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Posted by Steven in Colorado Springs, CO on 2/18/2012

It's been a fair bit since I last updated this blog, mostly because I didn't particularly feel there was much noteworthy to update about. After Google updated their photography with a frankly superb shot of Tanglewood I've mostly just been enjoying the winter, learning how this house works, doing some repair/cleanup work and slowly unpacking boxes of stuff that have been sitting since the initial move.

It occurred to me however that it might be time to provide an assessment of my solar PV system, since I've now got a good six months of time with it under my belt (really more like 7) not counting the frantic move-in period where I wasn't really paying attention to it much at all and the downtime in December when things weren't quite working right due to a dead inverter. There have certainly been highs and lows with the system since the move, in part because of struggles to understand exactly what it means to live “off grid” and in part because (in my opinion as an engineer) of some serious and sometimes downright baffling oddities in the way these systems work.

So what follows are some of the things I've learned since beginning to live with my PV system—the good and the bad, the frustrating and the baffling. Let me be clear that some of these are probably specific to my particular hardware as there's a wide variety of vendors and systems out there that one can buy from. Let me also hasten to add that some of this is from the my being an engineer and knowing there are better ways the manufacturers could be doing things--which for some reason they're not. I happen to be very pleased overall with my particular hardware and it's from one of the highest rated manufacturers out there, but there are definitely some limitations that various companies (including mine) are slowly (too slowly) beginning to address.

The Good

  • I absolutely love my solar! No utility bills. No weird power outages that have no real explanation forthcoming from the Utility Company. No dealing with ever-increasing rates to support some weird new utility expansion or upgrade that I didn't even get to vote on. The power is mine to do with as I please, without any worries whatsoever about bills—I made it, I can do whatever I want with it. It's tremendously liberating.

  • A good solar array produces power even on cloudy days. I hadn't quite expected this from what I'd read prior to putting the system into place, but as it turns out quality PV panels will produce decent power even on an overcast day. Over the past few months I've begun to loosely categorize days into four groups--”sunny”, “light overcast”, “heavy overcast”, and “dark”. Of course the system will work best on a sunny/bright day and we're blessed with a bunch of them here in the High Country of Colorado, but I'll make decent power on a per panel basis on the overcast days too... around 100-ish watts/panel on a lightly cloudy day and around 50-ish watts/panel on a heavily cloudy day. (This will of course vary wildly based on your solar exposure, your latitude, the types of panels you have, etc... these just represent my system and circumstances.) That's not a lot of power of course—your typical big screen TV uses maybe 100W per hour—but when you've got a lot of panels (30 in my case, soon to be upgraded to 36) that works out to a good 3kW per hour flowing into your batteries—not bad at all! I've had a couple of days in which we never really got “good” sunlight at all, but the cloud cover was light enough that my batteries actually hit a nearly full charge by the end of the afternoon... frankly astonishing!

  • No moving parts. One of the very best things about solar panels is that there aren't any moving parts to deal with at all—you just put them out there in a sunny spot and the power flows in. While I'm quite fond of wind turbines as a potential power source since they can operate any time of day or night (a big plus when compared to solar) I veered away from them early in the design of Tanglewood when I realized that not only would they require regularly physical maintenance, but the best location for them was way up high on a ridge around 600 feet from the house—not a trek I looked forward to making every few months with an armload of tools and oils and whatnot. Other than occasionally rinsing off the panels to remove the inevitable layer of dust that any sheet of glass will accumulate when it's outdoors, there's really nothing that they need. This summer I'll spend a couple of quality hours trimming down the scrub oak that I had to clear to install the ground mounts but that won't be hard, and in the process I'll generate some more kindling for the fireplace. Not an unreasonable tradeoff for such a low maintenance system.

The Bad

  • Batteries stink. There's simply no two ways about it—the single biggest frustration about living off-grid is dealing with your batteries. I've noted this before in various entries and I've really nothing very positive to add since those logs were made. The technology in this area simply hasn't kept pace with technological advancements in general and solar technology in particular, with the greatest innovation in the last 20 years being that manufacturers now incorporate straps to the battery case so you've got something to grab onto when you have to lift them.

