Living on 12 volt solar power for zero EMF

Part 2 – The Electrical System




This is the second part of four articles about how to use 12 volt solar power for zero EMF living.  The first part discussed the benefits and drawbacks of 12 volt systems and solar power, compared to the various alternatives.


This part covers the specific technologies used in a zero-EMF 12 volt system, such as solar panels, charge controller, batteries and wiring, etc.  Much of this information can also be used for 24 volt systems.  A 24-volt system has some drawbacks (see part 1 of this article), but may be necessary to use for larger solar systems, large houses or in retrofit systems.


Other articles in this series cover low-voltage lighting, pumps and other appliances, and various other issues.


The other articles are available at



off-grid, offgrid, 12 volt, 24 volt, low voltage, solar, low EMF



Much technology is available for solar systems today, but much of it does not belong in a true low-EMF house.  This article only covers low-EMF/zero-EMF technologies.


The author is an engineer who has tinkered with solar electric systems since 1994 and moved fully off the grid in 2008, in a house of his own design.  This article also includes experiences from other houses and RVs.


Much information is provided in this article.  Readers who intend to use such a system would probably need to re-read and consult this article multiple times, as well as read other sources of information, for essential details.  Common mistakes may be avoided.


This article describes what works for some people, but it may not work for others.  It may also be in conflict with some building codes.  In a few places, references are made to the 2011 National Electric Code (NEC).  However, it is the reader’s sole responsibility to verify compliance with all applicable codes and regulations, and determine that the described methods are appropriate to the specific situation.


Table of Contents for Part 2

    7.   Components of a low voltage solar system


           7.1       The solar panels

           7.2      The batteries


                       7.2.1  Sizing the battery bank

                       7.2.2  Where to keep the batteries

                       7.2.3  The myth about batteries on concrete


           7.3      The charge controller

           7.4      The wiring


                       7.4.1  Household wiring

                       7.4.2  Ground wires

                       7.4.3  Solar system wiring

                       7.4.4  Hybrid 12/24 volt system

                       7.4.5  RV systems


           7.5      Switches and outlets

           7.6      Instruments

           7.7      The generator


    8.   Sizing the system

    9.   Converting an existing house



7.  Components of a low voltage solar system

A low-voltage off-grid system is different from a regular electrical system in many ways that are not all obvious.  These systems are not rocket science, but many aspects are different than regular grid-powered homes.  Visitors will notice the solar panels outside, but they may not notice any other differences.


The components that are different are:


       solar panels


       charge controller


       switches and outlets



       appliances (lights, refrigerator, stove)

       heating system (possibly)


These will all be described in these articles.  See also the article series about the Desert Moon House for a specific example of a house using all these components.


7.1  The solar panels

Solar panels generate totally smooth DC electricity and are not a problem to be around for sensitive people by themselves.


In most modern solar systems, inverters, digital charge controllers and other electronics backfeed dirty DC power to the solar panels, which act as big antennas making them troublesome to very sensitive people.  Simple, well-designed low-voltage systems, as described here, do not have this problem.


Solar panels work by converting light directly into DC electricity.  They do this regardless of the outside temperature, though they do this a little more efficiently when it is cold.


Solar panels are produced by many companies.  Panels from different manufacturers can be put together, though it is more efficient to use panels of the same brand.


The panels work best in a sunny climate, though in a more cloudy climate one can compensate by buying more panels.


Direct sunlight is essential.  The panels must have totally unobstructed sunlight from at least 9 a.m. to 3 p.m. every day, especially during the winter when the sun is low on the horizon.


The entire solar panel will produce very little electricity if even just a small area is shaded.  Each and every cell must receive full sunlight for the whole panel to work (they are wired in series, just as four 1.5 volt batteries in series produce 6 volts).


Partial shading from tree branches makes these three solar panels produce
very little electricity.


The tilt of the panels can be adjusted seasonally to match the elevation of the sun for more power year-round, though it may not be necessary.


Trackers are available to let the solar panel follow the sun across the sky.  These are expensive and often not cost effective for off-grid residential systems as they provide extra power in the summer and not much in the winter.


Solar panels come in many sizes, from a few watts up to hundreds of watts.  Multiple panels can be added together in a system.  Two 80 watt panels will generate as much as one 160 watt panel.  Most solar systems have more than one panel.


