Planning for Off-grid Systems

The picture above is an off-grid house powered by the 1.2 kW of panels on the dual axis tracker in the foreground. We had no involvement in this project, but the photograph conveys exactly what most people think of when you mention an off-grid system. This photograph used by permission of the owner.

If you are planning to build a new house or cottage of grid, please consider the following information. An off-grid system still has to meet the Ontario Electrical Safety Code, and be inspected by the ESA. Some people might assume that this is not the case. Part of this is that a future owner of a house may wish to connect to the grid. If so, the wiring within the house has to be code compliant, otherwise, they would never be able to be connected. Secondly insurance companies want to know that the wiring has been inspected and is safe.

If you have some questions that are not answered on this page, please visit our off-grid FAQ.

Services to plan and deploy solar power for a new off-grid house

We recommend early planning for off-grid use during the house design. The size and cost of the cost of any off-grid system is determined by the electrical lifestyle that you wish to enjoy and the heating system you select. We provide scientific analysis and thorough planning for our projects. (No rule of thumb approaches). We prefer to engage on a whole building integrated approach for the application of solar power, and can provide all aspects of an installation. The services that we offer include:

We also provide planning and design and then supply a project specific kit for DIY installation.

Trying to decide if off-grid is practical for you?

This can apply to a new construction project, or to an existing cottage that you may wish to modernize,  expand or winterize. Your major questions are:

We offer a study of the practicality of incorporating solar in your new home or cottage. We do this on a consulting fee basis. We can also do an energy audit, by an NRCan certified Energy advisor, if you are planning to upgrade an existing home or cottage and need to improve its energy efficiency.

We have a slide presentation that we can do to inform you of all of the aspects of off-grid power, and to ask some key questions to determine some of the answers about the size and type of installation that would be ideal for your project.

We need a clear plan of electrical loads to make an accurate system sizing calculation. We do the calculations, but this requires your input. This can be done interactively. We have two methods to do this. We can start with a clean sheet of paper and a list of electrical loads. Many people prefer the alternative method where we select one out of seven types of buildings we have entered into our software and which is closest to your requirements. Then we add and subtract items from that starting point.

Then we deliver:

If you proceed and buy a solar kit or a complete installation from us, then we refund a portion of the consulting fee from your kit price.

Total Canadian Home Energy Use

Residential energy use in Canada by activity, 2010

From the graph above, if space heating, water heating is done with fuels other than electricity, and air conditioning is omitted, the balance is 18% of the home's energy need could be supplied by electricity. Further reduction of major appliances such as dryers, stoves and perhaps refrigeration from the appliance section is done by using propane. Now meeting these remaining needs from solar electricity becomes practical. One item is missing from this typical synario since it is dominated by urban households, off-grid homes require their own water pump.

Some conclusions can be made from this graph. Refrigerators are getting better, and so running electric refrigeration is less of a problem for off-grid applications than in the past. Both electric clothes dryers and kitchen range are not improving to any significant degree. Lighting is getting more efficient, due to CLF and recently LED lighting. The increasing trend for plug in loads implies that most of the lifestyle choices and compromises will be in the area of plug in electrical and electronic items.

We can supply a complete kit drop shipped to your location

We can analyze all of the input that we gather from you, and then design a complete site specific installation, and bill of materials. Then if you wish we can provide you with that kit, delivered to your site. The kit will supply everything you need for the project that you can't buy at a local building supply store or electrical distributor. We also will provide a complete document of the type of utilities to use, building changes that are required, and to guide you through the installation process. If required, we can come on site and assist you with the installation, or even do it all for you.

Naturally, we can't do all this work for free. We charge a modest consulting fee for our time working with you, and if you do proceed and buy a kit or a complete installation from use, we refund an appropriate portion of our consulting fee.

 

Arc Fault Interrupters

The ESA has announced "Effective January 1, 2014, AFCI protection is required for Photovoltaic systems with dc source circuits, dc output circuits, or both, on or penetrating a building and operating at a maximum system voltage of 80 V or greater". This will apply to most microfit and net metering installations. This may apply to off-grid installations, and would add a significant extra cost. This can be mitigated by changing the series string to two 60 cell panels, and operate below 80V. However this might require a higher rated charge controller, or two charge controllers to handle the higher current.

