Introduction: Independant (non-grid-intertie) Solar Electric System

About: I am an ordinary guy. Except that I live in an RV, drive a 250cc motorcycle, have a truck that runs on bio-diesel, am vegetarian, and have had almost 30 jobs in 10 years, including armored truck driver, bicycl…

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Most solar systems installed on houses are hooked up to a special electric meter which can both draw on the grid and feed back into it - which makes the meter run backward.

That is pretty cool!

However, these systems generally run from around $25,000 to $50,000 and take anywhere from 10 to 20 years to make up for their up front cost in reduced utility bills.

My solar photovoltic system is independent of the utility company.  It cost me about $400 (unless you happen to live in an RV, boat, or cabin, it will cost you just a little bit more)

I still use traditional electricity for some things, so I still get a bill each month, but it reduced my electric bill by almost $15 a month, which means it will pay for itself in a little over two years.

Step 1: Reduce Demand

The first step for any type of solar system is to find ways to dramatically reduce the power you use in the first place.

My previous instructable is a great place to start:

These are steps you should be thinking about doing anyway, but it becomes all the more important when doing a solar electric project.

This is because solar systems (whether grid-intertie or not) are priced by the kilowatt.  The fewer you need, the less your system costs, and the sooner it pays for itself.

Step 2: Decide on Grid-intertie or Independant System

There are advantageous and disadvantageous to both systems.

Standard grid-intertie system
-Its the standard.  There is a lot of information about it, and its easy to find someone to do it for you
(of course, if you thought having it done for you was a pro, you probably wouldn't be on instructables right now!)

-It increases the resale value of your home

-Its simple (from the user end, it is actually much more complicated to install)

-You can possibly get government rebate checks

-Some utilities will pay you each month you give them more power than they give you (others will just give you a credit)

-Its really really expensive!

-It will require a professional electrician, and probably a contractor as well, to instal it

-It will most likely require a building permit from the city

-It doesn't work during a power outage at night or in cloudy weather (which is when power outages usually occur)

-It requires additional equipment - an inverter and a new power meter at a minimum

Independent system

-Simple.  You can install it yourself in a day.

-You can make it any size, and expand when/if you want to

-It works during a power outage

-It requires more thought and maintenance in daily use (because of the batteries)

Step 3: Change As Much As Possible Over to 12v Power

I'm assuming if you are reading this instructable that your decision from step 2 was to go with the independent system.
If you want the ease (and don't mind the cost) of a grid system, there is lots of information out there about it.

For an independent system you want to run as much as possible on direct current (DC) electricity.

I bet most people reading this site already know electricity basics, but for those who don't, here's a quick summary:

There are two types of electricity. 
One is alternating current (AC)
The other type is direct current (DC)

As an analogy, imagine standing across from a wall. In your hand you have a rope, which is attached to the wall by a spring. You pull the rope, then let it move forward again, over and over. You are transmitting energy through the rope, even though the rope itself isn't going anywhere.  That is kind of like alternating current.
Now imagine instead of a spring, the rope is attached to the wall with a pulley, and it's a big loop.  (It has to be a loop, or else it would fall off at the other end.)  You pull it along in one direction.  Now, again, you are transmitting energy through the rope, but this time the rope is moving.  This is like direct current.

In alternating current the electrons are just moving back and forth.  The movement transmits energy, but they don't actually go anywhere.
In direct current the electrons move through the wire in one direction, traveling in a big loop to end up back where they started.

You don't actually need to know this.  I just wanted to use the analogy I came up with...

What you do need to know is that in the US, the standard voltage for DC is 12 volts, and the standard for AC is 120 volts.
(Technically, 12v power can range anywhere from 12.5 to 14 volts.  Household AC runs anywhere from 110 to 125 volts)

Anywhere you see the term "DC" it is interchangeable with "12v" and "AC" is interchangeable with "120v"
(there are a few exceptions.  For example forklifts and golf carts often run on 36v or higher DC, and household electric clothes dryers run on 220v AC, but unless it is specified differently, assume that most DC is 12 and most AC is 120)

12v DC is what you car runs on. 
120v AC is what comes out of the outlets in your house.

