Do Solar Panels Work in Winter and on Cloudy Days in NZ?

The Short Answer

Yes, solar panels absolutely work in winter and on cloudy days in New Zealand. They produce less than in summer, but they never stop generating electricity during daylight hours.

This is the single biggest misconception we hear from Kiwi homeowners considering solar. People assume panels need blazing hot sunshine to work. They don’t. Solar panels convert light into electricity, and there is plenty of light in a New Zealand winter, even on an overcast day in Wellington.

The real question is not whether panels work in winter. It’s whether the reduction in output changes the financial case for solar. And for most households, the answer is no. Solar systems are sized for annual production, not daily. Your summer surplus more than compensates for the winter dip.

Solar panels produce electricity from light, not heat. A cold, clear winter day can actually be more efficient than a scorching summer afternoon.

Let’s look at the actual numbers so you know exactly what to expect through an NZ winter.

How Much Less Do Panels Produce in Winter?

There is no point pretending winter output is the same as summer. It’s not. Here’s a realistic comparison for the North Island.

So yes, you’re looking at roughly half to two-thirds less production in winter compared to summer. That sounds dramatic on its own, but context matters. A 10kW system producing 15 to 25 kWh per day in winter still covers a significant chunk of a typical household’s daily electricity use (around 20 to 25 kWh for an average NZ home).

The South Island sees slightly lower winter output than the North Island due to fewer daylight hours and lower sun angles, but Canterbury’s clear, cold days often outperform cloudy Auckland ones. Geography matters, but not as much as you might think.

What About Cloudy Days?

This is the other big concern. New Zealand is not exactly known for wall-to-wall sunshine, especially from May through August. So what happens when clouds roll in?

Solar panels respond to the full spectrum of visible light, not just direct sunlight. When it’s overcast, something called diffuse radiation still reaches your panels. This is sunlight that has been scattered by clouds and atmosphere. It’s less intense than direct sunlight, but it’s very much there.

Here’s something most people don’t realise: New Zealand’s UV index stays moderate even on cloudy days. That is why you can still get sunburnt through clouds here. The same principle applies to solar panels. UV and visible light penetrate cloud cover much more effectively than most people expect.

If there is enough light outside to read a book, your solar panels are generating electricity.

Rain actually has a silver lining (no pun intended). It keeps your panels clean. Dust, pollen, bird droppings, and salt spray all reduce panel efficiency by blocking light. A good downpour washes all of that away, so your panels often perform better on the clear day after rain than they did before the rain came.

Why Cold Weather is Actually Good for Panels

This is the part that surprises people. Solar panels are electronic devices, and like all electronics, they perform better when they are cool.

Every solar panel has a rated output, measured under Standard Test Conditions (STC) at 25°C. When a panel gets hotter than 25°C, its efficiency drops. When it gets cooler, efficiency goes up. The typical temperature coefficient for a modern panel is around -0.3% to -0.4% per degree above 25°C.

Flip that around: for every degree below 25°C, your panels gain roughly 0.3 to 0.5% efficiency. On a crisp 5°C winter morning with clear skies, your panels could be running 6 to 10% more efficiently than they would on a 35°C summer afternoon.

Temperature vs. Efficiency

• At 35°C (hot summer day): panels lose 3 to 4% efficiency below their rated output
• At 25°C (rated conditions): panels perform at exactly their rated output
• At 5°C (cold winter morning): panels gain 6 to 10% efficiency above their rated output

Of course, winter’s shorter days and lower sun angle still mean less total energy per day. The efficiency boost does not fully cancel out the reduced sunlight hours. But it does narrow the gap, and it means those crisp, clear winter days are surprisingly productive.

Think of it this way: winter gives you fewer hours of sunlight, but each hour of clear winter sunlight can be more efficient than the same hour on a sweltering February afternoon.

NZ Sunshine by Region

Not all of New Zealand gets the same amount of sunshine. If you live in Nelson, you are in one of the sunniest spots in the country. If you are in Invercargill, you get less sun. But, as we will show in the next section, even Invercargill beats many of the world’s leading solar markets.

