HELP Solar Panels

quar

Doc
If this needs to be moved I understand.

i want to learn how solar panels work, how to convert the power and blah blah blah.

also any cheap places to purchase would be great also.
I am pretty handy. So videos would be great and some places to shop or scavenge. Thank you
 

Anti-Liberal

Veteran Member
I bought a 4 100w panel kit for about $1600+ but it also came with a 2000w pure sine wave inverter. It's still in the corner and I can't think of the name of the company.

ETA............Renogy. Many types of kits there, friendly, helpful sales too
 

dvo

Veteran Member
DW brought this up today as well. Not sure where the discussion should take place on the Forum. I’m fearing for a long dark winter. Sadly, solar has its limits up here.
 

Knighttemplar

Veteran Member
Use solar 4 months every year while in the camper. Have not run the genny during that time. We use 4-100 watt panels, 4-100ah batteries, and a 2000 watt pure sine wave inverter. the battery monitor and charge controller are Bogart engineering. We use only led lights and use this system to charge phones, watches, pads and computer. It also runs the radio, tv, pump, and furnace. Got info from Bogart and AM Solar. Did the build myself.
 

Anti-Liberal

Veteran Member
I bought a couple books that I thought would help explain solar to me but I just don't have the IQ for for electricity. I did learned a few things but the bulk of it is too much. If it involved a 351w V8 I think I would have some more interest in it.
 

rafter

Since 1999
I have 10 panels in my garage that I want to sell. They were up 1 year then taken down. I don't know the wattage....does it say on them? This was my DH's thing and I can't remember what size they are.
 

Big Bob

Senior Member
Harbor Freight has a solar kit that is ok for a start. It is enough to charge phones, hand held radios and run minimal lighting. Some friends in ham radio group have them. Don’t expect to run your house off a small panel. Read lots of catalog data and study all the options before spending much money. Remember they don’t do much on rainy days.
 

biere

Veteran Member
Hop on youtube, yeah evil google but it still teaches you a lot on some subjects, and search for rv solar. You will find many people have added or improved the solar on their camper and this goes for store bought campers or home made.

Depending on how much stuff you are trying to run and how far away everything is from other stuff you get some folks running stuff other than 12 volts.

For a small car system, a couple panels feeding into a properly rated mppt controller will charge a battery plenty to run common stuff like phones and laptops and keep them charged. If done properly you can run some higher power drain stuff for short periods but you need to learn your system.

Learning the system also applies to where you are located and how much sun you get. Having your solar panels track the sun to make the most of its energy is important in some cases..

A lot of the rv sites have a solar section all to itself as well. The tiny camper site does as well I think.

My opinion is I don't care what the solar panel does, I need to know its output. Not how it does what it does. There are 2 types of controllers for solar and mppt is more efficient but more expensive. Being more efficient I feel it is worth it.

I personally don't want to tie my solar into the electrical of the vehicle directly so the solar setup will have its very own battery. Things I want to run will plug into an invertor, and invertors can cost a lot of money if you get the good ones with very clean power.

The vehicle starting battery is just for that and I don't run the risk of a problem draining it and I also don't have to try and figure out how to make the solar setup deal with an old 12 volt battery and a brand new one not at all like what is in the engine bay.

Such a small setup would work for a shed or something as well. If you research your parts before buying the setup can somewhat grow.

You will find a ton of opinions on battery banks and if they can be expanded over time or not.

My personal concept is play with the van setup and leave it alone as long as it does what I want. If it won't do what I want, well sure something needs changed. If I want a larger setup I would make a 2nd setup for the shed and go from there.
 

WanderLore

Veteran Member
Upgrading my little cabin. Find some ways to work around things so you don't have to try to use the solar for everything.
Will Prowse has good starter videos and runs www.diysolar.com
I think that's the right one.
People can get really technical, but if your just planning a small set up that isn't necessary.

I have a 100w panel from Rich Solar. Ordered as a kit that came with wires and controller.
I bought an inverter from Walmart when my old one went out.
I have a good marine deep cycle battery.
I can give you more specifics if you give an idea of what you want to power.

I have more than enough power for my phone and laptop and charge dvd player if I want it.

I use oil, batteries, and solar yard lights for lighting.
Wood/coal stove for heat. Compost potty dumped in compost area. Haul water in jugs. Figure I use a gallon a day. I have a good filter and rainwater set up also.
No vacuum. No dishwasher, no TV. Wood floors. Big bowl makes a good sink. And for a bath.
Butane stove for warm months. No fridge.

