Many futuristic articles have already been written about Fusion power and how, in 30 years, this could solve all our energy needs and can free us from our nuclear waste while doing so.

Unfortunately, 30 years later, these articles still write about fusion power and that it will be a reality in 30 years from now. Fusion energy however, is already a thing, and you can get it for free. The supplier is called "the Sun". They don't have a phone number but at a certain point in time they will probably show up in front of your door, they claim to be having around 50% global coverage for some time now.

The sun provides over 10.000 times the amount of energy we consume on a daily basis. Pretty useless fact you may think and i agree, but it's a good intro none the less. More interesting probably is the question "how much of it lands on my property and how can i put it to work.

I live in the Netherlands and on average about 3,6 GJ per m² of sunlight drops per year, if this doesn't say anything to you no worries to me it also did not but the weather gods made the math easy for us here, this is exactly 1.000 kWh. In the Netherlands, where i live, the average electricity consumption of a single person household is approximately 1825 kWh per year so in theory just 2 m² could be enough, actually a lot less if the panel is positioned in the right angle. The shade that the panel drops will show you the actual solar surface that your panel receives.

How much energy is that?

Assumptions

Below are the prices i currently pay for my energy, i am leaving the fixed infrastructure rates out for the sake of simplicity and unless i get disconnected, which i won't they will be there on both sides of the equation anyway.

Energy prices

Heat capacitor capacity

My hottub will act as a heat capacitor to store, collect and transfer heat. Long term storage will be done underground in a closed loop closed loop geothermal system I will be pulsing a series of wells close by the hottub, these are to be used as my geothermal storage system.

As my wells are relatively small, probably somewhere around 20 meters deep, it probably makes sense to heat up the water as much possible or is tolerated before transferring it into these wells.

• Tap water in the Netherlands is somewhere around 10 °C, during summer slightly warmer.
• Soil temperature is also around 10 °C (which is logically the same as the tap water)
• The hottub is well insulated so the temperature only drops a few tenths of a degree overnight, this allows for gradual heating of the water over the cause of multiple days.
• Without a heat pump, the energy capacity of the system is relative to the input and output i have and want. Input is 10 °C we already know. The highest temperature i can send into the wells is 37 °C so whatever i get out of it is unknown but of course quite a bit less.

Geothermal storage

The thermal conductivity coefficient of the Dutch soil is somewhere between 1.5 W/mk (clay) and 2.5 W/mk (sand). The heat capacity is normally somewhere between 2.0 and 2.5 MJ/m³/k and the initial temperature will be approximately 10 °C .

Soil heat capacity

The theoretical capacity is per m3 at a 25 °C heat difference, from 10 °C to 35 °C.

Energy need

The amount of energy my house used in 2021.

Disclaimer: I am not 100% sure if this will work, i am building it anyway and will only stop until convinced it won't as i think it will.

Last summer i made a hot tub in my backyard, see my other article for more details. The moment i started filling up the bath for the first time was also the moment i started calculating the amount of energy that is required to heat the thing, of course i was aware of the fact that these things require a lot of energy but during the build i just decided that this was a concern for later.

Energy required for initial heating

Tap water comes out of my tap at approximately 18° C, the contents of my tub is around 1700 litres and the most relaxing temperature of a hot tub is somewhere around 38°C so there is a difference of 20°C that needed to come from some heat source. No need to know the math here (yet), for every problem there is some person that already made an online calculator which told me i needed a lot of joules but as this rings as much as a bell with me as "astronomical units" i will be using Kwh here as i think that makes more sense to most people. To heat up my bath to the desired temperature i need 39.53 Kwh. To get an idea, my Samsung Ecobubble washing machine uses 0.8 Kwh per 60 degrees cotton cycle. So that bath is an energy explosion.

DIY solar heater

I made a DIY solar energy heater for 20 euro's or so and was extremely surprised that a bath full of fresh water went from 18°C to 30°C in a single day. That is approximately 24 Kwh. In the Netherlands the average energy consumption per person is 17 Kwh so not bad, not bad at all. Especially when you consider that this solar heater is far from optimized.

Thermal battery

When my bath was heating so much during the day but was losing the same amount of heat again during the night i decided to put a very heavy and well isolated lit on it.The lit is constructed in such a way that an edge falls completely over the bath. On the inside a 15 cm thick layer of house insulation foam is added which is pressed against the edge making an almost air sealed cover. Most heat would normally escape trough the top so almost all the heat is preserved.

During late spring, summer and early fall I want to use my very well insulated hot tub as a solar powered heat capacitor that is used to use to preheat 1700 liters of water (and perhaps melt 300 liters of wax) to a specific temperature (35°) and as soon as it hits this temperature or whenever night falls, i want to transfer this heat into an underground heat storage. The heat will come from two sources, a bunch of DIY solar heaters and by adding tylene hoses underneath the roof tile's of my house.

Approximately 80% of our domestic energy consumption goes to heating and cooling things, of course this does not only include heating and cooling our houses but also the washing machine, a cup of coffee etc.

The majority of electricity consumed at home goes into heating and cooling things. Most of this heat is directly disposed into the sewer system after use, my washing machine dumps 40 liters of hot water into the sewer on each run, my dishwasher does the same thing with 13 liters of hot water etc. All these devices heat their own water with a heating element which is on it's own not very efficient. The price of 1kWh in natural gas is €0,09 compared to €0,24 in electricity so natural gas is a factor of 2,5. Most of these devices however do not only consume hot water but also use cold water at specific stages in the cycle so the equation is not 1:1.

Dishwasher

My dishwasher consumes 1,05 kWh of energy and 13 liters of water per cycle at 70 degrees Celsius. It takes 0,83kWh to heat up 13 liters of water from 15°C to 70°C so 79% of the electricity consumed by the dishwasher goes into heating water.

I run my dishwasher approximately 5 times a week which accounts for 4,15 kWh per week or € 1,07 in electricity, with natural gas this would be € 0,37. The heat battery should lower this down further.

Washing machine

My dishwasher consumes 1,05 kWh of energy and 13 liters of water per cycle at 70 degrees Celsius. It takes 0,83kWh to heat up 13 liters of water from 15°C to 70°C so 79% of the electricity consumed by the dishwasher goes into heating water.

I run my dishwasher approximately 5 times a week which accounts for 4,15 kWh per week or € 1,07 in electricity, with natural gas this would be € 0,37. The heat battery should lower this down further.

Dryer

A dryer does not consume water and therefor cannot be hooked