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Making a solar-powered live audio stream


Listen to the stream:

View stream on the soundmap ("brisbane - floodlands")
Just take me to the pictures

1. Making a power budget
2. Dimensioning the panels and battery
3. Equipment list
4. Other considerations
5. Buying the stuff
6. Putting it all together

I’ve been looking for ways to learn more about using sustainable energy ‑ it’s become more than clear that as technology users, our energy use is out of control, and much of it is generated using emissions-producing unsustainable fossil fuels.

I wanted to try and find some practical ways I could reduce my energy usage footprint and at the same time learn to be a little more self-sufficient. Living in Queensland, where there is no shortage of sun at any time of the year, going solar made sense. However, as a non-house owner I’ve never been able to install solar panels and take advantage of the abundant sunlight. My current house has a backyard with and old shed in it though, so I thought it could work as a good place to experiment with a portable solar panel.

My motivation for this was not only the practical side of learning how to live a lower-impact life, but to potentially use renewable energy in my art work. Since my work is of and about technology, I want my work to start interacting with the natural world a bit more, in ways that can talk about its impact on the environment*, and in ways that the environment may be able to shape the work itself – maybe we can learn something about our world through such mediation? Who knows. I initially started looking at hydropower because I really wanted to set up a live audio stream of an actual stream, powered by said stream, but it turns out you need a great volume of water rushing by – like a waterfall- to produce the kind of electricity that would be usable by a Raspberry Pi or similar.

(* not to ignore the impact of mining for the raw materials that make up solar panels and batteries on the planet and the people who do the mining!)

So with the stream-powered stream idea back on the shelf (how would I get access to set up a bunch of equipment in a stream anyway?), I decided to make use of what was available to me – the sun. I had been listening to some really nice streams (like the Pond station by Zach Poff) from the grounds of WaveFarm in upstate New York and found that they contributed to the Locus Sonus project. Locus Sonus has been operating since 2006, and features a soundmap of live audio streams from places around the world. You can select and listen to a stream from the soundmap, and mix them together if you like.

The great thing about Locus Sonus is that they make it easy to contribute by providing an operating system image to flash your Raspberry Pi with. This includes their streaming server software, and tweaks to make the Pi use as little power as possible (so there’s no GUI for example). They also provide a howto with recommended hardware, which I took some guidance from.

I really knew next to nothing about power, so I took a look at Dave Evans’ project, where he set up a solar-powered WiFi hotspot in a permaculture garden. This project also used a Raspberry Pi, so it gave me confidence that I could make it work. I should also acknowledge insPiration from Low Tech Magazine’s solar-powered web server as well.

So after a bit of research I had learned enough to figure out that I’d need three main components:

This is, of course, in addition to the thing you want to power, which in my case was a Raspberry Pi, which in turn powered a USB microphone adapter, which provided the phantom power that the condenser microphone needed.

Disclaimer: This is just the way, I , a complete novice, figured out how to make this thing work. I cannot vouch for the correctness or safe-ness or long-lastingness of this setup. On that note, I'm happy receive corrections also.

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1. Making a power budget.

The first thing you need to know to set up a solar system is how much energy your equipment is going to be consuming. You can usually estimate this based on specifications, but in my case I knew the Pi wasn’t going to be running at its maximum, and I wasn’t exactly sure how much power the microphone and adapter would use either.

Anyway, a power budget will at least give you a rough idea of how much power you will consume. Once you are able to set everything up, you can use a power meter to tell how much your equipment is actually using.

What you need to know at this stage is the voltage of your equipment – in my case the Pi uses 5v (this is the voltage of USB, which is why you can run them off a USB port or charger). The base standard USB supplies 1 amp, though newer USB standards (and the official Pi chargers) can supply 2. I made a guess that my Pi would run OK off the minimum (and tested it using mains power to make sure).

So I have 5v, drawing 1 amp. Given that I want this thing to run 24/7 I need to take that into consideration too. From here we just multiply: 5v x 1A x 24hrs = 120 watt hours (Wh).

Apparently solar panels are not 100% efficient, so it’s recommended to add 30% to your calculation. So:

120 Wh x 1.3 = 160Wh

At this point I should have added in the estimates for the microphone and adapter (I’d read somewhere that 20mA was about right), but given that the audio stream ran just fine off mains power with a 5v 1A phone charger, it was clear that the 1A supply was able to give this setup everything it needed.

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2. Dimensioning the panels and battery

A few things I’d read said that your solar panels should be capable of filling the battery in a day, and that the battery should be able to hold 2 to 3 days worth of energy in case of less than ideal weather. I guess this one is your call, and based on how important it is to have your equipment available.

I looked up the amount of full sunlight that Brisbane gets over the year on this handy page, and the minimum seemed to be an average of 4.1 hrs per day in June.