In order to have an efficient independent solar system at home, you want to use 12vDC in the house, because solar panels and batteries operate at 12vDC.
It is possible to use an inverter to turn 12vDC into 120vAC, but then you have to buy more equipment, and you lose a significant amount of power in the conversion.

One of the easiest things to power with DC is small electronics.  Anything that plugs into a cigarette lighter is already running on 12v.  Cell phones and iPods are obvious candidates.
In addition, anything which uses a "power brick" or "wall wort" - those big square boxes that plug into the outlet - is already running on DC.  If you look at the sticker on the back of the gadget it is powering, it will tell you what voltage it uses.
If it says "12v DC" then all you need to do is replace the cord with a 12v cord (see pictures above)

If it is less than 12v (everything from 2 to 10 is common) than you will need a small DC-DC converter to avoid burning out the gadget.  These are available for less than $10 from auto parts and electronics stores.
This will allow you to plug the gadget directly into your 12v system, and avoid the wasted power that is inherent to all power bricks.

In my home, I found my modem and router both used 12v input, so I unplugged the power bricks and plugged them into my PV system.  Now my internet connection is 100% sun powered!  My AA Battery chargers, my portable phone, my cellphone charger, and my amplified roof antenna (that gets me free over-the-air digital TV) are as well.

The next simplest thing is lighting.  You can find lights that run on 12v at any auto supply store - including LEDs (for WAY less money than the 120v equivalents which are now becoming available to consumers).  The solar panel kit I got came with two 12v lights built in.  Some homes have track lighting which already runs on 12v, so it would just need to be rewired to the new system.  For the most options, however, find an RV or boat supply company.  All RV and boat lighting runs on 12v, and comes in almost as much variety as standard home lighting does. 

While you are at the RV/boat supply store, check out some of the 12v appliances there (often camping supply places will have a few 12v powered things as well). 
Of course, if you read my Guide to Saving Massive Amounts of Energy While Also Saving Equally Massive Amounts of Money, you know that I don't advocate buying new stuff.
But if you actually do need to buy something anyway - say you just moved out of your old home and need to furnish the new one from scratch, or your old appliance recently stopped working - then you can take better advantage of a independent solar system by having as much as possible that runs on 12v, and as little as possible that runs on 120v.

There are some things which are not possible to change over - namely, anything which uses a regular straight plug with no inline converter.  Unless/until you increase the size of your system enough to accommodate an inverter, it makes the most sense to just leave those plugged into the grid.

Step 4: Figure Out How Much Your 12v Items Draw Altogether

Once you have found all the things you can potentially switch over to 12v, make a list of all of them.

Write down how many amps each one draws (they should say on the back, near the plug.  If not, google it)
Some may be listed in miliamps (mA), which just means amps divided by 1000.  To get amps, divide the number by 1000.
Some will list watts instead of amps.
Watts = volts times amps. (W = V x A)
We know the volts is 12, so amps equals watts divided by 12 (A= V / 12)

When you have everything, write it down on some (reused scrap) paper or in an Excel spreadsheet.
In the first column write the appliance/gadget name.
In the 2nd write the amp draw
In the 3rd write the wattage (remember, W = V x A, and V is 12)
In the 4th, write an estimate of how many hours per day you are likely to use each item
(put in an average for things that are only used once a week or so.  Use a fraction of an hour if its less than an hour per day)
Then in the 5th, multiply the watts by the hours, to get the total daily watt-hours (Wh) for each item.

At the very bottom, add up all the Watt-hours to get your total average daily electricity need.

Step 5: Look Up How Much Solar Radiation Your Area Gets

Find your location on a Solar Insolation Chart.

