A happy clam needs power!

SystemSystem Posts: 2,511 admin
Hey everyone,

My fiance and I are seasonal nomads in the high Sierra. He is a professional rock climbing guide and I am a biologist. We got tired of two of us camping out of a single Honda CRV in the seemingly endless late winter we had this May and June in the Sierra and broke down and bought ourselves a 10-ft clamshell tent trailer thingy we call, the Happy Clam.

We are simple, salt of the earth people with a tiny trailer and a movie habit. We want to set up a simple, yet effective solar power system for the clam that is enough to power a laptop, a stereo (with surround sound and NPR), and charge cell phones while we're off the grid.

We would like to install 1 12-volt deep cycle battery (does it matter if we get a gel or traditional battery?). How many watt panel would you recommend? Is there a kit out there anyone might recommend?

The system will primarily be used for a few hours during the evening, with the occasional rain day with prolonged use. I've been doing lots of research and price comparison, but I'm a little overwhelmed with all the choices ranging from seemingly too little to way too much. Any ideas and assistance anyone has would be most welcome. We would like to keep the budget $300 or less if possible. We figure we need the panel, a regulator, a battery, and an inverter. Thank you for your help, solar gods.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: A happy clam needs power!

    Welcome to the forum.

    If you want to stay happy as clams you need to design your system right. That means getting some real numbers for your potential loads. The best way to do that is to spend about $30 on a Kill-A-Watt meter and start taking some measurements of your equipment before you're out in the middle of nowhere.

    This will give you two critical numbers: the maximum Watts you will use at any time (which is key to getting the right inverter) and the number of Watt hours you will use daily (which is key to sizing the battery bank).

    Whatever you do, don't just start buying stuff and hope it will somehow all work out. That's about 80% of the questions around here: "I've got ..." followed by lamentations of how it doesn't do what is needed. It's very sad to see a clam cry.

    I can empathize with your movie addiction. Unfortunately TV's tend to use 100-200 Watts (depending on size and settings) over a 2 hour movie that's quite a chunk of power.

    The other problem is your budget. I'm sorry to say it is extremely doubtful that $300 will buy you any usable amount of off-grid power. You'd have to hit some really amazing deals on used equipment.

    Mounting panels on a clam could be difficult too. Fortunately they hold still fairly well so you have lots of time to work on it. :p
  • The Only SargeThe Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: A happy clam needs power!

    Hi Sally and welcome.

    I am just settling into my first system and can sympathize with the "confusion".
    These folks were a tremendous help for me.
    I'll share what I learned.

    First understand how many watts the various components are going to consume. Then how many hours you wish to run them.

    So using my own watt usage study I found my surround sound system pulls 80 watts. My laptop 85 watts, a 13 inch LCR TV w/DVR pulls 65 watts. So I add those up and get 230 watts. If I wish to use all the devices for 4 hours I would have 920 watts needed.

    To produce those watts I would need a minimum of 76 amp hours.
    So I would have to double that because I never want to run my battery below 50%.
    So I need 153 amp hours of battery.
    To charge the battery I would need a minimum of 5%-10% of my battery amp hour capacity. So I need a minimum of 15-16 amps of PV. Say 2 Kyocera 135 watt panels would give me roughly 12-15 amps.
    I would need a minimum of 4 hours of sun a day to generate the required power.
    4X270=1080.
    A 20 amp controller.
    A 300 watt inverter of the True Sine Wave variety. (300 watt minimum).
    Then throw in your fuses/wiring.

    So cost wise...
    (2) Kyocera 135 watt panels @$500 (tax and shipping)=$1000
    1 Controller $200
    1 inverter $250
    Wire/Fuses $200

    So I think we have blown your budget. And your "Happy Clam" collapsed under the panels :)

    Not to worry!

    Saving watts is cheaper than making watts. Look at a smaller sound system that utilizes less watts. Maybe you can use the laptop less that 4 hours etc. Then you could reduce your power requirements and have less solar requirement.

    My response is not all inclusive for sure but the basics that got me asking the right questions and thinking.

    I hope this helps you.
  • The Only SargeThe Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: A happy clam needs power!

    Dayum them Canadian guys can type fast! ^^^^
  • System2System2 Posts: 6,290 admin
    Re: A happy clam needs power!

