Energy-conscious/efficient off-grid tiny home setup help

[carbondrewtonium]

Hi. I’ve researched off and on for about a year. I’m running electric in my tiny home now so I am to the point of gathering up a cohesive system to be off-grid. I bought 7 Qcell 405w panels (I’ve been told 7 is a weird number to have, so I may sell one). I have two 12v Chvrge batteries but in researching, I believe I should get one 48v battery (Probably the EG4 I see so much hype about) and sell the two 12v batteries. I plan on getting two of these ground mounts: https://signaturesolar.com/eg4-brig...ck-kit-4-panel-ground-mount-adjustable-angle/
I’ve been told Victron is the way to go off-grid, but have also read good things about Sunny Islands and Outback inverters.
I have not looked into charge controller much because I don’t know what size inverter I need.
Am I wrong that the larger the battery voltage is, the smaller wattage inverter I’ll need?
I gave this thread the title because I want to emphasize I plan to have very efficient appliances and I am doing without some common appliances.
I’ll have a mini split (Senville 9k BTU, 20.5 SEER), (2) portable single induction cooktops, a Breville toaster oven, microwave, range hood, energy recovery ventilator, projector, ceiling fan, lights, outlets. That’s it. No water heater. No clothes dryer. Maybe a portable clothes washer later on. Oh, and I hope to power tools outside. Miter saw, table saw, etc. Maybe a CNC machine in the future.
I have a 100 amp breaker box, if that matters.

Anywho, if I want to ground mount 6 405w panels, what size inverter and controller should I look into that will give me the power I need?

Any wisdom on size, brands, etc. are welcomed and appreciated.

 

[E. Cho]

Go to the resources section and find the Energy Audit info and fill it in. Also search for Energy Audit online and maybe YouTube.

Basically, no one can recommend anything until you do the math, that means adding up all the watts of your appliances used for the number of hours required also added up. Then match up the power in watts needed with the watts that will produce the power, along with an inverter that is 50% or so greater at the voltage needed. The MPPT charger controller also needs enough capacity to charge the LiFePO4 battery and its reserve.

Also, 48 volt system has advantages for large systems but 24 volt hardware works well, is smaller and less expensive and should be investigated.

Its just math, addition mostly of watts and of hours, with some multiplication to convert watts to amps. There are also conversion calculators online.

After you know how many watts you use for how long, then recommendations will be easier.

 

[Rocketman]

Just to add what was said above. You need to figure out the watts of everything you will be using, how long in a day it will be used, and also what things will be running at the same time.

My guess looking at your list you will want more than one of the high draw item’s running at the same time. If you will have three big things running at the same time - say mini split, induction top, and microwave- that will require a bigger inverter than two, and may even require two of the batteries. You system will be very different at four or five large draw items than at two. That’s why the energy audit is so important. If it gets sized for one large item and you want to run four - you will be very unhappy with the system.

Don’t sell that seventh panel- get one more (must be the exact same panel). My guess in looking at your list - you will need even more than that one.

Good Luck

 

[BenQ]

Looking at all of the appliances you listed and the tools you want to be able to use, you will need a large system (miter saws and CNCs consume a lot of power…) once you do an energy audit then you can find an inverter to fit your power needs, batteries and a charge controller (CC) Combining the inverter and CC into an all in one (AIO) unit is a good way to go if you want to save yourself a little space and wiring. As it stands you have 7 x 405 watt panels for a grand total of 2,835 potential energy production (rarely will you realize this potential but you’ll need to work out your panel placement to get your array as close to this potential as possible). Then depending on the season and your location you’ll only have a certain amount of daylight hours to make your 2.8kw of potential power. It is rare to get more than 6 hrs of full daylight so without knowing any of your location information I’d say you’ll be lucky to get 6 x 2.8 = 13.6 kW of energy per day. 1 server rack battery is usually 48v 100ah 5.something kW hours so 3 of those would be able to drink up everything your solar panels could possibly pump out. Going with a 48 volt architecture you’ll want a CC (whether it’s in an AIO or on its own) that can handle the highest amount of voltage that your panels can output usually somewhere between 40-60 volts per panel, but combined in series. It’s much less expensive to run panels in series at higher voltage and lower amps because you won’t need a very thick gauge wire. If you put all 7 of your panels in series and estimating your panel voltage at 40-60 volts you’ll need a CC that can handle 280-410 volts. Most new AIO units can handle 500v of input these days so you’ll be good there, but stand alone CCs rarely go above 250 volts. You mentioned victron and Outback, but those don’t usually handle more than 250 volts. So if you’re sticking with the panels you have and want to wire them up most efficiently then I’d recommend an AIO unit that can handle up to 500v of PV (solar panel) input. Hoping to utilize all 2.8 kW PV at 48 volts you’ll want an AIO unit that can process all that power which is 2,800 watts divided by 48 volts = 58 amps since most AIO units can charge at up to 80 amps you should be good with anything that can handle your loads (still unknown until you fill out the calculator) and 500 volts PV input and charge at 80 amps. That should get you started!

