Solar Generator: How long does it take to charge? February 5, 2019 by Julian OH8STN

Hello Operators

Today we’re talking about solar generators . In fact we could be talking about any solar generator and solar panel combination. The question is naive enough, but the answer to this question is actually quite complex

Several times a week I receive a question like this;

How long does it take to charge that solar generator?

Here is how I answer it.

Although the question is a good one, it’s nearly impossible to provide an accurate answer. The answer here at 65° North is definitely different than the answer in Miami, Toronto, Barcelona or Guatemala. I know a lot of the other YouTubers are quoting the marketing specs for a solar generators time to charge, but it is complete bullhockey 

There are several variables we need in order to figure out the questions answer.

Here are a few examples

• How many amps are coming in from our solar panel, in the current wx conditions?
• How high or low is the sun in the sky?
• Is it cloudy, overcast or clear day?
• What latitude is the user?
• How many hours of sunlight do we have each day?
• What is the maximum input current of the charge controller?

Naturally these are rhetorical questions.

A YouTuber/blogger promoting the latest greatest solar generator, has no idea how many solar panels you have, the specs of your panels, the solar energy at your latitude, … so they quote some ridiculous number based on 5k$ of solar panels, or the fastest charge rate possible with the max input amperage, the solar generator can sustain. This is how they get away with saying “its completely charged in X hours, with a portable solar panel”. This is only true if you’re getting 20A of current from your panels. Moreover, we never see any of these bloggers or channels actually charging the solar generator with a solar panel. The upcoming DIY solar generator project has a nice tricks up its sleeve. Here are some of its features:

It will tell you itself

• How much energy is coming in.
• How much energy is going out.
• How much run time at your current load.
• Battery charge level in percentage.
• …

Solar generators (on this blog and channel) on are about emergency preparedness and sustained communications. The point of this project is having enough storage capacity for our requirements, and having enough solar capacity to break even. The break even point depends very much on the operator. For example if it’s an overcast day, I know that I’m not going to get as much solar energy as I would if it were a beautiful sunny day. So I compensate by reducing the output power on my rig, and turning off any unnecessary expenditures on the solar generator. Sure, I may reduce communications effectiveness with reduced power, but some communications is better than no communications isn’t it!? I also designed the solar generator to provide 1.5-2 times the capacity, than what the station requires for 24 hours in the field at 30 watts and a reasonable duty cycle.

So the answer to the question:

I rather promote the idea of each individual operator calculating those numbers based on the actual equipment they have, the conditions they have, and the amount of ah/wh in/out of the system. Anything other than that is just marketing.

73

julian oh8stn