Winter is approaching. As the weather gets cooler, the number of days that are cloudy and overcast are increasing. If you’re thinking about getting solar panels on your home, this may be a concern. You may be wondering whether solar panels still work when its cloudy.  Do solar panels need direct sunlight to generate power? How well do solar panels work on cold days? Will your solar panels produce enough electricity to power your home throughout winter?

On this blog:

• Do solar panels still work when it’s cloudy?
• How much electricity do solar panels generate on a cloudy day?
• How well do solar panels work on cold days?
• Which solar panels work best when it’s overcast?
• Can I still save on my electricity bills with solar over winter?

Do solar panels still work when it’s cloudy?

The answer is yes, solar panels still produce electricity on cloudy days. They just produce less power than on sunny days, depending on the quality and efficiency of the solar panels.

As most people living in Australia know, it’s a good idea to put on sunscreen even when it’s cloudy outside. That’s because solar radiation penetrates the clouds, even on overcast days.  That’s the same reason why solar panels still work on cloudy days.

It goes without saying that solar panels need sunlight to work. But what’s interesting is that the sunlight can either be:

• direct sunlight (like on a clear sunny day), or
• indirect sunlight (on an overcast day).

Once sunlight hits a solar panel, photons from the sun are converted into electrons. These electrons then pass through the cells of a solar panel and are converted into direct current (DC) electricity.

How much electricity do solar panels generate on a cloudy day?

With solar panel technology improvements in efficiency, modern solar panels still operate reasonably well on cloudy days.  The exact amount of solar energy production on a cloudy day depends on several factors including:

• thickness of the cloud cover
• duration of cloudy conditions
• quality and efficiency of the solar panels
• orientation and tilt of the solar panels on the roof

As a rule of thumb, a good quality solar panel will produce around 25 per cent to 40 per cent of electricity it would normally produce on perfectly clear sunny day.

When you request a quote from SolarRun, we’ll provide a graph showing the estimated monthly output for your system which will be specific to your property.  This is based on your location and the average number of peak sunshine hours each day (and by month) for your rooftop.

How well do solar panels work on cold days?

The thing a lot of people don’t realise about solar panels is that they work best on cold or mild sunny days.  When the temperature goes above 25 degrees Celsius, the output of solar panels reduces by a small percentage for every degree increase in temperature.

So how do you tell how much a solar panel’s efficiency drops when the temperature goes above 25 degrees Celsius.

This gets a little bit technical – but stick with it because it’s useful to know!

On every solar panel datasheet, there will be a statistic called the temperature coefficient of Pmax, or just Pmax.  This stat tells you how much a solar panel’s efficiency reduces for each degree increase in the temperature of the panel over 25 degrees Celcius.

The key thing is ‘temperature of the panel’ – not the ambient air temperature.  Given that solar panels are generally hotter than the ambient air temperature, this is something to bear in mind.

Pmax is always a negative percentage – for example -0.34%.  This tells us that the solar panel will reduce in efficiency by 0.34% for every degree increase above 25 degrees Celsius.

For example, if the solar panel has a temperature of 40 degrees Celsius and a Pmax of 0.34%, we can work out the loss in efficiency in two steps:

1. Subtracting the panel temperature (40 degrees) from 25 degrees = 15 degrees
2. Multiplying 15 degrees by the solar panels Pmax (i.e. -0.34%) = 5.1% efficiency loss

This tells us that the solar panel is working a 5.1% lower efficiency when the panel temperature reaches 40 degrees, compared to how it works at 25 degrees Celsius.

The main point with all this, is to show that solar panels work just fine when it’s cold – as long as there is sunlight reaching the panel.  So a cold sunny day in winter is actually perfect for producing lots of solar energy for your home!

Which solar panels work best when it’s overcast?

The more advanced, high quality solar panels have design features that allow them to convert a greater percentage of the solar radiation into direct current electricity than standard panels.

Some solar cells, such as SunPower, incorporate a ‘backside mirror’.  The way the mirror works is ingenious.  The mirror is a thin layer of aluminium underneath the solar cell which reflects the light photons that weren’t absorbed on the first pass through the cell.  When reflected, the photons get a second chance to be absorbed by the solar cell.  The result is a higher percentage of photons converted to electrons from the same amount of sunlight.

Another technology that’s good for reducing the impact of cloud cover is power optimizers made by SolarEdge.  Power optimizers come in handy when some, but not all the solar panels, are impacted by the shading caused by the clouds.

Power optimizers are little units that are fixed underneath each solar panel and make the panel work independently.  For example, if six solar panels were affected by partial cloud cover and the remaining 14 panels weren’t impacted, you’d still get maximum power output from the 14 panels.

In comparison, with a conventional string inverter solar system the entire array of solar panels would reduce in output to the level of the weakest performing panel.

Can I still save on my electricity bills with solar over winter?

In short, the answer is yes. Solar saves you money on your electricity bills because it’s a lot cheaper than buying grid electricity.

Here in Australia, we have some of the highest electricity tariffs in the world.

That’s the bad news.

The good news is that we’re lucky to be living in one of the world’s sunniest countries.  No matter where you live in Australia, you’ll typically get at least eight hours of sunlight a day. By harnessing that sunlight with solar, you reduce your reliance on expensive grid power – which means lower electricity bills.

Sizing your solar panel system to meet your winter and summer electricity requirements is a specialist task.  There’s no one-size-fits-all solution.  It all depends on how much electricity you use at different times of the year.

That’s why at SolarRun, we take the time to visit your home, assess your energy usage profile and recommend the best solar system for your needs.

Get in touch

If you’d like a customised assessment of the suitability of your home for solar panels, get in touch.

We use specialist software to work out exactly how much sunlight hits your roof throughout the year. We then access your energy data from your local network distributor to see when your electricity usage is highest.

We put this information together to design a solar power system that is sized right to reduce your electricity bills as far as possible, whilst keeping within your budget.

Find out how much you could save with solar. Talk to us today.