Larger solar panels come in both 12 volt and 24 volt versions.  Panels with capacities above about 140 watt are only available for 24 volt.  Using 24 volt panels is only possible if the whole system runs 24 volt.


7.2  The batteries

The batteries are usually lead-acid deep cycle or marine/RV types.  The marine/RV types are cheaper, and widely available, but do not last as long.  Most medium sized systems use golf cart batteries, as they are mass produced and often locally available so there is no shipping cost (large batteries are costly to ship).  If there is a golf course in the area, ask where they get batteries for their golf carts.  Some auto parts stores can also special order them.


Modest sized systems can use marine/RV batteries, which are available from many retailers including Walmart and K-Mart.


Automotive starter batteries are not designed for this use and will probably die within a year (an exception is the new automotive AGM batteries, such as Optima Yellowtop).


Some people with MCS use AGM type batteries or sealed lead-acid batteries.  These do not emit any hydrogen gas, but they are much more expensive and for a long life they need electronic (pulsing) charge controllers, which may be problematic for sensitive people.


If you need to keep the batteries in your living space, AGM batteries may be the best choice.


Choose low-cost batteries for the first set.  Everybody makes mistakes maintaining the system when it is new, and it is a lot cheaper to ruin a low-cost set of batteries.


The batteries in the battery bank must be of the same type (i.e. only flooded lead-acid or only AGM).  It is best that they are of the same manufacturer, size and age as well.  Mixing batteries that are not fully alike can dramatically lower their lifespan.


Buy the batteries when they are needed.  They cannot be stored for longer periods of time, without being charged.


7.2.1  Sizing the battery bank

The size of the battery bank should be calculated ahead of time, as it is problematic to add more batteries later on.  Any newly added batteries will not live longer than the existing ones, and there is a limit to how many batteries can be put together without them becoming unbalanced.  Most sources say a maximum of three parallel strings.


Deep-cycle batteries are rated in amp-hours.  For a 12 volt system, an amp is 12 watt hours.  A 1 amp-hour battery can power a 12 watt light bulb for one hour, or a 6 watt light bulb for two hours (in theory).


A 100 amp-hour 12 volt battery stores 1200 watt-hours, which can power a 35 watt light bulb for 100x12/35 = 34 hours, in theory.


In practice, one should only count on using half of a battery’s capacity.  So our 35 watt light bulb should not be on for more than 17 hours.  For a long battery life, it is best to use even less on a daily basis.


Battery bank of six golf cart batteries


Marine/RV batteries typically have a capacity of 100 amp-hours at 12 volt.  Up to three of them can be put in parallel, for a total of 300 amp-hours.


Golf cart batteries hold 220 amp-hours at 6 volt.  Put two batteries together in series and there are 220 amp-hours at 12 volt (total capacity is amps times voltage).  Four golf cart batteries will give 440 amp-hours at 12 volt, while six batteries give us 660 amp-hours at 12 volt.


If more than 660 amp-hours are needed, larger batteries will be needed, such as L16 types or even bigger.


If the battery bank is too big, the solar system will not be able to fill it up on most days.  Batteries that are not topped off frequently will not live long.


Some sources suggest a minimum solar capacity to be 1/20th of the battery capacity.  For example, with a 220 amp-hour battery, the solar panel must be rated for 220/20 = 11 amps or 11 x 12 = 132 watt.  In a desert climate, personal experience shows that 1/30th of the capacity works, i.e. the same 220 amp-hour battery only needs about 88 watts.


See part 4 of this article for suggested articles on how to determine the size of the battery bank.


7.2.2  Where to keep the batteries

Most batteries cannot be kept in the living space, as they emit hydrogen gas that is an irritant.  Since hydrogen is explosive they must also be kept away from open flames, such as propane water heaters and propane fridges.


They can be dangerous if short circuited by accidentally dropping a screw driver, a pair of scissors or a wrench across the terminals.  They must be kept out of reach of children and people in general.


A specially built battery box with venting directly to the outside is a good method to keep batteries inside (see resource section for plans).  Otherwise, they must be in a special room or similar place where people cannot accidentally get to them (NEC 690.71).


