SoPは，story-tellingの上手さと論理的な文章を書けるかどうか，モチベーションは何なのか，を判断される試験だと思います．それを考慮したうえで，SoPを組み立てます．
正解の文章構成はないと思います．自分の考えが最も伝わる文章構成を自分で考えるべきです．ここでは例として，私のSoPの構成を紹介します．（他の人と比べたら低クオリティだと思いますが．．．）
1段落目：大学院に進学したい理由と，大学院進学後に何をしたいのかを一言で述べる
2段落目：なぜそう思うようになったのか原体験を簡単に述べる
3～4段落目：これを達成するためにやってきたことを書く（能力をアピールする場所）
5段落目：3～4段落での経験を通して気づいた問題点・課題点を書く
6段落目：それを解決・克服するために志望大学院への進学が必要であることを書く（同時にどう貢献できるのかも書く）
7段落目：博士課程で培った能力を駆使して将来達成したいことを書く
以下，段落ごとに私のSoPと共に説明します．
1段落目：大学院に進学したい理由と，大学院進学後に何をしたいのかを一言で述べる
I would like to make renewable energy one of the main power sources. To achieve this goal, it is necessary to study Materials Science at —– University and to conduct research with Prof. —–.
できるだけでっかいワクワクする夢を書いた方が良い気がします．もっと具体的に書くべきだという人もいますが，1段落目なのでふわっと大きく書いても良いのではないか，と私は考えます．どうせ後から詳しく書くので．
2段落目：なぜそう思うようになったのか原体験を簡単に述べる
To begin with, I explain my own experience that made me have the goal. When I was in junior high school in 2011, I experienced the Great East Japan Earthquake and Tsunami. Water and electricity were not available for a long time, and my father, a nuclear researcher, was not able to come home for more than a month in order to deal with the damage by Fukushima nuclear power plant. Through this experience, I realized that distributed power generation based on renewable energy sources can reduce energy risks.
ここは自分の原体験（私を突き動かす原動力）の説明の部分です．アゴスジャパンの代表取締役とお話した際に，「ここはできるだけ具体的に書きましょう．」と言っていました．いつどこで誰が何をどうしたのか，これらを具体的に書きました．説得力が増します．
つなぎ：「上記目標を達成するためにやってきたこと」の段落への導入部分．
The biggest issue that renewable energy faces is the high cost and inadequate performance of energy storage devices. If next-generation energy storage devices are developed and renewable energy generation using solar power or wind power are promoted, it will be possible to own power generation facilities on a regional basis, thus minimizing energy damage during disasters. In addition, by storing energy in accessible devices, it becomes possible to cope with energy shortages.
A sector of engineering that fundamentally supports energy storage devices is materials science. Therefore, I have studied materials science and conducted researches on energy storage devices at — University, — University, and Tohoku University.
私の場合は，いきなり「上記目標を達成するためにやってきたこと」の段落に入ることが難しかったため，この2段落を追加してスムーズにつなぎました．それぞれのSoPで，こういった工夫が必要になると思います．
3～4段落目：これを達成するためにやってきたことを書く（能力をアピールする場所）
At — University, I took classes such as Quantum Computational Chemistry and Applied Materials Chemistry to understand applied materials science. In — Lab at — University, I worked on the development of MnO2 microbattery fabricated by 3D printer, and successfully improved the performance of the device. In — lab at Tohoku University, I researched quinone-based organic supercapacitors. In brief detail, quinones were impregnated in nanopores of functional Hard Carbon with high conductivity and porosity, which resulted in ameliorated battery performances in capacity and cyclability. This was published in an academic journal (Yuto Katsuyama et al., Advanced Sustainable Systems, [DOI] https://doi.org/10.1002/adsu.201900083) as the front cover of issue 11, volume 3, 2019. Moreover, I presented the research at three conferences. At the 3rd ECS (American Electrochemical Society) Yamagata University Student Chapter Symposium, I received the Excellent Oral Presentation Award as the only undergraduate speaker among other eleven graduate students. Currently, I am preparing my second publication, this time on applying functional hard carbon to anodes of lithium-ion and sodium-ion batteries and seeking to improve the anode capacity and rate performance. Further proving my research ability, I was awarded Funai Overseas Scholarship, which will cover two full years of graduate school tuition plus a stipend of $2,500 a month for living expenses.
