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question on 100 watt solar setup at cabin in Finland

 
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Dear all, I have a solar setup of 100 watts in mind with a 80ah battery at my cabin for some small appliances. At the cabin site there is no sun, but 30 meters (100 feet) away there is. So obviously the panel will be setup there. I am struggling with the following. Should I run a cable from the solar panel directly to the solar setup in the cabin (to the charge controller and battery) or should I place the charge controller and battery at the solar panel (in a box or something) and run a cable from the charge controller to the cabin appliances? Does this make a difference (e.g. voltage drop wise or something else)? Hope you can help.
 
gardener
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Hi Tim. If it were me, I would keep the batteries in the cabin so they are climate controlled. Battery performance drops when they get below freezing temperatures, and it worsens as the temperature keeps dropping. Hope this helps!
 
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Agree with James, though be aware that some batteries off gas or leak = hydrogen & oxygen = kaboom. You'll need to do some homework on battery type, etc.
 
Tim Visser
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Thanks a lot for the advice! Any thoughts on it besides the battery reason?
 
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There are several things to consider.  Are you using DC appliances or AC?  Will you have an inverter?   I don't know of any DC laptops.

1.  Batteries off-gas hydrogen gas that eats through everything, so hopefully you won't have them in the cabin with you, or in the same shed as your controller and inverter.

2.  Panels need to be near the batteries.  Panels and batteries are DC, so they go together first.  All the wiring coming off the panels needs to go directly into a shed where the batteries are.  Distances lose voltage, so keep everything as close together as possible, and rodent-proof/weather proof/bird proof all wires coming off the panels.  

3.   There should be 2 sheds you can stand up in, or a 2-room larger shed with a dividing wall, because you don't want to buy another controller after the hydrogen gas eats the wiring in your expensive equipment.
        -- one side of the shed for the controller and other equipment,
        --and one side of the shed for the batteries, with windows for ventilation, so you can stand up and add distilled water only to them without rain or snow or blowing pollen or blowing anything getting into them when you are filling them.
       -- this 2-shed configuration also makes it easy to keep everything together to work on things, like storing distilled water, cleaners and sprays for the battery connections, caulk, any outlets you want in the shed for shed use or an outside light.

4.  BOTH battery and controller sheds need to be together because there is a massive cable coming off the batteries going to the inverter, and those aren't long.  So once your inverter changes the DC coming off the batteries into AC, that should be sent via large gauge wire to the house electrical panel where there are fuses to protect for overages.  Underground in heavy PVC or ABS pipe below freezing level works.  

3.  Distance -- For every foot AC travels it loses some voltage, and so does DC but a little less, so you'll need some of the biggest gauge wire you can get (you'll need to do the math to figure out over 100 feet what it's going to lose, and use that heavy gauge wire to go to the house.

4.  100 watts isn't going to get you much more than a light.  Computer screens need wattage, so if a light is on there won't be extra for the computer if you've only got 100 watts.

5.  Applicances are often 1500 watts, coffee maker, electric hot water pot, an electric cooktop, and if there's a light on at the same time you'll blow a fuse with just a 1500 watt system.  

6.  Don't skimp on shed size, and plan for your system to grow.  An 8-battery, deep cycle setup will run a small cabin, with a 2400 watt inverter.  a 6x8 shed will hold 12 deep cycle batteries (connected in groups of 4) and still leave room to stand next to them to add water at least once a month.

7.  Buy the biggest wattage panels you can get, because even if you don't have a lot of batteries you'll need them to charge as fast as possible while the sun is at the best angle from 10:00 AM to 2:00 or 3:00 PM.

8.  Be prepared for big birds to perch on your panels with big talons, and little birds to perch on the wires coming from the panels and going to the batteries, and they will eventually scrape off the wire protective coating, so put all wires in small PVC pipe or there is some coating stuff you can buy that is like tar, you can paint it on.

This is your lifeline for being comfortable in a remote place, so the more you invest in it, the more satisfied you will be.

