Apr 30, 20207 min read

Off Grid Solar Power Plant Without Battery

Updated: Oct 4, 2020

Do you wants to go solar, but grid power isn't available to your place. Than off-grid solar power plant is the most solution for you. What will happen batteries are out of the equation too?

In blog, I will guide you, how you can go off-grid solar with battery back up.

lets began with some F&Q relative to off gird solar power plant.

Off Grid Solar power plant without Battery

Staying off gird means you cant have your own on-grid (also called gird tie) solar power plant. And if batteries are also out of equation than with the on-grid solar inverter, Zero Export device and any source of power like generator, you can go off-gird solar without battery. This type of solar and generator dual will also the reduce day time fuel consumption of your existing (or new) generator.

Can off grid solar system work without batteries?

The answer is no, off grid solar power plant require batteries to store electricity. If the grid power isn't available and batteries are out of equation too. Than you will need a grid-tie (on-grid) solar inverter, a diesel generator (for reference voltage to grid tie solar inverter) and a Zero export Device.

Diesel generator (or any other type of electrical power generator) will provide reference voltage to On-gird solar power plant. And Zero export device will limits the power generation out of grid tie solar inverter as per the load requirement also Zero Export device will make sure that generator set is 30% loaded.

Keep reading this blog to learn more about how zero export device make it possible to go off-grid solar even without batteries.

Off Grid inverter without batteries

The purpose of off grid inverter is to charge batteries. In other words it generator DC output voltage which can be used to charge batteries. If chemical batteries are not your options than you can go with some other mode of storing electrical power, like gravity battery. There other alternatives of chemical battery too.

Now lets have some in depth information how off-gird solar power plant without

Above illustrator shows the typical connection diagram of Zero Export Device with Generator.

To understand the same let's review different type of solar power plant.

All type of solar power plants consists, some common things, like solar panels, solar inverter, mounting structure, AC/DC Cables and installation accessories like PVC conduits, cable lugs and glands etc. How solar power plant will work is depends upon the type of solar inverter used in it.

If the inverter is OFF-grid type then the plant will be called off-grid type solar power plant. Off-grid solar inverter store the power generated from solar panels into the battery (or bank of battery) and load use this stored power by the means of solar inverter.

Or in other words, off-solar inverters charge the battery from solar panels and once the battery is charged at a certain percentage (20% to 80%) as per settings done in Inverter, it starts generating AC power for the load from charged battery meanwhile battery keep charging as long as sunlight is available.

And if the solar inverter is On-grid type, also called string inverter then the plant will be called On-grid type solar power plant. The on-grid solar inverter requires a reference power source to generate power. And the reference power source can be grid power or power from Generator (DG SET).

But considering Generator (DG SET) as a reference power source, cloud be a big headache, keep reading the blog to know more. For the first one-minute solar inverter study this reference power (during this time the whole load is on reference power source) and generate power in synchronization of reference power.

If the power generation from the solar power plant is less than the power required, the reference power source will serve the remaining required power.

And If the generated power is surplus (i.e, power generation > power required), then this surplus power will be feedback to the reference power source.

Also, there is a hybrid solar power plant which, has advantages of both ON-grid and Off-gird. In the beginning, it stores the generated power from solar panels into the battery (or banks of battery) and once the batteries fully charged, it starts working like an On-gird solar power plant.

It also required a reference source of power to work like an ON-gird solar power plant, and if there is no reference power source, it will work like an Off-grid solar power plant.

In other words, in absence of power source, it is an On-grid solar power and when the reference power source is available it will work like an Off-gird solar power plant.

Lets go off-grid without the battery

Yes, it is possible to design an Off-grid solar power plant without battery, but for the same, you can’t use Off-grid type or Hybrid type solar inverter.

You will be required string inverter (On-grid solar inverter) but as I said On-grid solar power plants required a reference power source. But if the reference power source for the string inverter differs from Grid power, we can call it Off-Grid solar power plant without battery

To design an Off-grid solar power plant without battery, you will be required solar panels, mounting structure, AC/DC cables, On-grid solar inverter (string inverter) and a reference power source other than the grid. For the same Generator can be used as the reference power source.