Conservation is less expensive than generation

Before diving into exactly how much power you will need, you should consider the appliances that you wish to power. It is far less expensive in the long run to use highly energy efficient loads for essential appliances such as refrigerators, than to generate the power to operate less efficient appliances with both a larger PV panel array and battery bank.

For most people living with off grid electrical power means becoming more parsimonious with the amount of electricity used.  Perhaps it means replacing some appliances with very energy efficient models. In particular there are specifically built refrigerators that are designed for off grid use and have far more insulation than a regular fridge and so greatly reduce its demand for electricity. Expecting to live off grid with the same electricity consumption as you have used while connected to the grid will either be unsuccessful if the solar system can’t meet all your needs because it is undersized, or if sized to meet the higher demand without energy conserving appliances and lifestyle may require a very large and therefore expensive PV system.

In addition to the refrigerator mentioned previously, you should switch to a natural gas or propane fired clothes dryer. An electric kitchen range should be replaced by a propane fueled range instead. You should use natural gas or propane to heat your hot water, possibly with a solar DHW system as well. One of the easiest changes is to use CFL or LED light bulbs to replace incandescent bulbs throughout the house.

Many small appliances consume power when they are turned off. A plug in energy meter can be used to check radios, alarm clocks, TVs, microwaves, entertainment equipment and your desktop computer to see what these standby of “Phantom” power loads are in your house.

Consider part of your investment in off grid living to be the purchase of high efficiency appliances.

Conservation and Air Conditioning

The very first steps in designing a new house for comfortable summer off grid living is to increase insulation levels above those required by current building code to reduce cooling loads. Secondly incorporate windows with low E coatings and window shading to reduce the summer heat gains from the sun.

Air conditioning may be something that would be hard to give up when switching to off grid living. Conventional AC which use mechanical compression and refrigerant gases such as freon requires a lot of electricity, even with 15 SEER units that are available today. There are some alternatives approaches which are both more expensive than a typical household central A/C unit. You could make use of ammonia absorption cycle units powered by propane or by a solar concentrating thermal collector. These are almost never used for residential AC applications, and in industrial applications are normally powered by natural gas. Very small scale propane fueled absorption cycle cooling is used in refrigerators for RV vehicles, boats and for cottages without electricity. The technology is proven and mature, but bulkier.

A more readily available and perhaps a more compatible method for air conditioning an off grid houses is to use a Ground Source Heat Pump (GSHP) with the ability to provide passive cooling in the summer. This means the compressor does not run, but the system operates to circulate the heat exchange fluid directly through the coils inside the air handling unit. This requires an air handling unit with two coils, one for heating mode that contains refrigerant, and a 2nd coil that is only used in the summer and circulates the water-antifreeze mixture. In the summer there is usually plenty of sun on the hottest days, so there is usually a surplus of electricity to run a GSHP. Even a GSHP without the passive cooling mode may be satisfactory. Even more economical would be to only install the passive cooling part of a geothermal system, and omit the heat pump part of it entirely. This could then be in the range of an ambitious DIY person, since no refrigeration mechanic's tools and equipment are required, and an air handling unit is a standard commodity item.

Most people who install a GSHP do so for heating in Canada, and this is possible in an off grid home. We recommend that In the winter the GSHP operates using the compressor to provide the heat transfer from the earth only when the there are sunny days, and during long periods of cloudy weather during the winter a non-electric source of heat such as a pellet stove or wood stove is used. During the fall and spring when there is more sunshine and the temperature difference is less the PV system may be able to power the GSHP to provide all of the house's heating needs, without any supplemental heat source. This should be the target when determining the design maximum electric load. Designing to meet 100% of the winter heating load would tend to make the PV panels and battery extremely oversized for the remainder of the year, and thus not cost effective.

Determining the Load

The most important planning step is to properly size the off grid system's electrical production to match the load, and to size the battery storage to handle a number of cloudy days without sun without resorting to a backup generator or running out of power.

The first and most important step in planning an off grid solar electric installation is to determine the average load, which is essential to determine the size of the battery system and of the number of panels that are required, and also for the inverter capacity.

