Almost Free Solar Hot Water System.


Almost Free Solar Hot Water System.

This page is about a solar hot water system I installed in 2018. It  provides us with free washing up water and free pre heated water for the kettle. Water is sent out from below the sink, through the wall and then through about 15 metres of black plastic tubes. The water stays in the tube and heats up during the morning. By 11am the temperature is around 35C (95 F) and later on the temperature can get up to over 45C. (115 F)

Black tubing strong enough to withstand house water pressure is very cheap and a system like this could be installed very easily by anyone with some basic plumbing skills.  If you take the concept a little further you could extend the black tube and provide a lot more water for showers etc. My system is quite untidy but if someone lives in a more urban place you could make the tubes look more tidy.

I am not a very good TV presenter but I made made this video to explain the system.
There are subtitles in English, Spanish and French. 

We are about to have a climate conference in Glasgow where the politicians will probably come up with inadequate solutions to avoid climate disaster.  As an individual it is very frustrating but at least we can try to reduce our carbon emissions on a small scale in our personal lives and save some money.

More info:
Several years ago I started using black PVC tubes to heat water up with  100 metres of 16mm PVC tubing which adds water to our swimming pool every day.  Black plastic tubing is very cheap and as long as you have some space to put the tube in the sun it is very easy. You see lots of complicated you tubes with coiled up tubing but if you don’t mind it being a little untidy you can let the tube just run over any surface.

We tend to have our main meal in the middle of the day which is normal in Spain so for months on end I use this hot water to do the washing up. It is also useful for preheating water for making tea. During the hours of strong sunlight I use a 900 watt electric kettle for boiling water and using pre heated water cuts down the boiling time considerably.

Some facts about black tubing:
In one metre of 32mm (1 inch) tubes there is  804cc of water.

In perfect conditions a 1 metre length of tube perpendicular to the sun would receive around 40 watts of energy.

In Spain 100 metres of PVC tube that can withstand 10 bars of pressure costs around 100 euros.

This system has been running for over 3 years. At first my tube was not long enough and it did not completely fill the sink, so I extended it. As the tube gets hot it needs to be good quality 10 atmosphere tube. 

To work out the length of the tube, you have to work out how much water the tube can hold. The best way to do this is to use a this online calculator. The formula is: pipe volume = π * (radius * radius) * length, where radius = inner diameter/2. Pi is 3.14 Asterisk means multiply.

If I were going to do this for a pool shower or for showers I would buy a 100 metre roll.  In my pool heater set up I have 100 metres of 16mm tubing in the sun. Even with flowing water it heats the water up to around 45C. By the way: Tubes don’t hold the heat for very long. By 4 or 5pm the tubes will have cooled down.

In the winter I empty the tubes during January and February because the tubes might freeze during the night.

Most efficient fridge in solar powered house.

How to use a fridge in solar house without using extra batteries

Warning:  This post contains ideas and instructions about electrical devices and wiring. I am not an electrician. You should be extremely careful when wiring electrical devices and if you are not sure, please use a qualified electrician. 


Introduction: We have been living off grid for many years and I think we have worked out the best way to have fridges and freezers. Before having electric fridges, we used to have a Butsir gas fridge. Gas fridges work OK for most of the time but they can suddenly develop soot problems, they turn off for no reason or they can become hard to light plus they tend to use a bottle of gas each month which is not ecological. At the moment, a bottle of gas is 15 euros so that is 180 euros per year. In this post, I am going to explain how to have an electric fridge in the cheapest way possible without having to buy extra batteries.

We have 2 fridges and a freezer.  We don’t have a massive solar array but we have enough solar power to run a 600 watt swimming pool pump for 3 hours a day between 11 am and 2 pm.  The maximum power generation we have is only about 1300 watts.  The swimming pool is only in use from June to mid September so that means that without the pool pump we have loads of power during the rest of the year.

If you don’t have a lot of solar panels, by far the best system is to use a chest freezer as a fridge, put it on maximum full power and control it using an external thermostat. The freezer tries to bring the temperature down to minus 20C but as soon as it reaches 1C, it is switched off by our external thermostat and when it reaches 2C, the thermostat switches it on again.

