Care and Feeding of Your Off-Grid PV System

Welcome to the exciting world of off the grid living. Self-sufficiency, freedom from the utility company, and the use of renewable resources for power are now in your grasp. However, with these benefits come new responsibilities. This guide will help make these responsibilities more clear to you, and hopefully create a better understanding of your new system.

Flow of Electricity in the System

Seems simple enough, right? Panels make electricity, which charges batteries, which runs your home. This is true, but there are a few other things you should know.

First, the PV modules (as they are known in the industry) create direct current, or DC power. This power must be managed in a way that the rest of the equipment downstream can handle. To accomplish this, the modules are wired in series (positive to negative) strings to create the correct voltage and amperage to connect to the rest of the system. Each series string is through a disconnect, typically a breaker, most likely found in a DC Combiner Box. This disconnect offers a readily accessible place for you or a technician to “turn off” one or more strings in the event that service is needed at the array. The disconnect also protects the system in case there is ever damage to the modules which could cause dangerous electrical currents to flow within the equipment.

Second, the power flowing out of the DC Combiner reaches a Charge Controller, which regulates the amount of power that enters the storage batteries, and prevents them from being overcharged. The Charge Controller does much more than this, however. This sophisticated device actually manages the overall energy harvest from the array of modules through variable charging algorithms. Another way of saying this: the Charge Controller can actually change the way that it charges the batteries depending on conditions affecting the modules. So when a cloud passes over the array, it can alter it’s charging strategy to yield the highest amount of power from the modules. It also is responsible in some ways for the overall health of the battery bank. The Charge Controller can not only limit power into the batteries, it can provide for timed overcharging of them. This is known as equalization, and is important for battery maintenance. More on that later. The Charge Controller, as you can see, is very much the brain of an off-grid system.

Third, power from the Charge Controller moves into the battery bank, the storehouse of energy. As important as they are, batteries are essentially quite dumb. They react chemically to an electric charge, and are able to reverse that process to release this charge. Each battery within the bank produces roughly 6 volts, and are wired in series to reach higher voltages to connect to the rest of the system, in much the same way as the array of modules. For a 24V nominal system, a minimum of 4 batteries must be wired in series to operate the rest of the equipment. To achieve greater depth of storage, more groups of 4 are added with parallel connections (negative to negative, positive to positive).

Fourth, power is removed from the batteries by the Inverter whenever you turn something on in your house. If a Charge Controller is the brain within the system, the Inverter is most like the heart. It is designed to do the hard work of converting DC electricity from the array and batteries into AC electricity to power lights and appliances, and do this 24 hours a day for life. The inverter also performs double-duty as a battery charger whenever you feed power back through it with your generator. Although not as smart as the Charge Controller, Inverters can sense when this power is available, and will connect to it automatically with an internal transfer switch.

Finally, power from the Inverter makes it’s way into your house wiring through it’s main service panel, where it is distributed among all of the lights, computers and other toys connected through outlets.

Array Maintenance

One of the beautiful things about photovoltaic power is that there isn’t much to do to keep modules running. They will sit on your roof or in your yard and continuously provide electricity day after day without complaint. Typical productive lifespan for PV modules is 30 years, although older panels have been found to be producing viable power for much longer. In fact, most manufacturers of PV modules warranty their power output at 80% nameplate rating over a period of 25 years. That means that a 200 watt module with this warranty would still be making 160 watts after a quarter century! This is not to say there aren’t a few things that you can do to help them make a little extra power here and there.

Rinsing off the dust and dirt that accumulates on the faces of modules does help keep them performing at their best. Heavy soiling can cause as much as a 10% reduction in module efficiency. Choosing a time to wash the array that is neither to hot or too cold is important, so that there is no risk of shattering the glass through heat-shock.

Seasonally adjusting the array can boost power output by as much as 15% if performed religiously throughout the year. Consult a sun-path chart for your latitude to determine the optimum seasonal angles for your location. In the desert southwest, summer angles are usually no more than 25 degrees from flat, and winter angles no more than 45 degrees. Adjusting array angle can be a difficult task, best accomplished with more than one person at hand. Take caution to be careful of wiring between modules, and loosen module wiring clips when necessary. It is very important to realize that the array can never truly be “turned off,” as the panels will continue to output power unless completely shaded.

DC Combiner Box

Be especially mindful of the dangerous voltages and currents within this box. Do not allow children or animals to play around this area. Do not remove the box cover unless there is significant reason to do so.

