Do You Know…
About Sunhours
It is a convenient way to represent the amount of solar irradiation (watts) that fall on a 1 sq meter (10.76 sq ft) area during 1 day. For example , if there were 2 sunhours recorded for a given day then that means that there were 2000 watts per square meter or 10.76 sq ft that fell during the day. A 2 sunhour day would suggest either very bad weather or a winters type day where the daylight hours are shorter. If the length of the day was say 10 hours then on average that means that each hour produced 200 watts.
About Solar Panels
Energy from the sun has to be converted into electrical energy by the solar panel.
Different types of solar panel have different efficiencies. Different manufactures use different quality solar cells to make their panel.
A reputable manufacture will test every solar cell to check its efficiency. These are rated into classes A,B,C,D and others.
Solar cells color ranges from blackish to purple to light and dark blue and all colors in between. So the next step in the testing process is to divide each class type solar cell into up to 14 different shades of color so as to have each panel have a consistent color across it. This can often mean that B and C class solar cells are mixed with the class A to make up the appropriate color.
This greatly effects the intended outcome.
About Batteries
A Lithium battery is an array of many small lithium batteries. Every lithium battery has a voltage range. They are not a fixed voltage. They generally range from 3200 mAh to 4200 mAh. Some manufactures will quote the lower value of the range whilst others will quote the higher.
The batteries are arranged initially in series with 3 or 4 batteries in series. This is to get the desired voltage. Then many rows are add in parallel to give the desired amp hours (ah).
This explains how some lithium batteries are a 12.6 volts (3 x 3200) and others are a 14.4 volts (4 x 3600). These are potentially the same battery.
Batteries are at their lowest level in the morning after they have been running all night.
About Battery Management Systems
The sole purpose of the BMS is to protect the battery from over charge or over discharge and control the input current.
The top of figure 1 shows potentially what could happen without BMS protection. The cells charge and discharge at different rates. This can cause overheating and even explosions.
The lower diagram in figure 1 show how the BMS balances the charging and discharging of the battery.
The BMS also controls the charging current. If the BMS is not matched (figure 2) to the battery and the output of the charge controller, then it won’t accept the extra input current. So one one hand you think a large solar panel and high current capacity charge controller will charge the battery faster, in fact the BMS slows the whole process down.
About Usable Energy
Imagine an 1000 gallon (liter) underground water tank. It has a suction pipe in it to draw out the water. Depending on how far from the bottom the pipe is will determine how much water cannot be used. So a 1000 gallon (liter) tank may only allow 900 gallons (liter)s to be taken out. This is a big problem if you have factored on there being 1000 gallons (liters) of usable water.
So it is with batteries. Just because you have a 100 Ah battery does not necessarily mean that there is 100 Ah usable capacity. If you have not taken this into account then your calculations about operating hours, Depth of Discharge and recovery will be wrong. The end result will be the failure of the battery and an unhappy customer.
Example
Here is an example of two batteries from different suppliers. Both batteries are quoted as 30Ah. The battery height and width is the same in both cases however there is a sizable difference in the lengths.
Even though batteries appear to be similar, there is significant differences in usable capacity, voltage, charging and discharging and many others details.
Some suppliers are conservative is the way they specify their battery’s details and others tend to specify the maximum range. So the batteries can appear similar but are actually very different.
The end result is that battery doesn’t perform the way you or the customer expects.
About Solar Panel Efficiency
Not all the energy from the sun is usable energy. It has to be converted into electrical energy by the solar panel.
The formula is:-
Watts = sunhours x 1000 x area of solar panel (m) x efficiency
For example:-
2 sun hours x 1000 watts x 1sq meter x 16% efficiency = 320 watts
2 sun hours x 1000 watts x 1sq meter x 22% efficiency = 440 watts
About How a Lithium Battery Charges
When the battery is first put on charge, the voltage shoots up quickly. This behaviour can be compared to lifting a weight with a rubber band, causing a lag. The capacity will eventually catch up when the battery is almost fully charged. This charge characteristic is typical of all batteries. The higher the charge current is, the larger the rubber-band effect will be.
So measuring the voltage during the chrging process will lead you to believe the battery has charged however there will be little power in the battery.
About Depth of Discharge
The most expensive component in battery solar lighting system is the battery. If you have found a cheap priced system then you have a cheap battery.
