New build off-grid

catdean6 · October 2017

Hello All,
Very new here and to pv in general. Planning to build an off-grid 600 sf home in Southern Colorado. Plan to have a small chest freezer, dorm refrigerator, few led lighting, a flat screen tv and washing machine. Wood Water heater, wood heating, and propane oven. Was thinking I probably need an 800 to 1000watt system with a back-up generator.
I looked at Renology panels, Midnite solar KID charge controller, 6v golf cart batteries, pure sine inverter, and a Honda generator.
I'm a grandmother with a grown son (an electrician) to help with the install. This will be my forever home. What would you suggest? Am I on the right track? Any recommendations and details on the products would be appreciated.

Photowhit · October 2017

I think you have some basics down. 6 Volt golf cart batteries are a good value for true deep cycle use. Pure sine inverter is needed to keep the compressors running well and efficiently in your fridge and deep freeze.

While anything is possible with a generator backup, Even with a moderately small system, and a relatively sunny environment. I would think you will want a bit larger array and a larger charge controller. We have found one constant and that is "loads grow".

Let's look at the loads you have planned, A chest freezer will run about half a Kwh each day, Small fridges About .650 - .700 Kwh's 230-260 Kwh's a year. That's not much less than small full sized fridges. If you check closely you should find 'full size' 9.9-12 Cu Ft fridges that run about 300 Kwh's a year or about .82 Kwh's a day, Chest freezers run about .4 Kwh a year and up... So roughly 1.2 Kwh's a year for new energy star appliances.

Tv's can be very reasonable, The 55 inch I bought a year or so ago, runs about 70 watts, will you have a Dish satellite service? Some of those machines run continuously unless you shut off power to them. How about internet service?

Computers should be laptops from a conservation stand point. Laptop's use 30-90 watts desktops and towers can run from 200 watts up.

Laundry will pretty much be a non-factor, so long as you plan on running it as an opportunity load when your batteries are fully charged. Front load machines tend to use a lot less energy. Line dry of course.

What do you do? and do any of those things involve electric? I use an electric tiller, chain saw, cook electrically mostly. Have assorted power tools.

Generally a very energy efficient home, with out air conditioning will run near 3 Kwh's a day. This is of course a ball park. I will also say generally 1st time off grid folks don't realize how much stuff runs on electric, so the conversion is more difficult.

With a generator, you can sort of start anywhere, but I would have a few suggestions;

If you are thinking 800-1000 watts of array, I would start thinking about a 24 volt battery bank system as a minimum. Perhaps this is what you are thinking already as the Kid would only handle 30 amps output at any voltage and 30 amps at 29 volts charging is about the max a 1000 watt array would put out.

I would also want an Inverter/charger, this will allow your generator to run at maximum efficiency when it's running as it will charge your batteries with energy not needed in your household.

There is 1 thing that you will want to determine, a single 24 string of 4 GC batteries only holds about 210 amp hours or about 5 Kwh's, So with just 1 cloudy day, with 2 nights, you will be drawn down below 80% State of Charge (SOC) So a couple cloudy days would require running the generator for a while to ensure good battery health. 2 strings with @10 Kwh's would handle 2-3 days with minimal charging. Batteries age together so I wouldn't add batteries after the first 6 months-a year until the bank is ready to be replaced.

catdean6 · October 2017

Wow, a lot to consider! I won't have an ac, I'm thinking I won't need one. I do have power tools to charge, laptop and phone to charge as well. I will be buying a new fridge so I will def look at getting the most Energy efficient. I Was thinking about a propane oven/stove. I just dont want to make a huge mistake purchasing the pv components. Thanks for sharing your knowledge!

mcgivor · October 2017

A refrigerator is a major load off grid, since you have not yet purchased, my suggestion is look at an inverter type with freezer, rather than running 2 units, not only are they efficient, they are kind on DC to AC inverters, not having inrush current. To be realistic the proposed array,battery, controller are probably not sufficient to support the loads, along with keeping the batteries happy, based on the 2 cooling appliances. The batteries are the most expensive component, being they have a limited life expectancy, shallow discharge, 30%or less will extend this life, deep daily discharges, below 50%, drastically reduce the number of cycles available.
It's always better to design a system to support the loads, rather than learning the hard way, as many have done, including myself, by building too small and having to upgrade later with new components.

Some information explaining inverter refrigerators https://www.bijlibachao.com/refrigerators/refrigerators-with-inverter-technology-can-help-save-electricity.html

Photowhit · October 2017

I forgot the planning part and the reason I suggested a 24 volt system voltage.

