Solar for the most part has a mixed bag of “experts” to rhetoric repeaters which has the effect of reducing knowledge and flexibility. I’m on a DIY group and for the most part, out of the thousands of members, actual DIY falls into around 4 of the groups members. But if your into hands on with solar and electronics, then this article may be right up your street.
NO MPPT, No Problem.
Charge controllers come in two main forms, the PWM and the MPPT. Most cheap solutions are PWM and most people will tell you to buy a MPPT Charge controller. They are probably not sure why they are saying this and what alternatives there are, and we will go into this here.
Here’s a basic and short summary of the factual difference between a PWM and MPPT solar charge controller:
- PWM (Pulse Width Modulation): PWM controllers are simpler and less expensive. They directly connect the solar panel to the battery, limiting the charging voltage to the battery’s voltage. This can result in energy loss, especially in lower light conditions or when the panel voltage exceeds the battery voltage.
- MPPT (Maximum Power Point Tracking): MPPT controllers are more efficient and can harvest more energy from the solar panel. They constantly adjust the input voltage to match the panel’s maximum power point, optimizing energy transfer to the battery. This results in higher energy output, particularly in varying light conditions or when the panel voltage is significantly higher than the battery voltage.
In summary:
- PWM controllers are cheaper but less efficient.
- MPPT controllers are more expensive but significantly more efficient, especially in suboptimal light conditions.
So now you understand the basics, Lets look at something different.
The Alternatives
Power is Volts X amps and for the most part, solar panels have a stable voltage, it is the current that changes though the day as the sunlight changes in its intensity.
In the above image we see a small 2 amp adjustable buck converter, we can use panels up to 23v on this, and out put between 1 and 17 volts which can be our battery voltage.
How it works.
Inside that tiny chip is a few parts that basically switch the power in to power out, however the power here is only voltage controller and not current controlled so you would not be able to use this for your solar project, unless the panels was tiny.
Before going on with your project, you would have done the math to find out what power you need. One of the things I see the most is the confusion because the simple terms and concepts of the power, is not entirely as perceived in many cases, so lets take a look at this.
Power factors.
The out put power of the converter should match your needs, and you will need to know how to math this in order to buy the correct hardware. So lets do that now so you can see:
Panel Voltage 37. Battery Voltage 12. Solar panel current 8 amps.
A solar panel with 37v and 8 amps is 296Watts of power. (37×8)
The difference between 37 and 12v is 3.08 times. (37/12)
Therefore we have to factor the difference in the current output as the converter will convert the voltage excess into current (amps); in this case its going to be 3.08 times the current.
The “charge current” will be 8 x 3.08 = 24.6 Amps.
The output power does NOT change it is still 296 watts of power ( 24.6×12) but in the real world there will be a slight difference, but as you can see in this scenario you would want to handle the high current output and a 2 amp controller, we showed above is not going to cut it.
The power factor will change based on the voltage difference between the solar panels voltage and what the battery voltage will be. For the most part, the panel in the example used here is a 24v panel, so typically a 12v panel would be around 19v. On a 24v system the power factor would be 1.54 and the output current would be 12.3 amps.
Other things needed for a charge controller.
For lead acid batteries, you can trickle the charge into the battery endlessly. Providing that you do not exceed the voltage and gas/boil the battery. Where the controller voltage is set, the current flow will reduce as the voltage balances out, and the same occurs with the state of charge of the battery.
As a battery becomes full the current slows down.
You would want to fuse the device and also have a diode to stop power flowing back from the battery to the controller or to the solar panels.
Another device may be a battery charge manager. This can control when the solar is on or off and also set when it will switch on and off, this is idea as a secondary control, but also for those using lithium batteries and what more control over the batter pack voltage.
What does this do? this is a battery monitor, it reads the battery voltage and will turn on and off the charge or output to protect the battery from discharge or over charge. There are a few different types, so be a a little cautious that you are buying the right one, if you are not buying our kits which you can get from the shop.
The monitor is also a secondary protection, should a converter fail, it would output full voltage, this would detect the problem and turn off.
There are various types of controllers, These work as AC or DC side and the current capacity differs depending on the SOC of the battery, the array voltage and the current from the panels and to the battery. Save to say, that a 9 amp solar panel wont out put just 9 amps.
The big boys toy.
The converter above is a 75v 25amp converter (1875W), this allows you to have 75v of solar and output 25 amps.
it is suitable for 600w of solar or less. Remember that we have to undertake the factoring when we consider this converter.
Typical installation would be 2x410w solar panels with a max current of 13 amps and volts of each being 37v (74v) 74/24 = 3.08 x 13 is 40 amps (960W)
We have other 50amp converters and some larger ones around 85amps.
Think! Having more current going to the battery wears the battery. take your Ah rating and 0.4c rate as your maximum charge current you want from your charger. A 100ah battery would be below 40 amps.
NOTES:
You can use a buck before a PWM charge controller. You can save your battery from the excess voltage, and add current if you wanted to keep the charge controller. The costs are about the same, A MPPT charge controller is around £150 this is near to the £60 mark, but you may want a case and the learning about this is good value. You may want to build one of our inverters!!
Wiring –
Solar panels to fuse to Converter, then DIODE, To battery Monitor, to Fuse and then to the battery.
Connect the battery voltage reading wire to the battery terminals.
Wire relay to converter switch.
Settings –
Set converter to float voltage of your battery.
Set monitor to be on until bulk voltage. On should be just below the float voltage to keep the battery charged.
Tools –
Wiring crimping tool and strippers.
Multi meter to set voltages.
Small Screw driver.
As you can see this is a basic solution for using solar panels to charge a battery, we have other projects which are smart and has wireless, these can tell you the current, watts and voltage as well as battery information.
QUESTIONS.
Can you use this for AC (grid) charging a battery pack?
Yes, you only need the monitor to do this along with a charger, the charger can be set to turn on or off by the battery monitor. You cannot use the items above as they are DC and Not AC items.
Can I use these with parallel panels?
You can if the power factor does NOT exceed the maximum power output current.
What solar panels can I use?
there are a lot of panels you can pick from, but there are generally low power. You could use used 250w panels as the current is around 8 amps on these, the newer panels are much higher current.
Can I use current limiting and should i?
Yes a current limiter is a good idea as you should not over current your batteries, some of the controllers will have current limiters
Is there something that I can use a lower voltage panel to charge a higher voltage battery?
Yes, I will be making another post about this, search for “solar charge booster”.
the system is more or less the same, however the converter is different. You math would reduce the input current to add voltage. so 37v and 8 amp charging a 48v battery would be 0.77 (negative), or about 6.2amps.
Solar without a controller (2). — RenewSolar
Solar Charge Controller Project — RenewSolar
No responses yet