Quantcast

Affordable Off-Grid Solar Electric

Print Friendly

Editor’s Note: This post is another entry in the Prepper Writing Contest from John D. If you have information for Preppers that you would like to share and possibly win a $300 Amazon Gift Card to purchase your own prepping supplies, enter today.


Would you like to add off-grid solar to your preps, but think it’s too expensive?  I’ll show you how to build an inexpensive system that can grow, as funds become available.  You’ll find your small system very useful, and you’ll look forward to the added capabilities that each upgrade brings.  If you can spare as little as $50 per month, you’ll have a substantial system in less than a year, and one that meets all of your needs for electricity much more quickly than you might imagine.

Before we look at the system itself, let’s consider your electricity usage.  As anyone who’s ever dabbled in off-grid solar will tell you, the first thing to do is to look for ways to reduce electricity consumption.  If you can reduce the amount of electricity you use, you can build a smaller system, saving you money, while still meeting your needs.  Since we’re talking about a small system, you can forget about central heating and cooling, and you won’t be using an electric water heater or range.  Those items require a lot of electricity, and I doubt that you want to cover your entire roof with solar panels.  But, that doesn’t mean you have to do without, or be uncomfortable.  As a prepper, I suspect that you’ve already considered alternatives.  You may have a fireplace, with a heat exchanger, that serves as an alternative to your furnace.  Or, maybe you have a wood-burning stove, and a good supply of firewood.  An outdoor fire pit can be used for cooking.  Perhaps you’ve considered using the sun to heat water for dishes and for bathing.  And, of course, who doesn’t have an ice chest for keeping food and drinks chilled?

If your alternative system has the capacity to power a refrigerator/freezer, you have the ability to keep food and medicine from spoiling.  However, because it runs 24/7, the overall use of electricity is high.  In the event that your alternative electricity system can’t handle that, consider an energy-efficient chest freezer instead.  A chest freezer uses much less electricity.  Besides keeping food frozen, you can use it to make ice for an ice chest.  Placing it in the coolest part of your home will also help to reduce electricity usage.

Kill A Watt Electricity Usage Monitor

Your alternative source of electricity will also be used for lights.  Since you’ll be using lights for several hours each evening, this is an area where cutting back is very beneficial.  Instead of 60 watt incandescent bulbs, use either compact fluorescent bulbs (CFL), or LED bulbs.  A 13 watt CFL puts out as much light as a 60 watt incandescent bulb.  Even better, a 10 watt LED bulb puts out as much light as a 60 watt incandescent bulb.

An electric frying pan also uses a lot of electricity, but perhaps for only an hour a day.  If using an electric frying pan, or if an electric deep fryer is important to you, then you must build a system large enough to supply that amount of electricity.  A microwave oven also uses a lot of electricity, but items cook much more quickly in a microwave than they do in an electric skillet, meaning that the overall use of electricity when using a microwave oven is much less.

Make a list of all of the items you’ll want to use in a grid-down situation.  Calculate the daily power requirements in watt hours (watts times hours), for each device.  If you don’t know how many watts a particular device requires, measure it with a Kill-a-Watt meter.  A Kill-a-Watt meter is an inexpensive device, available from Walmart, and many other sources.  For devices that use power intermittently, like a refrigerator, measure the total power used (watt hours), over a 24 hour period.  Add all of those, to give you a rough idea of your daily electrical needs.  You may come up with a number between 1,500 and 3,000 watt hours per day.  With that in mind as your ultimate goal, you’re now ready to build the starter system.  Add to it over time, as funds become available, until it meets all of your needs.

The starter system, as described, can provide 450 watt hours per day or more.

While you could start with just a battery and a solar panel, the basic system described here is a complete system.  Because it’s not tied in to existing house wiring, you’ll also need extension cords and power strips.

