Solar Power & Energy

I’ve been reading and studying a LOT of information about solar power in the last 6 months or so, because I’m making preparations to move to a remote area and live off grid. Our plan is to start with a small solar panel setup - just enough to run the work laptop so we can continue earning money since we work online - then we’ll add solar panels as needed and wanted over time.

Part of the planning process though, means we need to know how much solar power is needed for the bare minimum of our plans. And figuring that out isn’t so easy of a task.

I don’t fully understand watts, kilowatts, watt hours, voltage and amps… and I really haven’t yet grasped how all these relate to and/or depend on each other. So the learning curve for me has been a bit steep.

I initially came across information online which said laptop computers use an average of 45 watts of power. I then learned that my specific laptop appears to be rated at 90 watts DC power.

Now, I was under the impression that we would need to buy enough solar panels to generate at least 90 watts right from the start. I’ve since learned that’s not quite how it works.

As far as I can determine, the 90 watts needed for my own laptop (which is actually a large convertible Tablet PC) is the maximum amount it could use if I’m running everything at once. And that’s the maximum amount needed to charge it up at it’s fastest rate.

When I plug my laptop into the wall outlet in a regular house, it takes roughly an hour to fully charge the battery. When I switch to solar power though, the primary difference seems to be in the amount of charge time.

For example, if I choose a solar panel system that generates 20-30 watts of power in full sunlight and peak efficiency, it may take 3-5 hours to fully charge my laptop. This might also not be enough power to both use and charge the laptop at the same time. So I could choose to use the laptop at those solar power levels, or I could choose to charge the battery instead.

If my starting solar panel setup generates 50-80 watts though, that should be more than enough to allow me to use the computer while it’s also charging the battery. Again it will take several hours to charge fully though, so I’ll need to make sure I’ve started charging it well before sundown.

The solar power kit I’ve chosen to start with consists of two 36 watt panels - 72 watts total - which should be plenty on good sunny days.

To figure out how much power you need for various other devices in your home can get a bit complicated though. Some devices - like the refrigerator - pull power 24 hours a day, so you need to plan for that when you’re setting up a solar panel power system if you also plan to run a fridge. You might decide to change to a smaller RV or apartment size fridge to lower power consumption, or you might decide you want enough power from your solar panels to run the regular sized ones. Either way, you’ll need to know how much power that appliance draws so you’ll know how many watts of solar power you’ll need to be able to generate.

In most cases you can simply look at the power label on the device, and it will provide information which can be used to determine how much power it needs. If you want the specific usage amounts though, you can buy an inexpensive device called a watt-hour meter. You can buy whole house meters, or simple ones which you plug a device in to. This meter allows you to see how much power something is using in a given moment, and it lets you see how much it averages in usage over time.

Knowing how much power your solar panels need to generate will allow you to plan for a whole house off the grid install. If you also reduce your power consumption drastically by getting rid of extra electrical devices you don’t need, and scaling down your appliances, this will also make a drastic difference.

For our purposes we will start with the 72 watts noted above so we can run and charge the computer. We frequently use the same computer as a TV in the evenings too, so we’re not worried about trying to juggle charging multiple appliances and devices. The starter setup is probably going to be more than enough to charge smaller items too, such as the cell phone, camera battery, and rechargeable batteries. Once we put it into actual use, we may find that all we need to do is add extra storage batteries for the excess solar power being generated too.