Battery is the meat of the system. Get the best you can afford.
I'm trying to work towards complete independence on this matter.
Getting there and really enjoy it. Sorry to belabor the subject
 

Milkweed Host

Veteran Member
That's a big question.

Check out some Youtube videos on the subject.
Along with the internet and books on the subject.

Also, Monocrystalline is better than polycrystalline.

100 watt panels are still cheap to purchase. Any larger panel becomes heavy
to handle.

Large copper wires required between panels and battery bank. (check out charts)

If you decide on a 12 volt system, check the market with 12 volt lights, TV or whatever
you're after. It is better to use the 12 volt DC power instead of going thru an inverter to 120 AC.

The pure sine wave inverter will allow you to have more options.

Many options on batteries. If money is no problem, I'd go with, lithium iron phosphate (LiFePO4).

Otherwise, if the battery is for indoor use, it needs to be sealed and lots of options there.
 

rob0126

Veteran Member
Just my 2 cents from what I've learned about solar:

(This is for a small fries system only. 20-400 watts)

- The batteries will cost you the most.
- AGM's at a minimum. Lithium preferred. (Brands swing wildly here in quality. Do some homework)

- The next costly piece is a high quality pure sinwave inverter.
- Don't go cheap on this one. (Victron at a minimum)

- Then the charge controller.
- Get a half way decent one. Victron preferred on up. (Could get by on a Renogy)

- Then the panels.
- The sky is the limit here. (HQST at a minimum)
 

hiwall

Veteran Member
Many here have solar experience.
My first run was several years ago, about 300 watts on the roof of my RV. System still on and still works fine.
My second project was 3000 watts on the house with a fair sized battery bank to run 2 kitchen circuits. Been up for 1-1/2 years and is working fine.
 

LoupGarou

Ancient Fuzzball
What is your load? Are you looking to power a few electronics, an entire house, or something in between?

Always the best first question!

Quar, make a list of your loads that you want to be able to run, then write down how much wattage they take while running, and also write down how often and how long each day you use them. The wattage will be on the nameplate that is usually somewhere near where the power goes into the device. Some times it wont say wattage, but will tell you the input voltage and input amperage, which if you multiply the two together, you get wattage.

For example:
Code:
1 Table Lamp    120V (Volts)       100W (Watts) (Bulb rating) 2 hours (1 hour, twice a day for 2 hours total)
2 Radio         120V  .6A (Amps)   72W                        3 hours a day
3 Toaster Oven  120V               1,200 Watts                .25 hours a day (Two 7.5 minute periods)
4 Mattress Heater120V              65 Watts                   4 Hours a night (auto cutoff)
Here comes the first part of the math needed, to convert all of that to WattHours (WH) per day:
1 Table Lamp, 100W * 2 Hours = 200WH
2 Radio, 72W * 3H = 216WH
3 Toaster Oven, 1200W * .25H = 300WH
4 Mattress Heater 65W * 4H = 260WH

Total = 976WH per day needed to run the loads listed.
Which means that you need to not only "create" at least that much power per day with solar panels (assuming no cloudy days), but also store at LEAST that amount in your battery bank. Most batteries should not be drawn down to full "nameplate" capacity if you can help it. Most don't want to be drawn down past 50%, some no more than 20% before it starts really eating into their "charge cycles". Deep Cycle batteries, like trolling motor batteries and golf cart batteries really should be kept in the 80-100% SOC (State of Charge) range for best lifespan and highest number of Charge Cycles. This means that the "1000WH" (rounded) list of loads above would really need to have at least 5000WH of battery pack/bank capacity to keep it in the 80% or better range. If you bought good Deep Cycle batteries, or AGMs batteries that were designed for 50%, you would only need 2000WH or battery pack/bank. And that still does not cover cloudy days. If you have a cloudy day every two sunny ones, multiply that 5000WH or 2000WH pack size by 1.33. A cloudy day every other day, multiply by 1.5.