Additional paragraph – digression – skip if you want.
By the way, the difference between the 1C and 2C stated above is called the slewing range.  The default is normally 1C or 2C. The smaller the slewing range, the more times the fridge is switched on and off.  Some people the other day suggested that a fridge could be damaged by switching it on and off. This is just utter nonsense!!!

Why use a chest freezer? The big problem with using a normal, upright fridge is that as soon as you open the door, all the cold air falls out onto the floor. This is especially bad if you have a lot of guests. Rather than quickly opening and closing the fridge door, they will be casually telling you their life story while absent-mindedly looking for the beer and then afterwards not even shut the door properly. (The same sort of person who will  use their 2000 watt electric curling tongs and shut the house electricity down just when there is a penalty shoot out in an international football match) .

Chest freezers are spacious  and they can be filled with lots of liquid such as milk, beer, water, etc. The reason it is a good idea to have lots of liquid in the fridge-freezer is that they can be used to store the cold in thermal mass.  Thermal mass acts as a thermal battery. All the watts of power that you use to cool the liquids down when the sun is shining will be stored and will prevent the fridge or freezer heating up during the night. So you don’t have to spend lots of money on expensive batteries – you just store the energy literally in beer. This has the added advantage that you can have a cool beer any time you like. What is not to like? 

I normally start my fridge at 10am and switch it off at around 5pm.  At 5pm, the temperature is just above freezing and by10am the next day, the fridge has got up to maybe 10C which is an OK fridge temperature.  Most fridges and freezers use about 90 watts.

This is not just some untested bright idea I have thought up: I have been doing this for years and it works perfectly.

Instructions:  This is a very cheap and easy system to set up so even if you are a money-strapped absolute nincompoop you should have no difficulty in doing this.  Having said that, if you have never done any electrical wiring before, make sure that everything is switched off when you actually touch any wires and study the instructions that come with the thermostat.

The first thing to do is put your chest freezer in a suitable place. It could be in your kitchen. In the winter, it will work even more efficiently if you keep it covered outside in the cold.

Near the fridge, you need to have somewhere to put the digital thermostat. I have mine of a shelf above the freezer and I keep it in place with a G clamp I bought from a thrift shop for a couple of euros. You could use gaffer tape.

The only slightly difficult thing is wiring the thermostat. You need to go to a shop and buy some wire and an electrical plug to power the thermostat and also an electrical socket so that you can plug the fridge into it.

This is a plug socket. You can open it up and connect the wires to it.  The wires don’t need to be especially thick because a fridge or a freezer only uses a small number of watts.

This image below is the wiring diagram from the thermostat. The NTC are the wires that go to the sensor. The sensor should be put inside the freezer. This is how the above diagram translates into the actual connection.  The black cable goes to the plug socket (two images above) and the white cables go to the wall plug.
Everything should be covered in insulation tape to increase the safety so that nobody could touch any live wires.  We do not use an earth so there must be no exposed metal which could be touched and make sure that you have a good differential switch in your fusebox.  If you don’t know what you are doing, get an electrician. Don’t take any risks!!!!!!!

This is what a chest freezer converted to a fridge looks like.  The only problem with this idea is that people tend to prefer using a fridge with a forward opening door. The things that you use often are kept in the basket at the top and you would have to have good organisation of where things are kept to make it convenient.   In our case we also have a normal fridge but if you want a fridge without also getting bigger batteries then this works very well.

This is the type of automatic thermostat I use. They are very cheap and normally continue to work for at least a couple of years. I also use these as normal thermometers because I like to see the red numbers in my kitchen.

This is a typical chest freezer. As you can see the price is about the same as 1 year of gas for a gas fridge. I bought mine in 1996 and it is still going strong.

This is how I switch the entire system on and off at 10am and 5pm. It is a Teckin smart plug which works with WiFi. They use an app so I can switch everything on and off as long as I have my smartphone with me. They also have an inbuilt electric meter which tells you how much power they have used.  They would be worth buying just for the electric meter. If it goes cloudy, I can switch everything off from anywhere.

Of course, you also have to have a solar electric system with inverter and solar panels to supply the power which is outside the remit of this post.

Note: In this post, I have talked about converting a freezer into a fridge. You can use a similar idea with a freezer as a freezer.  Just put the freezer on maximum. It should get to -20C during the day and come up to  -5C by the following morning. If you have meat in it, you should be especially careful that is never goes higher than 0.  You could use a min max thermometer just to be sure. Using this technique your batteries never have to power the freezer.