Protecting the battery is the number 1 issue for the operation system. Allowing the battery to go flat will significantly shorten the life of the battery.
The only option then is to replace the battery and that is very expensive and time consuming.
About Timing
The battery, having run all night, is the flattest first thing in the morning. This is also the highest DOD the battery will ever have. Having the correct charge controller that can take advantage of the ’empty’ battery state, is critical to the recovery of the battery. Different charge controllers react differently to this situation.
The OziRoo patented design, starts charging earlier with a higher charge rate. This is extremely important because as the day progresses, the sun intensifies and the charge rate increases and the battery fills.
As the battery fills the charge rate decreases. As mid afternoon approaches the solar intensity diminishes quickly. Once the battery voltage is equal to the solar voltage (plus the voltage required by the controller requirement), the charging stops. Very little power is generated in the afternoon. Even if there is 2 or 3 hours of daylight remaining, the energy production is not sufficient to add much , if any , into the battery.
It is critically important to maximize the morning charge opportunity.
About The Fallacy of Autonomy
This is how many days the lights can operate without any additional charge.
It assumes:-
- the battery is full at the start of the autonomous period.
- that after the autonomous period, the days are bright blue-sky days.
- charging goes back to normal – replacing at least 1 nights operation worth of power plus a little bit more.
It does not take into consideration:-
- the operational requirements.
- The state of charge of the battery
- extenuating weather conditions
- how quickly the battery can recover
- the detrimental effect on the battery
About The Autonomy Days
If the system must have say 3 days autonomy then which days?
In Queensland Australia the summer our days are almost 14 hours long and in winter they are around 10:30 hours. Allowing for the worst case scenario, sun hours for winter days should be used as more power is needed to run the load because the night are longer. This will affect all aspects of the size of the system.
About Communications
Not being able to communicate and control remotely means that the solar system has to be set up initially on or before installation. Its parameters are set and cannot be modified without returning to the site later. A very costly exercise. Different states and county’s have different rules and regulations. And they can be changed by the authorities at any time. Even landlords can insist on changes.
Seasons, time zones, daylight saving, just about anything could necessitate the changing of the operating parameters.
being able to communicate remotely and make any adjustments on any system anywhere and do it from anywhere represents a significant cost saving.
About Security
No system currently available has the ability to
- add or delete users
- allow different users different access rights to different functions
- password protected
- tailored to suit users requirements
- stops unauthorized users from accessing the system
- stops unauthorized users from reprogramming the system
About Communications Methods
- none
- Pre-program.
- no flexibility.
- must be on-site
- must have access to the controller
- Pre-program.
- infra-red
- must have access to the controller
- must be on-site
- Bluetooth
- has a limited range
- must be on-site
- must be close to the controller
- Wifi
- Requires a permanent wi-fi connection
- 3G-4G-5G
- allows unlimited access from anywhere
About Communication Benefits
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About The Biggest Problem
Problems may not appear straight away. They will not necessarily be apparent during fine hot weather conditions. If they do then you have a real problem. Provided the components are reasonably matched, then it will appear to work. It will deteriorate eventually but the good weather conditions cover for the bad performance.
The problem occurs when the weather conditions are less than favorable or the operational requirements exceed the capability of the system. Winter, where the days are considerably shorter or heavily overcast during a rainy season which ironically is during the summer where the days are longer. It could be 6 months after the installation for the problems to appear. Usually with a disgruntled customer demanding a credit or refund is the first time you become aware of the problem. In some cases there may not be a solution. Adding more solar panels may not be an option. Increasing the wind loading on the structure may exceed the structural integrity of the support frame. Adding extra batteries may not work due to limitations on the charge controller and the BMS. Without the ability to adjust the operation of the load, the batteries could fail due to constant low voltage.
Solution
What you need is a specifically designed, built and proven system with highly efficient solar panels, a charging system with matched components, a battery system with the configuration and flexibility to readily accept charge, a lighting system that uses super efficient LEDs and a computer controlled management system that can reprogram the system’s operational parameters based on the weather conditions and state of charge, together with on-the-fly monitoring, reporting and management system to ensure that the condition of the components is managed for maximum performance, battery protection all with the customers brand and image in mind.
