Solar Stuff...

[Irving]

Can you direct me to a place to get a box to hold the battery for my solar project? I'm putting a panel on the roof of my van. I thought the best place to mount the battery would be under the hood, so I don't have to worry about venting it. It'd be a lot easier to do if I could mount it inside the cabin though. Any thoughts on the importance of the venting on a small battery? It's an 18AH battery.

Also, I came across this video the other day and I thought it was interesting.

[Irving]

Never mind about the battery thing. I just realized how stupid easy it would be to mount inside a box and vent to the outside. This may change my whole plan...

However, I'm pretty shaky on running the numbers to make sure that everything is compatible with each other as far as size of battery vs size of panel.

Can you talk a little bit more about what you expect to be able to charge with your system? I've got a 50W panel and an 18AH battery and I have no idea how long it would take to recharge the battery, or how many devices I could charge at the same time.

[Grant H.]

2. Solar Power solution for network gear in my house.

A friend of mine called and offered me 26 7.5AH 12VDC batteries for a great deal, since he got them as scrap when he refreshed a set of UPS's for one of his customers. They all tested at 12.3VDC or higher, so they are all good.

My plan is to move my fiber modem, router, switch, and access points to solar. The fiber network is all on emergency backups, so it all stays up/functional even when the power is out. So, if I keep all my gear powered up, I end up with internet access even with power outages.

Pointless? Sort of, but I couldn't pass up the deal on the batteries, and I don't have a better use for them right now.

So, with 26 batteries, I used 2 in the previous project, and used the other 24 for this. I wired them into 6x 48VDC cells, and will then use a collection of smaller solar panels wired into 48VDC arrays. I spotted an auction on eBay the other day for 48V specific controllers, and gave $15/ea for them, hence my 48V plan currently.

Morningstar PS-15M-48V - Used, but cheap/functional on eBay, so why not???
0518171949 by ARNEWB, on Flickr

Batteries placed into boxes temporarily, wired together to put on a trickle charger till I get it all finished...
0518171932 by ARNEWB, on Flickr
0518171937 by ARNEWB, on Flickr

The cabinets were free to me when I replaced them with metal boxes for a customer, so that's why I used two to start, but when I get them mounted in the backyard, I will condense them down and have the controller and the inverter mounted in one of them.

I'll keep this one updated as well in case people are interested.

[Grant H.]

Can you direct me to a place to get a box to hold the battery for my solar project? I'm putting a panel on the roof of my van. I thought the best place to mount the battery would be under the hood, so I don't have to worry about venting it. It'd be a lot easier to do if I could mount it inside the cabin though. Any thoughts on the importance of the venting on a small battery? It's an 18AH battery.

Also, I came across this video the other day and I thought it was interesting.

These guys would be a place to start looking for enclosures for in your car. https://store.solutionsdirectonline.com/storefront.aspx

What dimensions do you need? I may have used ones that I would sell cheap.

The video is similar to what I want to do with the supercaps in my solar usb charging setup. His solar controller makes the supercap pack very limited, and he acknowledges that in a different video. If you size the supercap pack to accommodate the VoC (Voltage, Open Circuit) of the solar panel (will be ~17-18VDC on a 12VDC panel), then you can eliminate the solar controller (less cost, less current draw), and it starts charging as soon as sun hits the panel. The use of a buck/boost DC-DC converter allows one to extract a lot more of the energy stored in super caps because it allows you to use 3VDC to 20+VDC out of the pack.

[Irving]

I find all this super capacitor stuff very interesting, and wish I understood it all better.

Thanks for the link to the enclosures. I think I may have to post up what I want to do in the DIY forum and make sure I have a system with compatible components before I move forward with anything, just in case I decide to go with a different sized battery, panel, or both.

[Great-Kazoo]

Grant, thanks for the nice write up. This project seems more reasonable for the entry level person.
Knowing you barter or buy used when possible. What price point for those who don't know how to barter would one be looking at for your finished project ?

Then there's weight of unit vs portability, or will this be a stationary one ?

Of course the final item would be footprint. Working with limited space could be (for some) a deal breaker.

[jerrymrc]

I used cast-off AGM batteries as well. Portable X-ray machines use a bunch and they have a mandatory replacement of 24-36 months. The ones I got were 29Ah each and I used a bank of 10 for 290Ah of capacity. 100 watt panel and a charge controller are used in the second garage. I have 3 strings of LED's that light it all up. Under normal conditions the panel put out around 4A and the lights draw about 5A.

[gnihcraes]

@ Grant H,

any recommendations of DC/AC Inverters? I need a good pure sine wave one. Difficult to find anything that seems decent yet reasonable in cost.

