Off-Grid FAQ

Off-Grid Power Systems Questions Answered

WHAT IS AN OFF-GRID POWER SYSTEM?

A stand-alone renewable energy system is one that is not connected to the national power grid.

WHAT IS A HYBRID OFF GRID SYSTEM?

A hybrid energy system usually consists of two or more energy sources used together to provide a better energy supply balance. For example, in the UK, a solar electric (pv) array could be coupled with a wind turbine, which would create more output from the wind turbine during the winter, whereas during the summer the solar panels would produce their peak output. Hybrid systems can make more economical sense than wind or solar alone, where total grid independency is required.

WILL AN OFF-GRID POWER SYSTEM COMPLETELY POWER MY HOUSE?

An Off Grid solar power system is completely disconnected from the main electricity grid so the installation has to supply all your power needs. Each system is carefully designed to meet an exact power requirement. Many installations include a generator backup which can supply power in the occasional circumstances, where the renewable components are unable to provide all power requirements. The installation includes an integrated management system that seamlessly manages the power storage whilst meeting the household energy demands. An off-grid system will be designed to minimize the requirement for any backup power from a generator, but a backup is always advisable.

The UK receives plenty of the suns radiation that generates heat the heat in the air that the unit needs to work very effectively, all year round and even on a cold winter’s day. The system will be able to supply your hot water heating requirements efficiently all year round.

DO I NEED PLANNING PERMISSION FOR AN OFF GRID SYSTEM?

Generally, planning permission is not necessary for the installation of solar panels. There are a number of exceptions to this. If you live in a listed building, a building with any kind of conservation order on it – or of any historical value, or if you live in an area designated as National Park, an area of outstanding beauty or with any other kind of special order. The same is largely true of small domestic wind turbines, as long as it is not visible from a public highway, and a certain distance from neighbouring properties. To find out if you need planning permission call your local council and ask for the planning department.

WHAT IS THE LIFE EXPECTANCY OF AN OFF GRID SYSTEM?

Many of the technologies we supply are expected to last more than twenty years. Technologies with moving parts such as wind turbines, will eventually require replacement bearings. Solar panels, which have no moving parts, last an extremely long time. Some of the earliest solar electric panels, made about 35 years ago, are still producing energy today. Recently, photovoltaic panel manufacturers have started offering 25-30 year performance warranties. Inverters tend to have a 5-10 year warranty, and batteries 7-10 years.

WHAT SIZE BATTERY BANK WILL I NEED?

Again, it depends greatly on your energy requirements. For example, if you just wish to run a notebook all day, LED lighting and a few small appliances intermittently, a 100 AH battery may suffice, assuming you have the correct sized solar panel to charge it. To run a household will require far more battery storage.

This depends on the power requirements and also on the required period of available storage -determined by climate and seasonal weather patterns; availability of standby power (or not); and not least budget! For a small system three days storage will be sufficient, but it all depends on the overall system design and whether it include both solar pv and a turbine, and especially if a back-up supply e.g. generator is available. Actual sizing is very difficult since the amount of wind or solar charging energy is highly dependent on the weather, consequently a system that incorporates both wind and solar inputs will require a considerably smaller battery than one with a sole power source. Other factors such as criticality of the loads (resulting in a larger battery store for fail safe operation) and whether seasonal patterns of consumption match seasonal patterns of generation (allowing a smaller battery) are also important.

HOW MANY SOLAR PANELS WILL I NEED?

This will vary greatly, according to the amount of power required and the need to oversize a system to maintain the required production levels in the winter months.

WHAT SIZE OF WIND TURBINE WILL I NEED?

This will vary according to the amount of power required, and the size of the solar pv array in place, however for a domestic system only a small turbine is usually required to supplement the pv generation in the winter months in particular.

HOW IS THE INVERTER FOR AN OFF-GRID SYSTEM SIZED?

