How much solar do I need?

[Spaceman Spiff]

Seems to be silent disagreement on the match up of solar to batteries size combo.

It also depends on your situation:  A person who spends a lot of time in the pacific northwest will have a different requirement from one who spends time in the southwest desert.  Same for prairie vs. forest.

 

[wayne49]

Not as easy as only size of battery bank and wattage of panels.
Don't ignore the ball of fire in the sky and relative humidity, etc.
A more complete equation might include average solar radiation per meter squared striking the ground for the general area of interest.
Weather Underground PWS (Personal Weather Stations) have solar radiation in five minute intervals, not all PWS, but most.
Then there is how much solar radiation can a panel process instantaneously. If more than 100 watts is hitting a 100 watt panel, the excess is unused. Calculus is required to go there.

 

[crofter]

It also depends on your situation:  A person who spends a lot of time in the pacific northwest will have a different requirement from one who spends time in the southwest desert.  Same for prairie vs. forest.

Here is a comparison.
-crofter

Description: link to map and article on PV potential and projects.
https://i2.wp.com/cleantechnica.com...-size-map_160x95mm-300dpi_v20191015.png?ssl=1

 

[jimindenver]

How much solar do you need?

You need to be able to produce more power than you use on the shortest day of the year.

How much battery do you need?

You need enough capacity to get you through the period of time that the solar is not producing. So at least the ability to get through the night to start with.

2 to 1 is a good starting point for solar vs batteries for two reasons. First is if you get a big lead acid bank discharged it takes it to get past the resistance of the battery to being charged. Otherwise you will see the bank hang at 13 or 13.1v. Secondly is in the winter low sun and short days effectively cut your overall production in half while you use more power than you do in the summer.

 

[tripper]

There is no need to do lots of math and theories. Put as much solar as you can fit and afford on your vehicle, and then make it work. If you have excess power, you will find ways to use it or just be happy your batteries are always full. If it is not enough, well since it was the most you could do to begin with, your just going to have to conserve power, which also is easy.

 

[jacqueg]

Another way to do it is to find a youtuber who runs the gadgets you'd like to tun, and copy their setup.

But the best way I found is to watch this video by Will Prowse and figure it out. It's not a complicated process -

 

[NomadicFoodie]

watch this video by Will Prowse and figure it out. It's not a complicated process -

SO helpful! Thanks, Really great 101 so I can strategically choose what items/ specs I will want to load my van with.
I was literally googling "nomadic solar for dummies" but this answered my prayer, LOL
I had a very bizarre, random, education so math is a mystery, but I will get there!

 

[Nature]

How do you guys survive winter on solar?

I've been trying to calculate solar needs and the winter month in northern Europe are harsh. Some calculations(based on realworld data for a solar panel station near where I live):
Averaged during the summer month, the solar panel will produce 4 times it's W in Wh per day. So 500W of solar will charge for 2000Wh every day.
Averaged during november (the worst month for solar), the solar panel will only produce 0,57 times it's W in Wh per day. So 500W of solar will charge for 285Wh per day.

My minimum usage per day:
Fridge: 60W * 25% duty cycle * 24h = 360Wh
Laptop: 13W * 8h = 104Wh
Lights: 30W * 4h = 120Wh
pumps: 24W * 0.5h = 12Wh
misc:  = 20 Wh
= 616 Wh

Watts required to supply this:
Usage / eff. coeff = 616Wh/0,57 = 1080 W
In November it would require a whopping 1080 W of solar on the roof.
That demand might decrease if it's cold and the fridge doesn't need to run as much, as it's powerdraw is based on 25° ambient temperature. However, that would be slightly offset by increased light usage. Assumption: fridge uses half it's power (180Wh) and light usage goes up (30W * 8h), overall needs are 556Wh, which still requres 975W of solar.

1000W of solar would be difficult financially and spacewise on the roof.
Am I missing something? This seems like a bummer, as it would require daily driving around to charge via alternator.

 

[user 423]

1000W of solar would be difficult financially and spacewise on the roof.
Am I missing something? This seems like a bummer, as it would require daily driving around to charge via alternator.

You could try to find a reliable, inexpensive place to periodically plug in to shore power.

Or buy a small generator to augment solar.

 

[MrAlvinDude]

Your calculations seems okay.


So use alternator - or better yet: the suggestions for alternate power sources.

OR

Find ways to lower your power consumption.


Solar, in winter, in nothern europe, is not easy, nor very reliable or effective.

 

[MrAlvinDude]

Are there any electrical vehicle charging stations near by?
Perhaps you can find a way to charge your batteries that way?

And perhaps a larger battery bank would help you to only need charging from the electrical vehicle stations every few days?