Here's one:
This one shows the difference between different seasons:

If those links don't work, just do a web search for "Solar Insolation Chart"

It tells you how many hours of full sunlight you can realistically expect to get each day.  It takes into account both latitude and weather.
In order to make the full amount of watts that a solar panel is rated for, it has to get direct sunlight.  Just because the sun is up for 12 hours doesn't mean you will get 12 hours of solar electricity.

Where I live, I can expect to get 5 hours of usable sun per day, on average throughout the year.

Step 6: Use the Last Two Steps to Calculate How Many Panel Watts You Need.

In my example, I expect to use 176 Watt-hours per day.

I get 5 hours of usable sunlight per day.

Dividing 176 by 5, I need 35 watts of PV panel power (on average).

However, during the winter there is a lot less sunlight than in summer.  In winter my location can only expect 2.5 hours of full sunlight!
In order to last through the winter months without resorting to plugging back into the grid, I would need twice as many solar panels, for a  total of 70 watts.

I began this project in early summer, so I have several more months to worry about that.  For now I have 45watts of power, a little more than I need right now, but not enough to last me through the winter.

Step 7: Batteries

Those 45watts of panel power, times 5 hours of sun, will give me 225 watt-hours of solar electricity each day.
But of course, I am not using all of my electricity all at once, all during the peak sun of the day. At mid-day I am likely to be a t work, and if I am home, I certainly am not using any lights.  That means in order to make use of those 225 watt-hours, I need to be able to store them somewhere.

Here is where an independent system really varies from a utility-intertie system.
The intertie system takes all the power generated and not used at midday, and pumps it back into the grid, so that your neighbors are actually using the solar power from your roof (and indirectly paying you for it, via the utility company, which takes a cut).
Then at night, when the sun isn't shining, you draw your power from the grid.  If you work during the day, you technically aren't using solar power at all.  Its more like you are leasing roof space to the power company for them to generate solar power for the grid, and then they give you free power later to compensate.

An independent system stores the excess daytime power in a battery bank, which you then draw from at night (or when its cloudy).

This means you need to have a big enough battery bank to store all the power your panels are generating.
In my case, I want a battery bank of at least 225 watt-hours, so that if I don't use any electricity during the peak sun hours on any given day, I can store all of it and none gets wasted. 
For longest battery life, they should never be drained below 50% capacity, so its better to get twice the calculated minimum capacity.
Batteries are generally measured in amp-hours, not watt-hours, so dividing 225 watts by 12volts gives me 18.75 amp hours of minimum battery reserve.  Considering battery life, I should have twice that much, or 37.5 amp hours, so that the batteries never get 100% drained.  Ideally I'd like to go even higher than that, to have plenty of reserve for cloudy days - say, enough for 5 days in a row of minimal sun light.  37.5 x 5 days = 187 amp hours.

I started out with two 115 amp hour batteries, for a total of 230 amp hours. I just recently bought an 8D battery, which have about 220 amp hours, bringing my system to a total reserve of 450 amp hours, so I should have more than enough to supply power to my 12v power draws for even a week of cloudy weather.

Step 8: Sourcing the Materials

Instructables accidentally erased everything in this section! I wrote this years ago, and I don't at all remember what was here.

Lets see...

Price solar power by the watt. There are a number of different types of panel, with different efficiencies, monocrystalline, polycrystalline, amorphic, thin film - but ultimately what matters is the power output, and it should put out what it says it does on the label. The only difference "efficiency" will make is in how much roof space in taken up to get a given power output.

In some cases it may matter if a panel is "shade tolerant" - unless bypass circuitry is built-in, a panel with just partial shade may stop working completely - but of course its much better to find a spot where there is no shade at all, and then that consideration becomes moot.

What I got, and is pictured above, is a kit from Harbor Freight, which included 3 15Watt panels, a mounting frame (preset to about the right angle for most of N. America) a charge controller with built-in voltmeter and 12v outlet, and a couple of 12v fluorescent light bulbs.
As of 14July2015, it costs $190 (on "sale"), though I believe I paid a bit less 10 years ago or so when I got it. They are constantly having different sales and specials.

