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In its review of the challenges and opportunities associated with massive deployment of solar PV generation, the Grid integration working group of the ETIP PV identified forecasting and observability as critical technologies for the planning and operation of the power system with large PV penetration. In this white paper ETIP PV set out to spell out in more details what features are needed from these technologies and what is the state of the art.

How much is too much? Asking this question with respects to photovoltaics would have seemed absurd just a few years ago. Yet from Japan [1] to Europe to the Americas, loud voices are claiming that Photovoltaics (PV) is reaching excessive levels on the grids or, at least, growing at excessive rates. Economic as well as technical issues are put forward. Indeed, PV power generation has moved in just a decade from a curiosity to a significant part of power systems around the world. Global investment in new PV generation capacity was US$ 173.6 billion in 2013, nearly two thirds of the gross investment in fossil-fuel power generation (US$ 270 billion) [2]. Solar PV is estimated to have provided 0.7% of the global electricity demand in 2013 [3]. The central point in Levelised Cost of Electricity (LCoE) at the beginning of 2014 was about US$ 150 per MWh; there is now a significant overlap between the LCOE ranges of PV electricity and conventional power generation (natural gas combined-cycle turbines, coal, nuclear) [2], which means that solar PV can be cost-competitive at the point of generation in some regions. As PV is essentially a distributed energy resource, it clashes with the centralised architecture of existing grids. Together with other renewable energy sources, it challenges the business models of incumbents in the power sector, be they network operators or power generators. Some of these incumbents may be tempted to exaggerate the negative impact of PV, and minimise its benefits. Others have already taken radical steps to adapt to this new situation [4]. The benefits of PV generation in terms of environmental impact and energy security are well documented [5]. This is why the European PV Technology Platform aims at enabling the massive deployment of photovoltaics into the power system. It acknowledges the technical challenges that come with it. We believe that these challenges are best addressed through rational assessment of the situation and co-operation between the power and PV industries. With this paper we set to clarify the terms of this discussion: how is penetration of PV into power grids evaluated? What are the current levels? Which barriers may prevent increasing these levels? Which concepts have been put forward to open these barriers? Which benefits can PV systems provide for existing and new grids? Immediate recommendations are formulated in this paper; we also expect that further collaboration with the power sector will lead to more robust knowledge and to a power system with PV at its heart.

Purpose: In the summer of 1999 I got the disease Guillain Barré syndrom. During my recovery I wrote a text about my experiences at the hospital. In this paper I investigate the patient perspective by using that text. To make the distinction between the patient and the doctor perspective clearer I have also made use of my medical journal. Methods: Qualitative text analysis. There are some extra challenges writing about oneself. To encounter this I invited three persons to read my text, and to meet me and discuss my findings. Results and discussion: Reading the text I found four important categories: 1) Meeting with the hospital, 2) confused relationship to own identity, 3) a changed perspective of time, and 4) emotions. In literature about GBS patients specifically as well as patient perspectives in general I find many of the same aspects as in my own text. In the meeting with the hospital I focus on the importance of information and the feeling of being a stranger as a patient. The confused relationship to my identity is expressed as a clear distinction between the unable body and the idle mind. The doctors and I had a different relationship to time, while they used time as an instrument to estimate my objective disease, I lived in the time with a “here-and-now” perspective. The text is coloured with different emotions. I am holding on to my conviction that I will recover. These positive thoughts get stronger when I experience progress. Visiting friends and family is also clearly important for my well being. I also describe fear, anger and disappointment, especially when getting worse and realizing my dependency on the nursing staff. In the medical journal I find some notes about my feelings, there is, however no recollection of the medical staff talking directly with me about it. Implications: The feeling of being a stranger to oneself and to the hospital explains much of the communication barrier between the patient and doctor. Knowledge about patient perspectives can help the doctors to communicate better with their patients. In specific I find that focusing on the patient as a person and including his questions and thoughts can reduce the feeling of being a stranger. Remembering the patients changed perspective of time can improve the timing of the given information. And at last, directly addressing the patient’s feelings and making the conditions easy for close visitors will help the patient to overcome emotionally.

