Best way to create a daylight charging station and for a laptop of 135W consumption with solar energy and lower battery capacity posible

I want to create a charging station and for a laptop of 135W consumption with solar energy, because in my area electricity outages are normal (5 hours per day or more), but I need some help?

1. I want to buy an mppt charging controller, some solar panels, an inverter, and a lower possible capacity battery.

2. Storing energy is not my priority I just want to use daylight to charge a laptop when possible from 8 am to 6 pm schedule on daily basis, but only when a power outage occurs, and if possible because wheather conditions.

3. In my area insolation numbers are: kWh/m²/day 4.43, 4.60, 4.70, 4.49, 4.71, 4.94, 5.10, 5.28, 5.32, 4.77, 4.31, 4.13

Well, I have so many doubts, but this is my plan: install a 300W solar panel, connect it to mppt charger controller (10 Amps is enough?), and the controller to the battery, and the battery to the inverter, a very simple and regular circuit, but my priority is not to store energy, just use to charge laptop it if possible or use power directly from solar panel using inverter, because this I want to use and 20 AH or 30 AH battery, just to stabilize charge of the laptop or power consumption but not to store energy.

I believe that if the battery is fully charged the inverter will start using the current directly from the solar panel using battery charge to stabilize it, that's what my idea is based on, but I don't know if I'm wrong?

Are there errors in my assumptions? or What modifications should I make to achieve what I am aiming for?

• It sounds about right. It's a pretty standard solar power arrangement. I can't comment on how much solar power you'll get (I don't know how to estimate that) Jul 21, 2020 at 14:20
• Why convert DC from panel to AC (inverter) and then convert it back to DC (laptop charger) ? What type of battery are you using ?
– AJN
Jul 21, 2020 at 16:15
• I want to use 110v from inverter to charge laptop and when no charging the laptop use that electricity for other 110v appliances supported by this circuit. I know I can do a more efficient DC to DC but t looks more difficult to me, probably I'm wrong but I don''t know how to build a circuit like that. Can I connect a DC 12v to 19v converter to battery instead of inverter and accomplish same stabilization like with the inverter?
– Xiul
Jul 21, 2020 at 17:57

Your plan is generally reasonable.

Needed current ratings all depend on the voltage of the batteries; I'm guessing that you're thinking of a 12 volt battery, but for a solar power system that isn't connecting to any other DC equipment meant for auto use, you should consider 24 or 48 volt nominal voltage to get more efficient operation and not need quite as heavy wiring. If only 12 volt lead acid batteries are regularly available, you can connect them in series to multiply the voltage (the batteries should be of the same model and all new when installed). Similarly, any panel voltage can be obtained by connecting multiple panels in series.

If you do use 12 volts, then a 10 A charge controller is undersized for 300 W of panels because it can transfer only 120 W of power from the panels to the battery, so it can't even keep up with the laptop. On the other hand, 10 A of 24 V would be 240 W, and so on.

But any voltage will work as long as components for it are available for sale; just remember to multiply your voltage and current to get power so that you're comparing on an equal footing. And don't forget that the inverter and charge controller both have some losses.

And your panels won't produce 100% of rated power all day unless you have no clouds and turn them to face the sun. You might want to expect wanting a battery sized for storage so you can store the energy when it's available and use it when you need it. Laptops will generally have batteries of at most 100 Wh, so at 12 V 30 Ah you have somewhat less than 360 Wh to use for charging, so that's perhaps two charges without fully discharging the battery, which sounds reasonable but I wanted to highlight what you're getting.

Also I would suggest including a "low-voltage disconnect" in your battery-to-inverter circuit. This is a device which will shut off the inverter when your battery voltage reaches a chosen threshold, so that you cannot overdischarge the battery by accident. The inverter likely has its own low voltage limit, but a settable one will help keep your batteries healthy since you're not trying to use the last bit of available energy.

Disclaimer: I am not an expert in this field; I'm just an electronics hobbyist who happens to have set up a similar mini solar system this very week and have done some research accordingly.

Depending on the laptop, the task may be as simple as 150W/24V solar panel + voltage limiting shunt for 150W/19V or 20V (where most laptops work) + the proper jack to get the power into the laptop. No MPPT, no inverter, shunts are way cheaper and simpler than MPPT or PWM controllers and the laptop will use whatever it can, depending on the available sunlight.

But you won't have any backup power when there is no sun, other than the laptop battery itself.

If you still want to use a battery and go for the more expensive MPPT (rather than PWM) solar controller, you may as well want a car-charger for the laptop. They are way more efficient (and generally cheaper) than an inverter and the original charger combined.

Things to consider:

1. Battery: if you use MPPT, go for 12V battery and 24V panel. If you use PWM, match the battery to the panel (both 12V or both 24V).

2. 150Wp rotating panel (even if you rotate it by hand) gets as much energy as 300Wp fixed panel.

3. MPPTs are rated for amperes at the battery voltage. So a 300W 24V (that really works somewhere 30V/10A) panel is matched by 20A MPPT controller for 12V battery.