solar /battery thoughts

Vbrig · August 02, 2016, 11:20:07 AM

New to the site ..thanks to all on it. learning a lot.. im a new upstate NY Catskills land owner with thoughts of a weekend small cabin build. looking at solar/ battery as my power source. Heres the question after the weekend is over and packing to leave.. what do you do with the solar system ? does it stay online and charge the battery's for my next visit or do you shut it down until another weekend . thanks

ChugiakTinkerer · August 02, 2016, 01:13:32 PM

Most folks take advantage of the available light to charge back up the system. My cabin is still a work in progress so my solar system is still conceptual, so value my advice accordingly.

A typical arrangement would be to turn off the switch/breaker to the cabin and leave the solar system active to charge the batteries. There may be reasons not to leave it on, but most systems are designed for continuous use. Over the winter, cold temps might be a consideration, but then again a battery best resists freezing if it is at full voltage.

August 02, 2016, 01:25:00 PM

thanks...any sound advice is valuable...

MountainDon · August 02, 2016, 03:24:44 PM

Lead-acid batteries self discharge when sitting idle. So keeping the solar charging side active makes sense. That is what we have been doing since we built our system 7 years ago. It pays to buy quality brand equipment, not cheap ebay material. Also buy and install good lightning surge protection devices. Midnite Solar has great SPD's and back them up with lifetime warranty. They recent!y repaired 2 of ours that succumbed to one too many lightning strikes. That is covered under their warranty; just pay shipping to them.

We leave the system run through the winter even though we are seldom there. A fully charged lead acid battery will not freeze until minus 90-something F.

OTOH, lithium ion battery technology has such a low self discharge rate they can be left with everything shutdown for months with no ill effects. They are still relatively new to the off grid world and costly. There are success stories to be found on the internet, but little info about people who may have had bad luck or have screwed up their expensive LFP's. LFP are something we are considering as replacements for our 7 year old lead-acid GC-2's.

NathanS · August 03, 2016, 05:38:09 PM

Part of a solar system is a 'charge controller.' The charge controller stops charging the batteries when they are at peak voltage (also acts as a choke on the panels if they're in full sunlight). You don't need to unplug anything when your'e not there, and as others have said it is good to leave things plugged in because batteries gradually lose their charge.

There are two types of chrage controllers, one is called MPPT and the other, i can't remember (PCM maybe, something like that). One is cheap and one's expensive. The cheap one is slightly less efficient than the expensive one. I've got the cheap one on my trailer and have never had any issues. As far as I know the cheap one limits voltage just fine, it's just not quite as efficient somehow.

August 03, 2016, 07:24:41 PM

The other is PWM.

PWM controllers are cheaper than MPPT.

MPPT controllers can use higher voltage panels effectively and those panels carry a lower per watt price tag. Under a dollar a watt.

PWM controllers should have the panel voltage carefully matched to the system battery voltage. In the case os a 12 volt battery based system, those panels usually carry a higher per watt price. $1.50 or more a watt is common.

The smaller, more expensive panels, well suited for PWM controller can often be shipped UPS. The larger higher voltage panels usually need truck freight shipping. For a small number of panels that can be very expensive shipping. This is part of the trade off thinking that must be considered.

We have higher voltage panels and MPPT on our cabin system. We also have a PWM and "12 volt" panel set on our travel trailer. Each system was deemed by myself to be the best bang for the buck for thir respective uses.

NathanS · August 04, 2016, 04:22:52 AM

Yep on the trailer with two 100w panels I remember the additional cost of the PWM didn't make any sense. If it's sunny, there is way more than enough solar to charge the two 6v golf cart batteries. I almost want to say it would have been about the same price to add two more 6v batteries than to upgrade to MPPT.

There's no one size fits all solution, that's for sure.

Hunterscabin · August 07, 2016, 08:42:14 AM

OK? for the one person in the room that knows NOTHING about solar (except it comes from the sun) what do you fellas suggest? Is there a book "Solar for Dummies" out there? Do I add up what " I think " I would be using in wattage? Is there a thread here that I could start educating myself with? The better half and I totaled up 6 LEd lights, 1 dorm size Fridge, recharging phones/Ipad and 1 small exhaust fan. I have a 4000 watt jenny, but, who wants to listen to that all the time?
Any suggestions, pointers or places to start?
Thanks all,

MountainDon · August 07, 2016, 12:08:45 PM

Re, book: sorry
I have nothing in particular to recommend.

Yes, you need to makeva good educated estimate kf how much power would be used in a typical day. Without that everything is a guess. Guesses waste money. We have an aid available here... http://countryplans.com/smf/index.php?topic=8192.0. The first part help calc the total loads. You can do the same on paper.

A kill a watt meter is useful for measuring actual AC consumption. There are also some DC meters available. Ask if you want a link. It's not handy to me right now.

Many of those dorm fridges are energy hogs... just be forewarned. There are some small (4 cu ft and under) 12/24 volt DC fridges available that are energy efficient. There are also some quite efficient AC fridges if you look carefully. Depending on the budget size that can work.

Is this for a part time cabin? Would the fridge, or anything else be left operating over absences? And lastly is the power grid nearby? Is your location solar friendly? Weather? Cloudy a lot like PNW or clear blue SW skies?

August 07, 2016, 02:39:19 PM

Part time cabin. @ the most, once or twice a month. Winters? Maybe not even once a month for Dec, Jan or Feb.
Everything goes off when we shut the door. No power nearby. Great southern exposure. No trees blocking and What I call great Blue Colorado skies.
Thanks for info. Will start with the link you posted.
Help always apreciated.

