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# Self-Sufficiency Basics: Electricity

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posted on Apr, 15 2020 @ 06:06 AM

The difference between kWh and kW:

A kWh (kilowatt-hour) is a measure of energy; one Joule is is one watt-hour and 1000 Joules is 1 kWh. That is going to apply to the batteries. A kW (kilowatt) is a measure of power, as in Joules per second. That will apply to the solar collectors and the appliances using power. One cannot compare between kWh and kW, because they are two different measurements.

A solar panel that outputs 12V at 10A under direct sunlight is producing 120 watts or 0.12 kW, not 0.12 kWh! It will (assuming 100% efficiency here for sake of discussion) put 0.12 kWh of energy in a connected battery bank in an hour's time. A microwave may use 15 kW of power; it will use 15 kWh of energy if left on for an hour. But that microwave is usually on for maybe 15 minutes a day, so over the course of a day it is only using 3.75 kWh.

The trick to designing a solar power system is careful consideration of the energy inputs and needs. The first thing to consider is the amount of energy you will need. This can be done with a Wattmeter. Just plug it inline with the various devices you use every day and keep track of both how much wattage is being used and how long it is on. You'll need both figures.

You may wind up with something like:
• TV: 100 watts - 5 hours/day
• Computer: 300 watts - 6 hours/day
• Coffee Maker: 1500 watts - 40 minutes/day
• Router: 22 watts - 24 hours/day
• Alarm clock: 2 watts - 24 hours/day
...and so on. It's important to check every single device that gets plugged in anywhere, even if it seems to be negligible. Also, some devices use more power at times than at other times; it's best to use the highest wattage used (in the case of something like a computer that may vary widely, use a little common sense... if it uses 100 watts all day except for 5 minutes when it was using 750 watts, you can just pad the 100 watt figure a little to cover that).

Now multiply the watts used by the number of hours used, total it all up, and that will give you the number of kWh needed during a single day. Total the maximum kW used and that will give you your peak power requirement. These are the numbers you will need (I'll get into the heavier stuff in a minute). You will need at least 120% (1.2 times) the peak load in inverter capacity, and your solar array size / battery bank size will need to be calculated based on a 24-hour cycle. I'll get to that later as well.

Now let's talk about lighting: I highly recommend LED lights. They use far, far less power than an incandescent bulb, and they will put less loading on your peak power than a fluorescent ("curly-q") bulb. Fluorescent bulbs use an inverter to produce the high voltage necessary to glow, and that means an inductive load that has a sudden high current draw when they switch on. It's not much in the case of fluorescent bulbs (the inverters in them are tiny), but it can be enough to cause a few milliseconds of voltage drop if you are running close to maximum. 98% pf people will never see this, but LEDs are just as cheap now and last just as long with similar loads for the same light; why take the chance?

All you need to add to your list are the actual wattage of each bulb (usually between 6 and 13 watts) and the length of time they are on. As with the rest of the list, remember to include every single bulb, even those that you only switch on for a minute at a time, like closet lights. They won't add much to your total energy usage, but they will affect your power usage.

Hot water is a big issue. It's amazing how much energy is needed to heat water. An average water heater will use two 1.5 kW elements for a total of 3 kW of power, and they run based on a variety of factors. The last thing you want is to decide to run the microwave for a minute at the same time your water heater decides to kick on, and everything browns out around you (or worse, it kills you system). For that reason, I would recommend an on-demand in-line water heater. It will not use any less power, but it also will not be turning on when you don't expect it to. The downside is that if the system fails, there's no reserve of hot water like a tank heater would have.

The alternative would be to simply assume the water heater is on for a certain number of hours per day. I would recommend being very conservative in that estimate, to prevent overloading the system.

HVAC: Forget it. If you have to have electric HVAC, just hire a pro, go with a grid-tie system, use the power company as your backup, and cover the roof with solar panels. This thread won't help you there, because an electric HVAC is extremely power hungry. My heat pump can account for 80% of my total power usage during winter and summer. A furnace using electric fans is not a problem; that can be handled just by doing some research into the power requirements for the fans and making similar assumptions as I mentioned for a tanked water heater.

I know that sounds like a lot of work, but it's necessary if the intent is to get completely off the grid. I'll stop this post here before I run out of characters, and go into some different types of systems in another post.

TheRedneck

posted on Apr, 15 2020 @ 06:56 AM
There are three main types of power systems that I feel need to be discussed:

Off-the-grid:

This is what I am personally after. The home is powered completely by self-produced power, and no power lines are necessary. The advantages include no power bill whatsoever and if there is ever a problem with the grid, your power stays on like nothing happened. The disadvantages are that if your system goes down, you're out of power. It requires a pretty big battery bank and would definitely benefit from regular maintenance. You're on your own with this kind of system, so you need to understand it pretty darn well.

