Cutting Your Power Utility Cord, by Dennis Williams – Pt. 2

Step 4: Equipment

Inverters

When setting up your off-grid power system, don’t buy the cheapest inverter that you can find on Amazon! There are several excellent inverter manufacturers out there. I have some that I love, some of them are okay, and some I will not install. Keep in mind, as a professional installer, my reputation is at stake on every project I put in. There are some cheap ones that may perform well, I can’t go there. Some of the “good stuff” out there can power your retreat, automatically start and stop the generator based on battery status, and be tied into the ‘net. I know, some people don’t like that option, but on my end, I can monitor my projects, and even tweak them without leaving my office.

Whatever you do, make sure it is a pure sine wave inverter. They are more efficient, and your equipment plugged into them will last longer. Be careful of the cheap junk available on the ‘net. I have seen an 8000 watt (rated) 12-volt inverter in person. It said it needed to be fused at 200 amps. Simple math folks, power(W)=current(I) x voltage(E), so W=200 x 12, power = 2400 watts. What kind of alien technology are they selling you for the low cost of just $249, that it can output triple the power input?

My business is totally off-grid, powered by an old-school Outback Power Systems FX series 2000-watt inverter. It powers my air conditioner in the summer, and powers my pellet stove all winter. My house has a Magnum Power Systems PAE4448 that I took in on trade a few years back when a customer upgraded to an Outback GS8048 Radian. It backs up our several deep freezes and refrigerators. It will soon power the fan for my LP furnace, and the wife’s freeze dryer. I also have a twelve-year-old Xantrex Pro Sine 1800 that was in the house for a few years, then was bumped out to my shop for several years. Now it is in one of my service trucks. One of my work trailers has a little Morningstar 300W unit, which is fine for running tool chargers, lights, radios, etc. None of them have ever missed a beat.

I install more Outback inverters than all the others combined, not an ad for them, just simple truth. I like their equipment. Inverters are available to power most anything you can imagine. Three of mine are just 120-volt units, which are great for small projects, or can do an entire house or cabin. The other option is a 120/240-volt unit like my Magnum, the Outback Radian, or the Schneider (formerly Xantrex) units. These can feed a standard electrical panel that we use in the states, with no changes. These inverters typically also have a battery charger built into them to charge the batteries from grid or generator power if necessary.

PV System Room

I am writing this from a little Third World jungle, where I am using three Outback GS7048E inverters stacked to put out 21 kW of 230-volt 50 Hz power, with 24kW of solar, 4500 Ah of battery storage, and three diesel generators, a 23, 110, and 220 kW. Might sound stupid in the states, but down here they are paying over $0.42 per Kwh for electricity, when they can get it. They just went through 16 months with no grid power after Hurricane Maria! You want to practice for tough living? These people are living it, and for the most part life is going on.

 
Batteries

Okay, we’ve made power. How do we store it? This question can be pivotal. I will admit, I am old-school, and prefer FLA (Flooded Lead Acid) batteries. They have a decent price point, can have excellent life, and can take some major abuse, if we give them some loving. I do use some SLA (Sealed Lead Acid) batteries, but typically only in instances where I feel maintenance may be an issue. FLA’s do not need a lot of maintenance, but with none, they will be an expensive lesson in frustration. Stay away from anything at a big box store that says “deep cycle” unless you want frustration.

Deep cycle batteries are not built the same as a typical car battery. An automotive battery is designed to give a big push of current for a few seconds to crank an engine, and then get charged back up right away. They typically use less than 10% of capacity, and as such, have many thin lead plates to give a lot of surface area to the chemical reaction. In an off-grid type scenario, we want batteries that will allow us to suck their life out, and then let them sit until the sun starts to shine again. This requires much thicker lead plates, so they do not warp when under the strain, and heat, of doing their job.

