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I've an old UPS for my computer which draws 50 W on average and less than 150 W at full load. With the the built-in battery I only have about 10 minutes of backup time.

I am thinking about getting a solar panel (around 150/200 W) together with a MPPT/PWM controller (around 10/20 A) so that I can charge the UPS battery (while it is running when utility power is not available). Assuming I just want to use my computer throughout the day, would the UPS be able to supply enough power to the computer as long as the sun is shining?

I also want to know if the above setup would prolong the battery's life because the MPPT/PWM charger will be constantly feeding DC power to the battery (which effectively, I assume, stops the battery discharging).

addendum - I think I should add the reason why I asked the above question. We are from a developing country in south east Asia. We get electricity only a few hours each day in winter and summer because hydroelectric power is not produced much at that time. This is a major hinderance for young people learning computer programming. Most people may not afford to get inverters along with large batteries or a few kW solar systems. So I am thinking what may be the cheapest way if we just want to use a laptop computer for a long time. Then I may be able to help others telling what can be done. Other options I am thinking include stepping up or down dc voltage of small batteries (about 40Ah or less) to match the laptop charging voltages. And I am not sure if it's appropriate to ask such a general question like "What is the cheapest way to use a laptop for a long time without utility power?".

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  • \$\begingroup\$ So - conceptually much the same thing as if you had a laptop charging from a solar panel instead of the mains. As long as you don't do anything silly there's no real reason for it not to work. \$\endgroup\$
    – brhans
    Feb 18, 2023 at 13:36
  • \$\begingroup\$ You may get more useful answers if you state nominal voltage and energy content of the battery. \$\endgroup\$
    – greybeard
    Feb 18, 2023 at 14:49
  • \$\begingroup\$ (Inverter/UPS may not be the best option depending on your computer's power input options: please state in the question body.) \$\endgroup\$
    – greybeard
    Feb 18, 2023 at 15:00

2 Answers 2

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old UPS

the built-in battery I only have about 10 minutes of backup time

Yeah, because most consumer (read: cheap) UPS's use lead-acid batteries, which have a 3-6 year service life. You need to replace it from time to time. They'd prefer you replace the whole UPS, they make more money that way (and so do you; as you surely have discovered, replacement part batteries are not cheap, and are not a good value compared to other lead-acids).

But a battery near its end of life is just not going to perform for you. I would not suggest solar augmentation as a substitute for battery replacement. I might suggest using a less expensive battery that maybe doesn't fit in the enclosure or is smaller. But yes, solar panels should be able to help augment the battery.

Again, do not count on the solar panels replacing the battery; you simply can't count on the sun delivering the energy required.

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[connected to a 150/200 W solar panel,] would the UPS [50 W on average] be able to supply enough power to the computer as long as the sun is shining?

This depends mainly on whether those 150 W are properly derated or nominal, and on insolation.
Nominal specification of the panel may be at standard test conditions (STC):
irradiance of 1 kW/m², air mass 1.5 and module temperature 25 °C, new, clean.

At least air mass will be greater near sunrise&sunset.

At less than 1 kW/m², you can optically concentrate sunlight onto the panel.

Reducing the charge in and out of an electrochemical cell should increase its lifetime rather than reduce it.
You may need to take measures to not overcharge your battery.
A bigger/additional battery may be a winning modification.

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