If someone wants to go with this kind of system, I'd highly recommend at least consulting with an electrical engineer during the project.

Backup reserve:

This is where you have an off-the-grid system, but also can use power from the power company. Most home generators are designed this way: they sit there charged and ready in case there is a power failure, and then turn on when that happens. The advantage is that this requires no change in lifestyle or major renovations because you're still connected to the grid. The downside is that you're still receiving a power bill like always, and there will be a flicker when the power fails while the generator kicks on. That power flicker may be fast, but it will reset computers and electronics. The alternative power source is typically some sort of fuel, although there are systems that will operate on alternate green energy sources. A whole-house generator is also expensive.

Grid-tie:

Probably the most popular system going. In this system, you are literally sharing power between your own small power plant and the power company. Of course there are still power lines connecting you to the grid, and you still receive a power bill, but that power bill is typically much less than normal. This system is also the most complex one, so it requires a little more explanation:

For starters, you must use a grid-tie inverter! Never, under any circumstances, try to use a regular inverter in a grid-tie configuration! The reason is that the power we are talking about is AC, alternating current. It is specified at 110 volts, but that can be a bit misleading as to what is actually happening. In reality, the power coming into your house is constantly shifting between ~180 volts and negative ~180 volts... the average power usage (defined as root-mean-square, or RMS) is about 110 volts. An inverter will also produce power shifting the same. If everything is in time, as in, the inverter is producing 180 volts when the grid is producing 180 volts and the inverter is producing -180 volts when the grid is producing -180 volts, everything is fine. But if the inverter is producing 180 volts when the grid is producing -180 volts, that's a dead short, blown fuses/breakers, and potentially a fire. The power grid is producing power at 60 cycles a second (Hertz, or Hz for short) and so is the inverter, but these are never exact... if the grid is actually on 60.001 Hz and the inverter is on 59.999 Hz, you will short out within a second or two enough to blow things.

The chances are better of being hit by lightning while walking past a Ford Escort on a sunny day while meeting Harrison Ford wearing a mankini than they are that you will just so happen to not short everything out.

Grid-tie inverters are designed to read the power grid they are attached to and adjust their own frequency to exactly match. Of course, more technology means more expensive, but it also means less battery capacity is needed to use them. Many are designed to immediately switch over to off-the-grid mode when no external power is sensed, and this is an advantage in that there is no momentary flicker of power to make the change. Usually, there will be a moment of flicker when the power comes back on (this is because the inverter has to shut itself off for safety while it readjusts the frequency) but his may be short enough to not cause a reset.

When a grid-tie inverter switches over to off-the-grid mode, you will need to have a switch to automatically switch off the main power lines as well, otherwise the power failure will completely overwhelm your system. Larger grid-tie units come with this, but smaller ones simply shut down. Remember, with grid-tie, you are not just taking some power from the grid and giving some back... you are a part of the grid! If it goes down and you can't immediately disconnect, you go down too. This makes it less than optimal for survivalist purposes.

Another word about using a smaller battery bank: this is a good thing if your intent is just to drop the power bill; it saves money on installation (batteries can be pretty expensive). But if the point is to still have power even when the grid is down, you will still need as many batteries as with an off-the-grid system! Once the grid goes down, you essentially have an off-the-grid system, just a very expensive one.

One thing that I don't personally like about grid-tie is that, although it is possible to sell the power company more power than you used and actually receive money instead of a bill, you will not get what your power is "worth" on the open market. Commercial power producers not only track how much power a power company receives, but when that power is needed. Wholesale price for power can be very high during peak times (like the middle of winter/summer, on weekends, etc.) but very low when the demand is low (like the wee hours of the morning or nice, temperate days). The equipment needed to track this is extremely expensive and completely impractical for the home producer, so the power company "buys" the power back at the lowest rate they paid for power during that month. If you are running solar, you will not be producing power during the wee hours of the night, but you'll be paid as though you were.

In addition, most companies, last I heard, still charged access fees whether you receive power or provide power. This shows up as a minimum when you receive power, but as a fee when you produce power.

You will also need to verify with your power company that your power meter is designed to handle grid-tie systems. Most are now, but it never hurts to check. Your power company will also inspect the wiring around anything that ties to their grid, and they are (rightfully) very, very picky; make sure you know what you are doing or hire a pro.

TheRedneck

posted on Apr, 15 2020 @ 08:02 AM
OK, a little information about the differences between a true sine wave and a modified sine wave.

Most things in nature are continuous, that is, they don't just switch back and forth instantaneously. That applies to electricity as well. Electricity, however, operates very fast and thus there are cases where the voltage or current can appear to not be continuous. Nature does not like that.