I use golf cart batteries in my solar powered golf cart. It hasn’t been plugged to an outlet in over two years. I use it to run around my property daily. In a building or house sized system, I start with L-16 size batteries, and go up from there. As you need more battery capacity, you are better off to go to larger batteries rather than more strings of batteries. Good practice is to not go beyond three parallel strings of batteries. I prefer to use two as a maximum, but will use three, if necessary. I typically use one string of large 2-volt batteries, using larger cells for more capacity, when needed. This way we can control the charging in that one string, and we don’t have strong and weak strings fighting with us. This leads to longer battery life, and if one should fail during a time that we have no option for a replacement, we can just jump out the one bad cell and change our charge controller settings down by 2.35 volts (approximately, check data sheet for your batteries), and just keep on running. If you lose a six- or twelve-volt battery in a string, well, good luck. You just lost a whole string, and either half or a third of your capacity, if not all of it. If you are debating on battery system capacity, (and you can afford it), err on the bigger capacity system.

So what about battery voltage? For a small system, there are some advantages to using a 12-volt system. On a 12-volt system, we can get many small 12-volt appliances from the RV and OTR trucking market. We can recharge them with jumper cables from a car or tractor.   If we are going to do a whole house, I would suggest going to a 48-volt system. That is the maximum allowed by the National Electrical Code in a residence. There are some commercial projects where we go higher voltage, and some of the new lithium systems are able to go higher (300-400V) as well, but that is not what we are discussing here. With modern inverter technology, we can use standard off the shelf lights, appliances, and wiring, with no need to run special DC circuits for a 12-volt system. We like to run the highest battery voltage we can, as this allows more power with less current, translating to smaller wires, less copper, and hence more pocketbook friendly.

I will readily admit that I feel the Lithium technology is going to be a game changer. I have worked with a few companies that are starting to repurpose Lithium batteries from electric cars into stationary applications. This greatly reduces the initial cost to get into this technology. Most of the major brands of solar charging equipment are already putting the charging algorithms into their controllers to work with this technology. To date, we have installed one new commercial lithium system and are encouraged by what we see. I am also extremely curious about the Iron Edison equipment, but have no experience with them as of yet. It looks like an excellent option, more up front, but longer life, and not a new player in the game. I try not to push stuff that I do not have real world experience with.

 

Solar Panels

Solar PV panels are presently the cheapest they have ever been. At this time, the most common panel is going to be a 60-cell module, which will measure about 40 inches wide and 65 inches high. The frames can vary from around 1.2 to 1.75 inches thick. The average solar cell generates approximately .5 volts when exposed to full sun, regardless of its size. As the cell gets larger, it can output more current, but still at .5 volts. The 60 cells in a typical panel are wired in series to make approximately 30 volts, depending on cell efficiency, and the temperature. Temperature is a very important thing we need to take into account. A solar panels efficiency is inversely proportional to its temperature. This is a fancy way of saying that the colder it is, the more efficient it is. When it is -20 degrees outside you may see your voltage go past 45 volts on the same panel we just talked about. When it is 90 plus degrees and the sun is wailing, it is possible that your panel will only be putting out 25 volts. There are several good books out there as resources with the formulas for calculating this information, and most any reputable charge controller manufacturer will have a string sizing tool on their website that you can put your numbers into, and it will calculate this information for you.

Due to the temperature coefficient, and my northern climate, I prefer ground mounted solar rather than mounting to a building roof. A ground (or pole) mounted array is going to be low enough to the ground that you can easily sweep snow off your panels with a broom. This can be difficult at best or downright dangerous when on a roof. The other advantage with ground and pole mounts is that we can put the panels where they will receive the best sun and have the proper orientation to maximize output. When we place the panels on a roof, we are typically stuck with the angle and direction that the building has, which is most of the time not ideal. In the northern hemisphere we would like to face our panels south and have them angled the same as our latitude. If your mount is adjustable, we can add 15 degrees in the winter, and subtract 15 from that in the summer. That will help us to maximize our annual production. Most roofs nowadays either don’t face south, have minimal pitch, or tend to have so many dormers and additional peaks on them that they become a solar guy’s nightmare. When we do mount PV panels on the roof, the racking they attach to is typically going to space them 4-6 inches off the roof surface. This is to allow air to circulate between the two, thus keeping the panels and roof decking cooler. This can’t compete with the cooling of an open-air rack on the ground.

