Unveiling the Power of Free Wind Energy: 7 Crucial FAQs Answered

Wind Energy is often downplayed by RE installers, the reason for this mostly due to inexperience. Wind is often cited as “unreliable”, high maintenance, etc. The purpose of this blog is to try and explain the more FAQ (Frequently Asked Questions) and not a total discussion of wind. Go the fREe Energy course page for more information on Renewable Energies, and Wind energy in specific.

FAQ 1. What kind of region can you install a wind turbine?

Logically, small wind turbines should be applied in the regions with sufficient wind resources, but how to determine this? Unlike Solar it is more difficult to determine wind power. It should be noted that choosing the correctly rated design speed wind turbine conforms to local wind speed. But in small wind turbines this is difficult to obtain due to 3 reasons:

• Wind power is determined primarily by the wind velocity to the third power; hence the power depends on wind velocity cubed. A 4m/s wind will have eight times the power of a 2m/s breeze.
• Turbine type: HAWT (Horizontal Axis Wind Turbine), or propellor type has the highest efficiency. VAWT (Vertical Axis Wind Turbines) have much lower efficiency, but are visually more appealing and capable of working in turbulent and lower velocity winds.
• Blade design: The “angle of attack” varies as to wind speed, yet in small wind turbines (HAWTs) this is not economically feasible so has to be designed to match the generator to be able to extract optimal energy when generator turning at max power.

NOTE: For small Urban applications we only look at HAWT turbines, this is due to the small installations and to maximize Power Factor Extraction. There are many VAWT products on the market – most are “Fake Watts” – and not advised.

Finally, the WASA wind map, for South Africa, has been released. It is a good generic indicator of wind availability as discussed in Wind Energy Blog.

A good resource with actual historic data has been found on Underground Weather, which lists the historic data from all the airport fields, international too, with hourly readings.

The annual average wind speed should be more than 3m/s, the effective wind speed 3-20m/s should be more than 3000h per year.

The WASA resource map gives though a good indication of generic annual wind speeds and most areas well above the 3m/s. For HAWTs the optimal number of blades is 3, but this is if have the wind resource. For averages below 5 m/s then go for a 5/6 bladed option, and 3 bladed above 5m/s. So, for Natal and the Highveld would advise on a 5 or 6 bladed option and 3 bladed for elsewhere. Basically, the lower the wind speed the more blades.

FAQ 2. How to calculate the actual power usage in my home to configure the appropriate power of wind turbines?

To be honest this is a sort of “how long is a ball of string?” question.

At present, batteries store the power generated from the wind turbine, then discharge to home appliances as required. So, the load power (power used) and the charge produced by wind turbine gives the amount of the actual power storage required. For example, the rated output power from wind turbine generator is 100W, and the continuous workable time of wind is 14 hours. This is from our setting, where we get a 60% load factor. The load factor is actual power acquired from wind turbine over year compared to the name plate power. This will vary as to your location, we are located at the sea near Cape Agulhas (Gansbaai), with high wind activity. The battery will be charged with 1400Wh from the Turbine during course of day.

It could be ‘quiet’ day though and you only have 4 hours of wind – so only 400 Wh would be generated.

But only about 70% power from battery can be discharged to the load, if using LiFe₄Po batteries, so the actual power which can be used from battery is 280WH.

If there are:

1. 15W Bulb x 2 Pieces, working 4 hours per day, consumption 120 Wh.
2. 35W TV x 1 set, working 3 hours one day, consumption 105Wh.
3. Radio 15W x 1 Piece, working 4 hours one day, consumption 60Wh.

For daily total consumption of loads above is simple addition of separate loads and equivalent to 285Wh per day. If you only design to install 100W wind turbine generator, the consumption total power will more than the power stored in batteries from wind turbine generator, of 280 Wh. In long period of time using power from 100W wind turbine generator, it will make the battery seriously depleted and will decrease your battery service life.

It is assumed that wind turbine will operate at rated wind power generation, but in fact, due to the variability of wind and that power of Three – it is highly variable. So, you should switch off some electrical appliances when the wind condition is low to protect your battery.