This is a true sine wave:
You can see it moves back and forth with time between a minimum and a maximum value smoothly. The power coming into your home is a true sine wave. That works great with most inductive loads like transformers and motors, because they can be tuned to work best with a single particular frequency of power. In the United States, that frequency is set at 60 Hz; In Europe it is set at 50 Hz. That's why some products made for use in Europe will not work in the US and vice versa.

But as good as it works with inductive loads, household power is just too much for most modern electronics. Your TV, computer, etc. all use DC power which never changes with time. The same with most alternate energy sources; they are DC, not AC. So as technology advanced, high inductive loads became less the norm and most things began to use DC power.

It's pretty easy to change AC power into DC power. To change DC power into AC power, not so much. Oh, it can be done, but it takes a lot of sophisticated electronics and produces a lot of wasted heat. So inverters initially used a square wave, like
This is very easy to make from DC, but as you can see, it doesn't look anything like a sine wave. It also causes some pretty big energy wastes (which become heat, which is bad) on inductive loads. So inverters began to use a modified sine wave like this:
That looks closer, but it still isn't a sine wave.

Now, without digging too deep into the math, any waveform can be thought of as a bunch of sine waves of different frequencies, all added together (that's what the Fourier Transform is for). So when we look at one of these modified sine wave patterns, what we should see is not a bunch of up-and-down lines connecting different voltages, but rather a whole bunch of sine waves of different frequencies. Now, remember when I said transformers could be tuned for a specific frequency? Well, doing so means it will just reject all other frequencies. Some loads will block them, while others will shunt them (like shorting them out). So now, with a modified sine wave, we have all these "extra" frequencies created by the pattern that are not being used. Power is used to create them, but they are useless waste for anything inductive and can even act like little heaters while they are being rejected.

To illustrate, let's look inside an electric motor. When you first apply power, it's not moving. All a motor is, is a coil of wire around metal that creates a magnetic field. Ever connected a wire between the ends of a battery? If not, please don't; a large enough battery will literally melt the wire! So why doesn't that wire in the motor just short out and melt? Because it starts turning!

As that motor turns, little switches inside it (the "armature") switch the power back and forth very quickly. The wires are wound in a way so that they create a magnetic field, which turns the motor, which changes the polarity, which creates another magnetic field, which turns the motor, which changes the polarity... over and over, faster than we can see. A coil of wire takes a certain amount of time to create the magnetic field, and everything is timed so that the energy is being used to create the field just long enough to do so, then everything switches again.

If an electric motor stalls (can't turn) it starts drawing massive amounts of power, because the wires have made their field and now they're just letting all the power through. That's why motors have built-in circuit breakers (some smaller motors use external circuit breakers). They prevent the wires from melting, just like connecting one between the terminals of a powerful battery.

But we have the same thing happening when a motor first starts up! It only happens for a split second, not enough time to melt anything, and the engineers who designed the motor took this into account, but it still looks to the power supply like a dead short. That's why some devices won't work on GFCI or even regular fuses/breakers... they are looking for those sudden shorts, and it doesn't matter how fast they are. Slow-blow fuses handle this, because they won't blow over very short times.

Now the motor is turning, and if it turns at the intended speed, everything works great! If it gets loaded down, it slows a little and that makes it draw more power, which means it has a little more mechanical power, and things even out. But when you start adding in frequencies that are not at 60 Hz, now it is also trying to turn at those frequencies, and it's simply not designed to do so. So to those frequencies, that motor either looks like it is unplugged or worse, like a dead short.

That's what I mean when I say "inductive load"... anything that works by a coil of wire. Transformers work similarly, but they have no moving parts. Incidentally, this is a large transformer:
They're usually easy to spot... they're the biggest part in there, and probably the heaviest. Most electronics uses some type of transformer somewhere, so you can safely ignore small ones. They don't have enough inductance to matter for what we're discussing. If it weighs less than 2 pounds, ignore it for this purpose.

Transformers, at least the large ones, are usually there to change the 110 VAC RMS power to something a lot lower that the device can safely handle. But transformers are very large, very heavy, and very expensive, so most modern electronics uses a different type of power supply: a switching regulator. This works by turning the power either completely on or completely off at very, very high speeds and feeding it into a small storage device called a "capacitor." By carefully controlling how long the power is completely on and how long it is completely off, any DC voltage can be stored in the capacitor. this makes power supplies cheaper, smaller, lighter, and more powerful... and non-inductive! A switching regulator can work just as well with a modified sine wave as with a true sine wave. Computers, flat-screen TVs, video games... they all use switching regulators and all will work fine off a modified sine wave.

Refrigerators, freezers, large power tools, and older high-powered electronics need a true sine wave inverter. They may work for a while with a modified sine wave, but those extra frequencies are doing damage internally and can cause them to fail prematurely.

