I’d like to start this time with a correction to the last post. Thanks to alert reader “Bear,” who pointed out that the batteries in my solar cart are, in fact, connected in parallel, not serial as I had originally posted. (The post has been corrected, if you hadn’t read it yet.)
The reason this is important has to do with how electrical things connect, and what happens with the electricity depending on those connections. I’ll not turn this into the multi-thousand-word post (plus pictures!) that this would require to fully explain. That said, here’s the dime version:
There are, basically, three values we look at: voltage, wattage, and amperage. These all measure the electricity in different ways, and they interrelate: voltage x amperage = wattage. (The “water analogy” is to think of water in a pipe: voltage is the water pressure, amperage is the volume of water. Wattage is the power they can provide.)
Solar panels provide DC voltage, typically in either 12V or 24V (although I’ve seen 48V panels, as well) nominal (they actually put out something like 17V or 32V, respectively). They will vary most by their wattage (50W, 100W, 200W, etc.). When buying panels, try to get them all from the same manufacturer, in the same size, and at the same time–they’ll all be “worn/used” at the same rate, and the system will stay more efficient.
Batteries also work DC, and are typically 12V, if bought as deep-cycle batteries. They are also rated in “amp-hours,” which indicates the volume (total amount) of electricity that can be pulled from the battery, theoretically. A battery rated at 100 amp-hours (abbreviated ah) can provide 1 amp for 100 hours, before being completely, fully dead. Or, it could provide 100 amps for 1 hour. Or 50 amps for 2 hours. Generally, we don’t like to draw batteries down by more than 25% (and by 10-15% max is better)–so, for our theoretical 100ah battery, we only use 25ah. (This has to do with maintaining the lifespan of the battery. If you drain it further, it won’t hold a charge as long, and will die completely, sooner.)
Inverters take the input DC voltage (12, 24, or 48 volts) and turn it into 120V AC, providing however many watts they’re rated for.
The connections work like this: If you connect batteries or solar panels in parallel, the voltage stays the same, but the wattage (of the panels) or amp-hour capacity (of the batteries) increases. A “parallel” connection means that all the positive terminals link up in a line, and all of the negative terminals link up in a line.
Contrariwise, if you connect them in series, the wattage/amp-hour capacity stays the same, while the voltage increases. When connected in series, the positive of each panel/battery connects to the negative of the next one, with the “ends” connecting to the next “device” in the system.
(Please, if you’re working this and aren’t completely familiar with all of the ins and outs, find a reliable source and study until it makes sense, or find somebody who understands it to do the work for you…)
So, if you have two panels, rated 12V and 100W, and you connect them in parallel, you end up with 12V at 200W. If you connect them in parallel, you have 100W of 24V. With batteries, if you have two of them rated 12V/100ah, and connect them in parallel, you end up with 12V/200ah; if you connect them in series, you have 24V/100ah. Generally, the idea is to pick a system voltage, and work with that. I chose 12V, because over 95% of inverters are happy with 12V, there are plenty of devices out there that run on 12V (mostly for RVs and boats), and you don’t have to worry about using ginormous cables, for the most part…
Whew. Believe it or not, that was the short version. I skimmed a lot of stuff there, and if you’re going to be messing with solar panels, I cannot encourage you enough to find a book (or three or four) on the topic and read up. Even one panel/battery/inverter can put out enough juice to kill–take care of yourself, and be careful with this stuff.
The “repairs” and “replacements” mentioned come down to other happenings around the homestead. I’ve had to make some plumbing repairs, lately, which involved belly-crawling around in a muddy, moldy crawlspace.
I’ll state for the record that I really dislike cast iron plumbing, copper only marginally less, and PVC is easier, but still a pain; unfortunately, they don’t do drain lines in PEX. (Something to do with having to maintain the right drop over the run.) I will suggest, though, for those who have to deal with it, moving away from the old purple PVC primer (and separate cement), and going with a combination primer-and-cement, which is clear, takes out a step in the process, and sets quickly.
The replacements involve us biting the bullet, and getting a new lawn mower–I need to replace the flywheel and stators on the old one–in addition to a new refrigerator, stove, washer, dryer, and water heater. (We’ll probably also replace the household water pressure tank in the near future, too–the current one is woefully undersized.) While having the new things will be nice, that really hurt$ in the wallet.
That’ll do it for this week, folks. Next time around, I hope to talk a bit about outdoor cookspaces–with luck, the Eastern Seaboard won’t still be in Deluge conditions by then, and I can do stuff outside. If you have questions or comments on the solar, or about cooking, please post them in the comments section!