Solar Electric Project

[3RRL]

Hayden,
Progress looks great and I can sympathize with your aching back.
I have two of those power vents, but in my hot solar shed it's not enough, even with the hydrogen collecting caps. Your basement will be ten times better though. Is there separation between the controllers and the batteries?
Access is my only concern. We find ourselves checking specific gravity, adding water etc. lol ... What about when you have to change the batteries out 10 years from now and you are old like me?
Also, do you have a spill tray planned for the batteries inside the box?

 

[hayden]

Hayden,
Progress looks great and I can sympathize with your aching back.
I have two of those power vents, but in my hot solar shed it's not enough, even with the hydrogen collecting caps. Your basement will be ten times better though. Is there separation between the controllers and the batteries?
Access is my only concern. We find ourselves checking specific gravity, adding water etc. lol ... What about when you have to change the batteries out 10 years from now and you are old like me?
Also, do you have a spill tray planned for the batteries inside the box?

Hi Rob,

Glad to hear you are checking the battery vitals - it's real important to maximizing their life.

My battery box and power panel are right next to each other, but there is clearance to open the battery box and gain access without the panel and electronics getting in the way. I think in some of the pictures you can catch a glimse of the relative position of the two. I loaded all the batteries with the power panel in place, so that's the ultimate test. If anything, the battery box cramps access to the panels a bit, but once it's all wired up everything can be controlled by the system panel which will be in the kitchen.

The basement has worked real well with my old system to maintain comfortable battery temps. They get down to maybe 50 in the winter, but warm up when charged. In the summer is stays below 80. I don't think I could ask for better than that.

Your batteries in that hot shed does worry me. Would it be possible to insulate the building, or at least the roof to moderate the summer heat?

Replacement 10 years from now? Hopefully I'll still be good and fit. Between the tractor, hand truck, and engine hoist, I got all 12 batteries from the yard, into the basement, and loaded into the battery box 100% by myself. We'll see how good a repeat performance I can do in 15 years. 15 years, that's how long these batteries are going to last .

I don't have a spill tray. I probably should, but I don't. Fortunately the outer case of each battery is itself a secondary containment vessel. The actual cells are another container inside, with two of them bolted together to give the 4V that each battery produces. There's RTV sealer around where the lugs come through the top cover, but otherwise the cover would just lift off. So, my rationalization is that I'm depending on the battery's secondary containment vessel for spill containment. Are you buying it?

I'll probably post some more pictures later tonight with an update.

 

[3RRL]

Hahaha, I know you probably don't spill a drop, but I always use the old Murphy's Law thing ... if it can happen it WILL happen. Hence my battery trays. Especially during filling and checking the SG, there's always some spillage on my end.
I've been thinking of adding another turbine to create additional venting and perhaps a little more cooling during the Summer, but might take the step to fully insulate? I don't know.

The reason I asked about separation between controllers and batteries was because of the potential for an electrical discharge of some kind. As you saw, my solar contractor made me seal the battery side 100% away from the controllers.
Your project is of extreme interest to me and I'm sure I will learn more about my system from reading your thread.
Thanks,

 

[hayden]

Rob, I think separation/sealing of the batteries from the electronics is all about explosion protection and corrosion protection. These are the only two issues I'm aware of. Explosion protection is the biggest issue since the batteries off-gas hydrogen while charging. Venting of battery compartments, either convection or powered, is designed to prevent hydrogen buildup.

I remember when I was in college there was a guy working on his car out behind my apartment. There was a huge bag and he went screaming into his house. Somehow he created a spark and there was enough hydrogen to explode the battery and launch sulfuric acid all over the place, including on him. He was OK, but it sure taught me (and I hope him) a lesson.

The inverters and charges have a number of relays in them which are ignition sources for hydrogen, so you want to be sure the gas doesn't get around the electronics.

One thing I did on my last system, and will do on this new one, is to carefully plug the battery cable conduit that runs between the battery box and the power panel to prevent hydrogen from venting through that path. I've also placed the conduit entrance a couple of inches below where the vent will be, which will help too.

One other thought on power venting - I don't think the in-line power vents that are sold for venting battery boxes will move enough air to impact the temp in your shed. I'm guessing that's what you have? Mine just arrived yesterday and it only moves 5-8 CFM. In comparison, a bathroom vent fan moves 30-40 CFM. If you want to cool the shed you will probably need a much bigger fan than the power vents. But if you put something in, be sure it is brushless and that any switches are outside the battery room (no sparks allowed).

The other issues I've heard of is corrosion from the battery gas. I think the other gas emitted is hydrogen sulfide, but I'm not sure. I gather it's corrosive.

 

[Lil_FarmerJim]

1st I want to thank you for posting so much information on a great project, as a long time lurker on the board and only a recent member I enjoy reading about such wonderful projects. I hope to do something similar at my place in the very near future, assuming the state actually gets the rebate program back.

But I do have one question that I'm suprised that no one else has asked. What about fire danger? I can't see where a wooden battery box will meet NEC or NFPA code for containing a fire. Do you have some kind of plans to put an extinguisher system in the box? I've seen some marine engine compartment extinguisher systems that would help.

Thanks,

 

[hayden]

1st I want to thank you for posting so much information on a great project, as a long time lurker on the board and only a recent member I enjoy reading about such wonderful projects. I hope to do something similar at my place in the very near future, assuming the state actually gets the rebate program back.

But I do have one question that I'm suprised that no one else has asked. What about fire danger? I can't see where a wooden battery box will meet NEC or NFPA code for containing a fire. Do you have some kind of plans to put an extinguisher system in the box? I've seen some marine engine compartment extinguisher systems that would help.

