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Monday 25 November 2019 12:11pm

The University of Otago is believed to have more solar panels than any other university in New Zealand – 112 kilowatts-worth.

Most are thermal panels that produce hot water at about 11 sites, usually out of sight on roofs around the Dunedin campus and on colleges.

These panels 'collect' heat from the sun to heat a fluid – usually a mix of water and antifreeze – that goes into a heat exchanger that heats a hot water cylinder.

While some electricity is still used as back-up to ensure the water stays hot, that can happen at much cheaper off-peak rates.

The remaining solar panels at our University – 27 kilowatts – are photovoltaic (PV) so turn sunlight directly into electricity.

We have mostly thermal panels because they capture more of the sun's energy for the same amount of area and the energy can be stored and used when needed, as hot water in the cylinder.

Our PV panels – and the battery banks they charge – supply power during peak times to cut costs and are usually for equipment critical to maintain during power outages – for example, freezers.

We are now investigating whether windows with PV panels built into the glass could work well at this University.

Our Energy and Building Controls Team has developed basic guidelines to show what needs to be considered when installing solar panels, created from the team's experience on campus:

  • Solar thermal is usually more economic unless there is a very low-cost thermal heat source (e.g. modern wood boilers)
  • Solar PV requires three-to-four times the surface area of solar thermal, due to efficiencies, but can be mounted on more areas than solar thermal
  • The minimum angle for collector self-cleaning is 45degrees. Aim between north-east and north-west. Never mount at less than 30degees
  • The ideal angle for solar thermal is 65-75degrees. Aim directly north +/-20°
  • The ideal angle for solar PV is 45degrees. Aim 20° east of north, to assist with morning peaks
  • Do not aim solar thermal more than 45° from north. While aiming solar PV east or west does not cause operational issues, the economic benefits reduce significantly
  • Vertical solar on north-facing walls or fences is as beneficial as roof-mounted solar angled between 30-45degrees

Energy storage is as valuable as the solar energy itself:

  • To be economic Dunedin solar systems should be paired with either large hot water vessels with two levels of controlled elements (for PV and thermal) or modern battery banks (for PV)
  • Battery banks create more savings and operational opportunities than thermal storage but must be specified for local needs. They should have the ability to charge from both the grid and solar.
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