One long deep pipe brings up cold water in an area of the ocean with higher surface temperatures in the tropics. OTEC ocean thermal energy conversion uses the small difference between the deep ocean cold water temperature and the hotter surface water temperatures to power low pressure turbine generators to make high quality base load electrical power 24/7/365 with uptime that rivals Hydro & large Fission reactors.
In many coastal locals worldwide, electrical power fetches a price premium. While solar PV & wind power can produce energy, the intermittent nature of the output means expensive energy storage needed to stabilize the output to match user loads & demands, or load following & 24/7/365 uptime, means that intermittent renewables need to be paired with base load capacity.
Thermal plants burning coal & oil have many problems if coal & oil resources are not locally available & must be imported from abroad. By taking advantage of the day to night temperature swings, air source heat pump systems for building structure HVAC are the most efficiency way to heat or cool an interior space for people or vehicles or computer equipment like servers or cloud computing infrastructure and data centers.
OTEC endlessly renewable with more than 10 trillion watts of power production possible without affecting the thermal structure of the oceans. Wave power another option, but more expensive & has lower total recoverable energy capacity if fully developed worldwide.
OTEC energy much more abundant like hydro without causing environmental damage, other than the capital cost & development needed to setup the large capacity OTEC power generating systems at the gigawatt commercial power generating scale and connect such installed OTEC capacity to the power grid to energize loads, like AC & Fridge & Heat pump appliance compressors, lamps, bulbs, pumps, ovens, stoves, microwaves, vacuums, computers, & other electrical equipment to charge battery electric vehicles of all kinds.
OTEC plants operate continuously as base load power supply for electrical power generation.
The small 25 deg temperature difference makes efficient power conversion capital intensive given the need to use low boiling point sealed refrigerant gases like ammonia & isobutane or propane or R134A, to efficiently extract heat energy from the hot surface waters to higher temperatures to increase the temperature delta difference between the cold & hot sides of the power turbine energy generator. This means the aluminum, copper nickel alloy corrosion resistant heat exchangers that are also easy to clean from ocean spray biofouling are expensive to make as one off custom parts with enough heat sink exchange capacity in the real world, meaning they have to be overbuilt larger for extra capacity at higher cost, just like you have to oversize a PV array for a all solar PV home, since the PV panels lose output initially & also gradually over time.
OTEC still an emerging market technology with great potential to improve temperature differential electrical conversion efficiency. Currently operating OTEC plants achieve 1 to 3 percent while the technology can be optimized to 6 to 7 percent to approach Carnot efficiency.
For a deep dive TLDR into OTEC check out the wikipedia entry
Ocean thermal energy conversion - Wikipedia
Related Idea based on Heat Pump Clothing Dryers
A use a 700w dehumidifier in our tiny home's ~80 square foot bathroom with stacked washer dryer unit, to warm & dry the bathroom while taking a shower. Hang drying high-speed spin-dried damp clothing to remove the residual water works well at warmer temperatures like 70-80 degrees F, and less than 50% humidity, so the vapor pressure of the water in the damp clothes can escape.
Waste heat from the dehumidifier warms the bathroom while the cold condensation coils created by the compressor driven refrigeration circuit causes water vapor to condense into collected in the discharge tank liquid water that we use to flush the toilet, since it's not sanitary, since I have never setup the machine to make sanitary water infused with minerals for human consumption.
The entire room can become a clothing dryer because waste heat from the dehumidifier warms the room while removing water vapor from the air, effectively turning the entire room into a slow warm dryer with water vapor removal. This way we do not have to use the exhaust fan to remove water vapor from showering, which would take heat energy out of our home & draw in cold outside air, making our 200 square foot tiny home colder, also requiring us to heat more wasting power. Same with the clothing dryer, since it heats air & then discharges the hot moist air from drying clothes to the exterior with no energy recovery. This means cold air drawn into to replace the hot air exhausted. If the dryer sent the hot moist air through a heat recovery ventilator, energy recovery of warming air could be captured while the moisture could still be discharged.
In this case, we see that the entire setup can act like a air source heat pump system. Though a properly designed mini-split for HVAC will have a much higher COP or coefficient of performance, meaning much higher energy efficiency for heating & cooling, or lower utility bills & lower operating costs monthly as the most efficient way to heat or cool an indoor space. I am only saying this because there are many ways to capture heat from hot water from the shower drain, from hot air from the clothing dryer exhaust, from the furnace exhaust heat, from waste heat from the fridge, microwave, there are many ways to exploit the energy difference between the inside air of the home & the cold outside air during the winter months.
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