Solar panel advice for the technologically incompetent?

I'm looking for advise on what size solar panel to get. It's for a tiny home for one person but I'll use it on a mobile home for a few months while my tiny home is being built (so it needs to be portable). I've been told a 1,000 watt panel and 2 batteries would be enough to power a lap top, phone and a blender I use once a day. I've been told that because I live in Ireland and light levels are low, I should get a 2,000 watt panel to guarantee generating 1,000 watts even on bad days. Does this all sound right?

I'd like to also have a small fridge. The mobile home already has a fridge (3 x 2 x 2 foot) which looks old and is most likely not an efficient energy user. How many extra watts do I need to power a fridge?

I've tried to research online, even using 'simple' solar energy calculators but I just don't have the head for this kind of thing. I'm busy growing food, designing a food forest, setting up a permaculture school and trying to get started on building the tiny home. It would be great if I could buy a solar panel system that meets my needs without having to learn too much or put too much time in - maybe that's expecting too much! Any advice would be greatly appreciated.

Hi Siobhan;  
Welcome to Permies!
Well lets see;  One person , a laptop,phone and a once a day blender.  What about lighting?  Radio, fans?
Now ,I'm afraid to my knowledge there are no 1000 watt panels. Perhaps you mean 100 watt panel? That is definitely to small.
I,m thinking you are going to want around 200 watts. In beautiful green rainy Ireland  maybe even 360 watts.
Here is a link to Ebay. https://www.ebay.com/itm/1-180-Watt-12-Volt-Battery-Charger-Solar-Panel-Off-Grid-RV-Boat-180-watt-total/272812576939?ssPageName=STRK%3AMEBIDX%
180 watt panel $175 us


Your refrigerator is not going to do well at all on solar. It will drain your battery's in no time.
I suggest a propane fridge , they commonly come in campers and should be easily available.

Battery's) Your going to want two 6 volt deep cycle battery's. Known as a T-105 golf cart battery.
You also will want a solar charge control to keep from overcharging your battery's.

Thank you! That's really helpful! A guy told me 1,000 watts but he may have been mistaken.

I forgot about lighting - will need that and speakers for my laptop but I won't need a fan - it doesn't get hot here.

It also depends a lot on the laptop: My small one uses about 20W, the big one 100W.

The 360W panel suggestion sounds good. If it turns out that it isn't enough, you can add another.

Two of these Wind Generators would give you 1000 watts both night and day in a 24 mph breeze. I'm a complete noob to these technologies also.

Ooops! One feedback comment isn't supportive of my wind speed estimate.

Yes, wind is definitely an option in Ireland.
Thing is, when using wind or a hydro the cost goes up. They need a constant diversion charge control and a full size power dump anytime they are working.
Solar on the other hand doesn't.  Solar panels can be disconnected while in the sun (that is how a solar charge control works)  wind and hydro must always stay connected while running or they produce excessive voltage and burn out.
Battery requirements for wind would be much higher.

Wow, there's a lot to consider. Wind might be the way to go. Would a small A-rated fridge be possible on solar?

Hi Siobhan;
Electric refrigerators are very poorly insulated and sadly no matter what foolish "energy star rating" they get. They will drain your battery's fast.
As an example for you. I have lived 100% off grid with solar and hydro, since 1983! I have bunches of excess power when the sun is up and yet...
I have a propane fridge! Yes, its as large as any "normal" fridge and cost on it delivered was $2500 US... ouch.
Just this year I spent another $1600 US and bought a Sundanzer 12 volt large chest freezer.  It has 4" of insulation throughout!  It is incredible and it sips 12 volt power!
They do make smaller 12 vt refrigerators as well. I haven't looked but cost on them will be high as well.

They do make and sell 12 volt Danfrost compressors and you can build your own super insulated box to install one.
This has been done and if your handy with tools you could build one yourself at a much more reasonable cost.

Here is a little info about wind generating.
To start they are noisy, anytime it is spun up.... an airplane will be landing in your yard.
Next, they require a serious support system to remain standing... geez its windy out there...
Next, unless your wind is steady and constant over 10 mph or better 15 mph you will not get the charge you are hoping for.  1000 watts is a lot but they only make that kind of power in a strong constant wind.
Now having worked with a fellow from Ireland.(I run large construction cranes)  He assured me that working near the north sea the wind is a big factor. Crane picks must be timed between gusts.
So if your tiny house is going to be on a bluff overlooking the north sea AND you have the finances to set up a wind/solar system then your Golden!
If not then I would stick with solar, its easier and cheaper.

