Does Solar Work on Cloudy or Rainy Days?

Yes, solar panels still work on cloudy and rainy days, they just produce less. On a heavily overcast day a typical rooftop system in New Zealand will generate somewhere around 10% to 30% of its sunny-day output, and on a light-cloud or "bright overcast" day it can still hit 50% or more. The reason is simple physics: panels run on light, not heat, and a lot of light still reaches the ground through cloud. NIWA's solar radiation data shows most of the country receives between 1,400 and 2,000 kWh of solar energy per square metre every year, which is plenty. The "New Zealand is too cloudy for solar" line is one of the most persistent myths in the market, and it does not hold up.

This matters because it is often the single thing that stops people from even getting a quote. They look out the window at a grey Auckland morning or a soggy Westland week and decide solar is a waste of time down here. It is a fair instinct and a wrong one, so let's walk through what actually happens on your roof when the sun is not blazing.

Panels run on light, and clouds don't switch the light off

The first thing to understand is that solar panels respond to light intensity, not blue sky. Even when the sun is completely hidden, daylight is still pouring down. That diffuse light, scattered through the cloud layer, is what keeps your panels ticking over.

Think about it from your own eyes' point of view. On an overcast day you don't need a torch to walk around outside. There's clearly a lot of light about. Your panels see the same thing. They are not sitting there in the dark waiting for a sunbeam.

What changes is the amount. Bright direct sun delivers roughly 1,000 watts per square metre at the panel, the figure manufacturers use to rate their gear. Thick cloud might cut that to 100 to 200 watts per square metre. Light cloud or high haze might only knock it back to 500 to 700. So output drops, but it does not vanish.

Diffuse light is a bigger deal than people think

Here is something the sales brochures rarely explain properly. A meaningful chunk of the energy your system produces over a year comes from diffuse light rather than direct beam sunlight. NIWA's measurements of global horizontal irradiance (the total light hitting a flat surface, direct plus scattered) consistently show that diffuse radiation is a real and steady contributor, especially in the cloudier parts of the country.

This is exactly why solar still pencils out on the West Coast, in Taranaki, and through a grey Waikato winter. The panels are harvesting scattered light all day, not just the few hours of clear sun you happen to get.

How cloudy is New Zealand, really?

Less than people assume, and it varies enormously by region. NIWA's long-run sunshine records are worth knowing because they kill the myth dead:

• Nelson, Blenheim and Whakatāne regularly top the national charts at over 2,400 sunshine hours a year. That is genuinely excellent, comparable to plenty of places overseas that are considered solar hotspots.
• Bay of Plenty, Hawke's Bay, Marlborough and Central Otago all sit comfortably above 2,000 hours.
• Auckland gets around 2,000 hours, despite its reputation for grey mornings.
• Even Invercargill, near the bottom of the country, records roughly 1,600 hours, and Central Otago's clear, frosty winter skies are a quiet solar advantage most people overlook.

For context, the genuinely cloudy spots are the West Coast and parts of Fiordland, where persistent cloud and high rainfall do drag annual output down. But "down" still means a perfectly workable system. It is a reason to size things carefully, not a reason to walk away.

The Invercargill-beats-Auckland twist

Roof orientation and tilt often matter more than your postcode. A well-pitched north-facing array in Invercargill can out-produce a poorly oriented west-facing array in Auckland, despite Auckland's extra sunshine hours. Southern roofs catch a lower winter sun angle, but a correct tilt recovers a lot of that, and cooler southern temperatures actually make panels run slightly more efficiently. Heat is the enemy of panel performance, not cold.

So the honest answer to "is my region too cloudy" is almost always no. The real questions are about your specific roof: its pitch, its direction, and what's shading it. If you want to see roughly what your setup might produce and save, our cost and ROI calculator is a sensible place to start sketching the numbers.

