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Sizing Solar

July 8, 2019

Entirely too often, when we start talking with the average “prepper” type, with their focus on some potential future singularity that will result in SHTF or TEOTWAWKI, we see an emphasis on trying to maintain the status quo as much as possible. This ranges from “I’m gonna stockpile enough fuel to run my BugOut Vehicle, because walking is for plebes” to “I need a 18.9 KWH stand-alone off-grid power system with PV panels and an automatic switchover diesel/propane/etc generator, because I want to run the same six televisions, four video game consoles, eighteen laptops and assorted other electronic devices, and I want to be able to leave the lights on all the time if I want.”

This is a ridiculous notion of course, and even though too many “preppers” unconsciously adhere to it, they still generally have the sense to at least verbalize, “Man, SHTF is gonna be rough,” even as they imagine themselves not suffering too much. The more I’ve studied and discussed things with experts in other areas, the more the concept of “Collapse Now and Avoid the Rush” has made sense to me. By reducing our supposed needs now, we enjoy two benefits: first, we begin to recognize how little we actually need, and thus, how much of our purchasing is a matter of being convinced by marketing that we “need” or “want” shit that we really don’t have any use for.

Doubt it? Look at the growth industry known as “self-storage.” The idea that you have so much shit that you don’t use daily, that you need a separate, off-site place to store it, is mind-boggling to me. I’ve rented self-storage units before, but only in the short term, while in the process of moving, or—in the case of the farm—while building the house.

Specifically today, we’re addressing the electrical demands of “off-grid” living during the decline. Typically, when I’ve looked at either installed package deals for off-grid PV/Solar, or I’ve read the descriptions in various books and magazine and web articles, there is this assumed notion that the purchaser is going to run what might be termed a “modern” household on the system. Of course, this includes not only lights, refrigeration, television and DVD, but also the requisite Amazon “Alexa” device, gaming consoles and Internet routers, food blenders and processors, microwave ovens, and a host of other things that I’m sure I’m overlooking, since don’t use any of it, let alone rely on it.

When people find out I’ve spent so little on building our PV system, they usually respond initially with “bullshit!” but then they want to know how I managed it.

There are two basic ways to determine how big of a system you need. The industry method is to determine what you typical daily usage is, factor in some marginal amount (10% for instance), and then multiply that by 3, in case of cloudy days or inclement weather, and then build your system around that demand.

In order to do this, you simply need to know the wattage of every electronic device you will use on the system. Some devices this is easy to determine, because it is listed on the packaging. Light bulbs for instance, almost invariably tell you exactly what their usage is.

For other items, like fans, or televisions, this requires a little bit of math. Fortunately, that math is pretty simple. If you look at the UL label on the back or side of various electric appliances and devices, it will generally tell you what the voltage is, and what the amperage draw is. By multiplying these together, you get to figure out the wattage. As an example, our bedroom fan (we don’t have A/C in the house yet), draws 0.6 amps, at 110 volts. So, 66 watts, assuming I just did my math right… Our television, on the other hand, also uses 110 volts, but draws 5 amps, so it is running 550 watts. By adding up the wattage of all of your electrical demands, you can determine what your total daily consumption should be. Then, you multiply that by a given modifier, representing a number of days, to account for the maximum expected days you might have total cloud cover, negating the panels’ ability to recharge the battery bank. It’s really pretty simple.

The problem with this, for us, was that we didn’t have any idea what our total demands might be. I might go all week without using my laptop at all, and then be on it most of the day on Sunday, prepping my articles for the blog for Monday. At other times, I might spend 5-6 hours every single day, for several months, working on a book. My kids don’t generally watch more than 30-60 minutes per day of cartoons on the DVD, but on a shitty weather day, we might let them watch a couple of movies, adding up to 3-4 hours. My wife goes through phases where she won’t watch a movie for weeks, and then she’ll go through a phase where she stays up late, watching movies until 1 or 2 in the morning, while I lay in bed reading.