While 2,000WH to 7,500WH of battery bank size seems rather large, figure that an average golf cart battery (6V * 210AH) has around 1,260WH of power in it and can be bought for around $100-$125 each (buy them in pairs since you need at least 12V battery packs to make chargers and inverters work). $200-$250 will get you 2 EGC-2 golf cart batteries if you shop around, which will give you 2,520WH of NAMEPLATE rated wattage. At 50% SOC, that gets you back to 1260WH of usable power per two EGC-2 batteries. At 80% SOC, that only gives you 504WH of usable power per two EGC-2 batteries. So you can scale your system capacity that way.

The batteries are where you end up spending a good part of the money of a solar PV system. It is also where you can do your math wrong (like using nameplate ratings on everything, or not factoring in cloudy days) and make a nightmare of a system that never gets a full days power to your loads and ends up killing batteries right and left. Yes, the batteries can get expensive. But wait, I'm not finished with the calcs. There are other options than trying to make it work for 2000-7500WH of battery bank design and 1000WH of actual power needed from the system...

First, let's look at the solar needed to run that load level...

Normally, most areas of the US get between 5 and 8 hours of USABLE sun per day. This does NOT usually include "Dawns frist light" at 7AM, or "Just before Dusk" at 6PM. Think more like 9:30-10AM till maybe 4-5PM. Let's play with the 6 hours a day theme, just for simplicity's sake. If you have a single 100W panel, and can keep it pointed at the sun for those 6 hours, you can assume close to 600WH of power from the panel. Again, nameplate ratings are just that, manufacturers specs that the manufacturer states to give you a ballpark of the capabilities of the panels in IDEAL conditions, not necessarily everyday use. I used to always derate the ideal vs. everyday conditions by knocking around 20% efficiency off the panels, especially if you don't have a way to "track" the sun as it "moves" across the sky. With this, a 120W panel gets thrown into the equations as a 100W panel, and a 100 watt panel gets treated as an 80W panel. There are other "losses" in the system as well, but for now, that is the one we need to concern ourselves over since we are talking about the panels themselves. So we need to be able to develop at least 1000WH of power a day (plus any cloudy day factoring).
Again, let's pick on 100W panels, which we derate to 80W of usable power coming out...

Code:
1 panel    80W * 6H = 480WH  (not enough)
2 panels  160W * 6H = 960WH  (getting there)
3 panels  240W * 6H = 1440WH (Good for one day, plus some overhead)
4 panels  320W * 6H = 1920WH (almost enough to recover for 2 days)
5 panels  400W * 6H = 2400WH (good for 2 days plus a little overhead)
6 panels  480W * 6H = 2880WH (good for almost 3 days of power, almost)
7 panels  560W * 6H = 3360WH (good for a solid 3 days of power)
Again, the extra days of capacity will work out IF your battery bank is sized big enough to COVER that load with no input and not go below the 50% or 80%SOC.

Here is one of the biggest secrets in Solar PV system sizing: Concentrate on reducing your power needs BEFORE figuring out what size PV system you want. So let's run through the list of loads again, this time swapping out the loads with more efficient ones:

Code:
1 Table LED Lamp   120V (Volts)      13W (Watts) (Bulb rating) 2 hours (1 hour, twice a day for 2 hours total)
2 PortableRadio    120V              15W                        3 hours a day
3 Microwave Oven   120V              1,200 Watts                .1 hours a day (Two 3 minute periods)
4 Mattress Heater  120V              65 Watts                   1/2 Hours a night (just before ya hop in)
Which now drops the WattHours (WH) per day way down:
1 Table LED Lamp 13W (13W rated to develop 100W worth of light), 13W * 2 Hours = 26WH
2 PortableRadio, 15W * 3H = 45WH
3 Microwave Oven, 1200W * .1H = 120WH
4 Mattress Heater 65W * .5H = 33WH

And all of a sudden you have the same capabilities, for only 224WH per day instead of 976WH per day.

Now, 3 panels will get you 1440WH per day, enough for several cloudy days, and two EGC-2 batteries will hold (to 50%SOC) 1,260WH of power, enough for at least 3 days of clouds. The system is MUCH cheaper if you pick and size the loads right first.
 
Last edited:

WFK

Senior Something
Buy solar panels used. Lots of them on eBay taken down by ppl who didn't want them anymore. Often offered in batches.
Find their specs. If you don't understand them, scrap your project.
 