 

[Tomthumb62]

Don’t sell the seventh panel. Keep it as a spare or add someone mentioned, add an eighth because you’ll probably want it once you do an energy audit and learn truly how much more energy you will use than you currently realize.

 

[Bluedog225]

And stop buying stuff till you have a plan. Will save you a bundle.

 

[E. Cho]

Here is a similar thread (there are many that can be searched for in these DIY forums) to this one which adds more info for the Original Poster.
Energy Audit and Basic System Thread

One person mentions an Energy Audit meter. This is often called by a brand name of "Kill-A-Watt" meter and can be found via this search link on Amazon. There are several versions of these, all with compromises and different costs. Some have backlights, some have memories, some have tiny display text, some have many different buttons to push.

Basically for the energy audit, a meter gives more real time accurate information but all appliances or tools will have a label that specifies it's power use in Watts and or Amps and voltage requirements that one can use along with the user time required to figure out how much energy, usually in Watts that the appliance will use. (EXCEPT the SURGE Power Required, such as for a Fridge, Freezer, Compressor, Vacuum Cleaner and other similar induction motor appliances / tools, which for accurate readings, one needs a specific Clamp Meter that states it can read DC Surge Loads, which are often occur in milliseconds and so are not seen or read by normal meters, that's another area where a search will provide more info) (Also, high surge loads often require Low Frequency Inverters, which is another area of Searching and not all Inverter manufacturers will state if they are Low Frequency (LF) or High Frequency (HF) Inverters and usually with the case of HF Inverters, what type of surge load that they can or cannot handle. VERY IMPORTANT TO FIND OUT BEFORE BUYING ANY INVERTER).

Hope this helps the DIY journey. Go slow, keep reading and as advised already, don't buy equipment until a better understanding is achieved.

 

[carbondrewtonium]

Go to the resources section and find the Energy Audit info and fill it in. Also search for Energy Audit online and maybe YouTube.

Basically, no one can recommend anything until you do the math, that means adding up all the watts of your appliances used for the number of hours required also added up. Then match up the power in watts needed with the watts that will produce the power, along with an inverter that is 50% or so greater at the voltage needed. The MPPT charger controller also needs enough capacity to charge the LiFePO4 battery and its reserve.

Also, 48 volt system has advantages for large systems but 24 volt hardware works well, is smaller and less expensive and should be investigated.

Its just math, addition mostly of watts and of hours, with some multiplication to convert watts to amps. There are also conversion calculators online.

After you know how many watts you use for how long, then recommendations will be easier.

Thanks! I have begun to fill out the spreadsheet and have attached a screenshot. For example with the induction cooktops, the backs say 1500w, which is the surge power, correct? How do I know how many watts they're running once turned on? Same for the mini split. It will run a bit all day, but of course not at full power.

 

[carbondrewtonium]

Just to add what was said above. You need to figure out the watts of everything you will be using, how long in a day it will be used, and also what things will be running at the same time.

My guess looking at your list you will want more than one of the high draw item’s running at the same time. If you will have three big things running at the same time - say mini split, induction top, and microwave- that will require a bigger inverter than two, and may even require two of the batteries. You system will be very different at four or five large draw items than at two. That’s why the energy audit is so important. If it gets sized for one large item and you want to run four - you will be very unhappy with the system.

Don’t sell that seventh panel- get one more (must be the exact same panel). My guess in looking at your list - you will need even more than that one.

Good Luck

If I cannot get the exact same panel, is it fine to get one more that is different than the other 7? Or even 5 more that are different if I need that many more panels?

 

[Tomthumb62]

For a device that heats up, yes, the wattage listed on the back is the wattage used. A heating device like your cook burner doesn’t have a surge.

But for your fridge or freezer, those have a compressor motor, which have one heckuva surge when they first start up. If you measure it uses 100W continuously, figure it uses approximately ten times that for the startup surge, so 1000W in this case.