    Just need enough power to keep the laptop going, no TV.
    Thanks for your thoughts.

    Adding a stereo is an afterthought so right now we just need to charge laptop and cellphone which are relatively low, laptop ~3.4 amps according to manufacturer, both cell and laptop regularly charge off car battery and inverter, so I know it's not a huge draw. Our other option is to install a solanoid off the car battery which has worked fairly well in the past with our 1984 toyota chinook.

    We want to go green, thanks, all the clams are doing it.
  • The Only SargeThe Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: A happy clam needs power!
    Just need enough power to keep the laptop going, no TV.
    Thanks for your thoughts.

    Adding a stereo is an afterthought so right now we just need to charge laptop and cellphone which are relatively low, laptop ~3.4 amps according to manufacturer, both cell and laptop regularly charge off car battery and inverter, so I know it's not a huge draw. Our other option is to install a solanoid off the car battery which has worked fairly well in the past with our 1984 toyota chinook.

    We want to go green, thanks, all the clams are doing it.

    I am sure the bigger heads will be along shortly :)
    Let me approach this from a different angle...
    Say a 45 watt panel http://www.solar-electric.com/spm040.html
    A controller http://www.solar-electric.com/ss-10.html
    A 300 watt inverter from WalMart
    A lead acid wet deep cycle battery around 60 amp hours

    This setup will get real close to your $300 budget and give you roughly a couple hundred watts to burn daily.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: A happy clam needs power!

    You know I think this is the third time today I've explained that the information provided by manufacturers regarding their equipment's power consumption is something akin to science-fiction. :p

    3.4 Amps @ 120 Volts would be 408 Watts. A desktop doesn't draw that! Is that Amp figure for 12 VDC? That I can believe.

    So if the main goal is just to keep the laptop and cell phone going and you can stick with 12 VDC you can save greatly. Again, it's all about the loads. Without knowing how minimalist you can be it's hard to judge.

    I personally know of a 17" laptop that draws 35 Watts maximum. That's pretty good. On 12 Volts that would be about 3 Amps. Run it for a two hour movie and you have 6 Amp hours.

    For about $60 you can get a 35 Amp hour AGM battery: http://www.solar-electric.com/unba35amseag.html That's up to 200 Watt hours: like running the laptop for 5 hours. It would require at least 32 Watts of panel to recharge. In the desert heat you'll lose more power, so perhaps a 45 Watt panel like this: http://www.solar-electric.com/spm040.html and about the simplest charge controller you can get: http://www.solar-electric.com/sg-4.html

    Unfortunately the panel alone is nearly $200, but depending on how you can do for yourself with wire and fuse it just might squeak in near the budget limit. Not much margin for error. And no 120 VAC supply either; you'd have to be able to do everything off 12 VDC.

    But that is only a suggestion for example purposes, not a specific recommendation. I don't recommend you drain your starting battery either; they're not made for it.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: A happy clam needs power!

    Not bad, Sarge. :D
    But the 45 Watt panel wouldn't do much for 60 Amp hours (especially in hot climate) and the Wal*Mart 300 inverter is bound to be a MSW clunker. If they can skip the inverter part altogether it's even better.
  • The Only SargeThe Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: A happy clam needs power!

    Thanks Coot....I need to take your speed typing class next I guess.
  • The Only SargeThe Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: A happy clam needs power!

    And for the record I dated a Biology major for 2 years. That girl had more extension cords and power strips in her apartment than Home Depot man. I just cannot see the 12v thing going on here. Mebbe I'm wrong though........................
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: A happy clam needs power!
    Thanks Coot....I need to take your speed typing class next I guess.

    You only need two fingers ... and forty years' experience. :p
  • BB.BB. Super Moderators, Administrators Posts: 28,599 admin
    Re: A happy clam needs power!

    Several ways too go...
    1. Measure your loads, design the system
    2. See how big a 12 volt battery you can fit, design system around battery
    3. $300 and try for as much bang for the buck
    All are perfectly valid ways of designing your system. However, they may not meet your needs--So do you have backup and/or are OK going "without" when the panel is not able to supply the power needed.

