From: EZG to GEM

I live in south Ga and have redone 4 or 5 EZGO (36 VOLT) and one Fairplay (48 volt). as soon as I can I’m going to get a GEM car (72 VOLT) I also am going to install some solar panels on the house.

Hi Madmex

Welcome to the forum and you have posted some interesting comments there!

Solar panels are becoming a more popular topic and I was wondering what kind of budget you had for your house and whether you would use the solar panels to assist in recharging your electric vehicle?

I was going to have three small 100w panels just for the carts, but after thinking more about i think I’m going put around $4000 of Solar panels on and wire into the house this year with room for more next year.just to get the tax credit.

Unfortunately, 300 Watts is probably not going to be enough. My GEM eL uses about 3 to 6 kWh to recharge for a 10 to 20 mile run. It takes 4 to 8 hours to do this and the charger draws about 1 kW during the full-current portion of the charge. So to do it right you’d have to be able to generate at least 1 kW for 4 to 8 hours a day to recharge a GEM.

By my estimates, you’d need to do all your driving at night and charge all day unless you have a grid-tied system which uses the grid as its “battery” so you could charge for free at night.

You can’t possibly carry enough panels on the vehicle to recharge any significant amount while driving or parked during the day. Maybe a little charging but not enough to make much difference. Now, if you parked it in the sun for days at a time and only used it occasionally for short trips, you might be OK.

Let’s do the math. Figure the battery capacity is 150 Ah at 72 Volts. That’s 10.8 kWh of which you can safely use about 6-8 kWh. With about 70% efficiency charging you’d need about 8 to 11 kWh to recharge the pack from that low a state of charge. That means you need 8 to 11 hours at 1000 Watts draw from the grid…

Great to see you “going green” but there are certain immutable laws of physics you have to be aware of and plan for.

Hi Bob.peloquin

You have written some very interesting and very informative comments about solar panels. I was wondering when/if you think solar power technology will improve enough to make a real difference to the process of recharging your electric car?

Recharging on the move would be ideal…but I guess that is still a long way off?

When solar panels with greater than 75% conversion efficiency are developed then we may see them become more prevalent for many power systems but right now we’re stuck with 12-15% efficiency. With a maximum of 1 kW of solar energy falling on each square meter (at the equator), a 6 kWh pack would require making more than 6 kWh of power to charge the battery over the course of a sunny day.

With today’s efficiency of 12-15%, you’d need a lot of panels; more than the vehicle could carry; to do the job. When we get to 75% efficiency someday you’ll begin to see the possibility of at least partial recharging while we’re at work for totally solar-cell-covered NEVs to be practical. But it’s physically impossible to reap enough solar power in the footprint of a regular-sized passenger vehicle to fully charge its battery for anything but a small, light, NEV or similar. There’s just not enough energy available to power the car for something capable of highway speeds in that small a space.

However, solar-powered charging stations with roofs made of high-efficiency solar panels might become practical in sunny parts of the world. Even at that, you’d need to provide enough Kilowatts over a fairly short period to get the vehicle fully charged. This would likely require on-site battery storage or grid-tied solar power systems to make it worthwhile.

If I lived in the sunny south-west parts of the US I’d definitely consider a solar car-port dedicated to this purpose. But here in the cold, wet north-eastern US we just don’t get enough insolation to make it economically feasible with today’s technology. I can’t dedicate most of my back-yard to solar panels just to save a few dollars in electric bills to be “green”.