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Simple off grid electric
- Thread starter garandman
- Start date
Working on it right now, I need to get 2 solar panels and the charger controller. Using LI-IO batteries and a 1000 watts pure sine inverter. Will post more pics once it's up and running.
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I have been curious about the systems that "plug in" to reduce your electric bill. A couple years ago a solar panel installer/electrician was on a job site with me and said the technology "wasnt there yet" but that it was really close. This guy was a riot, installing a system that was well over $10g's on this customers house while telling me it wasnt a worthwhile investment to save money yet.
ToddDubya
NES Member
It's the .gov subsidies and rebates that make it worthwhile. My buddy had a system installed and we calculated it'll take 7 years to break even. After that he's in the black. In the meantime he's paying less a month for the loan + electricity than he was paying before for just electricity.
If you're looking to build a solar system you want an MPPT charge controller, not a PWM controller. Simply put the PWM controller chops the voltage down from what comes out of the panel(s) to a set output voltage resulting in significant losses, and does nothing if the voltage drops below the set output voltage. The MPPT systems constantly adjust to the input voltage to allow it to charge efficiently with just about any output from the panels.
MPPT controllers can also be configured for different battery types, significantly extending the life of your batteries.
To be fair, the system I'm describing is not in the $325 ballpark so I'm talking apples to oranges.
If you're looking to build a solar system you want an MPPT charge controller, not a PWM controller. Simply put the PWM controller chops the voltage down from what comes out of the panel(s) to a set output voltage resulting in significant losses, and does nothing if the voltage drops below the set output voltage. The MPPT systems constantly adjust to the input voltage to allow it to charge efficiently with just about any output from the panels.
MPPT controllers can also be configured for different battery types, significantly extending the life of your batteries.
To be fair, the system I'm describing is not in the $325 ballpark so I'm talking apples to oranges.
I'm planning to install a small off grid solar system on my property in NH and I have a couple of questions.
The distance between the solar panels and the cabin is about 225'. Will the voltage drop over this distance make the system impracticable?
The load on the system will be small, just some L.E.D. lights and a video surveillance system.
What type of batteries should I use? The cabin will be unheated when unoccupied.
The distance between the solar panels and the cabin is about 225'. Will the voltage drop over this distance make the system impracticable?
The load on the system will be small, just some L.E.D. lights and a video surveillance system.
What type of batteries should I use? The cabin will be unheated when unoccupied.
ToddDubya
NES Member
Check out The CommsPrepper. He's done a lot of research and is always fine tuning his system. He runs the system at a "remote" retreat, so it has to be fairly self-sufficient. He does however have a way to monitor and control his system over the internet.
You want to make sure you keep the charge up and occasionally equalize the batteries. The CommsPrepper goes over a lot of this. A good charge controller will have settings for various battery types.
As for distance between the panels and the cabin you really want to keep that as short as possible. Losses are mainly a function of the square of current (I^2xR), so higher voltage/lower current will lower your cable losses. Larger cables will also keep these losses down but there you have only linear savings (I^2xR). When sizing your cable, refer to a table such as this to see what your resistance is per unit distance.
Examples:
12V panels feeding a 120W load => 10A. (we'll neglect conversion losses for simplicity's sake)
250' of 12AWG cable = (250/1000)*1.588 ohms ~= 0.4 ohms
Cable losses = I^2 x R = 10A^2 x 0.4 ohms = 40W
12V panels feeding a 120W load => 10A. (we'll neglect conversion losses for simplicity's sake)
250' of 8AWG cable = (250/1000)*0.6282 ohms ~= 0.15 ohms
Cable losses = I^2 x R = 10A^2 x 0.15 ohms = 15W
Same cables now use 24V panels:
24V panels feeding a 120W load => 5A. (we'll neglect conversion losses for simplicity's sake)
250' of 12AWG cable = (250/1000)*1.588 ohms ~= 0.4 ohms
Cable losses = I^2 x R = 4A^2 x 0.4 ohms = 10W
8 AWG cables and 24V panels:
24V panels feeding a 120W load => 5A. (we'll neglect conversion losses for simplicity's sake)
250' of 8AWG cable = (250/1000)*0.6282 ohms ~= 0.15 ohms
Cable losses = I^2 x R = 5A^2 x 0.15 ohms = 3.75W
You see that doubling the voltage cuts the losses to 1/4. You can run some panels in series to get the voltage up, but if one panel stops working, you lose everything.
Most of this comes down to how reliable you want your system, how much maintenance you mind doing and your budget. Good batteries will cost a lot (they can be the most expensive part of the system), but save you on maintenance and have longer lives. A good charge controller will give you better efficiency and extend your battery life.
Simple answer: it's not that simple.
You want to make sure you keep the charge up and occasionally equalize the batteries. The CommsPrepper goes over a lot of this. A good charge controller will have settings for various battery types.
