ULTRACAPACITORS for stability and spinning reserve in Alaska Wind Diesel Systems

William R. Thomson PE

(presented by Bill Stamm PE)

34 Wind Turbines

in 11 Villages

AVERAGE COMMUNITY LOADS 40 to 400 kW

These are all names for the same

technology: l Ultracapacitors l Supercapacitors l Double layer capacitors l Electrochemical double layer capacitors

What are Ultracapacitors? A capacitor on steroids A “mechanical battery” with very high power

to energy density Two Charged

Plates Separated by a

Dielectric

The greater the surface area of the plates and the closer together they are- the greater the

Capacitance

Great manufacturing advances in the last 10 yrs

Air Tank Analogy Volume of Air = Stored Charge

Air Pressure = Voltage How much AIR can you put in a Tank? It depends on the PRESSURE. If you raise the VOLTAGE you can put more

CHARGE on a Capacitor

Rating an ultracapacitor: Farads determine amps seconds for each volt change. Internal resistance determines how much heat will be generated when

receiving or delivering current. Maximum voltage is important not to exceed.

CONS Two big ones and one smaller one

•  Much more expensive than batteries (but the cost is dropping)

•  Size for Size they do not store as much energy as chemical batteries

•  There voltage drops more as they discharge so special inverters/converters are required

Ultracapacitors are perhaps ten times more expensive than batteries for much less energy storage, so why is AVEC installing them instead of batteries?

Compared to batteries, they work on a completely different principle –

They are electrostatic devices, moving

electrons and storing energy in an electrostatic field.

They are not chemical devices, they do not

change one chemical into a different type of chemical in order to store energy.

PROS

•  They don’t wear out, because there is no physical transformation back and forth, just electron flow

•  There is no loss of voltage between charging and discharging, so they are much more efficient for situations where they are being charged and discharged a lot (great cycle efficiency)

•  They can supply very high amperage for their size, because they have a very large surface area internally and are not limited by how fast you can push a chemical reaction.

•  Because there is no chemical reaction, they are unaffected by very cold temperatures, Broad Temperature range (-30C to +50C)

•  Can be completely discharged with no harm, good for durability and safety •  They cannot be boiled dry •  They don’t spill, the amount of electrolyte is very small •  Raw materials are inexpensive, so future cost per Farad may be very low in

volume production •  No fire hazard

A lithium battery bank at a Hawaii wind farm caught fire, there was no way to extinguish the blaze.

…and the clean-up was messy.

AVEC sees four applications for Ultracapacitors

l  UPS for electronics l  Cranking Diesels l  Providing Wind/Diesel Stability l  Providing Spinning Reserve for Wind

Turbines

DC Controls Support

For the last four years AVEC has been successfully installing ultracapacitors to assist weak station battery banks and also to keep vital electronics powered while engines are being cranked.

The left picture shows a Russian built ultra-capacitor that looks just like

a truck battery. The right picture is a Korean built unit. Both are used to power electronics and engine controls for up to 2 continuous minutes during engine cranking.

ENGINE CRANKING

This picture shows a Korean built ultra-capacitor that is connected directly across our nickel cadmium battery bank to assist cranking engines.

POWER STABILITY Medium and high penetration wind systems are notoriously hard to regulate Random frequency and voltage fluctuations that are visible to the consumer

often result. Currently AVEC stabilizes systems by modulating load banks, (heating

elements) which work well for stabilizing, But this is at the expense of diverting a percentage of the wind output to heat.

(That’s a one way trip.)

At mid-level winds, steepest part of the curve, a small variation in wind, provides large change in power

Northwind 100

Ultracapacitors well suited for improving Stability

•  No Harm from High Cycle rates •  Very Good Round Trip Efficiency •  Very Fast Reaction Time

SPINNING RESERVE Quickly losing the output of a single large wind turbine cannot be handled by

a smaller diesel sized for the net load. There are only the following methods to cope with this problem:

Run an oversized diesel at all times, to ensure sufficient capacity if a turbine goes off line.

Shed load - turning off at least some customers during events

Provide spinning reserve – batteries, capacitors, a fly wheel, compressed air reserve, many (expensive) options.

Power must be supplied until an additional diesel is started and put on line.

Additional complexity for AC Systems

An inverter to convert AC to DC and DC to AC is required

and usually a DC to DC Converter to accommodate the voltage range of the Ultracapacitor.

And a Controller to manage the power flow

The Good News- all the parts are out there, (we just need a package at an affordable price)

Toksook Bay, Alaska