Make sure there is room to access the top of each battery for maintenance, such as cleaning and adding distilled water.  There must also be access for swapping them out with new batteries.


Sealed batteries (AGM, gel-cel or sealed lead-acid) do not emit hydrogen as in normal operation, and may be fine inside.


In frosty climates, batteries are best kept in a heated space (50ľF/10ľC is fine).  They should also be protected from direct sunlight during the summer, to avoid overheating.


Keep in mind that batteries are heavy, most weigh 50 lbs (25 kg) or more.


7.2.3  The myth about batteries on concrete

There is a persistent myth that batteries should not sit directly on a concrete floor.  People say it will ruin the battery, or the electricity will leak out.


It used to be true decades ago, but no longer is.  In the old days, the nickel-iron batteries were encased in steel cases, which could discharge when in contact with concrete.  Today’s batteries are in fully insulated plastic cases, and this can no longer happen, but the legend lives on.


7.3  The charge controller

The ASC 12/16-A solar charge controller from Specialty Concepts.
It generates zero EMF, is temperature compensated, and very reliable.
It can handle up to 190 watts of solar panels; multiple chargers are used
for larger systems.  Also available for 24 volts.


The charge controller makes sure that the batteries are not over-charged, which would create a lot of hydrogen gas and eventually damage the batteries.  This is the case for all types of batteries.  Some types, such as AGM and lithium batteries, are more sensitive to overcharging.  Most charge controllers of today use sophisticated electronics to precisely manage the voltage of the batteries.  When the batteries are almost full, the charge controller rapidly pulses the power, which is called Pulse Width Modulation (“PWM”).


Another recent invention is called Maximum Power Point Tracking (“MPPT”), which pulls a little extra electricity out of the solar panels by modifying the voltages.  This uses radio frequency pulsing.


A solar house with a 12 volt system installed for the health of a sensitive person may wish to avoid these gimmicks.  They put dirty power on the household wiring, which may be troublesome.


Instead, simple on-off charge controllers can be used.  They simply turn off the solar panel when the battery voltage reaches a certain level (typically around 14.3 volts) and turns back on once the level drops down to around 13 volts.  This type of charger was standard in the 1990s, but is now only available in a few models.


If the batteries are not kept at room temperature, they should be charged to a slightly different voltage setting.  Some charge controllers automatically do this.  Others have manual adjustments, which then must be changed multiple times during spring and fall.  The simplest models do not allow for any adjustments.


If batteries are not charged optimally, their lifespan may be reduced.  This is particularly the case when using sealed batteries, which cannot be equalized.  Some people may find that acceptable.


Larger solar systems can use multiple charge controllers, each managing a separate solar panel.


If no suitable charge controller is available, one can be put together using a voltage-controlled switch and a blocking diode (details available on the link listed at the end of this article).  These can be outfitted with extra relays to handle large solar systems.


7.4  The wiring

7.4.1  Household wiring

The wiring must be thicker for 12 volt systems, compared to conventional household wiring.  The voltage will drop over a thin wire when electricity is consumed.  This is called line loss.  With a 120 volt line, it makes little difference if there is a one-volt drop to 119 volt.  But a one-volt drop is a lot for a 12 volt system.


The National Electric Code (NEC) has a few articles about low-voltage systems (NEC 411 and 720).  The main specification is that the wires must be at least AWG size 12 (American Wire Gauge), though it must be at least 10 AWG for appliances and receptacles (NEC 720.4).  For comparison, 120 volt household wiring generally uses 12 or 14 gauge wiring.


The 10 gauge wires work well for serving lamp fixtures and outlets in a house when using rather short runs (30 ft/10 m or so).  Larger gauges are needed for main wire runs and for longer distances.


Thinner wires are commonly used in travel trailers.  It works there because of the short wire runs and the low-wattage bulbs typically used to light up such a small space.


Houses are much larger than travel trailers.  Here it is generally not a good idea to use anything smaller than 10 gauge for outlets and light fixtures.  It is only for very specific purposes, such as a volt meter, an LED light or thermostat, where smaller gauges could be used.


Not much money is really saved by skimping on the wire size and it can be costly and difficult to later upgrade.