One last tip:
If you grow your own walnuts or almonds, put them in the freezer for a week to kill any moth eggs or larva and then put them in a well-sealed container. If you have ever had your almonds contaminated by moths, you will know what I am talking about.

Using Solar hot water for a Washing Machine

Using solar hot water with a washing machine

If you are living off grid or you have solar powered hot water then you may want to take advantage of the hot water that you have in the tank.

Washing machines and dishwashers can heat up their own water but the heating element tends to be between 2000 and 3000 watts.  You would have to have a very big off grid solar system with a large  inverter to use the actual dishwasher or washing machine heating element.

The simple answer is to plumb these appliances into your hot water system and always wash your clothes on the cold setting so that it never attempts to heat the water up.

If you are in an off grid situation it is probably  best to wash your dishes by hand.  Most dishwashers have a heating element and unless you have a big lithium ion system the solar inverter will shut the system down after a short time of having a draw of 2000 watts unless the sun is actually shining at the time. If you are connected to the grid then connecting your dishwasher directly to the hot system would be a good idea. Note: The time of writing this is 2021. In a few years it will be much more common to have large capacity batteries which will be OK with a dishwasher.

On the other hand clothes washing machines are perfect for solar power. As long as you have an inverter of over 700 watts they will work fine.   Most detergents nowadays are designed for cold washes. However from time to time it is nice to be able to do a hot wash. The most important thing with clothes washing is that the water that enters the washing machine should not be too hot for the type of clothes that you are washing. For this reason you need to install a mixer tap or mixer valve.

The photo at the top of this page is the mixer tap on our washing machine. Mixer taps have 2 inlets. Hot and cold. They have 1 outlet. The water in the outlet should be limited to the maximum temperature set on the control dial. I personally would not trust the mixer tap to have an accurate temperature setting and I would use an external thermometer to make sure the temperature is correct.

Note that using this method you will end up rinsing your clothes with warm water. If this is a problem you could switch the hot inlet off after a certain amount of time.

Warning: I still don’t know how it happened but my mixer tap has  some sort of back flow issue and it resulted in cold water being mixed with my general  hot water system. I solved this by putting a tap to stop the hot water inflow but beware if this happens to you, it took me a month to work it out.

Remember that even if you run hot water into the inlet of the washing machine you should choose a cold wash setting on the machine. (you don’t want the internal water heater to start) 

One last idea: Why not use the used water from the washing machine for irrigation.  Pipe the water onto some trees or into a container to be used for watering.

This is a link to a mixing tap on Amazon.
If you go to a plumbing shop in Spain ask for “Válvula Mezclador termostático or “Válvula de mezcla caliente y fría de 3 vía”.


Solar Drier


The easiest and most efficient solar food drier possible made from recycled objects.

Solar Drier

View of the Solar Drier

I spent many hours looking on internet for plans on how to make a solar drier. There are hundreds of different designs on pinterest and on homesteading sites. I almost started to make a couple of the most promising ones but fortunately I waited.  I eventually found one that I considered to have the best concept at  Elder Grove Homestead (see link below)  I then realized that I already had all the materials needed to make a solar drier without buying  anything and without building or constructing anything. My version uses a clear  window with most of the heating happening on the bottom corrugated iron  plate which generates a slow hot convectional current of air. 


A piece of corrugated iron painted black.
Some metal mesh with fairly small holes wired down to panels of an old chicken run.
Some circular sand sieves. (builders use them for sieving sand)
Some old windows.
Some ground which has a slight slope.

Solar Drier with windows

The above photo shows the solar drier in use:

How it works.

The sun shines through the window and heats up the black corrugated iron base. The heat and air is trapped in by the glass. As the solar drier is on a slope, the hot air moves slowly upwards  and then escapes from the top of the window. New air is constantly drawn in from the bottom. The food does not burn because as the temperature gets hotter the air moves faster. If it rains it is no problem the food is protected and it does not need to be brought in. The temperature is too hot for insects and even ants do not stay long.


We have two or 3 electric food  driers but after a few days using this one I packed them away because this works so much better. In the hot sun of August most things were bone dry in one day. I even used this system to dry a load of comfrey leaves so that I don’t have to put up with the smell of rotting comfrey. I can just add the dried comfrey powder directly to the plants.


