I have never bought from them and have no relationship with them but they seem to offer a lot of interesting systems at what appear to be decent prices. (If I was in the U.S., I probably would have bought my last grid-tie system from them but with shipping costs and import issues I elected to buy it locally.)

If you are looking for solar options, they web site will at least show you some options.

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.

It is easiest to think of this just like the regular grid-tie system with the addition of a local battery and the added function of the controller that it can disconnect itself from the electric grid if the grid fails. Thus, while designed to normally be connected to an operating electric grid it can safely operate independently as well.

Tesla has negotiated with some electric utilities such that end users can program their system to buy electricity from the grid when it is least expensive and sell energy back when it is most expensive. This benefits both the utility and the consumer as producing energy to handle peak load tends to cost the utilities much more than handling the base load.

The components of a grid-tie system consist of:

• PV panels to convert sunlight into direct current electricity
• Grid-tie inverter to control and route PV panel energy either for local use or to the grid
• Safety equipment to protect the panels, charge controller, batteries and you

PV Panels

These are flat panels of typically silicon-based cells. Typical panels of today will generate 400-500 watts per two square meter panel. They are totally passive (no moving parts) and tend to have a guaranteed life of from 20 to 30 years. 

Grid-tie Inverter

This is a controller that converts DC from your PV panels to AC synchronized with the electric grid and sends any excess power you are generating into the grid. It also has a "grid fault" circuit which shuts down the system if your grid connection. While this may seem counter-productive (that is, you would like to use the energy you are producing when the grid isn't available) it is necessary for the safety of those who might be working on the grid.)

Safety Equipment

Fuses or circuit breakers between the panels and charge controller and between the charge controller and battery should be installed to protect the equipment. You also should put a circuit breaker between the battery and the load.

A second important piece of safety equipment is lightning arrestor. This will protect the grid-tie inverter if a panel gets struck by lightning. Note that the metal frame of the panels needs to be connected to a good electrical ground.

Unlike with an off-grid system, PV panels are always  connected in series (with possibly multiple strings) to get a higher voltage suitable for inverting -- converting to the grid voltage.

The system consists of:

• PV panels to convert sunlight into direct current electricity
• Batteries to store the energy produced
• A charge controller to regulate the current from the PV panels to maximize charging but protect the batteries
• Safety equipment to protect the panels, charge controller, batteries and you
• (Possibly) an DC to AC inverter if you need 120V and/or 240V AC power

PV Panels

These are flat panels of typically silicon-based cells. Typical panels of today will generate 400-500 watts per two square meter panel. They are totally passive (no moving parts) and tend to have a guaranteed life of from 20 to 30 years. 

Batteries

This is where you store energy produced by the panels so you can use it when needed. Deep cycle lead-acid batteries have been the norm for decades but lithium ion batteries have finally become available at a realistic price. LiIon batteries have many advantages including longer cycle life and significantly less weight. Of the LiIon choices, Lithium Iron Phosphate (LiFePO4) batteries are the best choice as they have higher cycle lives than other lithium batteries, can be fully charged/discharged without degradation and cost less.

Charge Controller

This is a device that regulates the flow of current from the panels to the batteries. The least expensive charge controllers operate in a pulse width modulation (PWM) mode to limit the charge to protect the batteries.

An maximum power point tracking (MPPT) controller adjusts the PV load to maximize the charge rate of the batteries while still preventing overcharge. There are two advantages here:

1. You no longer have to match the PV panel voltage to the battery voltage. Besides a general advantage (for example, a 24 volt panel charging a 12 volt battery would be very inefficient with a PWM controller) you can connect more PV panels in series offering higher voltages at lower currents decreasing the cost of wiring.
2. Even with a decent match between panel and battery voltage, you will probably gain around 30% more energy from your panels.

Safety Equipment

Fuses or circuit breakers between the panels and charge controller and between the charge controller and battery should be installed to protect the equipment. You also should put a circuit breaker between the battery and the load.

A second important piece of safety equipment is lightning arrestor. This will protect the charge controller if a panel gets struck by lightning. Note that the metal frame of the panels needs to be connected to a good electrical ground.

Inverter

With the above equipment you have a "DC" system. What that means is that you only have the output of the batteries to run your house. Smaller systems tend to use 12 volt batteries and lots of 12 volt appliances and lights can be purchased so that may be sufficient. If, however, you want to run typical household appliances such as a refrigerator you will want to add an inverter to the system. The inverter converts the DC voltage from the battery to 120 volt and/or 240 volt AC current.

There are lots of considerations for sizing such a system -- number of PV panels, power handling capabilities of the charge controller, battery voltage and ampere hour capacity and inverter size. If there is sufficient interest I will add a pace on this information.

• 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.