Of course, that is daily life now, rather than in a post-grid environment, where we don’t have time for recreation, right? Well, not exactly. You’ve got to remember, after all, that we live this way every day. It’s not a summer vacation for us. We take care of the animals and the gardens every day, just like we will when things get worse. I spend time in the gym and on the range every day, just like we will when things get worse (We have a pretty decent Crossfit box in the backyard, as well as cross-country sprint interval tracks cleared and measured for 200, 400, 800, 1000, and 1600 yards. Anything longer than that, I map out a cross-country route, or just run the roads). The only thing that will really change much, in our daily scheduling, as things get worse, is we can reliably expect to have more people around, as various members of the clan decide it is time for them to emigrate to the farm from their homes in town. So, there might be slightly less television time for the kids, since they can be sent to play with their friends and cousins, more often than the 2-3 days per week they currently get to spend with our people.

There will be slightly less light usage, since I’m more likely to be outside after dark, providing security efforts, but even then, that will be balanced out by the demands of recharging batteries for night vision, flashlights, and etc….

(Which, in itself, is a great example of re-thinking traditional prepper concepts. When I was growing up, the conventional preparedness wisdom was, have lots of kerosene and/or white gas Coleman lanterns to see by after dark. For Night Vision, you still have people who seem convinced that “ten minutes after the lights go out, all the battery-powered equipment will be useless. My question becomes, which do you think is going to run out quicker? The amount of kerosene and white gas you can safely store in your home/garage/outbuilding/etc, or a handful of quality rechargeable lithium batteries for aircraft aluminum flashlights and battery powered lanterns? Take your time thinking about it. It took me a good decade to realize my older conviction on the matter was inherently flawed…)

Additionally, we had limited funds when we were building (we still do, to be sure!), and a lot of the appliances we already owned were not at all appropriate for an off-grid PV system. So, rather than sit down and try to pencil in hypotheticals, I sat down and determined what our absolute minimum “must-have” was, to keep my wife and kids from mutiny. Then, I looked at what I could afford to do. I realized I could probably do the above, with three days worth of reserve, based on the needs I had listed. Those boiled down to, “low wattage demand lights in each room, the ability to charge two cell phones, and two laptops, as well as the ability to run the television and DVD player, and a chest freezer (which I will come back to…).

Once I knew the wattage demands, I needed to convert those to watt-hours. To do that, you simply multiply the watt demands by the number of hours you expect each device to be used daily. So, if my television draws a hypothetical 500 watts, and it is turned on for 6 hours a day, that is 3000 watt hours, or 3 kilowatt hours (KWH). If I keep the lamp in the living room area on from around 9PM, when I go to bed, until 7AM, when I’ve finished getting out of bed, doing PT, and eating breakfast, then it is on for 10 hours a day. If the bulb draws 9 watts (it does), then I’ve used 90 watt-hours.

So, based on my total KWH usage, I can determine both the wattage of my panels needed, and the battery bank storage I need (and, in fact, to a lesser degree of importance, the size of the inverter I need. Lesser, because I simply oversized that to a 5KW inverter, so I knew I would have ample leftover load availability).

We’re far enough South that, even in the winter, most days, we’re going to get a solid 8-10 hours of sunlight on the panels. I have a 1.5KW panel array currently that, according to my charge controller, which is a 60 amp controller, produces around 58-59 amps, for 6+ hours a day, even in winter time. That means, my panels are producing more than 9KW per day. Really, they’re producing closer to 12KW, according to my half-assed record keeping efforts. Of course, that’s on sunny days. On overcast days, they produce less. I will say though, that, unless we are socked in with rain or fog, even on completely cloudy days, we’re producing at least 40-50% of those numbers.

Our usage at night is low enough that, usually by 9AM, my batteries are back at 100%, and are in a float and equalization phase, maintaining their life span.