私の場合は1段落で書いてしまいました（本当は良くないです）．ここは，複数の段落に分けて，十分に分量を割いて丁寧に書くべきだと思います．なぜ省略したのかというと，私の場合は推薦状で丁寧に研究について書いてもらえることを知っていたからです．なので，最低限の分量に抑えました．
また，これでもかというくらい成果を自慢しました．学部生なのに論文を出しました！表紙に選ばれました！学会では唯一の学部生だったのに賞を受賞しました！難しい奨学金に合格しました！と．研究で具体的に学んだことを書くよりも，こういった客観的な成果の方が説得力がある，というのが私の基本的な考えです．
太字などは，人によっては悪印象かもしれません．実際に数人に「太字は印象良くないかも．それならトピックセンテンスでアピールすべきだと思う」と指摘されました．これは，自分が信じる道を行くしかないです．私は「太字の方が，ぱっと目に入るからよくない？」と考えたため，これで提出しました．大学によっては太字禁止といったルールがあるので気を付けてください．奨学財団の申請書にも同じようなルールがあったように思います．
5段落目：3～4段落での経験を通して気づいた問題点・課題点を書く
From these experiences, I have learned two things. First, it is important to effectively use basic elements that are universally abundant on the earth. Current secondary batteries contain rare metals, whose demand is expected to exceed supply. Therefore, the development of next-generation batteries, which use abundant elements, is one of the most important issues for the success of renewable energy. The second is the importance of nanotechnology, which is indispensable to maximize the potential of materials. For example, I was able to increase the capacity of the quinone-based redox supercapacitors mentioned above by adjusting the pore width of the carbon material from 2.00 to 3.70 nm, which resulted in the increased amount of quinones absorbed inside the pores. Another example can be found in the case that the carbon anode capacity of Na-ion battery was successfully improved by controlling the thickness of amorphous layers covering carbon crystals. These findings made me realize that such innovations in nanotechnology are especially important when controlling micro structures of materials to improve device performances.
ここでは，二つの問題点や課題点を書きました．基本的に「大学院進学後に学びたいこと」を学ぶ必要があることに気づいた，という流れに持っていくべきだと思います．
6段落目：それを解決・克服するために志望大学院への進学が必要であることを書く（同時にどう貢献できるのかも書く）
In graduate school, I would like to deeply immerse my studies in the latest materials science centered on basic abundant elements and nanotechnology, then integrate that knowledge to develop next-generation energy storage devices here at —– University’s Materials Science and Engineering Ph.D. program.
At — University, I would like to work with leading researchers in this field. Many energy storage devices, such as Lithium-ion battery, have been developed at — University by utilizing latest nanotechnologies, and as a result, a huge amount of expertise has been accumulated. I have developed a particular interest in the desire to work with Prof. —– as he has made remarkable achievements in the development of inexpensive batteries that can be supplied in large quantities without exploiting rare metals. The development of SIB by his research group is a good example. SIB is an appealing choice for the next-generation sustainable energy storage due to a significant resource advantage. However, it faces several challenges such as unstable cycle performance and dendrite deposition on the metal anode. Prof. —– has made great efforts onto these problems by developing stable electrodes and flexible solid electrolytes which prevents dendrite. In addition, Prof. —– has not only developed materials for each positive and negative electrodes, but also fabricated full-cell batteries by combining both electrodes; advancing SIB close to feasible steps. I would like to make renewable energy one of the main energy sources by developing low-cost and high-performance storage devices using abundant elements on the earth.
I can contribute to the Prof. —–’s group by utilizing my wide research capabilities and knowledge with experience of instigating research projects. For instance, I can employ my experimental skills related to various material characterizations, electrochemical measurements and coin cell fabrications for research regarding most batteries conducted in the group.
5段落目で挙げた課題点や問題点が，〇〇大学に進学することで克服・解決できます，と書きます．具体的に誰の何の研究に従事したいのか，まで書いた方が良いと思います．同時に，私がどのようにその大学に（その研究グループに）貢献できるのかも書くと良いです．
7段落目：博士課程で培った能力を駆使して将来達成したいことを書く
After getting a Ph.D. degree in Materials Science and Engineering, I would like to continue my research as a university staff in order to develop cheap and high-performance energy storage devices, which are required for the effective use of renewable energies. In the future, I would like to be a principle investigator who will contribute to sustainable and clean energy by conducting advanced researches regarding next-generation energy storage devices.
1段落目ではふわっと大きな夢を書きましたが，こっちは具体的なしっかりとした目標を書きましょう．上記の原体験や今までの準備，大学院でやりたいことなどを相手に理解してもらった後に伝える夢の方が，何も私のことを知らない段階で聞く夢よりも響くと思います．これが，私が第一段落で夢を詳細に語らない理由です．
まとめの段落
By accurately recognizing the importance of next-generation energy storage device development as a disaster countermeasure from my own experience, I am able to devote myself to research on next-generation energy storage devices with enthusiasm, which is indicated by my research publication and academic awards.
何も詳しいことは言っていないので必要ないと思いますが，私はやる気をアピールしました．どれだけ意味があるのだろうか．．．
以上が私流SoPです．
人によって本当に様々だと思います．他の人と比べたら低クオリティだと思いますが．．．あまりSoPの質を上げることにこだわらずに，他のもっと重要なすべきことをしたほうがよいかもしれません．