~continued~

posted on Apr, 15 2020 @ 08:02 AM
~continued~

Sound systems are a special critter here. Large stereos are built with specific filters to remove the 60Hz power signal from the output. They are not designed to remove other frequencies! So test them out... a modified sine wave inverter will probably not damage a stereo sound system, but it can easily cause it to have "buzzing" in the output if the circuitry picks up on those extra frequencies.

And I have already exceeded the character limit... plus my fingers are tired. More later.

TheRedneck

posted on Apr, 15 2020 @ 12:24 PM

Excellent info!

Im not sure if you did this intentionally.. But starting off the second page with this more advanced info is just brilliant.

And yes, kWh and kW are quite different things. So, when I saw referencing a 10kW system, I thought it important to clarify.

Either way, making distinctions for something like a microwave is critical (and I didnt do that). Most will probably think of the larger appliances quite easily.. But there are smaller devices that many may not realize just how much they suck energy.

Microwaves
Toasters
Toaster Ovens
Space Heaters
Coffee Makers (!)
Electric Blankets
Hair Dryers
Clothes Iron

Like weve both said, using an inline meter like the Kill-a-Watt can be a super easy way to check these things. With the Kill-a-Watt, it even has tools to do some calculations built in. They are very handy, even if youve got tons of multimeters laying around. The results may very well surprise you on what does, and doesnt, suck a lot of energy. For instance: Even a pretty beefy Gaming PC can use less than a clothes iron.

I dont think it can be said enough; If the goal is 100% off grid with a typical modern house.. You are really looking at some serious work, and quite a large system (30kWh/day+).

But! We absolutely have ways to minimize use. Those LED light power saving are far, far beyond what most people will believe. Even some HVAC systems are designed to be quite efficient, and clever use of things that already produce something like heat can reduce this further. AFAIK, this really delves into the DIY side of things, though I wasnt personally aware of much about DC appliances, so there ya go. While strongly encouraged.. Looking for a lot of this stuff on the mainstream market is tough (at best).

posted on Apr, 15 2020 @ 01:11 PM

This is all just expanding a bit on what you are already saying. I figure you, Red, know that when Im saying "you," I may not be referring to you.

For emergency backup use, batteries that are rated as "10hr" are an overall better pick. When a battery discharges quickly, it can reduce its effective capacity (described by Peukert's Law).

So, if we have a battery that is 10ah/10hr, it will be designed to discharge its capacity over a period of 10 hours. A 10ah/20hr battery will be designed to discharge its capacity over a period of 20 hours. Putting aside the fact that with many of these batteries, you want to avoid discharging past 50% (and never more than 80%), the 10ah/10hr battery will be designed to deliver 1ah per hour while the 10ah/20hr will be designed to deliver 0.5ah per hour.

These are absolutely not hard numbers! But, these batteries (VRLA) are constructed, essentially, as a bunch of fins in a medium. With AGM, its fiberglass mats and Gel is a.. Gel
The advantages of this design are that they will not spill, and tend to be safer in terms of gassing (which is a consideration if you are going for typical lead acid batteries). The fiberglass mats or gel stabilize the internals, which means that they are less prone to problems from things like impacts as well.

The 10hr batteries will usually be designed with a bunch of thinner fins and the 20hr with less fins, but they are thicker.

How this effects the equations is that the 10hr batteries can effectively discharge more amps, more quickly.

In general, AGM will complement 10hr/emergency backup use while Gel is a better fit for 20hr/continuous use. AGM will tend to charge a bit faster, and can handle burst discharges a bit better due to its lower internal resistance.

Very nice coverage on grid tie, Red. It "sounds" nice, but it really isnt all its cracked up to be. Conceptually, I love it! But, the actual reality of it is a whole different thing.

Alternatively, one might think about discussing sharing excess power with neighbors directly. This will, of course, take some special considerations, including legal, and how its accomplished will vary GREATLY by how close those neighbors actually live.

Hmm.. Not really feeling so great here.. Might have to come back and finish later. Feel free to correct! Most hate it, I love it, and when things ramp up health wise for me.. I become much, much more prone to make mistakes (probably preaching to the choir there, eh?).

posted on Apr, 15 2020 @ 11:13 PM

Thank you for the kind words! I'm just gonna jump back in the middle here, because I want to add some more info to what you have already posted. There's several aspects to this that you have covered, but which can be pretty confusing to the average person.

I'm gonna get down to bare basics for a moment (and yeah, I know I'm just throwing out info in a rambling fashion here) because we're tossing around terms that most people may not be truly familiar with. There are four things that define electricity (not counting the more complex AC or DC question): voltage, amperage, resistance/reactance, and wattage. You can think of these as analogous to water in a hose. Voltage is the pressure behind the water, amperage is how fast the water is flowing, and resistance/reactance (I'm gonna drop the reactance from here on because it is dealing with complex math and can be considered the same as resistance) is the size of the hose. Wattage is how hard that water will hit you if you stand in front of it... the more pressure and the faster it is flowing, the harder it hits.