Our battery bank started out with 6 Everlast Marine/RV deep cycle batteries from Wal-Mart. Those batteries, that no serious off-grid solar person would look seriously at, cost me $70 each. They lasted the better part of three years (and some of them are still in use in different applications). When I replaced the battery bank, I wanted something better, but I knew I couldn’t afford to buy forklift batteries or any of the other typical high end off-grid battery choices. On the recommendation of a local acquaintance who specializes in off-grid installs, I went with Duracell AGM batteries from Sam’s Club, for $170 each. Initially, I bought six of them, each of which is a nominal 105 amp hours. Multiplied by the 12.6 volts of a fully-charged 12V battery (don’t ask, because I can’t explain why the fuck a battery is called a 12V, if a 100% charge is actually 12.6 volts….), that ends up providing just short of 8KWH of storage. Of course, if you discharge below 50%, you dramatically reduce the life cycle of the batteries, so functionally, that battery bank provided a mere 4KWH of storage. In theory, that should not have been enough, since it didn’t offer any leeway for cloudy days without sun. In practice though, we found that it did. All we had to do was, on days without clouds, the kids weren’t allowed to watch anything on DVD until after the batteries had reached 100%. Since we get some charge from the panels even on cloudy days, this really ended up not making any difference in their lives at all.

Nevertheless, in the interest of keeping the system more robust, I eventually added more batteries, as I was able. This is generally frowned on in the solar world, because if one of your older batteries is weakened, it will draw down and damage the brand new batteries. What I’ve found has worked well for me is to simply make sure I tear the whole battery bank down, and test each individual battery, before adding the new batteries to the mix. So far, this has worked well for a couple of years anyway, and I don’t foresee any sort of reason why it shouldn’t continue in the future. What I have ended up with thus far is 12 of the Duracell batteries. That’s a nominal capacity of 15.8KWH, or a practical limit of 7-8KWH. My 1.5KW array, as I mentioned previously, tops that off by 9AM, even in the winter.

For us, that means that, since the panels then maintain the battery bank at a float charge of 13.75 watts, until late in the evening (around 7:30PM this time of year, and—conveniently—because of latitude, roughly the same most of the winter as well), when the house shadow finally blocks the sun from hitting the panels, we can use all the electricity we want, with no concerns.

Assuming you paid the $1/watt for panels, the panel array could be put together for $1500. The battery bank cost me $2200 (I had to pay core charge on a couple of the batteries). My inverter was $500. My charge controller was around $300. So, for less than $5K, I’ve got a system that I barely put a dent in the maximum capacity of.

How did I do that? By reducing our demand. We collapsed now, and avoided the rush.

What do we have, in our house that runs off the electrical system?

A 54 inch flatscreen television. It’s not connected to anything except the DVD player, and occasionally my wife’s laptop when she downloads a movie to watch.

A small DVD player. Seriously. It was like $30 at Wal-Mart like 4 years ago.

7-9 watt light bulbs, throughout the house. Off the top of my head, we have 10-11 in the house. At any given time, somewhere between 2 and 5 of them will be turned on. We’ve conditioned the kids to understand that they have to turn lights off when they leave a room, and they know they are not allowed to sleep with the light on.

We have four fans in the house. Three are box fans that draw 0.6-0.8 amps. One is a small reciprocating fan in our bedroom area that draws 0.4 amps. For further air conditioning, we installed a “geothermal” system that involves 100 linear feet of 4” pipe, buried 6 feet below the surface, and coming up through the floor in two different places. It works…..meh. Between it and keeping windows open, it will keep the house 20 degrees cooler than the outside temperature. That’s significant…until the outside temperature is 120F…..

We charge two laptops (occasionally. My laptop usually gets plugged in on Sunday morning, so I can write my articles for the week. If I’m working on a book, I do it during daylight hours, and then unplug the laptop for the night). We charge two cellphones, and most of the time, I forget to plug mine in until I get in the truck to go somewhere.

