I have four things that need to be heated on my house:

  1. Pool (28.000 liters solar thermal heated)

  2. Jacuzzi (I think that is like 400-600 liters is gas heated)

  3. Showers (actually they are all electric)

  4. Sauna (not sure here but I think it's gas heated)

So, thinking about electric and water requirements, what would be better? I already saw studies saying that electric showers use less water and energy than gas showers but i don't know about pools and others.

Would just changing everything to electric and solar panels be more sustainable and economize on my bills?

  • Could you clairify the question? Are you proposing solar PV for everything, with battery backup? I very much doubt that would be beneficial for pool heating. Others I would expect could depend on use patterns.
    – jamesqf
    Feb 10, 2015 at 21:10

4 Answers 4


Depends on where you live but heating with electrical heating is likely the worst thing to do.

Odds are some portion of grid's power comes from thermal sources and typical efficiency from heat to electrical power are around 50%.

Unless the source is near 100% thermal energy free, heating with electricity is a double whammy: It takes twice as much thermal heat from gas or coal to produce heat by electricity down the line. Even if only 5% of the power came from thermal source, that thermal energy would be best used by heating things directly. Electricity is best for mechanical work (machines) and any heating should be done by other sources to avoid this waste.

From a sustainability point of view, the first thing to consider is energy conservation and consumption reduction. It is well worth investigating if all 4 of these hot wonders are equally used and valued to see where the overall energy footprint can be reduced.

Finally, regarding the shower water consuption, the direct heaters (no tanks) do consume less water simply because the heating coil inside the unit restricts the flow of water. The same water savings can be done with any kind of system by simply restricting the water flow. Both gas and electrical direct heat wall unit are very common her in Southeast Asia.

  • I live in Brazil , and you are forgetting that the energy input will be solar so i don't really care about wasting a few more energy as long i can keep and heat my things faster and using less water and less bills , and i use them quite alot
    – Freedo
    Feb 10, 2015 at 15:21
  • Hi. I understood from the question that only the pool was solar heated. Is it one of those roof top heaters with insulated tanks I saw quite often when I was there? The comment about electric heating still holds for Brazil where thermal power is less than 20%.
    – Hurelu
    Feb 10, 2015 at 16:21
  • I have read articles which suggest that heating with PV solar via a heat pump is now fairly close to solar water heat.
    – jamesqf
    Feb 11, 2015 at 6:01
  • @jamesqf it can be the case that PV+heat pump is roughly as efficient (in converting solar energy to usable heat), but that's only part of the story, and it does depend on a couple of crucial factors. It might be worth writing a new question on exactly this.
    – 410 gone
    Feb 11, 2015 at 7:05
  • @EnergyNumbers Indeed, heat pump can be an interesting option but as you implied, it quickly get complicated. We would need the seasonal ambient temperatures and the desired heated water temperature to get an overall efficiency indication.
    – Hurelu
    Feb 11, 2015 at 7:19

For heating water, you're far better off looking at solar water heaters, which take thermal energy from the sun to heat water. The power conversion formulae for converting sunshine into electricity and then electricity into heat is about 80% less efficient than just taking heat from the sun and putting it directly into the water. This is in no small part because solar panels are only around 15% efficient, then you lose at least another 10% of that in converting it to heat. I don't know the efficiency for solar hot water heaters, but it has got to be way better than that.

Also, solar water heaters are tremendously cheaper than photovoltaics. At their most basic, they're mostly just a black pipe exposed to sunlight, without modern wizardry for extracting electrons. We have more efficient ways to make it happen of course, but the basic principle is pretty simple.


Jamesq is correct, particularly if the hotwater use is for space heating, which usually requires hotter water (130-160 f) This requires sealed unit heat pipe type collectors which aren't much cheaper than PV. In addition PV gets more efficient with cold (.38% per kelvin) while solar hot water gets less efficient. Soon you get to the point where collecting electrons and running a heat pump is a better bet.

In Brazil, the need for heating is small, the need for domestic hot water then becomes the dominant use. This is almost trivial to do with a large coil of black plastic pipe laid flat on a roof. In use, you actually need to use PEX pipe. YOu can melt standard black poly.

I would suggest 1000 feet of black PEX pipe, split into 100 or 83 foot chunks, and a manifold at each end. This reduces the resistance of trying to push water 1000 feet. (10 pipes will each be 1/10 as long, which gives 1/10 the drop. In addition the flow velocity will be 1/10 as much. Net effect: 1/100 the pressure needed to get the same flow. Ball park figures. Even 5 pipes of 200 would likely be enough.

Now a small solar powered pump circulates water between the pool, jacuzzi. I'd suggest having some form of spill from the jacuzzi to the pool, and pump from the pool to the jacuzzi. This gives you the freshest hottest water in the jacuzzi.

You also should have a large display thermometer for the current temperature. I've heard of people getting their entire pool too hot to swim in.


In Brazil there are solar-powered thermal systems which work extremely well.

solar thermal http://www.entrepreneurstoolkit.org/images/3/36/Aquecimento-solar.jpg

I have no general numbers at hand, but just to give an idea, during a sunny day in São Paulo, four thermal panels will easily heat 200 litres of water to up to 70 degrees Celsius in a couple of hours (morning until after lunch).

The system circulates "naturally" as cold, heavy water pushes the hot, lighter water through the panels into the tank. Heating water with electricity will be both environmentally unfriendly and expensive. But Brazil has a lot of sun, so investing in enough thermal panels should be enough for the pool.

Since you want hot showers usually when it is cold, you can install an electric shower head that heats the water "on-the-fly". These shower heads are extremely cheap (about 50 R$ or 20 US$). But if there is few people using the hot water, you can even last for 3 days without sun with a solar thermal system only. (Careful, cheap electric shower heads only accept cold water!)

The only drawback with solar systems is that one has to be extremely careful not to freeze them. But then in most parts of Brazil the temperature never ever drops below 0 degrees Celsius, so I'd recommend you to go solar thermal all the way!

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