With some forethought, the sizes of the wires can be kept at a minimum.  This will both save money and make a better system.  This is mainly done by having mostly short wire runs, and just a few long runs.  However, it is also important not to put many lamps or outlets on one single circuit.


If the electrical panel is near the center of the house, it can receive electricity from the batteries through one single thick wire.  Then smaller wires can radiate out in all directions from the panel to light fixtures and outlets, like the spokes on a wheel.


If the panel is not near the center of the house, thicker wires may be  needed to bring power to junction boxes or sub-panels in other parts of the house.  Each junction box can then feed electricity onwards on smaller wires.


A 12 volt system becomes more difficult for larger houses.  It may need multiple electrical panels around the house and maybe even multiple solar systems to feed different ends of the house.  For a large house, it may make better sense to use a higher voltage (usually 24 volts) to better travel the distances needed.


The table below shows the recommended wire size for a given cable-length and expected amperage/wattage.  It is copied from the Kansas Wind Power catalog, with permission.


A wire loss of 5% is sometimes acceptable for long/high amperage wires.  For a 5% loss, multiply the distances in the table by 2.5.


Copper Wire Length Table
For 2% loss with 12 volt system
One way distance in feet is listed under each wire size gauge





























































































































For 24 volt systems, the distances are twice what is listed in the table above.  For conversion to meters, divide the distances by 3.


The table below, from the same source, shows the maximum amperage possible through a wire (regardless of voltage).  This table is based on the fire hazard and does not consider losses.


Maximum Amps for Copper Wire

Wire Gauge










Maximum Amps











According to these tables, a hefty 2-gauge wire can handle up to 115 amps (115 x 12 = 1380 watt), but if the wire is just 48 ft long, it should only carry 15 amps (15 x 12 = 180 watt) for a 2% voltage drop (line loss).


Metric Conversion Table

Wire Gauge








Wire diameter (mm)









The thicker wires are specialty items that are usually best purchased from electrical supply houses that serve professional electricians.  Since large-gauge wires are expensive, it can really pay off to shop around.


The installation of the wires is mostly the same as for 110 volt systems.  The screw terminals for electrical outlets can only accept up to AWG 10 wires, which should be enough in most cases.


Sometimes a junction box is used to distribute power from a larger cable, to multiple lights and receptacles in a corner of the house.


The convention is that black wires are positive and white wires are negative (the old convention was red for positive, black for negative).  Make sure all outlets are wired correctly, as reverse polarity can destroy many types of electronics.


Outlets are wired just as in a regular house.  One is shown here, pulled out of the wall.
The black wire carries the positive, while the white wire has the negative.


Using twisted wiring can help on backfed dirty electricity.  Some brands of 10/3 wire happen to be twisted already inside the sleeve.  The extra conductor (red) is simply not used.  The twisting can also be done using a power drill.


DC-rated breakers and breaker boxes must be used.  AC breakers may malfunction when you really need them.  Some breakers are usable for both AC and DC.  Look in the catalogs (see Resources).


QO-series breaker box from Square D,
which has breakers rated for both AC and low voltage DC power.


Each breaker must be sized for the branch circuit it is to protect.  It must be no larger than the maximum carrying capacity of the smallest wire in the circuit (i.e. max 20 amps for a 12 gauge wire).  The National Electric Code specifies a maximum of 20 amps for low voltage lighting circuits (NEC 411.6).


There would probably be a need for more branch circuits (and thus slots in the breaker box) than for a similar sized 120 volt AC house.  Having more circuits, with fewer lights and outlets served by each circuit, prevents problems with voltage drops.


The voltmeter in the house should be on its own circuit with its own breaker.  This reduces the voltage drops, so the voltmeter more accurately reflects the state of the system.


If there is wiring for both 12 volt and 120/230 volt in the house, make sure they are kept totally separate.  They cannot share junction boxes, outlet boxes, breaker panels or conduits (NEC 690.4.B).  This is to prevent possible hazards.


There is no need for arc-fault protection for low-voltage systems (NEC 690.11).


Wiring for DC is not much different than regular wiring.  A contractor should not have problems doing it, after studying these instructions, though some may not feel comfortable with it and decline the job.  Keep in mind that you may wish to convert the wiring to 120 volt AC in the future, such as when selling the house.


