Solar charging

I have a solar panel array on my roof and generate enough power for the house but not quite enough for the house and the i3. I would like to expand the roof array just a little to cover the car completely but if I do so my utility will consider it a new installation and I will lose my grandfathered net billing status. What I can do is to go completely off grid with the j3.

An off grid setup typically has a battery bank fed by a charger and feeding an inverter. This is expensive, leading me to ask this question:

Would it be realistic to design an EVSE fed directly from solar panels? Remember that the output from the panels varies from zero to several Kilowatts during the day and is DC. If such an EVSE cost less than a battery bank and inverter charger then it would be a commercially viable product.

Check out the output rate of battery storage systems. Most are around 2 kW currently, so charging your car would take around 10h from battery (without other consumers). With some solar help you would need less storage, but even then you'd need a 6-7 kWp array to cover this. Given where you live this may possible, but the investment would also be significant. I've looked into a 7kW storage system, incl compatible inverter and it would set me back around £7k. This does not include an extended PV array, which you've mentioned.

I think that currently you'd be better off keeping some grid supply and instead look into a storage system first, maybe keep the array size at the current level to keep the subsidies.

Anyway, that's just my 2p worth. Let us know how you're getting on.

The problem with batteries for storing solar power is the cost. If there were some way to use the DC from the panels directly that would be the least expensive. No way to avoid the cost of the panels ( about $2000 to make enough power to charge the car for several hours at peak sunlight ) but inverters, batteries and chargers add about $4000 to that.

I would be real happy to add no more than three or four KWh each day and have no use for local energy storage external to the car.

I solved the problem for myself by installing 30 kW in May ;-) Prices are much lower here in Germany, I paid 1143 €/kW / 1257$/kW. With 30 kW, even a cloudy sky will deliver enough power for charging.

Charging the i3 directly with solar is awkward, to say the least. You can`t charge with varying load, and you can`t make more than one break ( cloud ), otherwise charging will stop because of default.

Installing a battery in my view doesn`t make sense now, still much too expensive. You create losses, some 20-30% of the power directed to the battery will be lost in the cycle. I am waiting for a system which allows direct charging of DC with varying load into the battery of my car without using an inverter. Nothing in sight, may take some years.

What anyone can do is to reduce the power consumption in the household. 30% reduction should be possible anywhere. Avoid standby losses, change lighting to LED, use most efficient fridge and others. Saving power is usually much more cost effective than a battery. Doesn`t create losses, more power left for the i3.

Frank

@waitingi3

What if you don`t invest into an extension of your array yourself but become a customer of SolarCity. AFAIK SolarCity would be the owner then, you pay them a monthly fee for using the power produced. So those would be technically and legally two different arrays. Wouldn`t that preserve your net billing status?

Is there a current solution of having solar panels on the roof of the car to charge the batteries while sitting under the sun or even while driving? There is so much sunlight to power so many things including, I would think, these cars. Doable?

krumian said:

Is there a current solution of having solar panels on the roof of the car to charge the batteries while sitting under the sun or even while driving? There is so much sunlight to power so many things including, I would think, these cars. Doable?

Click to expand...

If you take the 4miles/kw average of the community, that's 250W/mile, and at say 60mph, that's one minute, or 250*60 for an hour. A solar panel the size of the roof on the i3 might make 50w/hr or less than one watt/minute...IOW, not a big dent, so unlikely to really make much of any effect for the relative cost. Throw in that there'd be at least some of that travel at night, and it becomes even less useful. Even if I'm off by a factor of even 5 or so, it's still not particularly useful. I'll leave the conversion to metric to those that prefer that.