Electricity just uses different names. Voltage (electrical pressure) is measured in volts. Current (electrical flow) is measured in amperes, or just amps. Resistance is usually a fixed value of whatever you're powering and is measured in ohms.

The basic equation for electricity is E=IxR, which is voltage equals amperage times resistance. If you know any two of those, you can find the other. Don't let the symbols confuse you just because they don't start with the same letter as what they represent... E is voltage, I is current, and R is resistance. Wattage, which goes by the letter P (for Power) is voltage times amperage, or P=ExI.

Most of what we will be discussing is wattage. That's not to say the other quantities are not valid, though, because batteries are built to hold a specific voltage and put out a specific maximum current. Some people may find it interesting that wattage does not just apply to electricity! It is actually an international unit of power. Auto enthusiasts will be familiar with horsepower ratings... that is the same thing. 746 watts is the same as one horsepower (most people round that off to 750).

So, if we have a battery that is 10ah/10hr, it will be designed to discharge its capacity over a period of 10 hours. A 10ah/20hr battery will be designed to discharge its capacity over a period of 20 hours.

Exactly right! That's one reason I still like the old lead-acid batteries. Newer batteries require a more precise "charge cycle," which is essentially just a pattern of how to charge the battery. For instance, one battery may need to be initially charged to 90% capacity at a certain rate, then the charge needs to be much lower to charge the remaining 10%. That's part of what charge controllers do: they are preset to know how to properly charge the batteries connected to them.

Lead acid is heavy, bulky, and takes up a lot of space compared to newer battery types. If you want to make something that can be moved around, lead-acid has some serious drawbacks. However, how often will a home generator system be moved? Probably never, and IMO that gives lead acid an advantage. They can take deep cycles (a cycle is going from maximum charge to minimum charge and back) (especially marine batteries), are easily available, fairly inexpensive, can provide for sudden massive current draw, and are very forgiving as to discharge rate. They do have a couple of "quirks" that can be a problem if not taken into account... perhaps the biggest one is the possibility of a "dead cell." A dead cell is actually a bridge between the plates (a short) that causes one cell to not put out any voltage.

A 12-volt battery has 6 cells inside it, so a battery with a dead cell will put out a nominal 10 volts instead of 12. Some readers might be thinking, "OK, I still have 10 volts," but it's not that simple. Electronic devices require a certain amount of voltage to operate at all, so a 12 volt system simply may not work at all with 10 volts. That's why when your car battery has a dead cell, turning the key only makes that weird clicking sound. The solenoid is getting voltage, but not enough, so it tries to engage, fails, tries to engage, fails, over and over. It needs 12 volts to work, not 10.

Everything in your power system will be the same way, requiring a certain voltage to work. Some of it may work under a range of voltage, but it still has that minimum.

So if you have a bank of 12 volt batteries, and one of them suddenly starts putting out 10 volts, that will literally pull the other batteries down to 10 volts! Power will flow from higher voltage to lower voltage. Now, understand that a battery that is at half voltage does not have half charge.... it is practically uncharged at all to get that low. A battery reaches its full voltage at around 20% charge (give or take), and then changes voltage very little during the last 80% of the charging cycle. So when a 12 volt battery is forced to top out at 10 volts, it can only hold a very tiny amount of energy. The whole battery bank becomes worthless.

I'm not on the right computer to illustrate how to overcome this, but there is a simple way to do so using diodes. A diode works like a one-way valve and will automatically isolate any battery that drops in voltage, while still letting the other batteries work normally. They are also inexpensive and easy to install.

Hmm.. Not really feeling so great here.. Might have to come back and finish later.

Oh, I know the feeling. Worked on the driveway today (which in my case generally means sitting down and panting hard while holding a shovel like a security blanket) and I am dead tired. So I'll stop it here, but I'll be back.

TheRedneck

posted on Apr, 16 2020 @ 02:42 PM

I have little to add on this one, other than: Spectacular primer here. Really and truly.

And, Ill whisper: "I use modified sine inverters" lol

Like I said, I was really trying to make it as accessible as possible while cutting off issues that someone new to this might have. Its a very tricky thing to balance, and Im not sure how good of a job I did. Im still proud of my work!

The original idea was to just.. deliver all this stuff to the customer in a larger package. It really eliminates a lot of issues that come from ignorance (not a bad word..) or intimidation.

You might be interested in my thought process on it. If you read this thread, you probably already note that I was heavily focusing on my personal "take" on automation.

The idea was to try to setup my personal platform to have increased manufacturing capability. In doing so, i figured that if I could just get to that point.. Then actually bringing it to a client in a reasonable time frame was doable.