7.4.2  Ground wires

The outlets and other equipment should be supplied with a ground wire, just as for a 120 volt system.


The grounding wires are sized for the maximum current they may carry, and not by voltage loss, as is done for the current-carrying wires (NEC 690.45.A).  This means that the grounding wires can often be a lot smaller than the ones carrying 12 volt positive and negative.


The grounding wire is sized after the following table and can be no smaller than 14 AWG (NEC 690.45.A and 250.122).


Max amps

AWG (copper)










The grounding wire is generally sized after the breaker protecting the circuit.


It is fine if the grounding wire is overdimensioned, such as when using ready-made cables.


7.4.3  Solar system wiring

The wiring of the solar system itself, i.e. solar panels, batteries, disconnects, etc. may require specialist knowledge to comply with current building codes, especially for larger systems.  Such information is available from the National Electric Code article 690, which has been greatly expanded in recent years.  Some rural areas do not require this adherence, however.


As most solar systems today use higher voltages, a solar installer may not be familiar with the requirements for low-voltage systems (i.e. 12 or 24 volt).  Some important points are briefly listed here, but it is not a complete list:


For wiring and breakers for the solar panels, see the article How to Install a Polemounted Solar-Electric Array in the listing of recommended articles in part 4 of this article.


Exposed low-voltage wires do not have to be protected by conduits/raceways (NEC 690.31.A), though it is usually a good practice.


All solar panels and metal junction/breaker boxes must be connected to a ground rod, called equipment grounding (NEC 690.43.A), i.e. grounding of the chassis.  The exposed grounding wire mounted on the solar panels generally should be 6 AWG (NEC 690.46 and 250.120.C).  This also provides lightning protection.  The solar panels must share a grounding wire with the equipment controlling the system (i.e. breaker box chassis, etc.) (NEC 690.43.B).


Low-voltage systems are allowed to be “floating”, i.e. there is no need to ground (or “bond”) the minus to a ground rod (NEC 690.41)


If you decide to connect minus to ground, there are two extra requirements:


      A ground-fault detector is required (NEC 690.5)

      There must be only one grounding point (NEC 690.42 and 250.164.B)


Having the grounding/bonding point by the solar panels helps with lightning protection.  It is important for sensitive people that there are no other grounding/bonding points, as that may cause stray voltage/ground currents.  This can again cause additional problems, such as unbalanced circuits and make any dirty DC more troublesome.


A common place where this principle can be violated is at breaker boxes, other than one mounted on the solar array.  For these other breaker boxes, make sure these have no bonding.


7.4.4  Hybrid 12/24 volt system

Using both 12 and 24 on the same system can be considered for some situations.  The battery bank could be a full 24 volt, with a center tap providing two 12 volt feeds.  This is called a three-wire system and is similar to how the 120/240 volt AC household systems work in the United States.


Such a system could be used to serve larger users, such as houses with multiple people.  The lights and pumps could be run on 24 volt, while outlets were at 12 volt, for instance.


The drawback is that the two 12 volt “sides” of the battery bank may not be used to the same extent, draining the batteries unevenly.  This can be mitigated by having two separate 12 volt charge controllers and solar panels, one set for each half of the 12/24 volt battery bank.


A hybrid 12/24 volt battery bank may need to serve three breaker boxes:  two each handling 12 volt and one for 24 volt.  An alternative is to use a two-phase AC/DC rated breaker box, if one can be found.


The center tap of such a system must be connected to a ground rod (NEC 690.41 and 250.162.B).  Make sure any “center wire” is dimensioned to handle the amperage from both “sides” of the system.


Another hybrid is to simply have both a 24 volt and a 12 volt system which are not connected to each other.


This author has never seen any 24 or 12/24 volt systems in actual use, so there may be additional issues to consider.


7.4.5  RV systems

The National Electric Code does not apply to camping trailers and other vehicles.  It is therefore fine to use thinner wires and cigarette lighter plugs there, when appropriate.


The wire-distances are generally much smaller in RVs, making the smaller wire sizes feasible.