 
Cristo Balete
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And for planning ahead, it is a good idea to put at least 2 extra large-gauge lengths of wiring in the same pipe as the large gauge wire that is sending the power to the cabin/house.  If some day you add a generator, you'll need that extra wiring already in that buried pipe.  Give yourself lots of extra wire on either end for being able to reach a generator.  It's about a $20 plan ahead thing that saves all kinds of work in the future.

And save enough large pieces of thick cardboard to cover the panels when you need to work on them.   The panels are "on" all the time, so don't take you mind off the wires coming off them, and don't get those wires crossed.   Another important thing to store in the shed.  Along with duct tape to tape them on.  Even with cardboard there will be a little power coming off the panels, enough to get an annoying shock, so be careful.

Also paper towels, a long-neck funnel for filling them, an old toothbrush for cleaning off corrosion, a tablet and pen to write down whenever you test the batteries and make notes to yourself about your setup, the battery tester, that red spray that stops corrosion  (at least for a while it does, but needs reapplying).....there are more things, but you can see storage matters.
 
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You didn't mention whether your appliances/ home will run dc or ac, or did i miss that? 100 watts does not seem like enough, when we ran off of a similar system we would charge AA batteries in the car on the way to and from work for a camping puck light, because we often lost power before bed time. The panels are usually placed close to batteries and charge controller because DC suffers from more line loss, you can slightly compensate by enlarging the wire gauge but keep in mind larger wire is much more expensive. After being converted to AC you can have a longer wire to the household power. Our household runs an electric fridge, 3 laptops and lights off 2k incoming power and 4 L16 batteries and we still need a back up generator for prolonged cloudy periods.
 
pollinator
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Hello Tim,

With a 100watt 12v panel and your environment (Solar panels like the cold, batteries like the same temperatures as we do), you're forced to bring your solar energy to the batteries into the warm. That means you need to use a very thick cable (probably the same cost as your panel) because the lower the voltage in DC (Direct Current), the thicker the wires you need to move it.

Have a look at this cable sizing calculator.

http://www.solar-wind.co.uk/cable-sizing-DC-cables.html

You didn't say what kind of battery you have - an "open" (meaning you have to add water from time to time) or a vented or gel battery but as long as you're (and your friends) are careful not to be silly around batteries (naked flames, smoking etc), they can live in a protected area in your cabin. Just don't put your controller too near your battery. (Learn more about this stuff.)

If I were you, I'd buy another panel with the same specifications as the one you've bought. Join the panels in series, making 24v and take that to an MPPT controller which will reduce the voltage to the same as your battery automatically.

Your cable will be less expensive (Use the link above and you'll see what I mean) and you'll have a much "longer day" to charge your batteries because the MPPT controller will keep on charging your 12v battery with as much sunshine as it can because it's using the beginning and the end of the day to keep it topped up with more volts than a PWM controller can. (If you don't know what I'm talking about, do your research on the difference between these solar controllers).

Charge everything during the day when your battery is full. A laptop is DC (It uses a battery) but don't use an inverter to charge it, use a car charger which costs about 29€ (this one is 18 years old)



You can also charge almost any small appliances such as torches, portable lights, telephones, tablets etc. with a 12v USB charger.

Keep your battery full for the evening/night and use LEDs or compact fluo lights - you'll be fine.

I've installed solar systems for friends with vans and yurts who only had a few hundred watts of panels and all of them are delighted with their lighting and their ability to charge stuff when the sun shines. Around the winter solstice it can become more difficult but you just have to get the candles out and enjoy the magic.
 
Tim Visser
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Thanks everyone for thinking along with me. Some extensive replies. Really appreciated. I run DC and basically only for a couple of LED lights, a security camera and a mifi for internet. Less then 50 watts for sure. If we are not there, we only need the camera and mifi to check the property (and with a DIN timer, I want to 'cut off' the devices every other day). I have an AGM battery.

By the way, the fridge is on propane. I have a back-up generator for power tools and other appliances if needed. If we go to the cabin, we try to be outside most of the times so usually we do not use a lot of power. We also manage withoud power, so the need is not high. We like candles

Some out takes from what I have read;

- battery goes with the panels (both DC)
- seperate the battery from the charge controller
- battery does not like cold so I need to insulate
- A MPPT controller probably works best looking at my cabin site (I currently have PWM..)

