La last week, I realized that the solar panel was not necessarily the best solution.

So I sent out a survey to all KissKissBankers, to ask them to vote among the following 3 options:

• Solar panel + rechargeable battery to be changed every 2-3 years.
  (RAM type. Replacement to be ordered on the Pioupiou website. Cost ~ 10 €)
• “Military” non-rechargeable battery, to be changed every 3-4 years.
  (Li-SOCl2 or Li-MnO2 type. Replacement to be ordered on the Pioupiou website. Cost ~ 20 €)
• “Classic” non-rechargeable battery, to be changed every year
  (Alkaline “Duracell” type. They can be found everywhere. Cost ~ 5 €)

results:

Solar panel + battery : 34 votes

Pile « military " long duration : 46 votes

Classic stack : 61 votes

I had lots of interesting suggestions. You can find all the details: here.

Chosen solution

I'm going with the non-rechargeable battery option. The Pioupious will automatically be supplied with a " military », with an autonomy of approximately 3 to 4 years. When this battery is empty, it can be replaced with a D / R20 format battery of your choice: alcaline 1,5V, or lithium 3V (LiMnO2) ou lithium 3,6V (LiSOCl2). It's up to you to choose according to your constraints. It should also work with rechargeable batteries, but I don't recommend it because the battery life will be much shorter.

To ensure good contact and prevent corrosion, the battery connectors will be plated with a very thin layer of gold.

As a result, the Pioupiou without a solar panel can be a little more aerodynamic, like this:

Why not solar?

" Why make it simple when you can make it complicated ? »

Our goal is to have the most reliable device possible. So generally speaking, the less stuff on it, the less stuff that will fail.

There are 4 things that are problematic with the solar solution:

Panel aging

The photovoltaic cells themselves have a lifespan of more than 20 years. But they are very fragile, and must be protected.

In large solar panels, we often have an aluminum frame and a glass pane. The glass is UV resistant, so no worries.

On the other hand, for small panels like ours, it is not possible to have a glass pane. There are then two types of panels: Epoxy or PET.

Epoxy panels are embedded in epoxy resin.

The problem is that epoxy doesn't like UVs at all. As a result, it becomes opaque and the panel loses its effectiveness. This solution is often chosen for toys and indoor applications. Lifespan: 1 to 2 years.

PET panels are coated with a layer of PET.

PET is the transparent plastic in soda bottles. This solution provides better quality panels than epoxy. More waterproof and less sensitive to UVs, it is more suitable for outdoor applications. But again, its lifespan is limited: between 2 and 5 years.

There are probably other solutions, but they are not standard. And therefore with a cost that is too high compared to the overall budget of Pioupiou. Our goal is to make a product accessible.

Assembly complexity

Let's say we find a panel that lasts long enough. It will have to be integrated into the box. In particular, it will be necessary to manage the tightness of the system. I'm not sure we can just stick it to SikaFlex.

Environmental

With a panel, we are dependent on what is happening outside. What happens if snow or dust gets on it?

Batteries

But I think the real weak point is that if you have a solar panel, you also need rechargeable batteries...

Why not rechargeable batteries?

In general, our Pioupiou will be exposed to difficult temperatures. Especially the cold, winter in the mountains.

Li-ion / Li-po batteries

For "home" use, they have good performance and a long lifespan.

But they behave less well in low temperatures. It's the GoPro syndrome that never has a battery when you go skiing...

The big problem is that it is not possible to recharge them when it is less than 0°C. It's related to the internal chemistry of these batteries, and it damages them. As a result, not very practical for spending the winter outside…

Batteries Ni-MH, Ni-CD

These batteries are sensitive to cold and have a very high self-discharge rate. That is to say that they empty themselves over time – even if Pioupiou is not on. Like our old VHF.

Batteries have lead

High self-discharge, especially when cold. That's why we need a big solar panel on our current beacons.

Rechargeable Alkaline Batteries (RAM)

These are a certain type of alkaline battery, designed to be recharged. But only if they have been discharged very little, which is not a problem since Pioupiou consumes very little.

The advantage is that they resist the cold a little better than other batteries. Let's say down to -10°C. They also have a very low self-discharge rate.

This is what I use in the current Pioupious (which seem to be wintering well so far). It's the best compromise I've found.

On the other hand, the lifespan is reduced: 2 or 3 years max.

What batteries?

Lithium

The most efficient. Not only do they have a long battery life, but they are also very resistant to extreme temperatures down to -50°C. They are reliable and do not leak. This is why they are used in military and space equipment, but also for applications designed for autonomy of up to 20 years: alarm systems, water or gas meters, etc.

On the other hand, they are more toxic than alkaline batteries and must therefore be recycled. Two solutions: they can be deposited in the "battery boxes" of the supermarkets, or I will provide you with free pre-paid packaging to send it back to me.

Pioupiou will probably have a battery life of 3 to 4 years with these batteries.

alkaline

Advantages: they are very economical and can be found everywhere.

They hold the cold a little less well, but it should go down to -10°C.

It will still be necessary to avoid stacks too much “ cheap which tend to sink.

With an alkaline battery, battery life should be approximately one year.