When trying to live off-grid with a solar system, it helps to get a little more in tune with nature. Try to use your big electrical loads when the sun is shining during the day, rather than at night or on overcast days. This allows you to use a smaller battery bank. By using the big loads during the day, the solar will power most of the load, and the battery will be a buffer to make up any difference. If you run the big loads when there is no generation, it will all come from your batteries. This requires a larger battery bank in order to not overload the system.

Hopefully this answered a few questions and provided some basic food for thought, without getting too complicated.




34 Comments

  1. Very well done. I use outback 4 kw inverters, 2 of them to get 240V at 8 kw, driven by a large array through two charge controllers. Two huge battery banks of Rolls 6V cells. Cheapest solution. I once calculated the expected cost of using electricity stored in that type of battery technology and it was around 24 c /kw. (due to battery replacement costs and expected cycles). So most of the time I *never* use the batteries but instead ‘sell” the power to the utility (and it never makes it past my 2 neighbors of course) — and keep those expensive batteries ffully charged at all times. With my huge banks, 38kwHr total i think, i end up having to add a total of 1-2 liters of water every 3-6 months and i try to do a test discharge once a month. Equalize at every addition of water. System makes me $1400 worth of electricity every year. But one problem with the outback’s of my system — there is some detectible radio frequency interference on the 80 meter ham band. It varies with inverter; my most recent installation has less noise. I have a Xantrex pure sine way 2 kw inverter for emergency usage and it seems to make ZERO ham radio interference. By comparison, i have an inverter generator (not a honda) and WOW! i had to go to huge lengths to solve the enormous S9++++ noise from that thing!!!! (i did succeed.) The prices on these quality inverters seem to be coming down. I got the 2kw xantrex for only $349. Amazing. The outbacks which can do grid connection were more like $1700 each.

  2. How long do solar panels normally last and stay efficient. I am skeptical of the time that companies say their panels last. I think of roofing shingles as an analogous subject when it comes to years they will last, i.e. a 50yr shingle probably wont last longer than 30yrs.

    1. I have ten modules that are more than 20 years old. They show no sign of degrading or loss of productivity that I can measure. I am a little hesitant to buy modules built in China, but I have no facts to back that up.

  3. Great article and parallels my life experience with solar in my cold climate. I find the clear, cold sunny days of February and early March are the most productive for my solar system.

  4. Great article Dennis. I’m just starting to learn about solar since I am thinking about a system for our home. This helps a lot. I’m looking forward to questions and comments from SB readers.

  5. I’ve been designing and installing solar PV systems for over 20 years and living completely off the power grid for over 20 years. I also live in the northern part of the US. You did a good job of touching on the basics. One point on generators and off grid. Readers need to stay away from the whole house standard type. In one system I installed PV, the owner bought an “eco-friendly” unit. It’s internal control circuits and battery charger are the system’s biggest load. You want your generator to consume zero energy when it’s off. In the electrical contracting I do, solar is the most complex to get to Code. The state actually sends two electrical inspectors out. They don’t do that for anything else.

  6. Nice basic intro to whole house systems, I’ve been working my way up to totally off the grid for several years and an ready to pull the plug this spring.

    One of the last upgrades I did was to replace my battery bank with a new forklift battery. My old bank was 8x 6 volt 8L16, which gave me 370ah at 48 volts.

    The new battery have 840ah at 48 volts and the research I did shows the forklift batteries designed to be moved and banged around are very durable and take a lot more abuse being discharged and recharged even down to 30%.

    Of course I don’t plan on discharging them below 70% and actually start to get antsy when it drops below 80%.

    If I was to use the L816’s it would take 16 of them times $300ish per piece or $4800 to get 740ah, I purchased the forklift battery online for about the same price delivered on a semi to my home.

