Photovoltaic gadgets in the test: how useful are solar power banks and backpacks?

»Due to the current energy crisis, the focus is increasingly on solar energy technology.

And if you can't put an entire photovoltaic system on the roof right away, you could take a look at solar gadgets like this power bank.

It's supposed to charge my cell phone, but unfortunately it doesn't.

And I'd rather ask an expert why not.

Mr. Jahn, you are an energy expert at the consumer advice center in Brandenburg.

What am I doing wrong?

Why can't I charge my phone here right now?"

»One thing that is obvious is of course that the sun is not shining, which means that the solar panels cannot produce electricity either.

If the sun were to shine now, you would also have to look, because it is specified with a maximum output of five watts.

That means five watts under laboratory conditions.

In reality, we would then probably see three to four at most.

And even with that, it becomes difficult to charge your cell phone because it takes five to eight watts.

You can probably charge the phone with it a bit if it would work.

But it would take a lot longer than it would in a normal outlet."

»Would it now be possible if I wanted to save electricity at home with this device, to charge it during the day and have my mobile phone fully charged with it at night?«

»It would be theoretically possible.

You can probably, if it's really good, produce a cell phone charge during the day and then put it into the cell phone at night.

However, that's 0.01 kilowatt hours, so you save 0.4 cents per day.

Calculated over the year, it's about 1.50 euros.

Well, the big savings cannot be achieved with it.«

»Now it's always said that solar energy is very green and I can save on fossil fuels as a result.

Does that also apply to a solar power bank?”

Center “The problem with power banks and batteries is that there are relatively high emissions during production.

The lithium is mined in South America and Australia, the cobalt comes from the Congo, under bad working conditions, bad environmental conditions.

Such a power bank and a battery are not really sustainable.«

»The second gadget we have with us is a solar backpack.

That means I can charge my phone while walking, I hope.

How do you look at such a product?

»In theory, it's a nice idea.

In practice, it will probably be a bit difficult, because of course electricity always works best when it is well aligned with the sun.«

»Let's take a look at how much electricity is actually used, because we have a measuring device with us and see whether my cell phone is really being charged or whether it is in fact going on and off all the time.

So my cell phone is charging and we can see what is displayed here.

Four volts at 0.2 amps."

»A little less than one watt of power.

As I said, a cell phone like this normally needs five to eight watts of power, so it now charges much more slowly, but it charges a bit.«

»Now it's over.

So the measuring device shows that no electricity has just been produced.

Now is that bad for my phone?”

»Exactly.

So it's bad for the battery, because every time it's switched on and off... it always discharges a bit and over the long term it doesn't last that long and somehow a bit of capacity is always lost.«

»Now it's gone again.

Sure, there are of course a bit difficult circumstances for the solar panel now.

For whom does such a backpack actually make sense?

»Well, if you're really completely alone in the wilderness and don't have any other power source, or if you're on a kayak, for example, it would make sense or on the beach if you can really lay it down and the sun is constant depends.

It might make sense there, but otherwise, if you somehow use your cell phone, ... i.e. if you go on a normal hike, you'll find a socket and can then charge your cell phone with it and it doesn't make much sense there. «

»The power backpack isn't really convincing yet, but we've prepared something else.

A slightly larger solar panel.

So this system obviously works, can produce electricity, my cell phone is charged.

Does that make sense now?

As a green alternative for my balcony at home?”

»Well, if I could use all of the electricity now, I would need a battery, which would make it much more expensive and then I could save on electricity costs.

I would say that for something like 100 watts, that's around 20 to 30 euros a year.

Of course, if I now spend 600 euros for it, plus the battery - so you can't really save money there.

It's a bit more sustainable because the electricity is then produced directly, of course."

»How can you judge these gadgets?

Does it make sense for me to get something like this for the home, or what should I pay more attention to?”

»They make total sense in theory, because we have to get to the point where we produce a lot more renewable electricity.

In practice, however, you then see that the amount of electricity they generate is simply far too small and then other problems follow.

For example, with the power bank, that a lot of resources are needed to produce it.

That's why I would rather advise against it and really rely on the right green electricity tariff from a provider who produces electricity himself, renewable, and also invests in the energy transition.

This is then much more sustainable and much better.

And the best thing is to have your own solar system, either a balcony or, if possible, directly on the roof, fill everything up.«