I thought propane was not suitable for indoor use due to carbon monoxide?

What do you think of this? I can't figure out from the description if it includes batteries?

https://www.ebay.ie/itm/Solar-Panel-Kit-100W-200W-300W-500W-600W-Solar-Panel-Module-Kit-12V-24V-off-Grid/222734398678?hash=item33dc0134d6:m:mtRL-aXckS3noDeEIwIKCVw

I'm leaning towards buying this and either a propane fridge or just a cooler that I can top up with ice from my friend's freezer 5 minutes walk from me.

Hi Siobhan;
Yes ,buy your own propane fridge.  You definitely can run one indoors I have for almost 40 years. Ice in a cooler is short term stuff not for daily living.
About the "kit" your looking at.  After looking it over, the only way I would recommend it, is if you buy the 400 watt upgrade.
If you look at the inverter's offered. Only the 1500 watt inverter is pure sine wave output.  This is critical. Do not buy any inverter that does not say it is pure sine wave.
The other inverters are a square wave and they are a waste of money. Motors will make noise,  computers & components can be ruined...
If you want an inverter, only buy a pure sine one. A smaller output than 1500 watts will not be overly expensive.

Shop around a bit more. Usually the complete kits are marginal.  
I think you can save money in the long run, buying individual components.

EDIT)  No that kit does not have battery's. You need to buy them close to home.  Shipping battery's is beyond expensive.

if you re willing to skip the fridge and blender, you can get by on a small panel for laptop, speakers, tv and lights...although with lights you will want to get very low watt like LEDs or something similar.
you can start with one small panel, and then as you go along add 1 or 2 more.

if you dont have multiple batteries in a battery bank, there's only so much power you can store at one time anyway.

so the amount of power you have available is more tied to the size of your battery bank and also the capacity of the inverter.

for laptops and low watt lights a 200-400 watt inverter will work... but for blenders, coffee pots, air conditioning, or a fridge...you would need a lot more. like over 1000 watt inverter. so yeah if you figure out alternative solutions for your fridge and blender, you could get by on a low watt panel and inverter.

so you will want to obtain either very high capacity batteries, or multiple regular batteries, to hook them up as a battery bank. and also the size of the watts on your inverter is more important than the size of the panels.

some good resources here are marina supply and also trucker supplies, but i dont know if thats around you. truckers and boats have much of the same issues with needing low powered cooking and fridge solutions, and people on boats also need low watt lighting and etc.

when i used solar for a long time i mostly used something like this as the inverter, so i could also take this and charge it on regular power at my friends houses...plus it was useful for my unreliable beater truck. -->

portable power sealed battery

or there's smaller ones that only have 12 volt output, which you can then get a power inverter that uses DC and changes it to AC...

sealed battery

then there's some all put together small systems -->

https://www.amazon.com/COOCHEER-Portable-Charger-Generator-Suitable/dp/B082W5HVGV/ref=sr_1_17?dchild=1&keywords=portable+power+solar&qid=1587299579&s=automotive&sr=1-17


or theres small foldable systems that are meant to be connected to a "solar generator" / sealed battery with inverter

foldable panels

foldable small panels

sealed battery --> 500 Watt Inverter / sealed battery

smaller capacity solar generator / sealed battery

well thats hopefully helpful to point you in a direction, and enough for now,
but one other thing you might want to look into is a DC powered low watt "cooler"  or thermoelectric cooler --->

cooler

actually one more one more last thing =)

someone on here was talking about using a regular mini fridge on a timer to drastically reduce the power requirements.

by not opening it a lot they were able to have it turn on for a very short twice a day and run it without going through all the power they had banked in the batteries.
maybe not as consistently cold as a normal fridge operation, but they had it working good once they dialed it in, and i definitely think this is a brilliant and simple fix for this...

if you do get a timer for an appliance it needs to be a super power timer...like most are smaller capacity...but they do make upgraded electrical timers that can auto shut off and turn on your appliances.

when i was using an electric hot water heater i used an electrical timer...so that it only turned on during the late afternoon and just used the hot water later in the day. it saved a LOT of electricity running it that way...

heavy duty timer

heavy duty timer

Siobhan Lavelle wrote:What do you think of this? I can't figure out from the description if it includes batteries?

https://www.ebay.ie/itm/Solar-Panel-Kit-100W-200W-300W-500W-600W-Solar-Panel-Module-Kit-12V-24V-off-Grid/222734398678?hash=item33dc0134d6:m:mtRL-aXckS3noDeEIwIKCVw

I'm leaning towards buying this and either a propane fridge or just a cooler that I can top up with ice from my friend's freezer 5 minutes walk from me.