You need to be involved to determine the electrical load for your house. A rule of thumb, or the number that your neighbour used will not be sufficient.  This determines how much energy must be produced. For many homes, the energy consumption is not the same year round, for example lights are used for a longer duration during the short winter days. Ceiling fans or air conditioning are not used in the winter, and furnaces are not used during the summer.

We have an interactive worksheet form for listing and calculating the design loads that you can request by e-mail which is designed to be filled in using Acrobat reader 7.0 or later. There are drop down boxes listing some of the most common electrical loads. You can type in other loads if the type you have identified is not present in the preloaded list. It also comes with an explanatory document to assist you in filling this out.

The amount of sunlight varies throughout the year, with the minimum available during the winter. Planning a properly sized system requires determining the load for each month ideally, or at least for each season and then evaluating the amount of electricity that can be produced by the solar panels in that month, to identify the critical month. With this, the system is sized appropriately to meet the demand. An undersized system will not operate satisfactorily, as there will be power shortages and very deep discharges of the batteries which shorten their life. On the opposite extreme, an oversized system will be more expensive and larger than required. Batteries are a high maintenance item, and will need periodic replacement. This should be budgeted into the on going cost of off grid living.

You are the best person to start the process of determining how much electricity you will be using. The rest of the steps of doing the sizing of the system are best done by an expert. You will make our first visit more productive if this is done ahead of time. You should compile a list of all of the appliances you need, and the amount of lighting, hot water, cold water, etc. You need to be very thorough, and realistic as to what comforts you can’t give up. For each appliance determine the average power and the maximum power, and decide how many hours a day you will be using each appliance. The consequences of an incorrectly sized system are a too expensive a price to pay for insufficient up front planning. We will refine and discuss your list of loads and looks for any problems or omissions in the list.

The maximum power requirements for each appliance can be found on appliance nameplates or in the manufacturer’s literature. For some appliances where the average use is unknown, you can buy a device at Canadian Tire called an Energy Meter for about $25 made by Blue Planet, model EM100 that will measure the instantaneous power use, and can also determine the use over a period of time, which is great for an appliance that cycles such as a fridge, freezer or pump. For City of Ottawa residents a fancier version of this (Kill-a-Watt) can be borrowed free of charge from the Ottawa Public Library. If there are appliances which have a very large startup current, such as a well pump that can't be avoided, then this initial current has to be supplied by the battery and converted to AC by the inverter. We need to know the maximum startup current for these devices. (There are well pumps that do not have a large startup current, which are highly recommended for off-grid homes.)

For appliances that do not have a constant consumption of electricity, and the manufacturer does not publish an average amount of electricity for one usage cycle of that appliance, the maximum power rating on the appliance is not enough information. The only way for many devices is to use the energy meter previously described to determine the energy use. When shopping for new appliances to use in your off-grid home, take an energy meter with you when you go shop and and ask to have the appliance demonstrated to you while plugged into your energy meter. That will permit you to determine if one brand is better than another in its energy use, and to obtain a value you can use in your calculations.

In order to correctly size your system we need to determine two different totals, which are:

  1. The average amount of power that each appliance uses per day, to calculate how much electricity you require on average per day, in the winter, and in some cases in the summer. This is used to determine how many solar panels are needed, and how big a battery system is needed to supply power at night and on cloudy days.
  2. The power that is required when all of the appliances that may used at the same time are operating in their steady state of operation, so we know how much current has to be supplied by the battery and by the inverter to correctly size the inverter. We also consider any loads that have an unusually high initial startup current, so that can be started when the other loads are present.

In most cases it will be more economical to size the solar electric production and storage to not quite meet the peak demand, and to have a gas, diesel or propane generator that automatically starts to also provide power to charge the batteries when a period of prolonged cloudy days occurs, or if an unusually high pattern of electricity use occurs as when guests arrive.

Most of your loads will be AC, but in an off grid system there may be some loads that can be replaced with alternatives that run off DC directly. The advantage is this avoids the losses that occur when an inverter converts the DC battery voltage into 120VAC. Thus your system is slightly more efficient. This may make sense for a sump pump motor, and for refrigeration. There are problems with unbalanced loads doing this on larger systems with 24 or 48V batteries.

