Solar Power Considerations
Well, I really need to get some solar power going. I'm too dependent on coffee shops and places to charge all my gear. Normally, this is the kind of thing I would love to spend a lot of time planning and designing. However, I need to put something together relatively quickly which dictates using off the shelf components. Unfortunately, I won't be able to use the open source Libresolar MPPT charge controller for this reason.
I like the compact form factor and portability of units like the GoalZero power packs. I don't want to use one of those because of the inability to expand capacity as needed and the price premium. For the portability factor, I'm set on LiFePO4 chemistry batteries because of the higher energy density, and longer life over alternatives such as lead acid. Yes, they are more expensive up front, but over the lifetime of the system, they are cheaper.
I don't want to mount panels to the exterior of my car for a number of reasons. First of all, I don't have a roof rack and aftermarket ones are expensive. Also, it makes it more obvious that I'm camping in my car and it's more work. Therefore, I'm thinking I'll just stick them in the back window and park with the rear towards the south when they need to stay in the car such as in urban camping situations. When I get to boondocking, I can pull them out and position them optimally towards the sun. This would also allow me to park the car in shade so that it doesn't overheat, but still get sun on the panels. When in the car behind the window, the panels will not be getting as much light so low light/partial shade performance is important. So given all that, here's what I've come up with.
I found these 50W Sunpower flexible solar panels that are highly efficient, light weight, compact, and durable. They are quite a bit more expensive that the standard framed panels but I think the advantages are worth it. There is also a 100W version, but it wouldn't easily fit in the back window due to it's size and the operating voltage may not be sufficient for the charge controller which I'll get to.
The cheapest place I found them was at Wholesale solar for $138 + Free shipping.
The best charge controller I could come up with in the time I had to look was the Victron SmartSolar. They have different models for different system voltages and currents. The controllers have bluetooth built in so you can monitor power production and history from your phone or computer which is nice. Also, some of the software and data interfaces are open source, unfortunately the whole device isn't. It is an ultra fast MPPT controller which is important because it will have have better low light performance than a PWM controller. Additionally, the panel voltage can be higher which will result in less power loss in cabling, not that there will be much. I think I'll have two sets of cables, a short set for when in the car, and a longer set for outdoor placement. That way I won't be taking more power loss in the car than I have to. Again, not the cheapest option, but a quality option.
There is one other thing to consider with this controller. It requires battery voltage + 5V on the solar panel before it will start up. I'm not really sure if one 50W panel will work. The startup voltage would be:
14.6V + 5V = 19.6V s
The solar panel voltage specifications are:
18 Vmpp
21.5 Voc
I could always add another one in series to bump up the voltage which would improve the efficiency anyways, but it also increases the cost.
The cheapest place I found it was on Amazon for $108.80 + Free shipping.
For the LiFePO4 battery, I've been looking at 12V 10Ahr batteries from various manufacturers to get me started. The one that looked the highest quality was from K2. It's 122.8 Whr which isn't a whole lot but it'd be enough to get me going especially for my phone. It has a built in BMS to balance the cells and protect against overvoltage and short circuits. I could always add more in parallel to increase the capacity if I need it. Additionally, all of my devices have their own internal batteries so my effective capacity is increased beyond this main battery. I also have a 55 Whr USB power pack for my phone. So during the day extra power can charge these batteries in addition to the primary battery.
The cheapest place I found it was on Amazon for $159.84 + Free shipping.
I'm a little less certain on a power inverter. I would only need it for my laptop and hair trimmers really. I could use a cheaper 12V to 5V DC/DC converter for all the rest of my stuff which can be charged via USB. I am currently considering a 350W victron model with pure sine output.
The cheapest I found it was on Amazon for $90.99 + Free shipping.
So that total cost excluding cabling and mounting hardware would be:
| Cost | Part |
|---|---|
| $138 | 50W Solar Panel |
| $108.80 | Charge Controller |
| $159.84 | Battery |
| $90.99 | Inverter |
| - | - |
| $497.63 | Total |
We'll have to see. I don't want to dig too deep into my savings now and that would be a pretty big hit.
You are showing a great example of bootstrapping a solar power system @vanarchist.
So in summary, this system you have put together is enough to power your laptop computer and hair trimmer use. What else do you use it for?
It's for my car camper. Phone and camera as well. Thinking about powering the car stereo and some lights also. Might need to add some battery capacity if I wanted to do this at night for anything more than a couple hours.
https://smile.amazon.com/gp/product/B01M260BAN/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1
This might be a comparable alternative... Its an all in one solution. You're probably looking into expanding and adding batteries, though, and I'm not sure how easy that would be with this system.
Ya, modularity and expansion are the main reasons I would prefer to build something out rather than an all in one solution.
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