Solar Charger Design?

[dwl]

Any solar experts out there sketched out a DIY-friendly design for a solar charging station a bit less expensive than this, this or this? Something that would charge our i3s in 6-8 hours every 2-3 days would be ideal.

Regards,
Dirk

 

[jadnashuanh]

To charge an i3 from 'minimum' takes somewhere near 20KwHrs of energy. To get that in two days, you'd need a reliable 2Kw/hr capable array, feeding a battery bank given maybe as little as 6-7 hours of production/day, feeding an invertor generating 240vac. Probably a bit more. Then, your invertor would need to be able to put out a reliable 7.4Kw, which is pretty damn large. To get that, depending on your location, shading, normal cloud cover, etc., you need a fairly large array, and battery banks aren't cheap either. Otherwise, you'd need an array that could put out about 4Kw/hr to charge the thing with a smaller battery bank almost simultaneously - using all of the power from the array, run through the batteries to the invertor.

I may be off a little on the numbers, but given today's cost of panels and the support equipment, it will not be particularly cheap. It would probably be better to just build an array for feeding back into the grid, and taking the credit to help offset your whole home's electricity use, even if it couldn't support fully charging the vehicle.

 

[KurtEndress]

Are you talking an off grid system with batteries like your last example?

For a stationary system where weight isn't a concern you want lead acid batteries for the lower cost. You don't want to discharge those more than 50%, so you'd need about 50 kWh of storage. Say two 1100 AH 24V forklift batteries at $5000 each and weighing 1700 lbs a piece.

You probably need around 5 kW of panels to account for the loses in the system. That might cost $4000.

You need an inverter to produce the 7400 watts of 240V AC for level 2 charging. Outback has an 8000 watt inverter for $4,150 that might work.

You might need a solar charge controller. Add another $600 for one that can handle up to 96A into the batteries.

So I've got it at about $19K for the major parts not including the structure, wiring, fusing, etc. That's left as an exercise for the DIY putting the system together.

Me, I'm looking into having Solar City put 7 kW of panels on my roof in a grid tie system. All the power that generates will be put to use immediately somewhere, by me or someone else. It won't be lost because the car's battery or the stationary battery is full.

 

[ultraturtle]

Any solar experts out there sketched out a DIY-friendly design for a solar charging station ...? Something that would charge our i3s in 6-8 hours every 2-3 days would be ideal.

I'm certainly no expert, but these guys are: http://pvwatts.nrel.gov/pvwatts.php

First calculate your annual kWh need based on mileage driven. The i3 BEV consumes 272 Wh per mile, the i3 REx uses 288 Wh as measured from the wall. Assuming 12,000 miles per year, you would need 3,264 kWh per vehicle for a total of about 6,500 kWh. Plugging that into the NREL calculations would show that you need a 5 kW system at your latitude, assuming an optimal installation (facing 180 degrees, at 41 degree tilt). This requirement of course scales up or down with your annual mileage.

It would be far less expensive, more reliable, and more useful to install a grid-tied system if that is an option. Not only would the grid be your energy storage, you would not need to deal with the expense and trouble of maintaining batteries. They are very expensive, and do not last long even if meticulously cared for. I only get about 7 years out of mine, and I baby them.

 

[dwl]

Thanks for the great replies -- just what I was looking for.

Grid tied definitely looks more attractive in terms of cost, reliability, and maintenance. Any insights from other New Jerseyans about SRECs and whether being grid tied is a good deal by the time you cycle your energy through them to charge at night assuming your i3's in use during sunlight hours paying the difference between average converted SRECs and ongoing electricity rates?

Also, do the other NJ contingent folks participate in the PSE&G CleanPower Choice program? Gotta say, the 24-page agreement is a pretty ugly read!

Regards,
Dirk