Solar for newbies

[Texas Tornado]

"It depends", a comment I have learned to loathe when it comes to trying to wrap my brain around solar and it is followed by "just use your electric bill to see what you are using now and go from there" at issue is I live in a large all electric house (1700) with central heat and air, so the bill will not help me in going into a off grid cabin of 12X40 that will not have central heat and air nor the kitchen that is all electric. It is called downsizing....

Things that will be in my cabin: Upright freezer,refrigerator (not a side by side), LED lighting, lamps, ceiling fans (2), circular fan, computer, a couple of food dehydrators.
When searching the www you see solar panels with this watt or this watt and a ton of things that ya have to have with it and don't get me going on the batteries because that causes my bp to raise to stroke level. All lead,gel,etc and have to do them in series (along with the panels) and yes a 6 volt battery can be used but ya have to yada yada yada (for those of you smiling that have been there done that, please chime in with some of your knowledge to help us that have not taken that step).
I could drag this thread into all the issues I am having in just trying to get a straight answer to what to me are some of the simplest questions and "It depends" is what I get.... 
TT

[Texas Tornado]

Wow 26 have viewed this and no one is chiming in?

[busted knuckles]

I am looking forward to replies also.

[UK4X4]

I did copy and past a whole document into a thread here somewhere, I wrote it for work , but works in any scenario

OK so you have listed all your electrical equipment you want to run..fine lets give you an example of just a fridge

You now have to look at each items power consumption...in watts or amps

then how many hours you want to run them each day. this is just a simple example with no fudge fators or losses included

ie fridge---110v---300watts and I want it to run for 24 hours....fridges consumption is arround 12 hours per day as the compressor is not always working..
so example

300 watts at 110 volts - gives you 2,72 amps of power consumed when the compressor runs

lets call it 3 amps........it only runs for 30 mins every hour so thats 12 hours of running per day

so 3amps for 12 hours means its consumes 36 amp hours in a 24 hour period

So take this as your only cabin requirement- you need 36 amp/hours of power

Check a solar map for your areas sunlight per day.............this is not sun up to sun down.....but a measure of usefull sunlight---lets take 6 hours

So in order to run my fridge for 24 hours I need to get 36 amps in 6 hours

So I need my panels to give me ---36/6 = 6 amps every hour

24 volt panels are pretty common now.........and sold in watts.........P=V*I.......24v X 6amps = 144 watts of solar panel

But thats 24 volts and not 110... and the conversion takes power.........so lets add a bit of power to the panels to take out the invertor losses call it 180 watts the next size panel up

so thats awsome we get 6 hours times 8 amps...giving me 48 amps per day back into my batteries to power me over that 24 hours

To size a battery, you need to look at the type.....lets take it simple--lead acid and my manufacturer says It does x cycles from 80% back to full

so its prefered usable capacity is only 20% of its actual size......so if i want that battery to run my fridge happily for its full life it needs to have a capacity of
48 amps..../20 *100 = 240amphour

Now theres a storm comming and 2 days of no sun.....your taking out 48 amps a day and getting zero back...........so you just abused your battery and lessened its life

so its best to add in some spare capacity to power you over those stormy days......lets say 3 days reserve...
so instead of 48 amps, I need 48X3days as my 20% of battery size.

48 +48+48 + 144 amps of power required to get me over three days with no sun....144/30*100 =720amphours battery capacity



I think mountain Don posted a spreadsheet somewhere where you list your gear and it does the math

[MountainDon]

Spreadsheet is over here in this topic....
http://countryplans.com/smf/index.php?topic=8192.msg105900#msg105900

The first part is the AC and DC load calculator. It is based on a WEEKS worth of use so the once a week laundry can be added in and then averaged.   I also have a version that is based on a single 24 hour day use period.


Second section takes the calculated load result and helps figure out batteries.

Third section is for PV panels and I will be the first to admit that part is kinda sketchy, assumes the user will do a lot of their own homework on picking potential panels.

[MountainDon]

Some thoughts that have randomly circulated my brain as I have pondered the question here today....  In no particular order, and not necessarily directly connected to one another...

First, is whether or not an off grid PV system gets the buyer the best bang for the buck? Off grid with energy storage still costs more than a grid tie solution, IMO. Sometimes there are very good reasons for installing an off grid power system; like the distance to the power grid is too long and too expensive. Sometimes a person just wants to be independent. Independence comes at a cost, both in initial outlay and some maintenance work and costs. If something goes wrong you are the power company. How are you going to handle things like that? Better to think about that now in the design process now, than later when the inverter fries for whatever reason.


Are you in a lightning prone area?  We wish we were not.


There is a simple solution to the problem of designing and building a PV solar system. We can hire someone to do the job for us. That in itself can present the problem of finding someone who can actually so the job properly and honestly. This involves more than having a web store with some prepackaged kits for sale. Sites like that offer an assortment of kit sizes, some more complete than others. They can not answer the question of how much power the person looking actually does really need. They can guess, for that matter so can you. But a happy system owner starts with knowing how much power they will use. Once the consumption is known, then and only then can all the parts that best suit the situation be chosen.



