Has wireless power technology that potential?  It doesn’t seem to matter much whether you plug in the power cable or place the phone on a charging pad.

Let’s do a psychological experiment to find out. Take your phone, connect the power cable, and place the phone on your desk. Do you feel any hesitation to pick up the phone to make a call? What happens when the phone rings? Do you feel annoyed that you have to unplug the phone? I do. It is a subtle effect, but it influences how I charge my phone. I tend to delay charging until the battery runs low or until I know that I won’t be using my phone for a while.

Connector-free charging changes that behavior. When people don’t feel reluctant they will charge more often and for shorter periods. And that will improve the user experience of high-performance, power-hungry, smart-phones.

The problem with wireless power in offices and living rooms is that the perceived value increases with the number of different products that can be charged wirelessly. In other words, only few consumers are prepared to pay US$ 50 for a dedicated charger. That perception changes when a wireless charger services many products.

In economics this effect is called a ‘network externality‘. Products with a  strong network externality benefit from co-operation between companies. Consumers see more value when many companies introduce products that work together.  That’s why companies work together on the standardization of wireless power. They all benefit from  increased sales.

Products with strong a network externality are hard to introduce in the market. On the other hand, once successful, the interface tends to stay around. New products benefit from interoperability with the installed base, and the perceived value of alternative solutions remains low.

When network externalities are strong it is, therefore, risky to invest in products that don’t work with the established standard. It can be surprisingly expensive to go against the flow.

It is pretty obvious why we are not using microwaves to transmit power through the air at home. But why did Tesla’s technology never make it into our homes?

There is a fundamental problem with magnetic induction – the efficiency drops dramatically if the distance through the air is larger than the coil diameter. There are also a couple of practical problems. Getting low standby power is one of those practical issues.

The fundamental efficiency limitation can be seen in the somewhat complicated figure 2 in this article on the transfer efficiency of magnetic induction. What it boils down to is simple:

1. Efficiency is reasonable (more than 30%) when the distance between the transmitter and the receiver is less than the diameter of the coils.
2. Efficiency drops below 2% if distance is more than two times the diameter of the coils
3. It gets worse when the transmitter and receiver coil have different diameters, or when they are not properly aligned.

Look carefully at the distance between the two coils when you see a demo of power transfer through the air. Here is a recent demo by Intel. And another one by WiTricity. The distance between the coils is about the same as the diameter of the coils. That’s not a coincidence. The demo would not work if you move the coils further apart!

This means that, if you want to charge your mobile phone with reasonable efficiency, the phone cannot be more than 5-10 centimeter away from the transmitter. That is not enough to be useful in practice.

The practical issue of low standby power is another reason why ‘power through the air’ does not take off. This is the problem: how can the power transmitter know that your phone needs charging? Your phone’s battery is empty – it is dead and not talking to the transmitter. The only way for the transmitter to know about your phone is to be ‘always on’ and searching for resonating coils in its surroundings. This search need not cost enormous amounts of energy, but it is significantly more than the standby power of a classic wired power adapter.

And I have not even discussed issues with the biological impact on the users. Here is a pointer to information about meeting regulatory EMF limitations. (These regulations limit human exposure to alternating magnetic fields).

For me, the right method to transport power trough the air is with sunlight and wind. Sunlight works great if the solar panel is large enough. But when you integrate the panel in the phone you get 5 minutes talk time for each hour of charging.  That is not practical, unfortunately. I would prefer to get 60 minutes talk time with 5 minutes charging. And my phone is usually in my pocket. Not baking in the sun.

Consensus costs time. Getting a standard developed by an SDO, and approved, typically takes many years.

Suppose you have a great product idea and need to agree an interface with products from other companies.  What do you do? Go to IEC or bring the relevant companies together in an industry consortium?

It depends on the type of standard, obviously. But an industry consortium works well for the wireless power interface. Decision can be made quickly provided (a) the consortium has agreed goals and clear requirements, and (b) the number of voting members in the consortium remains small.

The maximum number of voting members is a delicate balance between the need to involve different stakeholders and the need for speed.  Eight to ten voting members works well in my experience. With the right group of companies that will get you a standard within a year.

The finished result can then be offered to IEC or another appropriate SDO for fast track formal approval.

An industry consortium is fast, predictable, and costs less.

These are niche applications. What is holding back the application in mass market products like mobile phones?

The answer lies in the balance between cost and the perceived value of the transmitter. Would you pay $50 for a wireless charging pad? Ok, you might. But not many people would. They are not used to pay that much extra for a cradle, or for a power adapter.

The proposition changes when we lower the cost and increase the perceived value.

The Qi logo increases the perceived value. The logo tells the consumer: this product can be used with many other products. I am not buying a charger for this one phone, but it can also use it for my remote control, and for next year’s phone. This risk is much reduced: higher perceived value.

Cost must also be reduced. It must be feasible to bundle the power transmitter with a mobile device. At $50 per charger that won’t happen. The standard specification makes it possible. We enable the option to create simple low-cost transmitters.

Standardization opens up the mass market, and takes wireless power technology out of its niche.

We know that consumers love products without a connector, but it is impossible to beat the efficiency of a connector and copper wire. (No, superconductive wires are not more efficient than copper wires. The cost of cooling is prohibitive.)

So what can we do to create efficient wireless battery chargers?

We found that standby power consumption is the key. Standby power dominates total energy consumption for battery chargers that remain connected to mains power. By lowering standby power the total energy consumption is significantly reduced.

How low can you go? At first I thought we would have to trade low standby power against response time. You would expect that a responsive transmitter,  searching constantly for new power-demanding receivers,  will consume more power than a transmitter that goes to sleep and looks once a minute.

It turns out there is no need to trade response time. I have seen a Qi transmitter with a standby power of only 0.0001 Watt (100 µW) that detects new receivers instantaneously.

In the efficiency analysis that is published on the front page you can see what the effect is on total energy consumption.

The participants in a standardization effort usually have different requirements, different cultures and different solutions in mind. These differences slow down the technical work but the end result is more versatile and robust than a solution any one of the participants could have come up with alone.

I see that happening now. The tension between the different interests did not bog us down but sparked creativity. In the technology outline that is published on the front page you will see that it is possible to allow a variety of transmitter designs, all interoperable with a great variety of different receiver designs. That design freedom is the result of creative tension and the willingness to take other participant’s interests seriously.