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Power Build

Hobbyist Renewable Energy? 607

Posted by ScuttleMonkey
from the green-to-go-green dept.
vossman77 writes "I was looking into renewable energy from a hobbyist perspective, maybe generating a few watts of solar or wind power, just to reduce my electric bill. But upon further review, I found out that I need a special grid-tied AC inverter that shuts off when the grid turns off (for worker safety reasons) and makes the current in-phase with the grid. These two additional features, over the cheap inverters sold at department store, make the cost upwards of $2000, but support more watts than I need. While this is fine for large-scale projects, it is out of range for a small scale hobbyist. A Google search came with some home-brew hacks at best. So, are there any Slashdotters out there doing small-scale renewable energy projects with grid-tied systems? What are other options for the hobbyist to play around with renewable energy, other than charging a cell phone?"
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Hobbyist Renewable Energy?

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  • by Anonymous Coward on Friday May 02, 2008 @12:20PM (#23276842)
    use an induction motor as used in commercial windmills

    Induction motors can be used as generators
    and they automatically shut down when grid is down.

  • by spotlight2k3 (652521) on Friday May 02, 2008 @12:23PM (#23276874) Journal
  • by stox (131684) on Friday May 02, 2008 @12:25PM (#23276890) Homepage
    Sorry, a home brew solution won't cut it. The power company won't allow a non-certified piece of equipment to be hooked up, nor will your homeowners insurance. The liabilities are simply not worth the savings.
  • by Anonymous Coward on Friday May 02, 2008 @12:26PM (#23276906)
    You don't have to grid-tie to have solar power.
    You could run the energy to a bank of batteries.

    Does this mean your whole house is powered? No, but you could run quite a few things off of that bank of batteries, like a PC:,1685.html
  • by TigerNut (718742) on Friday May 02, 2008 @12:28PM (#23276934) Homepage Journal
    Tying into the grid (i.e. anything where you need to dig into the hardwired electrical system of your house) legally requires a development permit and inspection. In my location (Calgary) the homeowner can pull a permit and do the work themselves, provided it gets inspected after the fact. However, I'm pretty sure that installation of non-certified (UL or the Canadian equivalent) is strictly forbidden.

    The consequence of doing things like that without permits and/or inspection is that on the off chance that there was ever a problem, you'd be financially liable for any consequences.

    There are opportunities to do strictly off-grid stuff, or at least you could keep to the low-voltage side of things. If you have a UPS for your computer or phone/router infrastructure, you could put up a solar panel to keep the standby battery charged. To the extent that the system runs off of DC power, you could supplant the power drawn from the grid with a panel, and reduce your electrical footprint that way.

  • Re:go 12 volt (Score:4, Informative)

    by MoOsEb0y (2177) on Friday May 02, 2008 @12:40PM (#23277100)
    Yes. []
  • Re:go 12 volt (Score:3, Informative)

    by TypoNAM (695420) on Friday May 02, 2008 @12:46PM (#23277190)
    LEDs will work perfectly fine with AC, but they'll blink/flicker at the 60Hz or so of the alternating frequency (because LEDs are diodes, as in they only allow current to flow in one direction). Now if you hook up LEDs in a series make sure that the cathods ends connect to the non-cathods ends which I hope nobody is actually doing a series of LEDs instead of parallel because if you have say three LEDs and they consume 3 volts each, you'll need 9 volts to power them to get full light output.
  • by bcrowell (177657) on Friday May 02, 2008 @12:48PM (#23277230) Homepage
    If you have a pool, there are systems you can buy that run your pool pump off of photovoltaics. Pool pumps are infamous energy hogs, and you can run a pump off of DC, which cuts out the inverter. Getting rid of the inverter improves efficiency and cuts the cost of the project. This is not a grid-tied system.
  • by zogger (617870) on Friday May 02, 2008 @12:48PM (#23277236) Homepage Journal
    Conventional sources have had decades of government subsidies. For example AFAIK, there isn't a single commercial nuke plant out there (US) that has all private insurance, the government insures them for big failure, plus the government picked up the billions of dollars (in 1950s and 60s money) tab to even develop the things in the first place. Centralized magecorpos grid electricity relies on land seizures with no compensation to the owners for powerlines. buncha stuff. Back in ye olden days (1920s) they *forced* people to give up their early model windchargers (there was a really robust market then too) if they wanted to add into the grid. Basically killed that market off on purpose to prop up the fatcats who wanted to send you a bill every month forever. Anyway, here's an overview site: []

    So, as a corollary, if conventional sources were really cheap, they wouldn't have needed subsidies, and decentralized "green" power would have done much better (rent, or build equity and own, two choices there)
  • Re:go 12 volt (Score:5, Informative)

    by Technician (215283) on Friday May 02, 2008 @12:49PM (#23277250)
    You can try converting parts of your house to 12 or 24 volt, which would negate the need for expensive inverters and whatnot. All you'd need is a simple charging circuit for a battery (could be as simple as a diode) and then feed the 12/24 volt lights straight off it.

