Realize 100% Renewable Energy in Low-Latitude Pacific Ocean



Professor Emeritus, Chuo University Tokyo, Japan


Sailing Mega Solar-Module Raft Project in Low-Latitude Pacific Ocean & and Its Possibility





Gigantic solar PV raft always sailing low-latitude Pacific Ocean.

There, rich sunshine, mild winds/waves, and little typhoon risk.

Electricity transported by myriad EV batteries or H2-gas.

Solar PV modules, thin flexible type, integrated with solar cloths.

A 25km2 raft, consisting of 40000 subunits of 25m square jointed.

Estimated economically feasible if H2-gas price is 50% up.

Further innovation in design concepts realize 0.25 USD H2/m3.

Huge rafts should be accepted internationally to sail in ocean.



The Japanese Government recently declared to fulfil carbon-neutralization of the country by 2050. However, a realistic scenario toward that goal has not yet been visualized. With its limited land areas inhabited by more than a hundred million people, it is absolutely impossible for Japan to realize this target only by land-based natural energies such as hydraulic, geothermal, solar and wind, even with the aid of operations of preexisting nuclear power stations.


The most plausible strategy the government is going to take for that goal seems to be offshore wind power similar to many other nations in the world. A number of off-shore wind power farms have already been developed in northern European countries like Denmark, UK and Germany in these decades. They are all fixed-bottom types with their foundations constructed directly on sea-floor, wherein water depth cannot be greater than 50 m at the deepest because of technology and economy. Unfortunately, most coastal seas around the Japan islands tend to increase water depth in short distance from the shore, restricting the potential capacity of the fixed-bottom type. 

Hence, the floating type which can be sited in seas of 200 m or deeper are considered to be promising, wherein the wind turbine is fixed on the float moored and anchored to deep sea-floor. UK is proud of this offshore technology as a front-runner in R & D making the most of the experience in the North Sea oil/gas projects and planning to demonstrate the technology getting mature in a few years through a couple of test-site operations. The Japanese government appears to look forward almost exclusively to the floating type wind power as promising renewable energy because large sea areas may be able to be chosen as favorable sites.

However, the practical operation of the floating wind power has not yet been started even in European front-runner countries. In Asian countries like Japan and Taiwan where natural environments are more hostile with severe typhoon, high seismicity and tsunami, considerable technical problems will have to be solved before the power system can be dependable as a major player. A couple of test sites have already been decided and experimental floating wind power projects are tested for years in Japan, though their clear technical perspective has not yet been recognized publicly. Furthermore, fishing industries in Japan have historically had strong voices in using oceans all along the coasts, that may impose another constraint on the off-shore wind power.

Thus, it seems too optimistic to believe that we can depend exclusively on off-shore wind power to supply huge volume of renewable energy demand in Japan to realize the carbon-neutral. Instead, possibilities of other renewable energies conceivable in our particular conditions in the east Asian region also have to be explored.

In this respect, our research group have been proposing an innovative project for more than a decade (before the Fukushima nuclear disaster in 2011) that could be another possibility of huge renewable energy particularly in Japan; PV solar power in the Pacific Ocean, wherein huge sunshine energy affluent in low-latitude Pacific Ocean may be captured with reasonable economy by slow-sailing mega-solar module rafts if we can meet associated technical requirements.

It is no doubt the right of any countries authenticated by the International Maritime Law to make a sail in international open seas for commercial purposes, wherein renewable sunshine energy is exploited on purpose. Hence, it is considered possible to share a consensus in international forums such as IMO (International Maritime Agency) how to realize such innovative sailing for solar power generation in open seas by minimizing the impact on other sea-businesses there. Fortunately, the low-latitude Pacific Ocean are remote from major commercial sea traffics in the high latitudes.