While the panel obviously should be where the sun is and the battery where the panel is, it does mean I have to build a box with the battery and solar charger next to the panel. I am thinking of a pole setup with a box in which I can put the battery and somehome also the wiring and MPPT solar charger, although seperated and well ventilated. I guess the box needs to be insulated. From there run a wire (12 AGW or less?) to the cabin into a distribution box near the cabin from where the lights and some DC outlets are supplied.

Any thoughts on this setup?


 
Irene Kightley
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Yes Tim, I’m going to repeat myself a little here, so forgive me but I’d like to answer your message with a few comments on some of your points.

- battery goes with the panels (both DC)

I don’t understand what you mean by this to be honest as you won’t be using alternative current anyway.

In my last message, I suggested that you bring the cable from the solar panels (connected in series to make 24v) to the controller inside the cabin. An MPPT controller will then adapt to your battery voltage of 12v and your load output on the controller will be 12v too. (I suggest that you buy a controller with a load output which cuts off the load when the battery is low, most small MPPT controllers have them and that will extend the life of your battery.)

You’ll want to check the controller regularly to see if you have enough energy to run certain things and it’s handy not to have to go outside. If you keep everything outside and in 12v, you need to run a 35mm² cable which costs about 12€ a metre. That calculation is with a 3% loss in the cable. With a 2% loss, the cable will cost about 20€ a metre!

For 24v coming from the panels, 25mm² cable will do the job for up to 10 amps and is about 5€ a metre. It’s easy to find in the small ads - people often sell end of rolls cheap at the end of a big electrical job.

- separate the battery from the charge controller

Yes, but just make sure that the controller is no more than 50cms away and certainly not on top of the battery. AGM batteries gas less than an open batteries and they are fine used inside homes and in enclosed spaces such as camping cars.

- battery does not like cold so I need to insulate

An AGM battery is the best type for cold situations (Check the specifications for your battery for max and min temperatures) but, as I’ve suggested, put the battery inside or somewhere protected near your cabin but with decent air circulation and you won’t need to worry.

- A MPPT controller probably works best looking at my cabin site (I currently have PWM..)

In my humble opinion, there’s no point in buying an MPPT controller for such a small system unless you are going to use it for doing the job of reducing your voltage to keep the cost of cables to a minimum (Unless your site has some special thing that I don't know about).

Personally, I’d prefer to buy another panel with the same specs joined with original panel in series to make 24v and an MPPT controller which will cost in total around 300 euros, rather than buying 35mm² cable which will cost more than 600€. (12€ x 60 metres) This method will also give you a much better chance of charging your battery when the weather is against you.

A 20amp MPPT controller will cost from 120 to 350 euros. I’ve bought two cheap Epever controllers after reading several reviews and so far I’m pleased very with them. You can also find a lot of small second hand controllers as people sell them when they upgrade their system. I have a 20amp Morningstar which cost less that 50€ and it does the job perfectly after several years.

After reading you last paragraph, I realise that maybe I didn’t express myself very well in my last message. I’ll add comments to some of your ideas :

-While the panel obviously should be where the sun is and the battery where the panel is,

The battery does not need to be near the panel but needs to be near the controller in or near the cabin 30 metres away from the panels. The point of using an MPPT controller is that you can use smaller wires from the solar panels because you can run 24v to your controller which will then detect a 12v battery.

-From there run a wire (12 AGW or less?) to the cabin into a distribution box near the cabin from where the lights and some DC outlets are supplied.

12 AGW ? If you mean 12 AWG, a tiny cable this size will only carry 00.8 amps over 30 metres and will burn out very quickly and is extremely dangerous if you use anything over 10 watts! You need 2 AWG or 35mm² if you stay with 12v. Please look at the link for cable sizing that I put into my last message to see what I mean.

Sorry if it sounds like I’m being a PITA but I don’t like seeing people doing dangerous things or wasting their money. I’m not an electrician and I wouldn’t call myself an expert but I’ve more than 27 experience of installing and using photovoltaic solar panels.