I run a Ninja blender daily. It’s actually got a pretty high draw, but it’s only on for literally seconds, so it really doesn’t even count, as far as I can tell. Beyond that, we’ve got Streamlight rechargeable batteries for flashlights, Yaesu radios on chargers, a couple of cheap Cobra handy-talky radios on chargers, and a AA/AAA charger with rechargeables that gets plugged in when I need to charge some.

The only other thing currently on our system is a 7 cubic foot chest freezer. It draws a pretty significant amount (I want to say like 500 watts?) when it is running, but it only runs a couple hours a day, even in summer, so it’s not that bad. The big issue with the chest freezer is the same issue with running power tools and refrigerators off inverters, and that is the start-up surge. Typically, we tell people to budget for 2-3x the running draw for the start-up surge. It doesn’t hurt the battery bank or the solar panels, since it only lasts for a second or two. What it is rough on though is your inverter. We weren’t able to run the freezer on our first inverter. That was a 2KW inverter, but it was purchased at the local AutoZone, and is used by plugging cords directly into it. The problem with them is that none of the outlets will actually tolerate a 2KW draw. Each is only good for 500 or so watts. My 5KW inverter was fine with the load, unless I turned on everything in the house at the same time.

The current 3KW inverter that I purchased to replace the 5KW one, after it was damaged by lightning a couple weeks ago (ground your shit!!!!!), tolerates it, even plugged in to the outlet, but just barely. It will actually chirp the overload alarm. That’s an easy fix, I just need to add another breaker and outlet for it to the household power wiring. I’ve brought in a cousin who is an electrician to do the household wiring, and we’re waiting for him to be able to come back out and finish that task.

The same issue will arise with refrigerators. We have been using a propane refrigerator, bought used from a RV dealer. It works, but it’s a pain-in-the-ass, because it goes through so much propane. Since, even used, it cost me $1300, and it blows through a 20# tank of propane a week, it would have actually been more cost-effective to have simply bought a standard electric refrigerator, on the 5KW inverter system….(I’m familiar with the idea of using a chest freezer with an external thermostat plugged into it. We tried it. It didn’t work worth a damn for us, just because of the inconvenience).

The real moral of this isn’t how inexpensive a solar PV system can be built. We’ve covered that before, not all that long ago. What it is about is determining what you HAVE TO HAVE to live comfortably, if not excessively. What do you really need?

We can look at this from the rule of 3s….

Three minutes without oxygen.

Three hours without shelter.

Three days without water.

Three weeks without food.

Unless you’re on oxygen for health reasons, the only thing you’re really going to need electricity for is possibly ventilation fans, to keep stale air flowing, if you’re dealing with airborne contaminants outside of some sort, whether from an CBRN threat or smoke from wildfires, etc….

Three hours without shelter usually makes people think of staying warm in cold weather. Running electrical heat on solar is a non-starter. The demands because of inefficiency are simply too much. I’m aware that some people are running mini-split heat pumps that serve as both A/C and heat, but I genuinely don’t know how they are doing the heating side without it being ridiculously expensive.

More practical is what I mentioned previously. The use of strategically placed fans, with a properly designed house for the environment, will provide ventilation adequate to stay alive, and moderately comfortable. To be sure, if you’re used to year round climate control, and keeping your home frigid with modern A/C, it’s going to take some getting used to, but people forget, already, that the first practical residential scale air conditioning in the South didn’t come about until well after World War Two. (Carrier built the first electrical A/C unit in 1902. The first residential installation of electric air conditioning occurred in Minneapolis, in 1914. The first window unit was developed in 1945.).

One of the big applications of electricity in the household is one I’m currently trying to get caught up on, and that is running water. I’d like to stick with a 12V system, but the pump needs to be located far enough from the battery bank, on the opposite side of the house, that it’s not practical because of line loss. Instead, I will probably be using a high efficiency 110V pump, since it won’t run for long periods of time anyway. My backup water system, pumping water from the pond to the storage tanks in dry weather, when the rain doesn’t refill the tanks fast enough, I can get away with a 12V pump.