Here is a breakdown of annual sunshine hours by region, based on NIWA climate data.

Nelson and Blenheim consistently top the sunshine charts, which is why the top of the South Island is often called the “sunshine capital” of New Zealand. But even regions rated as “Moderate” receive enough solar radiation to make residential solar panels financially worthwhile.

Your region affects your expected annual output, which in turn affects your payback period. A system in Nelson will pay for itself faster than the same system in Dunedin. But both will pay for themselves, just on slightly different timelines.

The Germany Comparison

Here is a fact that puts everything into perspective: every single region in New Zealand receives more annual solar irradiance than Germany.

Germany is the world’s 4th largest solar market. They have over 80 gigawatts of installed solar capacity. German homeowners have been installing solar panels for decades, and the economics clearly work there. If solar makes sense in Berlin (which gets around 1,600 sunshine hours per year), it absolutely makes sense in Auckland, Christchurch, or even Invercargill.

NZ vs Germany: Sunshine Hours

• Germany (average): ~1,500 to 1,600 sunshine hours per year
• Invercargill (NZ’s least sunny city): 1,500 to 1,600 sunshine hours per year
• Auckland: 2,000 to 2,100 sunshine hours per year (30% more than Germany)
• Nelson: 2,400 to 2,500 sunshine hours per year (56% more than Germany)

The key takeaway: if you have been hesitating because you think NZ is “too cloudy” or “too far south” for solar, the data simply does not support that. The 4th largest solar market in the world operates with the same or less sunshine than our cloudiest, most southern city.

Beyond sunshine hours, NZ also benefits from relatively clean air (less atmospheric haze reduces light reaching panels in polluted regions) and moderate humidity. These factors mean our actual solar energy yield per sunshine hour is often higher than equivalent locations in Europe.

Why Annual Output Matters More Than Daily

When people worry about winter solar performance, they are usually thinking day by day. That is the wrong frame. Solar economics work on an annual cycle, much like a savings account.

The important thing is that your annual savings are what matter. A system that saves you $2,000 per year does not need to save you exactly $167 every month. Some months will be higher, some lower. Over the year, the total is what counts.

Tips to Maximise Winter Production

While you can not change the weather, there are practical steps to squeeze the most out of your panels during the shorter, darker months.

Do You Need More Panels to Compensate for Winter?

We get asked this a lot, and the answer is almost always no.

Here’s why: if you oversize your system for winter, you end up with a system that massively over-produces in summer. That surplus gets exported to the grid, but NZ buy-back rates (7 to 17c/kWh) are much lower than what you pay for imported power (25 to 35c/kWh). So you are essentially selling cheap and buying expensive.

The financially optimal approach is to size your system based on your annual consumption, not your worst-case winter month. A well-designed system covers 70 to 90% of your annual electricity needs. In summer, you will export surplus. In winter, you will draw from the grid. Over the year, the numbers work.

When Extra Panels Might Make Sense

• You are planning to add an EV charger or battery storage in the near future
• Your roof space can accommodate extra panels at minimal additional cost
• You are on a time-of-use plan that pays well for peak exports
• Your buy-back rate is close to your import rate (some plans offer this)

If you do decide to go slightly larger, the marginal cost of adding one or two extra panels during installation is relatively low ($400 to $800 per panel). The expensive part of a solar install is the inverter, mounting, scaffolding, and labour. Once the crew is on your roof, an extra panel or two adds minimal time and cost.

What to Do Next

If you have been holding off on solar because of winter concerns, hopefully the numbers above have put those to rest. Solar works year-round in New Zealand, in every region, even on cloudy days. The winter dip is real but manageable, and it does not change the overall financial case.

The best next step is to find out what a system would actually look like for your home. Every roof is different, and the only way to get accurate numbers is with a site-specific assessment.

Our free solar survey takes about 60 seconds. You tell us about your home and power bill, and we match you with vetted local installers who will provide tailored quotes. No obligation, no pressure, just real numbers for your roof.

Frequently Asked Questions