1 – 100 watt solar panel from solarproductswarehouse.com $113
1 – Battery, deep-cycle, 12v, 100ah locally from Costco, SAMS or WalMart $86
1 – Battery box locally from Costco, SAMS or WalMart $19
1 – Charge Controller, PWM, 30a from solarproductswarehouse.com $50
1 – Inverter, PSW, 300 watts from solarproductswarehouse.com $144
1 – Meter/Switch assembly (DIY):  parts from Jameco.com $18
1 – 40 amp circuit breaker NAWS store $10
Misc wire, connectors, fuses, hardware various sources $20
Total starter system cost: $460

The starter system, as described, can provide 450 watt hours per day or more.  You may be far from your goal (1,500 to 3,000 watt hours), but it’s a good start.  You’ll be able to charge cell phones and portable electronic devices.  You’ll have an abundance of light, using LED or CFL bulbs.  You might use a table-top fan, power a TV, cable box, game machine, and a wide range of other devices.

I’ve listed a 30 amp charge controller, while a less expensive 10 amp charge controller would be just fine.  I suggested the larger controller so that it doesn’t have to be replaced when installing additional solar panels.  A 30 amp charge controller will handle the current for up to 4 – 100 watt solar panels.

Make sure that the wire you use can handle the expected current, and that all circuits are properly fused.  A single solar panel might produce 6 amps of current at 12 volts, so a 15 amp automotive fuse will work fine.  Fuses, and in-line fuse holders, are available from any auto supply store.  10 gauge wire can handle the solar panel current.  For battery interconnects, and wiring from the battery to the inverter, use 7 gauge or heavier wire, and a 40 amp breaker.  If you can’t find wire that heavy, consider cannibalizing a set of automotive jumper cables.  For best performance, keep wires as short as possible.  For roof mounted solar panels, ground the frames, and a lightning-protection device is recommended.

The battery box is oversized for the battery you will be using, and it includes a spacer.  This extra space provides plenty of room for the charge controller, and fuses.  The battery box is properly vented, and should be located outdoors, in close proximity to the solar panel.  The manufacturer is listed as NOCO, and it’s called a Snap-Top HM318BK Group 24-31 Battery Box.

For roof mounted solar panels, ground the frames, and a lightning-protection device is recommended.

The Meter/Switch assembly is optional, but highly recommended.  The meter displays either the battery voltage, or the output from the solar panel(s), selectable via a two-position switch.  This allows you to get the most out of the system, and tells you what you need to know in order to protect the battery.  The parts can be ordered from Jameco.com.  Part numbers are:  2152323, 2135857, and 675489, for the meter, switch, and enclosure.  You’ll also need some 3 conductor wire.

Knowing the battery state of charge (SOC) at any particular time is important for two reasons.

  1. To make sure that the battery is fully charged, each sunny day.
  2. To avoid over-discharging the battery.

Chronically undercharging, or over-discharging the battery can shorten its life.  Unfortunately, measuring the battery SOC is not a straight-forward process.  However, after observing the system over time, and with a little practice, it’s not difficult.  First of all, what we consider a 12 volt battery is not really a 12 volt battery.  It’s a 12.7 volt battery.  When a battery is neither charging, nor discharging, it is considered to be “at rest”.  With that in mind, here’s what to look for:

  1. When the solar panel voltage is significantly higher than the battery voltage, it’s an indication that the charge controller is doing its job, and the battery is fully, or nearly fully, charged.
  2. Expect the fully charged battery reading to be 12.6 to 12.7 volts, while at rest.
  3. When the at-rest voltage drops below 12.1 volts, the battery is considered to be about 50% discharged.
  4. While charging the battery, and for a period of time soon thereafter, expect to see a battery voltage reading far above the “normal”, fully charged reading, perhaps in excess of 13.0 volts.  This is normal.  It’s called “surface charge”.  However, it makes determining the actual state of charge a bit more difficult.  You can “burn it off” by applying a load for a short time, or simply wait until it dissipates.
  5. The load (devices drawing power from the battery), affects the voltage reading.  Determine the SOC when no load is connected, and when the battery has been at rest for 1 hour or more.

Copy this chart, and place it near the meter:

Battery Voltage Load Approximate SOC Comment
12.8 or higher None unknown Battery is charging
12.6 to 12.7 None 100%
12.4 None 75%
12.1 None 50% Do not connect load

For best results, battery should be at rest for 1 hour before taking voltage reading.  Readings are taken at night, when solar panels are not generating power.

Your results may be different than that listed above because your batteries may be different than the ones I use, and temperature has an effect on battery voltage.  Until you’re comfortable with determining battery SOC by reading the meter, it’s best to estimate SOC based on usage, as explained below.

