Our low-light solar design
The team at The Cacophony Project are currently working on our low light solar design and I thought I'd share a few details on what we're trying to achieve here.
Like all of the technology we create this is an open source design. So anyone else can use it and modify it if they want. We may even sell it as a stand alone product if there was any demand. It will consist of a solar panel and battery pack with a connector that plugs into our camera. It will also have an optional charger for the battery pack, so you can put it out into the field fully charged.
The main criteria is that it will work in low light, so it can be used under canopy, with bad weather, in winter, on a southern facing slope (the batteries may have to tide it through a bit of this). Ideally we also want it to take advantage of bright light, so it can charge quickly if possible. We intend to sell it with a recommended solar panel for our camera, but will provide the option for different solar panels to be connected to match the environment that the camera is going to be in: smaller for high sunshine, bigger for low light.
Our battery pack will support up to 12 18650 cells, connected in parallel. These can be either Lithium Ion (3.7V) or maybe Lithium Iron Phosphate (3.4V) batteries (we need to test that). Our camera operates more efficiently at these voltages because it doesn’t have to step down the voltage.
For our NZ customers we can supply recovered cells from Lime Scooter batteries. These will be cheaper than buying them yourself. We can’t ship used batteries out of the country, so for customers outside of NZ, or those that want to use their own batteries will will supply an empty battery pack. This will include reverse polarity protection and notification if batteries are put in the wrong way.
We have been testing two charging circuit designs a linear charger which is designed for low light and a maximum power point tracking (MPPT) charger which can do both low light and high light charging. You can see the performance of these two circuits in the graph below. The MPPT circuit was able to match the performance of the linear charger in low light, while still supplying much more power in high light. This is the circuit we’re moving forward with and are testing more extensively now.
We're now working on the housing for the batteries and the connectors we're using for the solar panel and the chargers and mounting options. The battery pack should weigh less than a kg and will be much easier to carry than the current batteries.
We don't have pricing sorted out yet but are trying to keep it to about the price of a couple of batteries. This would mean the cost of ownership would be significantly cheaper because of the labour saved in replacing batteries.
We worked out exactly when this will be ready, however we hear there is lots of demand and are working to make it available as soon as we can.