Solar power and storage with heat battery

Abstract

This thesis provides an overview of the project Solstice. It tells its origin, the present stage and its potential future. The consequence of this is a very multifaceted thesis which tells the story of a newly developed energy technology that aims to defossilize the energy market and mitigate the effects of climate change. Solstice is a product that concentrates sunlight and via a newly developed energy transport technology heats a sand battery which is used to store energy as heat. The heat battery can thereafter be drained of heat to produce electricity via a Stirling engine or as heat directly. The thesis contains details about the design process, both experiments which have established working principles and drawings of specific parts. It also contains interviews with potential customers of the final product, namely energy companies, which describes its potential place in the future energy market. The design of the solar ray concentrating device in the form of parabolic mirrors is disclosed as well as the parameters of the battery, how its size relate to its energy storing capacity and required insulation layers. The energy transferring technology is through the experiments found to have an efficiency of 71%, although at low power levels. In the interviews several promising aspects for Solstices future prosperity was found, such as an increase in price for wood chips, which is the traditional fuel source for heat and that several companies have machinery at the end of its lifetime and therefore are actively looking for alternatives. Finally the thesis contains drawings of how a battery could be built for a demonstration prototype.

Abstract (Swedish)

Detta examensarbete ger en ̈oversiktsbild av projektet Solstice. Det berättar om projektets ursprung, det nuvarande stadiet projektet befinner sig i samt dess framtida potential. Konsekvensen av detta ̈ar en mycket mångfacetterad rapport som ̊aterspeglar hur nyutvecklad energiteknik avser att avfossilisera energimarknaden och minska effekterna av klimatförändringarna. Solstice ̈ar en produkt som koncentrerar solljus och via en nyutvecklad energitransporteringsteknik varmer upp ett sandbatteri som lagrar energin i form av värme. Värmebatteriet kan därefter tömmas vid behov för att producera el genom en Stirlingmotor eller direkt som värme. Detta examensarbete innehåller detaljer om konstruktionsprocessen, både om experiment som etablerar principer om hur teknologin fungerar och ritningar av specifika komponenter. Den innehåller dessutom intervjuer med potentiella kunder av den slutgiltiga produkten, nämligen energibolag, som beskriver dess potentiella plats på en framtida energimarknad. Konstruktionsprocessen av den solstrålskoncentrerande delen, som best ̊ar av paraboliska speglar, visas i rapporten, liksom batteriets parametrar, hur dess energilagringsförmåga beror på dess storlek och hur tjock isolering som krävs. Energiöverföringstekniken, som visas i experiment ett och två, har en effektivitet på 71 %, men vid låga energinivåer. I intervjuerna påvisas flera aspekter som ̈ar positiva för Solstices framtida potential, såsom att priset på träflis, som ̈ar den traditionella energikällan för värme, har ̈ökat och att flera energibolags maskiner ̈ar gamla och därför letar energibolagen efter nya alternativ. Slutligen visas ritningar av hur ett batteri för en demonstrationsprototyp skulle kunna se ut.

Popular Abstract

Today there is no dispute about that the energy sector is not only responsible for the environmental crisis the earth experiences at this moment but also for its resolution.

This means that whole industry needs to reinvent itself which might seem like a huge undertaking, but the energy industry is actually one of the industries with highest innovation level right now. Energy consumption is linked to worldwide prosperity and since the world actually is on the path towards increased general well-being energy consumption is also increasing. This furthermore enhances the dire need of renewable and sustainable energy production. There are today five major sources of renewable energy: hydro, geothermal, biomass, wind and solar. Hydro power requires specific conditions, such as high elevation and are usually found in mountain ranges. So does also geothermal, but its requirement is usually vicinity to tectonic plate boundaries where high volcanic activity also is found. Biomass, wind and solar also requires certain conditions but these conditions are not as limited to specific places on the earth. Regarding biomass however, there are other limitations in the form of restriction of total extraction from forests and heavy competition for it. This means that the upcoming increase of production of renewable energy will have to come from wind and solar. These are technologies that complement each other somewhat well; winds are most prevalent in coastal areas during the winter and solar is most prevalent inland during the summer. The method of harvesting wind and solar have matured for several decades and the most prevalent forms of wind turbines and photovoltaic cells are easily recognizable. However, there still are innovative progress in other forms of energy harvesting technologies, especially in the field of solar power, and the next wave of innovation might be in concentrated solar power.