Now if you have multiple surge-able devices hooked up to the same inverter, what to do if all then try to start up their compressor motors at once? One solution is for a large enough inverter to handle all of them at once, but that leads to issues like cost, massive wiring sizes especially if on 12v and higher idle consumption of the inverter. Another solution is to spread your surge devices across more than one inverter. Yet another but popular solution is to manually manage your loads. For example, if you can hear the fridge running, then you know it’s either going to stop running someone or otherwise isn’t going to suddenly surge. So that’sa safe time to run the microwave. But you can see this isn’t how anyone who has grown up on the grid is going to take easily.

 

[E. Cho]

Thanks! I have begun to fill out the spreadsheet and have attached a screenshot. For example with the induction cooktops, the backs say 1500w, which is the surge power, correct? How do I know how many watts they're running once turned on? Same for the mini split. It will run a bit all day, but of course not at full power.

No, that 1500 Watts for the induction cooktop is not the surge load, as already mentioned. It is likely the maximum wattage that the appliance can require at it's maximum setting. Also, since an induction cooktop has variable settings, it goes from low where watts pulse from 0 to Maximum to lower stable watts and up to the maximum watts of in your case, 1500 Watts. Eg: I rarely use mine above setting level #3 where it uses about 670 Watts at #3 vs. 1600 Watts at level #10. This I determined by using a Kill-a-watt type meter (I used a 15 Amp Ponnie Meter (brand name = Ponnie) (it has pros and cons but it's pretty accurate and at 15 amps)).

You measure how many watts an appliance uses while running and timed with an energy meter, like a Kill-A-Watt type (make sure it can handle 15 amps as some only handle up to 12 amps). These meters will show what the appliance is actually using in Watts, Amps, Frequency, Voltage and it has a timer and will calculate the Watt Hours of use of the appliance in use.

As mentioned, surge loads can only reliably be measured by DC Clamp Meters, not energy meters such as the Kill-A-Watt or Ponnie types, though I have seen mine jump when say my freezer kicks on but the energy meter does not record that surge and what I saw, say 600 watts for my freezer, was maybe or maybe not the peak of the surge.

 

[Rocketman]

As far as the question on the induction cooktop - you need both the max watts ( for sizing the inverter - for those times you run it at - high setting) and the average watts used in a day - for sizing the battery correctly (do you need one or three batteries). This is where a good “kill-a-watt” tool can help.

I was just watching my wife make her eggs omelet on induction plate- setting 1 (lowest) the power keep going up 800w for a second then down for about three or four - for the 5 minutes or so it took to make it. That’s hard to figure out without a good tool.

A lot of times you take your best guess on the energy audit - then ask if the sizes look right for batteries and inverter.

As for more panels that are “different specs”. You can add different panels on a different array - going into their own mppt. (Some solar charge controllers have multiple mppt for multiple arrays) or you add another Solar charge controller. If you put different panels on the same array there is a penalty- how big of one depends on the specs and wiring of the panels- that is a rabbit hole you can cross if you need it.

Good Luck

 

[E. Cho]

Mixing panel wattages can be done, but also can make things a bit more complicated if the other panel specs also don't match. Personally, I would avoid that scenario at the learning level that you are presently at.

My off grid 24 volt system is pretty simple but seems robust and reliable. It's a mix of good quality stand alone components (vs All In One) and I and the components are quite happy with no communication between components. They just work with no communication complexities. I recently completed and connected a larger capacity LiFePO4 battery, (which made my brain hurt learning), in order to use my back up generator in winter or low sun periods, even less than the little that I already have since upgrading from Lead Acid batteries.

My LF 4Kw inverter is 20+ years old and runs 24/7 using 16 watts at idle, which is about as low idle consumption as they get. I have no need for 240V tools/loads but if I did, I have a backup gasoline generator that could handle 240V. My home is a bit larger than a "Tiny" home, but probably my use or living is in tune with the Tiny ideal. In other words, my needs and energy management is happy with being frugal.

Off to bake some bread in my solar powered Oster "toaster" oven, as the sun is coming out.

 

[Tomthumb62]

As mentioned, surge loads can only reliably be measured by DC Clamp Meters, not energy meters such as the Kill-A-Watt or Ponnie types, though I have seen mine jump when say my freezer kicks on but the energy meter does not record that surge and what I saw, say 600 watts for my freezer, was maybe or maybe not the peak of the surge.

At least in my case, the killawatt gave me a “close enough” estimate of the surge of my fridge. The Poniie measured 600-800W surge when the compressor kicks on but since my 1000W inverter can surge up to 2400W, I’m good. So while a DC clamp meter would have been ideal, this estimate was good enough.

A common rule of thumb I have seen is for compressor motors, multiply by 10 to get the surge wattage. So if the highest continuous wattage you’ve seen on the killawatt meter is 110W, then use 1100W as your surge rating. It might be overkill in reality, but should be good enough for many ordinary household compressor motors.

