How do you know if your roof is good for solar?

Is Your Roof Right for Solar Power?

Solar power is a fantastic way to reduce both your electricity bills and carbon footprint, particularly in regions like Nelson, Tasman and Marlborough which are known for their high sunshine hours – but not every roof is suitable for solar panel installation. If you’re thinking about adding solar to your home, here’s a guide to assessing if your roof is suitable for mounting solar panels.

There are 3 crucial factors to consider when mounting solar panels to your roof

Roof Angle

The first thing to look at is the angle of your roof. The optimal angle for solar panels is generally equal to the latitude of your location to maximise sun exposure throughout the year. For example:

• In Auckland, with a latitude of approximately 36°, the ideal angle would be 36° from horizontal.
• Moving down to Nelson at the top of the South Island, where the latitude is about 41°, the ideal angle would also be around 41° from horizontal.
• In Christchurch, the latitude increases to about 43°, suggesting a similar pitch for those panels.
• Even further south, in Dunedin, the latitude is approximately 46° – and you’ve guessed it… The panels will work best at 46°.

If your roof angle differs from these ideal conditions, don’t worry too much. A deviation of about 10° from the ideal angle typically results in less than a 5% decrease in power output. In New Zealand, typical roof angles are between 15° and 35°, which are generally sufficient for effective solar energy generation. If your roof is flat, consider installing tilt racking to position the panels optimally. Despite the additional cost, the additional output from mounting your panels at a more optimal angle with typically result in a short pay-off period.

Roof Direction

The next thing you should consider is the direction that your roof is facing. In the Southern Hemisphere, a north-facing roof is perfect for solar installations. While north is ideal, technological advancements and reduced costs have made east or west-facing roofs increasingly viable. In New Zealand, where sunlight is abundant in many regions, an east or west orientation can still harness significant solar power. In fact, this may work well with your daily energy usage profile, providing good output earlier and later in the day when your demands are higher.

Previously panels needed relatively direct sunlight to produce a meaningful amount of energy, nowadays the technology has improved such that even south facing panels will provide reasonable production; similarly you’ll see production on overcast days. As an example, and this is not to suggest you mount your panels facing south(!), on a 15 degree southerly facing roof in Hobart, Tasmania (which at 42.9 degrees latitude, is south of Nelson) a panel will still provide 74% of what it would if mounted in the ideal direction over the year. However, it is worth noting the winter production will be fairly abysmal, generally only about 40% of their north-facing counterparts.

Today, the improvements in PV panel affordability also helps provide a solution. Where roof aspects are not ideal for all-day sun, it is often worth adding a couple of extra panels (so-called ‘over-panelling’) to get the most out of your system. This works very well where you have panels facing multiple directions (e.g. NW and NE) as it provides more consistent output throughout the day, as opposed to their being a large peak in the middle of the day.

Shading

The last one, the biggie… is shading. If any shade falls on your roof, then you must quantify whether that is going to be a problem – or how big of a problem it is going to be. Shading is a critical factor that significantly impacts the effectiveness of a solar installation. If trees, nearby buildings, or other obstructions cast shadows on your roof, it’s essential to conduct a detailed shade analysis. We generally work with 16 degrees being the angle above which we want to avoid any substantial objects that may shade the panels; this equates to the mid-winter sun angle at 10am.

Occasion shading of a small part of an array on a string inverter is not such an issue nowadays as it was in the past. Where in the past, microinverters were often used to manage potential shading by effectively individualising the management of the panels so shading on one panel wouldn’t effect the production of another, panel and solar controller technology has improved significantly meaning it will only limit the production from the shaded panels (and possibly only the shaded half). This improvement has meant there is generally less call for microinverters in installations than there once was.

Making the Decision

Determining whether to install solar panels on your roof isn’t just about having the perfect conditions; it’s about making the best of what you’ve got. Most roofs, while not ideal, can be adapted to significantly boost their solar viability. This is where a skilled solar installer becomes invaluable. They won’t just look at your roof and see an angle or orientation; they’ll see potential.

By carefully assessing the specifics of your roof’s angle, direction, and shading, a seasoned installer can provide you with a detailed analysis of what to expect in terms of energy production. They’ll give you the hard numbers on potential power output losses and weigh them against the benefits of going solar. This means you won’t be going in blind; you’ll have all the facts you need to make an informed decision.

Remember, if your roof isn’t viable, there may well be the option of a ground mounted solar array, so all is not lost. One advantage of ground mounted arrays is that you can generally position them to face the ideal way, at the ideal angle and avoid any shading.

For homeowners in New Zealand, considering these factors can help maximise the benefits of solar installations, allowing you to tap into the renewable energy market efficiently. This proactive approach not only supports the environment but also aligns with New Zealand’s goals for sustainable development and energy independence. By overcoming the usual hurdles associated with residential solar power systems, you not only contribute to a greener planet but also invest in long-term savings and energy security for your home.