If a giant mega-solar raft as 5 km square is considered for example, the electric energy generated only during daylight hours can be equivalent to 1 GW nuclear power stations of availability 100%, by assuming daily sunshine energy per area 8 kWh/m2, the energy conversion rate 12 % (of silicone solar module commercially available today). In the most part of low-latitude Pacific Ocean, the annual average of daily sunshine energy exceeds 6.0 kWh/m2 among that the highest can reach 6.5~7.0 kWh/m2 between the equator and 15° south in a sea expanding as vast as the Australian continent. Hence, it seems possible for the sailable raft to pursue seasonal optimal sunshine attaining 8.0 kWh/m2 (more than twice the average in the Japan island) by making an energy-saving slow-speed wind sailing.

As for the wind condition there, it is found to be very mild and stable with annually averaged wind speed of 3~7 m/s distinctly lower than in high-latitude oceans. The waves are not rough, 1~2 m high on yearly-average in low-latitude Pacific, unlike middle/high latitude throughout the year, though the solar module raft will be designed operational in much higher waves.

As the greatest risk to this mega-solar raft system, tropical depressions or storms, typhoon or hurricane, cannot be ignored. However, it should be emphasized that there are two wide sea areas literally free from the risk in the low-latitude Pacific. One is overlapping with the area of the highest sunshine energy mentioned above (due to exceptionally low temperature of sea current originated from Antarctica. Another is ±5° along the equator where tropical depressions cannot be born theoretically because of the Colioris Effect. In other areas, the risk tends to increase, though not so severe as in the middle-latitude, necessitating in-advance evacuations. It may well be expected that rapidly advancing meteorological knowledge/technology will enable reliable predictions of tropical depressions in a month ahead in near future. As for one more natural disaster, tsunami, the effect may not be critical to this energy system as long as it stays remotely from shallow coastal areas.

In our scenario to realize this system contributing to the carbon-neutral initiative by 2050, three major technologies have to become practically mature in 30 years as follows;

  1. The huge electric energy generated by the mega-solar module is transformed into hydrogen gas by alkaline water electrolysis and shuttled periodically either as MCH (Methylcyclohexane) or as liquefied H2-gas by huge vessels. Another possibility is to transport the electric energy directly by packages of myriad high energy-density EV batteries without energy conversion process.
  2. Thin and flexible solar modules (such as CIS-types or organic dye-sensitized types) seem to be promising for this project rather than conventional silicone types, thin (2 micron) with conversion efficiency of more than 12% and should be integrated with flexible sail clothes. The associated energy collection system from myriad modules all over the gigantic raft should be as simplified, cost-effective and durable as possible.
  3. The giant raft consisting of typically 2500 units of 100 m square, each of them further comprising 16 subunits of 25 m square on which 4 solar modules are set. All of them are connected by universal joints so as to deflect freely following wave motions. The gigantic raft is designed to be able to sail as a whole basically by wind and sea-current.

Though the hurdles to realize these widely diverged technologies seem to be too high to overcome, their technical bases are already present actually. What is needed in the next 30 years is to integrate the individual technical elements by scaling up the capacity, raising the efficiency for better performance and minimizing the cost.

In comparison with the floating wind power, this sailing solar power may look far unrealistic and more challenging. However, to construct thousands of 10~20 MW floating windfarms of 200~300 m high above sea-level in a few decades to supply enough renewable energy in Japan is also very challenging though this challenge has already been initiated by European countries and followed worldwide, while the sailing solar power concept has never been proposed before. One essential condition to realize this concept is to form an international consensus in UN or IMO accepting the sailing of huge rafts in low-latitude Pacific Ocean with due regulations for minimizing the effect on other sea-traffics.

The economic feasibility has already been estimated on the 25 km2 mega-solar raft by roughly extrapolating current state of technologies. It indicates that subsidizing the price of hydrogen by 50% will make it well viable. However, more cost-cutting efforts are further required to be commercially feasible for market-competitive hydrogen price. It is particularly needed for the giant raft to employ truly innovative design concepts for drastic cost reduction free from conventional float design concept. Essential chemical plants needed for the hydrogen transportation, if the battery transportation is not chosen, are also very costly and have to be drastically economized by incorporating advanced technology, scaling-up and mass production effects.

