# How many watts do I need for my solar panel to have to power my tiny house?

Registered Users Posts: 1
I am planning on running a small heater/AC (900 watts?), a small microwave (800 watts), a refrigerator (100 watts) and probably a light at some point. The refrigerator will be on 24/7 but the rest will be plugged in as needed, with the heater/AC running up to 12 hours at a time with 12 hour breaks. There may be other things here and there, but those will be my main energy-consumers. Any suggestions for solar panels?

• Solar Expert Posts: 795 ✭✭✭✭
Hi SarahEfim,
We need to have a rough idea where you are located to be able to make an approximation.
4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
• Super Moderators, Administrators Posts: 32,027 admin
First guess is somewhere in the Asheville NC region...

A refrigerator (full size Energy Star Rated) takes you to a medium size system:
• 400 kWH per year / 365 days per year = 1.1 kWH = 1,100 WH per day
The electric heater--If you run it 3 hours per day:
• 900 Watts * 3 hours = 2,700 WH per day
• 2,700 + 1,100 WH per day = 3,800 WH per day
If you want 2 days of energy storage and 50% maximum battery discharge:
• 3,800 WH per day * 1/0.85 AC inverter eff * 1/24 volt battery bank * 2 days storae * 1/0.50 max discharge = 745 AH @ 24 volt battery bank
Or if you use "golf cart batteries" (6 volts @ 200 AH per battery) = 4x parallel strings of 4 batteries per string = 800 AH @ 24 volt battery bank.

That is not a small battery bank (would probably suggest some other options, but it gives you a rough size of what such a battery bank would look like).

An 800 AH @ 24 volt battery bank should be charged at 5% to 13% rate of charge, and if full time off grid, probably 10% or more rate of charge:
• 800 AH * 29 volt charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,506 Watt array minimum
• 800 AH * 29 volt charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 3,013 Watt array nominal
• 800 AH * 29 volt charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 3,917 Watt array "cost effective" maximum
And then based on the hours of sun per day... Fixed array for Charlotte NC, tilted to winter power production (heater):

### CharlotteAverage Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 40° angle from Vertical:
(Optimal winter settings)  Jan Feb Mar Apr May Jun 3.79 4.03 4.75 4.89 4.66 4.43 Jul Aug Sep Oct Nov Dec 4.46 4.46 4.57 4.79 4.14 3.81
Based on a minimum of 3.81 hours per day (December) of average sun:
• 3,800 WH per day * 1/0.52 off grid system eff * 1/3.81 hours of sun December = 1,918 Watt array minimum (December "break even" solar power)
There you go with a really quick guess at your power usage. In general, running electric heaters from solar electric panels is not really cost effective. You can make solar thermal panels (hot water or hot air) and do something better for heating. And, just having a full size refrigerator really makes the system much larger than one just supplying lights, cell phone and computer charging, and a 12 volt water pump.

Using a Kill-a-Watt meter (or similar) can really help you understand your power needs and offer better guidance for design of your off grid power system.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 1,218 ✭✭✭✭
As bills analysis shows the heater is going to be an issue. For a start you need heat when likely your sun is the least, so its not a good match for solar. Also most tiny houses wont have enough roof space, however if you really want to try to power all that, you could look at a stand alone shed for the batterys and a ground mount system. Still, your going to be into the 20K ball park budget wise, with the heater included. Without it maybe 10K. Suggest you look at other heat sources.

1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
http://zoneblue.org/cms/page.php?view=off-grid-solar

• Solar Expert Posts: 766 ✭✭✭✭

How about forgetting about the electric heater and going with propane.

Not attempting to power an electric heater purely on solar should give you at least several thousand to spend on a heater and there should be a few dollars left over to buy some propane.

Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

• Solar Expert Posts: 5,658 ✭✭✭✭✭

...or heat with wood! there are more and  more, small wood heaters available. Learning bank them to burn long and low takes talent, I heated a camper with one. it will take some planning, but think about it now.

Wire wood is carbon neutral! Particularly if you cut it with electric from your array!

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Solar Expert Posts: 9,363 ✭✭✭✭✭
wood heating - http://www.inspirationgreen.com/masonry-heaters.html
2/3 down look for "Mark Twain on the Kachelofen" quote.   Kachelofen are NOT rocket stoves
An airtight wood stove banked down for an all night smoulder, emits a lot of air pollution.

Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

• Solar Expert Posts: 5,658 ✭✭✭✭✭
mike95490 said:
wood heating - http://www.inspirationgreen.com/masonry-heaters.html
2/3 down look for "Mark Twain on the Kachelofen" quote.   Kachelofen are NOT rocket stoves
An airtight wood stove banked down for an all night smoulder, emits a lot of air pollution.

You are slowing the reaction, couldn't find where they had claimed it emitted more pollution.

They do the math in this statement;

"Wood is a renewable resource and absorbs CO2 as it grows. Burning releases about the same amount of carbon monoxide, carbon dioxide and methane as would occur if the wood were decomposing naturally on the forest floor."

