Physical Size

Solar panels come in all kinds of shapes, sizes and weights. Most are rigid but some semi-flexible ones are available, often related to a specific activity like camping/hiking in the wilderness. Solar panels don’t necessarily go up in size and weight with increasing wattage so, for instance, you can’t assume a smaller wattage panel will actually be smaller in physical size. Two panels of equal wattage may be quite different in physical size and weight. And, a solar panel can be a weighty bulky item. Will you be moving it? Frequently? Storing it in a hard to get at spot? Consider the size and the weight.  For example, maybe two 50 watt panels would be a better choice as they’re easier to move around than one large 100 watt panel. Only you know.

Other “size” measurements: Watts

Solar panels are rated in watts. The watt rating is how much power a panel will produce in full sunlight at 77 degrees F.  (These are ideal conditions. In real life the wattage is less by 10%-15%. ) The watt size range of a singular panel could be anywhere from 1 watt to 300+ watts.

Most solar panels up to 135 watts are 12 volt panels. Many with wattage over 135 are of a higher voltage but designed mainly for grid tie applications. Most 12 volt panels operate at a higher voltage when working; as high as 17 volts. It’s an intentional boost for reasons you can find explained elsewhere if you really want to know.

The general rule of how many watts you might need in relationship to your battery size is approximately 1 watt of solar panel for every amp hour of battery. So a 100 amp hour battery for instance, could indicate that a panel(s) 75 to 130 watts would be in the right range. But, again, this depends on how you use it, what you use it for, what you can afford, what kind of space you have, how much sunlight your area gets and so on.  

Price per watt

Compare solar panel pricing by price per watt. It’s the only way to get around the variations between them taking their features into consideration.

Solar Panels & Batteries - Planning Your System Requirements

All components in your solar energy/electrical system are related to each other. The way you’re supposed to determine that initial battery and solar panel “requirement” so you can plan around anything making sense is to add up the power requirements (watts) of the things you’re going to run during a day. Your goal is to find out, in watts, how much electricity you need. Then figure the number of hours of sun your area gets during that day, etc., taking into consideration seasonal use. Theoretically you can put together a system that gives you that kind of power. For more information go to US Solar Radiation Maps. Y

Interestingly enough, most people that do this with a home plan in mind often end up thinking they need way more than they really do. It’s much easier with a small simple solar system. It’s a confusing task but important; a necessity in fact. Just think about those things you’d like to have working. It requires specifics. What thing? How long per day? How many watts per hour? How many things at the same time? A little thought in this area is better than the wild guess method. Pay particular attention to the higher watt consuming devices you might use.

Just to play around. Let’s say you know you want to run a 95 watt portable computer for 3 hours a day. That’s 95 watts x 3 hours = 285 watts on computer usage. If you had a 50 watt panel pumping in 50 watts an hour (hope for bright sun) you’d still be providing only about half or less of what you’d need for that period of time. If your battery is big enough to withstand the short fall, you could hope your sun lasts for enough hours when you’re done with your computer to make up for it before you need it again. Or, you need more panels. Solar panels can charge the battery at the same time you’re drawing energy from it.

Making your purchases with the idea that you could add on more panels is a good minimal approach.

Sometimes how big you can go is determined not by solar panel size or battery capacity but by affordability and space and you just have to deal with it by limiting or spacing your use.

Other good things to know about solar panels.

1-5 watt panels are considered “trickle” charge solar panels.  Solar panels like this can usually be attached directly to a battery without worry of overcharge. The general rule is that if a trickle charge panel puts out 2 watts or less per 50 battery amp hours you don’t need a charge controller. But, when in doubt, use one. Small ones don’t cost much. (More about charge controllers to come.)

Solar panels run on light, not heat. Ventilation is important. Heat slows them down.

Solar panels last a long time and lose a minimum amount of effectiveness (1% to 2% a year).  For instance, a common warranty on a wind turbine might be 3 years. On a solar panel, 30 years wouldn’t be unusual. Also, solar panels hold their value very well.

Small solar panels may recharge your battery as advertisements may claim but it could take days or weeks to do it. Just know a 15 watt panel barely exceeds trickle charge status.  Sometimes advertising can really over-blow this charging ability.

Charge Controllers