    None of the options you have when you build your system are particularly good, and they all have pluses and minuses.

    If you choose lead-acid batteries (the classic liquid-filled ones that most cars use) you'll be looking at a superb range of choices (lots of companies make these) which are easy to compare against each other and some of which have very large capacities (quite important for a larger house). They're very tolerant over overcharging since they can simply release gas if they get too warm, a nice feature. On the minus side, though, you'll be stuck with performing regular maintenance to add distilled water as needed (due to evaporation and overcharging) and regularly measuring the electrolyte's ability to hold a charge with a hydrometer so you can catch problems early. You'll need to be careful about handling them or shifting them around lest you spill acid all over yourself and/or whatever is nearby. And just for good measure you've got to keep them relatively warm (they prefer the same temps as you do), because if the temperatures should get below freezing they'll burst, transforming thousands of dollars of batteries into useless, acid-leaking junk.

    If you choose AGM batteries (spill-proof batts that use a glass mat impregnated with a viscous electrolyte) you'll have the advantages in that they won't freeze in low temps and are very rugged. They are dubbed VRLA (Valve Regulated Lead Acid) batts because you won't have to do any maintenance work at all on them—no water levels to check! Unfortunately, technology hasn't advanced as far on these batts as it has on the lead-acid jobs so they don't have as great a range of capacities, which limits your choices. Even more fun since they're sealed that means they can't outgas like their lead-acid cousins, so if you overcharge them you'll damage their capacities permanently—no second chances, period, finito. They also cost $$$ more—roughly 50% over lead-acid prices as of this writing.

    Your other option are Gel batteries. These look like and have many of the same characteristics as AGM batts, except that they're filled with a jelly-like electrolyte. Much like the AGMs, they basically won't freeze unless temps get below 30o F and they are extremely tough. Unfortunately they have basically the same drawbacks in terms of capacities, cost, and the dangers of overcharging as their AGM cousins with one added little bonus drawback—they have an “unusual” charging profile that means they generally (this varies by brand) can't charge quite as fast as either AGMs or lead-acid batts. This last bit isn't too big of a consideration if you've sized a large solar array (as I have here at Tanglewood) but if you're barely buying exactly the size you need, it could be an issue.

The Frustrating

  • Nobody wants to give you actual answers. For an engineer such as myself this is just inexcusable, and a sign that everybody apparently wants deniability in case something goes wrong.

    This can be seen in many areas when you're setting up your system, from the estimates your contractors-to-be will give you to the actual configuration of the hardware itself. Perhaps the most frustrating issue I found myself bashing walls over was how to configure the battery charging parameters.

    First a background. If you don't have an off-grid system, it's probably not something you think about too much, but the deep-cycle batteries used by solar systems are charged in three basic phases—Bulk, Absorb, and Float. Your regular car battery charger usually only does basic Bulk charging and you wouldn't want to use it on a renewable energy system--it's just not sophisticated enough.

    Bulk phase is the first phase, in which your system just charges up the batts as fast as it reasonable can until it hits around 80% of the battery's voltage level. This is good but only gives the batteries a “surface charge”, similar to your plugging in a cell phone for a few minutes to get one last call in—it'll work, but not for very long. The same goes for your renewable energy batteries--the Bulk charge is vital to getting them up to speed, but you wouldn't want to run your house on it.

    In the
    Absorb phase the system manages the amperage coming in from the charge controllers to “soak” the batteries, gradually changing this amperage to build a “depth of charge” rather than a pure surface charge. This is probably the most important phase of the whole process and hopefully where you spend most of your sun-drenched time--it can last for hours depending on your batteries.

    When the batteries hit
    Float they're fully charged (as far as the system knows) and the system switches to a basic “maintenance” mode. Energy coming into the system mostly just goes to driving any household loads with a tiny bit diverted to tickle-charge the batts to keep them fully charged. Some off-gridders hate this phase as they feel that it's “wasting sunlight”, but it's relatively rare that you'll reach this state if it's a typical bright and sunny day in any case.