 

[highdesertranger]

be very careful using car recharge stations to charge a non electric vehicle. it's illegal in some places. do your homework and find out before you attempt this. most of the pay to use ones are ok but the free ones are not. like I said do your homework. highdesertranger

 

[Qxxx]

Lights: 30W * 4h = 120Wh

Nature, sounds like your area is a real problem. All I can say is, it greatly helps to be able to adjust the angle of the solar panels to the angle of the sun. Many people mount the panels flat of the roof, but that's extremely inefficient, especially in winter. Also, I use a single 120VAC 60W dimmable "Led" bulb inside the van, and it only draws 10W of energy or so.

 

[Nature]

Thank you for the replies.

^ Yes, maybe it just too far north and the solution is to leave, it's a van after all, so follow the sun and go south might the thing to do. Tilting the solar panels is such a great idea. Using linearactuators to tilt the panel frame towards the sun might just be the best thing to do.

^^^there are charging stations around. I haven't been able to figure out, who can charge at them. However, their designated parking spaces are exclusively for electric vehicles. So with a normal engine, it wouldn't be allowed to park there for charging anyways.

 

[jimindenver]

How do you guys survive winter on solar?

I've been trying to calculate solar needs and the winter month in northern Europe are harsh. Some calculations(based on realworld data for a solar panel station near where I live):
Averaged during the summer month, the solar panel will produce 4 times it's W in Wh per day. So 500W of solar will charge for 2000Wh every day.
Averaged during november (the worst month for solar), the solar panel will only produce 0,57 times it's W in Wh per day. So 500W of solar will charge for 285Wh per day.

My minimum usage per day:
Fridge: 60W * 25% duty cycle * 24h = 360Wh
Laptop: 13W * 8h = 104Wh
Lights: 30W * 4h = 120Wh
pumps: 24W * 0.5h = 12Wh
misc:  = 20 Wh
= 616 Wh

Watts required to supply this:
Usage / eff. coeff = 616Wh/0,57 = 1080 W
In November it would require a whopping 1080 W of solar on the roof.
That demand might decrease if it's cold and the fridge doesn't need to run as much, as it's powerdraw is based on 25° ambient temperature. However, that would be slightly offset by increased light usage. Assumption: fridge uses half it's power (180Wh) and light usage goes up (30W * 8h), overall needs are 556Wh, which still requres 975W of solar.

1000W of solar would be difficult financially and spacewise on the roof.
Am I missing something? This seems like a bummer, as it would require daily driving around to charge via alternator.

Something isn't right here. I have 1185 watts and if that's all I could run, I would pack it up and move into a park.

First, get off the Wh thing. Our batteries are rated in amp. The output from the controller is shown in amps. The conversion from watt hours to amps is Wh divided by volt =amp hours OR  the conversion from amp hours to watt hours is Ah x volts = Wh

So

616 Wh divided by 12 volts = 51.3 Ah

There is hardly a need for over 1000 watts of solar. My 1185 watts on the shortest day of the year produced 215 Ah which is 2580 Wh. My highest production which wasn't even on the longest day was 651 Ah or 7812 Wh. I do have to admit that 435 watts can track the sun.

I run a 25 ft trailer. It has a furnace, a 40 quart Engel used as a freezer, a 450 watt Hott Rod for two hours a day as a water heater. A electric hot plate as a stove, a 250 watt personal heater while I'm in the bathroom, multiple hotspots and phone, a few computers, a booster, a TV, usually at least 6 LED panels and a huge porch light and a microwave. Things really get going when I run both of the 5000 BTU air conditioners all day.


Still think that you need over 1000 watts?

 

[Zythophile]

A semi-related question:

I understand the need to get a solar charge controller that is rated to handle the output of one's solar panels.

Is it a bad idea to get a higher rated solar charge controller than is needed at the time? With the idea of future upgrades, possibly adding a panel, or swapping panels for higher wattage models? Are there any inherent inefficiencies involved, or possibility of damage to the controller due to lower throughput than it's designed for?

 

[highdesertranger]

short answer is no. you can use a larger controller for future use. I am not aware of any bad effects. highdesertranger

 

[bullfrog]

There has been some discussion on advantages of duplicity when adding on panels. You may want to search.

 

[Zythophile]

There has been some discussion on advantages of duplicity when adding on panels. You may want to search.

Duplicity as in multiple ways to charge one's batteries? (Or do you mean something else? I'm not familiar with the term in this context.) I've done a fair bit of research on that stuff, and yeah, always good to have options.

In this case, I was more specifically curious about solar charge controllers and the wisdom (or not) of buying a higher-capacity unit for futureproofing, solely as far as adding a panel or two down the road. Shore power or DC-DC off the alternator are completely different scenarios.

 

[rvpopeye]

Go ahead and get the higher capacity controller , it will work fine.