Solar Power For Builders – Practical Considerations
Goals for the solar system
Assuming the homeowner would like to save money, the system should be designed to cover the electricity used by the house during the day, rather than over 24 hrs (the average figure shown on many power bills includes night-‐time use).
If it is a large house, the system may also need to meet a minimum BASIX requirement. In our experience, homes without a pool will need 2 to 3 kilowatts (kW), and homes with pools or large air-‐conditioning systems may benefit from systems 5kW and above. It is unusual to have a residential system larger than 10kW. The grid pays only a small amount for extra energy sent out to the wider electricity network, so there is no incentive to install a bigger system than needed.
Orientation – the direction panels will face
In pure energy terms, north-‐facing systems will typically produce the most total energy. However, if there is shading to the north, or if more energy is used within the house in the afternoon or morning, it could make sense to point the panels east, west or east and west – this will more closely match the energy production time with the time of consumption (better savings may be achieved). For this reason East+West systems have become more common. A typical 250Watt panel (4 per kilowatt) is 1650mm x 100mm.
Installation Considerations
Project Management – Gyprock/Plasterboard sheeting schedule
The cables running from the rooftop panel location to the ground level inverter must go in a HD conduit, unless micro inverters are used. Cables should be PV1F type, and an additional
4mm sq earth cable is required. It is very hard to install HD conduit in cavity walls once these have been sheeted. Hence it will make sense to install the conduit before the walls and ceilings are closed up. You can run external MD conduit if needed.
Roof Surface – flat roof types
For flat concrete rooftops covered by a membrane or insulating foam sandwich/laminate, threaded rod and sleeves may need to be installed before the membrane or insulating foam is applied. For Kliplok rooftops on very flat sheets, it will be useful to use a ballasted (weighted) system or a clamp type mount – this is to avoid penetrations in the roof. Conduits through metal& tile rooftops must be via dektite/flashing.
Meterbox or Subboard
Single phase connections will require 1.5 breaker/pole spacing in the board, a free unprotected neutral link hole/termination, 2 earth link holes/terminations and a spare AC busbar / active link space. 3 phase systems will need 3.5 pole spacing on the board face. You also need physical space for the inverter in the plant room or near meter box.
The meter will need to be specified as a bi-‐directional type, so involve your solar installer in the grid connection process via your site electrician. Generally speaking, the solar system will need to be installed before the grid company will permit installation of a bidirectional meter. You will save money if meter installation is only done once, rather than retrofitted.