RB900 in gale force winds

Manufacturers make claims about the survivability of their wind turbines in high winds. Over the weekend Northland was hit by a huge storm causing much damage in places. Gale force winds was were predicted ( 25 - 34 M/S or Over 90 KPH ) though no measurements of wind strengths available yet.
Picture shows an RB900 attached to a wooden pole Via a 1.5 meter long, 50 mm diameter tube. Winds was strong enough to bend the pipe. Looks like it was bent at the point where it is attached to the pole by a steel band. No damage to the propellers or wind generator. We will have to replace the pipe with a larger 82 mm diameter pipe.
The propellers of the RB900 is pitch variable and is not furled away from high winds. The 2.0 meter, 5 bladed design subject the machine to tremendous forces, which gives it good low wind speeds performance.
The RB900 is a 1000 watts peak machine list priced at $3950. Average production at 3 - 5 M/S wind is about 60 KW hrs a month.
Price does not include installation but the manufacturers do provide suggestions and help with advise. Each installation is different according to location and conditions. Some are guyed. This particular installation should be guyed as well but it is wise after the fact.

July 13 NZ Herald online " About 100 homes and businesses are still without power as the Far North recovers from a weekend of heavy rain and wind gusts reaching up to 140km an hour......"

RB900 actual output

We did a field test of the RB900 in 3 - 5 Meters per second wind speeds today. Auckland Met report had the wind speed at 10 - 14 MPH all day ( about 5 - 8 knots. ) We ran the RB900 in 12 volt mode.
I should mention that our battery bank was situated 60 meters from the wind generator. Perhaps with the bank directly under the generator we could have got better results.
The results we got were very encouraging indeed. 3 - 5 meters a second is really light winds. Most wind turbines need more than this to produce useful power.

We were averaging 5 amps at 12.6 volts. The results varies with wind gust sometimes peaking at 10 amps at 13.5 volts and dropping to nothing as well on occasion. Generally as soon as the turbine spins useful power was produced to charge the batteries. On average we were getting 60 watts. Over 24 hours this would have translated into about 1.5 kilowatt hours.

This is very good results as we often get this amount of wind all year round. We could not operate the turbine at 24 volts at this wind speeds as the turbine output voltages rarely exceeded 25 volts. To operate at 24 volts we will need a DC to Dc inverter. That will be our next project. For the time being we will operate the turbine at 12 volt and when the weather report predicts 20 KPH and above winds we can manually switch over to 24 volt operation.

Spinning away and no useful power in sight

Most wind generators manufacturers quote a cut in wind speed, and peak power. The one thing that they don't tell you is that it could be spinning away and yet the power produced is wasted until it is above that required to charge the batteries.
Solar controllers regulate the voltages produced to overcome this problem and it is easier to do because of the smaller range of voltages produced in solar panels. MPPT controllers further improves this.
What we need is an MPPT controller for wind generators as well. The standard practice is to run the power produced into the battery and then shunt excess power when the batteries are fully charged.
I am working on a solution to this problem.

Alternative Energy in Residential Surburb - The Green Plug

Part 2 : The Green Plug



The green plug above is designed to switch the household AC suply from the batteries to the grid. Solar and wind power generated is stored in the battery bank. The green plug first use the power from the battery bank through the inverter. When the batteries are low it will switch to mains power.

Advantages :
1) Many people want to connect to their power meter and turn it backwards in effect reducing their power bill by the amount they pay. This is actually illegal and unsafe for maintenance personnel working on the grid. The Green Plug is legal safe and has the same impact. It gives you maximum return on the power you produced ie including the daily charge when used in conjunction with Prepay power covered in part 1.

See Http://www.thebatteryclinic.co.nz

Alternative energy in residential suburbs - Part 1

Part 1 - Household electrical wiring
In residential suburbs using alternative energy where houses are already connected to the grid is difficult. This is because solar and wind energy produced are stored in batteries is DC while grid energy is AC. The whole house is wired for AC.
To integrate DC into the household wiring we invented the "Green Plug" This unit switches between battery power and grid power when the batteries are low. DC is converted to AC via the inverter and connected directly into the household switch board after the meter.
In New Zealand power company such as Contact energy and Mercury energy allows customers to install prepaid meters. Customers pay for power only when they use it. This means they can avoid paying for daily line charges when they don't use grid power.
Customers get units credited on their meter and this amount reduces as power used. One advantage of this system is that consumers become more aware of their energy usage and will make a consious effort to reduce energy consumption by changing to energy saving light bulbs and turning lights off.
In our first installation of an alternative energy system in a residential area we have the prepaid meter installed by contact energy. This cost $140 and we got 50 units of energy free. Energy cost 27 cents a kilowatt. This compares to 22 cents a kilowatt and 83 cents a day line charges on the normal meter.
This home has gas for water heating and cooking and so uses 12 kilowatts a day. At 27 cents a kilowatt it amounts to 60 cents a day line charges ( 12 X 5 cents ) which is lower than the 83 cents normal charge.
More about the equipment can be seen at our website www.thebatteryclinic.co.nz
Part 2 on energy pole installation soon.

