Kg for Lithium-ion battery. It gives hydrogen an advantage of extended range and also lightweight. This opens doors for its applications even in the aviation industry.
The Hydrogen powered vehicles can be refueled in less than five minutes whereas a Tesla Model S takes more than 3 hours to fully charge. But these figures might be deceptive as the cost for refueling 75 KWh battery for both the technologies is:
Although hydrogen is one of the most abundant element it is not readily available and is stored in water and hydrocarbons. The extraction of this hydrogen poses the biggest challenge as it needs to be efficient. Steam-Methane Reforming is one of the most common processes of hydrogen separation where steam and natural gas is combined to get hydrogen.
But the hydrogen separated from steam reforming has less energy than the natural gas used at the beginning of the process and while the fuel cell that uses hydrogen as fuel doesn’t pollute the environment but the process of preparation of hydrogen does.
Another process used in the preparation of hydrogen is electrolysis. Here electricity is used to separate hydrogen and oxygen by passing electricity. Although the electricity required can be fed using renewable sources but the energy input is much more than steam reforming process. Electrolysis also takes away 30 percent of the energy from electricity supplied.
Another process used for hydrogen production is Proton Exchange Membrane electrolysis where energy efficiency can reach as high as 80 percent with an added benefit of producing hydrogen on site.
For electrolysis, DC current is required and the rectifier is used for this conversion having an efficiency of 92 percent.
As hydrogen has a very low density so ensuring the optimum energy density we need to increase its actual density.
One way to do this is to compress the hydrogen at 790 ATM but it requires energy equivalent to about 13 percent of the total energy content of hydrogen itself.
Another process is to convert hydrogen into liquid cryogenically. But hydrogen is very hard to liquify and it is done by cooling it to -250°C, which causes an energy loss of 40 percent of the total energy content.
The transportation of hydrogen through trucks or pipelines can result in as much as 40 percent loss of energy. If we consider production and distribution on site, the losses can be brought down to 13 percent. This is not a general solution as al the hydrogen stations may not have enough space for generation on site.
For battery charging the losses are only in the form of grid loss which accounts for only five percent.
Tank to wheel conversion
To rotate the wheels the hydrogen in the tank needs to be converted into electricity again using a fuel cell. Fuel cell acts as a reverse Proton Exchange Membrane electrolyzer where hydrogen flows through the channels in anode in which the catalyst causes a reaction that separates the proton and electron. This flow of electrons gives electricity to power electric motors. The maximum efficiency of this conversion is about 60 percent.
In the case of batteries, the AC current from the grid needs to be converted into DC for storage into batteries. For this conversion, a charger is used which has an efficiency of about 92 percent. Now the motors work on AC current so the inverter converts the DC charge in batteries to AC again with an efficiency of 90 percent.
Efficiency of Electric motor
The electric motors have an efficiency of about 90-95 percent.
Considering the ideal case with 80 percent efficiencies of electrolysis and fuel cells the useful energy comes out to be just 34 percent.
In case of batteries considering the worst case, with charging and inverter losses of about 10 percent. The useful energy comes out to be 62 percent.
The hydrogen might take you further in one fillup but the inefficiencies make the costs rise astronomically. The cost for setting up a hydrogen station and profit derived by these places also drive the market.
By the time we set up the network of hydrogen stations the batteries might catch up in terms of range and this will trigger the revolution again.
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