Battery Maintenance

Batteries are the least glamorous and most time consuming part of your new solar system. They are the “necessary evil” that all off-gridders must endure. They’re big, stinky (just wait!), heavy and generally cantankerous. Think in-laws wired in series and you’ve got it. For all of their faults, there just isn’t anything else quite as good or efficient at delivering back what you put into them. Did I mention expensive? So, to protect our investment, we must take good care of them while they are with us. From Alan Sindelar, President, Positive Energy in Sante Fe, New Mexico: “Respect your batteries, for they are thy storehouse, and thy gold shall be quickly turned to lead.”

The first order of battery maintenance is ritual watering. Make sure to keep all cells topped off as often as you can. Most people realize how much water their bank will use after a year or so, but it doesn’t hurt to check. This amount will change over time. Newer batteries use less water than older ones, similar to oil used in a newer car versus an older one. Purchase a few large containers of distilled water and keep them by the batteries. Do not fill batteries with any other type of water. I have often used a small funnel and a little 6oz. Dixie Cup to carefully fill the cells. Each cell will have a “neck” that reaches down into the compartment. Your goal is to fill until the water is about ¼ inch below the bottom of this neck. This is difficult to see without a flashlight, or some strong overhead lighting. Try not to over-fill the cells, as this will reduce the concentration of the electrolyte in the batteries, reducing their efficiency. Not to mention, making a big mess that can be painful to clean up. When there is a spill, use baking soda to neutralize the acid. It is a good idea to have some on hand near the bank just in case. It can also be rubbed into skin and clothing to prevent burns. Eventually, the batteries will develop some corrosion on their terminals. A heavy wire brush will remove most of this along with a mixture of water and baking soda.

Applying an equalization charge regularly can help prolong the life of your batteries. This is a sustained high current charge designed to knock the build-up of sulfur off the lead plates inside each battery and back into the electrolyte where it can dissolve back into the solution. Equalization is activated through two sources: the Charge Controller, and the Inverter. You will need to tell each device to begin the cycle. If you are attempting to equalize with solar alone, you will want to minimize your electrical usage in the house to send the most available power to the batteries. If equalizing through the Inverter, you will need to connect and start the generator. Equalizing with both sources is recommended, as this increase in power to the batteries will guarantee the completion of the cycle within the allotted time. Battery manufacturers recommend different intervals for equalization, but a good rule of thumb is once quarterly. Newer batteries will not require equalization as often, older batteries a little more often. Before performing an equalization charge, it is good practice to check water levels in the cells. During the cycle, the batteries will use more water than normal.

A few other notes about your batteries: They like to be about the same temperature that you do. This is ideally 70 degrees or so as often as possible. You can insulate the building that the batteries are housed in, or build an insulated box around them. This second idea is often a better one since the power shed is a multi-use building for most. The box will prevent anything being dropped onto the batteries, or set upon them by accident. It’s all fun and games until a rake becomes welded to a few battery terminals, as well as energized. Also, be mindful if cables are to be disconnected for any reason. Insulate the handles of any tools you will use with electrical tape before you go to work.

Inverter

This is the real workhorse of your system. Surprisingly, there is little maintenance to be performed. Some models have a dust filter for their fan which will get dirty and impede the flow of air into the unit. Otherwise, there are no user serviceable parts within the inverter.

Most manufacturers include some kind of control device for programming and monitoring of the inverter. Consult the owner’s manual to learn how to navigate through the menus of your particular device. Do not fear accidentally changing important settings that could cause harm to your batteries or the rest of the system. If you reach a menu item that could lower performance of the system or worse, typically the parameter will require the entry of a password to make a change. Lesser functions often require you to press “OK” after making a change to be sure that you know you are making it. There is great information to be had from these devices. Lifetime kilowatt hours produced, diagnostic tools, current output stats, and more can be found with just a few pushed buttons. Another important function provided here is the ability to limit the amount of power flowing through the inverter’s AC to DC charger to the batteries. This will allow you to change the amperage input if you ever decide to connect a different generator to the system. Larger gensets will need to be current limited to around 20 amps AC, as the charger can only handle so much power. Give this some consideration before you buy that 20kW Kohler. You’ll really only be able to send about 2400W to the batteries, and then pass through a bit more to the house.

Final Thoughts

Living off the grid puts you in a much more direct relationship with energy. You must be conscious that your system was designed with a certain load (usage) estimate in mind. Adding appliances and plug-in devices in the future must be done with caution. Let your monitoring device be your guide. Seasonal changes specific to your site will affect the system’s output as well. Awareness of when storms will likely pass through can give you a heads-up for decreased power availability. Above all, you must maintain a good relationship with your installer, or develop one with an accredited local solar technician. This is the person you will want to be able to call at 10:00 PM for advice when your system crashes suddenly.

While owning and maintaining an off-grid PV system may seem challenging at first, you will be surprised how quickly all of this becomes routine. Most of my clients report that after a few years of life off the grid, they feel pride in their ability to understand how the system works, and happy that they accepted the responsibility. Good luck with solar, and welcome to the club!