    This is a common mistake and is only good for very low power stuff. In picking a wire size people often think going from 120 volts to 12 volts only involves the math of supplying a wire 10X larger to handle the current without overheating. In a 120 volt application, you are permitted a 5% voltage drop. This isn't much as 5% of 120 volts is only about 6 volts. No big deal when running a 1200 watt portable hair dryer. If you simply size the wire to now do the same thing on 12 volts, you no longer have a 5% voltage drop. At the same current you still have a 6 volt drop with the 10X larger wire but you now lost 50% of your power in the wire. Take a hint from the pro.. Use an inverter. The 10% the inverter lost is made up by the 45% not lost in the wire. Do the math. Engineer the project.

    Either your high draw items (Microwave, toaster, blender, etc) are either within 20 inches of the battery, or you will want an inverter. With an inverter you can use standard appliances. Look for energy effecient ones.

    Another item is to ditch the grid tie for small systems. It goes down with the grid providing no security. Put the critical load on an Outback inverter. It was made just for this application. Small solar, battery maitenance, load transfer to and from solar and battery, etc. You don't have a surplus to sell to the utility, so don't connect that way. Use it to supplimant your load and reduce your total load. As a bonus, you don't have to enter a grid tie agreement with the utility where they buy your power whosale and sell it back to you retail.

    Find Outback stuff here; []

    Disclaimer, I just use it. I am not otherwise involved with this company. The company has grid-tie stuff if you decide you really want it. I don't recommend it except for larger installations. This company has done a great job meeting the market. Their grid tie units are the first that I know of that operate instead of shutting down in the event of a blackout. They solved the number 1 problem with grid tie stuff.. blackouts. []

  • by Roger W Moore (538166) on Friday May 02, 2008 @12:49PM (#23277254) Journal
    Err...not necessarily a good idea. If you lower the voltage your current requirements increase for the same power load. This increases the heating in the cables and thus increases the chance of an electrical fire.

    I'm sure that you can do it safely but you will need far thicker cables than a 240V system and be careful that you have good connections. Plus you will loose 10-20 times more in power transmission than before.
  • by Roger W Moore (538166) on Friday May 02, 2008 @12:51PM (#23277260) Journal
    Sorry that should be 100-400 times more power lost in transmission - it goes as current squared.
  • by Anonymous Coward on Friday May 02, 2008 @12:55PM (#23277312)
    Any inverter you get should be in phase with the grid, since that's the type of power expected by your appliances

    I think you're confusing frequency and phase. Frequency is how often a signal repeats. Phase is what part of that repeat cycle you are on. Think of it like ocean waves; if you specify frequency as a function of distance, you could say something like "One wave exists per five feet of ocean surface", or in more familiar terms maybe "the waves arrive on the shoreline one per second"... in this example, phase would be like putting a floating ball on the surface of the water and asking "ok, what's the height of that ball above or below sea level right now?"

    To continue the analogy, mains and inverter power might both have waves five-feet apart... but that doesn't mean those waves would line up exactly if you superimposed them...

    I assure you, if I take my 12V car inventer, plug it into my car's socket, and compare it to my wall current... it will be out of phase. I'd even be willing to bet if I plug that same inverter up to a 12V bench supply in my house, running off of mains... the inverted signal would still be out of phase with mains.

    What happens when you put two signals on top of each other? Interference. Constructive interference (increasing the signal strength) happens wherever the two signals are in phase. Destructive interference (decreasing the signal strength - in this case the two electric fields meet and cancel within the wire, creating thermodynamic noise out of the electrical energy) happens whenever the two signals are out of phase.

    Basically, then...

    If the inverter is phase-locked with mains (like a grid tie-in inverter will be), you will add your generated power to the mains line (and your meter will credit you for the watt-hours)

    If the inverter is 180-degrees out of phase with mains, you will subtract your generated power from the mains line (and your meter will charge you for it!)