    Downside is you need a forklift cause the battery weighs in at about 2000 pounds, and I needed to get a pallet jack to wheel it into position in my garage.

    I stayed with lead acid this time around, IMO the new battery technologies that are bleeding edge right now will be far more cost effective in another 10 years and this new battery will last that easy.

    As for generators, I went with a Onan 13.5kw propane, works like a charm and I exercise it once a week for an hour which keeps the starter battery charged just fine. A interesting fact, if you are planning on going totally off grid the EPA will fine you if you have a larger generator. Don’t ask me why, maybe trump rolled that back but it was a factor when I purchased mine 3 years ago.

    The Onan uses 1.5 gallons of propane an hour and is very very quiet, and of course rated for hundreds of hours instead of the cheapy wheeled generators you get at home depot. The best price I could find was at Costco.

  7. Good primer on the subject. I to live in the north and have a 9KW pole mounted array with adjustable angle. Since 2014, this is the first year I have kept them at 45 all year rather than 35 summer, 55 winter. A neighbor has a similar sized ground mount array and while mine clear in a day of sun, his takes 3 days. Plus I designed the pole mounts to allow 8 feet of buildup before I have to deal with slideoff. My battery bank is three 48V strings of L16/6V. Time has proven that is a bad configuration for the reasons you mentioned, ie loss of one cell in one battery (out of 24) puts system critical, water consumption is increased due to inevitable imbalance between strings, and adding water misers becomes prohibitively expensive. My do-over would be two strings of larger 2V single cells in 25 cell configurations. This would allow loss of 2 cells from each string with simple setup reconfiguration. Water miser option would be two-thirds the cost. One important point not discussed well is when the system is grid tied and has a automatic whole-house backup generator. Just a couple months ago we lost grid for a day and the gen started. While the PV system shuts down with loss of grid, the PV system subsequently recognized the the gen as the grid and re-energized. Indeed, the PV started backfeeding the gen thus driving the diesel. This can be very destructive to the diesel as it will cut fuel to the point of starving it of necessary lubrication afforded by the fuel. My 10K gen used less than 2 gal in 12 hours. My Sunny controller has the means to eliminate this issue, but is cumbersome as it requires addition of relays and fishing additional control wires between the devices.

  8. Does anyone know how to prepare your solar for an emp? I have heard that the PV arrays and battery will probably survive, but the inverter and charge controller will be toast. The system is supposedly even more at risk if it is grid tied with battery backup. So what can you do to protect from or fix an emp strike?

  9. Thanks for the great article. I read the following, is this a concern for inverters?

    “Some inverters consume 100W or more per hour x 24 hours = 2400W = 2 solar panels per day. A common 6000W inverter consumes 5 panels of energy per day without anything plugged in. Make sure the Inverter idle power is listed and less than 30W. That’s less panels and batteries you have to buy”

    Thank you

    1. I was told by an electrical engineer who specializes in battery technology and works for a main solar equipment provider that you should avoid multiple strings if possible. The reason is that the strings can charge to different levels. A battery never charges to the proceeding level. This is why a battery has a number of what’s called Life Cycles. When one of the strings gets to the set charge the charge controller says “Charged”. The other string(s) may not attain their full charge. The less % you discharge before recharge the longer the batteries will last. This data is shown in the battery data sheet. I have lived totally off grid for 15 years. I used to run L16/420ah wet cells, 2 strings of 4x6v batteries. They lasted about 7-8 years and one string always started getting bad cells first. You also need to parallel strings with equal size and length cables. Last year I switched to one string of AGM (Absorbed Glass Mat) and will never go back to wet cells. No acid cleanup and no adding water. Dust them off once in a while.

  10. This was a very good introductory article and I hope it encourages other people to start their journey toward a self reliant lifestyle.

    Solar has become more affordable than it has ever been and opens up opportunity to live and build a home in places not thought practical in the past. My wife and I just completed construction of our off-grid home in the Pacific Northwest and are learning the ropes of the off-grid power lifestyle.

