Solar panel power in winter.

Found a solar panel of 30W to charge 12V battery but I can't find data about what power it gives on a cloudy day in winter. Do you have an answer based on experience?

Typical PV panel ratings are for a bright sun high in the sky.

Clouds reduce output. Output is also reduced because the winter sun is lower in the sky.

This results in wide variation of output. 50 percent is a reasonable estimate. Therefore it could be a good idea to use twice as many PV panels in winter.

BradtheRad said:

Typical PV panel ratings are for a bright sun high in the sky.

Clouds reduce output. Output is also reduced because the winter sun is lower in the sky.

This results in wide variation of output. 50 percent is a reasonable estimate. Therefore it could be a good idea to use twice as many PV panels in winter.

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Thank you BradtheRad, 50% sounds encouraging.

True, the light output is lower when the Sun is nearer the horizon but only because of atmospheric losses. Angling the panel so the light still falls directly on it will give almost the same output. Note that 'winter' can mean different things depending on your geographic location. PV panels at the equator for example see equal N and S tilt at extremes.

Cloud cover obviously reduces the available light, the specifications are for maximum light before the panel 'saturates' but how much it reduces under cloud cover depends on the cloud density.

Brian.

Vbase said:

Found a solar panel of 30W to charge 12V battery but I can't find data about what power it gives on a cloudy day in winter. Do you have an answer based on experience?

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sunlight is important for the panels, besides that if the weather is cool (temperature is low) voltage and power capacity will increase. A sunny winter day is the best for panels. (Maybe it is connected to distance between Sun and Earth also)

maybe 1/5 of 30W=6W

betwixt said:

True, the light output is lower when the Sun is nearer the horizon but only because of atmospheric losses. Angling the panel so the light still falls directly on it will give almost the same output. Note that 'winter' can mean different things depending on your geographic location. PV panels at the equator for example see equal N and S tilt at extremes.

Cloud cover obviously reduces the available light, the specifications are for maximum light before the panel 'saturates' but how much it reduces under cloud cover depends on the cloud density.

Brian.

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Hi Brian.
I found that over a period of a year (including night time) I get average of only 9% output. This makes electricity from solar panel costing more than 50 times the cost of electricity from mains, based on the idea that the panel will last 10 years and cleaned every week.

I looked at about 30 post of yours and I noticed that not only that you have vast knowledge you also understand electronics (understanding is rare in forums). You also always answer the question directly.
Your answer to my question must have been the odd one out, it was accurate but you only told me what I already know, I need an educated number based on experience.

Thanks Vbase.

I was trying to point out that the amount you can generate is highly unpredictable. If you want a pure guess, expect 10% output on an overcast but bright day. The amount of power a PV panel produces is not the same as the voltage it produces. The voltage will rise and then stay fairly constant as the panel moves from darkness to full light but under low light levels the amount of current it can produce will be much lower. They need bright light to be able to produce full voltage while under full load, looking at it the other way, less light means lower voltage under the same load. The power is the voltage it produces multiplied by the current you draw from it so expect it to drop quite quickly as the light level reduces.

This is why larger PV systems use MPPT controllers, they dynamically adapt the load to optimize the V and I at the same time. For a small system they are not economical to build though.

Brian.

Hi brian.
Your guess of 10% power on cloudy day is more similar to my measurements of 2%.
I use now a panel of 1W to charge 6V 4xAA cells to power a walki-talki (intercom) in the entrance to the farm 150 meter away from the house.
I use this circuit to charge the battery: https://www.moty22.co.uk/charger.php
I want to upgrade it to a video camera and 30W panel.