Wind Power Fundamentals For small generation

Power from the wind

Type 2 Weibull distribution

Wind speed distribution is derived by taking readings over a year. The distribution pattern we get will plot like the Weibull distribution curve above. Average wind speed above is 6.5 meters per second but will vary for different locations.
Should we pick a wind turbine that optimize efficiency at the average wind speed?
Let us look a how much power is in the wind.

Wind Speed	1	2	3	4	5	6	7	8
Power /SqM	0.6	4.9	16.5	39.2	76.2	132.3	210.1	313.6
Wind Speed	9	10	11	12	13	14	15	16
Power /SqM	446.5	612.5	815.2	1058.4	1345.7	1680.7	2067.2	2508.8

At the low wind speeds there is very little energy to harness. Doubling of the wind speed increases the power by a factor of eight.
Pick a wind turbine that optimize efficiency at the average power available. For a 2.0 type distribution above the average power is at 8.7 meters per second.

Wind Turbine Efficiency : The Efficiency of a wind generator is calculated by taking the output at each wind speed divided by the power available.

Wind Speed	4 M/S	5 M/S	6 M/S	7 M/S	8 M/S	9 M/S	10 M/S
Efficiency	0.01	0.15	0.25	0.35	0.44	0.40	0.38

Example of wind turbine optimize at 8 M/S wind speed.

Number of Blades : A wind turbine output voltage increases as the RPM increases. The ideal is to get a turbine that generates higher output voltage at the low wind speeds. This will enable it to start charging batteries at low wind speeds.
Higher number of blades optimises performance at lower wind speeds.

Generator Size : The higher the rated generator output the more power is needed to turn it. Conversely the smaller the generator the easier it is to spin in the wind. The faster you spin the generator the higher the output voltage

Rotor Size : The larger the rotor the larger it's swept area and greater the amount of power it can harness from the wind. The smaller the rotors the faster it can spin in low winds enabling it to start generating in low speeds.

Voltages : In order to charge the battery the output voltage of the wind turbine have to be higher than the battery's voltage. For a given generator because of back emf from the battery, a 12 volt battery bank will charge up at lower wind speeds but will require higher wind speeds to charge at 24 or 48 volts. This is because the generator's output voltage increase as the RPM increase. This is why small wind generators have 12 volt outputs only.

Whaka Rongo Moari Song and Lyrics by dave Henere

Number 1 criteria in selecting a wind turbine

Propellor Length. The bigger the propellors the more power you can generate from the wind. So the number one rule of thumb is get the wind generator with the largest propellor. Ok why don't all wind generator manufacturers put huge propellors on their turbines? The answer is that they can't.
For a given alternator or motor, there is an optimum propellor length, to maximise the power that can be generated. Too short and not enough power is generated. Too long and the RPM starts to stall and slow down as well. The propellors must therefore be tuned to the motor and there is a maximum optimal length after which the output actually declines.
Knowing this we can now deduce that when choosing between wind generators we should look for the longest propellor in our price range. This is like choosing the largest horsepower motor for our money.

Connecting up your wind generator

Connecting up your wind generator to your battery bank or directly to the grid is not as easy as connecting up solar panels. I will be posting more on this topic soon.

RB900 Wind Generator

This is the RB900. The next version up from the RB200. Bram Waters first introduced the first version of the RB200 in 1995. Over the years he has sold over 300 units mainly to yacthies.
We decided to revive this model as the RB300. It has proven to be robust and people that have them attest to it's performance.
If our plans are on track we will be able to bring this product to market within 2 months. We would like to modify it to work on houses. It will need to be vibration free with low noise and small but able to produce 300 watts peak.
Keep a watch out for this unit.

Factors to consider in wind power generation

I live in an area where the wind blows a lot of the time ans so decided to invest in a wind generator. Which wind generator should I buy and how do I install it.

Wind power is not as well developed as solar. This is mainly due to cost as the cost of a quality wind turbine is about $3000. However in a high wind area this is turbine will produce more power and it's equivalent cost in solar panels.

Types of wind generators

Horizontal axis - These are the most common. They could be generating upwind as in picture or downwind where the tail boom is absent. More expensive generators use sensors to help point the turbine to the wind.





Vertical axis - Not so common and possible more expensive for comparable power output.






While the design looks simple enough ie a propellor and a motor, the technical and design details that go towards making a good wind generator is very complex indeed.

First the motor : It is not true that you can just take and electric motor and spin it in reverse to produce energy. If existing motors are used, they are usually taken apart and rewound. The type of winding also determine the motor's efficiency. Usually brushless motors are chosen as these will require less maintenance.

Second the propellors : This is an art in itself. The propellors convert the energy in the wind to a rotating motion. It is not just a case of any propellr will do. Type of materials used in the construction and design are very important. In design there is also the trade off for low wind speed and high wind speed performance. The number of blades used is also important.

Third the ruggedness : In high winds the turbine can spin itself to destrucction. Some turbine turn away from the wind some introduce braking systems while the Aerotek RB series have self dampening built into the design of the propellors.

The amount of energy that can be extracted from the wind is a function of the area exposed to the wind. The longer the blades the larger the area. The main disadvantage of a vertical axis turbine is that the surface area exposed to the wind is small another problem is that while one side is working with the wind the other side is working against it. The advantage is that it does not have to be pointed into the wind.

The motors used are also single phase or three phase. Three phase motors are smaller and lighter for the same output.

Much more need to be considered including the controllers.