Clearly, I didnt get there.. It was just such a massive project and I couldnt really figure out how to pare it down because of the nature of the system.

Still think it would have been a cool "case analysis" in how someone could apply it to their specific situation.

posted on Apr, 16 2020 @ 02:56 PM

Audio, and video, really are a unique topic here. Id add in things like guitar amps to this discussion too. Depending on the system, something like a Corcom filter can be a very valuable addition.

I had actually been working on my own surround amps/DACs, etc. but honestly.. The mass produced stuff is just priced too well to pursue for anything other than personal enjoyment.

The speakers, on the other hand, have massive, staggering markups. So, I do have a few designs for those. Of course, all the drivers I picked (Peerless, Hiquphon, etc) all either changed their T/S params or outright discontinued their drivers.. With so much else going on, I never got around to making new designs.

But!

For those so inclined.. There are a lot of folks that share their very, very good designs for free and it can be a really fun project that is relatively beginner friendly. Plenty of kits on offer too, just duckduckgo "DIY speaker kits." Madisound has a really nice selection though, and Parts Express is one of the biggest names in the business for a reason.

I did end up (mostly, kinda) finishing that headphone amp that I think we had talked about at some point in the past.

Like I said.. Sorta kinda finished! It works (and well), so Just found myself using it as is. The enclosure is a old & gutted cd-rom drive. Obviously, if I get around to finishing it, the breadboard's gotta go. Things are too useful, and this ones been tied up for.. a while.
edit on 16-4-2020 by Serdgiam because: (no reason given)

posted on Apr, 17 2020 @ 05:30 AM

And I'll whisper back, "I use modified sine wave inverters, too" lol

I just like to point that out about the difference so people can make their own decisions. I used inverters when driving a truck; everything I had powered by it used a switching regulator, or the motor was so small it wasn't important. The one exception was my TV (CRT model), and it was an already-used set that I wasn't worried about. It would have cost me less to replace it than it would have to buy a true sine wave inverter.

If I were going to use one to power an expensive refrigerator or freezer full-time, it might be worth the extra cost to go true sine wave... and that's a decision everyone needs to make for themselves. If they have good information, they can do that; unfortunately, the information on places like YouTube is far, far too often just plain wrong (in some cases dangerous). I've seen a couple of vids of DIY home power systems where I was watching just to see the fire... somehow they managed to not burn their place down before finishing the video. Luck follows fools, it seems.

I have actually tried to write a how-to book on installing a personal power generator using solar, wind, or water power... unfortunately, I tend to get writer's block too often and it lies here as an unfinished work still.

TheRedneck

posted on Apr, 17 2020 @ 08:09 AM
I want to thank the OP and Redneck for all the information
they supplied here.I have been working on a off-grid type
deal for my vacation camper.
One of the things I thought about is what do I really need?
I have a stove top coffee pot,a key wind clock,no microwave,
a propane stove and fridge.I would need to run a small air
conditioner through summer,run a portable washer and use
a clothesline to dry.A TV would be nice and my computer also.
I could live without the TV and computer,it wouldn't be easy,but
I could do it.
In a SHTF scenario,what would you really need to survive?

posted on Apr, 17 2020 @ 12:41 PM

Youre welcome mama

First.. The TV and pooter really arent a big concern here if you are looking for full "alternative" power for your home (camper or not). They use much less than one might think, but everything does add up..

Right off the bat, Id also suggest moving to LED lighting if you havent already. There are a few ways to do this, with the main ones being direct replacements in the normal electrical system and another being just making it a 12v system all around. Typically in a camper or RV, plenty is using 12v already, so Id suggest that route.

For a normal home, we would look at electric bills. They usually will state how much power you actually use, and it might be stated as "kW," "kWh," etc.

We would want to look at the month with the highest usage and base your system around that.

Im not sure about campers, RVs, etc. but do you have it plugged into your house? We could do a little math to figure out what it might be using and also try to figure out if you are looking to supplement with a normal generator, vehicle engine, etc.

We could look at it in terms of "what you really need to survive," but honestly.. We dont "NEED" any electricity to do that. Beyond that, it becomes very specific to your life and use case. That said, moving a camper/RV to full electrical self-sufficiency tends to be a less daunting task than a home. The only stumbling block for me personally is that there are a lot of specific systems and standards used that I am not entirely familiar with. Thats not to say NO familiarity though, my own LV projects first prototype platform was going to be in an RV, so had to learn a thing or two

posted on Apr, 17 2020 @ 05:48 PM
Hi yall, good info in this topic. I have constructed a simple single accu, single panel system for my mum so she can pump water around her veggy garden. It was a struggle to figure out all variables but somehow I managed to create a system that is pretty maintanance free. It only needs removing the pump before winter and reinstalling it when spring comes.