This is posted with love and I'm only thinking about what's best for you.
 
pollinator
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There is no reason you cannot place the panel(s) in the sun and have the battery inside.
The battery capacity will be half your usable capacity. (Approx. 32ah usable at 80%dod and 30 deg. F.)

This only matters if you get temps that cold and the battery is at those temps.

If you had 2 modules (2x 50w or better, 2x 100w) and fed an mppt charge control at 30 or so volts, the resulting requirement for 1.5-1.75% loss is #8 or #6 for 100 or 200 w respectively. Hardly a log sized cable and cheaper than a battery upsizeif beating temps was the case...

Always run the calculations against presumptions of wire loss, better to actually know the loss before you build or  are discouraged from having it the way you like or which performs best.

Running 11v power 100' at 10a is a different story and why i would have the battery near the loads.

With an mppt controller, you can have a single 40v module and do even better on the wiring cost.
 
Tim Visser
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Thanks again everyone. Really appreciating your replies. It helps a lot and I am learning a lot.

I will go for 2 x 50 watts panels in series (can get them from a friend), making it a 24 volts system. If I am reading it correctly I have two options (or maybe just one realistic) in my situation;

1. Run a 20 meter wire from the panels to the cabin where the charge controller and battery is located. According to the cable size calculator, I would need at least 10mm/8AWG wire for 20 meters of cable (100watts/24volts=~5 Amps with a 2% cable loss). While the battery is 12 volts (which I have), the MPPT charge controller (which I also have) will convert the 24 volts to 12 volts automatically.
2. Or I place everything (battery and controller) near the panels. Which causes me to run a cable from the controller at the panels to the distribution box in the cabin. According to the calculator (if I used it correctly) I would end up with the same cable size while based on max 50 watts of appliances going through it, this would also result in ~5 Amps (50watts/12volts, 2% cable loss).

I am not sure whether the second calculation is correct. Though that seems not really sustainable while if I would add appliances (so increase the watts), the wire size would not fit at all. So option 1 feels the way to go.

Temperature wise it will not differ a lot. In the cabin it is probably equally warm/cold inside and outside in summer and winter
 
frank li
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[quote=Tim Visser
1. Run a 20 meter wire from the panels to the cabin where the charge controller and battery is located. According to the cable size calculator, I would need at least 10mm/8AWG wire for 20 meters of cable (100watts/24volts=~5 Amps with a 2% cable loss). While the battery is 12 volts (which I have), the MPPT charge controller (which I also have) will convert the 24 volts to 12 volts automatically.
2. Or I place everything (battery and controller) near the panels. Which causes me to run a cable from the controller at the panels to the distribution box in the cabin. According to the calculator (if I used it correctly) I would end up with the same cable size while based on max 50 watts of appliances going through it, this would also result in ~5 Amps (50watts/12volts, 2% cable loss).

I am not sure whether the second calculation is correct. Though that seems not really sustainable while if I would add appliances (so increase the watts), the wire size would not fit at all. So option 1 feels the way to go.

Temperature wise it will not differ a lot. In the cabin it is probably equally warm/cold inside and outside in summer and winter


#8 wire with 50w at 10.5v (typical low voltage cut-off) and 4.76 amps is 5.7%. 100w on the same would be 11.4ish!

The array at 32ish volts mppt is about a third the loss at any power level up to 100w on #8 copper and 1.45% voltage drop.

Any of these scenarios require a look at difference in price of upsizing to #6 as expansion and overhead capacity.

 
Cristo Balete
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Tim, maybe there's such a thing as a DC MiFi or DC  LED lights, but I wonder about that?   DC might seem less complicated, all DC appliances are very expensive and often require shipping.  You can't take advantage of local sales on simple things like a coffeemaker or a small refrigerator.

A 50 watt panel is way too small.  Panels have a 15% efficiency rating, meaning take off 15% of the wattage of the panel and that's what you will actually get coming in to the batteries.   It will take way too long for the batteries to charge since even a slight overcast will slow the process.  A 50 watt panel puts out 50 watts an HOUR, not a minute, so at max over 4 hours you'd get 200 watts on a perfect day, every day.  That doesn't happen day after day.    Storms can go for days, an overcast sky can go for days.  