    So all of that seems straightforward enough, right? Well, not really. You see most systems trigger those Bulk/Absorb/Float phases in accordance with the parameters that you, lucky system owner, programmed into the controllers. You'd think those numbers came with the batteries—but you'd be wrong. In most cases you're lucky to get a “technical sheet” that looks kinda like this (I'm not picking on these guys, it's just one of the first tech sheets I could find).

    Clear as mud, huh? You'll note that those number-laden charts are filled with caveats and that they don't actually give you
    numbers per se, they give you a range of numbers. What should you use? Oh, the battery folks say to defer to the specs provided by your solar equipment provider—who helpfully defer to the battery specs when you go dig through their documentation. Nobody wants to actually give you a set of numbers, presumably because if they did and your batteries fried/blew up/etc. it would then be their fault.

    You get basically the same kind of answers if you actually call somebody, too—they'll ask what you have and what you're trying to do, and then refer you to various pages in the documentation that you've already read and/or try to point you at the other manufacture. Which of course you already did before calling them in the first place.

    Not that any of those settings will help you all that much anyway, as they're all simply battery voltage levels—essentially triggers between the phases that are invoked when the batteries hit a given voltage level. The problem here is that voltage is a particularly bad way to measure how charged your batteries are, since it can vary wildly based on input (clouds passing in front of the sun) and output (loads in the household turning on/off). There are some loose parameters that have evolved into the system's settings that try to limit this inherent volatility by using timers (i.e., “don't transition into this mode unless you're at the triggering voltage for at least two minutes”) but those are crude controls at best.
    Far and away a better method for handling the charging of your batteries to measure the amps going in and flowing out, and you can do that—but that's a $400 optional add-on to the standard system.


  • Solar equipment is shockingly “old school” in terms of design. In part I suspect this varies wildly by manufacturer, but in lurking around various solar equipment forums the problem seems widespread. I think in large part this has been driven by the near hobbyist level of the industry until very recently, as only the most hard-core techno geeks would bother to install the systems in the first place and there probably hasn't been big money to revamp how they're put together. Nobody seems to understand what a monitor hookup is or provide you with an option to use one, and USB is a rare beast indeed—customized serial ports still rule this world long after it's become nearly impossible to find a laptop that has such things.

    And the menus on the hardware itself are simply
    pathetic. I'm talking 1982-level technology here—a basic 40-character by 5 lines LCD screen, with menus so nested that it's spectacularly easy to get lost without having the owner's manual in front of you. Options are usually at the bottom and are something terse like “Next”, “Inc”, “Dec” to allow you to move to the next screen or increment/decrement the current setting. Exits are spread about wildly—some menu paths make you walk through all dozen potential settings before giving you a way back to the top menu, while others provide you with an exit anytime they're not using all of the available buttons for something else. Just for fun, a few of the menus mix it up and give you an exit option that moves around—sometimes it's on the right-hand side of the LCD screen, sometimes it's on the left-hand side. Wrestling with all this while you're trying to program in those magic Bulk/Absorb/Float values is especially fun.

    A few manufacturers have started to discover Ethernet, at least. Outback makes a new device called the Mate 3, which lets you access it from anywhere around the world via its Ethernet connection, and Midnight Solar has a variety of devices that are beginning to understand both USB and Ethernet.

  • Optional equipment clearly isn't as “optional” as it seems. One example is the aforementioned device that allows your system to charge the batteries based on amp-hours rather than basic voltages. Another would be a nifty little device called a Remote Temperature Sensor (RTS). This little do-hickey glues to one of your batteries and lets your charge controllers adjust the voltage and amperage flowing into the batteries during charging based on the battery temperatures. It turns out that a cold battery charges a lot differently than a warm battery, and so having an RTS tied into the system lets it optimize the whole process and maximize your battery life. It's a very good idea and one which I'd opine flat out was a necessity, but of course it seems to be optional from most manufacturers.