If you start with a budget of $50.00 per month, you’ll have a complete, and substantial system in about 9 months, and a more powerful system in about 14 months.

Another way to determine approximate battery SOC is by monitoring the load.  With one 100ah battery, the expected usable storage capacity is about 450 watt hours.  (More about determining battery capacity later in this article).  If you add all of your loads, multiplied by the hours of use, you can determine how much of that 450 watt hour capacity you’ve used.  For example, if your load includes only a 35 watt fan for 12 hours, and a 10 watt light bulb for 4 hours, the total drain on the battery is:  (35 x 12 = 420 and 10 x 4 = 40) or (420 + 40 = 460), exceeding the recommended shut-down limit by 10 watt hours.  Until you’re very comfortable using the meter to determine battery SOC, it’s best to use this method instead.

Is this system something you would consider building?

If you start with a budget of $50.00 per month, you’ll have a complete, and substantial system in about 9 months, and a more powerful system in about 14 months.  This system will power AC-operated devices, up to a maximum of 300 watts.  The AC will be “clean” power, allowing you to run devices without performance problems, and without the fear of damage to sensitive devices.  With a budget of only $50.00 per month, you could have a system that meets all of your needs (1,500 to 3,000 watt hours per day), in less than three years.

Here’s an upgrade suggestion:

1 – 100 watt solar panel $113
1 – Battery, 12v, 100ah $86
1 – Battery box $9
Wire, connectors, fuses, hardware, and misc items $22
Upgrade cost: $230

With this upgrade, system capacity is doubled.  You’ll have 900 watt hours of power available after a full day of sunshine.  While you still may not have met your goal, your system will have the capacity to run additional devices, and for longer periods of time.  Partly cloudy days will have less of a negative impact.

By adding solar panels and batteries, you’ll be able to use more devices, and increase run time.  If, for example, you’ve used half of your available power in the evening for lights and TV, you still may be able to run a fan for 8 hours, while you sleep.

Also, at some point, you may want to add a more powerful DC to AC pure sine wave (PSW) inverter.  If you add a larger PSW inverter, you’ll be able to run devices that require more power, like a microwave oven, toaster, or vacuum cleaner.  I’m very pleased with the Exeltech 1100 watt PSW inverter I’ve been using for the past several years.  I paid about $570.00 for it.  However, I’ve seen high power DC to AC PSW inverters advertised as low as $200.00.  Before considering an expensive inverter, read the reviews.

Summary:

So there you have it.  In just over a year, on a budget of $50.00 a month, you could have a robust system that meets most of your needs.  In less than two years, you could have an even more robust system that meets all of your needs.  You’ll have plenty of light, you can keep frozen items frozen, you’ll have cold drinks, you can cook food and boil water, circulate warm or cold air, take a warm shower, watch TV or listen to the radio, use a computer or mobile computing device, use power tools, pump water, and run a vacuum cleaner.  In other words, you can power almost anything.  Until the next power outage, or before the SHTF, you can use your system daily, cutting your use of grid-supplied electricity, saving you money.  After all, it’s not like using a generator, where you’ll have to buy gasoline.  Solar electric is free power from the sun!

The system capabilities listed here are estimates, but representative of the results you can expect.  Short winter days, and extended cloud cover are your worst enemy.  You can either put up with that, cutting back on electricity usage when necessary, or build a system large enough to compensate for those things.  Until you can reliably power every device on your list, you’ll probably want to keep adding solar panels and batteries.  You can use the formula’s I’ve provided, or simply test the capacity of the system, once built, and each time you upgrade it.

You may be asking yourself if you really need this.  Think about what life will be like when your food stockpile is depleted.  Out of necessity, you might have to spend most of your time finding food?  Having a convenient way to process it (canning), and store it (freezing), will make post-SHTF life much easier.  For me, this means having the ability to cook, without needing an open fire, and to have reliable power for a chest freezer.  Assuming that I’ll have some success hunting, trapping, fishing and growing crops, I need not find food every day.  I’ll have ample time to take care of my other needs, and to rest.  I plan for comfort, not just survival.

