If you’re thinking about starting really small, perhaps just one solar panel, you might be wondering what to expect from such a system. This post will attempt to answer that question.
To simplify, I’ll assume that you’ve chosen the following equipment:
- A 85-watt solar panel ($400)
- A 110ah, 12-volt marine battery ($60)
- A 10-amp charge controller ($50)
- A 125-watt sine wave inverter ($205)
You’ll have to add wire and mounting hardware to the list, but the entire system can be built for about $800.00. To illustrate how much power you’ll be able to generate, let’s start with the solar panel.
The 85-watt rating is the result of laboratory tests. Under ideal conditions the panel can generate 85-watts, but it’s unlikely that you’ll get that much power from the panel in your installation. Let’s be optimistic and assume you’ll get 80-watts from the panel. Let’s further assume that you’ll have 4-hours of sunlight each day. The daily production of your panel is 80-watts times 4 hours, or 320-watts per day.
Next, let’s consider the battery.
It’s important to note that you should never fully discharge the battery, as that will shorten its life. We’ll assume that you use only half of the energy stored in it, or no more than 55ah. An alarm will sound when your inverter senses low battery voltage, so you’ll know when to stop using stored energy.
I’ve found that a 100-Watt inverter load results in about 10-amps of current at the input to the inverter. It follows then that the battery should be able to provide power to the load for 5.5 hours. (55ah divided by 10-amps equals 5.5 hours). Considering conversion losses, we’ll drop that by about 20%, and assume that the battery can provide 100-Watts for 4.4 hours. Since 100-Watts for 4.4 hours equals 440-Watt/hours, the solar panel doesn’t quite measure up to the capacity of the battery on a day-to-day basis. There’s nothing wrong with that, it’s good in fact. I prefer to somewhat oversize the battery for a given solar array output. A little extra stored energy helps to make up for deficits caused by cloud cover.
A typical use for a system of this size is to provide emergency power, or as a primary source of power in an off-grid cabin or camper. Here is an example of how you might use the available power each day:
Radio - 5 Watts - 4 hours per day - 20 Watts per day
CF Light Bulb - 13 Watts - 5 hours per day - 65 Watts per day
Fan - 30 Watts - 2 hours per day - 60 Watts per day
Portable TV - 60 Watts - 2 hours per day - 120 Watts per day
Cell-phone charger - 25 Watts - 2 hours per day - 50 Watts per day
The total energy used is the sum of the energy used by each device, or 315-Watts per day. As long as you have plenty of sunshine, you’ll have power to spare. Unless you upgrade to a more powerful inverter, you won’t be able to operate a microwave oven, toaster, or other high-power devices.
While the system described here won’t significantly reduce your electric bill, it can really come in handy during an extended power outage. If you need more power than the solar panel can provide, you can use your automobile’s electrical system to recharge the battery. This increases the usefulness of your system, but at the expense of burning fuel.
If you live in an area that experiences frequent power outages, you’ll probably want to enlarge the system to a point where it’s able to provide refrigeration in order to keep food from spoiling. I’m in the process of enlarging mine so that I can do all of these things, and also keep the motors running on my corn-burning stove. Meanwhile, I’m producing clean, quiet, non-polluting power. This is so much better than getting up in the middle of a cold night to refuel the generator.
Please let me know what you thought about this, and other articles on this blog, by posting a comment.