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Solar PV vs Solar Thermal Hot Water
06 January

Solar PV vs Solar Thermal Hot Water

Each year South Africans use more than 300 Gigawatts of electricity to heat water, accounting for more than 30% of residential energy usage. With an annual solar irradiation of 220W/m2, South Africa has one of the highest annual amounts of sunshine in the world. Solar Water heating technology is therefore a key factor in reducing our energy requirements in the built environment and harnessing our abundant natural and renewable resources.

Solar thermal systems (ie: flat plates and evacuated tubes) have dominated the hot water market in recent years. However, now with the increasing availability of Solar PV technology, Solar PV water heating is fast becoming the technology of choice.

The last ten years has seen the cost of solar PV panels reduce by 80%. At the same, the performance and output of the panels have significantly improved, from 200W panels with 15% efficiency 5 years ago, to 400W+ panels today with more than 22% efficiency.

These declining technology costs and improvements in performance have made Solar PV a viable and accessible option for creating long-term savings and effectively reducing water heating bills.

Key benefits of PV-driven Solar hot water systems

Where Solar Thermal systems are only capable of heating water, Solar PV provides the dual benefit of heating directly to the element and providing excess power the building as a whole. This is a huge step in improving energy efficiency. Solar PV also offers a number of advantages over Solar Thermal systems, including:

  • Less copper piping, lagging and less plumbing required
  • Reduced installation costs
  • Reduced stand by losses
  • Live performance tracking and monitoring
  • Little to no maintenance required
  • No risk of freezing or over heating

Disadvantages:

  • Requires more roof space
  • Unfamiliarity with new uses for technology

Developing Large-Scale Hybrid Hot Water Systems

In the last year we have had great success combining Solar PV and Heat Pumps to create hybrid hot water systems for residential apartment blocks.

By Integrating Solar PV with heat pumps and centralised thermal stores we have been able to create incredible efficiencies, effectively reducing the cost of hot water from 14c to less than 3c a litre.

  • The Heat pumps provide 24 hour dedicated water heating capacity while the Solar PV offsets the power consumed by the heat pumps and provides power to the building as a whole
  • Solar PV allows us to pre-heat water in daylight hours (direct to the element), with additional heating capacity provided by the grid and/or heat pumps in the evenings and cloudy days. This also reduces the strain on the heat pumps and in turn extends their service life.
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