The installation is working for 8 years now and I only needed to replace the agm accu last year. Mum uses the system like a beast, watering the garden untill the inverter falls into low power allert, so the accu gets kicked around a bit. I leave her be, I am glad she is happy using it and don't want to complicate it for her.

I have made mistakes, and was able to correct them but some where close calls. Like using connectors based on calculations made for the system being 25 years old. I have replaced some stuff that was charred. I didn't burn her shed down only because I had fused the incomming line from the panel. It was a 13A fuse, I never expected to replace, ever.

A thread like this would have been helpfull, even with such low power installation. The small ones are not much less complicated than the large ones. Accept maybe that with a larger installation, it would have burned something down.

I am planning for a system to power my garage plus appliances and wont take short cuts. The currents involved scare me, even with mums simple 600W pumping installation. When I start planning an installation large enough to freeride my power tools and ac on, I might come back here to consult this very usefull thread.

Thanks guys.

posted on Apr, 18 2020 @ 05:52 AM

One of the things I thought about is what do I really need?

That's the key... to use something like solar, you really have to whittle your basic needs down to the bare necessities.

Serdgiam makes some excellent points: LED lighting is something I consider a must. Incandescent just uses far too much electricity, and LED conversion is simple now. If you're looking at something like a camper, I would definitely take his advice to switch over to a 12V system wherever possible, too. That's just not practical for some things (it can be hard to fight existing infrastructure), but going with a DC system eliminates all concern over inverters and takes one of the least efficient conversions completely out of the picture.

He's also right that the power bill is a wealth of information! Here's how to work that evil math:

Look back over at least the last 12 months of power bills. You can discount the cheaper ones and focus on the more expensive months. Now take each of the more expensive months and divide that usage (in kWh) by the number of days in the month, and take the one that gives the higher answer. That is your maximum daily average usage.

Now look at how many hours per day the sun will shine that month. Here, we get between 10 and 14 hours of sun per day, depending on the month. So if my maximum usage was during December, I would use 10 hours; if it were during June, it would be 14 hours. Divide that maximum daily average usage by the number of hours of daylight, and you have the theoretical solar energy need.

One thing I always tell my math students is to keep one eye on the units. You started with kWh (kilowatt-hours) per month... went from that to kilowatt-hours per day when you divided by the number of days, then to kilowatt-hours per hour when you divided by the number of hours of daylight per day. How many hours are there in an hour? One! So the hours per hour drops off, and you are now left with kilowatts. You can multiply that by 1000 to just get watts.

Now comes the tricky part: If you are using exclusively solar, there will be days when there's just not enough solar energy hitting the panels and days when there's plenty. You'll need to check your weather history for that month: Weather Underground is a good source. They will tell you how many sunny days and dreary days during that month you will have in your area on average. You'll need to take the number of sunny days, then add the number of dreary days multiplied by something like 50% to get the number of actual days of energy instead of the theoretical number of days. Now re-run the above calculation.

I am running you through this twice to get a point across: solar is not dependable like we are used to.

I need to point out that that even on a dreary, rainy day, those solar cells will put out some power; 50% seems to be a good rule of thumb, and that is why I say multiply the number of dreary days by 50%. If you want to be a little conservative, you can multiply by a little less than 50%; if you want to live dangerously, multiply by a little more. That's up to you, but remember that this will also make a huge difference in your required battery capacity later on. I'll try to cover that before I pass out again.

Once you have your solar capacity, always add in a buffer... I recommend 20%, so multiply your final answer by 1.2. You will need a solar panel of at least that number of kilowatts or watts.

Now we need to talk battery capacity. Take your maximum average daily power usage from above and divide it by 24 (the batteries will work 24 hours a day). Now take your number of dark days and adjust that (again, you can be a little conservative and multiply by less than 50% or liberal and multiply by more than 50%). Multiply that by 24 and add in the number of hours of night-time you expect per day: that is your reserve time in hours.

Now it's time to convert from watts to amps, since the batteries are rated in amp-hours. Take your system voltage (12 volts for a single lead-acid, for example) and divide the number of watts per hour by that. Multiply that by the reserve time in hours, and you will have amp-hours to size your batteries. As before, give yourself a buffer (I still recommend 20% so multiply by 1.2). That is how many amp-hours your battery bank needs.

A "standard" 12 volt lead-acid marine battery will generally deliver around 50 amp-hours. Some will be rated for more; some will be rated for less, but that's a good rule of thumb. Whatever kind of battery you decide to use, the manufacturer will list an amp-hour rating. As mentioned earlier, that rating my depend on how fast the battery is discharged, so keep an eye on that; a battery will not provide as much power if it is discharged overly fast (some of the energy is used up as heat). Divide the number of amps needed by the amp-hour rating and you have the number batteries in your battery bank.

