An off-grid solar system is not connected to the electricity grid and therefore requires battery storage. Off-grid solar systems must be designed appropriately so that they will generate enough power throughout the year and have enough battery capacity to meet the home’s requirements, even in the depths of winter when there is generally much less sunlight.

The high cost of batteries and off-grid inverters means off-grid systems are much more expensive than on-grid systems and so are usually only needed in more remote areas that are far from the electricity grid. However battery costs are reducing rapidly, so there is now a growing market for off-grid solar battery systems even in cities and towns.

There are different types of off-grid systems which we will go into more detail later, but for now I will keep it simple. This description is for an AC coupled system, in a DC coupled system power is first sent to the battery bank, and then sent to your appliances. To understand more about building and setting up an efficient off-grid home see our sister site go off-grid/hybrid

Simple, affordable, small scale DC-coupled off-grid solar power system use solar charge controllers to manage the battery charging, plus a simple inverter to supply AC power.

The battery bank in an off-grid system there is no public electricity grid. Once solar power is used by the appliances in your property, any excess power will be sent to your battery bank. Once the battery is full it will stop receiving power from the solar system. When your solar system is not working (night time or cloudy days), your appliances will draw power from the batteries.

Backup Generator, for times of the year when the batteries are low on charge and the weather is very cloudy you will generally need a backup power source, such as a backup generator or gen-set. The size of the gen-set (measured in kVA) should to be adequate to supply your house and charge the batteries at the same time. Off grid power system does not have any connection with the grid. The utility company providing power is completely independent from any national networks and is thus fully responsible to service customers in the region. Any excess of electricity supplied is stored in batteries and can be re-used at night. In this instance, instead of the yam farmer selling the excess yams to another farmer, he or she would need to have a good storage area to keep the yams long enough without spoiling to be able to resell them later.

Off grid power is very helpful in rural areas that the grid may not be able to reach. The village or community could gather resources to get a system that supplies and stores power for themselves without having to rely on somebody else to do it for them. While It is more expensive (between USD 4,000 and USD 8,000 for a 4 kW Solar system without storage costs added) to set up an off grid solar system at the beginning, it may work out better after a number of years and could end up being cheaper in the long run as grid electricity costs keep escalating.

 

Main Components of a Off-grid Solar System

Solar Panels

Most modern solar panels are made up of many silicon based photovoltaic cells (PV cells) which generate direct current (DC) electricity from sunlight. The PV cells are linked together within the solar panel and connected to adjacent panels using cables. Note: It is sunlight or irradiance, not heat, which produces electricity in photovoltaic cells. Solar panels, also known as solar modules, are generally connected together in ‘strings’ to create what is known as a solar array. The amount of solar energy generated depends on several factors including the orientation and tilt angle of the solar panels, efficiency of the solar panel, plus any losses due to shading, dirt and even ambient temperature. There are many different solar panel manufacturers on the market, so it worth knowing which are the best solar panels and why.

Solar panels can generate energy during cloudy and overcast weather, but the amount of energy depends on the ‘thickness’ and height of the clouds, which determines how much light can pass through. The amount of light energy is known as solar irradiation and usually averaged over the whole day using the term Peak Sun Hours (PSH). The PSH or average daily sunlight hours depends mainly on the location and time of year.

  Solar Inverter

Solar panels generate DC electricity which must be converted to alternating current (AC) electricity for use in our homes and businesses. This is primary the role of the solar inverter. In a ‘string’ inverter system, the solar panels are linked together in series, and the DC electricity is brought to the inverter which converts the DC power to AC power. In a micro inverter system, each panel has its own micro-inverter attached to the rear side of the panel. The panel still produces DC, but is converted to AC on the roof and is fed straight to the electrical switchboard.

There are also more advanced string inverter systems which use small power optimizers attached to back of each solar panel. Power optimizers are able to monitor and control each panel individually and ensure every panel is operating at maximum efficiency under all conditions.

Batteries

Batteries used for solar energy storage are available in two main types, lead-acid (AGM & Gel) and lithium-Ion. There are several other types available such as redox flow batteries and sodium-ion but we will focus on the most common two. Most modern energy storage systems use rechargeable lithium-ion batteries and are available in many shapes and sizes which can be configured in several ways explained in more detail here.

Battery capacity is generally measured is either Amp hours (Ah) for lead-acid, or kilowatt hours (kWh) for lithium-ion. However, not all of the capacity is available for use. Lithium-ion based batteries can typically supply up to 90% of their available capacity per day, while lead-acid batteries generally only supply 30% to 40% of their total capacity per day to increase battery life. Lead-acid batteries can be discharged fully, but this should only be done in emergency backup situations.

Off-grid solar systems require specialized off-grid inverters and battery systems large enough to store energy for 2 or more days. Hybrid grid-connected systems use lower cost hybrid (battery) inverters, and only require a battery large enough to supply energy for 5 to 10 hours (overnight) depending on the application.

Electricity Switchboard

In a common grid-tie solar system, AC electricity from the solar inverter is sent to the switchboard where it is drawn into the various circuits and appliances in your home. This is known as net metering, where any excess electricity generated by the solar system is sent the electricity grid through an energy meter or stored a battery storage system if you have a hybrid system. Some countries however, use ‘Gross metering’ where all solar energy is exported to the electricity grid.