# Solar Battery Charging - Mahindra's Sun2Car tech



## Kamleshgk (May 24, 2012)

Hey guys,

This post is regarding charging your batteries using Solar Power.

Look at the brochure provided by Mahindra here in India to charge the Mahindra e2o (www.mahindrae2o.com/specifications.htm) using Solar Power

http://www.mahindrae2o.com/pdf/Sun2Car-Web-Brochure.pdf

If u read the brochure, they have 3 options to charge the e2o using Solar Power

a) Direct Solar
1 kWp Solar and DC-DC charger 1 kWp Solar and 1 kVA inverter
Rs 1,14,000 - $ 1886

b) Solar and Grid (no battery backup)
No Battery backup - Rs 1,38,000 = $ 2283

c) Solar and Grid (with battery)
￼￼1 kWp solar and 3 kVA inverter (4 kWh battery) - Rs 2,09,000 = $ 3458

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As per my noob understanding 

Option a) Direct Solar i think uses DC charging - where the power directly goes into the battery and is thus more efficient as there is not regulation and AC to DC conversion going on.

But the car needs to be parked on a sunny day for any charging to happen. 
Is that right? There would be no charging at night. Correct?

Option b) Is that ur car is charged either from Solar power or from the Grid. The Solar power when not charged is not stored in a battery and thus goes to the grid??
Do we make money if we sell power to the grid!??? I think i need to ask Mahindra this!

If we go for this option - Will Solar power be used on Sunny days? And Grid be used in night?
What if there are cloudy days?

What do u guys think?

Option c) is Battery based, 
With this option, i guess we can charge any time of the day and u guarantee to use Solar Power all the time!

Is that right?

Its hard to decide which is the best option.
Option a and c are greenest. But option c offers us the flexibility to charge the car at nights with clean power.

Id appreciate it, if experts here can give their opinion.


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## Ampster (Oct 6, 2012)

I would go with b), the grid tie option. but I would look at what the competitive pricing pr kwhr for a solar grid tie system.


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## Kamleshgk (May 24, 2012)

Ampster said:


> I would go with b), the grid tie option. but I would look at what the competitive pricing pr kwhr for a solar grid tie system.


Thanks Ampster for the reply.

Option b) would mean Solar clean power when charged during day, and Grid power when charged at night right?

Am curious, what would happen on cloudy days and during the twilight hours?

When u say this - 'the competitive pricing pr kwhr for a solar grid tie system', you mean that i check on other competitors on the price for such a system?

Also is $ 2283, does this seem right?
How much did u spend on ur 3.0kWhr solar panels for your Toyota RAVEV?


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## Kamleshgk (May 24, 2012)

Also with option b) Solar power with grid tie in.

According to the brochure they mention - 1 kWp Solar and 1 kVA inverter

What is the meaning of this?
Sorry am an electric noob! 

Does this mean, that the Solar cells produce 1 kWh power per hour?
The battery pack of the e20 is 10kWh. So would that mean it would charge the e20 in 10 hours!?

Also what does that 1kVA inverter do? (Convert AC to DC, i assume - but what is that 1 kVA)

Id appreciate replies!
Thanks!


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## Ampster (Oct 6, 2012)

I assume they mean 1 Kilo watt in panels. Google Kilo watt and kilo watt hours.

My 3.0 kilo watt system cost $2.50 per watt or $7,500. I did some of the installation myself.

As to your earlier question about charging during twilight or on cloudy days, you would get the energy from the grid. It is cheaper to store your energy on the grid than buy batteries to store it. That is what I do. 





















My 3.0 Kilo watt system cost


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## kennybobby (Aug 10, 2012)

i don't see where this system has an inverter that can put power back onto the grid, especially at the price offered.

The brochure does not indicate anywhere that this feature is included--only that you can charge your car using power from the grid or from the solar panels or from the battery pack that was charged by the solar panels. 

also there is no "direct" dc-dc charging from the solar panels, there is still an electronics box between the panels and the car, and that box is a dc-dc converter or some sort of voltage and current regulator.

Those solar panels typically generate 8 amps at 30 volts. With four of them you could get 16 amps x 60 volts= 960 Watts = ~1kWp (p=peak, on a bright sunny day). 

doesn't your car already come with an onboard AC charger for plugging into the grid at home? 

Where do you find the capacity of your battery pack at 10kWh? 48 Volt pack of lithium at 200 Ahr? for example is the pack 15 cells in series times 4 parallel strings of 50 Ahr cells? For now assume that is correct.

The specifications document lists charging at 220vac, 15 amps (3300 W input power) from the wall to take 5 hrs for full charge. That would be 16.5 kWh input from the grid to charge up the 10 kWh pack in 5 hours, and using the ~200 Ahr for your pack this is charging at 40-42 amps, about 3x more than the solar panels produce. 

So i predict that it will take 15 to 18 hours to charge your pack from empty to full, or ~8 hours to charge from half-empty to full when using the solar panel method. At least 3 hours in the solar panels to equal 1 hour in the wall socket.


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## Ampster (Oct 6, 2012)

I am beginning to understand that this may be a system you intend to install somewhere other than the USA. My comments only apply to the USA. I don't know anything about the grid interconnect process in India. My only experience is a holiday there in 2009. I did observe many power outages and bootleg power connections then. Local conditions may suggest an entirely different system than I would purchase in th USA.


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