Which solar panel should I buy?
March 23, 2015 2:31 PM   Subscribe

I want to get into solar by putting ONE solar panel on my roof, then plugging it into a generator. Which solar panel should I buy?

I want to put a solar panel onto my roof. Then I read that I can have a cord on it that plugs directly into a small, about 50 lb., generator like this. Then I would be able to run a TV, laptop, lights, or similar.

I live near Backwoods Solar so I would probably purchase from them if they carry what you recommend.

Where I am stuck is there are so many kinds of solar panels. Which one should I buy?
posted by cda to Technology (6 answers total) 5 users marked this as a favorite
 
Is there any reason not to go with the "Instapark 30-watt solar-powered battery charger" which is specifically included on that page under "Frequently Bought Together," which reviewers of the Duracell product recommend?

Other than that, you will need to figure out what voltage and amperage it is expecting on the DC charging port in order to match it up with an appropriate panel. This is unexpectedly difficult to find; in particular the Duracell webpage does not seem to specify it, but I've only spent a couple minutes looking.

Since the Duracell battery pack says it can charge off a car battery, which is 12V, and that Instapark thing also says it can "charge any battery pack with a DC input of 12 volts," I suspect the battery takes 12V in. And again, that Instapark claims to provide up to 1.7 amps, so the Duracell can probably handle that amperage (but I would check everything against manufacturer's instructions, if only I could find them, before plugging anything in). If you live close to Backwoods Solar anyway, perhaps you can pop in and ask them; they could also vet your plan end to end and let you know if it is realistic to just plug the panel into the battery and let it ride, or if instead you need other parts, like a charge controller for instance, to make it work safely.
posted by Joey Buttafoucault at 2:53 PM on March 23, 2015


Sorry, I guess technically the Duracell thing would be charging from the car's alternator; it would be dumb to run down the car battery to charge up a jumpstart battery. Anyway the principle is the same: likely 12V.
posted by Joey Buttafoucault at 3:45 PM on March 23, 2015


The Amazon item you linked to (which is really just a battery pack, not a generator) can only accept a maximum of an unregulated 12V 30W solar panel. That's a small panel that provides what is essentially a trickle charge, and will likely take multiple days to fully charge the battery pack unless it's a long summer day with no clouds overhead. You won't be able to run a TV of any size directly off of the solar - even an efficient 30" LED TV is probably going to use more than 30W, and a small tube TV can easily use 4-5 times that amount of power. Some laptops use less than 30W, some use much more depending on the processor and graphics card. The best you'll get out of that system is something you could charge up for a day or two and then power a small LED TV or common laptop for a few hours. That's not what it sounds like you're looking for. Plug a 100W incandescent light into that pack and it'll be drained in no time.

In designing this system, you'd need a panel or panels, a way to mount those panels to get maximum sunlight, a charge controller, a battery or batteries, and a DC to AC inverter. How big should each of those be, and how much will it cost? Well, that's the rub.

The hardest part of designing any solar system is sizing - ensuring that the system will generate enough power for your specific application year-round without over-engineering it and spending more than is necessary. In order to do that for an off-grid system, you need a pretty good idea of the maximum power you'll need to use, and for how long you'll need to pull power each day, along with an estimate of how much sun your particular location will get. Without some pretty granular details - different TVs and different lights used for different amounts of time can have a huge range of power requirements, and different locations get different amounts of sunlight - nobody here's going to be able to make a recommendation.

I will say that a complete off-grid 250W system - panel, charge controller, battery, cabling and inverter, and with enough power to run a TV and a few lights off of the battery for many hours each day - will probably cost around $1200-$1500.

If you're near Backwoods Solar, you should probably just go talk to them. They will be able to design you a custom system for your specific location and power needs.
posted by eschatfische at 4:24 PM on March 23, 2015 [5 favorites]


Solar systems, even small ones, are more complicated than this. If you really want to proceed, put yourself in Backwoods' capable hands. You will need more equipment than you seem to anticipate. At the very least some research might be in order.
posted by werkzeuger at 6:45 PM on March 23, 2015


So... that setup would give you around 120 watt-hours of electricity per (sunny) day. That's an almost trivial amount compared to what a house normally uses (less than 5% what I use, and my house is TINY), but you can actually do a lot with that if you're careful.

An 8-watt LED light is about as bright as a 40-watt incandescent. You could run two of those to light a room for 4 hours a day (64 watt-hours). You can get 12V DC models to avoid AC conversion losses (probably over 20%). You could supplement with a couple of little 1-watt LEDs which are plenty bright for reading or whatever. With care, you could have one room lit up to normal levels.

Then you could skip the laptop, and get your entertainment from a tablet. For 30 watt-hours, you can fully charge it. Get a mouse and a keyboard and it's practically like having a laptop. Again, it's DC-DC so you're avoiding a significant conversion loss.

Instead of a TV, get a micro projector to attach to your tablet. That has two advantages -- first they only use a couple watts, and second you have to turn the lights out to see the picture!

That leaves you at least 30 watt-hours, which you could use for a nice portable speaker, charging your phone, or powering whatever kind of Internet access you need (be careful to only use it while you absolutely need it!).

If it's just a short-term experiment to see what it's like to live with minimal electricity, and you have a gas stove and furnace and water heater, I think you could do just fine.
posted by miyabo at 9:20 AM on March 24, 2015


The reason I did not go first to Backwoods Solar is because I called them a number of years ago and they told me they are only a catalog and to get advice I would need to hire a contractor (not in my budget!) I think they have changed that policy so I intend on dropping by their office to find out.

I found another example of what I am looking for called "a solar suitcase".
posted by cda at 9:43 AM on April 9, 2015


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