LoupGarou

Ancient Fuzzball
And if you really want to get the figures right, get yourself a watt wizard or similar Watt Hour meter that you can plug into the wall, and then plug the device into it. It will show you over time what the actual device's power needs are. This is especially helpful for things like refrigerators and freezers that only really take power for a percentage of time per hour and then sit idle while the temperature starts to creep back up to the set point. Typically a "fridge" is on for 10-15 minutes and then back off for at least 30-40 minutes unless it is hot inside the house. Freezers are the same way, on for part of the time, then then off for even longer time. The freezer's nameplate wattage will be it's "running" wattage and may be in the 100-200 watt range. One of mine downstairs is 130W, but I am not looking at it taking 130W * 24H per day = 3,120WH per day. Instead it cycles on about 12 minutes per hour on average, so it actually takes more in the 130W * (24H * .2) = 624WH per day or less (I keep them on the North side of the house in the basement, and in the winter I don't heat that room so they rarely run at all (when the sun is hardest to get)).

Other things, like DVD players and TVs can take a LOT of power even when "off" as half of the circuitry is still active (mainly to keep a "watch" on the infrared remote sensor to see if you want to turn it on). I have a TV that is 85W when "on", and still takes about 30 watts when "off". Desktop (and some laptop) computers can be the same way, still taking significant power when "off". I know that 30 watts doesn't seem like much, but if you are trying to power it on solar, and don't know that it is still taking 30W when off, that 30W * 24H per day turns into 720WH per day for just that one device. That's the output of two more solar panels for the TV to just be sitting there doing nothing. And there are plenty of these "phantom loads" in a normal house.
 

one4freedom

Contributing Member
Anything that I find is a phantom load, I put on a switched outlet strip. There are however things that forget programing if left off too long so those are just phantom loads I put up with. Newer freezers and fridges often have smaller compressors but run longer, best bet is to meter them like with a P3 kill a watt meter or similar like Loup mentioned.
 

SackLunch

Dirt roads take me home
I'd recommend a "refrigerator only" unit for the solar powered, off grid kitchen plus a separate efficient chest freezer to replace the standard refrigerator/freezer combination.

EnergyStar rated at 293 kWh/yr


It's spendy, about $1200
The trade off is in battery capacity since refrigerators (and freezers) are a 24-hour load on the system.
 

Millwright

Knuckle Dragger
_______________
A big part of this is reducing load.

If you are going off grid, as opposed to supplemental/emergency capacity, here's something to consider, LP fridge, etc.

 

LoupGarou

Ancient Fuzzball
Something in betwee, however understanding the science behind it to have reasonable goals.
If you want to post your list of loads sometime this weekend, we can roll through it and get an idea of what you may be looking at as far as total load demands, battery bank sizing, and and solar array sizing. And then we can look at what options there are to possibly reduce some of the loads, as well as where you may find some good deals on the parts.
 

Bob the Builder

Contributing Member
Try and move any load you can to 12 volt, especially lighting. It's more power economical when using 12V.
Try not to run any heating element - water heaters or on demand heaters, hair dryers, toasters electric blankets, definitely microwaves are a power hog. Newer LED TV sets are not bad.
Power inverters used to convert 12V to 110V are a parasite load when running (and sometimes when in standby).

HandyBob's Blog is a little repetitious but has some good info for off grid or non grid tie.

Good practice if new construction or deep remodel is to rewire house for 110V and 12V as two separate systems. Any 12V load is easily moved and lights are prewired and switched. Keep 12V runs heavy gauge and short.
 

NoDandy

Has No Life - Lives on TB
Always the best first question!

Quar, make a list of your loads that you want to be able to run, then write down how much wattage they take while running, and also write down how often and how long each day you use them. The wattage will be on the nameplate that is usually somewhere near where the power goes into the device. Some times it wont say wattage, but will tell you the input voltage and input amperage, which if you multiply the two together, you get wattage.