If I was in a place where I could install a water tower for an elevated, gravity-fed system, I wouldn’t need the household pump, but I would build a water trailer, with a large tank, and a dedicated two battery bank, small charge controller, and its own panel.

Three weeks without food. The electrical application to this is obvious. Sure, we can—and should—can foods, dehydrate foods, salt and cure foods, etc, but the convenience of a freezer, for both long term and short term storage and preparation, cannot be denied. I don’t know that I’ve ever met a “prepper” that didn’t have a chest freezer. Too often, their stated plan when the power goes out, falls back on a gas or diesel emergency generator. That’s fine, as far as it goes, but its not a particularly resililent plan, is it? After all, if you’re prepping for anything beyond a short-term power outage, what do you do with all that meat and food when you run out of fuel? Even the prepper porn fiction regularly discusses some woebegone prepper’s wife suddenly forced to cook up everything in the freezer before it goes bad, and sharing it around the neighborhood.

Now, I’m the last motherfucker out there that is going to suggest that sharing food with neighbors is a bad idea, obviously, but…wouldn’t it be nice if you had a way to keep that food a little longer, and share it out in a more rationed approach? I think so…

(I’m also familiar with the argument that having solar panels will just make you a target for thieves and raiders. Meh. If raiders/bandits/outlaw bikers/cannibalistic San Franciscans are going to be a problem, they’re going to be targeting anyone who seems to have anything, not just people with solar panels….The defense for that is not a lack of preparedness, but rather, is projecting security outward, and interdicting them before they get close enough for it to matter. That, of course, is the entire point of Volume One of The Reluctant Partisan….

Of course, beyond just storing food, in the freezer, electricity also facilitates food production in the form of electric mixers and food processors that can be legitimate labor savers. Most of those devices don’t draw a particularly large load, and they’re generally not used very long (the exception would be “bread maker” machines. Those abortions of inventions are not practical, in my experience, off-grid.).

Beyond those, really, the big demands for the off-grid system, from our perspective, is just the ability to keep flashlight batteries, etc charged, and those don’t draw much at all.

Ultimately though, whether you’re planning on moving your entire house off-grid (I highly recommend it!), or you’re just thinking about building an emergency power system to power a few key systems like lights and freezers and maybe charge batteries for radios and flashlights, you need to come up with a way to size your system.

Sizing your PV array is determined by available sunlight hours daily (generally in the winter, since that will be your least sunny season), and the kilowatt hours of your battery bank, and total wattage of your load(s). Sizing your battery bank needs to be based on your expected maximum daily demand. If you’re going to draw 1000 watts, for six hours a day, then a 5KWH battery bank (nominally a 10KWH battery bank, remember!), is not going to be adequate. Really, for that 6KWH demand, you’d want at least an 18KWH storage capacity, but again, as I mentioned previously, that’s not necessarily realistic, and it may not be necessary.

On Batteries

Typically, when you talk to solar off-grid folks, the first thing you’ll hear about is not the PV panels, but the battery bank. Most battery banks are built from reused forklift batteries. These are massive—really MASSIVE—batteries, and are typically 6V, instead of 12V. In order to get to a 12V system, you’ll need to wire two of them together in series, and then each series can be wired together in parallel. The advantage of the forklift batteries is that they are so massive, they offer a lot more power available per battery. The disadvantage of forklift batteries is that they are so massive, you damned near need a forklift to install them. The other disadvantage of forklift batteries is that they are generally procured used, and when they are used in forklifts, they are used hard, and a lot of times have been overdrawn repeatedly, throughout their service life. That means they’re probably not going to last as long as you would hope.

