Commercial energy storage systems Design & Install

This paper introduces the configuration and calculation method of the photovoltaic Commercial energy storage systems through practical application cases.

Many users are new to the photovoltaic industry are not familiar with how to calculate and configure photovoltaic Commercial energy storage systems, so they cannot give accurate quotations for the budget.

What basic data that must be known before installation?

1. Voltage phase: First of all, it is necessary to understand the user’s voltage phase, is it single-phase AC 220V or three-phase AC 380V? This determines the output characteristics of the inverter;
2. Load Type: The second is the load type, is it an inductive load or a resistive load? This determines the load power and output waveform of the inverter.
3. Full-load running time: The third is the full-load running time of the load, that is, how many degrees do we need for the average daily power consumption?
4. Power(kW): If it is a photovoltaic grid-connected power station, since there is no energy storage device, it is only necessary to configure a reasonable power of photovoltaic modules;
5. Capacity(kWh): If it is a photovoltaic off-grid Commercial energy storage systems, the capacity of the battery must also be calculated, including the self-reserve power of the system when there is no photovoltaic power generation condition in continuous rainy days.

Read more: About PV Power Calculation Formula

Photovoltaic off-grid Commercial energy storage systems case

We take a small lake farmer photovoltaic off-grid power station as an example. Due to the high cost of long-distance power pulling, and the large power loss and voltage loss of the transmission wires, as well as when the typhoon is coming, the power consumption will be unstable, and unexpected power outages often occur, affecting production and domestic power consumption. For this reason, it is planned to use photovoltaic off-grid power generation. During the day, the intensity of sunlight radiation is high, so the photovoltaic power generation can directly inverts the output, provide electricity for electrical work and charges the battery at the same time. During the night, it will be the battery that inverts the output.

The voltage is AC220V 50Hz, and the electrical equipment mainly includes:

• Fish pond oxygen pump (300W) 10 sets
• TV + satellite receiver (200W) 1 set
• Rice cooker (750W) 1 set
• Induction cooker (2000W) 1 set
• Refrigerator (100W) 1 set
• Lighting (100W)

The loads are not used at the same time. The oxygen pump works during the day when the sun is shining, and does not work at night; the power of other electrical appliances is about 3000W, and the daily power consumption is about 10 KWh. Since the lake is well lit, the self-reserved power in rainy days is not considered.

Photovoltaic inverter

According to the above data provided by the user, in the design of this system, a high-end photovoltaic controller and a grid frequency sine wave inverter are selected, with a power of 96V 6KVA, which can meet the user’s electrical equipment output power requirements.

Battery Capacity

The energy storage device used in this photovoltaic off-grid Commercial energy storage systems is a commonly used lead-acid battery with large capacity and high cost performance.

The reserve power of the battery is 10KWh. Since the DC input voltage of the photovoltaic inverter is DC96V, the theoretical capacity of the battery can be calculated as follows:

10000VAh/96V=104Ah

According to the relevant technical standards of the battery, the discharge rate of the battery should be 0.5C2, which is more economical and reasonable. It can ensure the number of charge and discharge cycles  of the battery and effectively prolong the service life. Since the lake has sufficient sunshine, the photovoltaics can directly invert the output during the day, without repeated battery discharge procedures. During the night, the electricity consumption of electrical appliances is small, and the discharge time is short. Therefore, the design of this scheme appropriately increases the battery discharge rate to 0.6C2. Therefore, the battery’s Actual capacity calculation:

104Ah/0.6=173Ah

The value here is 200Ah, that is, the total capacity is: 96V 200Ah

The specification of the lead-acid battery is 12V 200Ah/pc, the connection method is 8 batteries in series, and a total of 8 batteries are required.

Read more: Top Lithium ion battery manufacturers in China

Photovoltaic module power

After the configured capacity of the battery is obtained through the above calculation, the power configuration of the photovoltaic module is then calculated.

The geographical location of the lake has high solar radiation intensity, and the effective sunshine time is as long as 6 hours. Polysilicon photovoltaic modules are selected, and the photoelectric conversion efficiency reaches 16%, which meets the standards stipulated by the National Energy Administration.

The calculation formula of photovoltaic power generation is: System power generation = Photovoltaic module power × Sunshine time × Comprehensive coefficient. The comprehensive coefficient refers to the loss coefficient caused by factors such as temperature change, line loss, controller (or inverter) conversion efficiency, etc. It generally takes a value of 0.5-0.7, and this time it takes a value of 0.6. Therefore, the power calculation of photovoltaic modules is:

96V×200Ah/(6h×0.6)=5333W

The specification of the module is 36V 275W, the size is 1900×980×45mm, and the area is about 2 square meters. The connection method is that every 4 pieces (144V) are connected in series as a group, and then 5 groups of components are connected in series and then in parallel. A total of 20 pieces of photovoltaic modules are required, the total power is 5500W, and the area of the photovoltaic module array is 40 square meters.

Photovoltaic lightning protection combiner box

The function of the photovoltaic combiner box is to reduce the connection between the photovoltaic module array and the inverter. Users can connect a certain number of photovoltaic modules with the same specifications in series to form a photovoltaic series, and then connect several photovoltaic series in parallel to the photovoltaic confluence lightning protection box. After converging in the photovoltaic lightning protection combiner box, the power is sent to the inverter through the DC circuit breaker.

Lakes are lightning-prone areas, and isolated huts and nearby forests are prone to lightning strikes. Therefore, photovoltaic power stations must pay attention to the impact of lightning on equipment. A DC high-voltage lightning protection module is added to the photovoltaic combiner box, which can effectively protect the safety of inverters, AC power distribution cabinets and other electrical appliances; at the same time, the combiner box has built-in high-power anti-reverse diodes, which can effectively avoid the battery reversely discharges the components and burns the components when there is no photovoltaic during the night.

Photovoltaic supports and cables

The solar panel bracket is absolutely indispensable to the photovoltaic Commercial energy storage systems. The function of the solar panel bracket is to fix the photovoltaic module. In order to reduce the cost, the user can also customize the bracket on site to achieve firmness and anti-corrosion measures.

Cables are wires that connect components, inverters, and AC power distribution cabinets. Some of them are exposed to the outdoors and exposed to the sun and rain for a long time. In order to ensure the normal operation of the system, high temperature resistance, oxidation resistance and UV protection cable wires must be selected. The cable must use thick copper core solid wire with large cross-section and low resistance to reduce the voltage drop caused by too long distance and affect the power generation efficiency.

To sum up, I believe that everyone will have an understanding of the calculation and configuration of solar photovoltaic off-grid Commercial energy storage systems.