What a cloudy day actually looks like on your monitoring app

If you watch a real system's live data through a grey week, you'll see the pattern clearly. Here is a realistic picture for a 6.6kW system (a very common size in New Zealand) on different days:

• Clear summer day: 35 to 45 kWh. The panels are flat out for hours.
• Bright overcast day: 18 to 28 kWh. Still a genuinely useful haul.
• Heavy, dark rainy day: 4 to 10 kWh. The low end, but never zero.
• Mixed cloud with sun breaks: often surprisingly high, because passing clouds can briefly bounce extra light onto the panels.

That last point is real and a bit counterintuitive. When the sun edges out from behind a cloud, light reflecting off the surrounding cloud bank can push output briefly above the clear-sky rating, a short spike installers call the "cloud edge" or "lensing" effect. It doesn't change your annual total much, but it's a nice reminder that clouds and solar are not enemies.

Does rain hurt the panels? Quite the opposite

Rain is not a problem for solar panels, it is a free cleaning service. New Zealand panels are sealed, weather-rated units built to sit out in the worst your region can throw at them, including coastal salt, Canterbury nor'westers and Southland sleet.

A decent rain shower rinses dust, pollen and bird mess off the glass, which keeps output up over time. Homes in genuinely dry, dusty spots (parts of inland Otago, say) can lose a few percent of output to grime between rains, but for most of the country the weather handles cleaning for free.

What does matter is the quality and rating of the hardware itself, because panels live outside for 25-plus years. The cell type and build quality affect how well a panel copes with low light and heat, which is exactly why it's worth understanding the gear before you buy. We get into the detail on cell technology in our piece on N-type versus P-type cells in the NZ climate, and the broader hardware picture lives in our guide to solar hardware and tech.

Newer cell types do better in low light

Here's a genuinely useful, hard-to-find detail. Modern N-type panels generally have a better "low-light response" and a lower temperature coefficient than older P-type designs. In plain terms, they hold onto more of their output when light is weak (your grey winter mornings) and lose less when it's hot (your January afternoons).

For a cloudier region, that low-light edge is not just marketing. Over a year of overcast Waikato or West Coast days, the difference in harvested energy can be meaningful. If you're weighing up specific panels, our review of DAS Solar and Tongwei N-type panels looks at exactly this kind of real-world performance.

The honest limits: what cloud genuinely costs you

Being straight with you: cloud does reduce your annual production, and winter is the real squeeze. The issue isn't that solar "stops working" in winter, it's that you get a double hit:

• Shorter days mean fewer daylight hours to generate in.
• Lower sun angle means weaker light even when it's clear.
• More cloud in many regions on top of that.

The result is that a system might produce two to three times more in midsummer than in midwinter. And winter is, of course, exactly when your power use peaks: the heat pump's working hard, you're drying washing inside, the kids are home and the lights are on by 5pm.

So the realistic truth is this: grid-connected solar will not zero your winter power bill, and anyone telling you otherwise is selling, not advising. What it will do is take a solid bite out of your bill year-round and a very large bite out of it across the sunnier eight months. You stay connected to the grid for the times your panels can't keep up, which on a wet July evening is most of them.

This seasonal pattern is also why the maths around exporting your daytime surplus matters. On a bright shoulder-season day you'll often generate more than the house can use, and what your retailer pays you for that surplus changes the whole equation. Buy-back rates vary a lot between Genesis, Mercury, Contact, Meridian, Octopus and the rest, and they're worth checking before you sign anything.

Who should think carefully (cloud or no cloud)

The "too cloudy" worry is usually misplaced, but there are real situations where solar is a weaker fit, and they have little to do with your region's sunshine hours:

• Heavily shaded roofs. A neighbour's mature poplar or a two-storey place next door casting afternoon shade over your panels will cost you far more output than cloud ever will. Shade on even part of a string can drag down the whole array unless you've got optimisers or microinverters.
• Nobody home during the day, no battery. If the house is empty until 6pm and you export most of your generation at a low buy-back rate, the savings shrink. This is the self-consumption question, and it's central to whether the numbers work.
• Renters and short-term owners. If you're moving in a couple of years, the payback window may not arrive in time.