800 watts minimum, yet I don't need much over that. (startup requirement is 800 watts of a device, run time is much less than that I believe)

[Grant H.]

Never mind about the battery thing. I just realized how stupid easy it would be to mount inside a box and vent to the outside. This may change my whole plan...

However, I'm pretty shaky on running the numbers to make sure that everything is compatible with each other as far as size of battery vs size of panel.

Can you talk a little bit more about what you expect to be able to charge with your system? I've got a 50W panel and an 18AH battery and I have no idea how long it would take to recharge the battery, or how many devices I could charge at the same time.

Sure. I'll run the calculations for my internet gear as an example.

Currently, (I have new gear on the way that is more power efficient/better technology anyway) I have 2 devices that I want to power to keep my internet service up during a black out:
1: Fiber Modem
2: Asus Wireless Router

Start with looking at the devices to see what they require as power input on the back/bottom:
1: Fiber Modem - 12VDC @ .4A
2: Router - 19VDC @ 1.58A

These numbers are usually, 99% of the time, the "worst case" numbers for those devices. If you want to, you can get a power meter and plug them in and see how much they actually draw on average and build against that. I don't like that method, so I always use the "worst case scenario" and pad that just a little.

Convert them to watts: VDC*A=Watts
1: Fiber Modem - 12*.4= 4.8W - I rounded this up to 5 Watts for my calculations
2: Router - 19*1.58= 30.02W - 31 watts - Power hungry little bastard...

Add them together, 36 watts, and multiply by 24 to get the total number of watts you will use in 1 day. 36*24= 864 watt hours per day.

So, the total consumption that I need to offset with panels and sun is 864 watts per day. If we assume we only get 4 hours of "full" sun in the winter, again the worst case scenario, that means we need 216 watts of panels to provide each day worth of usage. Now, that number has to be larger, because if you go days with less sun, the batteries will get pulled down to make up for the lack of solar. For my own non-critical projects like these, I tend to use 125%, so it would take 4 days of full sun to make up for 1 day of no sun (black blanket over the panel type of no sun). Even on really bad days, the panel will still generate some power, so I build on the smaller size. When I am building for a customer, and it's critical, I usually use 150-200% on the panels to make the system recover as quickly as possible.

So, 216*1.25= 270 watts of panels for this system. Part of the reason I am getting much more power friendly, albeit better network gear!

On to the batteries:

We know we are using 864 watts per day, so we can divide that by the voltage of the battery bank we are using to find out how many amp hours we need in a day. Since I decided to screw around with 48V on this system, we divide by 48.

864/48= 18AH per 24 hour day. Now, we have to account for batteries inability to drain to 100% and recover, so I multiply that by 2 so we only reach a 50% discharge level. Less discharge is better for lead acid, but 50% is safe.

So now we know that I need 36+AH of batteries to run my internet gear for 1 day on batteries alone.

Multiply that by the number of days you want to be able to use the gear without sun (autonomy), I said 3 days in my case, so 36*3= 108AH. I didn't get anywhere near that in the cheap UPS batteries, which also drove my decision to get new/better/less power hungry network gear.

So, that's kind of a rambling explanation of how I calculate solar numbers.

As for your 50W panel and 18AH battery, your 50W panel will provide just over 4 amps with full sun. Now, mounted flat on the roof of your van, it will have full sun for a short period each day during the summer, but significantly less during the winter. It will still likely be plenty to make up for a 50% discharge of your battery on any day.

As for how many devices you can charge, if you figure you have 9AH to use out of the battery, then with no sun you can charge up to 9AH worth of devices, and the battery will still recover when the sun comes up. I know it sounds dumb to say that that way, but you can usually find out how many mAH's your phone/tablet/etc battery actually holds. My LG G3 has a 3000mAH battery, that's only 3AH. You can probably safely plan on a full recharge of your phone being less than the actual battery rating, but for the margin of error, I just use the full capacity. But you could charge 3 phones from dead to full without hurting your 18AH battery. As for how many devices you can charge at one time, that is more a function of the 12VDC-5VDC charger that you choose. Your standard 2.1A USB charger is going to be 2.1A @ 5.1-5.4VDC so worst case, that's 11.34W, which on the 12V side is only .945A. Most batteries have a spec for max discharge current, but its usually in the dozens to hundreds of amps.

If the sun is up, then the solar controller should charge the battery to max capacity, then shunt any solar current to the load output of the controller, which is what you would want to wire your charging ports to, so then you can charge even more devices because you aren't pulling on the battery.

Hopefully my rambling helps.

[Irving]

Very helpful, thank you. I'll expand on where I get confused later when I have time.