 

[Daddy Tanuki]

Go to the resources section and find the Energy Audit info and fill it in. Also search for Energy Audit online and maybe YouTube.

Basically, no one can recommend anything until you do the math, that means adding up all the watts of your appliances used for the number of hours required also added up. Then match up the power in watts needed with the watts that will produce the power, along with an inverter that is 50% or so greater at the voltage needed. The MPPT charger controller also needs enough capacity to charge the LiFePO4 battery and its reserve.

Also, 48 volt system has advantages for large systems but 24 volt hardware works well, is smaller and less expensive and should be investigated.

Its just math, addition mostly of watts and of hours, with some multiplication to convert watts to amps. There are also conversion calculators online.

After you know how many watts you use for how long, then recommendations will be easier.

all good to go except 24 volt statement... currently top tier gear is almost same price between 24 and 48... go 48. I would go 96 if the gear was available. you save so much on wiring and connections that who cares about the extra 100 usd for the inverter?

 

[Daddy Tanuki]

all good info, but first and foremost... conserving is cheaper than making. good e3xample I just posted on another forum. this photo is of my older cabin that I bought and am now in the process after 8 years of sorting out. single pane, no insulation (for the walls, ceiling and floor had, but not walls). I cooled this daily in the summer and heated with a combination of split pack/kerosene in the medium months, and wood stove in the coldest. imagine my cost savings electricity wise if it had been insulated properly in the start... Cabin is 900 square feet for comparison. never fear.. full insulation and double pane enroute. and to be extremely rude... Take the current power estimate calculators estimate and just double it... you will thank yourself in the future when you do. too much is barely enough and overkill to the 2x is just right. this gives me 4-5 days of total solar independence.. no solar, no problems... GTG for 4-5 days. this is true offgrid thinking. bare minimum will sodomise you in the future.

 

[carbondrewtonium]

Looking at all of the appliances you listed and the tools you want to be able to use, you will need a large system (miter saws and CNCs consume a lot of power…) once you do an energy audit then you can find an inverter to fit your power needs, batteries and a charge controller (CC) Combining the inverter and CC into an all in one (AIO) unit is a good way to go if you want to save yourself a little space and wiring. As it stands you have 7 x 405 watt panels for a grand total of 2,835 potential energy production (rarely will you realize this potential but you’ll need to work out your panel placement to get your array as close to this potential as possible). Then depending on the season and your location you’ll only have a certain amount of daylight hours to make your 2.8kw of potential power. It is rare to get more than 6 hrs of full daylight so without knowing any of your location information I’d say you’ll be lucky to get 6 x 2.8 = 13.6 kW of energy per day. 1 server rack battery is usually 48v 100ah 5.something kW hours so 3 of those would be able to drink up everything your solar panels could possibly pump out. Going with a 48 volt architecture you’ll want a CC (whether it’s in an AIO or on its own) that can handle the highest amount of voltage that your panels can output usually somewhere between 40-60 volts per panel, but combined in series. It’s much less expensive to run panels in series at higher voltage and lower amps because you won’t need a very thick gauge wire. If you put all 7 of your panels in series and estimating your panel voltage at 40-60 volts you’ll need a CC that can handle 280-410 volts. Most new AIO units can handle 500v of input these days so you’ll be good there, but stand alone CCs rarely go above 250 volts. You mentioned victron and Outback, but those don’t usually handle more than 250 volts. So if you’re sticking with the panels you have and want to wire them up most efficiently then I’d recommend an AIO unit that can handle up to 500v of PV (solar panel) input. Hoping to utilize all 2.8 kW PV at 48 volts you’ll want an AIO unit that can process all that power which is 2,800 watts divided by 48 volts = 58 amps since most AIO units can charge at up to 80 amps you should be good with anything that can handle your loads (still unknown until you fill out the calculator) and 500 volts PV input and charge at 80 amps. That should get you started!

Thanks so much for all the information here. I appreciate the best guesses on what I may need. The issue I'm running into in filling out the audit is I am currently glamping to build the tiny house. I have no way to see what everything runs at, unless I get a meter and take all my appliances to a friend's and see how much they pull. Which is doable. I could take one or two at a time. And some things I just have to make best guesses on: mini split, energy recovery ventilator, range hood. I've read and some others have said here about mixing panels can be done. Is it more important that they are the exact same brand? Or that they are the exact same wattage?