Our Grid is Getting Smarter

We are about to see the convergence of two of the most influential technologies in the history of men. This statement may sound bold, but it is absolutely based in fact. The emergence of a nationwide utility infrastructure for delivery of household electricity revolutionized life as we know it in the United States. It paved the way for the media and computing revolutions, and the all-important networking infrastructure that ties them together. These technologies, one antiquated, the other in it's infancy, have changed the human landscape tremendously. Possibly as much as the development of firearms, or even the invention of the wheel.

The merging of our electrical grid with networking capability has seemed somewhat inevitable. Scientists and engineers have understood the benefits that could be provided by incorporating real time data into our power management scheme for years. Primarily, combining these technologies promotes a more stable utility system, by addressing the current grid's major problem: the speed at which production and delivery issues can be fixed. Real time data would tell computers, not employees, when and where energy transmission troubles arise, and deal with them accordingly. This system would reduce if not eliminate blackouts and brownouts which can cost our economy billions, as they have in the Northeast in 2003 and California in 2005. The eventual benefit to updating our grid system reads like a laundry list of positives. The new "Smart Grid" or "Intelligrid" as it has been called, would be more efficient, perhaps saving as much as 20% of the electrical energy that we produce today. Our networked utilities would rely less on power from one source, effectively decentralizing the grid, thereby making it more resilient and less attractive as a target for attack. A benefit of this decentralization is the ability to connect more and varied renewable energy sources, which further promotes our nationwide energy independence plan. This new structure would also allow consumers to be more involved in their electrical use, by incorporating devices which could be programed to operate only when demand-based utility rates are low, signaled by information available through their connection to an outlet.

Of course there exist many hurdles for this infrastructure change to occur. Three of the largest are the resistance and inability of utility companies to change, public concerns over increased governmental control of energy and household privacy issues. Certainly for any of these points to be addressed, there will need to be legal mandates that will bring financial muscle to bear upon the problem. This process has already begun, surprisingly in the previous presidential administration. After the strikes of 9/11, president Bush made a clear gesture that improvement of the grid was necessary, mainly to strengthen our defenses, which was then re-emphasized after the above mentioned blackouts. President Obama has picked up this torch, and carried it one step further. As a part of his administration's energy policy, the DOE's Energy Efficiency and Renewable Energy office has received $2.3 billion in funding, partly to aid in the development of smart-grid technologies. The recent economic stimulus package granted the DOE an additional $38 billion, much of which is earmarked to solving the renewable energy integration issue, in which grid limitations play a great role.

The final hurdle to a smarter grid lies partially in the technology itself. Costs of metering equipment for the home must be made affordable. Latency, or the delay in transmission of information within the network, must be reduced to within reasonable levels for the system to work at all. The argument could be made however, that we did not wait to perfect the personal computer before bringing it to market, and sales did not lumber along until someone deemed them perfected. Much of this technology may be refined as time passes, and we see it's real weaknesses. Business too must play catch up, and the practicalities of engaging a workforce must be embraced. In this era of unemployment rates in the near double digits, businesses only need to hang out their shingle and the workers will arrive, not to mention cash. In 2009 the Cleantech market received over half of the venture capital in the U.S. The Energy Independence and Security Act of 2007 put forth $100 million in matching funds per year through 2012 to get smart grid projects going on the state level.

This could be the single largest change to occur within my generation. Experts are saying that a significant portion of the grid modernization project may be in place by 2030. It will involve the unprecedented cooperation between the entities of government, the utilities, and the public, and it will be vastly expensive. The question is, can we afford not to enact this change?

General Thoughts on Solar Water Heating

Had a recent conversation with a co-worker that reawakened some feelings I have harbored about the use (and very often, misuse) of solar collectors for water heating. We spoke about the thermal system installed at her home, which was designed to offer supplemental heat for a radiant floor loop. This in-floor heating system is primarily operated with a gas boiler, which has been working overtime-her monthly propane bill in the winter is $500+. This wouldn't seem so shocking under normal circumstances. This is Colorado. The house is in a deep and sheltered valley, at high altitude. It's damn cold.

Here's the problem: the house was constructed of strawbales, and it's a one bedroom. So you've got a seriously well insulated structure, that's really small. This place should, on paper, stay fairly warm on it's own. The amount of energy required to heat it should be minimal. Did I mention she has had to run the domestic water a bit to flush the glycol (anti-freeze) out of the pipes before she takes a shower? Obviously there are big problems with this system, apart from the fact that it's not doing what it was originally designed to do.