Etter hvert som oppmerksomheten mot klimakrisen har økt de siste arene, har også interessen for bedre ytelse til grønne energikilder økt. Et eksempel på slike energikilder er monokrystallinske silisium solceller, for hvilke silisiumet produseres ofte ved Czochralski-prosess. Undersøkelse av blokker produsert ved denne metoden er nøkkelen til ytterligere forbedring av prosessen, noe som er viktig for å møte det økende materialbehovet. Oksygendefekter er en av hovedkildene til forverring av levetiden til monokrystallinske Czochralski silisium blokker for solcelleproduksjon. Innholdet og distribusjon av interstitiell oksygen i to silisium blokker produsert med forskjellige trekkhastigheter av Norsun AS, ble tidligere undersøkt i forbindelse med emnet TMT4500, Fordypningsprosjekt. Denne masteroppgaven hadde da som formål å studere effekten av oksygeninnhold og oksygenrelaterte defekter på elektriske egenskaper til prøvene ved bruk av Deep Level Transient Spectroscopy (DLTS) og Atomic Force Microscopy (AFM). Prøvene som ble karakterisert i denne oppgaven var varierende med hensyn til termisk historie, posisjon i blokken og trekkhastigheten som ble brukt ved produksjonen. Totalt seksten prøver ble preparert for undersøkelsene; åtte som ble gjort om til dioder og videre undersøkt for dypt liggende defekter ved bruk av DLTS-teknikken, og ytterligere åtte var ment til å bli studert for overflate-topografi og strømkart ved bruk av conductive Atomic Force Microscopy (c-AFM). Ytelsen av de preparerte diodene var studert ved IV- og CV-malinger som avdekket problemer med diode-preparering. Som resultat av de ovennevnte målingene ble en ny og mer stabil metode for diode-prepareing foreslått, som er det viktigste resultatet av denne masteroppgaven. Ingen direkte sammenheng ble funnet mellom interstitiell oksygen-innhold og de elektriske egenskapene karakterisert i oppgaven. Generelt ble det observert at de varmebehandlede prøvene viste en mer ustabil oppførsel under målingene, men en sikker konklusjon for denne mekanismen kunne ikke bli trukket på grunn av usikre resultater. Ingen klar sammenheng ble funnet mellom trekkhastigheten eller posisjon i blokken og de elektriske egenskapene, selv om det var forskjeller i resultater mellom prøvene. Videre undersøkelser av dette emnet bør utføres ved bruk av den nye foreslåtte metoden for diode-preparering. Nøkkelord: CZ-silisium, diode-preparering, termiske donorer, oksygenrelaterte defekter. As the attention to the climate crisis has been getting larger in the past years, the interest in better performing green energy sources has been increasing accordingly. An example of such a source are monocrystalline silicon solar cells, for which the silicon is often produced by the Czochralski process. Investigating ingots produced by this method is the key for further improvement of the production process, which is needed to fulfill the increasing material demand. Oxygen defects are one of the main sources for lifetime deterioration in monocrystalline Czochralski silicon for solar cell applications. The amount and distribution of interstitial oxygen in two silicon ingots, produced with different pulling speeds by NorSun AS, were previously studied for the purpose of TMT4500, Specialization Project. This master’s thesis work was therefore aiming to study the effect of oxygen content and oxygen related defects on the electrical properties of the samples, by the use of Deep Level Transient Spectroscopy (DLTS) and Atomic Force Microscopy (AFM). The samples were varying in terms of thermal history, different position in the ingot, and the pulling speed at which the ingot was produced. In total sixteen samples were prepared for the investigation; eight to be made into diodes, and further studied for the presence of deep level defects by the DLTS-technique, and another eight were meant to be studied for the surface topography and current maps by the use of conductive Atomic Force Microscopy (c-AFM). The performance of the prepared diodes was studied by IV- and CV-measurements which revealed problems with the diode preparation. As a result of these measurements a more stable method for diode preparation has been proposed, which is the most important result of this thesis. A direct correlation between the interstitial oxygen content and the electrical properties measured in this project, has not been found. It has been found that in general the heat treated samples show a more unstable behaviour during the measurements, however a certain conclusion to this mechanism could not been drawn due to unreliable results. No clear correlation between the pulling speed or the original position in the ingot and the electrical properties has been found, despite obtaining different results for the different samples. A further investigation of this topic should be performed using the proposed new method of diode preparation. Keywords: CZ-silicon, diode-preparation, thermal donors, oxygen related defects.

Quartz crucibles are, among other applications, used to produce monocrystalline silicon ingots for the solar cell industry. The crucibles must be of high purity as any gas bubbles or impurities close to the crucible-melt interface may end up in the silicon melt and influence the silicon ingot quality. This master thesis looks at three different fused quartz crucible types, including one reference. The crucibles have been compared with respect to bubble distribution and evolution which then have been related to their quartz sand quality and impurity content. The focus has been on the bubble distribution and evolution in the bubble free (BF) layer. Samples have been taken from the crucible wall and both new and industrially used samples were investigated. Heat treatments in a vertical gradient freeze (VGF) furnace and Czochralski puller have been performed to investigate the secondary bubble growth, the OH content and the micro-bubble formation as a function of heat treatment and crucible type. The results indicate that the sand quality, but also manually controlled processing steps such as crucible fusion, has influence on the bubble growth and BF layer bubble content. A reduction in OH content seems to correlate with increasing bubble growth. The reference (STD) crucible has the largest variation in bubble content and the largest average bubble growth for the samples studied in this work. Crucible B, which has the finest particle size distribution (PSD) and chemistry, seems to be the best choice for silicon ingot production as it experiences, on average, the lowest BF layer bubble growth and has the lowest density of bubbles below detection limit.