For Ireland you definitely want to invest in an mppt charge controller not that pwm piece of @#$% on the link. An mppt charger will allow a higher voltage solar panel to be used by a lower voltage 12 or 24 volt system and will still produce power even on cloudy days. I like the Midnite solar Kid, in the no name brands something like this one:  https://www.ebay.ie/itm/40A-MPPT-solar-charge-controller-with-LCD-screen-for-12V-24V-systems-up-to-100V/113143131776?hash=item1a57db2e80:g:kXYAAOSwiVJbRLcs I cant attest that model is good but its specs look good...
A 60 cell 300 watt panel like this one: https://www.ebay.ie/itm/300-Watt-Solar-Panel-Solar-Module-PV-Module-Solar-Cell-Mono-Crystalline-Solar/292698765882?hash=item442634ba3a:g:oVYAAOSw5WVbgr9F
cables, a cheap inverter like the original link and 2 6 volt deep cycle batteries... Good for a small house, no problem. Stick with a propane fridge or double the amount of solar...

Thanks for all the detailed advice. I don't fully understand everything but I can look for equipment with the keywords you've suggested even though I don't fully understand what those words mean. I cant emphasise enough how clueless I am or how difficult I find it to learn this stuff.

If I buy the parts seperately, can I safely assume they will be compatible with each other?

Siobhan Lavelle wrote:Thanks for all the detailed advice. I don't fully understand everything but I can look for equipment with the keywords you've suggested even though I don't fully understand what those words mean. I cant emphasise enough how clueless I am or how difficult I find it to learn this stuff.

If I buy the parts seperately, can I safely assume they will be compatible with each other?

Yes and no... so once upon a time the batteries ran at say 12 volts and the solar panels put out say 18 volts and the charge controller just controlled charge or dont charge... works fine in full sun but on cloudy days you get nothing... those are called pwm controllers.
An mppt controller takes a solar panel that puts out approx 36volts and adjusts it down to say 12 volts to match the battery... you would have to figure out wire gauges for cables and connectors...
Cheers,  David

Siobhan Lavelle wrote:Thanks for all the detailed advice. I don't fully understand everything but I can look for equipment with the keywords you've suggested even though I don't fully understand what those words mean. I cant emphasise enough how clueless I am or how difficult I find it to learn this stuff.

If I buy the parts seperately, can I safely assume they will be compatible with each other?

yes it can be intimidating, and theres a learning curve for sure. BUT its not as hard as it can be made out to be. also its getting easier and easier, like 20 - 15 years ago options were much different, harder to find and required a bit more research to figure it out.

and i will say for the most part - MOST pieces that you buy separately will be compatible with other parts. theres a few exceptions to this, BUT usually...most of the commonly found parts will be compatible with other brands, etc.

the ones that arent are usually harder to find parts, and some people create more elaborate systems, but you would have to seek out these more unusual parts.

but yeah i do hear you, when i first started with solar it was intimidating to me, and still people talk about stuff like running in series or parallel or why a 24 volt system is best, or a lot of other things and i am lost. but i got the gist of it enough to make it work, and thats all i need to know, i dont even need to fully understand why it works =) just - how to hook it up and get it working =)

this is how i am with the volt meter too, theres all these settings and numbers and i dont know half of what it does...but i know the setting and method for testing a battery or testing a current, and thats all i need to know =)

at the risk of over-explaining- i will break it down for you.

to set up a small solar power system you need -
~ solar panels, obviously  !!
~ a charge controller (some panels come with the controller already attached, which is great)
~ 2-8 batteries that you have in a "bank" to store your solar energy
~a whole bunch of cables that connect it all together. these arent to pricey individually, but all together it can get expensivce, sometimes you can salvage these too, they are commonly used in cars and other applications, and as such you can get them at an autoparts store. you need a bunch, for every extra battery you have you need more to hook it in.

also --->
~ an inverter, ideally 500-1000 watts, this converts DC (Direct Current) to AC (Alternating Current)
OR

/and IMO, a sealed battery/portable power cell/solar generator is what people have taken to calling these.
most of these serve as an inverter so you dont need another inverter...although the cheapest ones (like one of the sealed batteries) sometimes only have DC, which means you would need a separate inverter. another words, most sealed batteries also have an inverter, so thats all in one unit. also most of those also now offer USB plug ins for cell phones and tablet and etc, even speakers...too.

the different types of portable power units/sealed battery by itself would help in your situation, because you can plug them into regular power and charge them that way(charge on regular grid power at friends or whatever), plug them into your car lighter DC port to charge them, or charge them by connecting them to the last battery in your battery bank or just a fully charged battery by itself.

hope this is helpful anyway...

