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For over 25 years, PV has been used extensively as a distributed power source for industrial equipment located “off the grid”. PV systems are powering a variety of loads, such as microwave and fiber optic repeaters, instru-mentation, RTU/SCADA, rural telephony and traffic safety. Since many of these projects include a variety of requirements and special considerations, we offer the following project services:
- Site Analysis - Specification Preparation
- Personnel Training - Turnkey Installation
- Installation Supervision - O&M Manual Preparation
- System Commissioning - O&M/Service Contract
OEM service:
If you are a local Solar company with exiting selling channels which need the packaged appliances, we are hap-pily to offer our product by your brand name.
ODM service:
If you are a local electrical company with exiting selling channels which need the different appliances, we are happily to design the suitable product for your specific needs.
Planning & sizing
Grid-Tie Solar Power System
>Planning Concepts
Please confirm that local electric regulations allow solar system to tie-in the city-frid first.
There are some conditions must be clear prior to the paln:
If electric regulations forbid grid-tie systems, the kind of system should not be installed.
1. If electric regulations permit grid-tie systems but the exceeded solar power can’t sell back to utilities,the gen-erated peak power should be smaller than the concurrent load.
2. The electric regulations encourage renewable energy and allow the exceeded solar power to sell back to the public utilities. It is good for installing grid-tie systems. These systems will offset your utility usage. With the correct size system it will earn you a credit during the day that you would consume at night.
3. The installers must obey the electric regulations of local government.
>System Sizing
Solar power system generated power is proportion to the sunshine radiation. Want to estimate the amount of solar system generated power; the sunshine radiation data must be analyzed. Commonly the data can be ob-tained from local Weather Bureau, NASA global radiation database, or field measuring if previous calcuation required. The data should at least consist of one whole year. The more data obtained, the less inaccuracy may happen.
In meteorology the solar radiation unit is presented as MJ/m2 (Mega-Joule per square meter) or kW/m2 (Kili-
Watt per square meter). They can be exchanged by the simple formula: 3.6MJ/m2＝1kW/m2. Integrate the whole year radiation data and then average them by day, you can get the value of an equivalent sunshine hours, ESH. You can get the brief ESH data from some institutes. The digram below is the brief sunshine hours distribution in United State.
The above ESH is based on natural and horizontal conditions. There are some factors must be adjusted for fur-ther planning:
1. Temperature induced effect: The solar module rated power is based on the constant temperature 25℃ accord-
ing to ASTM E1036. Once the temperature rise up, the output power of solar module will decrease. Contrarily the temperature goes down will increase the output power of solar module. There is not an accurate formula to esti-
mate the effect of temperature in field. According to Hengs ecperiences, we suggest the coefficient: -1.0%/℃(T-
25℃) to estimate the temperature effect. T is a representative average temperature. For example: on average temperature 30℃ area, the temperature effect is about -5.0%。
2.Tilt effect: To get more sunshine radiation, the fixed type of PV array should tilt to face the sun the best of ability. The tilt angle is set to be the local latitude because of the geometry.
3.Orientaion effect: On the Northern Hemisphere, the PV array should face to south. Contrarily on the Southern Hemisphere, the PV array should face to north.
4.System loss:
Cabling loss: Should be smaller than 4% through correct installation.
Inverse loss: The inverter transfers DC power from PV array to AC power. There is loss during the transfer process. Today’s solar inverters emphasize their high transfer efficients. Most of the inverters offer >90% trans-
fer efficients, ie the loss should be smaller than 10%。
Transform loss: If the output voltage of inverter is different from local electric voltage of utilities, a transformer should be installed to change the output volatage of solar inverter. The transformer may cause a 5% loss.
Self drift loss: Caused by inverter and display.
There are many complicated procedures in above effect and loss considerations. The total effect and loss vary from -15%~-25% depends on different conditions.