Though further steps are still needed to reach to the gigantic 1 GW system, it seems possible to realize a smaller capacity mega-solar module raft to practically operate in low-latitude Pacific by 2050 because the basic technologies are already in our hands. Also note that such an innovative green energy initiative where international multidisciplinary cooperation is critical will surely lead to creation of next-generation disciplines in science & technology, new markets in business and job opportunities not only in Japan but all over the world. That will make an epoch bringing all human beings on earth to a new horizon to live a truly sustainable life without burning fossil fuels.

One may wonder if such a green-energy initiative in the low-latitude Pacific Ocean may be able to coexist with the current circumstances of US-China power struggle conducted right there. Because of that, however, it is really meaningful from a quite different perspective of world peace to start this initiative in cooperation firstly with Pacific Island countries as well as with many other interested nations.

Time will surely come sooner or later when developing countries have sufficiently developed and demand as much energy as pre-developed countries. Then, abundant sunshine energy in low-latitude Pacific Ocean will be targeted by many countries as indispensable natural energy resource on earth. To prepare for that time, Japan is a right country in a right position to take the first step to this endeavor in cooperation with many other countries including Pacific Island nations.

Thus, besides offshore wind power, we may possibly be able to have another option of huge renewable energy. Why do not we expand our sight and investigate the possibility to make use of abundant sunshine energy in the Pacific Ocean that nobody has ever tried.


References: Kokusho, T., Emoto E. and Kato, T. (2012): Sailing Solar-Cell Raft Project and Weather/Marine Conditions in Low-Latitude Pacific Ocean, Journal of JSES, Japan Sunshine Energy Society, 38 (1), 49-57 (in Japanese). Kokusho, T., Emoto E. and Kato, T. (2013): Sailing solar-cell raft project and weather and marine conditions in low-latitude Pacific Ocean, Journal of Energy Engineering, ASCE, 139 (1), 2-7. Kokusho, T. (2016): Feasibility of Mega Solar Raft in Low-Latitude Pacific Ocean, 42 (6), Journal of JSES, Japan Sunshine Energy Society, 42 (6), 49-57 (in Japanese).


The following is a PPT presentation material associated with a lecture delivered in Energy Committee of Japan Society for Civil Engineers in January 2020, where a more detailed information on this energy project is available as translated into English.





























































































中央大学名誉教授  國生剛治










メガソーラー筏の究極的には25km25km×5km)の大面積化を目指した場合,1日で得られる単位面積当たりの太陽エネルギーを8 kWh/m2,ソーラーモジュールの電気変換効率を12%(現時点の家庭用太陽電池の値)で試算すると、昼間の日照時間のみの発電にもかかわらず24時間連続稼働する100kW級の原子力発電所の電力に匹敵します。南北太平洋の低緯度海域で,メガソーラー筏や母船などからなる船団が長期気象予報技術を活用して晴天域を低速帆走しつつ,太陽光発電をします。

太平洋低緯度海域には1日あたりの日射量が年平均6.0 kWh/m2/day以上の海域は帯状に広く拡がり,赤道から南緯15°には6.57.0 kWh/m2/dayに達するオーストラリアやサハラ砂漠を凌ぐ広大な海域が存在します。これらの低緯度海域を筏船団が可動性を生かし季節変動を考慮しながら回遊することで, 8.0 kWh/m2/day(国内平均の2倍以上)の日射エネルギーを得ることは十分可能です。また低緯度海域は高緯度海域より全般的に風は穏やかであり、年平均風速は 37 m/sで風向も安定しています。それに伴い波浪条件も比較的静穏で冬場でも平均波高は2mを超えず夏場は1m程度です。