Burl Smith wrote:Two of these Wind Generators would give you 1000 watts both night and day in a 24 mph breeze. I'm a complete noob to these technologies also.

Ooops! One feedback comment isn't supportive of my wind speed estimate.

I highly recommend not to trust the figures manufacturers give about cheap products in general.
Especially when it is about battery capacity the "cheap chinese" manufactures are notorius liars,
probably the same applies to the power producing units.


For this specific unit one customer wrote:

Not to mention that THE CONTROLLER IS RATED FOR 15 AMPS MAX OUTPUT. Meaning the wires aside, the generator is falsely advertised as 500W, which is the point of my first comment.

Thnak you everyone! It's starting to feel doable.

What are some good, trustworthy manufacturers of solar panels, inverters, etc?

Max Panels
The avg tiny house is 8ft by 20ft, each solar panel is about 6ft by 3ft.
So you can fit about 6 solar panels on it. (20ft/3.25ft)
Each solar panel is rated for 333W, so 2000W in total. (333w x 6panel)
Daily Energy Production
Most formula states that we get 4Hrs of sunshine, but lets go with 2Hr for your area.
2000W * 2H = 4000WH or 4KWH. How much energy do you currently use? 4KWH is more than enough without getting any special low wattage/special timer setup.


For a list of reputable brand checkout this website. https://www.wholesalesolar.com/

Solar Panel = US$0.70 per watt, 345W for US$242 (you will need 6 for US$1,352)
https://www.wholesalesolar.com/1977433/astronergy-solar/solar-panels/astronergy-chsm6612p-hv-345-silver-poly-solar-panel

Charge Controller = US$324 (50A max, I would use a 48V battery system to match the 2000W of solar panel)
https://www.wholesalesolar.com/2940165/victron-energy/charge-controllers/victron-energy-smartsolar-mppt-100-50-charge-controller

Inverter = US$1,100 ( 4000W, with a surge of 8,000W, it comes in 120V aka US and 240V aka EU versions)
https://www.wholesalesolar.com/2923536/cotek/inverters/cotek-sp4000-148-inverter

subtotal = $2,800

Battery = 48V, there are so many different technology and permutations, so its hard for me to recommend any single one other than say 48V.

For space consideration, ease of use, long battery life, full discharge profile, high efficiency. LiFePO4 batteries are nice
$5900, 7.6KWH for a LiFePO4 battery
https://www.wholesalesolar.com/9580101/simpliphi/batteries/simpliphi-phi-3.8-kwh-48v-lfp-battery

Solar panels of different sizes and capacities can produce varying amounts of electricity. At the back of solar panels, you’ll find a list of numbers, one of which tells you how much energy the solar panel can produce if your location has ideal temperatures and the panels are positioned perfectly to catch the sunlight. It’s called the Standard Test Condition rating or STC. As of this year, a regular solar panel’s energy production ranges from 285 to 360 watts. If you find solar panels that can produce 285 watts or 0.285 kWh of energy, you’ll need 4 of these panels to meet your fridge’s consumption of 1.04 kWh. If you find those that produce 360 watts of energy, you’ll need 3 to run your fridge.

Some electricity basics.  Power is measured in watts.  Watts = amps X volts.  You can power something with high amps at low volts, or you can power something at low amps and high volts.  High amps heats the wires, and with too thin wire, can reach the point that it can start a fire.  On the other hand high voltage increases electrical shocking hazard.  Basically you want to balance the two, but in general most people agree that higher voltage is safer than higher amperage.  So, what are the voltage choices?

12V: small system, adequate for lights and TV
24V: medium system, adequate for lights, TV, refrigerator, power tools
48V: large system, high capacity capable of running large equipment such as well-pumps, large power tools, cement mixer, ect.