If you would like to get a more comprehensive reference book, which contains 29 pages on the topic of system sizing, I recommend buying or borrowing from a library the book “Photovoltaic Systems 2nd edition” by James P Dunlop. This is $CDN 107.50 at amazon.ca and $114.95 at Chapters.

It is also possible to have both a solar PV panels and a wind turbine both charging the same bank of batteries, to reduce the likelihood of a prolonged series of cloudy days causing you to run out of power.

Plan B load plan creation method

We also have a plan B method for doing this, where you select a sample building and lifestyle that is closest to your needs, and then you tell us how your situation is different. We dynamically add and subtract loads to come up with a suitable load plan. Many people feel reluctant to do the traditional load planning method previously described.

Going off grid only for economic reasons?

If you are considering going off grid for economic reasons, and you have the option of being connected to the hydro grid, then there are some other strategies for lowering your hydro bill to zero. These are:

  1.  “Net metering” which avoids the expensive battery bank, and is more reliable. This exports your surplus power to the grid during the daytime, and draws power from the grid at nighttime and on cloudy days. The grid acts as a virtual battery. As long as you generate more power than you use on a long term average, your hydro bill drops to zero. You are consuming no electricity from the grid on a yearly average, and are reducing your home’s effective CO2 emissions for electricity generation to zero. Your connection to the grid is done differently, and you require a service rated switch located outside between your electric meter and the grid, rated for the current of your service. That is if you have a 200A service, you need to install a 200A disconnect switch near your meter. You also need a dual circuit breaker position to be free inside your main panel. The power from the same type of inverter used for microFIT applications is wired to a new dual circuit breaker in your existing panel. When this is done and approved, the local Hydro will change your meter for a bi-directional unit. Then all the power that you generate that is not used within your home flows to the grid, and is used by other homes. At night your house consumes power from the grid exactly the same way as before.

    The local Hydro and OPA permit you to have both a net metering and microFIT installation at the same location, only if the combined capacity is under 10kW.
  2. A microFIT installation sized to generate as much revenue from selling electricity to the grid to match the amount that you spend in purchasing electricity for your own consumption. This will require a much smaller number of solar panels, and is often a much smaller investment than either off grid, or net metering. At today’s ground mount price of $0.291 per kWh, a solar system would require about 50% of the number of panels required  by an net metering system with both resulting in a zero Hydro bill cost. This has the least CO2 reduction relative to net metering. This approach does not provide protection against rising electricity rates, since the microFIT price does not escalate with rising hydro rates.
  3. Use the grid instead of a backup generator and proceed with an off-grid type of installation. The power you purchase when the batteries require recharging is less expensive than the fuel and maintenance of a backup generator.

Battery Banks

The design of a new off grid system should plan for a safe space to locate the batteries. These require periodic maintenance, and they are heavy. Some batteries can weigh up to 300 lbs each. There should be enough space to remove and replace them when they have reached the end of their life, and for you to work comfortably when doing regular maintenance. These will be the highest maintenance part of an off grid power system.

When a vented lead acid battery is being charged, and is approaching a full charge they emit Hydrogen gas, which is explosive. Therefore proper ventilation needs to be provided. Batteries work best at room temperature. If they are located in an unheated space, they will have less capacity, and so you will not have as much energy available to provide to your house. In addition if the batteries are nearly fully discharged, and the temperature is very cold, there is a risk of the battery freezing and thus being destroyed.

The US NEC recommends venting Sealed Lead acid batteries the same as Flooded Lead Acid types, as hydrogen production is possible. See HomePower magazine issue 141 for an article on battery boxes.

The lead acid batteries used for off grid use are not the same as used in a car. An off grid system needs to have deep discharge batteries in order for them to have a long lifetime. Car batteries are designed for shallow discharge service. Batteries can both be sealed or conventional vented types. Larger batteries are usually the vented type, and there is the issue of hydrogen gas.

To provide proper ventilation, a DC operated explosion proof ventilation fan is required to ensure no issues with hydrogen gas will occur. The floor of the battery area should be resistant to an occasional spill of a few drops of Sulphuric Acid without damage.