When we discovered the cost of connecting to the grid in our mountains it seemed the only solution for us was solar. Once that was decided I took over a year to learn about PV solar, batteries and all the hardware. I did not find any books that taught me much. If I had I would point to them. If any readers have found some good references let them tell us about them.

I did find Homepower magazine to be useful. They have an archive of all their issues available online. If you buy a one year membership you get access to the whole series. They can be downloaded and stored for reference.

I found the Code Corner articles very useful. John Wiles is well known in the PV world. One thing to keep in mind is that the electrical code evolves; it changes every few years. Mostly not big changes, but smaller. However, today's code is very different in some areas when it comes to PV solar. Mostly it is about being safe. It is electricity and once you get beyond a basic 12 volt DC only system it can kill you. If a person feels comfortable doing small electrical jobs around the home AND is actually capable of doing that work safely, then they may be able to design and build a PV solar power system.

Speaking of codes... the most recent NEC rules state that the AC connections from the inverter to the service panel be fully enclosed (conduit).  It does not allow for the use of inverters that have a plug in receptacle like so many inverters have. Equipment sold by Outback and other top line manufacturers are built with points for hard wiring and for the use of conduit. You find that type in many (all?) of the kits seen advertised.  What code is in effect varies. Enforcement varies.  Checking on what electrical codes are followed in your area is a part of the design process.



The Country Plans Forum member known as Dave Sparks designs solar off grid systems that work. Dave's email is  offgridsolar@sti.net   and his website is  http://members.sti.net/offgridsolar/    I would trust Dave to build a system for myself or my close friends and family. He has been at it for over 20 years. He and his wife live off grid themselves. I am very comfortable recommending him to anyone who wants to be off grid but feels they are not able to design a system.



For now, forget about the hardware needs. Before trying to figure out what equipment one needs one must know what amount of energy is to be consumed in a typical day. That will take some though, careful thought. More than the rated wattage of any appliance is needed. Time is a factor. knowing the amount of power and the numbers of hours it will be used every day will let us calculate the watt-hours. Watt-hours is how any power company measures the energy used.

Example:  food dehydrators were mentioned. I know nest to nothing about them. Do they use electricity? I suspect they do. How much? There may be a label on the unit with watts or amps listed. That's good but may not be everything one needs to know. Does the dehydrator use the label listed power all the time? Or does it have a thermostat that turns any heating element on and off? If so, a device like a Kill-A-Watt meter can be helpful.

FWIW, most system failures are caused by insufficient storage capacity caused by incorrect estimation of energy use and/or insufficient PV capacity.



One benefit from learning and planning and designing, then building a good system is you will likely be able to figure out problems and solutions better when issues do occur. 



Just like many things, electricity and solar is not something we can all do well.



I'd like to help as much as I can, but I honestly don't know of any lists that will be of much use. Specific questions are easier for me to answer. Sometimes.

[Texas Tornado]

UK4X4, Mt Don, thank you both! Both have given me questions I need to ask myself...

[fcpnorman]

All great information. As I contemplate my situation, I am inclined to think that a stand alone generator should be in the mix to keep the batteries cycled if you have a period of storms and limited sunlight that lasts for more than a few days. I think in California that may end up being a necessity to supply power to the jockey pump for the fire sprinkler system. One thing that I have been hearing is that some of the building departments have been requiring a separate pump and separate storage tank to run the sprinkler system( hence the jockey pump). I also have to figure out if the solar system they have advertised would be enough to run a solar water pump for the well, or do I need a separate system for the well.  A local solar outlet where I live does have a package deal that includes (3) 240 watt panels, a 1500 watt inverter/charger controller in a pre-wired e panel, and 4 deep cycle batteries for about $5400.00.  If we decide to build on the property I would build to capture all the sunlight I can in the winter to maximize passive heat and light.  I would plan on having a propane refer to minimize electrical draw.

One question- has anyone had an issue in cold climates with leaving the cabin un-heated during the winter months; such as condensation issues or issues with drywall seams etc?

This is such a great place to find out this type of information.

[Texas Tornado]

Where my place is we have heat to contend with in summer and I keep seeing that heat means your solar system does not do as well, perhaps someone can discuss the why's of that?
Most folks up there have generators as it is the normal for the power grid to go down when the wind blows.

[mlnk]

Cold wire carries electricity more efficiently than warm wire. Picture the molecules in the wire racing around as the heat goes up and causing a traffic jam for the electrons trying to flow thru. (resistance) The panels also produce more power in cold weather.
My PV system produces the most power , 2900 watts on sunny cold winter days.
To deal with the heat, we tie or clip the solar panel cables up off the roof surface and keep them in the shade below the solar panels. We try to keep conduit runs short and elevate them 3" or more off the roof surface.  The attic may seem hot to you , but it is cooler than the roof. Some installers paint the conduit white.
Of course this is for Copper or Aluminum, some conductors , such as carbon, conduct better when warm.

