An energy self-sufficient public building using integrated renewable sources and hydrogen storage

Abstract

The control of the use of fossil fuels, major cause of greenhouse gas emissions and climate changes, in present days represents one of Governments' main challenges; particularly, a significant energy consumption is observed in buildings and might be significantly reduced through sustainable design, increased energy efficiency and use of renewable sources.

At the moment, the widespread use of renewable energy in buildings is limited by its intrinsic discontinuity: consequently integration of plants with energy storage systems could represent an efficient solution to the problem. Within this frame, hydrogen has shown to be particularly fit in order to be used as an energetic carrier.

In this aim, in the paper an energetic, economic and environmental analysis of two different configurations of a self-sufficient system for energy production from renewable sources in buildings is presented.

In particular, in the first configuration energy production is carried out by means of photovoltaic systems, whereas in the second one a combination of photovoltaic panels and wind generators is used. In both configurations, hydrogen is used as an energy carrier, in order to store energy, and fuel cells guarantee its energetic reconversion.

The analysis carried out shows that, although dimensioned as a stand-alone configuration, the system can today be realized only taking advantage from the incentivizing fares applied to grid-connected systems, that are likely to be suspended in the next future. In such case, it represents an interesting investment, with capital returns in about 15 years.

As concerns economic sustainability, in fact, the analysis shows that the cost of the energy unit stored in hydrogen volumes, due to the not very high efficiency of the process, presently results greater than that of directly used one. Moreover, also the starting fund of the system proves to be very high, showing an additional cost with respect to systems lacking of energy storage equal to about 50%.

From the above, it can be deduced that, in the aim to obtain a quick, effective penetration of hydrogen into the market, it is at the moment indispensable to enact incentivizing policies, attributing to hydrogen production fares able to cover the additional costs due to its production, storage and reconversion.

Introduction

The control of dangerous climate changes presently represents one of the main challenges humankind has to face up. In this aim, significant importance attains to greenhouse gas emission reduction [1] that is fundamental matter of international Agreements, such as Kyoto Protocol.

In order to achieve the prefixed targets, attention must particularly be paid to the control of excessive use of fossil fuels.

In this aim, EU has recently fixed three main objectives to be achieved by 2020 [2]:

• 20% reduction in primary energy consumption through increased energy efficiency;

• 20% increase in the share of renewable energy sources;

• 20% reduction in emissions of greenhouse gases with respect to the commitments of the Kyoto Protocol.

In the last decades, the demand for energy has been steadily rising despite limited availability of non-renewable fuel resources. Hence, efforts to develop more efficient energy systems are becoming increasingly significant [3].

At the moment, in developed countries, a significant portion of total primary energy is consumed in buildings and can be significantly reduced by adopting energy efficiency strategies and using renewable sources [4], [5].

Consequently, a primary importance objective by 2020, strongly recommended by EU Directives, is the quasi-zero energy building, a passive building essentially making use of natural energy sources [6].

Anyway, presently one of the greatest limitations in renewable energy widespread use lays in its intrinsic discontinuity; consequently, in order to efficiently satisfy building energy demand, an integration with energy storage systems is required if the use of traditional, fossil fuel plants is to be reduced.

In this frame, recently hydrogen has shown to be particularly fit in order to be used as an energetic carrier [7], [8], [9] as it can be produced, stored and used in advanced systems associated with plants for energy production from renewable sources.

Consequently, research for hydrogen sources useful for feeding hydrogen-air fuel cells represents at the moment an important aspect of the hydrogen energy problems [10], [11].

Indeed, hydrogen and fuel cell technologies offer a pathway to enable the use of clean energy systems, reduce emissions, enhance energy security, and stimulate global economy. As a part of a portfolio of clean energy technologies, including energy efficiency, renewable energy and fuels and battery-electric vehicles, a widespread use of hydrogen and fuel cells in the economy will help to achieve the above goals. Presently sustainable global research, development and demonstration are producing the necessary technological breakthroughs for hydrogen and fuel cells to compete in the market with the following benefits [12]:

• hydrogen is a clean energy vector: when used in fuel cells, the only byproducts are water and heat;

• it can be produced from diverse domestic sources (among them renewable sources) and processes, freeing from the political instabilities that affect oil and gas supplies in the world;

• it is interchangeable with electricity: it can be used to generate electricity, while electricity can be used to produce hydrogen;

• over 100 years of safe production, transportation and use show that it carries no more risk than natural gas or gasoline;

• fuel cells have no moving parts, they are silent, vibration-free, and require little to no maintenance;

• they provide high-quality, direct-current power, that is ideal for many advanced electrical and electronic devices;

• they do not require time-consuming recharging and thus have much lower down-time and refueling requirements compared to battery-electric vehicles;

• they can provide energy at all scales, ranging from micro-power sources for small consumer devices to multi-MW power plants;

• hydrogen technology has the potential to strengthen national economies and create high-quality jobs in industries.

Within this frame, in the paper, in order to contribute to characterize energy saving techniques and spreading the use of renewable sources in the building sector, a self-sufficient system for energy production in buildings, also making use of hydrogen for energy storage, is presented in two different configurations. Both proposed systems aim at producing energy from renewable sources and make use of hydrogen for energy storage and reconversion in fuel cells. Particularly, the first system uses only photovoltaic panels for energy production, whereas the second one integrates them with wind generators.

Through the paper, the economic, energetic and environmental sustainability of the system is analyzed: particularly the system, although consisting in a “stand alone like configuration”, has been grid-connected in order to benefit from incentivizing fares provided by Italian Government, that are likely to be suspended in the next future.

On the whole, the main innovative aspects of the proposed system are:

• exploring the efficacy of integration of different natural sources for energy production;

• overcoming building dependence on energy discontinuity typical of solar and wind energy;

• testing the use of hydrogen as an energy carrier;

• testing the economic sustainability of the building energy self-sufficiency;

• taking advantage from the benefits provided from Italian Government for Renewable Energy Sources (RES) production;

• avoiding a considerable amount of pollutant emissions.