At 45 watts total, that works out to $4.22 per watt. This is very high compared to the price per watt when you buy a large quantity of bulk solar panels, but when you deal with very small systems price is disproportionately high. For a >100 watt system, including charge controller (but not batteries), $4 per watt is better than average.

For a larger system, you can find panels at less than $1 per watt, but you usually have to buy at least 30 hgh powered panels, for a system of 6-10 thousand watts.
Here's a list of (should be current) examples:

There are also a few instructables on here for how to source free damaged panels, and fix them yourself.

For the batteries, I've found the best deals at places that specialized specifically in used car and industrial batteries.
Battery Specialists on San Pablo. Google your own local equivalent. They are likely to have new and used deep cycle batteries at a fraction on what they cost at auto, boat or RV stores. I've also picked up deep cycles for a bit less than those places at truck stops.

Just as with panel efficiency, unless space is a premium, there is really no advantage to getting pricy fancy high-efficiency batteries. A 100amp-hour lead acid battery holds exactly as much charge as a 100amp-hour Lithium battery. The lead acid will be many times heavier and take up more room, but since these will just be sitting in a closet, this makes no difference. Save the high-tech light-weight batteries for your electric bicycle, where the weight will actually make a difference.

Step 9: Putting It All Together

This is the first step where you are actually doing anything, however after all those calculations, its actually the easiest part.

Find a place to put the solar panels.  Ideally it should not get any shade at any point in the day, and the panels should face south.  If you want to set them up once and leave it, they should be tilted at an angle equal to your latitude.  For maximum sun collection, the angle should be changed 2-4 times a year to match the changing angle of the sun
(see or or just google "solar panel angle" if those links become out of date)

Run some moderately thick wire (15-20 gauge, the thicker the better: )
from the output of the solar panel to the input of your charge controller.
You can use thinner wire, if that's what you happen to have, but then you must use more of them.  If the wire is 25% thinner than recommended, use two, running in parallel with each other (both going to and from the same place).  If it is 50% thinner, use four.

Then run wires from the output of your charge controller to the battery.

If you have more than one battery, wire them in parallel to each other, and run the charge controller leads to the positive of one and the negative of the other.  (If you aren't familiar with the terms "series" and "parallel", you should probably learn some basic electrical theory before attempting a project like this - or find someone who knows it to help you out)

Finally, (unless you happen to live in an RV), you are going to need a way to plug into your stored power. With the Harbor Freight kit I got (and many similar kits), it's easy, as the outlet is built right into the charge controller.
But even without one built in it should be pretty easy for a veteran DIYer (which I assume you, dear reader, are) - you just have to wire a few cigarette lighter style outlets (in parallel) directly to the battery. Then you just plug your 12v cords into those outlets. 12v outlets are available at auto parts and electronics stores, though you will probably find more options at an RV or boat supply store.

And that's it!

Step 10: Monitoring and Maintenance

Once you have gone through all the trouble and expense of setting up your new PV system, you are going to want it to last as long as possible.

An independent system does take slightly more maintenance than a intertie system, but it still doesn't take very much.

The most important piece of equipment to have is a voltmeter.
Often the charge controller will have one built in, but its still probably worth it to have a stand alone one for troubleshooting and convenience (the controller may end up outside or hidden away in a cabinet).

Battery voltage varies with its state of charge, so you can tell how charged or discharged it is by its voltage.
As a rough guide:
12.0 volts = 25%
12.2 volts = 50%
12.4 volts = 75%
12.6 volts = 100%
13-14 volts means the system is currently being charged.

Deep cycle batteries can tolerate being drained to 25%, however they will last much longer if you never drain them beyond 50%.