For some more information about batteries, visit the Surrette web page. This is a Canadian company located in Spring Hill NS.

Charge Controller

This is an element not present in a grid tied system. Its role is to adapt the varying DC voltage from the PV panels to the battery voltage so the battery is charged efficiently, and little energy is lost in the DC to DC voltage conversion. An important part of the operation of this device is to prevent over charging of the battery which will produce unnecessary amounts of Hydrogen, overheat the battery and will cause a drop in the electrolyte level and generally shorten the battery life.

Panels

If a charge controller that is capable of higher voltage step down, the same type of panels that are used for microFIT applications can be used to provide DC to the charge controller which in turn delivers power to the battery. The only difference is that the PV panel array will be wired up in a series - parallel method, instead os a series only method for most inverters. The total wattage of the panels must be based an a carefully study of the load of the house, and the sunshine available for the worst combination of the two during the different seasons of the year. It makes no difference as to the mounting of the panels on the ground or on a roof. A tracking mount can be used if the gain by the tracker is less than the cost of the additional cost of extra panels to result in the same annual yield of electricity.

Panels for off grid use may be less expensive since they do not have to have any Ontario content, and therefore they can be obtained from a much wider number of manufactures, including importing from other countries. On the other hand, then number of panels in most off grid installations is less than a microFIT installation, which tends to negate some of these savings.

Another temporary impact on price is that some distributors have some panels that are left over from 2010 when there was no requirement for panels to have Ontario content. So occasionally there are some bargains to be had on panels that do not qualify as Ontario content.

There is no difference in racking for off grid use, with the possible exception of the power to position a tracking mount. This may have to come from a dedicated battery, so it can be position if the battery bank is discharged or the inverter is not working.

Inverter

The inverter is a DC to AC inverter which increases the battery voltage to 240VAC, which is opposite to the role of a string inverter in most microFIT installations. They are not interchangeable. Grid-tie inverters including Enphase micro inverters can't be used because they are designed to detect a hydro grid and lock onto it. The inverter provides the split phase AC from the battery, regardless of whether the PV panels are charging the battery. On a sunny day, the PV panels are charging the battery in addition to supplying power to the house through the inverter.

In a very small installation, the inverter could conceivably only supply 120VAC. This would only be done in a building that had no 240VAC loads, such as a cottage or hunting camp. This would not be the system to use if there was ever a possibility of the house being connected to the grid in the future.

The inverter has to be sized to handle the absolute maximum load that can occur, and if not, then there will be a voltage dip. This maximum must be clearly identified during the planning stage. The inverter must be able to handle the peak inrush currents when devices with motors start, such as a fridge or freezer, or even worse for an AC system or water pump. These devices can draw several times the normal running current when they first start operating.

DC Loads

In an off grid system, as many loads as possible are supplied with DC if the voltage from the battery bank is suitable. This is done because there are less losses when power does not need to be converted by the inverter. The disadvantage of doing this is two independent sets of wiring for light fixtures, for instance. One for AC lights, and another for DC lights. The devices that can benefit the most are pumps for water and sump pumps, and circulation pumps for Ground Source Heat Pumps and for radiant heating systems because the inverter no longer has to handle the startup inrush currents.

Generators

Do you need one? Yes for a few reasons. The sizing of the panels and battery is less critical and can be slightly undersized if a generator is present. If a battery is discharged to its recommended limit and there is no sunshine expected, without a generator you will have to continue to draw power from the battery, shortening its life. With a generator the recharging starts at the right time and the battery life is preserved. The other reason is also for peace of mind, that if something goes wrong with the off-grid system you can switch over to the generator and not have to live without power until the problem is fixed. If you had a wind generator as part of the same system, then there would be less need for a generator, but it is possible to have a string of cloudy days and low wind so the generator still provides peace of mind.

What type of generator is best, DC or AC? Technically, an AC generator is called an alternator, just as it is in a car. A DC generator can directly supply part of the load, and charge the battery at the same time. If the sun is shining, solar energy can power part of the load. The generator does not have to be big enough to supply the entire load, and recharge the batteries at the same time, thus it can have a smaller output capacity. Another benefit of a DC generator is that there is no switchover and so no momentary interruption occurs each time the generator starts and stops. Is there any down side to a DC generator? Yes, they are much less common for consumer applications, and so the price is not as good and they may be hard to source. If you wish to use propane as a fuel, then your options are even more limited.

