Awhile back several members including myself engaged in a good discussion around Solar. Awhile back being 2017. You can find the thread here.

https://sigforum.com/eve/forum...935/m/9140038034/p/1 https://sigforum.com/eve/forum...935/m/9140038034/p/1

I asked Chat to summarize and modernize since tech has changed a lot in nearly 9 years. Here is a summary of that post on portable solar.

Portable Solar Panels & Battery Charging (2026 Update)

The old thread still has good advice, but portable solar has improved a lot. USB-C PD, LiFePO₄ batteries, MPPT controllers, and portable power stations have become the standard.

The basic principles haven't changed.

1. Think in Watt-hours (Wh), not mAh

Solar panels produce watts (W), while batteries store watt-hours (Wh).

Wh = Volts × Amp-hours

Example:

20,000 mAh battery

20 Ah × 3.7 V ≈ 74 Wh

A battery bank won't deliver all 74 Wh because of charging and conversion losses. Plan on roughly 80–90% usable energy.

2. Figure out your daily energy needs

Add up everything you want to charge.

Example:

Phone = 15 Wh
Tablet = 30 Wh
Flashlights = 10 Wh

Total = 55 Wh/day

For devices that list watts instead:

Energy (Wh) = Watts × Hours Used

3. Size your panel using Peak Sun Hours

Don't use daylight hours.

Use:

Panel Size = Daily Wh ÷ Peak Sun Hours ÷ System Efficiency

Example:

Need 100 Wh/day

4 Peak Sun Hours

75% efficiency

100 ÷ 4 ÷ 0.75 = 33W minimum

I'd buy at least a 50–100W panel to provide margin for clouds, heat, poor panel angle, and seasonal changes.

4. Expect real-world losses

A simple planning equation is:

Daily Solar Production ≈ Panel Watts × Peak Sun Hours × 0.7–0.8

Example:

100W panel

4 Peak Sun Hours

100 × 4 × 0.75 = 300 Wh/day

The biggest losses come from:

Panel temperature
Poor sun angle
Clouds
Partial shade
Battery charging
Voltage conversion

5. Charge a battery—not your phone

Instead of:

Solar → Phone

Use:

Solar → Battery Bank/Power Station → Phone

The battery acts as a buffer, allowing your panel to collect energy throughout the day while providing stable power to your devices whenever you need it.

6. Avoid unnecessary conversions

More conversions = more losses.

Best:

Solar → Battery → USB-C Device

Less efficient:

Solar → Battery → Inverter → Wall Charger → Device

Only use the inverter when you actually need AC power.

7. MPPT is worth it

Modern MPPT charge controllers harvest more energy than older PWM controllers, especially in changing weather and cooler temperatures.

Most quality portable power stations already include an MPPT controller.

8. Buy enough solar

The #1 mistake is buying the smallest panel that works on paper.

I'd rather have extra charging capacity than spend all day chasing sunlight.

If the math says you need 60W, I'd probably buy a 100W panel.

If it says 150W, I'd probably buy 200W.

9. Buy for your use case

Backpacking

20–30k mAh USB-C power bank
40–60W folding panel

Vehicle camping

300–700Wh LiFePO₄ power station
100–200W panel

Home emergency backup

1–3kWh LiFePO₄ power station
400W+ solar

Bottom Line
Calculate your daily Wh usage.
Use Peak Sun Hours, not daylight hours.
Plan on 70–80% real-world solar efficiency.
Charge a battery first, then your devices.
Buy more panel than the math says—you'll almost never regret having extra solar.

I picked up one of these for my get-home bag.
I didn't get chance to mess with it yet and actually see how it does charging - but I do like that you can connect your phone or something directly to it with no intermediary device.

I have a couple 100 watt solar panels from Harbor Freight that work pretty well. They were highly rated so I grabbed them on sale along with a different brand off Amazon. I don't have much illusion of 300 watts worth of panels being of too much use but they'll be of some use if ever needed.