Thanks,

I'm glad you are enjoying the post - I'm having fun doing it

That's a great question, and I think it's an example of one of the many areas where these types of systems are still really immature. I'll have to go check what NEC and NFPA have to say about large battery banks. For better or for worse, these plywood boxes are largely the norm in the industry for off grid residential systems.

It's an interesting tradeoff between wood and metal; Wood's insulating properties makes it much safer when handling or working on the batteries, but it's flamable. Metal poses much more danger with battery handling and maintenance, but would help contain a fire.

I haven't looked into them yet, but I like the idea of an automatic fire supression system. I was thinking about one over the generator, but one over the power system is a great idea.

I have to say that the home-built battery box was my last resort. It's ugly and makes the whole system seem less polished and professional. In looking for alternatives I found:

1) Open rack systems. These are designed primarily for the telco industry and other large UPS installations where you have large rooms filled with batteries. I visited one (computing data center) in Sacramento in the last year and it was quite impressive. This might be what 3RRL used in his battery house where he has the advantage of a whole room (though a small one) dedicated to batteries. In this case, the room is the battery box.

2) Small metal enclosures. These were mostly designed for small, remote communications and signalling installations. They are for much smaller batteries.

3) Mid size enclosures. These are targetted at the small scale RE system like mine, but are still too small or too expensive. I've got one of these for my current system and have been very happy with it. It's a fiberglass/foam box with a lid that encloses the batteries, has a vent hole for easy vent hookup, and is insulated. When I bought it there were different sizes available including one for the 8 L16 batteries in that system. Unfortunately, I couldn't find something similar for the Surrette batteries. I did find a large metal enclosure, but it was way too expensive - something like $5000 if I remember - so much that I dismissed it outright.

The best alternative I could find would have been 3 metal Jobsite tool boxes, but it would have taken up much more space, and the dimensions were problematic given my height restriction in the basement.

If anyone comes across any good boxes, I'd welcome the info for the next system.

 

[hayden]

It's been raining like crazy here, but the other day it broke for long enough to get the remaining batteries around to the basement outside entrance. I ended up take three at a time which lightened the load enough to keep from sinking. It also enabled me to drive over a drier, but more sloped section of the yard without fear of tipping over. Finally, they are all in as you can see in the first picture.

The next shot shows the first interconnect cable. I was playing around with how to best route them to be neat, but keep clear of the fill caps. The routing you see is what I settled on.

Next shows them all interconnected. 12 batteries wired in series with 4V each gives the required 48v. You can also see that I've replaced the fill caps with hydrogen recovery vent caps. These help reduce water loss subsequent filling.

Other than running the main cables up to the wiring panel and breakers, then only thing left is to install the power vent. I'll be sure to do that before hooking up the panels or other charge device.

 

[hayden]

Now on to wiring the panel. The first thing they recommend is to run all the low voltage communications and battery temp sensor wires. There are shielded chases in the back of the wiring panels that aid in keeping the wires isolated from the AC and high voltage DC. However, to get up to the charge controllers they have to venture out into the wiring space. In these pictures you can see the blue wires running into the two charge controllers, then the same blue wires connecting into the inverter. They are standard Cat5 cables, though the electrical protocol isn't ethernet. The silver covers in the lower back of the wiring boxed are the chases.

I also realized that I should not have the battery sensor wire running in the main battery cable conduit, so I ran a second small flex conduit from the panel to the battery box. You can see it in the last picture.

 

[hayden]

Next step was to hook up the AC. The panel comes with breakers for the generator, inverter, and bypass, and it's all prewired for connecting to the inverter so hookup is a breeze - sort of.

From the factory the panel is wired to have the inverter on the left and the charge controllers on the right. In my config I'm reversing it so I can get the panel closer to the batteries and keep the cable run to 5' rather than 10'.

The first thing I needed to do was move the 200A DC breaker for the inverter from the right to the left of the box. You can see it's original position in the first picture.

In the second picture you can see it's been moved to the left closer to the battery box and directly over the conduit entrance. Then I hooked up all the AC lines to the inverter. The idea was to keep all the AC lines grouped in the upper right and along the right side. You can see this in the picture.

The last picture shows the AC connections to the inverter. You can also see the inverter DC cables which also come pre-wired in the panel. Hook up was a bit touchy, again because everything is focused on being set up reverse to what I did.

 

[hayden]

And now for the DC wiring.

When I went to hook up the charge controllers, I had a bit of a surprise. Even though the controllers are designed to mount directly to the side of the wiring panel, and even though there are matching knockouts for running wires, you still need to fabricate and install external conduit between the panel and controllers . The wiring box of the controllers is split into two sections; the DC connections and the control/communications connections, and they are separated by a shield. The knockouts let you access only one of the two sections of the wiring box, and you have to run conduit for the other part. Given my left-side attachment, this meant my coms cables had a natural passage, but I needed to fabricate conduit for the DC cables. What a pain. This of course resulted in two trips to town for parts at about 3 hrs per trip .

Finally, the results are visible in the first picture. I pre-cut and labeled the wires and fished them all through before assembling the conduit ends. I don't know if you've ever tried to thread #6 THHN copper wire through 1" conduit with 90 deg elbows on each end, but it's not a happening thing. Now try 4 wires plus a #10 ground . Threading it ahead of time is the way to go.

The next pictures show each of the controllers all wired up. It's a pretty tight fit, but it works.