Solar panels and energy crunch forum

Some people are saying solar panels do not work on cloudy days, and others are saying they do? Can anyone help on this question?

Although some solar energy is blocked by cloud cover, some still gets through. In a nutshell, the amount caught and used depends on two factors:

1. The type of solar technology used
2. The density of cloud cover

There are various types of quality systems so the information is based on high level quality systems only.

1. Evacuated tubes are the best performers with clouds because they trap solar energy and store it more efficiently.
2. Second best is 'glazed' flat glass panels.
3. 'unglazed' plastic panels need direct sunlight only.

Also, PV solar electric panels work especially well in cloud although at reduced output levels to direct sunlight levels.

Using a car engine as an analogy, a solar panel is the same.

When the sun is directly hitting the panel, this gives ultimate output or (high end revs).

When in cloudy conditions, the panel may give less output (or moderate revs) depending on the clouds density.

The bigger sized system (or engine) you install, the more output you will get from your system.

I prefer to use hard facts. So it is easy to best this theory out.

A extremely crude way of making a solar heating panel is to paint a jam jar black, fill it with insulating foam and put a thermometer inside and outside the jar. The inside temperature will much warmer than the outside. Test it on a sunny day and a cloudy day too, make sure the jar is in the line of sight with the sun behind the clouds.

Another way to prove solar energy can penetrate clouds is so using a solar power calculator/radio or torch will do, outside facing were the sun is behind the clouds. Voila! Solar energy does penetrate clouds. I have tested this myself, and it works.

Clouds contain air and water, both transparent substances that hardly absorb any visible light.

Light can travel many tens of metres into cloud, but eventually it will it will hit a water droplet, which will scatter the light changing its direction although only slightly. Light will enter a cloud and be dispersed into random directions.

The solar energy hitting a solar panel will still be there, but less of a direct hit due to the scattering effect.

Think of shrapnel hitting as opposed to a direct bullet.

I have read these comments with interest as I wanted to validate them from my experience. I have had two flat panels working peachy for over 20 years. They have paid for themselves many times over and are one of the best investments I have ever made.

I am positively sure that with the latest evacuated tubes performance will be even greater efficiency than my older solar panels.

This is to tell you of my satisfaction with our solar heating system installed in January. It has performed admirably during the vile cold and wet weather since installed this February and March.

Mr Edwards in Dorset

They may look light and fluffy, but those big white things floating overhead are pretty hefty. A typical cloud has a volume of around 1km3 and a density of around 1.003kg per m3, about 0.4 % lower than that of the surrounding air, which is why they float.

The scattering effect mentioned above probably accounts for 1/3 of the solar energy being diverted away from your solar panels on your roof, so 2/3 will still reach your panels. Precisely why, we do not get a solar eclipse style blackout every time a cloud blocks the sun.

As clouds get closer to releasing its water as rain or get greyer, droplets merge. When light or solar energy strikes a droplet, some are reflected and some absorbed depending on the size of the droplet. The larger the droplet, the longer the path through the other side and so the more light will be absorbed, thus making the cloud seem grey and black.

1. Light wispy clouds absorb very little so your solar panels will absorb plenty.
2. Thicker white clouds will absorb some light but your solar panel will still work.
3. Grey or black clouds will absorb most of the light, so your panels will absorb very little.

Hope this rectifies this question.

This common misconception with solar panel technology is that you need direct sun for it to function, however, in our country where weather can cloudy, why would you install it onto your roof?

Solar PV and solar heat technologies use irradiant radiation in the form of light. This means that even on a cloudy day, if there's light, the system will produce electricity.

In scientific terms, it is the conversion of photons hitting the panel and transformed into electrons.

In laymen's terms; free energy!