Given that I wanted to produce 160Wh, over 4 hours I’d need 40 watts coming from the solar panel. To produce double I’d need 80 an watt panel, and for 3x I’d need a 120watt panel.

So knowing that I would be using a 120 watt panel, I could figure out the size of the battery I needed.

A thing to note here is to be sure of the output of your solar panels – many I looked at produced 18V at a maximum (maintaining a consistent 12V is one of the regulator’s jobs). I read conflicting reports about whether to use 18V or 12V in this calculation, but I ran with 18.

Taking in the 120 W, you divide this by the voltage and it gives you a number in amp hours. Here you apparently should add in an extra 15% for battery loss. So:

120 / 18 = 6.6

6.6 x 1.15

=7.6Ah

to be sure, I did the calculation for 12V and it came to 15Ah. Keep in mind that this is for 3 whole days of battery storage, so I thought that getting a 10Ah battery would do the job either way.

The final thing to figure out is the size of regulator you need. These things have a certain amount of amps they can handle (and if you overload it...it cuts out like a circuit breaker, I think?), so you just need to make sure it accommodates your needs. For this step you take the wattage of the solar panels and divide it by the solar panel’s maximum output voltage. So:

120/18 = 6.66A

I had also seen some good deals on 160W panels, so I calculated for that too

So a 10A regulator was going be just fine.

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3. Equipment list

So I’d figured out I needed:

a 120W solar panel

a 10A regulator

and a 10-15Ah battery.

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4. Other considerations

The only other challenge I foresaw was converting the 12v power to 5v to power the Raspberry Pi. I saw some stuff online about cigarette lighter adapters, but I also saw that some regulators had USB ports on them (presumably for charging phones). This seemed to do the work for me, so I looked for a regulator with a USB port (making sure it provided 5v 1A power).

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5. Buying the stuff

I found a solar kit designed for caravanning or camPing that included a portable 160w panel and a 10A regulator with 2 USB ports. It was selling for 40% off and was much cheaper than everything else I’d been looking at, so I nervously ordered it. (note: 1 week in, it seems to be working fine?).

I also bought a 12 volt 12Ah voltage regulated lead acid (VRLA)battery at my local Battery World.

I already had a Raspberry Pi and a nice long USB cable from a previous project, so I used those.

I ordered a Blue microphones Icicle USB -XLR adapter, as recommended by the Locus Sonus streambox guide, and bought a similar looking measurement microphone – a Behringer ECM8000. The mic recommended didn’t seem to be available anywhere.

I also needed to buy a weatherproof box, some gaffer tape, wd-40 and cling wrap.

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6. Putting it all together.

The solar panel package was cheap, and with cheap stuff there’s always a catch I suppose. The regulator came all wired up (great!) and attached to the frame of the panels with pop rivets (not great). I didn’t really want the regulator and its USB ports exposed to the elements in the long term, and given that the existing wiring was short (putting the regulator as close to the panels as possible is ideal), there wasn’t really anywhere else I could put the regulator, save rewiring everything. Perhaps in the future if it becomes a problem I’ll either find a weatherproof box for it, or protect it somehow. For now though, I’ve used a sandwich bag and gaffer tape to protect the USB ports from moisture. Hopefully I got a good enough seal or it will have the opposite effect. I’ll continue to monitor the situation.

I’ll let the Pictures tell the story here, but in short:

solar panels
||
||--regulator---Pi---adapter---microphone<
||
battery

Note that when you’re connecting the battery it’s important to connect the positive terminal LAST to avoid a short circuit.

I’d also read some DIY microphone waterproofing tips online, and from them I decided to:

- spray connections with WD-40 before covering with gaffer tape ( I know it leaves residue but as a permanent (or at least long term) installation, that’s not a worry to me.

- cover the diaphragm of the microphone with cling wrap and seal with gaffer tape.

There’s still the issue of how weatherproof the exposed lengths of cable (USB, microphone) are going to be.

Right now the solar panel is on the roof of the shed, but I may have to move it around to figure out the best spot for sun exposure – there are quite a few trees providing shade, which is usually a good thing, but not for this project.

I also put the Raspberry Pi and mic adapter in a weatherproof box, which had some nice rubber-sealed holes for cables, but it really impacted the ability of the Pi to Pick up a decent WiFi signal from my house, so I leave the lid open and hope that the geckos and snake that live in the shed don’t interfere.

The battery came with T2 connectors and the solar panels had Anderson connectors (the chunky grey plastic ones) and alligator clips so I’m using them for the battery, but surely there is a better/safer way for a proper installation.

Here are some photos of the project as it’s currently installed. Obviously there is a lot that can be improved, especially if I’m going to have this running permanently, but this is what it looks like 1 week in.


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