Can an off-grid inverter be used without a battery?

Installing a photovoltaic system is a good choice in some places where electricity prices are high and power outages are frequent. However, the grid-connected system cannot generate electricity during a power outage, which wastes some energy and makes the equipment unable to work, affecting the continuity of work. If a photovoltaic off-grid system is installed, photovoltaic power can continue to generate electricity during a power outage, which does not affect the continuous operation of the equipment and has better overall benefits. However, conventional off-grid systems must be equipped with a large number of batteries. These energy storage batteries are expensive and have a short lifespan, which increases the initial investment cost of the system. Therefore, the application of photovoltaic off-grid systems is also limited.

On April 22, 2020, at the Photovoltaic Elite Forum, Yuan Zhimin, Senior Product Manager of Growatt, delivered a live keynote speech on "Design and Selection of Photovoltaic Off-Grid Power Generation Systems", showing everyone a magical off-grid inverter that breaks people's conventional thinking and can work with less or even no batteries. In some specific occasions, using this off-grid inverter can reduce initial investment and increase returns. Let's learn more about the characteristics and application scenarios of this inverter.

Growatt's newly developed off-grid inverter SPF 5000ES has an inverter output power of 5kW. In addition to the basic functions of conventional off-grid inverters, photovoltaic priority working mode, mains complementary working mode, and battery working mode, it also adds a battery-free working mode. The battery-free mode means that when the system has no battery or the system has a battery but the battery is dormant for some reason, the inverter can still ensure normal operation when there is sufficient photovoltaic power.

The SPF 5000ES working modes are as follows:

1. When the system has both photovoltaic and mains, SPF 5000ES can be connected to the grid for self-use similar to a grid-connected inverter. When the photovoltaic power is less than the load power, all the photovoltaic energy is supplied to the load, and the insufficient part is supplemented by the mains. The photovoltaic and mains jointly carry the load. When the photovoltaic power is greater than the load power, the photovoltaic energy is provided to the load first, and the excess energy can be used to charge the battery. If there is no battery, the inverter adjusts the photovoltaic power according to the current load size to ensure that the inverter does not send power to the grid.

2. When the system has PV but no mains, SPF 5000ES can work off-grid to a certain extent, but when the load power is greater than the PV power, the inverter will stop working. This situation is suitable for loads that can change with the input, such as electric water heaters, or occasions where the PV power is much greater than the load power.

3. When the system has no photovoltaic power but has AC power, SPF 5000ES can bypass the load and attempt to charge and activate the dormant lithium battery.

In addition, SPF 5000 ES has developed two practical functions, timed charging and timed output. Timed charging: customers can customize the charging time period of the mains electricity, limiting the use of the grid to charge during the peak period of electricity prices, which can reduce electricity bills; timed output: customers can set timed output, and the inverter will automatically shut down during a certain period of time to ensure that the system's own losses are reduced.

SPF 5000ES is suitable for:

This off-grid machine supports up to 6 units in parallel and can build a 30kW single-phase or three-phase system. It is suitable for small commercial power stations with self-generation and surplus power that cannot be connected to the Internet, loads not exceeding 30kW, and applications where load power consumption and photovoltaic power generation are basically synchronized.

Not suitable for the following occasions: Equipment load is greater than 30kW, and photovoltaic power generation and equipment power consumption are not synchronized.

Typical design solutions

The equipment load of a certain family workshop is 12kW. The main equipment is an electric oven, which consumes about 1,500 kWh of electricity per month. Most of the time, electricity is consumed during daytime, and the price is 0.7 yuan per kWh. The electricity consumption in this place is unstable, with an average power outage of 1-2 hours a day. After the power outage, the electric oven will cool down, and it will take half an hour to heat up after restarting before it can work.

The design uses 48 340W monocrystalline modules with a total power of 16.32kW. The inverter uses 3 SPF5000ES in parallel. Each inverter is equipped with 18 modules, 8 in series and 2 in parallel. A 3-input and 1-output combiner box is connected to the load. The total cost of the system is about 65,000 yuan. It can generate 60 kWh of electricity per day on average, saving 15,000 yuan in electricity bills per year, and the investment can be recovered in about 4 years.