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.
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:
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.
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.
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.
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.
Posted in Miscellaneous
Should you put your panels on tilt frames?
Tilt frames are used to get solar panels to the optimum angle and maximise power output.
Here is really common dilemma:
“I’ve got 3 quotes for solar: The first company says my roof is at the wrong pitch and wants to charge me hundreds of dollars extra to put my solar panels on tilt frames to optimize the amount of electricity I get. The second mob say it is fine to just put the panels flush on my roof and the third guy says that, yes, my roof isn’t at the perfect pitch, but the best solution is to mount them flush to the roof and simply add an extra solar panel to make up for any reduced power output.
Now I’m really confused! Help!”
The problem here is that there are two extremes of solar installers:
At one end of the spectrum, you have “The Solar Purist”.
They are only happy if the solar panel is positioned for the absolute optimum power output – they are a perfectionist, highly technical, and have been in the industry since the dawn of solar, when solar panels cost 10 times what they do today. They think a few hundred dollars is a small price to pay to squeeze a bit more power out of those precious solar panels. And please, never, ever suggest to them that they use a non-German inverter.
Then at the other end of the scale – you’ve got the “She’ll Be Right” Solar Installer.
They just want to get the install done. If you’ve got a roof, and it doesn’t face south, and it’s not completely shaded they’ll bang the panels on and move on to the next job.
We believe that the best installation for your home is somewhere in the middle.
The best solution to maximize return on your investment.
You need to consider the financial consequences for each option and then decide whether tilt frames are a good investment or not.
So, let’s look at a typical scenario where tilt frames would be an option and see which of our 3 original options makes the most sense from an economic perspective:
To Tilt or Not to Tilt – that is the question
How to work out if tilt frames make sense or not:
Imagine you have a house in Nelson and you want to install a solar system. The house has a North facing roof that has a very shallow slope of 10° and you want to install a 3kW system. The perfect tilt angle for solar panels is the same as the latitude of the install location. Nelson has a latitude of 41°.So therefore the panels should be of the Latitude.
So, if we follow those guidelines, we’d have to use tilt frames for all our solar panels, right?
Panels at the perfect Angle:
If we crunch the numbers, then we can quickly work out that 3kW of north facing solar panels at the perfect angle of 41° will produce 12.0kWh per day averaged over 1 year. If we value our electricity at 25c per kWh, then that earns us $1095 per year.
Panels at 10° If we crunch the numbers for 3kW of North facing solar panels at only 10° then we discover that we get 11.6kWh per day which makes us $1058.
How much do tilt frames cost?
Assuming our 3kW system uses 195W panels, the extra cost of tilting 16 x 195W panels should be around $450. So to make an extra $47 per year, we are going to be spending $450. About a 9-year payback.
Whether you think this is a good investment is completely up to you. But your solar installer should give you the numbers so you can make an informed decision!
I personally wouldn’t bother, mainly because, if you use tilt frames on your roof, you can fit fewer panels on that valuable roof space.
Why?
Because you need to leave extra space between the panels so that one row of panels doesn’t cast a shadow on the row behind it. I also think that tilt frames are not so aesthetic to look at. But perhaps that is just me.
What about adding an extra panel?
The third option you have – is to make up for any lost power by simply adding an extra solar panel. A few years ago, when panels were 5 x the price, this would have been an insane suggestion (and some old school solar installers still think it is a terrible waste!) but in 2012 it can make a lot of sense.
The cost of one extra 195W panel will be about $440. Installed flush to your roof, this 17-panel system will generate 13.0kWh per day and make us $1186 per year.
So, your extra $440 investment is returning you an extra $169 per year compared to the 16-panel system mounted on tilt-frames at 41°. I’d say that the extra panel is a much better investment that the racking.
The third installer was right! (Oh! That’s us!) Call Current Generation today for common sense solar facts.
Note: One thing that you don’t want is completely flat panels (angle = 0°). You want them to slope at least 10° so that the rain flows down the slope and helps the panels self clean.