For example:
Code:
1 Table Lamp    120V (Volts)       100W (Watts) (Bulb rating) 2 hours (1 hour, twice a day for 2 hours total)
2 Radio         120V  .6A (Amps)   72W                        3 hours a day
3 Toaster Oven  120V               1,200 Watts                .25 hours a day (Two 7.5 minute periods)
4 Mattress Heater120V              65 Watts                   4 Hours a night (auto cutoff)
Here comes the first part of the math needed, to convert all of that to WattHours (WH) per day:
1 Table Lamp, 100W * 2 Hours = 200WH
2 Radio, 72W * 3H = 216WH
3 Toaster Oven, 1200W * .25H = 300WH
4 Mattress Heater 65W * 4H = 260WH

Total = 976WH per day needed to run the loads listed.
Which means that you need to not only "create" at least that much power per day with solar panels (assuming no cloudy days), but also store at LEAST that amount in your battery bank. Most batteries should not be drawn down to full "nameplate" capacity if you can help it. Most don't want to be drawn down past 50%, some no more than 20% before it starts really eating into their "charge cycles". Deep Cycle batteries, like trolling motor batteries and golf cart batteries really should be kept in the 80-100% SOC (State of Charge) range for best lifespan and highest number of Charge Cycles. This means that the "1000WH" (rounded) list of loads above would really need to have at least 5000WH of battery pack/bank capacity to keep it in the 80% or better range. If you bought good Deep Cycle batteries, or AGMs batteries that were designed for 50%, you would only need 2000WH or battery pack/bank. And that still does not cover cloudy days. If you have a cloudy day every two sunny ones, multiply that 5000WH or 2000WH pack size by 1.33. A cloudy day every other day, multiply by 1.5.

While 2,000WH to 7,500WH of battery bank size seems rather large, figure that an average golf cart battery (6V * 210AH) has around 1,260WH of power in it and can be bought for around $100-$125 each (buy them in pairs since you need at least 12V battery packs to make chargers and inverters work). $200-$250 will get you 2 EGC-2 golf cart batteries if you shop around, which will give you 2,520WH of NAMEPLATE rated wattage. At 50% SOC, that gets you back to 1260WH of usable power per two EGC-2 batteries. At 80% SOC, that only gives you 504WH of usable power per two EGC-2 batteries. So you can scale your system capacity that way.

The batteries are where you end up spending a good part of the money of a solar PV system. It is also where you can do your math wrong (like using nameplate ratings on everything, or not factoring in cloudy days) and make a nightmare of a system that never gets a full days power to your loads and ends up killing batteries right and left. Yes, the batteries can get expensive. But wait, I'm not finished with the calcs. There are other options than trying to make it work for 2000-7500WH of battery bank design and 1000WH of actual power needed from the system...

First, let's look at the solar needed to run that load level...

Normally, most areas of the US get between 5 and 8 hours of USABLE sun per day. This does NOT usually include "Dawns frist light" at 7AM, or "Just before Dusk" at 6PM. Think more like 9:30-10AM till maybe 4-5PM. Let's play with the 6 hours a day theme, just for simplicity's sake. If you have a single 100W panel, and can keep it pointed at the sun for those 6 hours, you can assume close to 600WH of power from the panel. Again, nameplate ratings are just that, manufacturers specs that the manufacturer states to give you a ballpark of the capabilities of the panels in IDEAL conditions, not necessarily everyday use. I used to always derate the ideal vs. everyday conditions by knocking around 20% efficiency off the panels, especially if you don't have a way to "track" the sun as it "moves" across the sky. With this, a 120W panel gets thrown into the equations as a 100W panel, and a 100 watt panel gets treated as an 80W panel. There are other "losses" in the system as well, but for now, that is the one we need to concern ourselves over since we are talking about the panels themselves. So we need to be able to develop at least 1000WH of power a day (plus any cloudy day factoring).
Again, let's pick on 100W panels, which we derate to 80W of usable power coming out...

Code:
1 panel    80W * 6H = 480WH  (not enough)
2 panels  160W * 6H = 960WH  (getting there)
3 panels  240W * 6H = 1440WH (Good for one day, plus some overhead)
4 panels  320W * 6H = 1920WH (almost enough to recover for 2 days)
5 panels  400W * 6H = 2400WH (good for 2 days plus a little overhead)
6 panels  480W * 6H = 2880WH (good for almost 3 days of power, almost)
7 panels  560W * 6H = 3360WH (good for a solid 3 days of power)
Again, the extra days of capacity will work out IF your battery bank is sized big enough to COVER that load with no input and not go below the 50% or 80%SOC.