    In the summer, there is no difference in how we live or use power than when we were on-grid due to long sunny days, but in the winter, we do have to pay attention to winter storms and short days and use power wisely in anticipation of several days of rain and overcast skies. We can use our generator to top off our batteries at any time but we would rather learn to be less reliant on the generator to make up for battery capacity as we move into the third or fourth day with little power input from the solar array. We have found that by making some minor adjustments in how we use our larger electrical loads, we can make it to the next forecast sunny day without resorting to the generator to top off our batteries.

    One thing I heard going into this journey and have found to be true is that it’s always cheaper to find ways to use less power than to buy more panels or a bigger battery bank. LED lighting and modern energy efficient refrigerators make comfortable off-grid living possible and within reach.

    Another thing I have learned is that there is no ideal system. Every system is unique based on the needs of the user, their budget and their geographical location. What this means is that you have to do your own homework and figure out what will work for your own specific situation and circumstances. In our case, we met a very competent solar contractor who also lives off-grid who was able to guide us in our decision making but we still has to do our own research.

    The basic design of our system features an adjustable, pole mounted solar array of twelve 350 watt panels (4200 watts peak output), an 8000 watt Outback inverter and 845 amp hour Solar One brand, 48volt led acid battery bank.

    So far, the system has been working very well for us and we are very happy to have joined the off-grid world in our journey toward a more self reliant lifestyle.

    PS: Federal tax credits which can amount to 25% credit towards your solar system expenses are set to begin phasing out after this year so there is no better time than now to do this.

  11. I don’t know why it is here in west middle Tennessee, but I contact solar installation companies and they either never return calls or they make an appointment and never show up. Pretty discouraging and doesn’t say very much positive about the industry contractors.

    1. The temperature of PV panels is not a major issue. They can be 150 degrees F. and still work fine, albeit with less efficiency. Typically, the hot days of summer are also the days with more hours of sunlight, so that makes up for the drop in panel efficiency.

  12. Great article!

    A little over a year and a half ago my wife and I escaped NE Illinois and built an off-grid home in the American Redoubt along the Idaho/Wyoming line. Our planning process and experience living with PV solar pretty much tracks the recommendations in the article. The only thing I might add is that we went with nano-carbon sealed batteries. They allow for deeper and more frequent discharges, in effect extending their life. It does need to be noted that they are quite a bit more expensive than Flooded Lead Acid batteries. We use a Kohler LP generator for charging during the winter months when there is less sunlight. We had good experience with Kohler for grid down backup in our last house. Kohler’s high quality output and reputation for reliability and longevity factored into our decision. For our domestic water well we made sure to select a 115 VAC soft start well pump to minimize the surge against the inverter. Finally we selected the most efficient pumps we could for our hydronic heating system. During the coldest winter months the pumps that move the glycol are a significant percentage of our electricity usage. Our current daily usage averages between 5 and 8 kWh per day depending on the time of year. Our house is very comfortable and we don’t see our lifestyle as lacking anything. As the article illustrates, planning is key.

    One last thing. We found Home Power magazine to be an invaluable resource for educating ourselves, not just about renewable energy systems, but building techniques as well. I suspect the politics of the editors and contributors to Home Power are significantly to the left of most readers of this site, but its pages still contain lots of useful knowledge.

    1. Home Power magazine rocks. I care less about the politics of someone than I do about good solid information.

      The people who help me here share only some of my opinions. I look past that to the good work they do.

      Carry on

      1. Just downloaded the past 3 years, 18 issues, 365 MB. Look forward to reading them. I’m guessing the older issues would still be good to have, but might included outdated tech or providers?

  13. Dont forget to check your state or local for rebates. When i built my stand alone system of solar and wind the peoples republic of ny rebated half the cost of materials (i did all the labor). Best thing i ever did when the power goes out i can plug in the heat pump and furnace fan and have the warmest house on the street. Please note make sure to NEVER plug in a unit without a double throw switch if you have grid power.

