After a short review of past and present EU green energy programmes, the article deals with the great surging interest on green hydrogen worldwide and the consequent programme of the EU. Considering the trend in the increasing percentage of variable wind and solar plants in the EU, a preliminary evidence on their variability is reported and based on their capacity factors during the different months of last year in France, Spain and Italy. The basic characteristics and ‘colours’ of hydrogen are underlined, and emphasis is placed on the current and future global demand in 2030 and 2050. The expected cost of the energy content of green hydrogen just at the exit of electrolysers (power to gas—P2G) fed by renewable electricity as derived by key international well-recognised organisations is presented. The high cost of hydrogen content of energy at the exit of electrolysers is underlined; even with the 2050 prospective low cost around €1.2/kg of hydrogen, it corresponds to €36/MWh to be compared with the EU present gas market price of €13/MWh that with a penalisation of around €130/t CO₂ will reach €36/MWh. Even if the compression, transport and distribution of hydrogen pose important challenges, the article is limited to its production subject to the effects of variability of wind and solar on the performance of large electrolysis plants characterised by a complex balance of plant composed of various subsystems. Based on almost instantaneous data logging from some Italian wind and solar plants, questions are raised about the effects of variability and intermittency on efficiency, flexibility, reduction of the load factor of the electrolyser for its inherent limits. This is relevant due to its minimum load for operation, frequent cold starts, time to ramp up to the operating power. This leads to concerns on the feasibility of operation of an electrolyser plant if it is fed only by a variable and intermittent renewable dedicated plant not connected to the network. Owing to the specific variation versus time of the renewable electricity feeding the electrolyser and of the constraints of hydrogen demand, the cost of hydrogen provided in the literature is only valid for general scenarios. A tailor-made approach case by case for the optimisation and design of the plant appears to be necessary. In contrast the possible smooth behaviour of an electrolyser connected to the grid with power purchasing agreements for electricity from renewable plants spread in the system is analysed; the existing regulations foresee increments in the price of this electricity to remunerate its transport and for ancillary, thus increasing the hydrogen production cost. On the other hand, a better capacity factor could ameliorate the situation but also in this case detailed optimisations are needed. In the conclusions, the still great technological, legal, regulatory and socio-economic challenges for hydrogen production, transport, distribution and final uses are pointed out with the necessity of rigorous analyses and prototypal experiments for a better definition of its market share and relevant timing; specifically it is suggested to concentrate efforts also on a possible new way of operation of electrolysers not as up to now connected to a strong electricity network but fed by RES plants isolated from the grid and characterised by daily, monthly and seasonal variations with time intervals of total lack of electricity at all and sharp up-and-down ramps.

在简短回顾了过去和现在的欧盟绿色能源计划之后，本文讨论了全球范围内对绿色氢以及随之而来的欧盟计划的极大兴趣。考虑到欧盟可变风能和太阳能发电厂的比例不断增加的趋势，据报道，根据其在去年不同月份在法国，西班牙和意大利的产能因素，对它们的可变性进行了初步证明。强调了氢的基本特征和“颜色”，重点放在了2030年和2050年当前和未来的全球需求上。电解槽出口处绿色氢的能量含量的预期成本（功率为气体-P2G） ）介绍了由国际知名的主要组织提供的可再生电力。强调了在电解槽出口处氢的能量消耗高昂的代价；即使2050年潜在的低成本氢气价格约为1.2欧元/千克，它也相当于36欧元/兆瓦时，与欧盟目前的天然气市场价格13欧元/兆瓦时相比，罚款约为130欧元/吨二氧化碳_2个将达到€36 / MWh。即使氢气的压缩，运输和分配带来了重大挑战，但该产品的生产仍受制于风和太阳能的可变性对大型电解工厂性能的影响，该工厂的特点是由各种子系统组成的工厂具有复杂的平衡。基于一些意大利风力和太阳能发电厂的几乎瞬时数据记录，人们提出了以下问题：可变性和间歇性对电解槽的效率，灵活性和负载因其固有限制而降低的负载因数的影响。这一点很重要，因为其运行的最小负载，频繁的冷启动，增加运行功率的时间。如果仅由未连接到网络的可变且间歇性的可再生专用电厂供电，则这将引发对电解厂运行可行性的担忧。由于进给电解槽的可再生电力随时间的特定变化以及氢气需求的限制，文献中提供的氢气成本仅在一般情况下有效。看来有必要针对工厂的优化和设计量身定制方法。相比之下，分析了通过系统中散布的可再生能源发电厂的购电协议，连接到电网的电解槽的平稳行为；现有法规预见了这种电价的上涨，以补偿其运输费用和辅助费用，因此增加了制氢成本。另一方面，更好的容量因子可以改善这种情况，但是在这种情况下，还需要进行详细的优化。结论中指出，氢的生产，运输，分配和最终使用仍然面临巨大的技术，法律，法规和社会经济挑战，并需要进行严格的分析和原型实验以更好地定义其市场份额和相关时机。 ; 特别是，建议将精力集中在电解槽的一种可能的新操作方式上，这种方式到目前为止尚未连接到强大的电网，而是由与电网隔离的RES工厂供电，其特点是每天，每月和季节性变化，时间间隔为完全没有电力，上下坡道陡峭。