Electric Vehicles

There are lots of concerns that the electric grid, particularly in California, cannot support EV charging. Rather than just being concerned and taking no action, you can address the problem yourself.

First, let's put the issue in perspective. In most "developed" places, peak grid demand is during the day -- that is, when businesses are operating. To meet this demand the electric utilities rely on what are called peaker plants to meet that demand. These are generally natural gas, coal and diesel generators which cost much more to operate than what handles the base load (e.g., hydro, geothermal and even nuclear). Demand drops off in the evening and is lowest from say 10PM until 6AM.

Charging EVs in this 10PM to 6AM slot is clearly the best for the grid. Charging during mid-day would be the worst. But, what if you generate energy to feed into the grid during the day? That would be the best to help stabilize the grid.

Generate How Much?

The EV Database offers energy consumption per kilometer for various EV models. While many models consume less, let's take 200 watt hours per kilometer and a good starting point. The second parameter needed is the distance you drive per day. Lots of studies have shown 30 kilometers is average. Adjust for your travel but I will use this for the example here.

Multiply energy per kilometer times kilometers to get the energy you would use. In my example, that would mean 6000 watt hours per day or 6kWh/day. Next you need to figure out how many watts of solar panels would be needed to produce those 6kWh/day. This will, of course, depend on where you live and if you do not live near the equator, it also depends on the season.

Using myself as an example (I live in Guatemala) each watt of PV panel will produce about six watt hours per day. Thus, to produce 6kWh/day I would need 1000 watts of PV panels. At current panel output, that amounts to about four square meters of panels. This is a very small installation so I would recommend a bigger system for economy of scale.

Putting it Together

You can see the page on a grid-tie system to figure out what you need. Or, better yet, go with a Grid-Tie with Battery Backup to get the added benefit of having power if the grid goes down. You will need to work with your electric utility as they will need to change your electric meter to properly monitor the bi-directional nature of you system. Note that here in Guatemala, you get paid the same price for power you generate and the power you use. 

My Example

I opted for a system that produces 10-12 kWh/day. That is big enough to meet all my electrical needs. Thus, I am effectively using the electric grid as a battery for my house. The system cost me about $2500 and will pay for itself in about four years, less if electric rates increase.