The battery needs to be charged as quickly as possible, within the 4 hours of 10:00 AM to 3:00 PM (assuming the sun is on your panels during that whole time)  because there are 3 stages to charging, and the controller will hold back on a complete charge until those 3 stages are completed.  

Panels these days are up in the 250-350+ watt zone, and are a reasonable size. It's a big relief to have a battery kept topped up going into darkness, especially in winter.   Deep cycle batteries can be rated for 200+ watts per battery, so doing the math, it takes hours to get each one back up if you don't have enough wattage coming through the panels.  We burned out a refrigerator, not realizing we didn't have enough wattage topping off those batteries.  Obviously the refrigerator was draining the batteries and panels couldn't keep up.

When we added panels, we added a second controller for those panels, and connected that controller into the system.  

Inverters have alarms on them that will warn you when the batteries get too low, so it's important to stay in touch with what's going on.

Also, the pole and frame for the panels need to be very sturdy, to be able to take strong storm winds.

I can't vouch for other countries, but our deep cycle batteries are all 6 volts, so they have to be joined with another 6 volt battery serially to bring two of them up to 12.  A 6-volt battery will boil and explode if it is charged with a 12-volt charger.  You're going to need upwards of 700-1000 watts worth of panels to keep a 24 volt system charged up.  Batteries last the longest if they never go below half, so taking them all the way down isn't good for the longevity of the batteries, but it takes long summer-type hours to bring those back up if you have less then 1000 watts worth of panels.  

Sounds like you are concerned about vandalism there, if you want a camera on all the time?  Solar panels are easily stolen, and in demand, as well as expensive controllers and inverters.
 
Cristo Balete
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All the hype about solar, solar, solar....just throw up panels and you've got solar!  Not!!  If the sun is up, you get solar power!!  Not!  

I think the industry is to blame for not making it clear what solar power actually takes, how it works, the expense of it, the maintence of it, the setup needed, and the serious knowledge about electricity, both AC and DC, that is required.  Overloads of electricity can start things on fire.

And, ironically, if batteries get too hot in the summer, after all of that insulation so they won't get too cold, they can explode.

And you're going to need a lightning rod pounded into the ground at the panels/battery shed to make sure this whole system is grounded.

 
Irene Kightley
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Cristo, almost all LEDs are driven by a DC power supply and all MIFIs are too.

Small appliances like fridges, and so on are often DC because they're used by caravaners, motorists and truck drivers in their 12v or 24v vehicles.

I totally agree that two 50 watt panels are too small for this application but if Tim can get them cheaply from a friend, then he can put an even number together in a series/parallel configuration to produce 24v.

The battery needs to be charged as quickly as possible, within the 4 hours of 10:00 AM to 3:00 PM (assuming the sun is on your panels during that whole time)  because there are 3 stages to charging, and the controller will hold back on a complete charge until those 3 stages are completed.

Tim already has a 12v AGM battery and AGMs batteries like to be charged slowly and with a low voltage charge rate of just over 14v. Unlike open acid batteries, they do not need a regular, final, high voltage equalisation charge. They can be equalised but only if they are showing signs of wear and I'd suggest only a couple of times a year and by somebody who knows what they are doing.

That's one of the reasons I suggested that he use a 24v array to connect to his MPPT controller, because there will be a high enough voltage at the beginning and end of daylight to charge a 12v battery. Even with very little light hitting the panels, the chances of having a good voltage to complete the absorption phase are high - even in Scandinavia in winter. (60° - 70° N)

A good solar controller will have the option to select the battery type automatically and will deliver the appropriate charge to AGM batteries with no intervention from the owner - apart from the initial selection when you install the battery.

Panels these days are up in the 250-350+ watt zone, and are a reasonable size.

When talking about big solar panels and a very small ah battery, be very careful about using too many amps to charge a battery. It's tempting to buy bigger and relatively cheaper panels but the charge rate for most AGM batteries is lower than 12% of the C20 amp hour rating. Check your battery specifications for the recommended charging amperage and don't go above that.

Inverters have alarms on them that will warn you when the batteries get too low, so it's important to stay in touch with what's going on.