The main advantage is that no construction is required. If the drier is not in use you can just pick up the pieces and stack them somewhere. No electricity. No moving parts. A lot of the solar driers you see on internet have one window leading to a whole stack of food trays. Even in hot weather this must be slow. With our design the food is dried very quickly, at first you can even see the moisture condensing  on the window. 


If you have to buy the windows it could be quite expensive however old windows are quite easy to get hold of. Other websites say that the mesh should be made out of food grade stainless steel. This is probably correct but I think I will risk it. If you paint the corrugated iron you should probably leave it out for a few days to drive off any volatile chemicals. (I did not actually paint mine) . The builder’s sieves can be bought from any builder’s merchant alternatively you can make some wooden frames and staple mesh onto them.


As you can see we have  two options of placing the food. On the sand sieves or on the mesh grids. Either work perfectly but the sieves are easier to load with produce and bring to and from the kitchen. The windows are not connected with hinges they can be lifted up with one hand while the food is slipped in with the other. If they get dirty they can be picked up and blasted with water.

Dried Food

Dried Food

The photo above are some of the dried foods on the kitchen shelf ready to be added to many dishes during the winter months. The Tsunami by the way is a failed attempt to make marmite from wine yeast. In the end I dried it out and decided that it will add some umami taste to some foods (hence the name)  In the year of COVID just the two of us managed to dry a massive amount of food during the summer.

For loads of technical details and useful information go to Elder Grove Homestead You don’t need all the hinges and fancy construction techniques that they use you can just do it like mine on the floor with a few old windows.

When does grid parity happen in the south of Spain?

A view of grid parity from someone who has been living off grid for 10 years.
The date of writing this post is 8th July 2017.

What is Grid Parity?

Grid parity  occurs when an alternative energy source can generate power at the same  price as buying power from the electricity grid. Or to put it another way: After installing an alternative energy system how long will it take the before the cost of installation will be the same as if the house had been connected to an electric company. This is called pay back time.

The Quick Answer

In case you just want a quick answer in my opinion it would take 8 and a half years.
Below I will explain how I calculated this figure.


Our annual electricty usage is 2005 kWh per year.
This is in our  house which is not connected to the grid.
The average occupation is about 4 people.
We do not use electrity for heating, cooking or AC.
The biggest electricty use we have is the swimming pool pump.
We live a fairy normal life and we have a freezer and  fridges.
We very occasionally have to use a generator when there is a prolonged cloudy spell but the cost is minimal. Maybe 20 euros per year.

We calculate the costs of the electric company by looking at the electricty bill we have for another house. The name of the company is Iberdrola.

We use the figure of 3000 watts as the maximum amount of power that can be used at any one time. (la potencia) The figure we use for the price of electrity is 0.16 euros per  kWh. There are other expenses such as electricty tax (impuesto), equipment hire (alquiler) and VAT (IVA).

The price per year of electricity from the GRID.

The cost if we bought the electricty from the grid would be 598 euros per year.
224 for additional costs and 374 euros for the electricity.

How much our solar electrical installation would cost.
To replicate our system you would need
1250 watts of panels – 840 euros 
50 amp combined inverter charge controller 750 euros
12 x 2v Lead Acid batteries 800 amp hours. 3500 euros.

Total cost 5090 euros

Total installation cost divided by GRID cost is 8.5

So time to parity is 8.5 years

There are lots of other variables such as battery life and efficiency of the batterys which we have not considered here but 8.5 years  is a good basic figure and it feels about right..  

If I lived in a city would I cut off from the grid?
No probably not. If you have solar power  you always have to be a bit conscious of the time of day and if there is sun or not. The battery technology is the most important factor.  Batterys like the TESLA powerwall sound very promising and could provide about the bare minimum which would satisfy most people. I imagine that within 10-15 years in the future we will see a green energy revolution with excellent power storage and the  demise of the internal combustion engine.

The best thing about this situation for me is that we have been here for 10 years so our electricty is now effectively free. I just hope that our existing batterys can hold out long enough so that there are very good possibilities are available when the time comes to replace them.  

Aparently  450g  of carbon dioxide is put into the atmosphere per Kwh for electricty bought from the grid.

According to these figures we have not caused 9 metric tons of C02 to be released into the atmosphere.