7.4.6  Concern about downsizing wires

It is sometimes necessary to downsize a wire, which has raised some concern.  This can happen if large-gauge wires feed an electrical outlet, as the screw terminals there can only handle #10 wire.  There a pig-tail can be used.  Another case is where large-gauge wires feed a junction box, which then distribute the power locally on smaller wires.


This should all be within the Code, as long as the breaker protecting the circuit is not larger than the max amperage of the thinnest wire — i.e. if the smallest gauge is #10, then the breaker must not exceed 30 amps.


This is not a problem initially, but sometime in the future another electrician may modify the whole system and put in a larger breaker, assuming the larger gauge wire goes all the way through.  This would be a fire hazard.


The solution is to only downsize in subpanels, with breakers protecting each of the sub-branch circuits.  Our hypothetical electrician should notice that.  And lugs can be used to make a large-gauge wire fit any screw terminals.


7.5  Switches and outlets

12 volt DC outlet with light switches.  This type of outlet
is normally used for 15 amp 250 volt air conditioners.


DC electricity wears out the contacts on switches faster than AC electricity does.  The reason is that there is more arcing with DC electricity.  There are no longer DC-rated switches available that fit in the standard wall boxes and face plates.  Using 120 volt AC switches of good quality (“heavy duty” or “pro grade”) works well for 12 volt, and are available at regular building supply and hardware stores.  The cheaper models may not last.  The author has used these switches daily for over five years, with no signs of wear yet (the switches control 4 amp loads).


The same switches will probably work fine for 24 volt DC, though this author has not tested that.  They are not going to work for higher voltages:  a colleague tried to use such a switch for a 120 volt DC system.  The switch was instantly destroyed.


Using cigarette lighter style outlets is not a good idea.  They are of low quality and cannot handle more than 7 amps (80 watts) which is a violation of most building codes that require a capacity of at least 15 amps.  A better choice is to use a more mainstream product that is not used for regular electricity so there is no possibility of mistakenly plugging into the wrong outlet.  In North America, the 15 amps, 250 volt receptacles are a good choice.  These are usually only used for window air conditioners and are different from those used for electric stoves and clothes dryers.  See the illustration for an example.


If you need a cigarette outlet for a specific purpose, you can easily make a conversion cable (see Section 10).


For people living in an RV, it is probably better to continue using the existing cigarette outlets rather than replacing them.


Correct polarity is extremely important for DC systems.
When the outlet is wired the same way as for a 120 volt AC system,
the positive and negative come out as shown.


7.6  Instrumentation


Voltmeter placed prominently on kitchen wall.


A voltmeter is necessary to know how the batteries are doing.  People in the house will then know if they consume too much electricity at the moment and it may also help noticing if there are problems with the system (such as needing equalization of the batteries, adjustment of the charge controller, etc.).  The voltmeter is as important as the fuel gauge in a car, especially for solar systems using simple technologies.


A voltmeter should be placed prominently in a solar house in an area where people spend a lot of time, so they can glance at it throughout the day.  The kitchen is a common location.


There are much more sophisticated instruments available today, but they are all digital and could be a problem for sensitive people.


People living off-grid have relied on the voltmeter for decades as their main instrument for keeping an eye on their system’s well-being.  It still works well.  See this author’s article about managing 12 volt solar systems for more information (follow link at the end of this article).


The simple analog voltmeter shown in the picture is the most accurate to use.  It can be left on all the time as it consumes extremely little electricity and radiates no EMF.  An alternative is to use the light-bar meters, which are popular in RVs.  They are easier to understand, as they show how full the battery is with little LED lights.  They are not as accurate as the analog voltmeter, and do not provide as much information.  Since they typically have a switch to turn them on, they may not be glanced at as often as a voltmeter that is always on.  A compromise is to have both types installed.


A low-cost multimeter is an essential tool for working with a 12 volt system.


7.7  The generator

A generator makes electricity using an engine that burns either gasoline, diesel or propane.  It is pretty much a necessity to have one when living off the grid.  A fuel cell system may  not work, as they have built-in inverters.


A generator can be used for many things.  In homes with smaller solar systems a generator may be used to run the washing machine and pump water from the well to a holding tank.  It may also run an electric clothes dryer, though it would be much cheaper to use a propane dryer.  A clothesline is even cheaper, the parts of the year it is feasible.


