Sun + water = heat

By - , Build 132

The case can be made that solar water heating systems should be a household choice because, used effectively, they are easy on the environment and the pocket.

READERS MAY BE AWARE of the recent report by the Parliamentary Commissioner for the Environment (PCE) Evaluating solar water heating: sun, renewable energy and climate change that expressed concerns about solar water heating (SWH) and how it integrates into the electrical network.

The report suggests that SWH doesn’t perform when it is needed most on a cloudy winter’s day and that load control technologies such as ripple control and heating hot water at night may be more effective.

That is because the report focuses on SWH supporting the electricity network but does not consider the benefits of SWH for homeowners.

A good choice at design stage

BRANZ has researched SWH extensively and thinks that it still has potential in usefully contributing to the overall goal of improved water heating in New Zealand.

When a house is built, much of the future performance is locked in by design and construction choices. A water heating system is a critical component, requiring on average 29% of the household’s energy use.

Traditionally, New Zealand households have utilised fairly basic technology for water heating. An article in Build 99 highlighted the fact that New Zealand has one of highest ownership rates of electric resistive hot water storage cylinders in the world.

This wasn’t much of a problem, but as electricity prices have risen and electricity has been generated from more carbon intensive sources, simple electric resistive hot water cylinders have become a less desirable environmental option.

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Easing the environmental load

The key to reducing the environmental impact of water heating is to ensure that, as much as possible, the energy put into heating water uses low-carbon sources.

SWH has the ability to displace large amounts – over 70% – of potentially carbon-intensive electricity by directly harvesting energy from the sun. This displacement occurs at the point of use, the household, so users save money and can be confident that low-carbon energy sources are contributing to their water heating needs.

On their own, load control technologies such as ripple control or heating the hot water only at night do not reduce the overall energy use requirements for water heating.

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Seeing the bigger picture

To understand the benefits to the electricity network, it is important to consider the different types of electricity generation at different times of day, the costs of the generation and their carbon consequences.

As an intermittent resource, solar cannot be expected to provide output at all times.

With SWH, it is important to consider how the balance of energy is provided. If this balance of energy requires electricity to be used during peak demand times, this may have a big impact.

SWH systems can store heat, and systems can be configured so they do not use electricity during peak times. Therefore, they can be well integrated into the electricity network, providing a range of benefits and savings to homeowners.

Research confirms that well performing solar water heating systems can reduce overall water heating energy use by over 70%. SWH is a proven, practical and cost-effective technology that, if used more, would be of wider benefit to New Zealand.

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