As a backup to the backup system:

Although I already have a robust solar electric system, I’ve decided to build a smaller one, as described here, for my own use.  After I’ve completed the system, and thoroughly tested it, I’ll pack it up and store it.  Having a portable system, packed and stored, offers several advantages:

  1. It will be stored in a Faraday Cage, eliminating the chance of damage due to an EMP. My existing solar electric system is exposed, and might be damaged by an EMP. If that happens, this system can replace my EMP-damaged system.
  2. In the event that my existing system is not damaged, this system can supplement my existing system.For any grid power outage, or when the SHTF, more power means more comfort.
  3. In the event that I need to bug out quickly, this system will be packed and ready to go.

Because this system will be in storage at some point, I’ll keep the battery charged, using my existing system and a battery selector switch.

Cutting your electric bill:

You can power household devices for several hours each day, but be careful not to over discharge the battery.  That process can be automated, by using an automatic transfer switch.  After building my own system, I’ll be building another one for a family member who lives in an area where electric rates are high.

To calculate the power generating capacity of a solar panel array (example):

If you have 2 – 100 watt solar panels, and you expect 5 hours of sun each day, you have the capacity for (5 times 200), or 1000 watt hours per day.  This power can be delivered directly to the load, or used to charge batteries.  You might have less, on some days, due to clouds, or because of shading from trees.  You’ll get an efficiency bump if you use power directly from the solar panels, during the day, instead of using power from the batteries at night.

For optimum performance, keep the panels clean, and at the proper angle for best exposure to the sun.  For mounted panels, this might include adjusting the angle twice a year, for summer and winter exposure.  Personally, mine are mounted on a second-story roof, and I don’t adjust for the seasons.  I would adjust, given a SHTF situation, if I needed to get the most from an undersized array.

About batteries:

For batteries, the best value is the lowest cost per amp hour.  For example, A 200 amp hour battery at $160.00 is a better value than 2 – 100 amp hour batteries at $90.00 each.  Make sure that you select deep-cycle batteries, not automotive starting batteries.

A 12 volt, 100 ah battery can theoretically supply 1,200 watt hours to the load.  (Watts = Volts times Amps).  In practice though, you should not discharge the battery more than 50%.  Therefore the usable watt hour capacity is 600.  However, there are discharging inefficiencies, and the rate of discharge affects performance.  As a result, the actual power that this battery can provide may be 20% less than the calculated value, or 480 watt hours.  Battery manufacturer ratings tend to be optimistic.  They may be accurate under ideal conditions, but you and I will never achieve that level of performance.

In my effort to get the most bang for the buck, I opted for 6-volt batteries in my system.  They’re designed for electric golf carts and floor machines.  They’re rated at 215 amp hours.  By connecting 2 of them in series, the result is 12 volts at 215 amp hours, per pair.  Here are my calculations for this battery pair:

12 volts at 215 amp hours (12 X 215) = 2,580 watt hours
50% usable (2,580 divided by 2) = 1,290 watt hours
Accounting for losses (1,290 x 80%) = 1,032 usable watt hours

This suggests that I can:

Power a 100 watt load for a little more than 10 hours (100 X 10) = 1,000 watt hours

Power a 43 watt load for 24 hours (43 X 24) = 1,032 watt hours

In practice, I’ll tend to use the most electricity in the evening hours, and less while I’m sleeping and during the day.

As you perform upgrades to your system, aim for more battery capacity than solar panel capacity.  Batteries last longer, and operate more efficiently, if you don’t discharge them too deeply.  And, with additional battery capacity, you’re less likely to have a shortage in the event of cloudy conditions.

If your battery is the wet-cell type, check water level once in a while, and add distilled water as necessary.  Avoid spills, and don’t let battery water come in contact with skin or clothing.  Keep a container of baking soda handy, to neutralize battery acid, in case of a spill.

Other things to consider:

As an alternative to the pure sine wave (PSW) inverter, you may have considered a less expensive modified sine wave (MSW) inverter.  Don’t do it!  MSW inverters may damage sensitive devices.  It’s also likely that a noticeable buzz will be heard in audio devices, such as radios.  Motors may run at the wrong speed, or overheat.

