Energy Systems

Permaculture, a Step by Step Change, Part III – Solar Water Heating: Change and Save

Welcome back to my Step by Step permaculture process.

We have been studying the uses of passive solar space heating around the house; now it’s time for solar water heating.

Solar water heating can be as simple as filling a transparent PET bottle with water and leaving it in sunlight, nevertheless, efficiency and high output both come as a result of precise engineering and attention to detail.

Before making a decision to change from your electric or gas system to solar, you must learn a few things to dismiss the myths and learn the reality about solar water heating.

First, you have to know that even though the heating energy of the sun is always present during the day, on cloudy days the intensity can drop dramatically, and if you have several days without direct sunlight, your water may not be heated more than 10°C over the tap water temperature.

This problem can be easily addressed with different systems; everything depends on how hardcore you want to be regarding energy consumption. In my case, since I installed my solar water heater, I decided I wouldn’t spend a penny on water heating again, but this has raised a few complaints from my wife and kids, even though they love the idea of having hot water to bath without spending a penny on heating it.

So, the myth is that you will never run out of hot water, unless, perhaps, if you have a fairly big system or if you have a backup system to support it. If your system is adjusted to your family (50 gallons per day per person) and you bath freely without regards to time and consumption, you will find yourself with cold water on rainy days if you don’t have a backup system.

Second, you have to be careful with your water usage. If someone takes a bath at 5pm, this may lead to a temperature drop in the system. Depending on the size of it, this may mean that water will be a bit colder or a lot colder. Your family must be aware that solar systems are different from those energy-consuming tank water heaters. Obviously, if you spend a lot on energy, you will have limitless hot water, so you can waste and take tub baths all day, but, with a permacultural mindset, you may want to take tub baths only on days with full sunlight throughout the whole day.

And third, either way you take it, solar water heating systems are true energy savers and you will quickly see a return on your investment. This is one of the solar technologies that are more widespread and efficient, so you can have one confidently.

They myth says that the systems are too expensive and that they never repay themselves. This may be true if you buy a system too big for your family or if you want to ensure you have never-ending hot water. Of course you have to change the way you do things in order for sustainability to kick in. The first thing you have to have in mind when you want to change to appropriate technologies is that waste is out of the question.

So, let’s get busy.

Change and save

In the following paragraphs I will try to describe my story of water heating, from the energy guzzler days to the zero carbon days, with all pros and cons concerning them.

Young and cocky

When I started to build my home, I was young and cocky (25 years old). I was making good money and I felt like I was on the top of the mountain. Saving a few cents and caring much about energy usage were not priorities in my mind, so I built my home with lots of bathrooms and hot water everywhere.

It was fantastic to open every faucet and get scorching hot water from it. Our tub baths were epic and we stayed as long as we wanted in the shower. But then, things changed.

2001 and the economic crackdown

After 9/11 we felt a hit. Our business was not growing any more and we acquired a lot of debt based on our projections of growth, but these projections didn’t include al-Qaeda hitting the WTC.

So, money began to be a little bit scarce and we had to start trimming our budget and expenses in order to be able to pay whatever we had to pay. Obviously, the 800kw/h a month bill was too much. Almost 50% of that was our pleasure of having never-ending hot water at our disposal. We had to do something about it.

Our propane gas water heater

So, we bought a propane gas water heater and left the tank unused. Of course, still a little bit young and cocky, I bought the biggest and the most technologically advanced. It had electronic automatic ignition and produced 20 liters p/minute of very hot water, enough for almost three showers at the same time with high pressure.

Together with this, I closed all hot water faucets in the house, including those of the washing machine and the kitchen sink (my wife didn’t like this), but with these changes, we saved almost 50% of our energy bill. I was thrilled.

Hitting the water heater at 5am, on the roof, in the middle of the rain

I appreciate that I can look back in time and laugh about this…

For some reason I don’t know, the gas water heater and its electronic spark mechanism worked only when they wanted. I called the technician who dismantled it, cleaned it and charged me a lot, but after a few days I was up on the roof again trying to reason with the water heater while my wife was chilling under cold as hell water with her head full of shampoo bubbles.

So, after dismantling it myself (I learnt from the technician’s visit) and checking everything was OK, I got frustrated, and hit the water heater. Bingo! It started working again. So, we learnt that the water heater was a sort of S&M junkie, and almost every morning, we had to climb into the roof to give the gas water heater some spanking until it began to work well. Take a look at the water heater, all beaten up….