 

[E. Cho]

Thanks so much for all the information here. I appreciate the best guesses on what I may need. The issue I'm running into in filling out the audit is I am currently glamping to build the tiny house. I have no way to see what everything runs at, unless I get a meter and take all my appliances to a friend's and see how much they pull. Which is doable. I could take one or two at a time. And some things I just have to make best guesses on: mini split, energy recovery ventilator, range hood. I've read and some others have said here about mixing panels can be done. Is it more important that they are the exact same brand? Or that they are the exact same wattage?

On the high wattage appliances like the mini split, if you have it already, I'd try to do a test at a friend's place (on the grid?) in real time over a real time use as it would seem it's a large energy user and it's real world power requirements might be a big surprise based on a guess? Most appliances that heat or cool air or water can be HUGE energy users and for air, will vary greatly depending on the ambient conditions. Heating and cooling can require BIG (expensive) storage / battery capacities too, so knowing exact energy use over so many hours will give you more info to size and afford your panel and battery needs (as well as wire, fuses, charge controller(s), inverter ...) Or as suggested, and you have the space and money, just double or tripple your guesstimates and build / over build / over buy your needs? Guessing could undersize or oversize your end system. Undersizing being a PITA to redo or add on to components and oversizing taking up space and costing more money, neither of which you mention, ie: your available space and or your budget.

This will be a bit vague as I am not technical enough to remember and to provide the best explanations but regarding the solar panels, READ the rear spec label of the panels that you have and search the web for what each value means. It's more important to match the Voltage parameters of the solar panels than the wattage or the brand. Eg: Some low wattage panels operate at 12 Volts or 24 Volts and some higher wattage panels at much higher voltages. As well, you need this rear info in order to connect your panels properly to your local climate / coldest temperatures in order to safely size a correct MPPT Charge Controller for your system and climate. Then you need to use the info for Amps and Volts to safely configure the panels into Parallel and or Series combo strings, again which you need to understand. So combining just "WATTAGE" on it's own is kind of meaningless and unsafe as an end goal, there are more important variables to consider.

This REAR LABEL Specs of solar panels is extremely important to learn and understand and to use for safety in combining any panels, including the same wattage and brand.

If you don't have the panels in hand, then go to the manufacturer or retailer's website to find the label specs for the specific panels that you are considering. For the same exact panels, the manufacturers and Solar Charge Controller manufacturers provide Solar Panel Calculators that take into account the rear panel specs and operating temperatures and wattage needs to help guide your panel build and needs.

 

[BenQ]

On the high wattage appliances like the mini split, I'd try to do a test at a friend's place (on the grid?) in real time over a real time use as it would seem it's a large energy user and it's real world power requirements might be a big surprise based on a guess? Most appliances that heat or cool air or water can be HUGE energy users and for air, will vary greatly depending on the ambient conditions. Heating and cooling can require BIG (expensive) storage / battery capacities too, so knowing exact energy use over so many hours will give you more info to size and afford your panel and battery needs (as well as wire, fuses, charge controller(s), inverter ...) Or as suggested, and you have the space and money, just double or tripple your guesstimates and build / over build / over buy your needs? Guessing could undersize or oversize your end system. Undersizing being a PITA to redo or add on to components and oversizing taking up space and costing more money, neither of which you mention, ie: your available space and or your budget.

This will be a bit vague as I am not technical enough to remember and to provide the best explanations but regarding the solar panels, READ the rear spec label of the panels that you have and search the web for what each value means. It's more important to match the Voltage parameters of the solar panels than the wattage or the brand. Eg: Some low wattage panels operate at 12 Volts or 24 Volts and some higher wattage panels at much higher voltages. As well, you need this rear info in order to connect your panels properly to your local climate / coldest temperatures in order to safely size a correct MPPT Charge Controller for your system and climate. Then you need to use the info for Amps and Volts to safely configure the panels into Parallel and or Series combo strings, again which you need to understand. So combining just "WATTAGE" on it's own is kind of meaningless and unsafe as an end goal, there are more important variables to consider.

This REAR LABEL Specs of solar panels is extremely important to learn and understand and to use for safety in combining any panels, including the same wattage and brand.

If you don't have the panels in hand, then go the the manufacturer or retailer's website to find the label specs for the specific panels that you are considering. For the same exact panels, the manufacturers and Solar Charge Controller manufacturers provide Solar Panel Calculators that take into account the rear panel specs and operating temperatures and wattage needs to help guide your panel build and needs.

Exactly! Rear label is key! Volts, amps and watts!

Technically, you wouldn’t be “combining” panels. They would be in two different arrays/groups.

 

[BenQ]

And if you don’t/can’t separate them into separate arrays, here’s a great video on that.