What is off-grid inverter system?

Off-grid power system is the most widely used system at present which can be used in completely separate environments. It can be used to solve the problem that a place away from urban areas, and the electricity is inconvenient, or with power shortage , especially that it suitable to use in the place where needs an independent power supply, such as the mountains, the fishing-boats and so on.http://www.jinhuasunrise.com/en/article/Whatisoff-gridinvertersystem.html

Off-grid system components Figure

1,The devices for Off-grid systems: The most basic device include solar panels, off-grid inverter, solar charge controller, battery and so on, which we introduced in the article “How inverter works“.

2,Date reference for off-grid inverter system configuration: the size we configured for off-grid power generation system is mainly to see the size of the load power, and the working time of the load, that is to say, you should figure up the total power you want to use. And the back-up time also should be considered, if continuous rains, you should calculate the working days for your loads. All of the above factors must be considered. We can know that the power load is 1000W, continuous working time is 5 hours, then the amount of electricity consumed is 5 kWh, if you want to send out 5 kWh, theoretically 1000-1500W is sufficient. But in fact, our configuration is 2KW, because of the reason of efficiency. For solar panels in off-grid systems, the actual and theoretical power generation capacity is still a big gap, that is to say, there will be some loss of power when the solar panels being charged, and under normal circumstances, the conversion efficiency should be about 70% when the allocation of voltage is in a reasonable case. And of course, there will be power losses between any devices, but more or less only. Overall system efficiency from the network should be around 50-60%, due to that, the efficiency of the panel is 70%, the battery discharge depth is generally about 80%, and the efficiency of inverter is usually around 90%, integrated down, the efficiency of the system is 50- 60%.

3,The following sets of conventional configuration instructions to do next:

To do a system that can supply power for TV, computers and other small appliances. The problem we must first consider is the power, we should know how many hours the above appliances to be used, if there’s still a sunny day, we should calculate how long can emit so much electricity. And then, the issues such as solar panels and batteries should be considered. Please check the configuration I recommended as follows: 500W solar panel, 2 units of 50AH battery, 1 unit 1000W off-grid inverter, and 1 unit 20A controller. And here I want to explain the reason why use two batteries. Because most cost-effective solar panels is now the 36V 250W polycrystalline panel,  its good to the charge battery with 24V voltage, if you are use it to charge a 12V battery, and use of an ordinary PWM charge controllers, then when you actually charge the maximum power is only 12V * 8A = about 96W, so the actually power for use is less than 100W for 250W board. This way will cause great waste.

How to choose the inverter. There’s a very important relationship between the efficiency and the allocation of voltage in above mentioned things in this series. Operating power of the inverter is usually recommended within 80% of nominal maximum power, that is to say, for 1000W inverter, we recommended maximum load with less than 800W, which can improve the safety of the inverter.

The configuration of voltage is mainly refer to the power of the load, and the voltage of the solar panel. And here we recommend the configuration relationship as follow: for Load of 1000W or less, you can use a voltage of 12 to 24V, for 1000-2000W load, we recommend using a voltage of 48V or 24V, and for 2000W or more load, be sure to use a voltage of 48V.

The reasons are as follow:

For 1000W load with 12V voltage, the current is about 85A, it’s very high, not very safe.

For 2000W load with 12V voltage, the current is near 170A, it’s very unrealistic. .

For 3000W load with 12V voltage, the current is near 250A, theoretically feasible, but in reality, really not seen. You should imagine that how thick the wire you need if the current over-250A

If using 24V voltage for above loads, the current will be decreased by 50%, if the system with 48V voltage, the current will be decreased by more 50% which is only a quarter of the current above. And it’s obviously to see the Safety and feasibility.

About the battery capacity. The decisive factor is that how much electricity you want to save, and it can be calculated by the power of load and the working time. For example, you have a load of 1KW to run four hours (four kWh of electricity). A 100AH the battery can save about 1.2 kWh, relatively speaking, the depth of discharge is 80%, then 1.2 * 80% = 0.96 kWh or so, that is to say a 100AH battery usually has a kilowatt or so, if you want to keep four kWh of electricity, it will need four batteries. I said above. 1KW load recommended 12V-24V system, this is also not absolute, if you have four batteries, they can be composed of whole system, that is 12V, and also the whole string can be 48V with two strings in parallel and two strings in series, that is 24V, this also should combine your board to decide. We recommend this power system with 24V or 48V voltage because of the high efficiency and the good scalability. Late upgrades do not have to consider the problem that replacing the inverter and controller.

How to choose the controller: the type of controller, usually we use PWM type, in the above configuration, we have this controller is based mainly in terms of, if you want to use MPPT controller for the above system, the voltage of this configuration can be appropriate to relax. For example, you can use the panel of 30V to charge 12V battery, which is entirely possible. And the efficiency is the same with the efficiency for PWM controller to charge 24V Battery.

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