A generator is handy to run power tools during construction and upkeep of a house, though contractors usually bring their own generator.


In the winter, generators are usually used to charge the battery bank during cloudy days.  It may also be used to equalize the batteries if the solar system is not powerful enough.  A special battery charge controller is needed, the automotive types do not work well with a generator.


There may be other uses, such as powering a vacuum cleaner, charging various cordless devices and even a car’s engine block heater.


It is best to avoid uses where there are cheaper alternatives, such as water heaters, clothes dryer, stove and space heating.  These are better run on propane in most cases.


It is not realistic to use a generator to run appliances that must be on all the time, such as a refrigerator.


It is expensive to run a generator.  They consume fuel and they need upkeep.  The cheaper models do not last as long as the better models; you get what you pay for.  One catalog company suggests that people buy the best model they can afford, and then use it as little as possible.


Using a generator to run more than one thing at the same time is a more efficient use of this expensive resource.  If the generator is big enough, an off-grid household may use it to wash clothes, pump water and vacuum the house at the same time.  Putting larger loads on a generator is not free, it consumes more fuel, just as a car does by going faster.  But the wear is about the same, just make sure not to overload it.


The electricity generated by a generator is typically not as high quality as power from the grid.  This is especially the case for small generators.  It may be a problem for some electronics.  Some generators have an inverter built in, to make a smoother sine wave, but the inverter itself is then an EMF problem.


Very sensitive people may be bothered more by generator power than regular grid power.  It may be best to confine generator-powered equipment to a separate outbuilding or garage, and not connect the house wiring to the generator.


An alternative to a generator is to have the washing machine, and perhaps other appliances, in a different location.  Some people have a separate outbuilding with grid power or use appliances in someone else’s home.  Some wash clothes by hand and have no need for regular electricity at all.


7.7.1  Choosing a generator

There are many generator models available.  Look in various tool catalogs.


The issues to consider include:



       fuel type


       noise level

       inverter option


The size needed depends on what the generator will power.  Look at the nameplate rating of each appliance and add them together.  If the list includes any electrical motors (such as well pumps and washing machine), triple the number to account for the starting surge and the power factor.  Then add a hefty margin.  This should give a good idea how big a generator is needed.


A generator that is too big will be a waste of money, and also consume more fuel.  Too small a generator will be overloaded and wear out faster.


There are three fuel types available:  gasoline, diesel and propane.  Propane is by far the cleanest burning and it is also the safest to transport.  A gasoline or diesel generator often stinks, even when not running.  A propane generator does not.  If your house has a propane tank, it may be possible to feed the generator directly from it.


The downside of propane is there are fewer generator models available.


Regarding quality:  you get what you pay for.  Diesel generators tend to last the longest, while gasoline models wear out the fastest of the three types.  Generators with a low rpm (typically 1800 rpm) should last longer than those that run at a faster rpm (typically 3600 rpm).


Engine noise is a big issue for many people with environmental illness.  Some people get actual symptoms from noise.  Many generators are very noisy.  Noise is simply not a design criteria in most models.


For low-noise models, look for those with a low rpm.  The National Park Service has a program to certify generators for use by RV campers in their parks.  These models are much quieter than the regular designs.


Some generators have a built-in inverter that makes the AC sine-wave smoother.  But inverters send out high-frequency EMF that is very disturbing to some sensitive people.  These models are best avoided.


8.  Sizing the solar system

An off-grid system must be tailored to the situation, there are no standard sizes to just pick.  The size of the solar array and the battery bank must be determined prior to installation.


The size depends on:



       family size


       generator availability



A system that works well in the sunny desert of Arizona would probably not perform well in states like Vermont or western Washington.  Arizona has an average of five hours of sunshine a day in January, while overcast and northerly Vermont has only two hours a day, on average.


Vermont also has more days with total overcast, where the solar panels will produce very little electricity, so the battery bank or a generator must carry the load.


The more people who live in a household, the more electricity will be consumed.


The lifestyle of the residents is all-important.  It is a change for anyone used to unlimited electricity to go off-grid, where the electricity can simply run out.  A lifestyle change is always needed.  Turning off lights when leaving a room or when it is light outside must become second nature.


