Step 1: Cheap solar, Step 2: ???, Step 3: Profit
July 22, 2017 11:44 AM Subscribe
If I installed an inexpensive solar system without tying it into the grid, what are some useful things I could power with it? This guy set up a cheap 100w panel and used it to power a lamp and charge his computer. I'm looking for other similar ideas that would reduce my electric bill a bit without the big investment that full rooftop solar requires.
His setup is also nice because it doesn't require hooking into the grid. I live in a pretty typical suburban house, and am trying to figure out what I could power with a similar setup (maybe 2x200w panels). That wouldn't be enough capacity to power an appliance, but would like to utilize as much of the power as I could to justify the investment. Any ideas?
His setup is also nice because it doesn't require hooking into the grid. I live in a pretty typical suburban house, and am trying to figure out what I could power with a similar setup (maybe 2x200w panels). That wouldn't be enough capacity to power an appliance, but would like to utilize as much of the power as I could to justify the investment. Any ideas?
Your panel will not generate a steady flow of electricity, so you'll want to have a battery to store the power. A typical battery will provide 12v power, so you might use an inverter to get to standard US current for charging your phone and laptop, powering a radio and lights, things you might want in a power outage. They sell kits labeled solar generators for this purpose. You pay a lot extra for the spiffy name. Prices for solar panels keep dropping, but if you have any need for power generation, it makes sense. Camping, for instance. I did a big road trip and camped out a lot. Bought a solar panel so I could keep things charged.
posted by theora55 at 1:13 PM on July 22, 2017
posted by theora55 at 1:13 PM on July 22, 2017
My first thought would be to get an e-bike with a spare battery that can be charged fairly easily off your solar system.
(I'm not sure if it's feasible to do this without going solar -> inverter -> charger -> battery. If you're handy with circuits maybe you could rig a charger that works without the inverter.)
Swap batteries as needed, commute on your e-bike, and ditch your car. That'll save you a lot more than just the electricity bill...
posted by sibilatorix at 1:34 PM on July 22, 2017 [3 favorites]
(I'm not sure if it's feasible to do this without going solar -> inverter -> charger -> battery. If you're handy with circuits maybe you could rig a charger that works without the inverter.)
Swap batteries as needed, commute on your e-bike, and ditch your car. That'll save you a lot more than just the electricity bill...
posted by sibilatorix at 1:34 PM on July 22, 2017 [3 favorites]
A 12V battery or two, and/or a 12V-appropriate solar panel, opens you up to the world of 12V RV appliances.
There are a number of small battery chargers (like for AA, AAA, C, D, and 9V batteries) that use a 12V power transformer. I successfully hooked mine, instead, directly to my 12V solar panel charge controller and use the sun to charge my camera and other batteries.
Many charge controllers also have a USB jack, so you can charge your phone or other USB device -- at the same time as you are charging your 12V battery.
Also, computer fans! They are also 12V. I have two set up right now. They are cooling, also good for drying laundry hung on a rack, and can even be a kind of impromptu air conditioning along with that damp laundry (or a purpose-wetted towel).
A search for 12V solar charge controller USB led me to the links in this comment.
Many people like to convert their solar power to AC, but the more steps you go through (sun->device vs. sun->battery->device vs. sun->battery->inverter->device), the more raw power is lost. In general, the fewer steps, the more energy. So, if you have a 12V DC lamp, or even another straight battery-powered lamp, you'll get more light over more time than if you take the same power and run it through an inverter so you can use your house lighting through an AC power system.
I'm hoping to figure out how to charge my cordless drill next!
posted by amtho at 1:36 PM on July 22, 2017 [3 favorites]
There are a number of small battery chargers (like for AA, AAA, C, D, and 9V batteries) that use a 12V power transformer. I successfully hooked mine, instead, directly to my 12V solar panel charge controller and use the sun to charge my camera and other batteries.
Many charge controllers also have a USB jack, so you can charge your phone or other USB device -- at the same time as you are charging your 12V battery.
Also, computer fans! They are also 12V. I have two set up right now. They are cooling, also good for drying laundry hung on a rack, and can even be a kind of impromptu air conditioning along with that damp laundry (or a purpose-wetted towel).
A search for 12V solar charge controller USB led me to the links in this comment.
Many people like to convert their solar power to AC, but the more steps you go through (sun->device vs. sun->battery->device vs. sun->battery->inverter->device), the more raw power is lost. In general, the fewer steps, the more energy. So, if you have a 12V DC lamp, or even another straight battery-powered lamp, you'll get more light over more time than if you take the same power and run it through an inverter so you can use your house lighting through an AC power system.
I'm hoping to figure out how to charge my cordless drill next!
posted by amtho at 1:36 PM on July 22, 2017 [3 favorites]
Response by poster: Right - the setup would be something like the link: a panel or two plus a battery and inverter. The question is how to use that power, given that I won't be hooking it into the grid powering the rest of the house. Set up an outlet or two and power... something? (Water heater? Lighting? Minifridge? Charging station for laptops and tablets?) I feel like there must be something that fits within that capacity and would be used regularly enough to justify the investment.
posted by chrisamiller at 1:51 PM on July 22, 2017
posted by chrisamiller at 1:51 PM on July 22, 2017
Don't forget to budget for module mounts, 'cos you don't want them flying around when it gets windy.
Many really cheap charge controllers/inverters produce huge quantities of radio interference unless you shield them very carefully.
posted by scruss at 1:54 PM on July 22, 2017 [1 favorite]
Many really cheap charge controllers/inverters produce huge quantities of radio interference unless you shield them very carefully.
posted by scruss at 1:54 PM on July 22, 2017 [1 favorite]
I don't know what the power consumption for a normal minifridge is like, but I bet you could run a super-insulated fridge off it - either a DIY version or a commercial one.
Fridges tend to be in constant use and are working hardest during the day when you have sun, so that will minimize losses from storing energy in batteries. (Though maybe some batteries would do better with a full charge-discharge cycle instead of a pass-through setup?)
posted by sibilatorix at 2:07 PM on July 22, 2017
Fridges tend to be in constant use and are working hardest during the day when you have sun, so that will minimize losses from storing energy in batteries. (Though maybe some batteries would do better with a full charge-discharge cycle instead of a pass-through setup?)
posted by sibilatorix at 2:07 PM on July 22, 2017
You don't necessarily need an inverter if you stick with 12V DC (direct current) devices like those RV items, computer fans, the battery charger I mentioned, etc. Inverters are only needed for AC (alternating current).
Batteries, and wall-wart type transformers, and solar panels, output DC. Anything that uses a battery uses DC, and anything that will run off car power uses DC, and a lot of other devices also.
Those wall warts are for making DC devices work with your AC house power - and they get hot when you use them, because not all the power in your house AC is actually going into the devices.
The fan is my favorite, really useful as I work at home, and very easy (and low risk) to set up.
Charging your phone is also trivial with the right charge controller. Again, no inverter needed.
posted by amtho at 2:13 PM on July 22, 2017 [1 favorite]
Batteries, and wall-wart type transformers, and solar panels, output DC. Anything that uses a battery uses DC, and anything that will run off car power uses DC, and a lot of other devices also.
Those wall warts are for making DC devices work with your AC house power - and they get hot when you use them, because not all the power in your house AC is actually going into the devices.
The fan is my favorite, really useful as I work at home, and very easy (and low risk) to set up.
Charging your phone is also trivial with the right charge controller. Again, no inverter needed.
posted by amtho at 2:13 PM on July 22, 2017 [1 favorite]
Keep fire hazards and insurance claims in mind with all this. If electrical stuff is not up to code and you have a fire, they'll use it to deny liability.
Mostly what you're proposing usually isn't terribly practical if your goal is saving money. It's great if you don't have access to a grid, but when your house and its contents already exist based around having easy access to AC, having a small amount of DC doesn't typically pay off financially.
You're talking about 400 watts, which technically can run a small mini fridge, but that's assuming perfect output from the panels (and doesn't help at night). Does adding a mini fridge actually solve a problem in your life?
Once you add batteries, that's more expense and they have to be maintained properly or they can be dangerous as well.
Charging laptops and devices is an option but the actual cost of doing so on the grid is probably low enough that it would take a very long time to pay off the cost of the panels.
posted by Candleman at 3:04 PM on July 22, 2017
Mostly what you're proposing usually isn't terribly practical if your goal is saving money. It's great if you don't have access to a grid, but when your house and its contents already exist based around having easy access to AC, having a small amount of DC doesn't typically pay off financially.
You're talking about 400 watts, which technically can run a small mini fridge, but that's assuming perfect output from the panels (and doesn't help at night). Does adding a mini fridge actually solve a problem in your life?
Once you add batteries, that's more expense and they have to be maintained properly or they can be dangerous as well.
Charging laptops and devices is an option but the actual cost of doing so on the grid is probably low enough that it would take a very long time to pay off the cost of the panels.
posted by Candleman at 3:04 PM on July 22, 2017
You can't run a fridge reliably off that. You can charge batteries. I'd stick to that for indoor use. And it's good for outdoor use, pumps are relatively low energy and you can power a pump for a pond or irrigation or to heat raised beds using a solar heater to heat water you run through the beds with a solar pump. Fans use a lot of power, I wouldn't plan on running fans much off your set up.
posted by fshgrl at 6:04 PM on July 22, 2017 [1 favorite]
posted by fshgrl at 6:04 PM on July 22, 2017 [1 favorite]
there's another article here, where he makes the point that running DC appliances directly off of your battery-saved DC power saves you about 30% (compared to converting DC to AC, then plugging in an AC-to-DC wall wart). computers, cell phones, and LED lights all use DC power.
How to Get Your Apartment Off the Grid
posted by ivan ivanych samovar at 7:11 PM on July 22, 2017 [2 favorites]
How to Get Your Apartment Off the Grid
posted by ivan ivanych samovar at 7:11 PM on July 22, 2017 [2 favorites]
DSL/Cable modems and wireless routers are relatively low-power, can be run from DC (often 12V), and are steady, predictable loads. Bonus: if they're off-grid, you still have internet access when the power goes out (assuming the phone or cable lines are not down, too). No inverter needed, though an inverter would be a bit easier. You would just plug in the devices' existing AC adapters instead of figuring out how to make cables to go from your charge controller/battery setup to the jacks on the devices.
In a similar vein: smart home hubs, voice assistants, media devices, home servers, and other techy things.
posted by whatnotever at 9:57 PM on July 22, 2017 [2 favorites]
In a similar vein: smart home hubs, voice assistants, media devices, home servers, and other techy things.
posted by whatnotever at 9:57 PM on July 22, 2017 [2 favorites]
Of interest? $200 solar self-sufficiency — without your landlord noticing. Building a solar micro-grid in my bedroom with parts from Amazon, from Hackernoon.
"I turn the inverter on when I get home to use AC lights and charge the Macbook through the power brick, and turn it off before I go to bed to avoid energy drain. My phone’s USB (which is direct current) can charge all night straight through the solar controller itself (which has USB ports) and doesn’t require the inverter. My laptop is a DC device and could be charged straight off the 12V battery, but I found it easier to just charge it with the AC power brick through the inverter."
posted by MonkeyToes at 4:16 AM on July 27, 2017
"I turn the inverter on when I get home to use AC lights and charge the Macbook through the power brick, and turn it off before I go to bed to avoid energy drain. My phone’s USB (which is direct current) can charge all night straight through the solar controller itself (which has USB ports) and doesn’t require the inverter. My laptop is a DC device and could be charged straight off the 12V battery, but I found it easier to just charge it with the AC power brick through the inverter."
posted by MonkeyToes at 4:16 AM on July 27, 2017
This thread is closed to new comments.
Let's say you buy 400W of panels for about $400, a deep-cycle battery for $100, an inverter for $100, and a charge controller for $50. Call it $700.
Let's also assume you live somewhere in the middle of the US and you get about 5 kWh of solar radiation per square meter every day. Assuming your panels add up to about 2.5 m^2, and they're about 20% efficient, you'll be able to source about 2.5 kWh of energy from them a day, limited by how much you can store in your battery.
Before looking at specific appliances, what's the payback period on this? Assuming you use all of the solar energy every day, you'll be able to shave 912 kWh/year off your power bill. At $0.14/kWh, that's about $125/year. You probably won't realize that savings because you won't use all of the energy every day, but that might be a good ballpark upper bound. At that rate, you'll pay off the system cost in about 5.5yr.
To my eyes, that savings isn't quite worth it – I would probably wait a little while and buy a larger system where you can realize some economies of scale and sell power back to the grid. But if this is more of a learning project than a money saver for you, it could definitely be fun.
posted by aaronbeekay at 12:50 PM on July 22, 2017 [1 favorite]