This brings me to my point. After all of the experimentation that has occurred in this arena starting, lets say, in the early seventies, you'd think that we'd have dialed this technology in to the Nth degree by now. I asked if she knew when the building was constructed. Apparently, it's only a few years old. This startlingly bad system was recently commissioned. I think the truth is, we have dialed this stuff in pretty well. So what's the issue?

A little about my experience in this field. I had the pleasure (or horror!) of installing domestic solar hot water systems for four years or so. I also did a few tie-ins to radiant floor systems as well. This by no means makes me an expert, but I feel like I have had enough of an opportunity to see what works well, what the trouble spots are, and how the technology can be put to good use. The majority of the systems I worked on were more or less packaged deals, sort of "standardized" to work for the most homes. However, the company I worked for previously would entertain almost any customer and their wild fantasies as to what could be done with the power of the sun. This being said, I did see some systems, that probably would have made more heat if they'd been set on fire, and should have been.

My opinion on why there are so many failed or failing thermal systems is based on several factors:

1. We ask too much of the equipment. There are practical limits to the amount of heat that can be produced by a single flat-plate solar collector, not to mention harvested by the system. You may be able to provide enough heat for hot water in your house, but it is highly doubtful that you will heat your entire home with only one panel. I understand. These collectors cost thousands of dollars, and if four would do the trick nicely, why not get two and be happy with half of the bill taken care of by mother nature, right? Wrong.
2. There are all kinds of vagaries that affect the way these systems perform. Flow, pressure, thermosiphoning, etc. Most of us do not possess the skills to determine exactly what area of collector square footage will be required for a given goal, versus storage tank size, factoring in pump size and energy consumption... You'd need a team of NASA scientists to know exactly every detail that could have an effect on ultimate production. The best we can hope for in most cases is to under-produce (supplement) rather than over-produce (spend too much money and potentially create to much heat; read: steam, system failure).
3. Human beings. We make mistakes. Thermal systems offer amazing potential to make more of them. In my short (thank God) career of putting these things in, I cannot tell you how often my soldered joints failed. It seems like that's just the way plumbing goes sometimes. Bad fittings, valves, pin-hole leaks, all happen with regularity, and sometimes it's just installer error. Aside from what we can do wrong in the building process, there's our seemingly insatiable lust for bigger and more complicated systems of all types. This must have something to do with the need for a feeling of more power and control in our lives. The fact that you could potentially outsmart nature with a strong dose of electronics and engineering. I dunno. I know that I have witnessed systems grow with the logic of, "well if this works, wouldn't this work if we installed another valve here, and another pump here to do this?"

To be fair, solar thermal is much more reliable than it has ever been, and there are fewer troubled systems out there. I would like to think that this is the result of the "throttling back" of the industry, and the common realization that simpler is truly better when it comes to design. As for our plagued system here in Colorado, I suspect that it may have been installed by someone that was new to solar. My co-worker mentioned that she had heard that the glycol in the solar system was to be separated from the potable water supply by pressure alone. She also said that when it came out of the faucet, it was black, a sure sign that it had been burned by overheating at some point. That just ain't right. There are a lot of new faces entering this business everyday, some clearly with dubious technical know-how.

I am psyched that my first solar gig allowed me to see both the functional and the non-functioning, the useful and the useless in solar hot water. Though I appreciate the technology and desire my own system, I am now equally psyched not to be installing solar thermal at all.

Thanks for reading.

Champion of the Luddites

If you are arguing against renewable energy sources in this day and age, you might as well hang a sign on your face that says: "I am an idiot." Check out the link to the left...

While I believe strongly in a worldwide switch to available renewable energy sources, I don't believe that a "Silver Bullet" technology currently exists to replace our fossil fuel addiction. The expression "Silver Buckshot" more appropriately speaks to the answer. Taken singly, it is easy to criticize PV, wind power, geothermal, tidal energy, biomass, ethanol, etc. Yes, problems exist with each of these sources. If people continue to seek one perfect solution, they will be sorely disappointed. Herein lies the rub: no known renewable energy system is as efficient as burning fossil fuels. Therefore we must accept that they will be used in combination if they are to be used at all.

When it comes to technology, you can run, but you can't hide. Making the argument against renewables because implementing them is complicated is akin to sticking your head in the sand and waiting for the apocalypse. I am not impressed with the scientific analysis presented in the site, or the flip way that the author offers up bicycles as an alternative form of transportation. Yeah, I've been riding a bike for years. This isn't a new concept to me. Perhaps he should take a look into how bikes are made and the real energy balance associated with them. I would posit that a single PV module achieves energy neutrality far ahead of the average bicycle from Korea (that's right. Most of the bikes we own are mass produced in either China or Korea). In this light, maybe he would see that solar electricity isn't such a bad idea.

Way to be a part of the problem.

Want to know more about your bike?
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