Off-grid Power System Design
At Sunstore we are trained and very experienced at off-grid power system design. We have many years’ experience in specifying, building and maintaining on-grid and off-grid solar systems.
An off-grid solar power system is made up of:
- Solar panels
- Inverter to convert DC power to AC
- Charge controller
- Ancillary equipment to link panels to battery and battery to your home
The panels generate solar energy and feed the batteries. The batteries are connected to the inverter and then to your home. It’s a closed system that should generate enough energy to run your property all throughout the year.
Designing an Off-grid Solar PV System
The main component of an off-grid system is the battery. Effectively a battery is the off-grid part of a solar power system. Without a battery, it is a solar power generation setup rather than true off-grid.
The battery powers the load either directly or indirectly. Direct loads are DC and run straight off the battery. These systems are usually low voltage 12v, but can be 24v or 48v DC devices.
Running directly in this fashion is the most efficient method. Indirect loads may use an inverter to change the DC voltage from the battery into AC voltage the same as your home 3 pin socket. This has a loss of efficiency of around 20% overall. In some cases, this is unavoidable, such as a permanent home off-grid system.
In most scenarios, smaller systems are DC and larger homes and power supplies are AC through an inverter.
When you design an off-grid solar PV system, an efficient way to size a battery is to ensure you have enough power to run the required load for 24 hours. Then it is essential that you have a method to recharge this battery in full each day. This may be a mains charger, solar panels, generator or other power source.
Having more batteries than one day is added expense to a product that is decomposing and only has a specific life. Invest in the recharge option over a larger battery store as this is a one off payment vs replacing costly batteries regularly.
Check out ‘How to size an off-grid solar power system’ for more information on sizing an off-grid solar power system. For a deeper dive into solar battery sizing, check out our ‘Battery bank sizing for off-grid systems’ page.
Adding solar panels to this setup is one really good method of recharging the batteries. Ideally you will have enough solar panels to charge it up every day the system is required. If you want the system to work all year round a far larger array of solar panels will be required than a summer only setup.
Please use our off-grid solar power calculator to work out how much solar is required for your project.
Off-grid Solar Power System Sizing
Sometimes the amount of solar panels required is not feasible due to cost or lack of suitable space. A common mistake here is to add more batteries. This only delays the inevitable of running out of power and stressing those costly batteries. Look to add a secondary power source such as a generator instead. This can provide adequate power without stressing the system.
With DC off-grid electrical system design the solar energy charges the batteries with a charge controller. This converts the varying power of the solar panels to the battery voltage and ensures that when the batteries are full, the power is disconnected and the batteries are not overcharged.
Please look at our charge controller articles for help on choosing the best size for your system design.
Solar Power Inverters
AC or indirect off-grid systems may use a grid-tied inverter as this can sometimes be cheaper and more convenient when the batteries and solar cannot be located close to each other.
An on-grid inverter is used to put power into the system’s power supply anywhere on the AC electrical system. The power is then used to run your AC appliances directly before charging the batteries through an inverter/charger. This is less efficient at charging but slightly more efficient at running the devices directly. This is a better scenario for larger output systems.
If you are using an inverter for an indirect system design, you must choose a size that is larger or equal to the maximum power consumption. Usually this is the largest item you need to run plus a little more for safety. If you have an on-grid solar inverter then this must be taken into consideration as well and treated as a load item so that it can be controlled and used for charging without damaging components.
Our guide on the Best off-grid power inverter offers an excellent grounding if you would like to know more.
When designing a system, make sure that fuses on batteries and RCDs and MCBs are used where necessary to protect the system, the engineer and most importantly the operator/user!
A solar power charge controller is an essential component of battery-fed off-grid electrical system design. It’s job is to ensure the batteries do not get overcharged and prevents energy reversing current. Some charge controllers will also prevent batteries from fully draining, further protecting your system.
Charge controllers come in 6V, 12V and 24V sizes. You need to calculate the total wattage of your solar power system, the battery bank voltage and multiply them together using Ohm’s law. Amps x Volts = Watts.
For example, a 3,000 Watt solar panel with a 48V battery bank = 62.5 amps. Your charge controller will need to be able to cope with this and a little more to be safe.
An off-grid power system design also requires the cables, connectors and mountings for the panels, batteries and inverters. Exactly what you need depends on the off-grid power system design you’re using. We would be happy to assist with this if required.
As will all design it can be a minefield. Contact the experts at Sunstore and we can design a system for you free of charge and without obligation.
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