    The real situation of course will be in between the two - some part of the phase loop, you'll be adding, some part, you'll be subtracting. The average case will be, therefore, no overall change (assuming the inverter's phase wanders somewhat randomly - it's most likely not going to be the exact same measure of 60Hz that the electricity company is giving you... thermal effects alone will likely drift it enough on top of that to make it change over time)

    So, just hooking up any old inverter... is useless at best, and a huge fire hazard at worst. And as others have pointed out, non-UL listed equipment will invalidate your insurance, put your building out of code, and make your children grow horns, so DIY seems a bad way to go. A quick search on hobbyist solar and wind power sites reveals that those who publish pricing information on grid tie in inverters generally do charge $2000 and up for mid-to-large systems... and like the OP, I couldn't find published prices for smaller equipment...
  • Re:Renewable fuel (Score:5, Informative)

    by rs79 (71822) <> on Friday May 02, 2008 @12:57PM (#23277330) Homepage
    Your problem is you use too much power. I had the same problem and just unplugged or rplaced everything that was overconsumptive. 700W desktop tower goes away in favouir of 45W laptop. Cordless drill that takes hours to recharge is replaced by a fast charginbh lithium ionh one. etc.

    I cut my power to 1/4 doing this. THEN went solar. Your 30K cost is now 7K.

    The OP doesbn't need a grid tie invertor. That's for selling excess power back to the power company.

    I run a sat receiver by having it plugged into a ups with a ubiquitous 7Ah SLA battery, fully charged, with two 30W solar panels hooked up directly to the battery. It just sits there and works.

    I have lots of solar panels, i just hook them up in lotrs of little autonomous systems than do one thing. Free, and forver (or until some part beaks or the sun stop shining).

    I've got a bunch of these setups for various things with various batteries and inverters.

    I can't for the life of my see how "small scale" and "grid tie" relate at all.

    If you had an 18Kw hydro plant I could see it but...
  • by mollog (841386) on Friday May 02, 2008 @01:00PM (#23277404)
    Off the top of my head, a $100 fan center could shut the power connection when the feed from the power company goes down. Attach a 24V AC transformer to the power company line and wire it to the fan center's controller. Power goes down, circuit opens.

    I can probably fabricate a circuit with an oscillator that syncs up to the 60Hz of power. After that, it's a matter of how to convert from DC to AC. It doesn't seem hard to me.
  • by Ellis D. Tripp (755736) on Friday May 02, 2008 @01:05PM (#23277468) Homepage
    Having a renewable energy system backfeed the grid under normal circumstances is perfectly fine (and lots of fun to see your electric meter spin backwards). It took a lot of effort by system manufacturers and RE hobbyists to get utilities to reluctantly accept so-called "net metering", and allow small producers to sell power back to the utility. But there are very specific requirtements for doing so, including automatic isolation of inverters and a visible, accessible disconnect switch on your house so that you can be physically disconnected is required.
  • by netsavior (627338) on Friday May 02, 2008 @01:07PM (#23277500)
    unfortunatly I am a software developer, so I tend to resist all forms of documentation. Here is my rundown (the setup of my house means I didn't even run any wires through the house so this was so freaking simple:

    Wall unit AC (was what we used before the conversion) is on the back wall of the house) 115v 10,000 BTU unit I think they retail for ~$400-$500 (but we already had it)

    My solar panels were second hand, so they were cheap, they were operating at ~81% their original capacity, so the company sold them to me for less than 1$/watt I have about 1300 watts, and the AC when it is on (it switches off and on throughout the day) it uses up to 875 watts. I got very lucky on the price for the panels, and the additional wiring and stuff, so maybe my $1000 number was not very "honest" maybe double or triple that if you are buying with urgency instead of waiting for a killer deal like I did. The capacitors I use are a cluster of those 2000 Farad Car stereo ones (I know I know it is not the right thing to do but it is the cheap thing to do, and they are firewalled). They are before the inverter, to feed it continuous power. And seriously that is about it, I mean wiring solar panels is about like wiring batteries (parallel banks of your desired series of voltage), then do the same with the capacitors, then the inverter, which can be bought for cheap from a Truck Supply store (some bigrigs use them, to run things like 1000 watt Routers, jackhammers, etc) From there, my inverter is mounted on my back porch (near the A/C unit) and the A/C is plugged directly into that (it has A/C outlets in it).