Here is one of the biggest secrets in Solar PV system sizing: Concentrate on reducing your power needs BEFORE figuring out what size PV system you want. So let's run through the list of loads again, this time swapping out the loads with more efficient ones:

Code:
1 Table LED Lamp   120V (Volts)      13W (Watts) (Bulb rating) 2 hours (1 hour, twice a day for 2 hours total)
2 PortableRadio    120V              15W                        3 hours a day
3 Microwave Oven   120V              1,200 Watts                .1 hours a day (Two 3 minute periods)
4 Mattress Heater  120V              65 Watts                   1/2 Hours a night (just before ya hop in)
Which now drops the WattHours (WH) per day way down:
1 Table LED Lamp 13W (13W rated to develop 100W worth of light), 13W * 2 Hours = 26WH
2 PortableRadio, 15W * 3H = 45WH
3 Microwave Oven, 1200W * .1H = 120WH
4 Mattress Heater 65W * .5H = 33WH

And all of a sudden you have the same capabilities, for only 224WH per day instead of 976WH per day.

Now, 3 panels will get you 1440WH per day, enough for several cloudy days, and two EGC-2 batteries will hold (to 50%SOC) 1,260WH of power, enough for at least 3 days of clouds. The system is MUCH cheaper if you pick and size the loads right first.
Thanks Lou, good info !
 

WFK

Senior Something
Quar,
To understand the overall problem you can play it all through with one load, the refrigerator.
It will need 1 to 1.5 kWh pro day. It will have more hours without sun than sun PER day. You decide how many hours.
So you have a predictable LOAD to supply every day and you have to look for a predictable source for that.
That is where it begins. You will soon see that you need energy storage to cover the times when the sun doesn't shine.
And there you have to make assumptions that affect the cost and the reliability of your system.
THEN you decide what you want to power, with some of the valuable info from above (like don't power heating devices.)
See the concept first and then expand it.
 

Thinwater

Firearms Manufacturer
Get used panels from Marketplace and Craigslist. Current prices under 30 to 40 cents per watt. There are a pile of companies doing some kind of lease BS using .gov subsidies and remove them in 3 to 5 years then sell to second hand dealer for pennies on the (government) dollar.

I bought 2KW worth of panels last month for $400. Battery storage is the bigger issue and anothe topic. I got an Outback 80 amp charge controller and two 1500 watt true sine wave inverters for a system I am building.
 

desert knight

Contributing Member
i just switched my solar system from lead acid to lithium iron phosphate batteries yesterday. hopefully the investment was worth it. will see how it goes. also switched my measly 500 watts of solar panels from parallel to series to go along with the new mppt charge controller. not 100% sure which is better for the charge controller until i run it thru about a months worth of cycles.
 

Hi-D

Veteran Member
I'd recommend a "refrigerator only" unit for the solar powered, off grid kitchen plus a separate efficient chest freezer to replace the standard refrigerator/freezer combination.

EnergyStar rated at 293 kWh/yr


It's spendy, about $1200
The trade off is in battery capacity since refrigerators (and freezers) are a 24-hour load on the system.
This is what I have. Rated a 3 amps. It's about 4/5 years old now. Time flies.

Samsung 30 in. W 21.8 cu. ft. French Door Refrigerator in Stainless Steel-RF220NCTASR - The Home Depot

I also run this. A good share of my energy storage system in the winter is heat in the floor.

TW025-1USC-FXX Bosch Water-To-Water Geothermal Heat Pump | 2.0 Ton | Unit Mounted Controls (hvac.place)
 
Last edited:

marsofold

Senior Member
We have had solar for seven years and I have learned a few things. Most people underestimate their power needs. And if you live in the great white north, you will not be able to keep those batteries charged in winter without a generator during periods of dim light. You will need much more battery weight than you might prefer. Tips:

#1 Batteries are the biggest issue. Lithium batteries are expensive and have issues with shorting out (google Tesla fires), burning down the house if inside. So if you go lithium, keep them away from the house. Lead batteries are heavy, and generally don't last much past eight years unless you use forklift batteries which last 20 years. If I had to do it all over again, I would buy two small lead forklift batteries. I currently run four 125 Lb Trojans (four 6-volt 370 amp-hour batteries) for my 1260 watt solar array. Lead batteries must be charged at an amperage of 5% to 13% of their standard 20-hour amperage rating. Too low charging amps and they will run down and die, too much and they overheat to be damaged. There is a certain ratio of panel total watts to Lbs weight of lead batteries that must be maintained. In my case: 1260 watts x 90% real world conditions = 1134 watts actual. 1134 watts x 93% typical charger efficiency = 1055 watts. 1055 watts divided by 24 volts = 44 amps charging the batteries. 44 amps divided by 370 amp-hours = 11.9% (OK). Not much room for expanding my array and staying under the upper 13% limit. Buying enough batteries to keep the charging rate down to 5% will enable you to go twice as long on a dark period before they are discharged.

