Customer Story : Techie uses Amberroot REhub to DIY his Solar install

Do it Yourselves (DIY) : Adding Solar PV in your house !

I have below a detailed blog from a ‘Techie’ Ajeet Sharma who set up a Solar plant in his house – all by himself. He used Amberroot’s REhub MPPT for the same. Like a true engineer, he is continuing with his experiments with tracking the sun on the roof top.

Thank you for choosing Amberroot, Ajeet and best wishes on your further experiments!

Link to his Blog is here 


Saturday, April 30, 2016

Powering Up!

In January, I had posted the last update on my solar power project, that I have been working for quite some time now. Over time, working in the evenings on workdays and almost through the day on weekends/holidays, I have finally started my own solar power generation generation system, that is now functional, partially. The tracker that had been in testing for around three months now, finally got to host what it had been designed for, and all this while, was carrying a really small solar module.
Just a few days back (20th of April, 2016), I finally installed the solar modules on the tracking platform, and hooked it up to the existing power backup system, I had installed some time back for my home. And the result, free power for my home, which, for now, will service the loads partially, thereby resulting in a reduced power bill for the utility power I have been using. Over the period, I have planned to upscale the capacity of my solar power system, which, will then be self sufficient to provide power for all the needs of my house.
Now, the system has been installed and is functioning, what’s left is to begin the tracking system, which, for now is non functional, because the tracking system appeared to be ill equipped to handle such a large load, and thus, I am tweaking it a bit to make it capable enough to do what is intended to, without breaking a sweat. Since this is something I am doing for the first time, and without any theoretical or practical knowledge, there was no way I could’ve anticipated what was in store for me, once I had the solar modules installed on the tracker, which, for the time it was working with that small module, appeared pretty capable enough to efficiently complete its task without a problem. This, I know, is a part and parcel of DIY, for you learn with what you do, and over time, there comes a point where you achieve perfection, and what you wanted to do, and this is what I have been trying to achieve.
Over time, I had to change a lot of things in the planned tracking system. To say the least, the entire idea of the tracking system we had planned to take up to work on, as we moved our application in the Mahindra Rise Prize’s Solar Challenge, has changed. The use of linear actuators has replaced one of the gear based mechanisms, again, this actuator based mechanism is up for an overhaul as we build ourselves a better, more capable actuating mechanism, just because we need to have a better one, and buying this one off the shelf is out of question. Why? Firstly, because these cost a bomb, and secondly, we do not have too many options to look for, because looking for parts like these needs a massive hunt for places which deal in such speciality parts, which, is a very great impediment in doing almost anything. Also, I had to improve the light sensor setup, improve the overall reaction to light changes over the sensors, and am required to add some more ways to make the tracker work better, be a completely autonomous system that is capable enough to do the tracking throughout the day, and reset itself back to east at dusk, to begin a new day of tracking, all on its own. What more in the store is a web based realtime monitoring system that lets me check out on vital stats of the system, from anywhere in the world with the help of a website that will be fed by a variety of sensors reading some vital stats of the system, viz Voltage and Current (both of which will give me the total output in watts), Cell Temperature, Location (in terms of direction of the tracking platform), a planned anemometer, which will be helpful in case of a storm, to keep the modules relatively safer.
Now the good part is, I have enquiries pouring in from neighbours and whoever can see my solar modules on the tracker, facing the sun, on my rooftop. Appears, this is also a chance where I could cash in the advantage I have, over the regular solar power system integrators, most of whom, just do a static installation, for a cost that is be more than double of what I had to shell out for this system.

Did I make you curious? In case you would like to take a look at the specifications to get to know this better, you can take a look below:

The components/parts I bought off the shelf:

Part Qty Make/Specs
SOLAR MODULES 2 Nos. Canadian Solar 265 watt @ 24v (Another 40 watt 12v solar module to provide power supply for the tracking electronics)
SOLAR CHARGE CONTROLLER 1 No. Amberroot ReHUB MPPT (12/24v, 40A)
INVERTOR 1 No. Luminous 1500VA Pure Sine wave
BATTERY BANK 2 Nos. Luminous 150Ah @12V Flooded Lead Acid Batteries, connected in series to make this a 24v configuration.
The components/parts I have built myself, again with parts I have procured to be able to build the parts I needed:
MOUNTING PLATFORM 1 No. Dual Axis Tracker (that I have built myself)
DRIVE MECHANISM Self designed, with the core of the system being controlled by the awesome open source Arduino Platform running with Atmel’s ATMEGA 328 running in its heart.