AC generators are the ones that you see on specials at your local building supply stores, and they come in many types. They are designed for standby service for a home that is normally powered by the grid. They are available in a variety of fuels. When they start up in an off-grid application, they switch off the inverter, and the generator supplies the entire load of all of the appliances, and it also must supply power to recharge the battery. This requires a larger sized generator to meet this load. When they switch, they can take 1/60th of a second interval without any power. In this case, some sensitive appliances may think there has been a power loss, and loose track of time, or shut off, or reboot. The lights will flicker briefly. Since they supply all of the power used in the house while the alternator is running, they would use more fuel. Also an AC generator has to have the capacity to start all high initial start loads that occur when it is running. This can cause a further over sizing of the Alternator. In comparison a DC output generator can share supplying power to the load, and so more power comes from solar energy and less from the generator's fuel. The main advantage is that these are so much more readily available, that they are probably less expensive than a comparable sized DC output generator. Some generators have 240VAC output, and if you have only 120VAC in your off-grid house, and need 120VAC to feed into your inverter/charger then you will only be able to use 1/2 of the generator's capability. If the generator can't be reconfigured to deliver all of its power on one 120VAC output, then you will need a step down transformer to be able to use all of the generator's output. For example the Kholer RES 8.5 is popular for off grid use, but has this limitation.

Both types of generators should be capable of remote start and stop by a two wire signal from the house's inverter, so that the generator turns on automatically when required. If this is not the case, and you are not at home when the battery bank has been discharged to its recommended maximum depth of charge, and the generator does not turn on, then the battery bank can be damaged and have a shorter life due to an excessive amount of discharge.

A weekend only use cottage, which does not rely on electricity for refrigeration or for unattended heating has other generator choices. For these, a pull start Honda gasoline powered generator may be satisfactory. It would be stored inside where it is warm, and wheeled outside and plugged into a 240VAC receptacle similar to a clothes dryer or electric stove. It will be a lot less expensive than the remote start models.

The generator should be big enough to handle the entire load without the solar panels and batteries, so you will still have power if an inverter or battery problem occurs. It should have additional capacity beyond this, so that it can also recharge the battery if the batteries are discharged due to insufficient sun. Therefore in the case of an AC generator, it should be about twice the capacity of the design load.

One benefit of an AC output generator is that it can be used as a source to operate power tools during the construction phase.

Generator Engines

For off-grid applications where the generator will run 100s of hours a year, the long term cost and durability are important factors. If an off-grid system is designed to have power available from renewable energy 95% of the time, then a backup generator would run about 438 hours a year. A generator that runs for more then 500 hours a year is considered a prime generator, and is a much heavier duty item.

An Otto cycle engine has spark ignition and this is typified by our lawn motor and car engines that use gasoline as a fuel. A diesel engine uses compression ignition, and fuel injection.

A liquid cooled unit will have a longer life than an air cooled motor. A 1800 RPM generator will have a longer lifetime due to the slower motor speed, but 2 pole 3600 RPM generators are lighter and less expensive to build. 1800 RPM is also a better speed range for industrial diesel engines, and they would be quieter, with everything else equal.

In theory it is possible to use the waste heat from a liquid cooled engine for heating a building, which is known by the fancy name of co-generation. A diesel or Otto cycle powered generator produces more waste heat energy than it does electric energy.

Do not select a generator with a small tank, unless you want to get up in the middle of the night to refuel your generator. If using diesel fuel or gasoline, then choose a model that can be fed fuel from a large external tank. Note that in the winter a thinner, more expensive grade of #1 diesel fuel (Kerosene) is required to avoid fuel gelling or freezing. This is not an issue if the tank is located indoors in a temperature managed location, as long as the fuel line is insulated and perhaps heated.

Propane is a very convenient fuel for a generator, and you do not need a dedicated tank unlike for diesel fuel, if you have other propane appliances. Nearly all propane powered motors for generators are Otto cycle engines. A propane fueled motor is normally quieter than a Diesel cycle engine.