There are a great many things to consider in the design of an off-grid solar electric system.  I’ve tried to get the most bang for the buck, while not ignoring safety.  You might have noticed that a pre-packaged system costs many times more than the one I’ve described here.  Because you’ll be making your own cables, assembling all of the components, and not buying things you don’t need, you’ll save a small fortune.

I’ll be happy to answer questions, via comments to this article.  Good Luck with your system!

John D

Here’s a link to a video that you might find helpful:

https://www.facebook.com/altEstore/videos/10153206088184520/

26 Comments

  1. Bill

    January 27, 2017 at 10:37 am

    John D: As I understand it, you must control device between the panels and the battery. Then you need a device to control it from the battery to the power using appliance. Is this correct??? Also, when using 6 volt batteries for storage, would you not need twice as many 6 volters than 12 volters??

    • John D

      January 27, 2017 at 11:48 am

      The Charge Controller is placed between the solar panels and the battery. It controls the rate of charge to the battery. The Inverter is connected directly to the battery. It converts the battery’s 12 volts DC to 120 volts AC, for operating lights and appliances. The six volt batteries I use can deliver just over 200 amp hours. Two of those six volt batteries, wired in series, provide 12 volts at 200 amp hours. A typical 12 volt battery might deliver 100 amp hours. Two of those 12 volt batteries, wired in parallel, provide 200 amp hours. Wiring in series doubles the voltage, while wiring in parallel doubles the current. Since the system is designed to be a 12 volt system, if you decide to use 6 volt batteries, you must use them in pairs. As far as battery capacity is concerned: Two 6 volt 200ah batteries will provide about the same storage capacity as two 12 volt 100ah batteries. (Per battery it’s 6 times 200 or 12 times 100).

    • BobW

      January 28, 2017 at 4:06 pm

      Thanks for bringing up the issue of 6V vs 12V. As an RV camper, I’ve been disappointed at 12V battery staying power overnight. If the heater runs, I might not make it to dawn before the battery bonks out. And this is with a fresh name brand RV battery.

      Many of my friends converted their trailers to a 2x 6V system for the added duration. No issues getting the genny cranked in the AM with the long-hour 6V batteries in serial configuration.

  2. Bill

    January 27, 2017 at 3:55 pm

    John D Monocrystalline or polycrystalline panels??

  3. christopher

    January 28, 2017 at 8:17 am

    when i started researching solar, i found the cost is pretty expensive versus what you pay for utility power. my decison for a small system wasn’t a main goal to save money, (which i do) but was to have constant power for my alarm, surveillance and ham radios and some lights when power went out. if you plan to power fridges, freezers and/or heat burners, you will need a larger system and good sunlight. I do keep my security on solar pretty much 95% of the time which I save 1- 2 kilowatt a month. On longs weeks of cloudy days, i switch to utility power. I would suggest get the best controller you can. most cheap 30 amp controllers wont treat your batts the way they should be treated for charging. if you just want to charge cell phones or a laptop (both which will probably be useless in a real STHF, execept for entertaiment purposes) a small 30-100w system is fine. you can charge flashlights, FRS radios etc. Having cut off switches, grounding rods and fuses, smoke detectors, fire extingusiers are extremely important since you dont want to burn your house down!

    • John D

      January 28, 2017 at 10:29 am

      A good PWM charge controller charges batteries in four stages: Bulk, Boost, Float, and Equalization. I’m not sure why you believe they don’t treat batteries the way they should… MPPT charge controllers are much more costly, but offer little, if any, advantage over PWM controllers for a small system like this one. I’ve described the kinds of loads that can be powered by a small system, and you’ve made important additions; communications equipment and alarm systems. Those have low power requirements, when compared to AC and Heating devices, and a small system would have no problem powering those. Personally, I consider powering my chest freezer a high priority, and I made sure my system could handle that, even considering extended cloud cover. I agree with your comments regarding safety, and I cannot overemphasize the importance of the 40 amp circuit breaker shown in the drawing. Thanks for your comments.