If you start with 12 volt, and choose later to switch to 24 volt, You would need to replace the inverter. We have found that 1000 watts is about the largest reasonable 12 volt system. Charge controller are based on there amperage output. a 1000 watt array will be about the maximum practical array on a single charge controller (CC)and you would not be able to run it on a single 'kid' CC. Basic equation for solar is amps x volts = watts, so a 12 volt system that maxes out at 1000 watts can handle 2000 watts at 24 volts and 4000 watts at 48 volts.

Also wiring becomes difficult for low voltage systems with larger inverters, since they input requires such high amperage.

It's great that you are thinking these things out now!

Estragon · October 2017

Another possible consideration... what kind of water supply (well, or ?).

catdean6 · October 2017

So sounds like a 24v system maybe bigger than I had orig thought would be best. No dish or internet, water is from cistern. Good thinking on the fridge/freezer. Probably better than propane. I'm trying not to be dep on fossil fuels. So what would you put in place? 24v 1200w? Or bigger yet?

mcgivor · October 2017

A 24V system is not necessary bigger, it's just when the loads exceed a certain point, it's better to choose a higher voltage, which in turn reduces current, thereby allowing smaller conductors, fuses or circuit breakers and so forth.
Once a refrigerator is involved it's better to choose a voltage above 12V nominal, 24V is much better in that it allows a series battery, of course 48V has the same advantage as 24 has over 12, but from your description 24V may be the happy medium. Another point is, as voltage increases, the charge controller will be able to support a larger array, thereby actually saving on the hardware. Please understand I'm not trying to overload you with information, but building a system involves selecting all the nessary components to build a ballanced system, ballanced being the key word. We all want you to succeed @Estragon and @Photowhit and others all have a willingness to help, proceed slowly, and the rewards will be satisfaction, don't rush, as of now you are in the infantry stage, so baby steps.

catdean6 · October 2017

I'm still a month or so out. You are right...trying to educate myself now and get a good understanding to keep the mistakes to a minimum.
I appreciate ALL the feedback. You guys are awesome!

BB. · October 2017

Ok. Not sure of loads yet--Always recommend conservation over just making a larger system as being the most cost effective. Typically, off grid solar power costs around $1.00-$2.00+ per kWH when you run everything together (battery bank, charger, inverter, solar panels, etc.). And add that batteries (if golf cart) last around 3-5 years, electronics 10+ years between replacement. Even a genset runs around $1+ per kWH just for fuel costs. Compare that to much of the country where you pay $0.10 to $0.30 per kWH.

A medium sized off grid system is around 3.3 kWH per day (3,300 WH per day) or ~100 kWH per month (i.e., $10-20 per month utility bill or ~$100-$200 per month for off grid costs). A 3.3 kWH per day system will give you a near normal electrical existence (LED lighting, full size Energy Star rated refrigerator-freezer, washing machine, well pump, LED TV, laptop, cell phone charging etc.). Albeit with a lot of conservation.

So, to give you an idea of what a system might look like using our rules of thumb that give a reliable and cost effective system. Note, I like to start with the battery bank first. Loads/power needs drive the size of the battery bank (i.e., two stormy days, no sun, no solar power--use genset on 3rd stormy day). For any battery bank over ~800 AH, I suggest looking at the next higher voltage (i.e., 800 AH @ 12 volts = 400 AH @ 24 volts = 200 AH @ 48 volts--same size/cost of battery bank, but the charging/discharging current and size of wiring is much less):

3,300 WH per day * 1/0.85 inverter eff * 2 days of storage * 1/0.50 maximum battery discharge * 1/24 volt battery bank = 647 AH @ 24 volt battery bank

Then there is the solar array. Two things to look at. First is the size of the battery bank--Larger battery banks need more charging current. 5%-13% rate of charge is typical for solar power charging. 5% can work for weekend/seasonal systems. 10%+ is recommended for full time off grid power systems (5% of 100 AH @ 20 Hour Discharge Rate of battery is 5 amps):

647 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,218 Watt array minimum
647 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,437 Watt array nominal
647 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,168 Watt array "cost effective" maximum

And then there is the sizing of the array for your loads and average amount of sun. Fixed array facing south:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Pueblo
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 52° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.49	4.93	5.61	5.74	5.88	6.10
Jul	Aug	Sep	Oct	Nov	Dec
5.79	5.62	5.95	5.72	4.68	4.30

