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Case Study: Zero Export Device Used For Residential Solar By OffCarbon

1 Kw Solar Panel System Installed In Chennai with Zero Export Device by OffCarbon.

Introduction

Mr. Satish from Chennai is a solar energy enthusiast and he always wanted to power his house with solar panels when he constructed one for himself. When he finally started constructing his house, he started reaching out to solar installers in Chennai.

After speaking to a number of installers in the city, he decided to go with us for one simple reason. We found a new age technology yet economical to solve his problem

They were professional from the word go. The best thing I liked about OffCarbon is that they were very very patient in explaining to me in detail about solar energy and the entire economics of it. My problem was very peculiar because we don’t use a lot of electricity at home during the day and since there is no Net-Meter in Chennai to export the generated units back to the grid, we hit a roadblock until OffCarbon found us a way.

SATHISH kUMAR

The Roadblock

Mr. Sathish and his wife are working parents and they hardly spend time at their house during the day. They also have kids who go to school throughout the week. This basically meant that their day time electricity consumption was very less.

A Net Meter solves this problem as any unused or extra units (Kwh) generated by the panels are sent back to the grid. Thus earning the customer credits which they can later redeem during the night. However, as there is no Net Meter in Chennai, the customer was about to drop his plans of installing solar panels for his home.

The Solution: Zero Export

To tackle this problem, it was important to think out of the box. The customer wanted a unique solution that was also cost effective. After speaking to multiple solar inverter manufacturers, we were able to suggest the zero export device to Mr. Satish. A device which is integrated in the inverter itself and adds a minimal cost to the solar panel system. Before we jump into more details, it is necessary to understand what a Zero Export device is.

1 Kw On-Grid Inverter with inbuilt Zero Export Device installed at Mr. Sathish’s residence.

What is a Zero Export Device?

In Simple terms, a Zero Export is a device that makes sure no excess units (Kwh) generated by the panels is exported back to the grid. It ensures that the inverter only supplies enough energy to meet the customers load requirements. Also, any extra units (Kwh) generated by the panels is dissipated in the form of heat.

As mentioned earlier, a Zero Export device is usually integrated with the inverter, which is the CPU of the solar PV system and maintains all communications with the grid. Therefore, at the point of interface between the grid and the solar pv system, this excess power must be dissipated so there is no situation where there is excess power being created from the perspective of the grid. It is as though the grid is always being told by the inverter that there is either enough power or a lack of power and never excess power that is must take care of.

The Numbers

After calculating Mr. Sathish’s solar requirements, we suggested a 1Kw solar panel system to take care of his day time energy needs. The system sizing is done after extensive calculations and understanding the customers precise energy needs. The calculation ensures that the chances of excess units generated by the panels is highly unlikely. We will explain the numbers below,

Approximate average units (Kwh) produced by 1 Kw Solar Panel System per day = 4

Approximate average units (Kwh) required by Mr. Sathish during the day (8AM – 3PM) = 3.8

Excess units (Kwh) generated by the panels per day = 0.2

Approximate average units (Kwh) dissipated in the form of heat yearly = 0.2 x 365 (days) = 73

The system will dissipate approximately 73 units (Kwh) yearly. When we consider the savings achieved by installing solar, the no units (Kwh) dissipated can be ignored.

If there was a Net Meter installed, the 0.2 units (Kwh) generated by the panels would have been exported to the grid.

Now you may ask, why do we need a Zero Export if there is no Net Meter? Why can’t we still export the excess units generated by the panels using the Uni-Directional Meter? For this, we need to brief you on the predominantly used Meter we have in India.

Currently, every household in India is connected to a Uni-Directional Meter. It is the same meter which the DISCOM uses to bill you for your electricity consumption. A Uni-Directional meter is a device that calculates how much electricity we consume from the grid. It measures a uni directional flow of current. However, a Net-Meter measures both (How much we consume and how much we export back to the grid).

A regular Uni-Directional Meter installed in Indian households.

Why Zero Export?

Even after extensive calculations, Solar PV system sizing is not accurate to the dot. As a result, there can be situations where there can be either a mismatch between the power production of the Solar PV system and consumption. Three situations can therefore occur,

  • Excess of power production compared to consumption,
  • Lower power production compared to the consumption and,
  • One where the power produced by the panels is exactly matched by the consumption.

No matter the situation, energy supply and demand must always match in the power grid, and in this case, the grid being the closed-circuit system of the house. Naturally, in the case that there is excess of or lack of energy, there has to be a certain set of actions taken in order to ensure this match between supply and demand. The third situation automatically fulfills this criteria, therefore poses no complexity.

For the situations where the power produced by the panels is lower than what is required, In systems connected to the grid, the lack of power can be dealt with by power extracted from the main grid to make up for the deficit. In systems which are off-grid, this deficit is made up by the local energy storage system. Finally, in hybrid systems, this deficit is made up either by the energy storage system or by the grid, depending on the situation.

The complexity is posed mainly by situations where this is excess power. Depending on the economical arrangement agreed with the utility, this power produced is compensated financially by the use of net-metering. Regardless of the type of the economical arrangement, the excess power must be delivered somewhere. Similar as the situation with lack of power, in grid-connected systems, this excess power is sent to the grid. In off-grid systems, this is sent to the energy storage system (if any). In the case of hybrid systems, if the energy storage system still has spare capacity, this is used. If there is no spare capacity to store this excess power, this power must go to the grid.

Current Scenario In India

Now, in India and most developing countries, the penetration of batteries (energy storage system) is low. Therefore, most Solar PV systems are grid-connected since battery costs render the project economics in-feasible. Therefore, as discussed before, this excess power must be sent to the grid. To manage these power flows, there must be device that is able to keep track of the power flows to and from the grid.

This is different to the power grid as we know it since traditional power grids only have one-directional power flow, that is, from the grid, to residential/commercial/industrial loads. Due to the advent of small-scale energy production systems such as Solar PV, there are Bi-Directional  flows of power. As mentioned above, the device that keeps track of the power flows is caused a Net Meter. Therefore, any solar PV system when installed, in an off-grid connection must also be accompanied with the installation of a bi-directional meter.

Going back to the questions “why do we need a Zero Export if there is no Net Meter? and ” Why can’t we still export the excess units generated by the panels with the Uni-Directional Meter”. If we install solar panels on the roof with the existing Uni-Directional meter, any excess energy generated by the panels and exported back to the grid will also be calculated as energy consumed from the grid. And yes you read it right. It sounds irrational and illogical. Sadly this is how it works. Which is why it is necessary to install solar panels with either a Net Meter or a Zero Export device.

Conclusion

After the Zero Export device was installed, Mr. Satish eliminated the risk of sending any extra units generated by the panels. Thus making sure that the system only supplies the energy that is required by his loads. Ultimately, the customer switched to solar without adding too much cost to the existing system.

Lastly, in India, many users of Solar PV systems have suffered problems since the provision of bi-directional meters has been slow and in-efficient, plagued by bureaucracy and red-tape. Thus making the entire process lengthily and frustrating.

With the Zero Export device, we at OffCarbon were able to eliminate this slow and cumbersome process of procuring the bi-directional meter. By using a net-zero export device this process can be side-stepped in order to accelerate the project lead-time and help the consumer use the installed solar pv system as soon as possible. 

Installation at Mr. Sathish’s rooftop underway.

Praveen Sridharan,

CTO | OffCarbon

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