This is particularly interesting as it is an adventure for him to learn the right answers. He will be paying for all this stuff himself so there will be no payola -- you will get an honest evaluation of each product.

Basically, a homeowner installs PV solar and some kind of battery/inverter system such as the Tesla PowerWall. They then sign up to be a Virtual Power Plant (VPP). In doing this they agree to sell power back to the grid when required to meet peak demand.

As grid demand varies utilities need to do something to meet peak demand. Traditionally this has been to run expensive generation plants -- typically run on natural gas or diesel -- to meet the peak demand. These plants are many times more expensive to run than systems that support the base load.

By being able to buy power from the VPPs they can save a lot of money and pass on that saving to the homeowner. Additionally, there is more saving because the power is produced locally decreasing transmission loss.

This is available in parts of California and expanding to other states. This could easily become the future.

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.

Bottom line is that a PV panel will produce over 100 times more energy than the energy went into manufacturing them. PV panel life has also increased with some manufacturers offering 40 year guarantees.

• A two square meter panel can produce 500 peak watts in most areas
• In the tropics you can expect about six times the peak panel wattage in watt hours per day. For example, two 500 watt panels will produce about 6000 watt hours (6kWh) per day
• Panel cost prices vary but can be found for less than $.50/watt
• There are system options including off-grid and grid-tie
• A system such as a Tesla PowerWall is a grid-tie system that allows you to use the energy you have stored even when the grid is not operating

Stay tuned for a lot more about PV solar as I have installed both off-grid and grid-tie systems in multiple locations.