    There are inexpensive panels out there--many are thin film which require ~2x the surface area as crystalline panels to gather the same amount of sun (thin film tends to be less efficient). So--you may not have an area large enough to even install/store such an array.

    In general, going off-grid with solar is a game of using as little power as possible (conservation). That includes getting efficient devices (smaller laptop computers, perhaps using the lap top or portable DVD player for videos, smaller radio, etc.).

    Lets take some guesses at what you might want to power:
    • laptop computer 30 watts * 4 hours a day
    • Lighting: 10 watts * 4 hours (LED, etc.)
    • Radio: 5 watts * 4 hours a day
    • total: 30w*4h + 10w*4h + 4w*4h = 176 WH per day
    Say a 12 volt lead acid battery running a small 120 VAC inverter (85% efficient). Assume 2 days of use and 50% maximum discharge:
    • 176 WH per day * 2 days * 1/0.50 max discharge * 1/12 volt battery = 59 AH battery @ 12 volts
    Assume that you will be out camping in reasonable weather--around 4 hours of sun per day. Assume 52% end to end efficiency (panels, charge controller, battery bank , AC inverter):
    • 176 WH per day * 1/4 hours per day sun * 1/0.52 sys eff = 85 Watt panel
    Double checking the panel size against the Battery Bank size--We look for ~5% to 13% rate of charge (and assume 0.77 derate for solar+charger efficiency):
    • 59 AH * 14.5 volts charging * 1/0.77 derating * 0.05 rate of charge = 56 watt minimum array
    • 59 AH * 14.5 volts charging * 1/0.77 derating * 0.13 rate of charge = 144 watt (cost effective) maximum array
    So--For your system, using my above guesswork for numbers, you are looking at a ~85 to 150 watt solar array with a ~59 AH @ 12 volt battery bank.

    Some other details... You can be a bit more efficient if you do not use an AC inverter... However, some DC devices do not like the wide voltage range an off grid battery bank can present to the loads. A car is around 12.5 to 14.2 VDC. A normal off grid system is ~10.5 to 15+ VDC. On occasion, some computer adapters and other devices have failed to operate or even just plain failed. But--for a few devices (cell phone, laptop, radio, LED lighting, going straight 12 VDC may be fine--just turn of 12 VDC power when "equalizing the battery bank" (charging >14.5 volts, typically once every two months).

    Second, I did the above assuming a standard 12 VDC flooded cell deep cycle battery (not car battery, not marine battery). They do need to be topped off with distilled water every ~2 months (or filtered rain water).

    AGM batteries are much nicer (cleaner, spill proof, better electrical specifications)--However, they do cost 2-3x the cost of a flooded cell battery.

    For the first time off-grid power users--typically it is not a bad idea to start with a flooded cell battery first. Most people accidentally "kill" their first battery in months or 1 year--instead of the 3-5 years you should get from a small battery.

    How much will this all cost... Probably 3-4x your $300 proposed budget.

    So--we can look at it the other way--what can be purchased within your needs...

    But, I would like to understand your power requirements more first. (kill-a-watt meter--used to measure how much power your 120 VAC appliances use).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bluewickedburnerbluewickedburner Solar Expert Posts: 78 ✭✭✭✭
    Re: A happy clam needs power!

    Or try this:

    We're talking about a 10' clamshell here. First, you don't need brand new shrink wrapped anything. While it is nice, it isn't necessary.

    2 135 watt panels- maybe $350, used, no tax no shipping, pick them up. Just look around. You can get the mounts included. Easy to test.

    Inverter - practically free if you look around on craigslist, RV people get rid of them all the time and not bad stuff- Magnum etc. About $50-$100 tops. Easy to check to see if it works. A MSW inverter will work just fine for what you're doing (a radio, a TV and a laptop right?)

    Use the laptop to play movies on DVD or get a video adapter for it for broadcast stuff (about $75) and you can even record TV from it. (still in that 10' clamshell right?) Plug the output from the laptop into the surround sound. a 17" laptop of recent manufacture will use about 45 watts.

    Get yourself some nice surround sound speakers made for the laptop, maybe 20-30 watts (10' clamshell right?) Place the speakers in the best place and you probably won't notice the difference.