Diesel motors can have problems with light loads called wet stacking, but are great with a full load. Diesel units are always heavier, increasing installation costs. For comparison, a diesel powered generator using a Kubuto engine is about twice the cost of a propane fuel unit of similar capacity. Diesel engines are more familiar to mechanics, and may be simpler to maintain, particularly mechanical injection models.

The operating fuel costs and equipment lifetime are usually better for a diesel motor than for an Otto cycle motor.

All types of gasoline, diesel and propane motors are hard to start when they are cold, and for the coldest part of the year they may require block heaters and battery heaters to keep them warm enough so they start upon demand. This is an extra load on the off-grid battery system.

 

120 or 240V AC?

All modern houses connected to the grid are 240V AC, which is also referred to as split phase. The Hydro provides two lines and a center tapped neutral which is grounded. Each leg is 120V relative to the neutral, and 240 V from leg to leg.

What items are 240V powered in a typical grid powered home?

Nearly all of the above items except for the pump could and should be designed out or replaced by propane fueled equivalents. The central AC is probably handled by doing without, or using passive geothermal.

An off grid house can be wired to have only 120V loads, and so use only one inverter to produce AC from the battery. This is the lowest cost approach. If 240V is required, then two inverters are required, with the 2nd one running 180 degrees out of phase to the first one. Most off grid loads are 120V AC, with the most notable exception of a deep well submersible pump. If there is only one 240V load, then it may be more economical to select a 120V AC submersible pump, or to use a step up transformer for the well pump to avoid the cost of a 2nd inverter.

If you do have two inverters to permit using 240V appliances, there are some benefits such as:

If you are planning on two inverters for 240VAC, then we recommend that you wire all receptacles as a split receptacle, so that if one inverter fails, you just move a plug into the other half of the receptacle to switch a load to the other working inverter. Normally only kitchen outlets are wired as split outlets.

If building an off-grid house from scratch, then we recommend using a standard 240V load center and feed only one of the main lugs with 120VAC from an inverter, and populate every 2nd breaker position. The other main lug would be unconnected. If in the future a grid connection became available, then it would be simple to switch to 240VAC by simply shifting the circuit breakers to balance the load between both input lines.

Water Pumps

One could reasonably deduce that there are very few off grid houses with municipal water service. Therefore the vast majority of off-grid houses have a well and a pump to supply potable water.

Many pumps have a very high startup current that can tax the inverter's capacity, and if the inverted can't supply the locked Rotor current for long enough to start the motor, a failure to start the motor will occur, and/or the inverter will shut down or could be damaged. This might be the single highest peak current demand in an off-grid house. The selection of a water pump needs to be done carefully.

As mentioned previously, a water pump might be the only load that would ideally require 240VAC, to minimize wire size and voltage drop along the long wires to a submersible pump.

One solution is to select a 110VAC powered pump even though it may not be as powerful as a 240VAC model. The high inrush current remains a concern.

Another way to avoid both 240VAC and 120VAC pump loads with high inrush currents is to use a DC submersible pump or DC powered constant pressure pump and operate it directly from the batteries. This means matching the battery voltage to the pump voltage, and running bigger wires to the submersible pump. The DC pump may have a lower flow rate than the more powerful AC powered units. If the battery voltage is greater than 24V then this load is only on part of the batteries which is not desirable. One manufacturer of a 2 gal per minute 24V pump is Shurflo. Another manufacturer is Grundfos who has a line of pumps that be powered from a wide range of DC voltages, for example the 3 SQF-2 model can run off DC from 30 to 300V, and the same unit will also run off 120VAC with a low inrush current.

There are also AC powered submersible pump with a slow startup so that they do not have a high inrush current when they start, and so are much less stressful on the inverters and generators found in an off grid house. Grundfos is an example of a company that makes a 120VAC pump that does not have a high inrush current, for example the model P-5SQ05A-180.

You should be prepared to know how many litres of water you will need per day. (329 litres per person is the Canadian average. Also to estimate the electrical demands of heating hot water, the amount of hot water needed per day is also required. One study concluded that 95 Litres per person was typical in Seattle. Number for Canadian households seems to be hard to locate.