      • christopher

        January 29, 2017 at 8:55 am

        saying “treat batteries they way they should” wasnt a clear as i could of been..LOL.. i am saying if you are spending 150 dollars per 100amp hr batt, and you will have to replace that battery multiple times in the lifetime of your system, it pays to get the best charge from that controller whether its a PWM or MPPT. Most of what I have read (I am not a expert on subject) is that MPPT controllers are more efficeint (anywhere from 10-20% per most articles) and in cooler & hotter weather and in low light. wouldnt you want to make the most of your solar panels that charge your batteries to do it quicker? Especially if your in an area where you have extreme weather or minimun sun exposure? MPPT has more selections as far as voltage, battery types etc.. I am not saying you have to go out and buy a 200 dollar MPPT controller.. but if you have (4) 100amp hr batteries at cost of 150 a piece (total 600 dollars) , i would think you would want to spend a little more than 14-50 dollars for a 30 amp controller whether its PWM or MPPT. That is just my thinking!

        • John D

          January 29, 2017 at 11:47 am

          As I understand it, a MPPT controller offers no advantage when the system has only one solar panel. The more panels you add, the bigger the advantage of MPPT. (assuming that you’ll wire the panels in series, not parallel). The MPPT advantage is efficiency, not prolonging the life of the battery. Battery life is affected by depth of discharge, and the number of discharge/recharge cycles.

  4. Rich3 Co

    January 28, 2017 at 12:43 pm

    Good article, got me re-energized about solar. Question about 6 v. 215 Ah batteries. Connecting a pair in series = 12v. 215 Ah. Connecting in parallel = 6v. 430 Ah. Is it ok to connect in Series-Parallel = 12v. 430 Ah. i.e. are there system equipment issues? Looking at starting this endeavor small, scaling it up as budget allows. Thanks again for your article .

    • BobW

      January 28, 2017 at 4:03 pm

      I’m no electrical engineer, but from what I’ve read, as long as the 6s are in series to 12V, THEN paralleled to increase amp hours, your g2g.

      Check with someone smart on this stuff.

    • John D

      January 28, 2017 at 5:10 pm

      You are correct. My system has 3 pairs. So I have 3 X 215 = 645ah capacity, at 12 volts, with a total of 6 batteries.

      • Rich3 Co

        January 28, 2017 at 8:01 pm

        Ah, ok that’s a curve ball, not expected. Why only 625 from 3 pair? If connecting two each 6v 215 Ah together in Series-Parallel = 12v. 430 Ahr. Second pair connected same in Series-Parallel = 12v. 430 ah, then connecred to the first pair in parallel, would that = 12v. 860 Ah.? Then 3rd 12v. 430 Ah pair connected in parallel then add another 430 Ah to = 1290 Ah? Im apparently not understanding the full principle here?

        • John D

          January 28, 2017 at 8:32 pm

          When batteries are connected in series, the voltage doubles, but the current stays the same. Try drawing it out. First draw two 6 volt batteries connected in series. This gives you 12 volts at 215ah. Then draw that two more times. You now have three pairs. Connect those pairs in parallel, and you have a 12 volt array, at 645ah, which is 215ah + 215ah + 215ah.

          • Rich3 Co

            January 28, 2017 at 9:20 pm

            Smile:) I’ve done just that and see the error of my way,,,, should have done it before asking the second question. Thanks for being patient, hope it helps someone else who may be trying to figure this out…

  5. BobW

    January 28, 2017 at 4:13 pm

    Why do folks seem concerned about powering their current house grid with solar? So many circuits on the panel, so many items daisy chained together, unless a person had an individual circuit for every wall outlet, light, etc in their house, there will be waste in charging up the house panels.

    Sourcing cheap alternatives that run on 12V output, like RV lights, and wall mounting a minimalist circuit board that only powers very specific, prioritized items makes more sense to me.

    Thoughts? What about hybrid electric/propane heaters, refer/freezer systems that run on 12V?

    • John D

      January 28, 2017 at 5:17 pm

      You could run everything on 12 volts DC, but then you would have to buy lights, fixtures, appliances, etc., and 12 volt refrigerators are expensive. With an AC system, you can use the things you already have, like lamps, fans, refrigerators, freezers, frying pans and deep fryers, radio’s, TV’s, cable boxes…. Well, you get the idea. You can tie into your existing house wiring, but I prefer to use extension cords and power strips.

