A PhD thesis is the last opportunity to be guided in a systematic way by a tutor. The achievement of a master program is a requisite for initiating a PhD therefore the student is expected to already have advanced knowledge of a subject including both theory and applied methods; analytical skills, critical assessment and some ability to work independently. During a PhD, a student works independently but guided by one/two supervisors. After several years of work, typically ranging between 3 and 5 depending on the country, a dissertation is worth a PhD when the study and the student meet three different criteria: novelty, considerable amount of work for this title and the proof that he/she did it on his/her own. These three requirements, and in particular the last one, are checked by means of the final exam and presentation which is referred to as PhD viva voice exam in the UK.

In my case, I decided to undertake a PhD after being a research engineer at the Solar Energy and Heat Pump laboratory of the Spanish Research Council (CSIC) in Madrid (CSIC). After considering some options in Spain and abroad, I won a studentship to do a PhD at The University of Nottingham (The University of Nottingham) funded by the European Union. I arrived at Nottingham (UK) in September 2010. The scope and objectives of some PhD projects are sometimes very well defined. For example, they can be specified by a company which is funding the project and/or they can be suggested by the future work discussed in a previous thesis. In my case, I knew that the topic of my PhD was renewable energy integration before moving to the UK. This was delimited to energy storage after the first meeting with my supervisors Prof. Mark Gillott and Prof. Gavin Walker.

Although there was some agreement on investigating energy storage for distributed renewable energy generation embedded into the built environment, no research question was stablished to start with. Finding the specific research gap was not straightforward for me since energy storage is a multidimensional solution which should be treated from a multidisciplinary approach in order to be successfully integrated across the energy sector. At the end, it took me one year to specify the research question but at the same time I could find some demand data and develop some models, e.g., PV and fuel cell models.

I finally decided to focus on energy storage for communities and in particular, I evaluated the impact of the community size, type of energy storage technology and energy storage application on the economic attractiveness of community energy storage.  But doing a PhD in the UK is also an experience which goes beyond a new academic degree: I had the opportunity to meet true friends and travelled to many spectacular places; but especially, I met my wife.

Abstract of my thesis

The UK government determined that 30% of the total electricity and 15% of the total energy should be generated from renewable sources by 2020 according to the Low Carbon Transition Plan. However, most renewable energy technologies are intermittent because they depend on weather conditions and they do not offer matching capability. Energy storage is attracting intensive attention as a technology which converts renewable energy technologies into a dispatchable product which meets variable demand loads. There is increasing interest for energy storage located very close to consumers which is able to augment the amount of local renewable generation consumed on site, provides demand side flexibility and helps to decarbonise the heating sector.

This thesis optimises community energy storage (CES) for end user applications including battery, hydrogen and thermal storage performing PV energy time-shift, load shifting and the combination of them. The optimisation method obtains the economic benefits of CES by quantifying the levelised cost, levelised value and internal rate of return. The method follows a community approach and the optimum CES system was calculated as a function of the size of the community, from a single home to a 100-home community. A complimentary methodology was developed including three reference years (2012, 2020 and zero carbon year) to show the evolution of the economic benefits during the low carbon transition. Additionally, a sensitivity analysis including the key parameters which affect the performance and the economic benefits was developed. The community approach reduced the levelised cost down to 0.30 £/kWh and 0.14 £/kWh for PV energy time shift and load shifting respectively when projected to the year 2020. These values meant a cost reduction by 37% and 55% regarding a single home. A cost of the storage medium of 275 £/kWh for Li-ion batteries (equivalent to a 10% subsidy over the assumed cost, 310 £/kWh) is the break-even point for Li-ion batteries by 2020 for an electricity price equal to 16.3 p/kWh (R2=0.6).

Secondly, this thesis presents a new community hydrogen storage system integrated in a low carbon community and the experimental results when performing PV energy time-shift, load shifting and the combination of them. Long term ES was demonstrated when the community storage hydrogen system performed load shifting and the capacity factor of the electrolyser increased by 116% when PV energy time-shift was performed in addition to load shifting. This system was designed in collaboration with industrial partners and the key findings obtained during the construction and testing phases are shared.

A link to my thesis:

My Thesis

An introduction to The Univeristy of Nottingham: