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I want to use solar panels to create a power backup for a router(9V, 1A). I'm aware I'll require solar panels and batteries but am not sure how to choose suitable ones. Please help suggest me on selecting these. Also, what other things do I need? Where can I find them for bargain prices online?

Also please post any links to tutorials I might find useful.

  • I'm assuming this is a network router not a woodworking router. If that's the case you'd be better off asking on electronics.stackexchange.com – ChrisF Feb 8 '11 at 9:30
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    How long do you want to run for, when solar power is not available (overcast or night)? Why are you fixated on solar as a solution? What will you do when your laptop battery dies? – Jay Bazuzi Feb 8 '11 at 10:23
  • @infoquad, so how is it going? Care to post your solution here for people who are also interested in this? – Pacerier Dec 18 '13 at 6:38
  • Toss the router in the trash and buy any of a legion of them that want 12V. My last 6 routers have been 12V, and yeah, I've been thinking about doing exactly this. Might want to shop for low power consumption while you're at it. – Harper - Reinstate Monica Nov 30 '17 at 2:11
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1.) Golf Cart batteries are the easiest supply for a home electric backup battery bank.

2.) Bigger is better with the solar panel array. If you're only going to be running the router (why not the modem too? Or is it combined?) you can probably get away with a cheap small solar kit from these guys : Silicon Solar They offer some great battery charger kits that pretty much take all the work out of it for you. You'd still need to wire these to your battery and convert the current to your AC plug for the router.

3.) For connecting the Router to the power grid you've created in Steps 1&2 you'll need an inverter. Depending on your interest in making something pretty to look at and safe to handle you might want to do some more research on an inverter you can wire to your power grid.

Here's a graphic that should help explain the setup and get you thinking visually on the setup explained above:

Basic Solar Power System

In your case the panel box would be replaced with the inverter output device combined as one item since you're only looking to power 1 device.

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    If it's just this single DC load, you can actually power it directly from the batteries (provided they are 9V, or you step it down to 9V: eg circuitdiagram.net/12vdc-to-9vdc-converter.html). Instead of using the power adapter that comes with your router, you'd wire it directly to the batteries. This skips the inverter (DC->AC), since you're just going to convert it back to DC anyways. – gregmac Feb 8 '11 at 16:31
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The first thing you need to decide is whether it will be manually turned on once power is lost, or whether it will be automatic.

In expensive solar installations, when the loss of the grid is detected, it flips an automatic transfer switch that isolates the "critical load panel" (i.e. a second breaker box,) which is what the solar & batteries are connected to. The reason for this is that you CANNOT use solar panels to power your home when the electrical grid is down unless you disconnect those solar-fed live circuits from the grid. (Otherwise you can electrocute an electrical worker.) I'm not sure if there's any minimum-wattage associated with that requirement. It's possible that there's a rule saying that under 100W is ok without any sort of means of disconnect, but you'll need to find an electrician competent with transfer switches and the NEC requirements on the matter.

If a manual system is good enough for your needs, then you'll need is a solar panel, a battery of the proper voltage (i.e. matching your router), and a small charge controller. With all of that rigged up to a DC outlet and cord, you should be able to run your router just fine... but you'll have to switch it from its normal AC/DC adapter to the DC cord manually.

Once you decide what kind of system you want, then you can start looking at parts. As far as price difference goes, I'm not sure about that. It's possible that you could put a manually switched system together for ~$100, but it's hard to say what a good minimum estimate for an automatically switched system.

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For short-term loads, the easiest solution is a UPS.

Solar has some problems as a backup power source. It's expensive (panels + controller + inverter + transfer switch + wiring + installation). Chances are your home is not an ideal location to collect solar (shadows, latitude, roof orientation). The sun is often unavailable just when you need it (winter storms).

On the other hand, a UPS will charge from the wall, produces a very high quality output, is reasonably priced, and is trivial to install.

Regardless of which technology you choose, there are two important measurements: maximum load (how much power you can draw at any given time) and capacity (how long you can run at a given load). A simple network router is a very small load, max load won't be a problem.

For occasional use, one option is to use your car's 12V system to power your router. You can get a cheap adapter like this one. Idling your car's engine for just this purpose would be terribly wasteful, but if you do it rarely it would be OK.

As a very simple hack, you may be able to just connect a regular 9v battery to your router.

  • +1 Great points, lateral thinking, and comment about car running being wasteful. – user66001 Jun 24 '15 at 17:34
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Yeah, this is a great idea.

First, junk that router

The vast majority of routers these days are looking for 12 volt DC, tip positive. Build for that because it's a lot easier.

A few routers want AC power in the 9-12 volt range, but if you crack them open, incoming power's very first stop is a bridge rectifier. For this type (AC+bridge), it can accept DC voltage - the rectifier will automatically make it the correct polarity. If its AC voltage is 9-12, good chance it will work fine on 12 volt DC.

While you shop for routers, look sharply for low power draw. You can't go by nameplate, but need to look at actual power draw in actual use. You want the 12V power draws (if only you could find a Kill-a-Watt that was 12V!) looking at the 120V draw of the power block doesn't help all that much.

It really matters. Here's why.

Battery

The heart of the system will be a large battery. Large.

How do you factor battery size? Talk to the off-grid solar people, but sizing for 3 days of no sun is about right. Lead-acid batteries really do not like to be bottomed, not even deep-cycle types, so with those, size for 5 days. That's 120 hours at 1A so 120 amp hours. Couple of golf cart batteries. Hence the value of a more efficient router.

Even with no solar system whatsoever, this setup needs to work. Solar, wind, microhydro, jumping off your car, or a grid powered battery charger are just add-ons to provide makeup power.

Solar charge controller

The charge controller's job is to take the ~19 volts coming off a solar panel and buck it down to whatever voltage will correctly charge the battery without overcharging it (cooking it). There isn't one magic voltage number here, there's some black magic in proper battery charging.

Needless to say, quality matters: cheap Cheese charge controllers won't perform as well or could ruin your battery pack. I like Morningstar's $30 low-end unit, it does the job and it's from a design bureau that makes high-end controllers.

An MPPT controller will do a much better job getting all available power out of your panel, and solar panels are rated for this. If you aren't using one, derate your panel by about 1/3.

Panels

From there you connect your panels to the charge controller. Make sure you are accounting for voltage-drop from the distance the wires must travel from the panels. I've seen projects essentially fail because a guy tried to carry 12 volts 100 feet on #6 wire. For his large panel, #0000 wouldn't have been excessive.

How much panel? Again ask the off-grid homepower folks, but an example might be to be able to recharge 3 days of usage in one good solar day in the winter. Figure 1/3 of the day gives peak panel power, and must make up for 3 days, so 9x your load, or 9 amps. 108 watts, but if you're not using an MPPT charge controller, more like 160 watts. But don't let that discourage you, you can always add capacity later, or use alternate charging methods on cloudy stretches.

Transfer switches, inverters, subpanels, and all that jazz

That stuff is all for running 120V loads off solar. You can do it, but it implies a rather large and ambitious solar system. There's something inherently stupid about using an expensive inverter to convert 12VDC to 120VAC to run a wall-wart to make 12VDC. Why on earth would you do that?

It is always better to find a way to run your loads on low-voltage DC, rather than provision an inverter to run 'em on AC. If you're trying to run a modem, router, TV, tablet/phone charger, etc. then that is easy.

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