The platform works with the help of an array of light sensors designed such that once the sun is near perpendicular to the light sensor array setup, it’s rays fall on all the sensors uniformly. Once the sun deviates a little, one or more sensors experience shadow because of the divider that has been put between the four light sensors. The MCU (Arduino, in this case) is used to feed in the data from the light sensor array which then makes the comparision based on the software code we have put inside the Arduino to take decisions based on the realtime information provided by the variety of arrays of sensors we will be feeding the data from, in the Arduino. Once the MCU takes a decision regarding the direction of the movement, it sends the relevant instruction to the H-Bridge Motor Driver based on the powerful L298N motor driver which can handle both of my 12v DC geared motors, having a stall torque of 45kgcm. The motor driver sends a signal, based on the input from the arduino for the relevant motor to move, in the direction, the MCU told the motor driver to move the motors in. Once this happens, and all the four sensors are again aligned such that the sun’s rays are again falling uniformly on all of them, with no shadow on any of the four sensors, the MCU tells the Motor driver to stop the motors till the time one of the light sensors again experiences shadow, which makes the aforementined process, start again.
As for the updates, they are not yet over. I have a lot of work yet to be completed. No, not about the functioning, as the system is up and running fine for around ten days now, since I first hooked up the panels to the charge controller, ten days back. What needs to be done is more of the stuff related to additional functionalities, that, I expect will add to the system’s geekiness, a lot more. Some of these things, that I can hgive you a glimpse, though, textually, here are – 1. Adding the Gyro sensor to: a) limit the movement of the panels and the tracker, at the extreme ends. b) realign the panel to east, in the morning after the earlier day’s tracking aligns the panels in the west. Right now, this is being done manually, though, I don’t have any issue in doing this manually, because, afterall, I do visit the rooftop daily, to take a stroll around my plants, and water them. 2. Redeploying the solar tracking functions. As it turned out to be, the actuator we had worked upon, for the test rig, was not capable enough of single handedly handing the extreme pressures of the solar panels, and if adding the additional stress exerted upon, by, say, a strong gust of wind blowing directly into the panels’ large surface area of around 3.2 square meters, hanging on, 30 feet above the ground, it is not much far from disaster. So, I decided to look for linear electric actuators, only to give up again, seeing the costs. And finally, I have thought up of a new design to make this happen, properly, and work on this new linear actuator is yet to start, as I am waiting for the parts. For the time being, I will just mount the new threaded rods I had bought, to replace the previously used 6mm threaded rods, which buckled down due to the extreme pressure of the modules and the frame. This new 10mm threaded rod in stainless steel, should ideally be capable enough to take care of the load, itself, so, I’ll go ahead and give it a try, for the time being.
For now, I will leave you guys with a couple of pictures of what’s happening these days and how the system, I have been posting updates on, for quite some time now, has transformed over time, to being the final product, something, that I had only envisaged, but had never visualised, the way it looks, and works, today.
The new mounting frame for the two solar modules. With the hand drill, and too less an experience, it was quite hard to get through this thing, especially, when one is working with steel.
Both the solar modules, ready to be mounted on the tracker. The size, did appear to be intimidating, but then, I had to do this, at all costs, and so this was done, finally.
Powering up! It felt great to see my dream realize.
While I ultimately powered up, it was evening, and since there was still power, being generated, the charge controller chose solar power over the mains power, and the above shot is a result of the inverter batteries getting discharged, because of the loads were still extracting power, but there was not much being supplied to charge the batteries, so, this one shows the batteries being charged with mains power, after the power from mains to the inverter was restored after the solar out put was quite less.
The modules facing the morning sun. For now, I have tied them (using the frame) up to make them stationary, and to check their movement under the influence of winds. Once the actuator is finally ready, the ropes will all be gone, atleast for the time the weather is good. I had to make separate arrangement for the shade net for my plants that are placed around this part. of the roof.
The modules facing the morning sun.
The peak output I could see/capture.
Finally, the cumulative power generation by the solar modules, since I powered up the system up around ten days back.
Since, the work on this is system is still underway, I will be coming up with a few more posts updating here, the work in progress, the status of the project and how it ends up, once the work is complete. And, maybe, my power bill as well, at the end of this month, to compare what’s the difference since I installed the system.

Adding Solar PV to Existing Inverters

How to get real savings in Electricity bills and keep the batteries safe!