    The roof vents are just seperate left over panels, with DC fans that run directly wired to the panels.
    So basically I bought cheap ass panels, some consumer electronics, and put it all on my roof/porch. Doesn't sound as glorious when I put it that way, but in all I have almost made my money back in energy savings as compared to the bills from last year... and that is significant for me since I really only did it for fun. I think I will be in the black in August of this year, and the gear is still going strong, so hopefully it will be an actual cost savings.
  • by smellsofbikes (890263) on Friday May 02, 2008 @01:18PM (#23277656) Journal
    I'm curious about this, because I've paper-designed some similar things -- trying to use car alternators as generators by driving the field coil with AC from the grid, so the output is automatically synchronized with the grid. The problem is that since you're feeding power back into the grid, how do you detect that the grid's down? coz it won't be if you're feeding power back into it. Likewise, you seem to be doing the same sort of thing: how is your fan controller going to know whether the electricity it sees is from the local coal plant or from your little cogeneration setup? If your setup works, I'd love to know how and why, because I'd love to build something like this. I just can't figure out how to get it to work without resorting to ugly, dangerous things.
  • by jsimon12 (207119) <> on Friday May 02, 2008 @01:21PM (#23277696) Homepage
    Check in old issues of Home Power Magazine []. There were articles where people were setting up grid tie solar setups on a small scale safely without some of the expensive utility work. The articles were titled Gorilla Solar.
  • Re:go 12 volt (Score:4, Informative)

    by DerekLyons (302214) <fairwater AT gmail DOT com> on Friday May 02, 2008 @01:46PM (#23278060) Homepage

    Another item is to ditch the grid tie for small systems. It goes down with the grid providing no security. Put the critical load on an Outback inverter.

    The purpose of the grid tie isn't to provide security or to support a critical load. The purpose of a grid tie is to prevent the home power system from powering the grid when the grid goes down - if you pump power into the grid when it's down, you risk the health and life of workers trying to restore the grid.
    For example - A line went down that supplies my road. Before workers started repairing the line, they isolated it at the substation, rendering it safe. Without a grid tie the line remains powered from the home systems - which can kill.
    If you have a critical load, put it on a UPS. Don't skip the grid tie unless your home system is entirely isolated from the grid.
    Seriously, there's times to home brew and jury rig and save a few bucks, this isn't one of them. Do it right and don't put lives and property at risk.
  • by Thelasko (1196535) on Friday May 02, 2008 @01:49PM (#23278102) Journal
    A company called Solatube makes pre-made solar powered attic fans []
  • Re:Renewable fuel (Score:3, Informative)

    by TooMuchToDo (882796) on Friday May 02, 2008 @02:10PM (#23278398)
    Selling power back is indeed a side effect of grid tie. Please remember the following: A grid tie system disconnects itself from the grid when a power loss is detected. This is the most important reason to get a grid tie inverter if you intend to have it wired to the utility power lines. If this is not done, you'll electrocute line workers when they're repairing a downed wire
  • by Roger W Moore (538166) on Friday May 02, 2008 @03:05PM (#23279032) Journal
    Heat = Wattage which is Voltage * Current

    Common mistake: voltage here is the potential drop over the resistance, which in this case is the wire. Since power is V times I, and this is typically what needs to remain constant for the device, reducing V by a factor of 10 means that you must increase I by a factor of 10. This will also increase the potential drop along the cable by a factor of ten and so you have 10 x 10 = 100 factor increase in the heat. A better formula to use is P=I^2 R in this case.

    Or do you think Americans have double size wires in the streets/homes compared to Europeans?

    No, you have lower power limits on your appliances. For example in the UK it is easy to buy a 3kW kettle or electric fan heater since the current drawn is ~13A which is the mas for a UK plug. In Canada and the US you can't get much over 1.5kW (at least when I looked) and even then the flex gets warm to the touch unlike in Europe. I first noticed this with electric lawn mowers. In the UK these things are great over here in Canada I made the mistake of getting one not realizing that the power was roughly half of the European models - as a result it is useless at cutting a lawn.
  • Re:go 12 volt (Score:2, Informative)

    by bluelip (123578) on Friday May 02, 2008 @03:14PM (#23279142) Homepage Journal
    DC Power? Edison would be proud! :)

    I'm all for it. It's waste to keep converting from AC-DC.