This is a technology that directly utilize the heat radiated from the sun and concentrates it to reach very high temperatures. Concentration means that there is a relation between the total absorption area and the secondary area which essentially means that a smaller area receives all the sun light from the total absorption area. The reason for this to be a potential revolution can be attributed to energy value, or the concept that high temperatures are more usable than low temperatures. Intuitionally we know that it is easier to cool something hot than to heat something cool. Behind this concept there is a great field of physics which quantify the value of high temperatures and on which the idea about concentrated solar power is based. To clarify what usefulness of energy means it relates to the form the energy takes and different forms can be used for different things. Solar rays for example can be used to tan skin or drive photosynthesis it cannot however drive a car. Today we have both electric and engine driven cars which relies on different forms of energy to drive them, namely electric and chemical. Once any kind of energy is harvested it can be transformed to another in some technical way, but this transformation is always related to an efficiency. Energy can never be destroyed (or created) but in the transformation from one form to another there is never a 100\% conversion to the desired type. There always is a loss in transformation to a third, undesired, type. How much of this extra type of energy is created in the conversion process decides the conversion's efficiency. Regarding conventional solar power the original type of energy is solar rays which is converted to electrical energy through the photovoltaic effect. The efficiency of a solar panel is usually around 20\%. The remaining 80\% is converted to heat and since solar panels have large surfaces the heat is well dispersed and dissipated to the air. If also these 80\% could be assigned value a great benefit would be achieved since it would also contain a significant amount of energy.

Are there other processes than the photovoltaic effect with higher efficiency? Not if the goal is to create electricity, but it is not the only useful form of energy. Previously chemical energy was mentioned which is what photosynthesis is converting solar rays to, but this is a process that technology have not been able to mimic on a large scale. Also, the value of high temperatures has been mentioned and a way to achieve it, which is concentration. Could this be the path towards more efficient solar energy conversion? It depends on the goal. If the goal is to produce heat it would most certainly improve the efficiency but if the goal was to produce electricity an improved efficiency is not viable. Electricity however is not the only useful form of energy; heat is also a greatly needed resource and a heat-based electricity producing system could in addition to produce electricity make use of the otherwise lost heat. So, depending on how efficiency is measured it could be 20\% (if only electricity is considered a benefit) or 100\% (if both electricity and heat is considered a benefit).

Another difference between solar panels and heat based concentrated solar power is the possibility of energy storage. Electricity is a product that is consumed the very moment it is produced and therefore it is very important that production pattern matches consumption pattern. The renewable energy sources, wind and solar, are intermittent which means that they are not always available for harvesting. The consequence of this is that production and consumption patterns do not always match and the disparity between them is a big problem. Historically this have not been a problem since non-renewable energy sources generally are on demand produced. To fully defossilize the energy sector needs to utilize energy storage. This means that there must be an overproduction of energy when it is available and a storage of the overproduction to be used when it is not.

How does this relate to heat based concentrated solar power? Unlike solar panels which produce electricity the very moment sun light hits them a heat based system can use the extra conversion step as a storage stage. The heated medium can be held at a steady stage and wait for the demand of electricity to rise before the electricity production begins. This is not a simple solution, but it is a solution with the added feature of storage. This thesis dives into the detailed technology of what a heat based concentrated solar power system could look like and its potential uses.

• author: Hammarbäck, Hampus
• supervisor: Lei Wang
• organization: Department of Energy Sciences
• course: MVKM01 20232
• year: 2023
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Energy technology, Innovation, Heat battery
• report number: LUTMDN/TMHP-23/5557-SE
• ISSN: 0282-1990
• language: English
• id: 9141644
• date added to LUP: 2023-11-27 09:59:40
• date last changed: 2023-11-27 09:59:40