Therefor, its a good idea to check voltage daily, so you know how discharged they are getting.
(esp. first thing in the morning, when the sun has been down - and therefor not charging - all night).  Test it with nothing plugged in.  If it is below 12.3 volts frequently, or below 12.0 volts ever, you need to either increase the number of solar panels, increase the number of batteries, or decrease the amount of load you plug into the system, in order to maximize battery life.

You also want to check voltage during the day now and then, to make sure the system is charging properly.  If you get 12.7 or less when it is sunny out, the battery is not being charged (depending on the charge controller, it might just be because the battery is already fully charged).  If you get more than 14.4 volts your charge controller isn't working, and you will fry your batteries.

Maintenance for the solar panel just means keeping it clean.
For the battery, check the water level of each cell every month or two, and top it off with DISTILLED water if the water level isn't at least a cm above the metal plates inside.  Use distilled water.  Seriously. 
Not tap water.  Not filtered water.  Not mineral water.  The bottle needs to say either the words "Distilled" or "Deionized".
A gallon costs less than a dollar, and it will keep your $100+ battery lasting years longer than if you use tap water.  This is pretty much the only time you should ever buy bottled water.

If corrosion develops around the battery, wipe it up with a baking soda solution (make sure the caps are on tight and you don't get any baking soda inside the battery) and then scrub the metal terminals with a wire brush.  A coating of vasoline will help keep them from corroding.  The same goes for all of the electrical connections.

Keep all electrical connections screwed down tight, or solder them if you don't expect to ever need to reconfigure anything.

Any time a problem develops, check the fuses first.  There may be a fuse in the charge controller (if not, you should add one inline yourself) as well as inside each 12v plug.  If all the fuses are good, check the electrical connections. 

Look up some resources online and you will be able to troubleshoot electrical issues in no time.  You can feel comfortable learning and experimenting because a 12v system doesn't have enough power to electrocute you (disclaimer - unless you plug something into it which steps up the voltage internally and/or has a capacitor; don't take things apart if they have a label that says "don't take this apart")

Step 11: That's It!

Congratulations! You are now part of the solar revolution - and you didn't have to take out a bank loan to do it!!

A independent 12v solar system won't take most normal houses off the grid entirely.
My computers, TV, entertainment center, fridge, chest freezer, and kitchen appliances all still rely on the utility company.

The 176 watt-hours of 12v I use each day is much less than the 7400 watt-hours of 120v AC I use each day on average.
However, by moving just a few things to solar, the effect is tangible, and it adds up to more than it seems like it would.

One reason for that is because most things that can run on 12v operate more efficiently when they run on it directly.  Those power brick plugs waste a lot of energy converting 120v to 12v (you can tell by touching one when it has been plugged in a while - anything that is warm to the touch is wasting electricity in the form of heat).  12v lighting is also inherently more efficient, and using it allows me to use affordable LED lamps which use 1 watt each (a opposed to a 15watt florescent, or 60watt incandescent).

If I had everything in my solar system running on 120v AC it would use up to 400watt hours!
That's more than twice as much, to provide the exact same amount of end-use power.  The majority of the difference would be waste heat - which in summer could end up costing me even more, as I run additional fans (or even AC) to cool the house down.

Another reason my tiny solar system helps disproportionately is because many utility companies have a progressive rate structure.  The more you use, the higher the price per kilowatt-hour (KWh) (the opposite of a bulk discount).  Dropping just a couple hundred KWh allowed me to stay entirely under the baseline, lowest rate.

I'm still working on ways to lower my electricity useage even further.  I recently discovered my chest freezers compressor was staying on even when the temperature was below 0 degrees (F).  I adjusted it to go no lower than 10 degrees.  I also started charging my truck almost entirely with solar, which means less household AC being used by its onboard charger.  I'll see how much that helps next month.  
(update - after my last shopping trip, I realized the chest freezer was still only half full, so I moved some things around, and packed everything into the little freezer built-in above the fridge.  The door just barely closed, but it meant I could unplug the chest freezer completely, which is one of my biggest remaining 120v grid draws)

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