Electricity supply in India has improved enormously in the recent past. The Southern region is expected to have an high Peak shortage (Power cuts !). The Eastern region is expected to have an energy surplus in 2015-161. With increasing power availability, consumers are looking to add Solar PV to help in reducing electricity bills. In the absence of grid tied options, adding Solar to existing Inverter based back up makes economic sense. Adding Solar to existing Inverters allows the reuse of the investment already made in Inverters & Batteries.

With this approach, the Solar PV panels & a Charge Controller that controls the charging from both the existing Inverter and Solar PV is retrofitted to the existing Inverter. The combined system is expected to work as a single unit, maximizing the use of Solar PV and providing sufficient power back up in case of power cuts.

Most retrofit charge controllers control the Mains input to the Inverter, switching off the Mains supply, when Solar PV is available so that the loads connected to the Inverter are powered from Solar PV (and the batteries).

A good ‘retrofit’ charge controller MUST control the Charge Rate to the batteries if they aim to really save electricity bills with the addition of Solar PV. To get real savings in electricity bills, the Solar PV addition must generate enough energy to completely service the day time loads connected to the Inverter. For example, in a typical home, the day time energy consumption might be 2-3 Units (kWHr). A kWp of Solar PV panel would generate about 4-4.5 Units per day. A Solar array suitably sized would be capable of generating the required energy. The conflict arises becase of the size of battery back up available. Most existing Inverters would have Lead acid batteries of ~ 150Ah capacity. Lead acid batteries must not be charged at a rate higher than 10 -15% of their battery Ah. When charged at an higher rate, the batteries reach gassing Voltage before they are fully charged.However, a Solar PV array to take care to day time loads might deliver Current that is higher than the optimal Charge rate. Installing larger batteries is expensive & not very useful. Installing smaller PV capacity is counter productive – in the end, the energy deficit would be bridged by the use of Grid supply and will result in increased bills. Not what the user wants either. The retrofit charge controller Must monitor the net current delvered to the batteries and Must control this current to the optimal charge rate – so that Loads get the required power and the batteries are used safely as an effective buffer for the variations in load and generation.

Therefore a good solution to add Solar to existing Inverters to be of real benefit to users must allow sufficient Solar capacity to take care of day time loads and keep the batteries safe at the same time.

1Page i.. Anticipated All India Power Supply Position for the Year 2015-16. Load Generation Balance Report 2015-16. Central Electricity Authority.


Installing REhub MPPT -A Customer Video.

My Eco Day is a Solar Startup run by Ifthikar Javed. My Eco Day  has an online Solar store and recently they have also opened a brick and mortar Solar shop in Calicut, Kerala.Yesterday a  customer called me up asking for REhub after seeing a video done by My Eco Day on Youtube. MyEco Day promotes Solar DIY in India.

I have posted a link to the video below. Ifthikar is doing the voice over: Watch his explanation of how REhub reacts to different scenarios of Solar and Battery availability. Since REhub  is all about adding Solar to existing inverters, the question frequently asked is ” Is Solar going to be used the maximum ? ” If so how ? Check this out.


PWM, MPPT and measuring real output

Yesterday I received a call from a system integrator – who has been installing solar systems using PWM charge controllers and is looking at switching to MPPT charger.  He has an experimental set up with a 200 AH batteries, 48V, 2500 Wp Solar panels : 250 Wp X 10 nos , a PWM charger and a MPPT charger which he had acquired from his recent visit to Bangalore. (Its not from AMBRT though)

He was aghast that contrary to his expectations the back up power from PWM charger was longer than that of the MPPT charger.

Questioning him further – revealed two common issues with comparison. 1) Unlike the PWM charger , the MPPT charger is expected to have a different input Voltage and current compared to its output. If the MPPT charger is working to its full potential- then the Voltage in the input is likely to be the Maximum power point Voltage – Vmpp.  If you would like to compare two chargers – they are ideally done in parallel  connecting to the same battery voltage and are extracting power from two arrays under same conditions of solar incidence.  If this is not possible, then calculate the total energy delivered – on a few days – hopefully with similar solar incidence.

Note : The wiring of the array using PWM charger may not work for the MPPT charger. In the above example, with just two panels in series, the Voltage of the array could be in the lower end of the input Voltage range of the MPPT charger , BUT the current  might be higher than the input current limit. Therefore the array may have to be rewired with 3 Panels in series instead of two in series.

2) Battery Voltage matters. As I found out in this case, the MPPT charger was not pushing the battery voltage to beyond 54V – based on settings in the charger. The PWM charger on the other hand was pushing the battery voltage to much higher – so definitely not an apples to apples comparison. What was probably happening was that the MPPT charger was backing out when the battery voltage reached 54V. The MPPT charger was then regulating to keep the battery voltage nearly constant , allowing the battery to draw as much current it wanted. The MPPT charger was no more operating in the MPPT point.

so what is the best way to compare both the chargers?

