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On Grid [Grid tie] Solar Power Plant with Generator backup

Updated: Dec 20, 2020


The two main part of On-grid solar power plant is solar panels, on-grid [grid tie] solar inverter. And these PV plants are suitable for areas with low or negotiable power failure.


But, during power outrage grid connected solar power plant are impractical even in the sunniest days of the year. Because on gird solar power plants can't generate electricity without reference power source [grid].


Grid are not the option available to generate to reference power source for gird tie solar power plants. Other options like home inverters, UPS with batteries or generators can also generate reference power for the grid tie solar power plant.


Now, the problems with these other options is that If PV plant generates excess power. Than this excess power will be reverse back to the source of reference power.


Expect grid, non of the other options of reference power source can take this reverse power and survive.


But with right equipment and knowledge anyone can electricity from on-grid solar power plant with grid power


Both home inverters and UPS required batteries and they both are useful as long as batteries are charge. Or you have solar panels size big enough to charge our batteries and run your appliances.


Also you will required a solar charge controller to charge batteries.


Where are generators are more suitable because storing fuels drums are much more easier and cost efficient than installing a large battery bank.


In this blog I will cover all the information required to use gird tie solar power plant in synchronization with generator.

On-grid [grid tie] solar power plant with generator backup.


On-grid solar power plant requires a reference power source for the generation of electrical power in synchronization with the reference power. Gird power or Generators can be used as a reference power source.


Any solar inverter which can be controlled by an export limiter (also known as zero export device or solar export device) are suitable for generator backup. With the available technology, only On-grid type inverter (also known as String Inverter) and hybrid inverters are commutable with an export limiter.


Whereas micro inverters and off-grid type inverters both aren’t compatible with an export limiter.


Do you wanna learn more about export limiter? We make a whole page on “Export limiter (a.k.a Zero Export Device)” go and checkout and it will help you will be able to select the correct solution for your need.


Places where the repetition of power failure is high (like above 5-10 hours per day) or where grid power is not available. Are the most suitable place for the on-grid type solar power plant with generator backup.


Also, if the load is domestic (like lights, Fan and AC) and continuous load is not much higher than 3 kW. Then going on-grid solar with the generator isn’t advisable. In this case, an Off-grid solar power plant with a suitable rating of battery backup is more suitable.


But both grid power and batteries are out of the equation, a gird-tie solar power plant with generator backup is a suitable option.


If you already have a generator and you what to sync it with On-grid solar power plant. Then export limiter (also known as Zero Export Device) is requiring for the same.


Export limiter limits the power generations of solar inverter, so that surplus power (when power generation > connected load) can’t be generated from the solar power plant.


Otherwise, surplus power will trip the breaker of the generator. And, if the breaker isn’t available it (surplus power) will burn down the armature coil of the generator. Learn more about how to operate the generator with the grid-tie solar power plant.



Related blog:

Reverse Power flow protection for grid-connected Solar power plant.
Grid tie Solar power plant without Net-metering

Procedures of synchronization of Generator with solar power plant.


Step by step procedure of synchronization of Generator with solar power plant (PV plant).

Step#1: Install a (set) of current transformer(s) at the coupling point of diesel generator and load. For the measurement of power drawn from DG.

Step#2: Connect the output of current transformer(s) to Export Limiter via 10 core, 1.5 Sqmm cable.

Step#3: Take one power source (voltage source) before coupling point of DG and load to Export Limiter via 3 core, 1.5 Sqmm cable. For the internal power requirements of Export Limiter and voltage reference for power analysis.

Step#4: Connect grid tie (on-gird) PV inverter (solar inverter) with Export Limiter via LAN (CAT 6) cable.

Step#5: Connect Export Limiter to local internet via LAN (CAT 6) cable. For the online monitoring of PV plant, DG and Grid.

Step#6: In Export Limiter, set the sharing point of load on DG SET at 30% of DG capacity, to keep DG SET minimum 30% loaded.


Backup generator size for On-grid [grid tie] solar power plant


Generator size should be around 1.25 time of the continuous load. This is because the generator needs to serve load, while sunlight isn’t available or solar inverter/plant is in maintenance.


Solar Panels and Inverter rating


If the frequency of power failure isn’t much high and you want to sync your generator with the on-grid plant, then the plant size doesn’t matter. You can have any size of the plant.


But if the rate of failure of grid power is very high or gird power isn’t available. Then the solar plant size should not higher than 1.2 times of the continuous load.


If the plant size much higher than the continuous load, you won’t get full utilization of the plant and lots of power generations will be lost in the process of export limitations.


Which make of on-grid [grid tie] inverters are compatible with export limiters?


All major grid-tie solar inverters like ABB, SMA, Hitachi, Consul Neowatt, Huawei, Solar Edge, Kaco, Detal, Solis, Kirloskar, polycab, Sungrow, Growatt, Fronius, REFU Sol, Schneider, Zever solar and many more are compatible with Export limiter [a.k.a Zero Export Device].


Can I use a large backup generator for on-grid solar power plant?


Generator size should not be higher than 3.3 times of the continuous load. This is because of the continuous running generator at load lesser than 30% of its rated capacity affect it negatively.


Learn more, about the effect of continuous running of the generator at a load of less than 30% of its rated capacity.


Can I use a smaller size of backup generator for On-grid solar power plant?


The generator should be capable of taking load when the sunlight is not available (night and heavy raining days). Generators consume more fuel at overload, ideal load on generator should not higher than 80% of its rated capacity.


Advantages of On-grid solar power plant with generator backup

  1. Independent of grid power availability. But can also work with Grid too, learn more.

  2. Reduces the fuel consumption of the generator, up to 75%. Generators consume less fuel per hour at low load.

  3. Increase the life span of the generator. Operating Generator at low load (not less than 30%) increase its life span and reduce its maintenance cost.

  4. No requirement of battery backup.

  5. Highly profitable for factory load, where having battery backup is not possible due to high inrush current. And generator is the only option available during power cuts.


Disadvantage of On-grid solar power plant with generator backup

  1. Not, economical for the lower size of plant with domestic loads.

  2. The maintenance cost of the generator increases the O&M cost of Plant.

  3. If the new generator is brought for the plant, it will increase the ROI period of the investment on plant + generator.


If you have any question, please leave a comment below.

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