Tim will probably never need an inverter, they use current to operate and with only a small ah battery, the energy stored in the battery won't last long. An inverter alarm is useless if you don't hear it and I know many people who have ruined their battery bank by relying on an inverter to protect it. If it's really necessary, a tiny inverter could be used (We used a little 300w MSW inverter with a 300 watt system which we had) but used it only for a very short time each time and only on a sunny day.

The more expensive inverters cut off to protect the battery but all solar controllers with output cables to a load will cut off at a high enough voltage to protect your AGM battery. Use the controller to monitor what's happening, you'll get much more data than you'll get from an inverter - which either turns on or it doesn't !

You're going to need upwards of 700-1000 watts worth of panels to keep a 24 volt system charged up

Tim's system (Unless he decides otherwise of course.) will be a tiny 12v system.

Tim, I think using solar is a bit like buying a car, it's up to you to learn how to drive and maintain the car. Anybody can drive (ahem) but if you don't know how to maintain and install a solar system, then you learn until you know exactly what you're doing and why, or you get somebody you trust to design it for you and you learn as you go along - but always with safety in mind.
 
Cristo Balete
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Irene:

>>Small appliances like fridges, and so on are often DC because they're used by caravaners, motorists and truck drivers in their 12v or 24v vehicles.

I didn't say there weren't DC fridges, and they are rare in my neck of the world.   It's just that the local store with the best sales usually sell AC appliances.   Again, I can't vouch for every country.  And having burned up the motor to the AC refrigerator, in my early inexperienced days, I was very glad the motor didn't cost much.  

-----------------


>>> Unlike open acid batteries, they do not need a regular, final, high voltage equalisation charge.

I wasn't referring to equalization, which is different from the 3-stage charge that the controller does of all batteries, acid or AGM.   And isn't it always the case that the controller seems to choose an overcast day to equalize the batteries?  We had to change that to manual override.  The controllers do a fine job of equalization.


---------------------------------

>>>>The battery needs to be charged as quickly as possible, within the 4 hours of 10:00 AM to 3:00 PM

What I meant by this phrase was that the best chunk of hours when the sun is directly on the panels are in the middle of the day, maybe 4 or 5 hours.  That's a short period of time.   Of course the controller will not allow it  "quickly," in the sense of minutes, but the controller also has less to work with on either side of those hours.  I think people are under the impression that if the sun is up their panels are working at full capacity, and that's not the case.  And I can't vouch for people living on the equator where it's a whole 'nother story.

------------------------------------------

>>>>Tim will probably never need an inverter,

I've never had any problem with the inverter using so much power that there were any problems with that.   But I am in love with AC current, and I am very grateful for the inverter, and so it's part of what has to happen in the setup.

I still say he should plan for a bigger system, or at least have that option, that runs his whole cabin, with easily gotten and repairable appliances, but of course, that's up to him.

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>> An inverter alarm is useless if you don't hear it

I guess I don't understand why anybody would commit to a solar system, and then not pay attention to what's going on in the equipment shed a minimum of a couple times a week in winter, maybe once a week in other seasons, once they've had experience.  A new system should be watched daily if someone is inexperienced, even if it's only a 5 minute check and one is learning what the panels are doing as the sun moves, the clouds pass by, the angle of the sun changes.   My inverter is 75 feet away from the back door and I can hear the alarm just fine.  If it's farther away than that, then all sorts of things have to be taken into consideration, like loss of voltage over too big a distance, etc.

And I've never relied on the alarm.  I am always keeping track in my mind just how much sun has happened on a particular day and whether going into darkness requires special care, like no printers going for any length of time, no ironing, etc.  And despite my 20 years of experience living with solar and batteries, a couple of times that alarm has gone off.  One time was one of the batteries was faulty.   The other time was learning that we didn't have enough panels to keep the refrigerator going.  It's more of a backup alarm.  I've always said in all of my posts on this site that solar isn't something we install and walk away from.  It has to be kept in mind all the time, even if it's just cleaning pollen off the panels.  As batteries age they need keeping track of.  

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>>>Tim's system (Unless he decides otherwise of course.) will be a tiny 12v system.

I thought in Tim's latest response he mentioned a 24V system.  I guess he was just talking about the controller automatically adjusting.