So, to get back to that “ball of string” If your budget is enough, it will be better to install a diesel generator set or install solar panels at the same time [hybrid]. It also depends on your scenario, three scenarios are:

• Off-grid; with no connectivity to grid, you want fREe energy to power your house. These examples were for off-grid, then have to do an energy audit to calculate how much power storage you need, then only how much fREe energy input you need to supply.
• On-grid: For on-grid then the battery storage can be minimal (see next FAQ).
• Loadshedding: this an off-grid scenario, do energy audit and find power requirements over the 2-hour loadshedding window. Size your batteries/inverter to supply this during window.

In Short, you do not look at how much power you can generate – you look at how much power you need/use.

FAQ 3. How to select the correct battery capacity store power from wind turbine generator?

This is for an on-grid scenario. Generally, the battery capacity should be equal or smaller than the power from wind turbine generator. A rough indication is for our 60% load factor here:

1. 100W wind turbine generator matches 60 Wh battery.
2. 200W wind turbine generator matches 120 Whbattery (or 60 Wh x 2 Pieces)
3. 600W wind turbine generator matches 360 Wh battery ( or 120 Wh x 3 Pieces)

On the norm you should install the batteries at 60-80% of wind turbine rated power. So a 600 W wind turbine can be matched to 360 to 480 Ah batteries, to reduce costs. This is for an on-grid scenario. For this scenario the batteries are supplementary for storage but more for energy conversion. The correct storage will not be determined by the Wind Turbine – but by your inverter and power demand – just ensure more than this minimum figures given.

Q 4. What scale of winds for wind turbines can generate electricity?

In general situation, about 3 level on Beaufort scale to start charging the battery (the wind generator voltage then is higher than the battery voltage). For installation of wind turbines must be aware of your local wind resources – as discussed in FAQ 1. For the annual wind speed in the 3-5 level, we proposed the 400W or 600W small wind power generator. If more than Scale 5 wind resource in the usual year, can choose the 1000W wind generator, if got the space.

Q 5. How to confirm your wind situation?

Since it quite tricky to find out your wind resource, South African generic wind map only came out in 2022 [Refer to FAQ1], lets refer to The Beaufort wind scale:

Level 1: smoke will trail with the wind.
Level 2: wind felt on the face.
Level 3: leaves and small twigs in constant motion.
Level 4 level: raises dust and blows paper
Level 5 level: bushes and leaves begin to sway
Level 6: large branches in motion
Level 7: whole trees begin to sway
Level 8 level: twigs break off trees
Level 9 level: slight structural damages, loose tiles picked up
Level 10: uproot trees, structural damages
Level 11: widespread damages
Level 12: Devastation

FAQ 6. Why the wind generator brake/stop turning?

Our products come with a handy built-in LED indicator light on the wind turbine. When generating power this LED will blink and the intensity of LED also indicative of the amount power being produced. There will be times though that the wind is blowing, but the Turbine rotors are spinning slowly -or motionless? Do not worry , this is normal response of the fan controller and may be due to two factors:

• The battery is full, then the controller will apply brakes, to protect battery and prevent overcharge.
• Wind is too strong and Turbine over-charging. Then the brakes will also be applied to protect the battery and/or the HAWT.

Actually, in our scenario, we like to operate under 40km/h winds as this seems the sweet spot/area. So, when high winds are experienced then a circuit breaker has been installed that connects/shorts the three Vac lines from turbine. This will automatically apply brakes to turbine, until the gusts abated and open switch again for normal operation. This is to protect equipment from sudden power surges due to wind turbulence.

Q7. How to mount the Wind Turbine.

Turbine Mast Design Parameters:

NOTE: These are just general design parameters, and not fully indicative, please ensure Tower Design is to local codes. Special attention has to be given to tower and guy rope plinths/bases that confirm to local code.

These are just the generic specifications to give an idea of mounting tolerances and spacing distances. For residential areas we only stock the 400W, 600W and 1000W HAWT– as these can be mounted on 6m masts. This is often the height restriction in residential areas, and no extra permissions required.

Included in purchase will be a manual giving you full instructions on base plate sizes as well as Civil Work dimensions required for baseplates and guy rope anchor points, etc.