Solar hot water running costs and greenhouse emissions

Grey shower head, running water, white tile background
Image by tookapic from Pixabay

I have always enjoyed using copious amounts of hot water at home, focussing my guilty conscience on my excessive water wastage, but not sparing a thought for the energy consumption. Given that Australia and sun are synonymous for most people, you might assume that this is because I have been blissfully using solar hot water to wash away my energy worries but unfortunately you would be wrong. Everywhere I lived in Australia I used instant gas hot water, while in the USA I used an electric storage tank. This disclosure led to shock and confusion in my partner, whose family home in not so sunny Central Europe has apparently been happily relying on solar hot water for years.

Wooden house with solar panel. Mountain with snow and pines in background.
Image by pasja1000 from Pixabay

Being almost totally ignorant about how these systems operate, I always associated solar hot water services with images of an adrenaline spiking adventure into potentially icy waters, rather than a green energy utopia. From the piecemeal uptake of this technology across Australia, I would guess that I am not alone in this. The most recent surveys from 2012 and 2014 suggest that only 10–13% of households have solar hot water¹ ², very low for such a sun saturated country, and quite surprising given we were at the forefront of developing this technology in the 1950s³. In comparison, solar hot water has been a success story in many other countries, particularly those that have mandated its installation in new buildings, such as Israel, Greece and Barbados⁴ ⁵ ⁶.

Solar hot water technology, though it has had low uptake in many parts of the world really is very effective at what it does.

solar hot water system
Image by rasamoydas from Pixabay

The system works a bit differently to your standard rooftop photovoltaic solar panels and has a number of advantages. A solar hot water system uses plates or pipes to directly transfer the suns heat to water, this water is then stored in a highly insulated container until it is used. In contrast, photovoltaic cells need to convert solar energy to electricity and then use this electricity to heat the water, which is much less efficient. The storage tank is a key feature of solar hot water systems. It is insulated enough to guarantee hot water overnight and even across the next day if it is overcast. And, no fear! Almost all solar hot water systems are installed with a gas or electric back up, so you are never short of hot water, even if the sun is not shining.

Solar hot water sounds great, so why is it not popular in Australia?

Sustainability Victoria⁷ gives a nice chart to compare energy costs and greenhouse gas emissions for different water heating systems based on calculations of the average 1- 4-person household in Victoria, Australia. I made some simple summary graphs of the stats for a 4-person family.

Greenhouse house gas emissions of different hot water services. Adding a solar boost lowers the emissions of full gas or electric services.

This chart shows the minimum and maximum greenhouse gas emission produced for running different hot water systems. Emissions vary based on whether the system supplies instant hot water, uses a storage tank, or for electricity, if they it is used during peak or off-peak times. This chart shows that a fully electric installation generates by far the most greenhouse gas emissions. Solar boosted with electric is much lower, so, if you already have an electric system, adding solar hot water panels will make a big difference.

The rub is that for a system with an electric boost it still produces more emissions than gas alone and how much really depends on the details. If the electric boost is used in off-peak times, that is overnight when supplies are not needed for businesses and industry, there is no solar input into the grid, meaning the electricity is mainly produced from greenhouse gas rich coal rather than renewable sources, spiking the emissions as we see here.

Annual cost of running different hot water services. Solar boosted with gas is the cheapest to run due to currently low gas prices in Australia.

In Australia, a solar system with a gas back up is by far the cheapest. Again, a solar system boosted with electric is definitely cheaper than a fully electric system run off of mains electricity but it is not necessarily cheaper than a full gas installation. And here we can see why this technology has not been broadly adopted — why invest a lot of money up front into a solar hot water service when it may not even save you any money relative to a gas installation?

So why not change to gas?

For many people the upfront investment in solar hot water is challenging and the benefits are just not apparent. Gas seems likes a cheap, easy and even environmentally sound choice compared to electricity… at least in the short-term. However, natural gas is non-renewable and produces greenhouse gases, a lot, even if at a lower level than coal, so this is not a long-term solution. As electricity is produced more and more by renewable sources the emissions associated with electric boosted solar systems will drop, especially if other technologies like solar battery storage are successful for ensuring overnight electricity supplies. The current cheap gas prices are also not guaranteed into the future and these fluctuate quite a bit year to year as it is, though how this plays out will largely depend on government policies that either promote renewables or the mining industry.

It is difficult to provide clear incentives for adoption of renewables in countries where there are large fossil fuel supplies, as costs and energy security are not major barriers to continued usage of traditional hot water systems⁵. So far, Australia’s policies towards renewable technology such as solar hot water systems have focussed on the environmental benefits, relying on people’s commitment to going green and offering short-term rebates that differ across the country to prompt uptake. This facilitates those who are well-off and so-inclined to take up these initiatives but those who cannot buy-in pay increased energy prices to cover the gap left by solar adopters, further worsening their financial situation, leading to what is known as ‘energy poverty’⁸.

This a problem for wide-scale change but, lacking supportive government policies, for those who are in a position to invest, solar hot water will reduce the costs and emissions associated with an existing gas or electric service. Often the choice of hot water service is a rushed decision at the moment it breaks⁹. There are many pros and cons of every system and practical considerations that are unique to each home, so if this is something that interests you it is worth looking into the details now, so you can make an informed decision that best helps you and the environment.


¹ Government of Australia (2019) Water heating In Energy Rating, <viewed 1 December 2020>

² Australian Bureau of Statistics (2014), 4602.0.55.001 — Environmental Issues: Energy Use and Conservation, <viewed 1 December 2020>

³ CSIRO (2011) Solar hot water systems In CSIROpedia, <viewed 1 December 2020>

⁴ Martinopoulos G, Tsalikis G (2018) Diffusion and adoption of solar energy conversion systems — the case of Greece, Energy, 144: 800–807 Doi: 10.1016/

⁵ Li W, Tzameret RH, Onyina PA (2012) Comparing solar water heater popularization policies in China, Israel and Australia: the roles of governments in adopting green innovations, Sustainable Development, Doi: 10.1002/sd.1547

⁶ Climate and Development Knowledge Network (2012) Seizing the sunshine: Barbados’ thriving solar water heater industry, <viewed 1 December 2020>

⁷ Sustainability Victoria (2019) Hot water running costs, <viewed 1 December 2020>

⁸ Pereira DA, Marques AC, Fuinhas JA (2019) Are renewables affecting income distribution and increasing the risk of household poverty?, Energy, 170: 791–803, Doi: 10.1016/

⁹ Urmee T, Walker E, Bahri PA, Baverstock G, Rezvani S, Saman W (2018) Solar water heaters uptake in Australia — issues and barriers, Sustainable Energy Technology and Assessments, 30: 11–23, Doi: 10.1016/j.seta.2018.08.006

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Patching the Planet

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Questioning the everyday to find inspiration for a sustainable tomorrow. Exploring the challenges of this wondrous, complex world and the changes we can make.

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