If the array cannot be made parallel and each half connected to a different charger – the next best thing is to

a) Connect the charger to the batteries on two different days – note the sunlight conditions and judge if they are similar.

b) Log the Battery Voltage and measure the Current at the output of each of the chargers in regular intervals. – Say every ten minutes – through the day.

c) Make sure a load is connected to the battery so that the battery is not fully charged. For example in the 48V system , adjust the loads so that the Voltage of the batteries are maintained at around 51V.

d) Multiply V and I and sum the values to determine the amount of units ( kWHr) of energy delivered in the same time frame. This should give you an approximate estimate of the performance of the two chargers.

Note : For the MPPT charger – the wiring of the panels may have to be changed due to the different input current ratings.

Does MPPT make sense in Indian Conditions

As we interact with a variety of different solar system installers, we have got this question repeatedly – does MPPT make sense in Indian conditions.

The implied question is – MPPT controllers cost more than the PWM counterparts – is it worth the while to add this cost to the installation.

First : The difference between MPPT and PWM chargers. There are ton’s of literature on this subject on the net- briefly  PWM chargers essentially short the panels to the battery and the power from the panels is extracted at the battery voltage. i.e Power extracted is Vbatt X I – which is the current dictated by the PV panel’s characteristic I-V curve at Vbatt. This Voltage and therefore Current I, when different from its Maximum power point Voltage, the PWM charge controller ends up extracting lower energy from the Panel compared to the maximum possible. The panels are matched to the battery voltage and the Vmpp of the panels chosen is always higher than the highest battery voltage. That is why, for example for 12 Volt battery systems, the so called ‘12V panels’ have Vmpp of 17V.


In Indian conditions, the cells in the PV panels are operating under ambient temperature conditions that are much higher than the ideal name plate Wp conditions i.e 25 deg C. The maximum power point voltage shifts to a lower value – and hence closer to the battery voltage.  The difference between the Vmpp and Vbatt is considerably reduced . Hence the extra power extracted using a MPPT charger is reduced. 

Note that the MPPT charger is going to deliver extra energy – BUT the addition over PWM chargers is reduced because of typical India conditions (at say ambient of 36 deg C and NOCT – 47 deg – the difference is about 15% ) For a 100 Wp system – this is only about 10 Wp in typical conditions and based on today’s Solar PV prices, that allows only ~Rs500 extra for a MPPT charger. However as the Wattage increases – the head room for MPPT is better – for a 500 Wp install the extra cost afforded for a MPPT charger is ~Rs 2700/- and so on. That is to get the same performance of a MPPT charger with a PWM charger – the installer has to spend Rs 2700/- worth of PV panel extra in a 500 Wp installation.

However this calculation completely ignores the other benefits of using MPPT chargers.  With MPPT chargers, the need to match the PV panel Voltage with the Battery Voltage is no more present. The system integrator can choose mass produced PV panels that cost lesser on a per Wp basis.

Further if the MPPT charger is designed well – the input range of acceptable voltages is high and this means that the input can be operating at higher voltage – thus reducing the wiring and connector costs.

In conclusion : MPPT chargers can have the effect of reducing the system costs and deliver more energy even in Indian conditions.

How a good MPPT charge controller (e.g. REhub) reduces system costs

REhub  is based on an high efficiency MPPT charge controller with the ability to accept a wide input MPPT range ( e.g 17 – 65 V for a 12V battery system).

System_integrators can use this to their advantage by

a) Selecting PV panels that are mass produced and therefore of lower cost. E.g to set up a 400Wp installation – using 4 X 100 Wp panels cost more than using 2 X 200 Wp panels. Yes, the 100 Wp panels are selected in installations today because of the need to match the PV panel output voltage to that of the battery system voltage – not needed any more with REhub.

b) Wire the panels in an all series arrangement. Typical Voltage at the Maximum Power point ( Vmpp ) for a 200 Wp , 60 Cell panel is about 30V. Wired in series the combined voltage is at 60Vmpp. REhub converts the input power at Vmpp to Vbatt ( the battery voltage) efficiently. The higher input voltage would mean that wiring costs are lesser compared to having all panels in parallel and operating at 17 V.

c) Lesser civil work and structurals on the roof top. Lesser panels : lesser cost .

Check out for more details.