A bank built of 12V batteries will require more batteries, but they are much more manageable. Additionally, the availability of maintenance-free, deep cycle batteries makes them damned near idiot-proof (evidenced by the fact that I’m managing to deal with them successfully….). I’m completely sold on the Duracell DTG31AGM batteries I am currently using. They’re only 105ah each, but they are holding up remarkably well, and they are maintenance free.

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15 Comments
  1. SharpsShtr permalink

    Great info on an important subject. I have a couple of questions if I may.

    1) Did you look into Lithium storage batteries? I’ve heard good things (deeper draw without damaging the batteries, a great many more cycles, etc.) and bad things (much more expensive, don’t live up to expectations) about them. Any thoughts?

    2) I’ve heard that lead acid batteries (like the forklift batteries) need to occasionally be desulfanated. Is there any need to do that with AGM batteries?

    3) For your geothermal system, is that passive? If so, do you think that putting some small fans on them to draw the air through would be worth the current draw?

    Thanks so much.

  2. LowKey permalink

    Regarding batteries for your PV system, look into nickle-iron batteries aka Edison batteries.
    -They use an KOH (lye solution) as the electrolyte and the cell plates are not consumed by the reaction over time.
    -They aren’t harmed by overcharging or by draining them to nearly zero charge.
    -Have a working lifetime well over 80 years. If they start to have issues you simply drain the old electrolyte from the cell and replace with a new, and you can make lye yourself from wood ash if need be.

    Downsides are their power to weight ratio compared to lead acid (but you’re not moving them in a home PV system), and a higher self discharge rate than lead acid (also not a problem on a PV system), and they cost more per watt than lead acid.
    Short term you’re probably better off with lead acid (cost, ect) but as these NiFe batteries absolutely do not suffer from the problem of adding new cells to an existing bank you could add a few over time as funds permitted with the goal of having a very robust low maintenance battery bank. Obviously not a top priority thing, but maybe something to keep an eye out for.

    Wish I could send you all the data I have on them, as well as lead acid battery manuals from back in the day when such things were serviced and repaired rather than simply replaced.

  3. jimd303@reagan.com permalink

    When I installed an Earth Tube, I used 4″ pipe ( the cost was hard on me and those are cheap ). Wasted effort ( and I hand dug the trench ). My neighbor told me, too late, to use sewer pipe instead. And he had a mobile home instead of an RV. And he only needed fifty feet to my 100. You need that few extra inches in diameter. As for a microwave, it isn’t necessarily a luxury. I eat “nuke bread”, which is whole wheat flour and water ( one half water to the wheat ), spread on a ceramic plate and microwaved. 1 1/2 minutes one side and 1 minute the second and done. Yeah, it tastes as bad as it sounds. But dirt cheap bread for a lot of my calories. 150 watts is a big hit for making two of those breads, but much cheaper than propane and you can eat them for breakfast instead of waiting on the solar cooker. Not a necessity, but not exactly wasteful either. I appreciate your previous mention of the sealed batteries. Info I wished I had before all those Wal-Mart marine batteries. They will be my future replacements.

  4. Vagus permalink

    I dunno about the cell plates not being consumed in the Iron Edison batteries; KOH is corrosive, the literal definition thereof being how much steel is reacted over a time period.

    As to battery equipment, my tactical light is a rechargeable battery, as well as my hand warmers, emergency/ night lights, etc. I’ve seriously considered getting a battery chainsaw, because as you stated I can keep batteries topped off for roughly infinity longer than I’d have gas (side note below). I’m a big fan of rechargeable battery banks for phones and tablets, and with a small temporary PV system my plan for now is to charge the battery banks, and then use those to charge my electronics. Much less efficient, but if something goes horribly wrong I’d rather smoke a $50 battery than a $700 phone.

    Side note: Like me, you’re in the Appalachians. Around me you can find coal veins where roads were blasted; I’m told that it’s not rocket surgery to heat coal and shale to extract kerosene. That coleman stove may well be fueled for a long time after all.