Notice none of those is "my town is too grey." Cloud is rarely the dealbreaker. Roof, shade, and when you use your power are the things that actually decide it.

What to do next

If cloud was your main hesitation, you can set it aside and look at the things that genuinely move the needle:

• Get a proper shading assessment. A good installer will model your roof through the seasons, not just glance at it. Ask to see the production estimate broken down by month, so you can see the winter dip honestly.
• Ask for low-light performance specs. Ask which cell type the panels use and what the temperature coefficient is. Reputable installers will happily tell you.
• Check the warranty and panel tier. Panels facing decades of NZ weather need a manufacturer that'll still be around to honour the warranty. We explain what the labels actually mean in our piece on what "Tier-1" really means for your warranty.
• Match the system to your daytime use. The more of your own generation you use directly, the better the return, cloud or shine.

Frequently Asked Questions

Do solar panels work when it's completely overcast?

Yes. On a thick, dark overcast day a system typically produces around 10% to 30% of its clear-sky output, because diffuse light still reaches the panels. It's a reduced harvest, never zero. You'll see the dip on your monitoring app, but the panels keep generating right through the day.

Is New Zealand too cloudy for solar to be worth it?

No. NIWA's records show most regions get well over 2,000 sunshine hours a year, with Nelson, Blenheim and Whakatāne topping 2,400. Even cloudier spots like the West Coast still produce workable amounts thanks to diffuse light. Your roof orientation and shading matter far more than your region's reputation for grey skies.

Does rain damage solar panels?

No, the opposite. Panels are sealed, weather-rated units designed for decades outdoors in NZ conditions, including coastal salt and heavy rain. Rain actually helps by rinsing dust and bird mess off the glass, which keeps output up over time with no effort from you.

How much less power do panels make in winter?

Expect midwinter production to be roughly a third to a half of midsummer, depending on your region and roof. The drop comes from shorter days, a lower sun angle and more cloud all stacking together. Winter is also when your power use peaks, so solar trims your winter bill rather than erasing it.

Will solar still save me money in a cloudy region like the West Coast?

It can, but size it carefully and be realistic about winter. The West Coast and Fiordland are genuinely the cloudiest parts of the country, so annual output runs lower than sunnier regions. A good installer will model your specific roof and give you an honest monthly production estimate before you commit.

Do better panels really produce more on cloudy days?

Yes, to a degree. Modern N-type panels generally have a stronger low-light response than older P-type designs, meaning they hold more output when light is weak. Over a year of overcast days in a cloudier region, that difference adds up, which is why the cell type is worth asking about.

Do I need a battery to make solar worthwhile in cloudy areas?

Not necessarily. A battery stores your daytime surplus for evening use, which lifts your self-consumption, but it adds cost and isn't always the best return. Whether it pencils out depends on your power use pattern and your retailer's buy-back rate, not on how cloudy your region is.

Can solar panels overheat in summer and produce less?

They can lose a little efficiency in extreme heat, since panels are rated at 25°C and output dips slightly as cell temperature climbs. This is why cooler southern regions get a small efficiency bonus and why modern panels with a low temperature coefficient are worth choosing. The effect is minor compared to the gains from long summer daylight.

The bottom line

The "New Zealand is too cloudy for solar" myth costs people money, because it stops them looking properly. Panels run on light, diffuse light is everywhere, and NIWA's own data shows most of Aotearoa is genuinely sunny by any reasonable measure. Cloud reduces output on the day, but it almost never makes the difference between a good investment and a bad one. Shade, roof orientation and when you use your power do that.

If you're ready to see real numbers for your own roof rather than guess from the weather, have a play with our cost and ROI calculator, and when you want the gear explained without the sales spin, start with our hardware and tech guide.