We can roughly decide the scale of PV array. If the yearly power saving target is Qn, The total effect and loss is assumed as 25%. Required PV array is about:
Qn÷[ESH×(1-25%)×365]＝PV
For example, the yearly power saving target is 10,000kWh, ESH is 3.8hrs, and the scale
of PV should be:
10,000kWh÷[3.8h×(1-25%)×365]＝9.61kW
>System Electricity
The output of grid-tie solar inverter must meet the local electricity of utility competely. Otherwise, local electric power company will ask some protections as the system grid to the utility for safety. The installers must under-
stand these regulations and requirements thoroughly. The main points are:
1.Inverter: To choose the inverter whose voltage, frequency (60Hz or 50Hz), phase (1P2W, 1P3W, 3P3W,3P4W) corresponds with local electric power.
2.Transformer: If the output volatage of inverter is different from the utility, a high efficient isolated
transformer is required.
3. Protection:
i.The inverter should have anti-islanding function. It can shutdown automatically as the utility failed. And return to operate, as the utility is normal.
ii.The inverter should complete protection such as over current, over/low frequency, over/low voltage and ground fault, etc.
>System Planning
1.Series and parallel connection:
i. All the modules in one system must be the same model.
ii. The voltage of series connected modules should always locate in MPPT range no matter in high or low temper-
ature conditions.
iii. The open-circuit voltage of connection should not exceed the range that inverter can accept.
iv. Inverter capacity: Should larger than 85% of the scale of PV array. For example, a 10kW PV can use invert-
ers rated power at least 8.5kW.
2.PV installation required area:
i. Crystalline silicon type PV arrays require 8~10m2/kW.
ii. Amorphous type PV arrays require 15~20m2/kW.
iii. BIPVs require areas depend on their architecture shapes and functions.
3.Orientation and tilt:
i. On the Northern Hemisphere, the PV array should face to south. Contrarily on the Southern Hemisphere, the
PV array should face to north.
ii. To get more sunshine radiation, the fixed type of PV array should tilt to face the sun the best of ability. The tilt angle is set to be the local latitude because of the geometry.
iii. There are many solar trackers can trace the tilt and direction on the daytime. They can increase the output of PV up to 30%~40%.
Please refer our following example to design your optimum solar power system. Please feel free to contact us if you need any assistance. Send your question to: tech@kingenertech.com
Solar Grid-Tie System Design Example
Assumed Conditions
● Yearly saving target: 20,000kWh
● Latitude: 25 degree North
● Monthly average radiation (horizontal): 400MJ/m2
● Yearly average temperature: 28℃
● Utility electricity: 220Vac, 3P3W, 60Hz
System Planning Procedures
1. Equivalent Sunshine Hours: 400 MJ/m2÷3.6÷30days＝3.70kW/m2/day＝3.70hrs
2. Factors Adjustment
● Temperature effect: -1.0%×(28-25)＝-3%
● Tilt effect: Sunshine radiation increases about 8.5% from horizontal to 25 degrees tilt
● System loss: about -19%
i.Cabling loss -4%
ii.Inverse loss -8%
iii.Transform loss -5%
iv.Self drift loss -2%
※ESH is revised as: 3.70hrs×(100%-3%+8.5%-19%)＝3.20hrs
3. Required PV array: 20,000kWh÷(3.20×365)＝17.1kW
4. Solar module selection: Kyocera KC170GT, 170W rated power. Totally 100 pieces used, the total power: 170×100＝17kW
5. Inverter and tranformer selection:
● Use 1 set of Xantrex PV15208 grid-tie inverter, rated power 15kW＞17kW×85%，OK！
● Xantrex PV15208 outputs 3P3W, 208V, 60Hz, little lower than the utility. One 20kW isolation transformer
used to transform the voltage.
6. Series and parallel connection
● 20 pieces of KC170GT in one series, series voltage: 20×23.4Vdc＝468V
● Voltage of series open circuit: 20×29Vdc＝580V
100 modules parallel in 5 series connection, total current: 5×7.27Amps＝36.35Amps
7. Required installation area
PV array area: 100×1.29m×0.99m＝127.7m2
PV array tilts 25 degrees, horizontal projection area: 115.7m2
20% space reserved : 115.7m2×20%＝23.1 m2
Total area requires: 115.7m2＋23.1 m2＝138.8 m2