Bright Green Blog

If you plan on using a battery charger with GEL or AGM batteries then you do have to be careful to ensure that the battery charger is able to work with your chosen battery.  If you connect a GEL battery to a charger that has the incorrect charge settings then your GEL battery will be damaged.  A good charger normally has manually adjustable pots that can be set to the correct battery type to ensure correct charging.  Of course, if you don’t know what you are doing when adjusting the pots then just get the battery charger manufacturer to preset the settings for you. It will save you a lot of money in the long run.

Maintenance of remote power systems is crucial and it cannot be overlooked.  The key issue is reliability and as such systems are, generally, located in remote and hard to access areas it follows that technical support can prove to be expensive.  An often overlooked factor with remote power systems is the provision and quality of training that accompanies the system.  Remote power system that combine wind turbines and solar PV are not just consumer items, at least not yet, that take “one size fits all” approach.  Insufficient education and training does lead to lots of technical support calls and unnecessary time wasting.  If you’re going to supply a customised system then ensure that the client is properly trained in the use and support of the system.

As interest in the use of solar PV increases we are constantly surprised by the lack of information available as to how pv can function within a building.

Of course there are many considerations to take into account, but these can be reduced to the following:

1. Architectural - solar pv can be used for generating electricity and can be fitted to walls, roofs, act as windows, skylights, facades and even shades. 

2. Load Management - solar pv can be used to offset peak loads and depending on time of year this can have a significant impact.

3. Energy Control Management - solar pv can be used to drive all sorts of devices, pumps, fans etc.

4. Hybrid Energy Systems - providing emergency power supplies, lighting, pumps etc.

Whatever your function it makes sense to take a modular approach to the design and implementation of the array.  Modular means simple to design and implement, allows for redundancy of the array where shading may occur, details array aspect and orientation and elevation and positioning.

Batteries for use in remote systems must be of the deep cycle type.  Most suppliers offer “solar” batteries and these should be used wherever possible.

Don’t forget that a function of the “days of storage” of batteries is the relationship between array size and load and this is known as loss-of-load probability.  Battery storage gives availability of energy in relation to the array size.  Of course this varies by the season of installation (summer or winter installations).  This measn that certaiin factors come into play on the solar array:

• the array size and tilt angle must be considered together before the installation takes place.
• increasing the tilt angle gives a more uniform output for all year round generation.
• the array generation should not be too far below that of the load.  After all you don’t want the generator to be running all the time.
• system voltage is important. Opt for 24v or 48v system and choose inverters to suit.

All wind turbines have some means of controlling the speed of the rotor in high wind conditions.  Most, if not all small wind turbines, except for a couple of rare exceptions, furl, or fold about a hinged joint that move the rotor towards the tail vane.  Some turbines furl the rotor vertically whilst others furl the rotor horizontally towards the tail.  Some designs furl by pitching the rotor blades and others furl by pitching the blades and furling the rotor.

For small wind turbines to furl properly the axis of the rotor is offset from the furling axis.  You can see this on many of the models available on the market today.  If the wind turbine is going to be sited in windy location then a furliing wind turbine would be advisable. 

Micro Turbines

These superb range of turbines are suitable for almost every imaginable application including, but not limited to: off-grid battery charging systems; motorhome and RV power; marine (boat) power; remote cctv; telecom base realy stations; roadside lighting and a host of other applications.

So how do you choose a wind turbine suitable for your purposes?

You may think that the power output of a wind turbine is all you need to know, but you must not overlook the wind speed at which the turbine is rated.  There is a huge difference between power at 9 m/s (20mph) and power at 12 m/s (27mph) wind speeds.  It is easier to understand therefore that in wind speeds of less than 12 m/s, a small 150 watt turbine could produce as much power as one rated at 300 watts.

The amount of wind power at your site will determine the amount of power you can expect from a wind turbine.

How do you work you the power generated from a wind turbine?  It is quite straightforward really!

