Solar wiring questions (newb)

**frohickysmolder** · July 27th, 2012, 21:58 PDT

Well that is an incredible amount of information.

As it stands right now I'm probably going to hook up just the four batteries and use the fifth to rotate in. I like that idea primarily because both I bought 5 batteries, and I think it adds to the resiliency of the system without further purchases.

So based on that it probably throws of some of your calculations, however I am going to need to let your post sink in so ill have to wait to clarify for you, but I have been thinking of keeping that inverter I have and using it singularly with the extra battery should the need arise.

Besides it sounds like you are saying that the batteries I have (if i had the 6 for 600 ah) could use a bit more panels than i have. So my guess is that downsizing to 4 makes the system more fitting. However, I am going to guess that the 4 batteries at 400 ah couldn't be used to run a well pump? I havent really been considering usage of a well pump, im more thinking that i will just use a pulley and a pvc bucket from the well. I guess

So do some of the emergency applications i have mentioned lose effectiveness when i reduce to 400 ah ?

It sounds like in the winter my system will barely be able to do anything other than power up some minor electronics. and i am ok with that. i spent months camping in cold weather, and i have a basement which is a little more moderate than outdoors, I could probably hook it up to a pellet stove and I have been interested in adding a wood stove anyway.

Thanks to everyone so much for helping, and bantering. I don't mean to criticize anyone as i said in the conversation about CFL. You all have helped me appreciate the true cost of electricity as has trying to develop this system. I do not believe we pay enough for grid electricity when we consider all the factors, and CFL's do have something to say about that.

My batteries arrived today. Whew! Heavy. So now I have the main components (tho i will need a new inverter still, brands, specifics?), and I am ready to get started. Does anyone know of a good video that shows exactly how all these components are pieced together? A comprehensive look at the wiring? I guess what confuses me the most currently is the wiring of the breakers. For some reason i can't picture that.

PS- have any of you ever seen the biolite camp stove? I just got mine in the mail today. its a cool gadget havent been able to try it out yet. It allows you to boil water over a little stove with a generator in it to charge USB devices. it also powers a little fan and an internal battery for the fan.

**BB.** · July 27th, 2012, 23:22 PDT

Originally Posted by frohickysmolder

As it stands right now I'm probably going to hook up just the four batteries and use the fifth to rotate in. I like that idea primarily because both I bought 5 batteries, and I think it adds to the resiliency of the system without further purchases.

Several issues--I don't like things that I have to rotate in/out every few months. I tend to get distracted and forget to do that.

Also, it is more batteries to monitor/keep charged (typically, a flooded cell battery should be recharged every month. AGM's every 3-6 months or so). I am cheap and have not found very good "small" battery chargers (cube on plug ~1 amp trickle chargers, etc.)--One cheap way around it was to get a lamp timer and set it for ~1 hours per day. That was usually enough to keep a battery float charged without boiling it dry (I do this for several cars that are not driven much). If you need more time set for 2 hours a day, etc...

So based on that it probably throws of some of your calculations, however I am going to need to let your post sink in so ill have to wait to clarify for you, but I have been thinking of keeping that inverter I have and using it singularly with the extra battery should the need arise.

It is a change for many people when we tell them that they have too big of battery bank.

In the old'en days, when off grid users were "running out of power", the standard suggestion was to get a bigger battery bank. Mostly they did this because batteries were "cheap" and solar panels were expensive.

And, as you see, there is a minimum rate of charge (5-13% recommended rate of charge using 20 Hour amp*hour capacity). When you get too big of battery bank, it takes a long time to recharge the bank (partially charged batteries sulfate faster), and don't have enough "energy" to properly condition the plates, plus for "tall" batteries mixing of electrolyte with some bubbling. And batteries have self discharge (older forklift batteries can get upwards of 1%-2% self discharge per day "near the end of life").

For larger systems, we suggest 24 or 48 volt battery banks--So an "odd number" of batteries cannot be rewired from 12 to 24 (or 48) volt systems.

If your loads are small (typically under 1,200 watts continuous) and your battery bank under 600 AH or so, you can do OK with a 12 volt inverter/charger (I try to keep under 100 amp nominal current at 12 volts--helps keep wire diameters "reasonable").

Also, there is a really nice 12 volt 300 Watt TSW inverter. If you can keep your loads low--It is about the "perfect" lower power inverter out there (with features rarely seen on inverters that cost many times more--such as "search mode" and remote On/Off input). Note there is a 230 VAC 60 Hz version available too.

Besides it sounds like you are saying that the batteries I have (if i had the 6 for 600 ah) could use a bit more panels than i have. So my guess is that downsizing to 4 makes the system more fitting. However, I am going to guess that the 4 batteries at 400 ah couldn't be used to run a well pump? I haven't really been considering usage of a well pump, im more thinking that i will just use a pulley and a pvc bucket from the well. I guess

Don't know--There are 12 and 24 VDC well pumps out there (submerged or surface pumps--depending on your well). And perhaps you can get Grundfos pumps for a bit more reasonable price than here (these are remarkable pumps).