    Even here though the “old thinking” of the system's design is evident, however. The particular hardware I have allows for a single RTS to be connected, apparently in the assumption that all of your batteries will have essentially the same temperature. Maybe this is a reasonable default if your batteries are stashed in the basement under your house, but if they're deployed on a rack way off in a shed because you have a ground mount system, it's not as helpful as it might be. Why the heck can't a person plug in 2, 3 or even 8 different RTS sensors (one per shelf perhaps) and let the system manage charging by battery cluster? No idea, other than that the manufacturers apparently never considered such a thing.

A Partial Solution

Over the course of writing all of this up, it occurred to me that Microsoft has a great solution with their Windows operating systems that could serve as an example for how the solar equipment and battery manufacturers could make the setup process a whole lot easier. I don't think they're likely to actually do this since it might shift responsibility for a poorly-configured system to them, but offering something like the following sure would make life easier on installers and owners alike.

Here's how configuring the system for your batteries ought to work:

  1. When you hook up your system and turn on the power, the first thing it should do is say “Welcome to your new SuperSolar System™!” on either an 80-character by 40-line LCD text display or on the computer monitor you plugged in during setup.

  2. Next up would be a series of interactions with the system:

  • Battery database is dated 1/1/2012—should I update it?” – Just as with Microsoft Windows, you let it go out on the Internet via the built-in Ethernet connection, it downloads the latest battery database from the manufacturer, and then it proceeds.
  • What kind of batteries do you have?” – Let's suppose you had 24 Surrette S1725s, so you scroll down the list of batteries and select that one.
  • How many batteries do you have?” – Punch in the number (“24” in this case) and hit ENTER.
  • How many strings are these batteries in?” – Perhaps you have them deployed in a total of 3 strings with 8 batteries each, so you punch in “3” and hit ENTER.
  • The system blanks for a moment and then pops up something like, “Total amp-hours per string is WXYZ—is that correct?” – You check the number provided (which it pulled from its battery database) and hit ENTER.

  • The system then displays a message along the lines of “Setting Bulk/Absorb/Float values” (again, using the values it downloaded from its battery database) and you're done.
  1. Yes it could be this simple. No I don't think they'll actually do it. Sigh.


Despite the annoyances, I'm really quite pleased with my solar. I've just recently incorporate the oh-so-how-did-they-not-make-this-standard amp-hour battery charging device, and I'm getting ready to expand the system out to 36 panels (the maximum the two existing charge controllers can manage).

Later this spring I'm rebuilding the solar shed.  Colleen did a great job with it working with what she had, but let's face it--it's cold and sits on stilts, so I don't trust it not to fall over some day (and that would really be a mess!). The new shed is going to be constructed out out BuildBlock just like Tanglewood is and will incorporate a solar-heating system so I can make use of these bright winter days--a big plus from the current insulate-and-pray approach the shed has now. I'll document all of that once we start that project, of course.

The fun never stops... and that's fine by me!  ;)

Steven in Colorado

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Posted by Steven in Colorado Springs, CO on 2/21/2012

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Howdy Mary!

Thank you for both the comments and the link! I did not know of that site, but it certainly looks interesting and I plan to comb through it thoroughly.

I seems a no-brainer to me that since I'm going to build a new shed anyway and I love the radiant heat system in the house proper, that I go with something like that in the new shed. We have a lot of bright sunny days combined with cold dark nights, and something like this to take advantage of the one to ward off the other just makes a lot of sense to me.

For the most part no, we don't schedule around the sun. I have asked folks to pay attention to the sunlight try to do things like washing when we've got lots of light, but it's not a hard and fast thing. I'm honestly paying more attention to the propane at the moment, since that's not a "free" resource, so if somebody wants to bake something I ask them to stack up two or three things to maximize usage of the oven's heat.

It's all an interesting learning experience as I'm still figuring out how this house works!  :)

Steven in Colorado

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