    • GM_Man permalink

      Yes, KOH is corrosive, hence the necessary safety measures such as goggles, face mask, rubber gloves and chef’s apron are required. However, Edison used the combination of nickle and iron in his batteries in order to take advantage of their galvanic scores. KOH is used as the electrolyte and the charging current from your DC source (solar, or converter) prevents both the iron and the nickle from being consumed. However, the H20 in the electrolyte does get consumed during the charging process and produces Oxygen and Hydrogen in small amounts, such that de-ionized water has to be added to the batteries as a maintenance task. The plates are simply not harmed for the most part that I am aware of.

      • Vagus permalink

        Neat. I hear so much advertising for Iron Edison in prepper content that I was starting to suspect that they were a gimmick.

        I’m not an engineer or electrician, but I’m aware that some machinery uses sacrificial cathodes to divert galvanic action. I’d be amazed if something wasn’t getting consumed somewhere.

  5. Jim Irwin permalink

    Curious about charge controller and inverter recommendation and your experiences . Also the connectors used and wire size.

  6. Edwin Camino permalink

    Your “buried geothermal system” – I assume natural, not forced air, circulatiion; do you have temperature differential info – input and output temps? How do you protect the inlet side (I assume it’s outdoors) ? Did you examine buried water lines, and small pump and heat exchanger(s)? Do you have enough on-site grade to utilize thermal siphoning in a liquid system?

    Well pump – deep or shallow well? What depth? What 110V pump(s) look promising, and what’s their capacities (gpm, pressure and amp draw)? Are your storage tanks pressurized? (years ago to combat intermittent grid power I used a 240V generator to power a 8.5 gpm deep well pump and installed two pressure tanks each with 46 gal draw down; I noticed as tank pressure increased (50 PSI shutoff – higher pressure meant more water in the tanks, I finally installed a pressure regulator on the output side set at 35 PSI) amp draw increased substantially. I could pump for 12-14 minutes and with water saving appliances and careful use not have to re-pump for 6-12 hours.)

    Food storage – did you examine 12v high efficiency freezers?

  7. GM_Man permalink

    Regarding sizing: Back when we bought our current home I reviewed the history of our AC use via the monthly invoices. For the life of me I can’t recall the numbers so I won’t go there. I looked for the one month with the highest level of KWh in the year (it was January of course). I converted the KWh in January into KWh/day and designed a pure-sinewave system that could produce twice the daily power requirement. I designed a platform for the solar panels that can tilt as well. The platform can hold 12 solar panels for a total of 2KWh when the sun shines. I have a primary battery system of Edison-style batteries (only 200 watt-hours which is very small). I have only installed 8 solar panels over 20 years. The system is doing fine. I have a small portable generator. I can’t recall the last time I used it. During Irene and a November ice storm we simply adjusted our life style a wee bit. Both were major National Disasters. I know this because all of MSM came to visit and we couldn’t get to town to resupply. TV/Internet wasn’t available for weeks. We lost no food with a refrigerator and a separate freezer. We have two TVs now. One LCD and one LED. I highly recommend both LCD and LED, and skip the power hungry plasma and the larger screens. AM/FM stereo, CDs, DVDs, etc are a wiser solution of news until TV/Internet/Telco are up and running. I have noticed that AM/FM isn’t what it used to be. Damn near everything on AM/FM appears to be recorded and then played back during their time slot. News information is just not timely anymore. Rgds to all!

  8. Paul Foreman permalink

    Thanks for an excellent article. This has made me think of what I can do (baby steps) for myself as I am just starting to look at power needs once the ‘grid’ is down and/or gone.

    I think I am going to look at it backwards – meaning that I will look at the long-term minimum need first. This, for me, is battery power for portable lights/flash lights and communication / radios. After that I am viewing anything else as a luxury just to see what that will produce.

