How to Build a Small Solar Power System | Hacker News Reader

How to Build a Small Solar Power System

solar.lowtechmagazine.com

67 pointsAkashic10117 comments

I have been building, rebuilding, optimizing several small-scale solar installations off-grid for nearly 30 years. These systems need to "just work" for guests and family, not be so finicky and fragile that people are afraid to use them.

The number one innovation that has made off-grid life more than just tolerable is low-voltage LED lighting. It's wonderful to be able to work in a well-lit space without worrying so much about battery life. All lighting is on mechanical timer switches, walking out of a room and leaving the lights on is a bad habit that's hard to break.

The next innovation to increase utility and practicality will likely be LFE (LiFePO4) batteries. In 30 years I have worn out or accidentally destroyed dozens of lead-acid batteries in various forms. They are fragile and heavy. Moving them by boat is brutal. I have high hopes that my current set of replacements will be the last ones for many years.

Electrical loads keep increasing. First lights, then radios and phones. Now laptops and a long-range WiFI link for remote work, and overnight power for CPAP machines. Next up will be DC solar powered refrigeration to displace propane. That will require more panels, more batteries but will have an immediate and long lasting benefit.

It has been a long and mostly satisfying project which has benefitted everyone around me.

likely be LFP? I think those batts are already available. The problem is they arent that great. Power density is low, they are advertised for 2000 cycles so I guess reallife is sth like 1500, so around 5 years only. We really need great bettery innovation with decent lifetime (minimum 10 years, 20 years preffered) and decent energy density. Once that will kick in, we could really start smart grid revolution.

I am watching performance of the new LFP battery. Weight is not an issue in a stationary installation like mine, longevity and ruggedness are everything. The space is unheated throughout the winter and cold has done terrible things to previous batteries.

So far the one LFP battery I have deployed has been operating properly but there were some initial compatibility issues - my solar regulator did not interact well with the BMS despite alleged compatibility. That cost me several hundred dollars in downstream equipment damage due to voltage surge.

I am watching the new solid-state lithium batteries with great interest.

Oh I read the wiki article about them. Looks interesting indeed. Decent density, they claim 10000 cycles so if its real world 5000 cycles to start with thats solid 10 years!

What about sodium batteries?

> Even under frigid conditions, sodium-ion batteries can maintain a high degree of ion mobility within their electrolyte. This increased mobility ensures that the battery can continue to deliver reliable performance when temperatures drop.

https://nadionenergy.com/why-sodium-ion-batteries-perform-we....

Or is it temperature cycling that causes your problems?

Sodium batteries aren't exactly commodified yet, LFE is readily available and not terribly expensive.

For the most part I don't actually need batteries that work in the freezing cold, so much as survive it unmaintained for months at a time. I had solar panel damage last winter that allowed one battery to discharge enough to freeze. That is fatal to a standard flooded lead-acid battery.

If my test battery survives this winter then I will consider using the same type to replace lead-acid ones as they age out.

Lithium Titanate will probably last 20 years. It's just expensive. AliExpress sodium ion batteries are claimed 4k to 6k cycles, no idea if that's real but it's cool to see stuff happening there.

Ever use the EG4 18KPV? I’ve been looking to build a grid tied off grid-style system because it’s very difficult to unplug where I live legally (thanks PG&E!) and they look fantastic. Just curious if you’ve ever used them?

No grid to tie into, so no need for that level of interoperability. I'm more likely to centralize my battery storage and solar collection once I understand the tax credit ramifications of a non grid-tied system.

Gotcha. They make a product called the eg4 6000xp for fully off grid applications that looks kinda awesome.

I just want to unplug. I think that you can claim the full 30 percent if you’re in the US.

I looked it up for you and here’s what I found…

https://www.energy.gov/eere/solar/homeowners-guide-federal-t...

Solar is such an amazing tech. It's not perfect, but what else lasts 30 years, but doesn't involve compromising and giving up features? Even people who hate green energy all seem to like solar for some things, they just don't believe it's the answer to everything.

The batteries are the weakest link, but now we have LTO batteries (20k cycles), and Sodium ion starting to be available.

If you’re looking to do something a little bigger, I think these guides are better:

* https://faroutride.com/electrical-system/

* https://www.mobile-solarpower.com/

This is nice - I built a system along these lines about 4 years ago, and I struggled to find a comprehensive resource like this.

In particular I like the ‘do you really need a battery’ part. My system is over-spec (partly because small solar panels aren’t really worth buying any more) but the battery is really overkill for the lighting setup it currently powers.

The nudge to think about using a convertor plus Lithium-Iron power banks would have probably made me think about switching to that approach until I needed higher amounts of storage.

I've been wanting to build a solar powered above-ground pump for a waterfall into my pool. The pump will not be submerged, so I'd like to use a well pump.

There are a ton of dc pumps that run directly off solar.

I originally heard about a company called SunRay doing it but I’ve seen seen them on Amazon and heard of a bunch of other ones.

There are also a bunch of DC air con units and heat pumps.

We live in good times for off grid and hybrid solutions.

The concept of direct drive solar is very interesting to me.

One thing about solar is that existing commercial solar generators are really good. They're cheap and reliable and packed with features.

Plus, they're self contained and protected and have built in CYA. Not that it's all that hard to do this stuff safely, but off the shelf has a certain peace of mind.

LiFePo4 ones are meant to last 2000 cycles. They can charge via USB-C as well as from solar, and they have inverters as well.

Obviously, anything lithium isn't environmentally perfect, but I would imagine it will all be recyclable eventually, if it fails before then, just keep it and wait, it's small.

There's a bit of environmental issue with the non-replacable built in battery, though, but one could probably get around that with some hacking if they really want to replace it.

Portable folding solar panels are also insanely cheap for what they offer, sometimes they're less that $1/W, and they often have USB-C output to direct charge devices, in addition to 2.1mm.

Lithium does not like to be charged below freezing, which is another advantage for having everything compact and portable so you can bring it in.

I think that if I were going to build a fixed and permanently installed small solar setup, I would just want a panel with an outlet inside for a solar generator.

I'd add a switch, fuses, a reverse blocking diode, and a decent quick connector of some sort.

I might also add a voltage meter, and perhaps a USB charger, or even cigarette lighter outlet(with a 2 or 3A fuse, at most, definitely wouldn't trust a cigarette plug with 10A)

Most likely, I'd use Anderson PowerPoles for the main output, they seem to have a semi-standard for solar power (https://oh8stn.org/blog/2020/07/11/when-standards-get-in-the...)

Then, I would make a pigtail (With it's own inline fuse, in case the panel ever gets swapped with a much bigger one!) going from Anderson to 2.1mm, and plug that into the off the shelf solar generator.

I'd probably make a shelf for it, and position stuff such that the cable wouldn't easily bump into some rusty bucket of screws and short out.

In all the research I've done, aside from using batteries with built-in heating, I've never seen any easy way to recharge lithium in very cold temperatures.

The closest I've seen to a solution would be insulating the battery, and using two temperature switches, one to cut charging below zero, and one to turn on heating to warm it above zero using the solar energy. No idea how practical that would be, though.

Or, just using ultra capacitors, as I'll probably do if I get around to building a Meshtastic solar repeater.

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