People who wish to run a TV all night will need a larger system than those who just wish to run a light for a few hours a night.  People who are nocturnal will need a bigger system than those who wake up with the sun every day.  It is very individual what is needed.


If you can use a generator to charge the batteries during cloudy weather and short winter days, the size of the system can be reduced.  It is best to use a generator as little as possible, as they are costly to use regularly.  But, they can be used with a small solar system, until more solar panels and batteries can be afforded.


Sometimes finances simply dictate how big a system can be purchased.  Then the lifestyle must be adjusted to fit the energy budget.


Off-grid solar systems come in all sizes, from a very modest RV system at about $500 to a luxurious large-home system costing above $30,000.


It is possible to add to a system over time, but it is best if the wires and spaces for batteries and solar panels are sized for future growth.  There are books and magazine articles available about estimating the size of the solar system and battery bank.  Some solar catalogs also have excellent information.  See the resources section at the end of part 4 of this article.  Making at least a rough estimate is highly recommended.  The battery section of this article also has useful information about battery sizing.


As the prices have come down, it is now cost effective on smaller systems to oversize the solar panels, which reduces the wear on the batteries.


A single person in a desert climate may do okay with as little as one 80 watt panel and two marine/RV batteries to power the lights and a pressure pump in a small RV.  Most people would need more than that.  A system with 1000 watts of solar panels is probably the largest one could realistically build using 12 volts.


This author lives in Arizona with a dual system.  One has two 220 amp-hour golf cart batteries and a 120 watt solar panel, to run two water pumps.  The main system powers everything else, using six golf cart batteries (660 amp-hours) and 250 watts of solar panels.


9.  Converting an existing house

If converting an existing house to 12 volt, it can be done by replacing/upgrading some of the existing wiring or by having extension cords running along the walls.  There would be less of a need to upgrade the wires if 24 volt is used instead of 12.  There are some drawbacks to using 24 volts, which is discussed in Part 1 of this article.


Some people start with the extension cords, later upgrading the existing wires in the walls.  Extension cords are only recommended for a small starter system with a couple of lights.  This may be the only option for a rental house.  Use sturdy medium-duty extension cords, which are sold at hardware stores.


Some of the existing 12 gauge wiring in the walls may be usable for short distances and when only serving one light bulb or a small radio.  Any 14 gauge wiring is probably only usable for LED lights.  Experiment to see what works.


Wiring or re-wiring an existing house is not uncommon work for an electrician.  Some houses were built before electricity was available and older wiring is often upgraded.  An electrician may be able to pull new wires through the attic or crawlspace and fish them through walls to existing outlet boxes.  Various types of decorative conduits and baseboards can be used to hide wires along walls.


It may be fine to only convert/upgrade some circuits in the house.  Identify which outlets and lamps are actually needed and leave the rest.  Most ceiling lights will probably be needed.  One-bulb fixtures with 12 gauge wires may not need upgraded wiring if the distance to the breaker panel is rather short (within 15 ft/5 m).


The switches and outlets may need to be replaced (see section 7.5).


Some thought must be put into what to do about fuses.  The existing AC breaker box may be able to be outfitted with DC-rated fuses.  Otherwise, it could be replaced with an AC/DC rated breaker box (such as the QO series from Square D).


A hybrid solution is to install a new DC breaker box near the battery bank.  One circuit from the DC breaker box could then feed electricity to the old AC breaker box and thus the old wires.  New wiring would go from other breakers on the new DC breaker box.


In this hybrid version, the old AC breakers are left in place.  They simply conduct 12 volt electricity, but are no longer relied on to trip in case of a short.  The breaker on the new DC breaker box now provides the protection.  However, that breaker can only carry 15 or 20 amps to the entire AC breaker box, as that is how much any of the old AC circuits can carry.


If there are any 14 gauge wires in the old wiring, the breaker must be 15 amp.  If all wires are 12 gauge, a 20 amp breaker is safe.


Using the old AC breaker box is thus only enough to serve a few lights or outlets in the entire house and they cannot be far away from the AC breaker box as the wires are thin.


Keep in mind that you may wish to convert back to 120 volt AC in the future, such as when selling the house.


For more information

For more details, resources and examples, see


March 2012 (last updated October 2013)