I can give you some guidance based on my own homestead's solar systems.  I have two, a 48V system for my cabin, and a 24V system for my workshop.   System voltage is the voltage range that your battery bank is set at.  There are many, many batteries out there.  12V and 6V are the most common, though you can buy 2V, 4V, 6V, 8V, and 12V.  I have three 8V batteries in series to create my 24V system, and twelve 4V batteries to create my 48V system.  Batteries are rated in how many amphours of power they store.  You wire batteries in series to get the watthours of power you need.

Battery size is directly proportional to how much power you want to pull out of them.  In general, you don't want to pull out more than 10% of capacity at a time, and 10% only for short periods.  You also want to charge your batteries around 1/10th of their capacity.   The math is simple, though there is some math.  Easy to do on a 1$ calculator.  

Let's built a 24V system for you.  You could buy four 6V golf-cart batteries with a capacity of 250Ah.  At 24V that's 250Ah X 24V = 6000Wh of power.  Let's assume that you never want to deplete your battery bank less than 50% for long life for the battery.  That means you get to use 3000Wh, or 3.0kWh of electricity.  Now, just because you have 3000Wh of power available that doesn't mean you should use 3000Wh every day.  You have to take cloudy/rainy days into account.  If you expect 2 days of rainy weather before the sun finally comes out, then you should use only 1000Wh per day.

I use about 2.5kWh per day with lights, TV, and the refrigerator running 24/7, so maybe golf-cart batteries might be too small for that amount of power draw.  Maybe two parallel strings of 250Ah batteries, or 500Ah total.  That would give you 12000Wh of power, 6000Wh useable.  That could work out to be 2.0kWh of power per day, assuming you get 2 cloudy days.

Now, what would you need to keep those batteries charged.  Assuming you want to charge at least at 1/10th C and C is 500Ah, that's charging at 50A.  If the voltage the battery charges at is 25V (for a 24V battery), then the math is 50A X 25V = 1250W of panels.  Since panels are typically produce no more than 85% of their nameplate rating, that works out to be 1250W/0.85 = 1470W.  That just happens to be the wattage that the last panels I bought are, 245W Astronergy.  If you bought six 245W Astronergy panels you'd get exactly 1470W of power.

Six panels should fit on the roof just fine in portrait.

Now, you need a charge controller to manage the batteries.  You can NOT just hook the panels straight to the batteries.  Because you need to charge at least 50A into your batteries, I'd buy at least a 60A controller.  Look at this one.  There are cheaper controllers out there, but not that can handle 50A.
https://www.ebay.com/itm/352541593982?hash=item52151dd17e:g:CQsAAOSwuWJbuH2K
Note that the max voltage it can handle is 200VDC.

Those 245W panels I bought put out 30VDC while producing power, but have a Voc of 37.5.  Voc is the voltage when no power if flowing.  It's like how the water pressure goes up when you shut off the flow.  But, when the connection first gets made when the controller switches on, the electronics will be exposed to the higher Voc for a fraction of a second, before it drops down to the Vmp, the power producing voltage.  So, you can wire six panels all in series because the Voc would be 37.5V+37.5V+37.5V+37.5V+37.5V+37.5V= 225V.

Alternatively, wire your six panels into two parallel strings of three panels.  Each string would be producing ~8A at 90V, or a Voc of 112.5V.  So, the MPPT controller would take the 16A at 90V, and transform it into (1470W/25V) X .85 = 50A at 25V.

Lastly, you need an inverter to convert the battery DC into household AC.  I'm assuming your power in Ireland is 230V 50Hz?  For sure, buy ONLY a sine-wave inverter, because the motor on the refrigerator will be ruined by cheaper square-wave units.  I am in the US, so I work with 120V 60Hz, but I think you should be able to get 1500W sine-wave inverter for <600 USD.  I would get at least an inverter of that size because the refrigerator motor will have what's call startup surge.  That's a very brief <1 second surge to start the motor that might be 4-5X the running power.

Hi Siobhan,
While it’s possible to utilize a solar panel separately to run devices, this is not highly recommended. A refrigerator requires three times more power than when operating; this is probably more than what the solar panel can produce.
You can use 300 watt solar panel, a 300-watt solar panel produces a steady AC load of 270W; note that this already allows for 10% inverter losses.
With a 300W flexible solar panel kit, you can operate home appliances like vacuum cleaners, blenders, treadmills, and desktop computers. Aside from these home appliances, it can also run a refrigerator that comes with a 120Ah lithium battery.