The main object was to investigate the effect of donors, thermal donors and defects on the lifetime on n-type Czochralsky (Cz) silicon. Cz is a technique for making monocrystals by dipping a monocrystalline seed into the melt, and pulling the ingot up as the melt solidifies. Samples were prepared by sawing, grinding and polishing. Copper decoration and preferential etching was done to reveal the defects. Resistivity measurements were performed to investigate the donor distribution. The lifetime and oxygen concentration was measured.The lifetime may be influenced by donors and traps. Traps may be metallic or non-metallic. Dopants and metal contaminants are usually Scheil distributed, which typically involves a relatively stable distribution in most part of the ingot, and a rapid increase in concentration close to the bottom. Metal contaminants may be introduced from the feedstock, and dopants (either n or p dopants) are added to the melt.Oxygen is dissolved from the crucible. The oxygen concentration typically decreases with increasing length, and is controlled by the rotation speed. This was confirmed by the interstitial oxygen measurements. The oxygen concentration showed no change after heat treatment, but the presence of oxygen in itself may contribute to produce lifetime reducing agents, such as precipitates and thermal donors. Thermal donors were found in the first 18cm of the ingot. Both the resistivity and lifetime measurements was used to calculate estimated lifetimes and donor concentrations, respectively. This estimated values were compared with the measured ones, revealing that the lifetime in the ingot was SRH dominated. Thermal donors were found to have less influence on the lifetime than the trapping. Oxygen precipitations may explain the low lifetime found in the center of the ingot up to about 30cm from the crown. Such precipitations are often gathered in defect bands in the sample. CDI of a Cu decorated sample revealed a pattern of different defect densities, which also showed up at the surface of the sample after preferential etching. An H- or L- band was believed to be situated here, which both consist of small oxygen precipitates. Defects arize as a funktion of the pulling parameters, and a low growth rate was connected to the low lifetime here. Indications of the presence of non-metallic traps were found throughout the ingot. However, oxygen precipitates could not explain the non-metallic traps that was found on the outside of the ingot, and the cause of these is therefore unknown. It is however likely that these traps may be connected to the pullrate/temperature gradient-ratio. Most likely metallic traps were also present. It is uncertain whether the non-metallic or metallic traps were the most important to the lifetime of this ingot, as the relative distribution of the two cannot be decided with certainty from the results in this thesis.Contrasts in CDI and steep curves using PCD measurements vs length plots were believed to be due to the lifetime degrading agent that changes the fastest. Metallic traps and the phosphorous dopant are known to be Scheil distributed, hence they appear transparent for the lifetime measurements in areas where the distribution is stable. Thermal donors and non-metallic traps are thus more likely to create contrast in the top parts of an ingot. However, it is not necessarily the phenomenon that causes the contrast that is the major lifetime degradation contributor.

By applying a texture to the front surface of solar cells, less light may be reflected and the incoming light may be given a longer path length inside the solar cell causing a better light absorbance for the solar cell. The textured layer is today made by etching with an acidic etch with a large part hydrogen fluoride. In the future a more environmental approach for creating textured solar cells may be favoured. There are many ways of creating textured surfaces, one of them are by imprinting the surface by a template, and remove the template when the process is completed.In this project the diatom species Coscinodiscus walesii and an undefined Coscinodiscus species were cleaned and processed for investigation. The work done can be divided into four tasks. The first was characterisation and investigation of the pore structure. The second were manufacturing and characterisation of gold for use as templates. The third were deposition and characterisation of thin films of silicon and silicon nitride on diatom frustules. The last part were to make structures are very similar to solar cells with diatom frustules incorporated into them.The diatom frustules were characterised by SEM and the pore structure were cut through with FIB to characterise the structure. There were structural differences between the two species. The Coscinodiscus walesii was grown in a cultivation chamber, and lacked the circular inner pore structure which the undefined Coscinodiscus species had. This was the only real difference between the two species.On the cultivated species were deposited a gold film, which a small rectangle were lifted off by a tungsten needle in FIB. The small rectangle were characterised with the SEM-column in a dual beam FIB. Pore structures down to 40 nm were replicated by the gold film lifted off the frustule. By depositing a relatively thick film of gold on a glass substrate covered with diatom frustules and dissolving the glass substrate and diatom frustules with hydrogen fluoride, a template were made with a replication of the diatom frustule pore structure.Silicon and silicon nitride were deposited on diatom frustules and characterised with FIB to investigate how those materials followed the frustule topography. A good conformity of films made of those materials was confirmed, and 4 different samples which were similar to solar cells were manufactured and characterised by light microscopy, SEM and FIB. Two samples were made to be similar to crystalline silicon solar cells. One had dried frustules on top of a silicon surface and the entire surface of the sample were coated with silicon nitride, a blue colour were observed in the entire surface and the silicon nitride had also been deposited on the diatom frustules. For the other sample similar to crystalline silicon solar cells another layer were deposited between the frustule and the silicon substrate. The double silicon layer made the sample surface yellow, the diatom frustules did not get darker due to a layer above and a layer beneath them. Only in some places where the frustules had loosened from the sample the sample were blue as the silicon nitride layer were the same as a single layer of silicon nitride. For the last two samples, thin film solar cell structures based on amorphous silicon deposited with PECVD were made. A sample there a aluminum coating were deposited on a glass substrate and diatom frustules were dried on top of the aluminum coating, afterwards a 5 µm thick film of amorphous silicon were deposited. SEM images showed that the film were distributed even across a diatom frustule and a light microscopy investigation showed that light were spread when it hit the diatom frustules, hence creating a longer mean path through the solar cell.