Solar Hydrogen and the Electron Economy

According to the US National Academy of Engineering, the electric grid was the most significant engineering achievement of the 20th century.38 The interconnected series of transmission wires, metal towers, voltage converting substations and their associated control structure that make up the electric grid is of course existing infrastructure of immense value (Figure 3.26). It will be used increasingly in the solar hydrogen economy, in which a continuous source of power – solar hydrogen accumulated during the day – will be burned (or oxidized in fuel cells) to meet cus­tomers’ demands and provide power at night and on cloudy days, as well as when demand peaks.

In other words, once generated in CSP hydrogen plants, electricity and not compressed hydrogen will be sent directly to the appliances using the grid (an existing infrastructure), exploiting the intrinsically higher efficiency of what Bossel has called the ‘‘electron economy’’. In Bossel’s words:5

An electron economy can offer the shortest, most efficient and most economical way of transporting the sustainable ‘green’ energy to the consumer. Electricity could provide power for cars, comfor­table temperature in buildings, heat, light, communication, etc.

In a sustainable energy future, electricity will become the prime energy carrier. We now have to focus our research on electricity storage, electric cars and the modernization of the existing elec­tricity infrastructure.

image144

109

Figure 3.26 A scheme of the US grid in 2009.

(Reproduced from Ref. 38, with kind permission.)

Solar hydrogen is, indeed, an excellent way to store electricity. Even though the efficiency of the solar hydrogen economy will be affected by wastage in the two conversions – from physical to chemical and from chemical to physical energy – it will be sufficient to deploy more solar collectors and low cost electrolyzers in order to obtain the required amounts of hydrogen to power the world’s current (15 TW) and future power needs.

In other words, a solar hydrogen economy is based on two such conversions (electrolysis and fuel cells or hydrogen engines) along with electricity generation from a free fuel (sunlight), whose immense abun­dance will allow us simply to overcome the efficiency limitations of this double conversion of energy (physical —chemical —physical).

Moreover, in the ‘‘distributed generation’’ scheme in which ever more grid homes and industrial customers are contributing, by producing some or all of their own power, solar hydrogen will help us to face the changes required to adapt the grid to allow more flexible options for future electricity production, transmission and distribution.39

Increased use of solar energy generation means more variable power supplies that have to be backed up by storage or by other power gen­eration systems. Demand response for both large and small consumers is

image145

Chapter 3

Figure 3.27 The smart grid will be formed of mission lines, equipment, controls and new technologies working together to respond immediately to our new demand for electricity.

(Reproduced from Ref. 39, with kind permission.)

becoming an increasingly viable way to deal with peak energy use. Advances in distributed generation, such as home solar panels, both assist and are assisted by the creation of the smart grid (Figure 3.27). The load production is closer to where it is needed and can help to balance peak load needs.

For example, in Canada, BC Hydro converts surplus hydroelectric power generated at its Clayton Falls hydroelectric plant in Bella Coola, British Columbia, into hydrogen, stores it and then uses it in a 100 kW fuel cell to provide power as needed.

Hydro power is already a good storage system for electrical energy, because utilities can postpone energy production by pumping the water backwards in the dam, with good efficiency.40 In the case shown below the hydro power is actually micro-hydro power, with no storage for water, namely it is a ‘‘run of river’’ system (Figure 3.28) which does not provide the typical output control a traditional dam provides.

In the Clayton Falls Hydrogen Assisted Renewable Power System (HARP) system, two methods are used to store the electricity. In the first method hydrogen is produced through electrolysis, and is then stored as a gas in high pressure tanks. The second method uses an electrochemical regenerative fuel cell, known as the flow battery, to store the energy. A microgrid controller manages the power system (Figure 3.29) by monitoring supply and demand and determining when

image146

image147Figure 3.29 The Hydrogen Assisted Renewable Power (HARP) system. A schematic
of microgrid system from Bella Coola, British Columbia.

(Reproduced from Ref. 42, with kind permission.)

to convert power into hydrogen and when to generate power from hydrogen to meet spikes in demand.

During peak periods the stored hydrogen (Figure 3.30) is fed into a 100 kW fuel cell to generate electricity. At the same time, the flow bat­tery produces 100 kW of electricity directly to the community. Together these two generators in the HARP system reduce annual diesel con­sumption by 200 000 L.42

image148

Chapter 3

Figure 3.30 Clayton Falls BC Hydro’s HARP project is an energy storage system that converts off-peak electricity from a renewable source into hydrogen via an electrolyzer. The hydrogen is used for energy later on, during times of peak demand.

(Reproduced from Ref. 42, with kind permission.)

According to the company,43 renewable hydrogen is a very cost – effective and convenient way to store renewable energy; it is more eco­nomical than importing electricity from Alberta or from the USA to provide customers with power at peak times.

This insight immediately refers the reader to a sector in which solar hydrogen will play a role, namely in the production of valued peak power through the grid, resulting in consistent ‘‘peak shaving’’ of the price of electricity for the customers of the grid. This phenomenon is already taking place in Germany and in Italy, where an impressive 13 GW overall of PV power has been installed between 2008 and 2011. Indeed, thanks to generous feed-in-tariffs and to the concomitant dra­matic fall in the price of PV modules, between 2008 and 2011 Italy has become the world’s second country for installed PV power, with over 13 GW of grid-connected PV plants present in the early days of 2012.44

The impact of all this power on the electricity market started to become clear in the early months of 2011 (Figure 3.31).45 The valued PV power produced in the sunny hours during the day ‘‘pushes’’ out of the market the most expensive power plants, namely the expensive open cycle ‘‘turbogas’’ plants running on natural gas only. By doing so, it effectively cuts the market price of electricity, resulting in a clear benefit for the grid customers.

Similar findings have been reported from the Hydrogen and Renew­ables Integration (HARI) project, run from 2003 through late 2011 at West Beacon Farm in Leicestershire, UK. The project involved the integration of an electrolyzer, hydrogen storage and fuel cells with an existing renewable energy system. In full agreement with Bossel’s insight

image149

mentioned above, the researchers found that the efficiency of passing through the cycle from electricity to hydrogen and back to electricity is (at typically around 20% or lower) poor (Figure 3.32).46

In Gammon’s words,

Clearly, converting energy from electricity to hydrogen and back to electricity again is a very wasteful cycle, which must be con­sidered only as a last resort, but which may be unavoidable in certain situations.

Wherever possible, the electricity that is hard-won from renewable (or any other) sources should remain as electricity until it is con­sumed by the end-user appliance. Once converted to hydrogen, the energy should only be used in applications, such as transport and remote or portable power generation, where only a fuel is able to do the job.

However, because hydrogen is a means of energy storage it can be harnessed for powering the grid with electricity or, directly, for vehicle propulsion and heat generation. Overall, the combined use of fuel cells, electrolyzers and hydrogen makes it possible to use the grid as the major means of energy distribution and supply – for electricity, heat and transportation – thus removing the distinctions between these three energy forms and, at the same time, increasing the overall energy efficiency.

Eventually, as stated by Gammon,46 complementary solar hydrogen and electricity will be used in a symbiotic partnership to derive max­imum benefit in terms of flexibility and efficiency, but electricity that is easy to dispatch will certainly continue to play a large and increasing role in our energy system, even when carbon-neutral solar hydrogen is readily available.

Leave a reply

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>