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Some of my responses are for anyone who happens to be reading this thread, not just Tim.  And hopefully everybody is studying all of these things from multiple sources, multiple internet sites.   I can only say from my experience what I would do again.   I have a situation with less need for power that is separate from the house, and inevitably it needs a vacuum (1500 watts) or a power tool running for an hour or more (1500 watts), or guests who just don't understand the limits of a small system.  If we're going to buy all the things that are needed for a small system, it doesn't take much more money to get a bigger and much more usable system.

 
gardener
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food preservation greening the desert solar trees
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Hi Chris, the OP has already said clearly that he is not going to use (heat producing, high load) devices like a coffee maker etc. He has already mentioned that he has minimal load, just a couple of  small electronic devices and a few LED lights, and it's a vacation cabin where he doesn't mind much if power runs out and they have to use candles sometimes. His total load as mentioned is well under 100W. So I would agree with suggestions to make the system a bit larger than just 100W, but don't worry about making the system 1500W since he knows not to attach any heat producing (ie high load) devices like a cooker, kettle or coffee maker.
 
frank li
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For an 80ah battery, 10a is a good charger and 13a about max charge amps, depending on the battery. We use controller max amps to limit reasonably oversized panels and arrays.

Some controllers can take most all you give them (within max amps on the pv terminals) and limit nicely, better is a controller with an adjustable max charge amps setting.

100w pv and an 80ah agm is a nice micro system. A 6.5a charger (100w pv less 15% derate) is a fine source, about 6 hours peak sun from 50% dod to full.

I have a "Solar Roller" which i use for trade shows and it is mainly a "shop charger" for batteries that are out of cars and not in use.
110w sunwize and a stecca 8a charge control with meters. Great rig. It has an 80ah Alpha gel cell battery that is inside and used for radio comms and our projector, regharging personal electronics, anything 12v i can plug into it.
It charges from a 224w sharp mounted on the house at a steep angle 65 or 70 deg., and faces west.... in the shade half the day or more, so mostly ambient light after 11:30am. It feeds a morningstar SS mppt 15 control and has only hit lvd once in 4 or 5 years, because i left everything on for three days of dead overcast!

The light is always green and the battery is 6 or 7 years old! Alpha!

If the load is simple comms and lighting, it will be a great addition to your cabin, Tim!
 
Cristo Balete
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Irene, I was thinking about your replies.  I don't mean to make anyone upset with my suggestions.  And if it sounded as if I was saying that an AC system is better than a DC system, I didn't mean to.  There are differences between AC and DC, and I meant to show the differences, and to say to anyone deciding to do solar, to be prepared for those differences.  But it wasn't meant as a judgement of anyone using a DC system.  I'm sure there are plenty of people on this forum who have DC applicances and are perfectly happy.

In the US, DC is rarely on the retail radar, and an AC system is just easier to live with.  But in other countries DC may be more mainstream, and I did try to say that I can't vouch for other countries.  

Haven't seen you around lately, but I have always wanted to say I've been inspired by your garden pictures many times, and the creativity and hard labor that goes into it really shows.  :)
 
Cristo Balete
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Rebecca Norman wrote:Hi Chris, the OP has already said clearly that he is not going to use (heat producing, high load) devices like a coffee maker etc. He has already mentioned that he has minimal load, just a couple of  small electronic devices and a few LED lights, and it's a vacation cabin where he doesn't mind much if power runs out and they have to use candles sometimes. His total load as mentioned is well under 100W. So I would agree with suggestions to make the system a bit larger than just 100W, but don't worry about making the system 1500W since he knows not to attach any heat producing (ie high load) devices like a cooker, kettle or coffee maker.



Hi, Rebecca....if you mean me  (by "Chris"), yes, I understand the original idea of the OP was a small system.  My responses are suggesting if he's going to pay money to buy just about as much stuff for a small system as he would for a medium system that he could really take advantage of, it wouldn't be that much more money, and is something that is very valuable and usable in a remote cabin.  Solar equipment doesn't get any cheaper, that I've seen.   It's just from my experience,  having lived with solar for 20 years, that I would recommend.   :)
 
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