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Solar Expert Posts: 3,739 ✭✭✭✭
Photowhit said:
You are slowing the reaction, couldn't find where they had claimed it emitted more pollution.

They do the math in this statement;

"Wood is a renewable resource and absorbs CO2 as it grows. Burning releases about the same amount of carbon monoxide, carbon dioxide and methane as would occur if the wood were decomposing naturally on the forest floor."

That's just plain wrong.  COMPLETE burning does not release carbon monoxide or methane.  Incomplete burning, such as smoldering all night in an airtight woodstove, can release all sorts of pollution that doesn't occur on the forest floor.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 5,658 ✭✭✭✭✭

Trees absorb Carbon gases as they grow, a smoldering fire will release more back into the atmosphere, but it can't create more. Carbon neutral...

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Solar Expert Posts: 9,363 ✭✭✭✭✭
edited February 2016 #11
http://www.inspirationgreen.com/masonry-heaters.html

here right near the top:
Igniting and then drawing the heat out of the combustion gases turns almost every ounce of wood into energy. A slow burning, low temperature, low oxygen fire produces tar and hydrocarbons, a fast, hot, air-fed fire burns the pollutants up. Add a storage battery (the masonry) and you have a very efficient, non-polluting heating system. A metal stove gives out its heat rapidly, thus never allowing the inside combustion temperatures to achieve the 1100 degree F plus needed to ignite all the gases.

The Tars and Hydrocarbons are the soot and smoke the EPA is concerned about. Metal stoves also emit carbon monoxide, The firebrick liner of masonry heaters reflect and contain a lot of heat inside the firebox, which becomes nearly incandescent white coals and is hot enough to burn and consume the CO and only emit CO2 and water vapor.  Only the beginning of the burn, when the heater is still cold, are there much emissions, and a top-down burn style gets rid of a lot of that too.
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

• Solar Expert Posts: 5,658 ✭✭✭✭✭

I understand the EPA and the concerns in the 'Big City' We are truly infested with humans...

I try to (I purchased a cord and a half this year) burn wood with in a few hundred feet of where they pulled the carbon gases out of the air. My trees don't mind the gases. my nearest neighbor is fin with it. Most metal stoves are lined with fire brick. It hasn't been above 32 outside for a few days, and my 'tin can' would not support (or at least is not designed to support a masonry stove. I have no problem with masonry stoves!

BTW, the discussion centers on a Tiny house, most of which are built on wheels...

I only have issues that burning wood in a smolder is somehow going to produce more carbon gases than it consumed in the creation, it's much like the hydrogen from water argument.

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Solar Expert Posts: 5,183 ✭✭✭✭
Photowhit said:

I only have issues that burning wood in a smolder is somehow going to produce more carbon gases than it consumed in the creation, it's much like the hydrogen from water argument.

Whit, the issue is really that there is not any more CARBON in the equation it is what FORM the carbon is in, and TAR and CREOSOTE are just plain BAD for  humans!
We burn wood, a lot of it  at the lake house in winter, cut  >dead  6 years and dried , if possible, for another year (summer season) or 2.  Minimal creosote in the stack after a year, < 3 cups per 20 + feet of insulated pipe, but lots of ash in the cook stove...

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada
• Solar Expert Posts: 5,658 ✭✭✭✭✭

I only burn a 2-3 cords over the winter, I have a straight drop and wanted to be sure to clean after 2 years often smoldering, and had very little in the way of particles. I've only pulled less than 2 'popcorn tins' of ash, perhaps 2 gallon size of ash out this year, I think less than 4 all winter last year.  If one heats with only flaming fires, often only the area around the stove is warm, as more air must be drawn in to maintain the fire.

I have a stove that can be setup to draw combustion air from outside, but most are not designed this way. If I didn't smolder, I would be up every 4 hours feeding the fire, and be too hot or too cold often. This is the advantage of having a large thermal mass of a masonry stove. If I'm around, I will burn hot after feeding the fire before reducing the draft, this may reduce the build up.

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Solar Expert Posts: 1,218 ✭✭✭✭
Hopefully those concerned about solid fuel stoves emssions, arent on grid using coal or nuclear for their home heating. Solid fuel is a time honored sustainable heating source with no where even remotely close, i mean orders of magnitude less, compared to some of the sheer stupidity modern man calls energy. That stuff has the potential to total the planet. For good.
1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
http://zoneblue.org/cms/page.php?view=off-grid-solar

• Registered Users Posts: 43 ✭✭
This topic would go down in flames real quick where I live at lol. This morning it's 10 degrees out here in the country. Since probably every other house near us has a wood stove, my neighbors would say with gun in hand get off my land and stay out of my business. Man has been burning wood since he figured out how to lit it.
• Solar Expert Posts: 1,218 ✭✭✭✭
Yeah well of course the rapid deforestion caused by early wood use particularly in the steel industry, isnt something we should be too proud of. Part of that can be attributed to the industrial revolution, part to the epic waste that is warfare, and the other part to overpopulation. Nothin in this life is simple.
1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
http://zoneblue.org/cms/page.php?view=off-grid-solar