The thermal recovery efficiency of High Temperature Aquifer Thermal Energy Storage (HT-ATES) systems can be limited due to the effect of buoyancy flow of the injected hot water. This thesis has researched the application of a Multiple Partially Penetrating Wells (MPPWs) as a well design method to counteract the effect of buoyancy flow and improve the performance of HT-ATES systems (>60°C). A MPPW is a well with more than one screen that allows injection and extraction of water at different depths in the aquifer.This method to counteract the effect of buoyancy flow was tested through numerical modelling with SEAWATv4. The modelled HT-ATES systems were running for four recovery cycles each including injection-storage-extraction-rest phases. The thermal recovery efficiency was determined over these cycles for 7 different scenarios and four different cases: a) A regular HT-ATES system with a fully penetrating screen, b) a regular HT-ATES system where buoyancy flow is neglected, c) an HT-ATES system with a MPPW with two screens, d) an HT-ATES system with four screens. The latter case was tested for three different control approaches based on data from four different locations in the aquifer.For the reference scenario where 90°C water was injected, a regular HT-ATES system had a thermal recovery efficiency of 0.61. With the application of MPPWs for both two or four screens this was 0.81 in the fourth recovery cycle, which approaches the case without buoyancy which had a thermal recovery efficiency of 0.88. The application of two or four screens did not show significant difference in thermal recovery efficiency after the first recovery cycle.A sensitivity analysis showed that the absolute increase in thermal recovery efficiency of an HT-ATES system with a MPPW compared to a regular HT-ATES is higher for larger buoyancy flow (i.e, high injection temperature and high (vertical) hydraulic conductivity), smaller injection volume and larger aquifer thickness. An applicability analysis showed that application of MPPWs is beneficial if the buoyancy flow (which is defined as the vertical hydraulic conductivity times the density ratio of the ambient groundwater and injected water) is greater than 0.1 meters per day.

Due to climate change and growing cities, water scarcity is becoming one of the futures biggest problems. On top of that, the population and prosperity of cities around the equator are growing fast. Meaning that the need for electricity, cooling and drinking water will grow fast in the following decades. ROTEC’s vision is that these growing problems require a sustainable approach for the future.
A solution to these challenges can be found in the oceans temperature difference. The top layer of the ocean is heated by the sun, while the deeper layer remains cold. This causes around the equator a temperature difference of more than 20 degrees over the ocean’s depth. This offers a lot of opportunities. It can be used as a vast source for electricity production (OTEC), large scale drinking water production (ROTEC) and for cooling (SWAC). Indonesia is one of the best locations worldwide, due to the easy access of cold deep sea water and the abundant presence of hot surface water. North-Sulawesi has a unique access to these sources. Due to the steep slope of the seabed the cold deep seawater can easily be reached.
Team ROTEC conducted a research in Manado for two months and came up with several solutions that can contribute to a more sustainable and beneficial future of North Sulawesi. There was mainly focussed on performing a need assessment for the capital Manado and the touristic Bunaken Island. This pointed out that Manado can reduce their electricity usage during peak loads by implementing a new way of cooling of malls and hotels along the boulevard. Bunaken needs electricity and drinking water in a way that is more easy to maintain and operate. Data analysis and measurements showed that both Bunaken and Manado have a high theoretical potential, since cold deep seawater is close to shore and found at relative shallow depths.
For Manado a new seawater district cooling system is proposed. This system uses cold deep seawater to cool the large buildings along the boulevard, instead of conventional chiller-cooling-tower units. The solution reduces their electricity usage for cooling by 96% and more electricity is left for the grid of Manado. The yearly costs for the operation of the cooling is 92% cheaper and the investment for the installation is earned back within 6 years after construction. Peak loads in the grid are decreased and emissions reduced; equivalent to 19,000 tons CO2 per year.
For Bunaken an integrated drinking water and electricity solution is found. By just using the temperature difference in the ocean, to produce clean and constant electricity and drinking water from seawater. The proposed installation provides the base load (80kW) for Bunaken for the same price as current solar PV and diesel generators together. Clean drinking water for the villagers is 12 times cheaper than Aqua Danone and 1.4 times cheaper than the not drinkable water from fresh water wells on the island. Such a kind of installation can produce 24/7, is stable and that without the need of fuels.