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Solar Panel System Design – My Experience

What was I Trying to Accomplish with this Solar Panel System?

The point to this solar panel system was to allow me to charge/use assorted small electronics in an extended disaster scenario, such as my wife’s Ipod phone, my Ipod, recharge AA and AAA batteries, and maybe some limited use of my laptop. I wouldn’t mind if I could also use our portable DVD player for the kids entertainment but it’s not on my priority list.

My Background

Let me first state that I am NOT extensively knowledgeable in either DC systems or electronics. Everything I share below is what I’ve pieced together in attempting my first solar system experience. Please also understand that the reason I’m sharing my first solar panel system experience is because I had a difficult time myself finding reliable information that explained how to build such a basic DC solar system. I always felt like I had to be an electrical engineer to understand their instructions. Basically, this is my attempt to demystify the process.

The Components

There are several components required to put this system together, here they are…

Part 1: Solar Panel

Obviously there’s no solar system without a solar panel. There are certainly many to choose from, so how do you know which one? From what I gathered, you at least want a solar panel that is equal to or greater than the maximum voltage required to fully charge your batteries, which is about 14 volts.

Long story short, given that you probably won’t get 100% efficiency out of your solar panel most of the time (due to limited sunshine, clouds, poor solar tracking, wrong time of the year, etc) then you want to over-compensate for this problem with a larger panel. I gather this should be more than 15 watts (a common panel size) and so the next largest size is 20 watts, which is what I have.

Of course, it’s not as simple as just buying any 20 watt panel. What you’re really looking for is the output voltage to be significantly larger than 14 volts; this panel, for instance, outputs about 17 volts under load which is just about right (as near as I can tell) to fully charge my batteries. I encourage you to read this on the relationships between amps, volts, and watts to get a better understating of how they relate.

Part 2: Charge Controller

The charge controller is a critical piece of your solar system in that it is the brains of the operation. While I’m sure that smarter people than I have figured out how to charge batteries and stuff without such a device, I wouldn’t have a clue how to do so. Besides, the charge controller makes everything easier, definitely safer, and probably extends the life of your components as well.

So, how does it work? It’s fairly simple, actually. The charge controller has three connections: one for the solar panel, one for your battery (or battery bank), and one for the device you want to use. The best part is once everything is connected you don’t have to worry about ensuring your batteries are properly charged (even overcharging) or swapping battery connections from the solar panel to your output device (the auxiliary plug). IMO, it’s a must have item.

This particular controller is rated up to 10 amps, which is more than adequate for this system as well as any substantial upgrade. If you think you’ll want even more power then perhaps a HQRP 20A Solar Panel Battery Charge Controller is more appropriate.

Part 3: Deep Cycle Battery

I ended up buying two of these batteries (UPG UB1280 Sealed Lead Acid Batteries) with the intention of storing one as a backup. I was trying to be cheap as well as to have some redundancy in the one piece of my solar system that I knew would go bad eventually. Unfortunately, I larter realized that I couldn’t do this and still expect the battery to work when I needed it to. So, I bought one deep cycle battery (12-volt 35Ah wheelchair battery) instead, which gave me more power and was a bit easier to connect because there was only one battery to deal with.

Anyway, what you need to know about solar system batteries is that they MUST be truly deep cycle batteries and NOT the normal SLI (Starting, Lighting, Ignition) batteries we use in vehicles BECAUSE the SLI batteries are NOT meant to be discharged any more than a few percent of their total capacity, which is not at all plausible in a solar system. The way to tell if a battery is deep cycle or not is whether it’s listed as having cranking amps or as having amp-hours; if it lists cranking amps then the battery is NOT what you want. Rather, deep cycle batteries are listed in amp-hours, that is, how many amps of current it can supply in X number of hours. SLI batteries, on the other hand, provide A LOT of power in a very short period of time and are not designed to provide long durations of power.

The battery I bought is rated at 35Ah. In other words, this battery could theoretically supply 1 amp for 35 hours or 35 amps for 1 hour or some combination in between. Of course, the reality is quite a bit different given that you wouldn’t want to discharge your battery below 50% charge (that’s what they say anyway), so I’m limited to something more like 17Ah total for this battery. As an example, if I’m charging my AA batteries using the battery charger I have, and it pulls approximately 4 amps/hour, then I could use this device for about 4 hours before discharging my deep cycle battery to 50% charge.

The other thing you should know is that your solar system battery should be 12-volt if possible. While you could use 6-volt batteries there’s no reason to since 12-volt batteries are just as plentiful and suited for such a system. For more details on deep cycle batteries I suggest you read this battery FAQ.