You have a good amount of sun in the winter there... Say plan on 4 hours average minimum sun (you want to avoid genset use):

3,300 WH per day * 1/0.52 off grid AC system eff * 1/4.0 hours of sun per day = 1,587 Watt array for December (a bit better than "break even")

So, a 2,437 Watt array would do very nicely for you and keep a battery bank quite happy (4x 6 volt @ 220 AH golf cart sized batteries in series x 3 a parallel strings for 660 AH of storage @ 24 volts--12 batteries total). That is a good size bank for "golf cart batteries"--But it is nice to start with "cheap batteries" for your first set--Many people "murder" their first set of batteries (under charging, deficit charging--using a bit more energy and not getting the batteries full 1-2x per week), don't check water levels, kids leave everything and kill battery bank, etc.).

A 600+ AH battery bank battery bank will run upwards of a 3,000+ Watt AC inverter and solar array. Your home would need a minimum of ~1,200 to 1,500 Watt AC inverter to run the refrigerator (most difficult load you have). I suggest around 2,000-2,400 Watt AC inverter is the maximum I would start with (larger inverters waste more energy--especially when you have small loads on average).

Before we get into the details--How does this system work for you?

And, regarding genset--Do you have any preferences? Need a larger geset to run shop tools? Or a smaller genset to keep battery bank charged during bad weather? Gasoline, diesel, propane?

-Bill

mike95490 · October 2017

reconsider the cheap dorm fridge. They are usually poorly made and not efficient, The new, full size energy star fridges will consume less power then a dorm fridge (unless it's an energy star model

myocardia · October 2017

mike95490 said:

reconsider the cheap dorm fridge. They are usually poorly made and not efficient, The new, full size energy star fridges will consume less power then a dorm fridge (unless it's an energy star model

Indeed. Cat, read this thread for more info on dorm fridges, and how inefficient they happen to be:
http://forum.solar-electric.com/discussion/10915/just-how-bad-a-small-frige-is

catdean6 · October 2017

Okay so I have been doing my homework assignments! Here is what I think I know...
Based on my calculations and needs consisting of usage of: coffee maker 800w, tv 150w x 3hrs, laptop 30w x 3hrs, DVD player 40w x 3hrs, microwave 800w, energy eff chest freezer 1080w, energy eff fridge 1200w, 4 led lights 10w x 4hrs....i come to around 4692w per day.
An assumption of 4 hours of sunlight, in sunny southern colorado, puts me at 1173w per hour.
Sooo... a 1200 watt system should account for my needs. Back-up gen would cover a once a week washing machine (Natural air dry, of course) And any power tools used.
Hot water will come from wood stove/fp. So will heating. Water is from gravity fed cistern.
So that's where I'm at...a 1200w system.
I found 300w panels reasonably priced for pick up.
4 of them should do the trick.
Any thoughts on what charge controller is best? What about the best inverter? And the the battery bank??
I was looking at the samlex pst1500-24 pure since inverter, the 1500 mppt Midnite charge controller 45a, and 6 Costco golf cart batteries. Topping off with a Honda gen
Any opinions, thoughts??

Estragon · October 2017

Golf cart batteries are typically 6v, so 6 wouldn't work for a 24v system. 8 would give you 2 strings for ~ [email protected] Basically enough for 1 day of cloudy weather, then start the honda. Probably a good starter bank.

Having gravity water simplfies things, but you still have some loads that can take significant current, so you'll need to manage them some with a single 1500w inverter. For example, you wouldn't want to have the fridge and freezer kick on while you make coffee and microwave breakfast. It can be done, but it's a question of convenience. Some inverters can be stacked in a way that leaves one or more mostly sleeping on low power until load requires them. I use a pair of 3500w inverters in this way most of the time. There are times though (like when charging with the little honda) when loads have to be managed, so I have switches to turn off fridge, pumps, etc.

My guess is you'll be looking for more pv, and more bank before long with a ~5kw/day load, so I would plan for expansion.

nickdearing88 · October 2017

Please splurge on the inverter fridge/freezer! I got an LG two months ago and it is amazing! 280w rated max load and zero (0) startup surge on your inverter. So far the Kwh meter has a low day's usage at only 0.21Kwh and a high day's usage at 0.62Kwh with fridge/freezer at 37F/0F and ice maker running.

(edit)I run mine on a PSW inverter but I did test it with a 300w cheap modified wave inverter and it ran with no problem due to the inverter.