  14. Been looking into it, but have questions about tracking. Does anyone have any recommendations about the tracking system? I’ve read that it can increase overall output per day by 30 to 35%. I’ve seen 1-axis and 2-axis powered systems and an oil filled non powered system that moves the oil and thus the panels with the sun.

    The powered tracking systems I’ve seen 2 controlling systems. One tracks the sun by light strength, the other tracks based on GPS location, date, and time moving the panels whether there is direct sunlight or not.

    I know the electrical, it’s the fine details that is the problem. There is almost too much information based only on what some sales person has in stock, not on the most functional system that provides the most output and longest life for money invested.

    1. I’ve used a Zomeworks passive tracker. It was very low maintenance. They don’t use external power. They tilt with temperature change, and then re-set automatically, after sunset, to face the next dawning sun.

    2. We have a couple of pole mounted arrays totaling 3.4 kW. We looked into tracking systems. One of the things I learned by taking a solar installation class through the Midwest Renewable Energy Association years ago is if the tracking system fails to a point where it has to be replaced, you have to take the entire array apart just to get the tracking system off and replace it. My wife and I decided that the less moving parts and the simpler the design the better. We took the money that we would have spent on a tracking system and just bought more capacity in our PV panels to make up the difference of what a tracking system would have allowed us to generate. I can still adjust the tilt manually depending on the time of the year. This works for us because we have an unobstructed solar window to the south and we can generate more electricity than we need for all but a couple months of the year. In a situation where you need to maximize all you can get out of your solar window, a tracker might make more sense. As the article noted, every installation is different.

  15. I live off-grid in Utah. I’m small potatoes compared to many responding here. I use a single, 24 volt forklift battery and 3300 watts in PVs. 4kw Magnum inverter. The ground mounts and short pole mounts are fine if you don’t have elk and deer around who want to rub their antlers on the array. I suppose one could fence around it to keep large critters from causing mischief. I chose to go high, using a heavier gauge pipe for the mast.
    After a good snowfall, only two hours of direct sunlight is required to clear the pole array. The nifty thing about a forklift battery is that cabling between cells is not an issue. One can acquire a forklift battery with removable cells enabling easier placement and replacement of a bad cell. The manufacturer tells me that running a 1500 watt water heater on the battery is not a problem, and I’ve found that to be the case. 72 amps divided amongst 12 cells is only a 6 amp pull on each one. I can heat 38 degree water (incoming) to 115 degrees at night for about 4% of capacity, assuming I arrive at the cabin at night and don’t fire a generator. In the summer, the water (heater is in the loft, where it’s hot anyway) is already around 86 degrees and taking it to 115 takes only about 1.5% of capacity. Naturally, I prefer heating water in the early afternoon.
    At work, we had an old electric forklift that never required a battery replacement the whole 30 years I worked there, despite much neglect. It’s still running, ten years after I left the company.
    If a national emergency (loss of grid) ever eliminates the supply chain, battery life will be a huge consideration.
    Dennis Williams did a super job on this topic and I hope he writes more.

  16. I am not from the USA.

    What is LP?

    We use 240V in my country (asia). Have written to Kill A watt about whether they have a 240V version but they did not reply despite numerous re-sent. Appears to be pretty arrogant co. Please recommend alternatives products / brands I could use.

    Could you recommend sites I could visit to get a good understanding on how to set-up a PV system for my whole house that runs on 240V system.

    Thank you pat 24/02/19

    1. I don’t see a problem having a 240v system, just get an inverter that does 240 and plug it in. I use a Magnum 4844 (or is it 4448?) any way its a 4400 watt inverter with a 48v battery bank and it gives 240v output. I only need 240 to run well well and my welders but thats a big thing, it handles all my 120v needs too.

      I could see where having 240v everything would be a very economical advantage.

      1. When buying high voltage DC to AC inverters, double check to make sure that they are ones built for the U.S. market. Most foreign 230-240 volt AC countries have their power at 50 cycles instead of 60 cycles. You don’t want to fry any of your 240 VAC electronics.

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