    Once the above ‘baseline’ is figured out, tested and evaluated and I satisfy this first priority I want to look at the next level up to add in computer/data storage support with a following step of refrigerator and freezer support this could also include area lighting. TV and ‘entertainment’ gear may fit in there somewhere but will be considered an “add on” for my first go at planning. This should be interesting!

  9. john mcginnis permalink

    Born in Florida in a time that the only places with AC were the bank, the movie theater and the Sears store. We had what were called attic draft fans. They were the size of the roll about industrial fans. Installed between the ceiling joists with louvers, they sucked air into the rooms of the home and exhausted it into the attic. That was when I was a kid.

    Residing in Texas today I have been conducting an experiment in living without AC. The question I asked myself was — “Could I survive without AC as an adult? Unit has been turned off since May, wife out of town. My May bill was $92, June $70. Usual bill is just north of $200/mo. Now I have the following primary loads during the experiment —

    – 1 side by side refer.
    – 1 full size chest freezer.
    – 1 elec range.
    – Washer/dryer. (dryer rarely used, switched to ersatz clothes line.)
    – LED lights through out.
    – Ceiling fan.

    Average high this date has been running 96deg. Inside temps rarely approaching 85. With the ceiling fan on it feels even cooler. I find it tolerable, so I am judging right now that I can do without the AC.

    I have dropped 2/3rds of the load and could lower it more if need be so I see where the author can rationally size a PV system so cheaply.
    ———————-

    “Even the prepper porn fiction regularly discusses some woebegone prepper’s wife suddenly forced to cook up everything in the freezer before it goes bad, and sharing it around the neighborhood.”

    In a total outage we might do some sharing, but for the most part we would go into a mega canning session using the propane cookers.

  10. Vagus permalink

    I forgot to mention earlier, if you can’t find the volts/amps info you can get a device called Kill-a-watt for $15-$20 that plugs in as an intermediary, it will tell you how many watts something is pulling.

    Beware of the start-up surge of refrigerators and freezers, they will bump you into a much higher class of inverter.

    I’ve got a few Harbor Freight panels and inverter that I’m toying with, besides camping the goal is to be able to charge my portable electronics/ tools in case I lose power for two weeks. I’d love to be able to run a mini-fridge as well, that’s the mid-game.

  11. Jesse permalink

    Great article!

    I’ve read a lot of your stuff, but have never felt I had sufficient expertise to comment. However, I’ve spent my adult life focused on carpentry, HVAC, house as a system, low energy buildings, etc. You pretty much nailed everything, but some elaboration might be useful. Was hesitant to post this – sorry if it’s too geeky.

    – Resilient buildings should probably have somewhere between good and amazing thermal characteristics. Design for a max of 24,000 btu/hr heat loss/gain (2 tons of AC). Yes, this is completely viable. I’ve retrofit dozens of regular houses to below this level, and hundreds to a slightly shittier level. Not applicable to your specific situation, but individuals with primary + secondary heating and cooling systems should make the secondary a 1 ton minisplit on backup power. You can use this calculator, but add another 25%-50% for infiltration: https://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

    – Minisplits can do pretty well for heating relative to other commercial sources of btus. Currently a bit cheaper than oil heat in super cold climates (VT). For coolish climates expect a 40%-50% cost reduction relative to oil. More expensive than natural gas and free firewood, less than everything else.

    – For efficient ventilation in resilient homes, Panasonic currently makes one of the lowest energy fan motors (measured in watts to cfm). Their optional continuous duty fans (WhisperGreen iirc) can double as inexpensive fresh-air ventilation. Ideally this would be secondary to distributed fresh air, but whatever. All ventilation from outside should be temporarily shut off and intakes covered during crises that compromise outdoor air quality (fire, radiation, CO, etc).

    – Did you do any solar projections in PVWatts? Probably wouldn’t have added much, but might be useful to Individuals with electric billing history: https://pvwatts.nrel.gov/

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