    If the screen on the laptop isn't big enough, get a 20-24" led display with TV tuner about 25-35 watts. You can buy them all over the place. Again, craigslist is a good place and easy to test out. Computer nerds are selling super nice LED displays with TV tuners built in for under $175 all day long. That eliminates the TV tuner card if you want.


    So we have 2 135 watt panels used about $350.
    A TV tuner card for $75
    An inverter for about $75 in the 300-1000 watt range with a charger.
    Wire and fuses, maybe $50. For $200 you can wire a 45" motor coach for solar.
    Used solar controllers are a dime a dozen. Same place you ask for that inverter. Most RVers are just looking for an excuse to upgrade and will dump their nice controller for peanuts. Ask.

    Get your wire from an electrical supply house. They have cut offs for cheap. Thinking a little outside of a retail store here. Just ask, it works. Lots of times they can get you what you want for nothing- again, talking a 10' clamshell here. Tell them what you're doing, you'll be surprised.

    Batteries? Used, not new. Plenty of RV people out there will gladly sell you their perfectly good 12 volt marine/rv batteries for the same price as a core charge because they are upgrading. Ask around. We're talking like $30 for two. Not true deep cycle but guess what? They'll work fine for you.

    The thing to keep in mind is that you are using a 10' clamshell, doing things for some roughing it and don't need store bought anything. That is the whole idea of inexpensive.

    So what if the batteries only last maybe a year, they were 30 dollars! A true sine wave? Not unless you are running laboratory equipment but not needed for a radio, laptop and TV for sure.

    Think 10' clamshell.
  • BB.BB. Super Moderators, Administrators Posts: 28,599 admin
    Re: A happy clam needs power!

    Out in the middle of no-where without spares... I would humbly suggest a TSW inverter.

    Depending on the size of the laptop--I have larger laptops that will run OK on MSW. And small (net books) with different power cord bumps that can overheat on MSW (non-power factor corrected). I also have a 8" or so DVD player and its 120 VAC adapter also overheats on MSW.

    Again--trying to provide a range of hardware.

    And I agree with bluewickedburner, if you can pick up stuff on Craig's list nearby for a good price--why not.

    Be aware that larger panels (typically >~135 watt) may be more costly to ship as they are so large/difficult to pack. Anything you get over the Internet, check out the price delivered to your door (with insurance for solar panels--they are just large pieces of glass in the end).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: A happy clam needs power!

    Thanks all for your replies.
    I think we are envisioning a much smaller and simpler system than what most folks are trying to do.

    We really just want to use the laptop for a few hours. Its own battery lasts 4 hours.

    We currently manage just fine just charging of the inverter while driving. Just want to supplement.

    No lights
    no tv
    no dvd
    no radio

    just laptop in the back of a rolling tent.

    Thanks
    SS
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: A happy clam needs power!
    Thanks all for your replies.
    I think we are envisioning a much smaller and simpler system than what most folks are trying to do.

    We really just want to use the laptop for a few hours. Its own battery lasts 4 hours.

    We currently manage just fine just charging of the inverter while driving. Just want to supplement.

    No lights
    no tv
    no dvd
    no radio

    just laptop in the back of a rolling tent.

    Thanks
    SS

    Like Thoreau, eh? :D
    So step one: can your needs be met with just 12 VDC? That eliminates the expense and power drain of an inverter. Many laptops have 12 Volt "car adapters" which may (or may not) work with a solar recharged battery. They don't use a lot of power either: <40 Watts usually.
    Step two would be how long you need to supply the power for. 40 Watts for 1 hour is 40 Watt hours, or less than 4 Amp hours on 12 VDC.

    If you have an existing remote power system of any kind that you wish to supplement with solar charging, please describe it in as much detail as you can. If it is the vehicle system, I'd recommend an entirely separate set-up for your remote power; you don't want to risk not being able to start the engine in the middle of nowhere. I know; I live in the middle of nowhere!
  • System2System2 Posts: 6,290 admin
    Re: A happy clam needs power!

    Thanks guys, for all the help.

    We'll see what we can come up with. You've definitely provided plenty of information about potential loads, etc.

    We've done without for a long time and it works fine, so any system we put in would be an upgrade.

    We'll keep you posted on what we come up with.

    cheers,

    SS
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