一方、この構想の成立性に深刻なリスクとなり得る熱帯低気圧(台風・ハリケーン・サイクロン)についてですが、赤道から±5°以内は地球自転によるコリオリ効果が作用しないため原理的に発生・存在ができません。さらにその危険性がほぼゼロで(南極寒流の影響で海水温が低いため)、かつ太陽エネルギーも最強のサハラ砂漠より広大な理想的な海域が南半球に拡がっています。それ以外の赤道から±20°以内の海域については熱帯低気圧の危険度は我が国近海ほどには高くはないもののゼロではないため退避行動が不可欠ですが,1ヶ月程度先の熱帯低気圧に特化した予報技術を発展させることで熱帯低気圧を確実に回避できる筏船団の航行が可能と思われます。 また津波については沖合深海域での影響はほぼ無視でき、地震については浮遊物体へは横揺れのエネルギーは伝わりません。このように可動性を生かすことで自然災害への備えは大幅に軽減され、筏の設計簡素化が可能となります。









國生剛治 (2016):低緯度太平洋メガソーラー発電筏の概略成立性,太陽エネルギー 日本太陽エネルギー学会 Vol.42,No.6,61-67.

中央大学理工学研究所プロジェクト研究2014年度報告書(2014):「低緯度太平洋ソーラーセル帆走筏発電 システムの成立性」、低緯度太平洋ソーラーセル帆走筏発電システムの成立性研究会 http://www.civil.chuo-u.ac.jp/lab/doshitu/top/houkokusyo%20honsastu.pdf


























Energy-Based Liquefaction-Potential for Induced Strain and Settlement -Evaluation Steps & Example Cases –


Takaji Kokusho

Professor Emeritus

Chuo University, Tokyo, JAPAN.


Why Energy is Recommended ?:

It is widely recognized that Dissipated energy in soils during earthquakes is a key variable determining liquefaction behavior uniquely independent of wave forms rather than Acceleration currently used in Liquefaction evaluation practice.  The graph below vividly shows how uniquely the dissipated energy can decide pore-pressure buildup up to 100% during two earthquakes of quite different time duration and wave form; 2011 Tohoku EQ. (M=9.0, lasting 3 min.) versus 1995 Kobe EQ.(M=7.2. lasting 10 sec.).

To practicing Engineers:

Please try this once to compare the results with the conventional stress-based evaluation or sophisticated numerical methods. Hopefully, you can recognize its simplicity and convenience in comparison with other methods by only implementing Excel calculations. Please email koktak@ad.email.ne.jp if you have any questions.



Liquefaction potential and its consequence are predicted here in Energy-Based Method [EBM] in contrast to conventional Stress-Based Method [SBM] by comparing capacity (cumulative dissipated energy) with demand (upward earthquake wave energy).

Studies on soil profiles indicate that EBM (in the 1st stage evaluation) tends to yield similar results to conventional SBM for ordinary earthquakes but can  reproduce actual performance better than SBM for peculiar earthquake waves with exceptionally large/small energy in contrast to acceleration.

Induced strain and settlement can further be evaluated in the second stage of  EBM by assuming that equal demand energy is allocated to every layer predicted liquefiable in the first stage.

This two-stage evaluation applied to examples of uniform sand and case-history sites demonstrated its reliability in comparison with SBM results as well as with actual performance and soil settlements in case histories.

Thus, liquefaction potential including induced strain and settlement in 1D soil models can readily be determined in multiple-step Excel-calculations, without resorting to complicated time-increment effective stress analyses.


Kokusho, T. (2021):Energy-based liquefaction evaluation for induced strain and surface settlement – evaluation steps and case studies –, Soil Dynamics & Earthquake Engineering, Elsevier, 143, 106552.

It can be downloaded free until April 6, 2021 at:








      エネルギーに基づく簡便な液状化判定と       発生ひずみ・沈下量の算定法ならびに適用例

中央大学(名誉教授)  國生剛治






液状化に密接に関わる累積損失エネルギーに着目し、それを地震波動エネルギーと比較することにより簡便に液状化判定できるエネルギー法を提示  (1次評価)。




参考文献:國生剛治 (2020):エネルギーに基づく液状化評価法による発生ひずみ・沈下量の簡易計算と既往事例への適用,地盤工学ジャーナル Vol.15,No.4,683-695.