So--you can still pump. Just not with 1-2 kWatt pumps. Typically, use a "slow pump" to bring water up to a cistern and then a second pump (like a 12 volt RV pump) to pressurize the home/cabin water system (you can add a pressure/surge tank to even water flow).

Some folks have a "large" well pump that is not worth changing out... Use a big genset to fire up the in well pump for 20 minutes to fill a cistern. Then use the small DC pump for a week or two of water usage around the home.

There are many other options out there--But we can put that off for now.

So do some of the emergency applications i have mentioned lose effectiveness when i reduce to 400 ah ?

A 400 AH battery bank and 300 Watt 12 volt TSW inverter can be a very useful emergency/portable/long term survival system. One person (Wayne from NS Canada) has even managed to run his fridge/freezers from a 300 Watt TSW MorningStar inverter for many years (not sure many other people have the knowledge and patience to duplicate his work).

It sounds like in the winter my system will barely be able to do anything other than power up some minor electronics. and i am ok with that. i spent months camping in cold weather, and i have a basement which is a little more moderate than outdoors, I could probably hook it up to a pellet stove and I have been interested in adding a wood stove anyway.

Cloudy weather (as well as "any shade" on a solar PV panel) just kills output... I have a 3.5 kW GT system that can output 15-20 kWH per day... But during bad weather in winter, it can drop to below 1 kWH per day (5% of "nominal" output). In the end, no sun, no power with solar.

Thanks to everyone so much for helping, and bantering. I don't mean to criticize anyone as i said in the conversation about CFL. You all have helped me appreciate the true cost of electricity as has trying to develop this system. I do not believe we pay enough for grid electricity when we consider all the factors, and CFL's do have something to say about that.

We don't expect everyone to agree with every view/suggestion/etc. There are folks here with many differing views. And enjoy reading their observations/conclusions too.

My batteries arrived today. Whew! Heavy. So now I have the main components (tho i will need a new inverter still, brands, specifics?), and I am ready to get started. Does anyone know of a good video that shows exactly how all these components are pieced together? A comprehensive look at the wiring? I guess what confuses me the most currently is the wiring of the breakers. For some reason i can't picture that.

Assuming you are in Germany/Europe--Some of our other posters here can give you some better product suggestions. Victron is another good European brand.

But--I would suggest defining your needs/goals regarding power levels first. There are just too many products out there to start throwing out names and model numbers without knowing the ultimate size of your system.

I also really like to suggest some sort of Battery Monitor for systems (Victron is another good one). It is, almost, the equivalent to adding a gas gauge to your car (I remember the old VW's that did not even have fuel gauges) and more.

Anyway, some more reading (I like to call the Battery Bank the "heart" of a system... Everything revolves around keeping the battery bank "happy" and not exceeding it capabilities--for long life):

Deep Cycle Battery FAQ
www.batteryfaq.org
All About Inverters
Choosing an inverter for water pumping
All About Charge Controllers
Read this page about power tracking controllers

PS- have any of you ever seen the biolite camp stove? I just got mine in the mail today. its a cool gadget haven't been able to try it out yet. It allows you to boil water over a little stove with a generator in it to charge USB devices. it also powers a little fan and an internal battery for the fan.

Yes, I have read about them. Efficient use of local fuels--hopefully can address many issues for poor countries.

TEM (Thermal Electric Modules) used to generate power--Let us know how well it works out. TEMs tend not to be all that efficient and can be damaged by high heat.

The battery version of the stove--Not quite sure that makes sense for "third world" use... But don't know as I have never tried it.

Almost tempted to get (or build) a solar oven--We have bit better sun than you--But normal gas or electric stoves/ovens are so easy to use.

-Bill

**frohickysmolder** · August 8th, 2012, 10:19 PDT

Alright so now I'm interested in knowing the way in which to figure out my original question which is wiring. Lets say I have 20 feet between the panels and the equipment. The voltage running through the wire should be about 77. Based on my guessing i was thinking 10 gauge?

**BB.** · August 8th, 2012, 20:43 PDT

OK--This is what your system will be?

4x 240 Watt panels (wired 2 in series/2 parallel strings)
Vmp-array ~ 77 volts
P=V*I
I=P/V= 4*240 Watts / 77 volts = ~12.47 Amps Imp-array
20 feet one way wiring run.

Nominally, we recommend around 1-3% voltage loss (less than 1% is very expensive copper wiring for little gain, above 3% starting to waste a fair amount of power). So the voltage drops we are looking at:

77 Volts Vmp * 0.01 = 0.77 volts rough minimum
77 Volts Vmp * 0.03 = 2.31 volts rough maximum

Using this generic voltage drop calculator, entering 12.47 amps and 20 feet of one way wire run, try different wire gauges (remember, to 1/2 or 2x wire resistance, is ~3 awg change in wire size):