Solar? Natural gas? Combine!

atmosphear added an entry about make a smaller ecological footprint:

I wrote this reply originally elsewhere and I thought it might be useful for others as well. Correcting my mistakes is always welcome.

Tankless models are very popular in Portugal. I’d say that if you can aid heating of the water with “solar hot water collectors”http://en.wikipedia.org/wiki/Solar_hot_water it would be great.

Otherwise tankless heater might be a good choise: heating the water only when needed. Of course this means that you will be having an open flame on top of a gas source, which many people find unpleasant as a thought, but I think that a continuous small flame might actually make it more safe (since it burns the leaking gasses continuously as well).

Tankless – at least to my engineering part of brain – cannot be completely hermetic (i.e. closed from the environment) so there is always also the problem of carbon monoxide and dioxide. Well-planned ventilation is essential.

I think that a hybrid would be ideal: heating the water (I’ll draw a quick sketch now) with solar power, storing it into a container and using gas heater to warm up the missing heat.

The idea (attached somewhere around) is rather simple:

  1. Cold water is brought to solar heater
  2. Solar heater pushes warm water to water storage
  3. Newly heated water pushes semi-warm water back to the solar heater (natural cycle, doesn’t need a pump)
  4. When hot water is used, warm water will be drawn from the water storage (or from semi-warm line) and heated up with a gas burner

I lack the practical experience completely, so consult a professional before following too closely… :)

The same idea can be attained also by using electricity to heat up the water in the water storage: thermostat will reduce the electricity used for heating according to incoming water temperature (from the solar heater).

This idea is then again very popular in Greece. I don’t know – since I didn’t have a chance to visit any local households on Crete – if they used natural gas or electricity to heat the water in the night time, but solar heaters were very popular.

Since using electricity to heat up water gives energy efficiency of approximately 50% at best (e.g. combi power plants, which are still quite rare) and usually around 10-20% (which is still a good ratio) from fossile fuel burning, it is rather self-evident that natural gas burnt locally is a very good way to heat up the water.

If you have some kind of an infrastructure for natural gas, I’d say to go for it. If possible, use solar energy (not solar electicity, because that would waste huge potential of solar power).

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