The amount of power (p) in the wind is a function of air density (p), the area of the turbine blades intercepting the wind (A), and the instantaneous wind velocity (V), or wind speed.  An increase in any of these factors will increase the power available from the wind.

Air density is affected by temperature and height.  Warm air is less dense than cold air therefore a wind turbine will produce less power in the summer than winter, when it is colder, for winds of the same speed.

Depending on location relative to standard conditions at sea level, power can reduce by up to twenty (20) percent, and maybe more.

Power in the wind varies with the cube of the wind speed. Double the wind speed and you increase the power by eight (8) times.

The SWEPT AREA of a wind turbine directly affects power output.  If you double the area you effectively double the power available.

Wind Turbine Height

Wind speeds do typically increase with height. This is very important.  If the turbine is mounted in an area of rough terrain then height is important and the higher the better.  Height equals stronger winds and less turbulence.  

Estimating Performance

So, how much power does a wind turbine generate?  A good question? Simple, but deceptive.  If you’re into number crunching then it shouldn’t be a problem.  On the other hand, if your working out the detail for your battery charging sytem then results can be difficult.  Since there is no international standard for agreement on performance we must feel our way along.

Given that there are two different types of wind turbine uses: grid connected and off-grid (battery charging) systems we can work out what the norm should be for both types of wind turbine system.  With a battery charging wind turbine system, and when the batteries become fully charged, the wind turbine must be able to dump, excess energy available.  Some manufacturers offer dump loads with others offering special controls and circuits to get rid of the excess energy generated.  In truth most small wind turbines simply disperse the left over energy.

As discussed in an earlier topic solar modules can be connected together in series, parallel or a combination of both.  When the modules are connected in series the output current remains that of the individual modules and the output voltage is the sum of the voltages of the individual modules.  When the solar modules are connected in parallel, the overall output voltage remains constant and the output current is the sum of the individual modules.

What connection configuration should I choose - Series or Parallel Connection?

In a grid-tied system solar modules are usually connected in series strings.  Why?

1. the higher voltage allows the use of smaller cables (cross-sectional area , CSA) is reduced;
2. the installation is less complex thus making the install simple and quick;
3. there is little or no shading of the modules.

You should connect the solar modules in parallel if the modules are would be shaded or of different sizes (wattages) mixed together.  These latter points are very important as you do not want the voltage levels to vary too much as damage to the inverter will result.

Let’s assume you’ve done your homework and you have calculated that for your 24v remote power you will need 2400Ah of battery capacity to meet your load requirements of 10kwh.

Your preference is to choose 24 x 100Ah AGM, 12V batteries. Simple enough!

To meet the 24v system voltage requirement you will have to connect 2 x 100Ah batteries in series (2 x12v to give 24v).  Each set of two batteries would then be connected in parallel so that the overall system voltage of 24v remains constant.  You end up with a series/parallel battery configuration, perhaps 12 rows x 2 batteries.

Satisified you do a check to ensure that your battery capacity is still 24 x 100Ah = 2400Ah. 

But is that correct?

Remember, batteries connected in series voltages add and capacity is constant.  Batteries connected in parallel capacity adds and voltage is constant.   Thus, our series/parallel combination results in a total of 1200Ah of storage capacity, which is not what we originally envisaged.

We’ve had quite a few questions recently about the correct settings for charging AGM batteries. 

Q: When charging an AGM battery do I charge it at the setting for Lead Acid or GEL?

A: You need to set the charger to lead acid, assuming the charger does not have an automatic equalization setting, which will boil the battery.
This is not good for either Gel or AGM.

The efficiency of solar cells decrease with a corresponding increase in temperature.   Crystalline cells are sensitive to heat and for every one degree Celisius increase in cell termperature the ouput descreases by approx 0.5%.  Ampophous cells output decreases by approx 0.2% for every one degree Celsius increase.  During the summer months, solar panel temperatures can go as high as 70 degrees C.  If solar panels are to be used in in very hot climates then care must be taken to ensure that the correct panel is chosen.