    Let's get something standardized.
  • by Iron Condor (964856) on Friday May 02, 2008 @03:42PM (#23279532)

    But for a small scale system, the ability to tie in to the grid is essentially useless.

    It is amusing how easy it is to spot people who have never actually thought about the matter by comments like these.

    The purpose of grid-tie is to avoid having to futz around with batteries. Batteries need charge-controllers, they need to be serviced, they have a finite life-time and they're either over- or under-speced because no two weeks will ever have the precise same power.

    So you used the grid as your battery. It's as simple as that. You over-produce in the afternoon (assuming solar -- maybe in the evening for wind)? Just feed it into the grid. You don't produce at all in the night? Just take it right back from the grid. Here in the pacific southwest, loads peak in the afternoon when everybody runs an AC - so the power company will be more than happy to receive your added input. And loads are lightest around 3am, so they'll be just as happy to "give you back" your electricity then. Actually they're giving you cheap power in exchange for expensive power -- but in return you don't have to think about batteries at all.

    In addition, with a grid-tie you're as scalable and as granular as you want to. Got some bucks to spend on a Panel this week? Great, you're now producing 5.37% of your household's electricity over what you were doing before. Without having to run new circuits or worry what consumer in the house will run on 5.37% of your total consumption. Without the grid-tie, you either produce all the electricity your fridge needs or it'll die. Or you change plugs whenever it's cloudy.

  • Re:Renewable fuel (Score:3, Informative)

    by TClevenger (252206) on Friday May 02, 2008 @05:11PM (#23280300)
    I bought a DeWalt 12V drill a couple of years ago, and the gear stripped out, so it only goes on low speed now. My dad is an electrical contractor, and has moved away from DeWalt due to problems he's found. DeWalt used to make great stuff, but since they were bought by Black & Decker, I think the quality has gone downhill.
  • Re:Really, $2000? (Score:3, Informative)

    by TigerNut (718742) on Friday May 02, 2008 @05:34PM (#23280468) Homepage Journal
    It's got nothing to do with ignorance. A live wire looks the same as one that has zero potential. Electricians and line workers take precautions, but they also necessarily make basic assumptions about How Stuff Works: I trip a breaker between the source and the load, and after that I expect the load side to be dead. Not generating random amounts of power depending on the wind or sunshine.

    What if the main line supplying your grid-tied juryrigged safe-to-you system goes down for an unrelated reason, in the middle of the day while you're away? How will the linesman shut down your end so they can fix their problem?

  • by sjames (1099) on Friday May 02, 2008 @09:39PM (#23281830) Homepage

    These grid tie inverters are no more complicated than a computer power supply which will cost you about $0.08/watt.

    You realize that a grid tie inverter is the opposite of a computer power supply don't you? They don't even have to consider phase, their output doesn't HAVE a phase.

    Meanwhile, the non grid-tie inverters often output stepped voltage rather than a sinewave (and so harmonics). It's cheaper by far and good enough for many applications, but not for feeding into a big iron core transformer. They don't care about phase either. They just need to be somewhere close (ish) to 60 Hz.

    They may still be overpriced, but not by 25 times as you suggest.

  • by kesuki (321456) on Saturday May 03, 2008 @06:48PM (#23287328) Journal
    tying into the grid is nice, if you're going to be producing enough power to light up 5 homes with an insanely large wind turbine, but this guy was talking about a hobbyist sized deal, where he's gone wrong is thinking he needs to tie in the grid at all. Batteries, cheap lead acid car batteries, they're really easy and cheap, and for a small project you might only need one $25 dollar battery and some cheap electronics that are quality but not certified for tying in the grid... then you can run a few lamps, maybe a refrigerator, maybe a tv, maybe even a computer... if you can predict the amount of energy produced all day, and the amount consumed, you can design the setup so the battery never dies, and always stays charged up...

    why tie into the grid, when you're only producing enough wattage to power a single light bulb? eg: a home made windmill with a used car alternator.

    why would you even consider tying into the grid instead of using a recyclable efficient lead acid battery?

    as an example a nice DIY windmill might cost you $200 for a 16' pole, $30 for a used alternator, and $10-20 for wood and screws, and $40 for a new lead acid battery, plus $20-40 for wiring and electronics parts all told a DIY windmill for under $350 again it will probably only run a couple lamps, but the whole project is DIY

    why tie into the grid when they sell lead acid batteries so cheap?

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