      • BobW

        January 28, 2017 at 7:17 pm

        Thanks, John D. I guess that I don’t see solar as a cost effective alternative to staying connected to the electric grid. As the tech has matured, federal and state subsidies have also declined, putting it all on consumers to convert if they want to. The ROI is just not there for the average consumer. The only place I can see the ROI being worth the investment is a small solar system to power a well pump.

        With my concept of building a 12V system it is truly about the system being a prep, not a cost-ineffective alternative to grid power.

        I don’t see this as a camping world spending spree. I see it more of a junk yard safari, with certain new elements. There are tons of old RVs that use small incandescent bulbs for the offing in junk yards. Spools of wire at big box stores, or electrical supply. New electric or electric/propane heaters and refer/freezers seem a requirement. The most modern heaters and freezers are typically the most efficient, but honestly, the computer control is a weak link, as the boards are temperamental, and fail too often.

        I envision building the system, running it in, then disassembling, and putting it all in a faraday cage.

        I’d love to get input energy consumption AC vs DC.

  6. John D

    January 30, 2017 at 10:13 am

    Important System Update: I plan to locate the inverter within an enclosure, outside of the house. If I were to locate the inverter inside the house, I would have to use heavy gauge wire for that, and the potential exists for a short circuit at the entry point. Although the circuit breaker provides protection, I want to minimize the danger from this high-current circuit. Instead, I’ll bring AC into the house via an extension cord. In the event of a short circuit in the AC line, the inverter would shut down very quickly.

    • BobW

      February 1, 2017 at 5:33 pm

      I’d caution on using extention cords from inverter to house.

      The ‘A’ answer would involve a hard shut off switch on the outside wall of your home, that allows complete disconnect of ‘shore power’ from the home. Just after that connection, wiring in heavy duty electrical wire (outdoor, proper gauge wire) that can connect your in-house circuit breaker to your power management system.

      Running ext cords is for the birds. dig the wire into the ground, have it pop up where you build/install your power management pieces, such that it is water/moisture proof, and can be quickly connected to your PMS.

      Electricity is not to be played with. Take the time to either learn or pay an electrician.

      I’m neither, but my neighbor is an electrical engineer, and has pushed me toward doing it right vs jimmy-rigging things. This will minimize risk of electrical fires, shorts, and protects your home’s sensitive components from spikes. Using those circuit breakers is an investment in risk management.

      • BobW

        February 1, 2017 at 5:35 pm

        Oh, I would encourage putting a second hard shut-off switch on that added line going to the PMS. Forgot that part.

  7. Efficient Pilgrim

    January 30, 2017 at 3:40 pm

    Most remote, off-grid sites have a generator for backup. On cloudy days, the generator kicks in when the batteries have hit 70 or 80 percent of discharge. Is there a way, with this system to use a generator to charge the batteries?
    Bonus, while the batteries charge, other things can be plugged into the generator … like a saw or air compressor.

    • John D

      January 30, 2017 at 5:23 pm

      Yes. For best results, use a “smart” charger, one that charges in stages (bulk, boost, and float). Northern Arizona Wind and Sun sells them.

  8. John D

    February 7, 2017 at 7:19 pm

    Update: If you’re building the system described here, don’t put the inverter or charge controller in the same container as the battery. Flooded batteries (the kind you add water to), generate corrosive fumes, which may result in damage to those components. Also, make sure that the battery enclosure is well ventilated, and located outside if it’s a “flooded” battery type. If you want to locate the battery indoors, make sure it’s a sealed battery, which doesn’t generate fumes. Be safe.

    John D.

    • John Hertig

      February 21, 2017 at 3:01 am

      If you use flooded batteries, every time you charge them, some of the water will become part of those corrosive fumes. If you let the levels get too low, the batteries are toast. So you need to “top off” the water (with distilled) every so often. You can get a system of special caps and hoses which run all the cells to one hose, and a simple squeeze ball fed by your water source can fill every cell to the exact right level. Much quicker and less prone to error than manually filling each cell. And great for hand strength, too 🙂

      • John D

        February 21, 2017 at 8:58 am

        Thanks for the tip John Hertig. At the very least, design your battery enclosure to allow access from the top. Provide easy access to the filler caps, and a good view into the battery, for checking the fluid level.

Leave a Reply