Technically it isn't this much easy to considered, Generator (DG SET) as the reference power source. For this type of DG + Solar power plants, there are two possible ways, by which solar Plant can damage DG SET.

a) If, Solar power Plant Output Power > Load Connected,

Then excess power will be feedback to Generator (DG SET) and this reverse power feed will trip the breaker connected with the Generator (DG SET). In many cases, I have seen that breaker of DG SET is absent at the site (mainly due to poor engineering work) instead of that an ON-Load/Off-Load isolator is connected with Generator (DG SET) to connect and isolate it from grid power.

In the case where Generator's (DG SET) breaker is absent, surplus power generated from solar panels will burn out the coil of Alternator of DG SET.

b) If, Load - PV Output Power < 30% Rating of DG SET

Then DG SETS will continuously be running on 30% or on less loading and it isn’t advisable.

operating a DG set at a load less than 30% its rated capacity for extended time periods impacts the unit negatively.

These impacts include engine exhaust slobber, which is also known as exhaust manifold slobber or wet stacking. Engine slobber is a black, oily liquid that can leak from exhaust manifold joints due to extended low- or no-load scenarios.

If the condition ‘b’ is satisfied, condition ‘a’ will be satisfied too.

To overcome these problems, you will be required Export limiter or Zero Export Device

Export limitation means that the amount of solar energy in the system is controlled by adjusting the set point of the inverters in the system.

The integrated power analyzer of Zero export device measures the total power at the point of coupling and compares this with the adjustable set points of the controller. When the consumption from DG SET is above this set point, the solar energy will be increased, when the consumption is below this set point, the solar energy will be reduced.

In addition to Zero Export Device, you will also require 10 C x 1.5 Sqmm cable with a suitable rating of current transformer (one for each phase) and 3 C x 1.5 Sqmm cable for load feedback to Zero Export Device and CAT-6 LAN cable for connection of Zero Export Device with inverter (number of inverters) as well as the local network.

Let says, PVout = amount of power solar panels can generate.

Pload = Power of connected load, or power required by connected load.

Also, DGkW= Rating of DG SET.

During the commissioning of the Zero Export Device, the sharing point is set at 30% of DG set’s rating.

If, PVout > Pload - 30% of DGkW.

Then Zero export device will ramp down Output power of on-grid inverters to match the below equation.

PVout = Pload - 30% of DGkW.

And If, PVout ≤ Pload - 30% of DGkW .

Then Zero export device won’t do any change in output power of On-grid inverter.

Also If, Pload ≤ 30% of DGkW .

Then Zero export device will switch off (via control signals over LAN Cable) On-grid solar inverter. And there will be no power generation by Inverter.

And as soon as Pload become > 30% of DGkW, Zero Export Device will switch ON inverters but the generating power will be, PVout ≤ Pload - 30% of DGkW.

Similarly, Zero Export Device can be use to design On-Grid Solar power plant without netmetering, Click here to learn more

To successfully design such type of unusual power plants, here are some pro tips.

Rated capacity of DG SET should be 1.25 times of the average load, so the DG set can take care of the load when the solar power is not available.
Solar power plant size should not be higher than 70% of the DG rating, to prevent the oversizing of the solar power plant.

Advantages of such type of solar power plant

Can also operate with grid power, If available (Curious about the same, learn more).
Reduces of fuel consumption of DG SET (generator), because at the low load fuel consumption of DG SET reduces. (click here to refer Diesel Generator fuel consumption chart)
If the load have high inrush current (like motor, pumps) and high frequency of switching on and off, the battery will get drain more frequently. Adapting generator (DG SET) in place of a battery (or battery bank), will overcome from this issue.
No need to get permission or approval from any government or non-government authorities.
Highly profitable with ROI of 3 years, if DG SET (generator) is the only power source available or frequency of power failure is very high.
Can be designed with any make of DG SET (generator).

Disadvantages of such type of solar power plant.

Not profitable if the frequency of power failure is very low (like 1-2 hours in a month).
Not advisable is the type of load is domestic (light and fans only).

We also have this simulator for your better understanding