It was an expensive purchase but absolutely worth it for me.

(edit)PS: I bought an LG washer/dryer combo at the same time. It uses an inverter motor and is also extremely efficient. No stats measured yet though.

catdean6 · October 2017

Thanks estragon, the switches are a good idea. I'll go with 8 on the batteries!

nickdearing88, i was wondering about the washer/dryer combo! Good to know on the LG fridge/freezer, I will def look into that. What inverter do you suggest? Thanks!

MichaelK · October 2017

I think you are still overly optimistic about production, and your planned storage is too small. Assuming you're using 4 golf-cart batteries in series to get 24V, that gives you ~5.4kwh of total power. For Trojan T105's for example, they are 225ah X 24V = 5400watthours. Assuming you never want to drain more than 50% of your battery (2700wh), you'd be draining past that point every single day. They will not last long under conditions like that. L-16s are about twice as large as golf-cart batteries, and are a better choice because you won't have to double them up in parallel strings.

Secondly, don't simply expect a 300W solar panel to produce 300watts. That does not happen much in the real world. Don't base your expectations on STC values. If you want numbers you can count on, look at the panel's NOCT rating. In my own real-world testing with a voltmeter and a clamping ampmeter, I find that NOCT reading are dead on. Expect a 300W panel to actually produce about 225 watts at noon in the real world. I'd get 9 of those panels. Get the Midnight 200V controller instead of the 150V, then you can wire 3 in series to give you about 110VDC.

(1800watts x 0.75 derating) / 29.6 charging volts = 45.6 amps, which is right at the top of where you should charge L-16 batteries.
Assuming L-16s are 370ah, then 370 ah X 24V =8880 watthours, or about double your daily needs. If you need more capacity then that, you can get IND-9s.

With 1800 watts of panels, you can run two strings of three panels 3S2P, using much cheaper copper wire.

My recommended list would be...
Nine 300watt panels
4 L-16 batteries
midnight 200V charge controller
1500-2000 watt 24V inverter.

catdean6 · October 2017

Thank you michaelk! That's just what I need to hear. Apparently I still have so much to learn.

Photowhit · October 2017

catdean6 said:

Based on my calculations and needs consisting of usage of: coffee maker 800w,

Watts is a measure of power usage at any given time, Watt hours is what you should be concerned with. Brewing coffee and then transferring to a stainless steel vacuum thermos with keep it hot for hours.

I will suggest hooking up a Kill-a-watt meter to measure actual use of the products. I suspect the coffee maker might have a maximum energy use of 800 watts, but that it will fluctuate during the use. Kill-A-Watt meters are pretty cheap and I saw that they are available at Harbor freight;

P3 International 93519 Kill a Watt Electric Monitor

P3 International 93519 Kill a Watt Electric Monitor

https://www.harborfreight.com/kill-a-watt-electric-monitor-93519.html

catdean6 said:
tv 150w x 3hrs,

My 55 inch TV, newer LED model, uses about 80 watts. I may have a maximum of around 150...

catdean6 said:

microwave 800w,

800 watts, but how long do you run it? 10 minutes a day? so about 130 watt hours.

catdean6 said:

energy eff chest freezer 1080w, energy eff fridge 1200w,

Here is a link to 2017 energy star fridges. Any using less than 365 Kwhs per year will be less than 1000 watt hours a day.
https://www.energystar.gov/most-efficient/me-certified-refrigerators

Here is a 10.6 Cubic foot freezer at Lowes that uses 218 Kwh's a year divide that by 365 days, and you get about .6 Kwh's a day or 600 watt hours.

catdean6 said:

I was looking at the samlex pst1500-24 pure since inverter

This is about the minimum inverter I would recommend, but understand this is NOT an Inverter/charger. If you go with an inverter charger, you can run your generator at maximum efficiency charging your batteries while operating your household.

Here's a link to one Samlex version;
https://www.solar-electric.com/samlex-evo-2224-inverter-charger.html

catdean6 said:

1500 mppt Midnite charge controller 45a,

I have 3 Midnite Classic 150 charge controllers, Someone suggested the 200, which would only be desirable if you have long runs between your array and battery bank. They are fine charge controllers. They have internal fans so do create some noise, I wouldn't mount to a bedroom wall. They will handle 88-96 amps in a 24 volt system depending on the incoming voltage.

catdean6 said:

6 Costco golf cart batteries. Topping off with a Honda gen

They do make 8 volt golf cart batteries, but suspect 8 - 6 volt is what you will want. I think with your sunny area, you will find they meet your needs. We still don't have a firm handle on your loads. Run a Kill-A-Watt meter on those other things you use and see what your use is.