Fed up of S&M

After a few years, we lost our enthusiasm for hitting the water heater, and with the cold outside in addition to the rain we had to endure some days without hot water, giving us the feeling that we had to change systems again. So, I began to check for solar water heaters.

Building my own solar water heater

I downloaded a lot of information on thermodynamics and learnt how to build a water heater myself, which I did, but for some reason I left it on the roof without connecting it for more than five years.

So, finally, I decided to buy a glass tube water heater.

My glass tube water heater

So I bought it. It was quite a steep price, but I did some math and determined that it should pay for itself quickly. I installed it myself; I wanted to learn how to do it in case it was an S&M junkie too.

The first three days we were devastated. We had full sun, everything (I thought) was in place, and yet the water was as cold as if it had been pulled out of the fridge…. Well, maybe a degree hotter.

I was puzzled. It had no moving parts, everything was coupled well, there were no leaks, and we had full sunlight. My wife was far from happy and I feared for my well-being.

So, I finally dismantled it and put it together again. I thought that maybe the vacuum tubes should be upside down and I turned those 180°. Eureka! That was it. The next day we had full hot water without spending a cent or spanking anything. At least now I know that tubes in a solar water heater should hold water, not air….

Not enough

As happy as we were with our solar water heater, we still felt no remorse in bathing for as long as we wanted. But then, the last in the line to use the hot water started to complain. Maybe 200 liters for seven people is not enough, but that is what I bought.

My options for upgrading

I started to analyze my options and evaluated a myriad of them: Back to spanking, back to spending, add another water heater, put a resistance inside the one we already had, build a biomass water heater…, etc.

One day I looked at the neglected solar water heater I had previously built myself, and thought that I could add it to my new system. Surely I could boost it and solve my problem, so I hooked it up and hoped for the best.

Better, but not excellent

After I connected the new/old panels, I thought it would double the amount of hot water, so I said to my wife: "Tomorrow we will have very hot water." When tomorrow came, she bathed and said: "The water was the same!"

I went back up and analyzed the system and tried to figure out what had happened, and got into the fine tuning it needed to work better.

Fine tuning

If you lose heat, you will have colder water. Any opening from where hot air escapes is a heat leak, so I bought a couple of bottles of silicon rubber and sealed every small opening from where hot air may have been leaking out.

Also, I covered every tube with a 6mm rubber sheet and hoped for the best.

There was some increase in our hot water, but not as much as I would like to have.


I came to the conclusion that my home-made solar panel was (sadly) not as efficient as the water heater I bought with 24 hollow vacuum tubes.

You have to be honest with yourself: research and engineering pays. Mine is rustic and inefficient compared with the bought one.

Nevertheless, I feel happy to have my handiwork helping, if only just a little. Sure, I may have to study it more and add something else in order to get as much hot water as we would like….


I may have a few options I am willing to evaluate, but adding electricity is not amongst them. After giving it a lot of thought and research, I found something I will try soon: A biomass water heater.

I found out that if you put a certain amount of biomass in a barrel, drum or container and run a tube with your water through the biomass, after a couple of weeks the rotting starts and the busy bacteria heat up their surroundings to around 60°C. So, this seems like a suitable system to add to mine.

Once I have it designed in my mind, I will produce blueprints and execute them. After that, I will write an article about it to let you know my experience…. Wish me luck!

In conclusion, we are happy with our solar water heater and love it more than the S&M junkie or the power junkie.


  1. Hey Juan,

    Solar hot water is quite tricky to get working well, but it is worth the time. We had a few problems here which took a while to sort out, but now all is well.

    I have an 8kW wet back in my wood heater, which also heats the house and has an oven and hot plate to cook on. Nice stuff if you have access to a wood lot.

    The heat from the wet back moves to a collector tank via circulating hot water currents (convection) and returns on a slightly lower pipe to be heated and sent back up to the collector tank again. No pumps are involved as you wouldn’t want it to fail…

    Might be worth thinking about, if you have access to a wood lot?


  2. I do have a few trees. If you can send me pictures or drawings, with your authorization, we can publish it. Thanks!!

  3. Hey Juan,

    Shoot me a private message on the permaculture global website with your email address and I’ll email you directly with some photos for you to publish. Lookup “Fernglade farm” under projects. Wood is a great way to heat a house + water. Like your work.

    Regards. Chris

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