Solar Hot Water Systems: Will They Work When There is a Blackout?

In Australian homes, hot water is something often taken for granted—until it runs out, that is! Having a reliable hot water supply usually comes with a hefty price-tag – in fact, conventional hot water heaters typically account for a whopping 30% of household energy use and are significant carbon emitters. Investing in a solar hot water system, however, offers significant savings on your energy bill while reducing your carbon footprint.

But what happens when there’s a blackout? Will a solar hot water system provide enough hot water for your family to shower, prepare food, do the dishes or run a washing machine cycle when the sun has gone down or if the power goes out? Will you need a battery to store energy for it to work at night-time or when there are blackouts? This article will answer these commonly asked questions and more.

An evacuated tube solar hot water system

What is a solar hot water system? How do they work?

Firstly, let’s cover some solar hot water basics. A solar hot water system (or heater) uses natural thermal energy from the sun to heat water for your home. There are three types of solar hot water systems; flat plate collector, evacuated tube collector and heat pump systems.

For flat plate and evacuated tube collectors, roof-mounted collector panels use a dark surface to trap the sun’s heat and transfer it to the fluid circulating inside. Hot water is then stored in an insulated tank, ready for use. Heat pump systems, on the other hand, covert solar heat from the air and use it to increase your water temperature. While heat pumps still use electricity to facilitate this process, they use around 75% less electricity compared to a conventional electric water heater. Heat pumps are best-suited to regions of Australia that have high-temperatures year-around.

This article will focus on flat plate collectors and evacuated tube collectors.

If you would like a more in-depth explanation on how solar hot water systems work, check out our dedicated article on the topic.

Selecting a solar hot water system

When it comes to selecting a solar hot water system, there are quite a few options to choose from depending on your requirements, preferences, roof structure and budget.

The first decision you will need to make is whether you want a passive or active system. Passive systems require no pumps and rely on gravity to move hot water through the system. Passive systems are cheaper but typically bulkier and less efficient in colder climates. Active solar hot water systems do not rely on gravity but instead contain an electric pump that pushes the water through the system. Active systems may also use environmentally-friendly anti-freeze to transfer heat to the water, something a passive system does not do, and they need electricity to operate, whereas passive systems do not. Active systems are more expensive than passive systems but offer greater flexibility and control.

Next you will need to choose between installing either a stand-alone solar hot water system or one with a ‘booster’ that uses either natural gas or electricity from the grid as backup to ensure a reliable supply of hot water. Boosted systems are much more cost-efficient to run than a standard gas or electric system.

How much money do you save with solar hot water?

On average, if you install a solar hot water system, your water heating bills should drop 50%–80%.

What are the environmental benefits of a solar hot water system?

Electrical water heating is the largest single source of greenhouse gases from the average Australian home, producing almost a quarter of household emissions.

Installing a solar water heating system will reduce the average household’s carbon emissions by 2.4 to 3 tonnes.

Will a solar hot water system provide enough hot water when the sun has gone down?

If you’ve installed a stand-alone solar hot water system, the answer is ‘most likely’. Your solar hot water system works hard during the day to heat water that’ll still be hot enough for use at night and all through to the next morning. A typical Australian family of 3-4 people uses between 248 – 500 litres of hot water per day depending on how efficient the home is (i.e. if they’ve invested in water efficient shower heads, taps and appliances). As a rule of thumb, each person in a household will use around 75 litres of hot water a day.

A two-panel solar collector should provide around 300 litres of warm water each day, which is sufficient for most average families’ needs even on cloudy days or during winter months where sunlight hours are shorter. The amount will vary depending upon regional climates and other environmental factors such as shading from nearby buildings etc., but generally this would be more than adequate.

If you use more water than your solar panels are designed to heat—then you will eventually run out of hot water. This can be avoided with the addition of an electric or gas booster, which ensures a continuous, reliable supply of hot water at desired temperature – just keep in mind that regular booster use will increase you energy bills and carbon emissions.

Do solar hot water systems work during a blackout?

Whether or not your solar hot water system works during a power outage depends on whether it relies on mains electricity.

Passive solar hot water systems aren’t connected to the grid and will continue to provide heated water during blackouts. Since active systems rely on electrically powered machinery, they won’t work during a power outage.

Do I need a solar storage battery for my hot water system to work during blackouts?

If you want to be 100% sure that your hot water system will work when it’s needed, a solar storage battery can offer you that assurance.

Solar storage batteries are connected to your home’s main electrical panel and can be used for both active solar hot water systems as well as passive ones with a booster.

During a blackout, the battery will power up all of your household appliances that use mains electricity including your active solar hot water system and boosters. The only downside is that these types of batteries aren’t cheap and you will need to weigh if they are worth the investment in your particular circumstances.

Are solar hot water systems worth the investment?

Yes. If you install a solar hot water system, you can expect to pay back your initial investment within five years and see savings of up to 80% on your energy bills for 25+ years afterwards.

The average Australian family spends $2000 on water heating every year. If you install a solar hot water system in your home, the savings will add up quickly and once you’ve paid off your initial investment of around $3,000-$7,000 depending on the system—they’ll start going straight into your pocket!

If you want to ensure a reliable supply of hot water when the sun isn’t shining, we recommend adding an electric or gas booster which are still considerably more efficient than conventional water heating systems.

Start now on your environmentally friendly and cost-saving solar hot water system! Contact our team of friendly experts for free, no-obligation advice or try our solar hot water quoting system! Don’t forget to check out any applicable rebates and our specials.