Part 4: 12-volt Power Outlet and Adapters

Another piece of the puzzle you’re going to need is a basic 12-volt power outlet (a.k.a. “cigarette lighter outlet”). You’ll use this outlet to connect your DC applications to the solar system, so ensure it is fairly rugged because it will get a lot of use.

A few points to consider: You’ll want to ensure that it is an add-on style outlet so that it has bare wires to which you can connect it directly to the charge controller. It would also be advantageous for the power outlet to have an in-line fuse, which I suspect most do. If you prefer, you can also find this adapter at a local Radio Shack like I did, but I think I would have opted for the outlet I have shown above due to it’s–seemingly–more rugged design.

Part 5: Assorted Components

There are a few additional pieces that you need to bring everything together…

Power Pole Connectors

Originally I figured I didn’t need these connectors. To be honest, you don’t “need” them (you could use just wire nuts instead) but they sure do make everything easier, and probably safer too. This is especially true given the expectation that you could be connecting and disconnecting a variety of components (solar panel, trickle charger, etc) multiple times which is A LOT easier to do when you have these. A pack of four red and four black should suffice. Remember, these connectors also make this project safer. I couldn’t figure out how to use them at first, but I found this power pole connector tutorial that made sense.

Primary Wire

You’re going to need a bit of wiring to bring everything together. What you’re looking for is primary wire (a.k.a. automotive wire). For such as system I would suspect that anything between 12 gauge and 16 gauge wire would suffice. (Note that the smaller the number the thicker the wire and hence the more current it can handle without bad things happening. For example, 12 gauge wire is thicker than 14 gauge wire which is thicker than 16 gauge wire). For larger whole-house systems you would want much thicker wire but there’s no need in this system.

I went with 14 gauge wire for no other reason than because I wanted a bit more safety. I also choose to buy both Red Primary Wire – 20 ft. and Black Primary Wire – 20 ft. in order to ensure positive and negative connections are clearly marked. If you prefer, you can easily find this wire locally such as at Walmart, Radio Shack, or an auto parts store. If you think you’re going to expand then just go with 12 gauge wire; you can’t go much bigger because the power pole connectors would accept larger wire.

Replacement Fuses

I would also suggest you purchase packages of replacement fuses appropriate to your equipment. Typically these are tube fuses that are rated between 5 or 10 amps at either 125 volts or 250 volts. I suggest that after you buy your equipment you purchase the appropriate fuses for that component since that’s the best way to know what fuses to buy.

Part 6: 12-volt Trickle Charger

A basic trickle charger is another item that I didn’t think I would want or need until I later realized that I couldn’t just store these batteries indefinitely (disconnected, of course) until I needed the system.

The thing is that batteries are best stored with a full charge. Although deep cycle batteries, in particular, are able to sit for a month or two without fully discharging, it’s just not good practice for any battery. As such, my first thought was to simply charge them periodically using my solar panel.

Unfortunately, this posed two problems. First, I recognized that while I may choose to do this for the first few months, it was inevitable that the newness would wear off and I would probably neglect them and allow them to discharge too far too often. Second, my understanding is that even allowing these batteries to discharge to, let’s say 20% over a month or two, still wears them down and thereby limits their total available cycles and, hence, their useful life.

Since the point in this setup was to have a system that I could rely on if/when I really needed it, a trickle charger keeps my batteries ready to go at a moment’s notice. Again, while not necessary, I encourage you to have one. This Battery Tender Junior 12V Battery Charger I have pictured above got good reviews and I’ve been pleased with mine thus far.

How It All Went Together

1) The charge controller was attached to the battery with heavy-duty velcro I had laying around the house.

2) This bundle of wires will attach to the solar panel (not shown) using the power pole connectors discussed above (and detailed in item 3 below). The solar panel has identical connectors attached to its wiring. Thus, when I want to use the solar panel to charge the system I just plug these connectors into the solar panel connectors and I’m ready to go.

3) These are the power pole connectors. They are designed so that the positive (red) and negative (black) connectors can be attached to each other so that only one, quick connection needs to be made. That’s really nice. I must admit, however, that they were very difficult to get properly attached to the wiring. You will probably need to fiddle with them quite a bit.

4) Although difficult to see, on the right side of the picture I have a single power pole connector attached to each end of the negative (black) wire that goes between the charge controller and the battery terminal. I did this so that I can keep the charge controller disconnected while I have the trickle charger hooked up. Since that will be all the time (because I want the trickle charger to keep the battery fully charged) this connection will only be made when I’m using the solar panel. When the time comes I can quickly connect the two ends of the wire and have the charge controller functioning as it should. On the left side of the image, the positive (red) wire is directly connected from the charge controller to the positive battery terminal.

