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Thursday, March 22, 2012
Solar energy storage with Battery or Hydrogen?
Renewable energy industry has slowly but steadily started expanding in many parts of the world in spite of high cost of investment and high cost of energy. Countries like US, Germany and China are now investing on large scale solar and wind technologies, opening new avenues for investments and employment opportunities. Many of these technologies will undergo number of changes over a period of time before it can completely substitute fossil fuels. How long this process will take will depend upon number of factors; but the single biggest driving force will be ‘the issue global warming and its consequences” and also on uncertainties over oil reserves in the world. Nothing dramatic will happen in the near future except the concept of alternative source of energy will expand rapidly. It is also an opportunity to discover new forms of fuels, power generation and distribution methods. The concept of solar energy is now well-recognized as an alternative source of energy because, it is abundantly available, it is clean, generates no pollution and it is silent. The major raw materials such as Silica and Gallium Arsenide are also available but some of the rare earth materials used in PV industries and batteries, are available only in certain parts of the world. China is endowed with many such rare earth resources. For example, Lithium has limited resources and currently bulk of it is produced from natural brines similar to the one at Atacama deserts in South America. It is also available in the form of minerals and ores which many countries are now trying to exploit commercially. The storage of energy from solar and wind is currently done using deep cycle batteries, most of which are Lead-acid batteries. Bulk of the used Lead acid batteries are recycled but the demand for such batteries keeps increasing. The sheer weight of these batteris, space required to install them, capacity utilization, capacity constraints, regular requirement of maintenance and life cycle are some of the issues that are critical for renewable industries. In deep-cycle batteries, discharging stored energy below certain levels dramatically reduces the life span. Hot climate conditions have certain impacts on maintenance of such batteries. Life of a battery is critical because when you calculate the cost of energy over the life cycle of 25 years, the number of replacements of batteries and their cost will have a dramatic effect on the cost of energy. Batteries are indispensable tools in energy industries but, their usage can be minimized to a great extent by using Hydrogen as a storage medium. Let us analyze a simple example of a PV solar system for power generation. We made a computer simulation on three different scenario for a PV solar system for a small residence with power consumption at 15,500kwhrs/day. First simulation was based on PV solar, direct grid connect, without any storage batteries but connected directly to the grid, assuming the grid power tariff is at $0.10/kwhrs and sale to grid tariff at $ 0.30/kwhrs.The second simulation was based on grid independent system using battery storage for 8 hrs autonomy. The third simulation was also grid independent, but solar power was connected to an Electrolyzer to generate Hydrogen and store it in a tank. We used a small capacity battery, less than twenty percent of the capacity used in the previous case and a Hydrogen storage with Fuel cell along with an inverter. The stored Hydrogen was used to generate power to meet the requirement of the residence, instead of supplying power directly from the battery. The cost of energy using direct grid connect was the lowest $$0.33/kwhrs, while Grid independent with battery storage ,the cost of power was $1.20/kwhrs.In third scenario with Hydrogen and Fuel cell, the cost of power was $ 1.90/kwhrs, but there was surplus Hydrogen in the storage tank. With Hydrogen as a storage medium, the cost of power is high due to initial investment but it is maintenance free and ideal for remote locations. The Hydrogen and Fuel cell solution though expensive, has a number of advantages. The power generated by PV solar is stored in the form of Hydrogen instead of storing in batteries. A single battery is used to maintain a steady current to Electrolyzer but bulk of the energy is stored in the form of Hydrogen. Another advantage with this system is that stored Hydrogen can also be used as a fuel for residential heating as well as to fuel your car.