ChugiakTinkerer · August 07, 2016, 05:21:17 PM

Unless you're planning on spending more than a week at a time there, your best bet might just be to use a high quality cooler instead of a fridge. Ones like the Yeti, Grizzly, etc. have phenomenal insulation that seem like they would be more than sufficient for weekend trips. Of course if a fridge is in the plans be sure to take it into account in designing your system.

MountainDon · August 07, 2016, 05:44:13 PM

A note regarding batteries. The most common batteries are FLA, flooded lead acid, heavy duty versions of the battery in your vehicle, but with removable cell caps so the fluid level can be seen, added to and the specific gravity checked with a hydrometer. Then there are sealed types like AGM's. Both of these need to be kept full or nearly fully charged as possible for best lifespan. Winter absences as mentioned can be a problem unless the solar PV part of the system is built to be left running all the time. With good equipment this is not much of a problem. Note that a fully charged FLA will not freeze until 90-something F below zero.

Then there are other batteries such as lithium based technology. These don't have to be kept full when left idle for periods of months at a time. But they have other negative points such as cost and they should not be charged when below 32 F.

Minimizing the amount of energy that must be stored is a good first step. That will set the battery bank size. That in turn will indicate how much PV must be used. So start with the usage estimate. The "super coolers" that were mentioned are superb performers. We've used a couple different ones over the years for week long camping in the hot SW. We've been pleased. They can be a great alternative to a fridge.

Propane fridges like the Servel work well, but do cost and use propane. Could be a pound a day, depending on temperature. No electricity needed; 4 D cells for the inside light.

NathanS · August 08, 2016, 09:02:17 AM

Yeah if you eliminate the fridge, 6 LED lights draw almost no energy.

For scale, our travel trailer has two 100w panels running in parallel (to produce roughly 12v) with two golf cart batteries in series (about 105 or 120amps ... 6v + 6v in series = 12v). This runs all the LED lights we can imagine, we have been watching the olympics on our .. um 20 something inch LED TV? from 830pm to 11pm or midnight every night, charging our phones or laptop, running the electrical portion of our propane refrigerator, running the DC water pump to take showers.

I bet the batteries are fully recharged by noon.

Now, if we have cloud cover all day we would have to tone down the TV watching. That is the real trick with solar. If you have a sunny day, no problems. If it is cloudy, now you are calculating how much battery storage/holdover you need. It gets really expensive really fast. The batteries are actually what runs everything, the solar just collects the energy when it's available. That is why everyone needs a backup generator. Colorado is a good place for solar. When we were in the pacific northwest I thought our charge controller broke because there is something with the sun out there, it just doesn't work well. So when people are designing full time off grid, they might want a battery bank that could run everything for 5-6-7 days without the sun. That is freakin expensive.

If not the super efficient cooler, a propane fridge has been great. Running the fridge + doing a lot of cooking we will get about 2 weeks on a 20lb propane tank that we refill for around $10 right now. We have been grilling lately so we are getting closer to 4 weeks on a propane tank.

Generators more than just the noise are a pain. Sometimes they don't start, you gotta move them around and they are heavy. You got start em and stop em a few times a day. And a decent generator will cost more than a 200w solar system. If I had to start a generator to make coffee in the morning.. . well that would last about 2 days then I wouldn't be drinking coffee anymore.

kenhill · August 08, 2016, 02:24:52 PM

I run a 2000 watt generator, a little ice machine, and use the ice for the cooler and drinks. The ice machines go on sale for about $99.

August 10, 2016, 05:43:41 PM

Thanks All. I certainly do appreciate all the input.
Think that i need to get comfy, watch the sun go down and process all this.
Raising a Jameson for all the help, Thank You

hpinson · August 11, 2016, 12:46:40 AM

I found this book reasonably helpful with understanding basics; I see you can get it on amazon for 4 bucks used. Library probably has it too.

https://www.amazon.com/gp/offer-listing/0865715203/ref=dp_olp_all_mbc?ie=UTF8&condition=all

upa · August 11, 2016, 10:29:06 AM

Quote from: Hunterscabin on August 07, 2016, 08:42:14 AM
OK? for the one person in the room that knows NOTHING about solar (except it comes from the sun) what do you fellas suggest? Is there a book "Solar for Dummies" out there? Do I add up what " I think " I would be using in wattage? Is there a thread here that I could start educating myself with? The better half and I totaled up 6 LEd lights, 1 dorm size Fridge, recharging phones/Ipad and 1 small exhaust fan. I have a 4000 watt jenny, but, who wants to listen to that all the time?
Any suggestions, pointers or places to start?
Thanks all,

Your refrigeration is the killer in this equation. There are already some great suggestions around that but if you really must run the bar fridge you will likely need to get a little more serious and financially deeper into the solar. If this cabin is used very infrequently your most cost effective solution may be a generator/ battery hybrid system to minimize cost and noise. I would look at a battery/inverter (that can support your fridge startup) and charge it up with your genny for a few hours a day and then run your loads off of the battery after that.

OlJarhead · August 11, 2016, 11:31:08 AM

You could run a camper style fridge with DC/AC and Propane options.

I run my system year round and frequent the cabin sometimes weekly for a few days. I shut down the inverter, open the fridge door (I run a full sized fridge with no freezer), disconnect the battery on the genset and leave. Batteries are always 100% when I return.

While I am gone I have a 24vdc to 12vdc converter running full time to allow 3 12vdc fans to run continuously in my back room to circulate heat in the room (where my water enters the cabin and my composter is).