OFF-GRID FOR HOME AND BUSINESS

Solar Systems for Remote Areas or living Off-grid

 

SOME INFORMATION THAT YOU MAY FIND USEFUL…

For those who are getting serious about installing a new off-grid power system and haven’t lived with one before, the following information should be helpful.

Living with Off-Grid Solar Power

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Living in a house that is powered from an off-grid solar power system will usually mean that there will be limitations on what sort of appliances can be used, and it will require an awareness of one’s energy usage. It is not difficult though and once you become familiar with the system and your appliance power ratings knowing the limitations will become second nature. The operation of most systems is fully automatic and using power in the house is no different to that in any other house that is wired to mains power.

It is important to be aware of the state of charge of the battery bank so that you know when you need to conserve power or to run a generator in order to maintain the health of the batteries. Most of the time there will be more than enough power available and running a generator or conserving power will not be necessary, but it is important to recognise the events that may lead to an energy shortage. These events will almost always be one of, or a combination of, the following:

  • A series of overcast days at any time of the year
  • One overcast day within approximately 2 months of a winter solstice
  • Increased power consumption from extra people staying at the house or from a particular appliance or combination of loads

We recommend the use of a display that can be mounted anywhere in the house and gives the system owner accurate information about the state of charge of the batteries, energy usage and other features. Easily being able to know what your system is doing is an essential tool in being able to manage it well.

System Limitations – (1) Maximum Instantaneous Power Output

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For systems which run AC appliances through an inverter, the inverter will have a maximum power rating. A common sized inverter for household applications is one which is rated at 3000W continuous operation (and at least double for very short periods of time). This capacity allows you to operate any appliance that is designed to plug into a standard mains 240V outlet (10A outlet). A situation may occur where the capacity of the inverter is exceeded though, when more than one high powered appliance is being used at once, or several lower powered appliances are being used simultaneously. All appliances should have a power rating printed on them somewhere, and it is advisable to become familiar with the ratings of your appliances so that you can manage your power consumption effectively. A high powered appliance (for this purpose) is one which consumes over say 1000W such as an electric kettle or toaster. The sum of the power ratings of all of the appliances (including lights) that are operated simultaneously must be kept to less than 3000W for an inverter this size.

Example: If an electric kettle, rated at 2200W, 4 x 20W light globes and a 75W television are all being used, the load on the inverter will be 2200 + (4×20) + 75 = 2355W. Supposing someone then pushed the toaster, rated at 1500W on, the total load on the inverter would then become 2355 + 1500 = 3855W which would overload the inverter and most likely cause a circuit breaker to trip at the main switchboard.

Usually it is not difficult to manage your appliances such that the system is not overloaded. The toaster/kettle combination is one of the most common scenarios to watch out for, also if you plan to use a large power tool, just make sure that no one else is operating another high powered appliance before you start. Observing the system display is another good way to see the total amount of power that is being consumed in the house at any one time.

 

System Limitations – (2) Maximum Energy Consumption per Day

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The total energy consumption over a period of time is different to instantaneous power consumption. It is measured in Wh (or kWh, which are the same units that appear on a mains power bill) and is calculated as the product of the power rating of the appliance (in watts) times the duration of its use (in hours). Similarly, the amount of energy gained from the solar array is also calculated in this way. Having an awareness of the daily totals of energy collected and energy consumed is important, as they directly affect the state of charge of the battery bank. Each off-grid system will be designed to provide a nominal amount of energy on an average daily basis. During summer months it may be able to provide much more than this design amount.

As you become familiar with living with a off-grid power system you will get a feel for how much energy you can use at different times of the year and what effect that has on the battery charge. Likewise you will be able to evaluate the amount of charge received on a cloudy day compared to that on a sunny day, which appliances consume the most power, and so on. You will find that living with off-grid power system is a very effective way to gain an appreciation of how much energy various appliances use and also how usage habits effect energy consumption.

Appliances such as a toaster, microwave oven, circular saw or angle grinder draw a large amount of power for a small amount of time, therefore the energy demand on the battery system resulting from a single use is low to moderate. Appliances that draw a large amount of power for a long period of time (such as an electric heater, clothes drier, electric oven, split system air-conditioner or electric hot water service) should not be used at all with most stand-alone power systems. The energy demand on the battery system is too large.

Appliances such as a computer, television, refrigerator or lights draw a relatively small amount of power but are often operated for long periods of time (or continuously) and therefore can have a major contribution to the daily total energy consumption.

Frequently, during the process of system design and energy auditing (see below) we establish that the refrigerator/freezer(s) will have the highest average daily energy demand of all of the appliances. Accordingly, we recommend that system owners give some serious thought as to what they really require in terms of refrigeration and consider upgrading to the most energy efficient appliances available. Highly efficient fridge/freezers are available that operate on a dedicated 12 or 24V DC input. They can be expensive to purchase, however it often works out that it is more economical to spend the money in this area rather than on a larger size stand-alone system that will be able to run your old and inefficient fridge/freezer.

Battery State of Charge & Battery Service Life

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The service life of the battery bank is dependent on how deeply it is discharged on an average daily basis. The Narada REX series gel batteries that we supply are some of the latest technology in lead-acid batteries and have a design lifespan of 20 years when operated such that they are not allowed to discharge below 80% full and regularly reach the fully charged state.

A system may be operated such that regular deeper cycling is accepted (say down to 75% or 70% charged) however it is important to realise that the lifespan will be reduced if operated in this way.

The batteries should never be fully discharged. Various methods are put in place to prevent this from happening. Occasional discharge to say 50% will not adversely affect the battery service life but should be avoided whenever possible.

System design parameters

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Other than the expected energy consumption, factors contributing to system sizing calculations are:

FOR BATTERY CAPACITY

  • Design autonomy – This is the number of days that the system is designed to operate for without sunshine before needing to be charged from a generator (usually 2 days +)
  • Maximum depth of battery discharge (see above).

Note that a battery bank cannot be upgraded. Connecting new and old batteries together will damage the new batteries.

FOR SOLAR ARRAY SIZE

  • Geographic location
  • Array orientation & tilt angle
  • Shading
  • Solar charge regulator type

Other important design considerations for a compliant system eligible for STCs (see section….) are:

  • Location of the battery bank. The batteries must be in a dedicated equipment room or battery enclosure with restricted public access. They should be in a place that is at a stable temperature (tin shed is not ideal) and has suitable ventilation. They should also be as close as practically possible to the PV array to reduce cable losses.
  • Location of the inverter, regulator & other equipment. These must be in a dedicated equipment room with restricted public access located with or directly adjacent to the battery bank.
  • The electrical installation to which the system is connected to must comply with relevant standards (ie. be able to pass an electrical safety inspection)

As the amount of rebate (from sale of STCs) is calculated by installed PV capacity and does not take into account battery capacity, it makes economic sense to design the system with more PV capacity than required and slightly less battery capacity than required (if concessions are to be made). The increased PV capacity will, to a limited extent, allow the system to still function well with reduced battery capacity.

Renewable Energy Certificates (Rebate) for Off-Grid Systems

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Most off-grid  power systems that are professionally installed in a fixed location are eligible for the creation of Renewable Energy Certificates (see About RECs & STCs).

The system must be permanently connected to a main AC switchboard, and this switchboard and all associated wiring circuits must comply with  relevant standards and have a Certificate of Electrical Safety (CES) in order to be eligible.

Pricing and system design examples

Indicative pricing for a range of off-grid systems is available at Off Grid Solar System Pricing