Refrigeration

This can be powered by three methods, which are in order of preference:

The first two methods remove refrigeration from the inverter's load, and thus help with inverter sizing. If the propane fueled fridge can be found at a price comparable to regular fridges, then there will be savings achieved from requiring a smaller number of panels, batteries, etc. For some houses, this is the single biggest load, and shifting it to propane will lower the system cost, or extend the run time between sunny days. Removing the inrush current for the refrigerator from the inverter's peak loads will also help with keeping the inverter cost moderate.

In case you do not know of any brands of propane refrigerators, here is a list of a few that we are aware of:

Propane Kitchen Range

This is preferred to an electric range which uses a huge amount of electricity. Most modern propane stoves use a 120VAC circuit to power timers, clock and to light the burners when you turn them on. Older propane stoves may use a pilot light and have no electric components. The timers don't use much power, but what you want to avoid is a stove that uses a "glow bar" to ignite the propane. The glow bar uses a lot of electricity. What would be ideal is a propane stove that uses a piezo igniter, similar to a gas BBQ. The 2nd best type would be called a "standing pilot" system, which has a tiny flame all the time. This is a simpler system, and would be much better for off grid than a glow bar, even though it does use propane energy all the time. This link is to an an electric free propane range that uses a standing pilot, made by a name brand manufacturer.

Converting a glow bar range to operate without the glow bar is not practical. Another name for the same system is hot surface ignition.

The Peerless Premiere company makes a line of gas ranges that use electronic spark ignition, and both the top burners and the oven can be lit with a match and used without any power. The 120VAC consumption for a model without a timer is 0.07W. With a timer and clock the 120 VAC power used is about a watt or less. These are perfect for off grid living. At the end of 2011 the USA regulations are changing, and glow bar ignition will become almost universal to meet the requirement to have mercury free controls. This company will continue to make CSA approved products that do not use glow bars, and will introduce some models that use a battery for the spark ignition system and timer that will last at least 3 years and so use no 120VAC at all! This company does make a few lower cost models that do have glow bars for contractor grade stoves, and so be certain to insist that you get a non glow bar model. This company's products are available in Canada through a distributor in Mississauga, but not at the big box stores. You can order them through an Ottawa retailer.

As an oven with a glow bar cycles off and on, the glow bar is on only while the oven gas is flowing, so the glow bar is only using electricity part of the time, and not 100% as might be supposed. A glow bar uses 250 to 500w, depending upon the manufacturer.

Propane Clothes Dryers

Electric clothes dryers should be avoided for all off grid applications. Even the highest efficiency electric units, including the newest condensing models use far too much electricity to be practical. The best alternative is a gas unit, fueled by propane. These have a motor that is electrically operated, which is unavoidable. However avoid a unit that uses glow bar ignition and keeps the glow bar on the entire time that the unit is calling for heat. That would increase its electrical energy consumption by a very significant amount. Highly preferred are units with electronic spark ignition which would use a miniscule amount of electricity for the propane ignition.

It seems to be very hard to find out what type of igniter is used by the gas dryers. They all seem to have glow bars, which may not be avoidable in a dryer. A dryer with glow bar ignition is still vastly superior to any electric dryer for off grid use!

Most of the gas powered dryers are sold setup for natural gas. You will need a propane conversion kit to change it to propane. Buy both at the same time, after becoming absolutely sure that the manufacturer offers a conversion kit. Be prepared to pay for the conversion kit, and if you are not good at following instructions, to pay for a service call to have a gas technician install the kit for you.

Note that clothes dryers are not Energy Star rated, and the reason is that the rating agency concluded that all dryers used about the same amount of energy, and so there was no point in rating them. Unfortunately that does not give consumers any way to compare different models and brands on the basis of energy consumption.

Plan for a possible future hookup to the Grid

We recommend that you wire an off-grid house exactly as if it would be grid connected one day, by putting in a circuit for an electric range, and an electric clothes dryer. It would cost very little to run the wires inside the walls during initial construction, as opposed to added them later when a grid connection became possible. Also plan where a meter would go, and where a mast or an underground cable to the nearest pole would be placed.

In the future, if connected to the grid you could still make use of your PV panels by changing to a grid-tie inverter and operate as a net-metering installation.