Bài 2: Speaking and Listening

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Advantages of Alternative Energy Sources
There are many advantages produced by alternative energy when we replace fossil fuels with cleaner sources of power.
1. Is A Renewable Energy Source That Never Runs Out
Fossil fuels are considered non-renewable energy sources because they are finite sources of energy due to the fact that they will run out in just a few decades.
Alternative energy is considered a renewable energy source because provides a sustainable and stable supply of clean energy in the long term.
2. Is Friendly With The Environment
Alternative energy is good for the environment because renewable energy sources like wind and solar produce zero emissions.
Biomass (wood chips) is another renewable energy source (trees regrow) that produces very low emissions (lower than natural gas).
3. Is A Reliable Source Of Power
Alternative energy is considered a reliable source of energy because the technological development in recent years allowed these clean energy sources to enter more and more into the global energy mix.
However, the renewables represent today a very small percent in the world energy mix, but the continuous technological development of the human society will allow the alternative energy sources that are less reliable today (solar and wind) to consolidate their position in the energy mix of every country up to the level when the world energy mix will consist only of renewable energy sources.
4. Can Create Energy Independence
Alternative energy sources are the solution to getting energy independence for every household.
In the society of the future every household will produce and store its own clean electricity produced by the renewable energy sources available in that place.
Places with plenty of sunshine will harness the power of the Sun to produce clean electricity that will power the house during the day, but also during the night with the help of advanced energy storage devices.
Disadvantages of Alternative Energy Sources
Alternative energy has a few disadvantages mainly represented by the low-carbon energy sources, which are not entirely clean.
1. Renewable Energy Has Its Limits
The today’s technology used to generate renewable energy (clean electricity) has its limits.
Wind turbines harness the power of the wind.
Wind turbines harness the power of the wind.
The low efficiency specific to these technologies creates a problem with the feasibility of such projects because the investment may return in a long period of time, which in some cases does not justify the initial investment.
2. A Very High Cost
Sadly, even if alternative energy sources have appeared to replace the fossil fuels that pollute, the green technology of today is still expensive for most of the population.
Without governmental incentives and subsidies that support the development of the green energy sector in the world, many green projects developed today would be remained only on paper.
3. Is Not A Constant Source Of Energy
If we take each alternative energy source to see if it represents a constant source of clean energy, we see that some of them rely pretty much on weather conditions.
Solar panels do not produce electricity during the night, and low amounts of electricity during cloudy and rainy days.
Wind turbines produce clean electricity during the day and also during the night, but only if there is wind.
Wood chips that are burned as biomass to produce low emission electricity requires huge quantities of wood (to produce wood chips) every year.
Biomass is a reliable source of power
However, the latest energy storage devices available on the market allow us to store the clean electricity produced by our solar panels or wind turbine for a later use (during cloudy days, during the night or during days without wind).
Also, if we want to have a continuous source of clean power at our disposal, we need to combine solar and wind power because if there is no sun, it means that is night, or it is a cloudy day, so there are plenty of chances for a good wind that can be used by our small turbine to produce clean electricity.
The Sun is a constant source of clean power.
The Sun is a great source of clean power.
The latest battery created by Tesla for the home and small business (Powerwall 2) can store now 14 kWh of clean energy and deliver an output of 7 kW.
At utility scale, Tesla provides now an improved battery called Powerpack 2.
4. Is Less Developed Compared to the Potential Of Power Generation From Fossil Fuels
Today, is very difficult to generate enough clean energy to power a medium town, a big town or even an entire country.
Renewable energy is produced in small scale compared with the global demand of energy, and to increase the generation capacity in the world up to a level which would count in the global energy mix, we need to use large surfaces of land (which can be used for agriculture) and huge financial efforts of the governments around the world.
Conclusion
Green technology needs to evolve in the future to replace the dirty energy produced by fossil fuels.
An improved efficiency of the devices used daily, would decrease the power consumption on the planet and would make renewable energy more efficient.
The further decrease in costs for installing solar PV systems and wind turbines would facilitate the creation of new green projects around the world that would increase the generation capacity and the presence of the alternative energy in the world’s energy mix.

Chào em, cả cụm environmentally friendly (adj) là thân thiện với môi trường.

Chào em, Câu 19 chỉ cần 1 cụm danh từ bổ nghĩa cho Norman Weiner nên dùng "a" là hợp lý. Câu 20 cũng tương tự vậy nha em.