As for distance between the panels and the cabin you really want to keep that as short as possible. Losses are mainly a function of the square of current (I^2xR), so higher voltage/lower current will lower your cable losses. Larger cables will also keep these losses down but there you have only linear savings (I^2xR). When sizing your cable, refer to a table such as this to see what your resistance is per unit distance.
Examples:
12V panels feeding a 120W load => 10A. (we'll neglect conversion losses for simplicity's sake)
250' of 12AWG cable = (250/1000)*1.588 ohms ~= 0.4 ohms
Cable losses = I^2 x R = 10A^2 x 0.4 ohms = 40W
12V panels feeding a 120W load => 10A. (we'll neglect conversion losses for simplicity's sake)
250' of 8AWG cable = (250/1000)*0.6282 ohms ~= 0.15 ohms
Cable losses = I^2 x R = 10A^2 x 0.15 ohms = 15W
Same cables now use 24V panels:
24V panels feeding a 120W load => 5A. (we'll neglect conversion losses for simplicity's sake)
250' of 12AWG cable = (250/1000)*1.588 ohms ~= 0.4 ohms
Cable losses = I^2 x R = 4A^2 x 0.4 ohms = 10W
8 AWG cables and 24V panels:
24V panels feeding a 120W load => 5A. (we'll neglect conversion losses for simplicity's sake)
250' of 8AWG cable = (250/1000)*0.6282 ohms ~= 0.15 ohms
Cable losses = I^2 x R = 5A^2 x 0.15 ohms = 3.75W
You see that doubling the voltage cuts the losses to 1/4. You can run some panels in series to get the voltage up, but if one panel stops working, you lose everything.
Most of this comes down to how reliable you want your system, how much maintenance you mind doing and your budget. Good batteries will cost a lot (they can be the most expensive part of the system), but save you on maintenance and have longer lives. A good charge controller will give you better efficiency and extend your battery life.
Simple answer: it's not that simple.
I'd personally rather build around the power loss and add a panel, than run the voltage higher. My reasoning is I'd rather run 12V lighting and appliances and not need to use a another voltage converter. Converters are going to create their own losses, plus they become another failure point. If you're going to run your house on solar at 110V you're going to need a huge array (read lots of $$$). The whole point is to keep the cost down and reliability up. I'd rather run a generator for larger loads if needed and keep the solar for basic needs.
ToddDubya
NES Member
You can run off higher voltage panels, charge 12V batteries and have everything running off 12V. The voltage rating of a panel is under ideal conditions and it will likely not output that voltage unless you have clear blue skies.
In fact, a lot of people use 6V batteries and it's not a big deal to set it up to work. It might seem overwhelming but it's all ben dun befo.
Here's an example using two parallel sets 6V batteries in series.
In fact, a lot of people use 6V batteries and it's not a big deal to set it up to work. It might seem overwhelming but it's all ben dun befo.
Here's an example using two parallel sets 6V batteries in series.
I have a high end charge controller if anyone is interested, not sure what it's worth I'd have to go grab the make/model off it. It was originally spec'd for use in off-grid radio tower situations.
Id love to have a cabin in nh and off grid power.. i should have went to college. Lol
ToddDubya
NES Member
I could be tempted. I don't have any plan for a solar system right now but I really want to dabble and get my feet wet.
cockpitbob
NES Member
Keep an eye on D.C. (Washington, that is). I heard a news blip that they thinking the subsidies have done their job and are going away soon. I'll be glad when I'm no longer having to pay for my neighbor's solar panels.
I live off grid. My panels are 175ft from the batteries. My battery bank is 12v and charged with a MPPT charge controller. One advantage to MPPT is that you can wire the PV panels in series to reduce voltage loss over the cables. The charge controller takes 60v from the panels and converts it to 12v for charging. Low light performance of this setup is amazing.
I try to run whatever possible on 12v because inverters use a lot of power on standby...my inverters are only turned on for a few minutes each day.
Edit: I use 8awg submersible pump cable for my PV lead. If you keep the batteries (lead acid) charged they will be fine down to -60F or lower. I recommend keeping the batteries in a heated space for better performance.
I try to run whatever possible on 12v because inverters use a lot of power on standby...my inverters are only turned on for a few minutes each day.
Edit: I use 8awg submersible pump cable for my PV lead. If you keep the batteries (lead acid) charged they will be fine down to -60F or lower. I recommend keeping the batteries in a heated space for better performance.
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Steve had already PM'd about this stuff but if he decides he doesn't want it or it's too expensive (not sure what the pricing is yet) this is what I have for gear:
Phase three charge controller - PT-24-20CE
Outback power systems - 60MPPT - pretty sure it's the 60mppt I can't read the sticker the way it is in the box but it looks right.
WesPower GreenMeter - Can't find a listing for this thing anywhere, it's a power tracking box.
Phase three charge controller - PT-24-20CE
Outback power systems - 60MPPT - pretty sure it's the 60mppt I can't read the sticker the way it is in the box but it looks right.
WesPower GreenMeter - Can't find a listing for this thing anywhere, it's a power tracking box.
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