[MountainDon]

Resistance does rise in a wire as it is heated, but the big culprit are the PV cells themselves. Increasing temperature decreases the voltage output of a PV cell by large amounts.  PV panel ratings are measured at Standard Test Conditions (STC); a temperature of 77 F with a sun brightness of 1000 watts of sunlight energy per square meter and an air mass of 1.5. Don't worry about what that is; but it covers most of the populated areas of the USA and Canada at elevations from sea level to a thousand feet or so.   STC is somewhat like the conditions EPA uses to rate automobile MPG.

As PV cells get hotter their voltage output decreases. When the cell temperature falls the voltage rises. That is just the way it is. That is cell temperature, not air temperature.  PV cells produce heat as well as electricity when sun strikes their surface. So they self heat. Plus they are dark and dark surfaces heat more than light surfaces. The air temperature could be 68 F but with sun shining brightly the cells could reach temperatures over 120 F.  This is one reason a panel advertised as a socalled 12 volt panel will have a Vmp (maximum power voltage) of 18 to 19 volts.

Altitude also affects panel output. In a nutshell, higher altitudes means the sun passes through less air. More energy strikes the panels. This increases the amperage, not the volts. But volts x amps = watts, so the power output rises.  I forget the precise numbers but at an elevation of 9000 feet it can add something like 20% to the output.

Back to temperature for a moment...  The cold temperature causes PV output voltage to rise. That can be a problem when PV panels are connected in series. In series the voltages are added. The peak voltage on a cold day can produce voltage high enough to damage a charge controller. So that is another factor that has to be taken into account when designing a system for a location. Outback, Midnite and Schneider/Xantrex all have online calculators for sizing PV  arrays properly.


If that is not enough about temperature, temperature also affects lead acid batteries. High temperatures can make a lead acid battery increase it's rated capacity; high temperatures can make a battery able to supply more energy. However, higher temperatures also shorten a battery's life. Cold, OTOH, decreases the battery capacity while increasing the battery life.  That is assuming the battery is not abused.

High temperatures can also affect the life span of electronic components.  Plan for ventilation.

[MountainDon]

mlnk does make a good point on the placement of panels. There should be an air space behind the cells in order to help with ventilation and cooling of the panels. In that respect pole mounted panels may be better than roof top panels.

[Texas Tornado]

Based off what I have read and seen on youtube, I want the solar panels on poles with a tracker and to have the connections close to where it comes into my place, I understand that you also lose when your wires have to long of a run from panel to control box (chime in from those who deal with that issue please).

[Texas Tornado]

I would upload pics and a video of just what the conditions and area is like that I will be dealing with but my cpu is getting fixed and no idea how long before it is home...
I have no trees on my 5 acres and a clear shot to south and west with no near neighbors to worry about trees blocking the panels.

[MountainDon]

Trackers work. However, you should check the pricing before leaping. When PV cost $3, $4 and more a watt trackers made a lot more sense than today when PV costs are $1 a watt and less. The last time I looked a tracker that could handle 1000 watts or so worth of PV cost almost twice the cost of the panels themselves.

I have seen an installed array that was divided into three parts. One group faced easterly, another southerly and the third westerly. That owner had calculated that was better than doing trackers with fewer panels. Of course he had many acres of land all with all the trees to the north. The panels were in a ground mount system in an area that enjoys very little snow.

Just something to think about after you know what the power needs are.

[Texas Tornado]

Any pictures showing something like that Mt Don?

[MountainDon]

I don't have any photos. It was roughly divided into three groups though I think the west and south groups were a little larger than the east. Makes sense as A/C loads are higher noonish and later.

[Texas Tornado]

http://suncalc.net/#/51.508,-0.125,2/2015.02.06/15:52
pretty neat that you can zoom in to your place and track the sun!

[Texas Tornado]

http://suncalc.net/#/33.958,-96.76,19/2015.02.06/13:49
switch to satellite and ya can see my place....
so 10-11 hours of sunlight? 

[Texas Tornado]

change the date and it makes me re-think where I would get a better position to place them...

[Texas Tornado]

Searching youtube I found this, does some nice explaining...
http://youtu.be/SRxIt2Z8nKE

[Texas Tornado]

Home made sun tracker..
http://www.instructables.com/id/Solar-PV-tracker/#step1

[UK4X4]

Hours of sunlight is not sun up till sun down, it's to do with the amount of usefull solar radiation

Look for a solar map for your areait certainly won't be 10 ....for example

http://tyconpower.com/learning_center/insolation-map.png

[Texas Tornado]

Anyone use these?
http://www.vmaxtanks.com/Solar-Batteries_c_21.html

[Texas Tornado]

Holy Moley what a system!
http://youtu.be/VDJ0QjPgDH8