I'll give an example with numbers in the next post.

TheRedneck

posted on Apr, 18 2020 @ 07:10 AM
OK, here's some actual numbers to follow along with. These are fictitious, just to show how to do the calculations.

Let's say I have the following energy usages from my power bills:

January: 9.87 kWh
February: 8.43 kWh
March: 8.81 kWh
April: 7.56kWh
May: 7.88 kWh
June: 8.01 kWh
July: 9.15 kWh
August: 10.03 kWh
September: 9.39 kWh
October: 7.47 kWh
November: 8.74 kWh
December: 8.99 kWh

I divide these all out by the number of days in the month to get:

January: 9.87 kWh/31 days = 0.3184 kWh/day = 318.4 Wh/day
February: 8.43 kWh/28 days = 0.3011 kWh/day = 301.1 Wh/day
March: 8.81 kWh/31 days = 0.2842 kWh/day = 284.2 Wh/day
April: 7.56 kWh/30 days = 0.252 kWh/day = 252 Wh/day
May: 7.88 kWh/31 days = 0.2542 kWh/day = 254.2 Wk/day
June: 8.01 kWh/30 days = 0.267 kWh/day = 267 Wh/day
July: 9.15 kWh/31 days = 0.2952 kWh/day = 295.2 Wh/day
August: 10.03 kWh/31 days = 0.3235 kWh/day = 323.5 Wh/day
September: 9.39 kWh/30 days = 0.313 kWh/day = 313 Wh/day
October: 7.47 kWh/31 days = 0.241 kWh/day = 241 Wh/day
November: 8.74 kWh/30 days = 0.2913 kWh/day = 291.3 Wh/day
December: 8.99 kWh/31 days = 0.290 kWh/day = 290 Wh/day

OK, now I can see that my maximum daily usage is in January and August, so I'll just work with those. I go to Weather Underground and see that on average, in January I get 19 sunny days of 10.5 hours a day and in August I get 24 sunny days of 13.5 hours per day. Now I re-run my calcs for those two months. I want to be a little conservative, so I'll assume 40% efficiency on a dreary day:

January: 19 sunny days and 12 dreary days
19+(12*0.40) = 19+4.8 = 23.8 sunny days in January
23.8 sunny days * 10.5 hours per day = 249.9 hours of sunshine in January

August: 24 sunny days and 7 dreary days
24+(7*0.40) = 24+2.8 = 26.8 sunny days in August
26.8 sunny days * 13.5 hours per day = 361.8 hours of sunshine in August

In January I used 9.87 kWh and I get 249.9 hours of sunshine; that's 0.0395 kWh/h = 39.5 watts.

In August I used 10.03 kWh and I get 361.8 hours of sunshine; that's 0.0277 kWh/h = 27.7 watts.

So I now know that January will be my hardest month. I use more power in August, but I also have more sunshine available... so all of my future calculations will be made using January numbers. (This will probably be typical for most people in the northern hemisphere.)

Now, I add in my buffer and I get 39.5*1.2 = 47.4 watts... I want a 50 watt solar panel.

Now, I looked back at the previous winters online and I have decided I want to be able to get through a three-day streak of bad weather. OK, that's going to be 72 hours, right? Nope, it will be 72+13.5 = 85.5 hours... don't forget that three days includes 4 nights, you have to add in those extra 13.5 hours of nighttime.

My January power usage was 318.4 Wh/day. 318.4/24 = 13.27 watts. Let's say I plan to use 12 volt lead-acid batteries, so 13.27 w/12 v = 1.11 amps. You have to supply that for 85.5 hours, so that's 1.11*85.5 = 94.9 amp-hours of reserve power I will need. That's two 50 amp-hour batteries, right? Wrong! Don't forget the buffer. 94.9*1.2 = 113.9 amp-hours of reserve power, so that's either three 50 amp-hour batteries, or maybe two if you can get 60 amp-hour batteries. Remember that the capacity depends on the discharge time... in this case, that would be over 85.5 hours.

You will likely not find an exact capacity at that that exact discharge rate; use the closest discharge rate. Also, keep in mind that more reserve capacity is preferable to less; more reserve capacity means less complete cycling and therefore longer battery life, plus it allows you to last a little longer should you get a longer-than-expected period of overcast skies. In the above scenario, I would opt for three 50 amp-hour batteries.

All of this is to size the solar panel and the batteries. The next step which takes into account the maximum power usage is where the power draws for the various appliances come into play.

TheRedneck

posted on Apr, 20 2020 @ 04:49 AM
I like to add one more small thing.

Solar panels degrade over time. Most panels are warranted to have an 80% output after 25 years. If you are looking to build a long term investment you might wanna keep this in mind and take that percentage into account when calculating your installation.
edit on 20/4/20 by D.Wolf because: (no reason given)

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