In the electric market, the Wuling Hongguang Mini EV is a best seller. Hundreds of thousands of them have been sold.

Other manufacturers have entered the market. The Ora Good Cat and Chery QQ Ice Cream have been on sale for some time. The newest player is is from Geometry (a mark of Geely) and is called the M2.

You may be wondering if such cars make sense outside of China. I think the answer is yes. These vehicles tend to be able to travel at highway speeds with ranges of 100 km or more. And, probably more important, they cost in the $7000 range in China. Even for $10,000 in the US or Europe, they seem like an ideal second car.

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.

• EPA -- This is a range rating scale from the U.S. Environmental Agency
• WLTP -- Worldwide Harmonized Light Vehicle Test Procedure
• NEDC -- New European Driving Cycle
• CLTC -- China Light Duty Vehicle Test Cycle

The EPA rating is commonly used in the U.S. and fairly accurately reflects the actual range you will achieve with your electric vehicle. WLTP is typically used in Europe and, like the EPA, if fairly accurate.

NEDC and CLTC tend to be very "generous". That is, they tend to indicate a much greater range than you will actually attain in real world use of the vehicle. NEDC is an old standard pretty much replaced by the WLTP.

CLTC is a new standard but that doesn't make it accurate. In general, it tends to be 15% to 25%  more generous that actual driving experience.