5) Here is the 12-volt DC auxiliary plug that I can use to connect any auxiliary plug I want, including my battery charger and I-phone charger.

6) These are the connections for the Battery Tender Jr trickle charger mentioned above. It is permanently connected to the battery terminals using ring terminals. It’s a simple connection, positive wire to positive terminal and negative wire to negative terminal.

7)  Again, although difficult to see, this is the quick disconnect for the trickle charger. I would simply disconnect the trickle charger here when I connect the charge controller and solar panel.

My Thoughts and Concerns

I have a few problems or concerns with my solar panel system that are either difficult to remedy, too costly, or I should have know better (by doing more research beforehand)…

No Power Inverter

If you’ve noticed, I haven’t discussed a DC to AC power inverter yet. If you didn’t know, this type of inverter converts 12-volt power (such as your car’s power) to 110-volt power (your house power) so that you can plug in and use/charge equipment that only has an AC cord. My phone is an example because it only has an AC cord to charge it.

While I considered buying one (and I still am) I’ve avoided it thus far because my understanding is that this is quite inefficient because you are wasting energy converting DC to AC by using the power inverter and then converting AC to DC again when you plug the equipment you intend to use into the inverter. Anyway, if I had a bigger system and expected to power a variety of equipment that only uses AC then such a power inverter would be necessary; for this system it is not.

Solar Panel Wattage

My solar panel only produces 20 watts, which means at 17.2 volts (the voltage it is rated to output) the max current it will generate is 1.17 amps. (Note: it’s a simple formula relating watts, amps, and volts: watts = volts x amps.) The problem is that this is roughly equivalent to a trickle charger so it will take a long time to recharge my battery even under good conditions. If I were willing to spend about double my cost for the 20 watt panel I choose to purchase, I could have got a 40 or 60 watt panel instead. Eventually I will need to add another panel or upgrade.

No Redundancy

This is a big problem. As the saying goes: “two is one and one is none”. Absolutely every component of my system does NOT have a backup, so I would be in trouble should any of it fail. I can remedy this but that would be costly, so I’ll just hope for the best.

Time to Recharge Battery

The initial charge using the trickle charger lasted about 24 hours with an initial voltage of 12.1 volts, which I think is roughly 50% charged according to what I have read. I monitored the voltage of the battery over this time and found the voltage varied from a low of 12.1 volts to a high of 14.2 volts and eventaully settled at about 13.0 volts when fully charged. I have yet to use the solar panel to charge the battery but, as I mentioned above, I would still suspect a rather long charge time especially when deeply discharged because the max current of the solar panel is only 1.17 amps, whereas the current of the trickle charger is 0.75 amps. My guess would be about two days of full sun would do it.

Total Cost

When you add up the cost of all these supplies you’re talking between $200-300 dollars for even this basic system. That’s a lot of money to me, especially for something that I can never guarantee I’ll use. And, unfortunately, to add more power will cost significantly more because I’ll have to purchase more panels and more batteries. It’s just not in the cards right now.

Was It Necessary?

This is the big question. Was my first solar panel system worth it? After it’s all said and done I spent about $250 in order to have a basic DC power system that I can rely on to charge/use basic electronics such as a cell phone, ipod, laptop, and to recharge batteries. Honestly, I can’t even use my laptop yet because I haven’t purchased an appropriate auxiliary plug (or power inverter) for it which is another $20-30.

Another question is whether any of these devices would even be usable if there is a lengthy city-wide power outage. After all, should I expect that cell service will work when the lights are out? Maybe. Cell phone companies have been working to make their systems more robust in recent years but there’s obviously no guarantee. The same question can be asked about Internet service. I would expect that the Internet certainly wouldn’t work so my laptop just became a lot less useful to me.

Perhaps the driving force in this solar system was the ability to recharge batteries for a lengthy period of time. Given that the majority of my flashlights, lanterns, and radios use either AA or AAA batteries, this is important to me.

Of course, there is one other option I have touched on: in most cases you can simply use your car’s electrical system to accomplish the very same goal assuming that you have enough gas in y0ur tank (or filled gas cans) to do so. I would suspect that this strategy would work for quite a while if you’re able to make very efficient use of the time you have your car running.

One last option would have been to buy loads of AA and AAA batteries. I probably would have spent significantly less and had batteries coming out of my ears.

So, what do you think? Was it worth it or not at all?

Damian Brindle

Blogger at reThinkSurvival
Blogging about all things survival and emergency preparedness, including experiences with DIY projects and ideas, gear reviews, living frugally, cooking in unconventional ways, and more! All while linking to the best videos and articles each day to help YOU get better prepared.

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