In addition to the average power consumption, peak power consumption needs to be considered in sizing the inverter. This is estimated by adding the wattages of the largest number of devices that are likely to be operated at the same time. The continuous rating of the inverter should be greater than this figure. Most inverters have an overload capability, for short periods, of two or more times their rated output, and this is needed for it to cope with the starting surges involved in electric motors -often three times their rated power. If several motors can start automatically (e.g. fridge and freezer) then it is possible for them to start simultaneously, so their combined starting surge must be taken account of.

DO I NEED TO HAVE A BACKUP POWER SOURCE?

Wind generator &/or PV output characteristics, together with averages and patterns of windspeed or sunlight hours, must be considered in choosing the generating equipment.

Wind and solar resources are often complimentary (high winds & low sun in winter and vice versa) so combining both can result in a smaller battery store and a overall cheaper and more efficient system.

In order not to oversize the inverter (and so also save on battery and wind/solar costs) a back-up generator can be incorporated.

The generator should be sized to cover the likely peak power consumption of all appliances, and the aim should be to run it for short periods at full capacity, and for it to charge the battery bank.

WILL I NEED TO CHANGE MY APPLIANCES AND ALTER THEIR USAGE?

When planning for an off grid renewable energy system it is vital to assess your specific requirements … i.e. what appliances – lighting, heating, cooking, refrigeration, pumping etc – you want to power from the installation. The power requirement of these functions must be determined, as well as their frequency of use (and in some circumstances the likely timing of their use, so that the peak requirement at any one time is known). Conservation of energy usage may be feasible in some situations, through for example changing appliances or adjusting ones lifestyle. After determining these requirements, and having decided which sources of renewable energy are most suited to the location, it is necessary to carefully match the individual parts of the system – batteries, inverters, generators etc. This process enables one to make the most efficient use of the energy available, and to have energy available at the time(s) it is needed.

Both existing and/or anticipated power requirements must be ascertained as a first step in sizing a system. Factors to consider include:

Variety of loads to be run: e.g.. domestic lighting, refrigeration, pumps, etc.

Peak Consumption: total loads that might be required to be run at any one time

Average Consumption: typical loads that need to be run most of the time

Minimum/Continuous Consumption: any loads that need to be run all the time

Voltage and frequency: of required loads, DC or AC

Pattern of usage: daily, weekly, and seasonal

Degree of automation required: whether supply needs to have 100% availability

In designing a power supply it is important to consider the whole home as a system; loads are interrelated, eg. correctly placed windows can help with heating and lighting; insulation reduces heating requirements etc.

Conservation

This plays an important role in keeping the costs of any energy supply down. The use of energy efficient appliances and lighting, use of non-electric alternatives wherever possible, and increased awareness of patterns of use, all contribute towards the success and potential for a renewable energy system.

Cooking and Heating

Conventional electric cooking, space heating and water heating use a prohibitive amount of electricity. Electric cookers use about 1500 watts per burner, so bottled gas and solid fuel stoves are usually used for cooking. A microwave oven has a large power draw, but since food is cooked much more quickly, the total power consumption may not be too large. Good passive design and proper insulation can reduce the need for heat, further space heating can be provided by propane or solid fuel. This is also used for water heating and can be combined with solar water heating systems.

Refrigeration

If an electric fridge is to be used then it should be a high efficiency type. The higher cost of good quality DC refrigeration is more than made up by savings in other system costs.

Lighting

Low energy bulbs are always advisable .

Small Appliances

Many small appliances such as toasters, irons and hair dryers consume very large amounts of power but require very short or infrequent use periods. This means that if the system inverter, battery and charging system are large enough they may be usable. Electronic equipment, e.g. stereos, televisions, videos and computers etc. have a low power consumption. See also: Energy Saving Trust website for useful hints & advice.

HOW IS AN OFF-GRID POWER SYSTEM SIZED?

The precise balance and size of the components of a wind/solar system depends upon your location and anticipated power requirements.

A wide range of high efficiency appliances, batteries, controllers and inverters are available to meet most needs. The number of consecutive days without sun or wind, together with patterns of use and peak power demand, determine both the battery store size and inverter or back-up generator requirement. Seasonal as well as daily variations are important. If preferred a flexible approach can be adopted with components added in order of priority and a system expanded by the addition of additional battery store or generating capacity as needs change or finance allows.