The generator wll only be able to charge the batteries if you buy an inverter charger or a separate battery charger;

https://www.solar-electric.com/iota-engineering-dls-27-40-iq4.html

Estragon · October 2017

We don't know where in southern CO you are, but if you're a cool, high altitude spot, you may do a bit better than NOCT output.

To get a sense of what to expect, you may want to check out pvwatts.nrel.gov

Horsefly · October 2017

Careful not to use the output rating on the microwave. If you see an ad for a 1000W microwave, that is how much cooking power it will generate. The amount of electrical power it will consume will be quite a bit higher. For example, we have a 600W microwave at our off-grid cabin. The spec said it would consume 800W, but the kill-a-watt meter says it consumes just about 1000W, and that has been confirmed by how much current it pulls from the battery bank (just under 50A at 24V).

Also: It doesn't look like you are accounting for the inefficiency loss of the inverter. Most will be about 85% efficient, so to get 1000W out at 120V you need to pull 1000 / .85 = 1176 watts from the battery bank.

nickdearing88 · October 2017

catdean6 said:

Thanks estragon, the switches are a good idea. I'll go with 8 on the batteries!

nickdearing88, i was wondering about the washer/dryer combo! Good to know on the LG fridge/freezer, I will def look into that. What inverter do you suggest? Thanks!

Lots of good inverter options out there. I'm too early into my solar experience to make specific recommendations but I don't mind sharing my experiences and mistakes so far. I'm very happy with my Samlex SA-1500-24v but as other's have mentioned, I would consider an inverter/charger combo. I would also say a larger Magnum inverter/charger would be in my future.

I'd also agree that you should size the inverter to the loads as measured but also plan some future "expansion room".

MichaelK · October 2017

nickdearing88 said:

Lots of good inverter options out there. I'm too early into my solar experience to make specific recommendations but I don't mind sharing my experiences and mistakes so far. I'm very happy with my Samlex SA-1500-24v but as other's have mentioned, I would consider an inverter/charger combo. I would also say a larger Magnum inverter/charger would be in my future

I weigh in on the inverter question. I've very happy with Schneider's equipment. I have an XM, which has just laughed at any of the loads I tried to run on it. It powers my 1.5hp 240VAC well pump without even noticing.

You don't need anything that substantial (yet) so I'd like to recommend Schneiders 2524 inverter.
https://ressupply.com/inverters/schneider-electric-conext-sw2524-120240-invertercharger
It's has the capability to run as a charger, can also put out 240VAC, and importantly, can be linked to a second SW to double output.

This would be great for a starter system that needs evential expansion. You still buy more panels, more batteries, but you link two systems together to double capacity that's in phase with each other. If you go with the slighty larger, slightly more expensive SW4024, a doubled system will have enough capacity to run a fairly large 240V well pump, or similar big-ticket item.

BTW, Samlex does offer a 24V inverter that has charging capability, though it's only ~ 100$ cheaper than the SW 2524.
https://ressupply.com/inverters/samlex-evo-2224-pure-sine-wave-invertercharger

mryimmers · October 2017

If the suggested minimum she will need seems to be 8 golf cart batteries, shouldn't she be looking at 48 volts to make things simpler? (I learned that from all you guys!!)

BB. · October 2017

Inverters tend to be a key component in the system design. 2,400 watt 24 volt DC inverters are typically easier to find vs 2,400 watt 48 vdc inverters.

Also, if you want to run some DC loads, 24 vdc appliances are easier to find. Also 24 vdc fuses, breakers, fans are a bit easier to find too.

Roughly, if you want/need a 2,400 to 4,000 watt or larger inverter, then 48vdc battery bus would usually be better.

Do several paper designs and see what works best for you. Inverters that are higher wattage than you need, tend to waste more power too.

-Bill

Photowhit · October 2017

mryimmers said:

If the suggested minimum she will need seems to be 8 golf cart batteries, shouldn't she be looking at 48 volts to make things simpler? (I learned that from all you guys!!)

It's not a bad suggestion, but I think she's in the ball park, there are other larger capacity batteries she could get in the future. L-16 size or even a forklift battery. It's her first setup so a double string of golf cart batteries should be a good starter set.

New build off-grid

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PuebloAverage Solar Insolation figures

Pueblo
Average Solar Insolation figures