*** The approximate ratio of lead battery weight to solar panel kilowatts should stay between 360Lbs/kilowatt to 940Lbs/kilowatt.***

Otherwise you will be outside the charging limits your batteries can tolerate without dying early. You can only discharge lead batteries down to a 50% charge. Go under that and they die very early. Just to max out my battery life, I don't like going under 75% charged. You gotta water the cells of the batteries about every six weeks if heavily used. Do not get gell cells, AGMs, or any other variation because they just won't last as long. Just stay with the regular type needing water filling at intervals. Only use distilled water to fill them.

#2 Solar panels stuff: Monocrystalline panels' output decreases less per year than polycrystalline ones. Solar chargers generally don't go above 140 volts upper limit without damage. So you can only add panels in series up to 140 volts. Since the panels' voltage goes up when cold, I limit my arrangement to 120 volts total. You can only parallel TWO strings of panels without a combiner. I have two strings wired directly in parallel to keep things simpler. Since that is a real thing, if you don't want to buy a combiner, I would recommend getting larger area panels to get more power since you are voltage limited by wiring them in series. The ratings on panels are generally only 90% of what is claimed since perfect weather conditions are assumed (cold day at noon in June). Think twice about putting them on a roof if you ever might consider selling your house. I did, and I had to deal with removing them and "fixing" the roof to look cosmetically acceptable to most people.

Inverters: Go with a minimum 24 volt pure sine wave inverter/charger combo. So you don't have to buy a dedicated charger for winter. I like Outback Power products. If you want an 1800 watt outlet (15amps AC), buy them for 2000 watts since often they are sold by PEAK watts, not continuous watts. Outbacks' inverters automatically switch to generator (or grid) power when it senses voltage input there. So mine charges from the grid (or generator) by default, and not from the panels. My setup is mostly for a survival situation when the grid ceases forever.

Solar Chargers: there are two types: MPPT and PWM. The MPPT ones are more efficient and cost more. The PWM ones generally want their voltage at around 18 volts. That means you have to buy 18 volt panels and parallel all of them. More than two panels and you'll need a combiner. Most people only buy PWM chargers if they want under 1 kilowatt of power, since they can't wire the panels in series to get above above 18 volts. I went with an MPPT charger. Solar chargers are radio noise generators, so if you are a ham radio guy, look into this issue before you buy. I bought a low noise model just for this very reason, since I listen to shortwave radio.

Battery Cables: Battery cables are generally short and thick. As in 10 foot long and 00 size or larger. This is due to the fact that they will be carrying a very heavy amperage which will decrease the voltage seen at the battery under varying loads, which can be a very significant problem too deep to go into here. As a practical matter, you will need to locate the inverter to be around 10 feet or so from the battery box or less. You also want to put a low voltage fuse or circuit breaker on the positive lead to avoid fires in the event of a short circuit. Such are usually rated at 100 amps or higher. I use a fuse at the center connections of my battery setup and a circuit breaker on the final positive lead to the inverter. Make sure the connectors are tin plated or better. eBay sells such cables in the marine cable section at reasonable cost.

Power education. You get much less than you might guess from any setup. The math in my setup: My panels are rated for a total of 1260 watts. 1260 watts x 90% real world values = 1134 watts. 1134 watts x 93% solar charger efficiency = 1055 watts. 1055 watts x 80% battery efficiency = 844 watts. 844 watts x 93% inverter efficiency = 785 watts. My solar charger continuously indicates panel output which says useful power is received for only five hours per day in summer. Averaged over 24 hours per day, that means the continuous power is: 5/24 --> 21%. 785 watts x 21% = 165 watts continuously. That's right. My 1260 watt array only outputs 165 watts around-the-clock. The system can output 2 kilowatts peak, but over 24 hours only averages 165 watts. So it can run...my small meat freezer (90 watts average), two LED lights (30 watts), my 15" laptop (40 watts), and my T-mobile MiFi mobile router (5 watts) for internet. And that's all!!! Still thinking of going solar? Think about the math first.

Best site for solar info: Northern Arizona Wind & Sun Solar Forum
 
Top