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Need some solar panel advice please….


Stuart1971

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Hi all,

I run a small 30w heater in my obsy overnight each night when not imaging, just during the winter, my back garden faces south west and would like to fit a small solar panel to power a battery for this 12v heater, but have no idea where to start, so any advice on what I would need and where to buy from, there are hundreds of different ones on Amazon, and it’s a bit mind blowing…..

‘Thanks in advance…

Stuart

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Given the amount of power taken out of the battery over (say) a 10 hour period to put that back during the winter days will require a sizeable solar panel and controller. In the summer months no problem but in the winter a 150 watt panel would struggle.

 

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6 minutes ago, Tomatobro said:

Given the amount of power taken out of the battery over (say) a 10 hour period to put that back during the winter days will require a sizeable solar panel and controller. In the summer months no problem but in the winter a 150 watt panel would struggle.

 

So any advice on what I need and where to buy from, would be a help…👍🏻

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I am using a Ecoflow River max to run my equipment currently. It takes about 3 hours or so to charge from 25% to 95% with a couple of generic portable folding 125w solar panels or you can charge it from 12v dc in a car or 110v in the US, not sure if they ship with an adapter for your local power requirements. It is 600w output with 600wh of power so you’d need to calculate the wattage of your heater to determine how long you can run it. Heaters are generally very power intensive. The lowest power I have seen is 200w so theoretically I could run a 200w heater for 3 hours if I wasn’t running anything else. A 30w could theoretically run for 20 hours…
 

The delta is lighter than a car battery and is self contained with a carrying handle soot is convient.

Not sure this helps you but it’s a nice power option…

-Jim

Edited by JimB1
Edit, I have the River max not the delta
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1 minute ago, JimB1 said:

I am using a Ecoflow Delta max to run my equipment currently. It takes about 3 hours or so to charge from 25% to 95% with a couple of generic portable folding 125w solar panels or you can charge it from 12v dc in a car or 110v in the US, not sure if they ship with an adapter for your local power requirements. It is 600w output with 600wh of power so you’d need to calculate the wattage of your heater to determine how long you can run it. Heaters are generally very power intensive. The lowest power I have seen is 200w so theoretically I could run a 200w heater for 3 hours if I wasn’t running anything else. 
 

The delta is lighter than a car battery and is self contained with a carrying handle soot is convient.

Not sure this helps you but it’s a nice power option…

-Jim

My heater is 30w @ 12v 

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If you run your heater for say 10h each night, your power consumption is 0.3KWh (10h * 30W)

I'm running full scale solar array for my house now (10KW), just got connected and running for 10 days, and my average at the moment is 1/4th of nominal power per hour (I produce about 25KWh in about 10h of daylight, so 2.5KWh per hour on average and that is 1/4 of 10KW installed).

It has been rather sunny last 10 days, so I estimate that in winter time, with more clouds  - this will drop to about 1/10th of nominal power, per hour.

Say that you have 6 hours of daylight in wintertime and you need to get 0.3KWh per day - that is about 50Wh each hour, and if that is 1/10th of nominal power - I'd say you'll need 500W of solar panels.

That is quite large solar panel. I have 585W panels (18 of those) and they are massive.

Depending how large is your battery and how often do you run heater (I guess it is not every night as sometimes you use obsy) - you might get away smaller solar panel.

Another thing that I did not factor in is losses in conversion. I'm running 3 phase inverter which has peak efficiency at ~98% - so that is quite high.

Not sure what would efficiency be for simple DC device (charge controller to charge your battery).

 

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6 minutes ago, vlaiv said:

Not sure what would efficiency be for simple DC device (charge controller to charge your battery).

About 75% based on measurements I have made in the past.  I agree about the size of the panel required (about the size of the observatory?)

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1 minute ago, Tomatobro said:

About 75% based on measurements I have made in the past.  I agree about the size of the panel required (about the size of the observatory?)

Depends on efficiency of panel

Baseline is 1KW per square meter under ideal conditions - clear sky and sun at zenith shining perpendicularly on panel.

Most panels now have about 20% of efficiency, so we would need 5 meters squared for 1KW of nominal power, or if we want 500W - that would be 2.5m2 in panel surface.

Here are specs for 585W panel (maybe exact model I'm using - although I'm not sure which model is installed on my rooftop):

  • Rated Power in Watts-Pmax(Wp): 585
  • Open Circuit Voltage-Voc(V): 41.10
  • Short Circuit Current-Isc(A): 18.11
  • Maximum Power Voltage-Vmpp(V): 34.22
  • Maximum Power Current-I mpp(A): 17.10
  • Module Efficiency (%): 20.7
  • Solar cells: Monocrystalline
  • Cell configuration: 120 cells (6 10+6• 10)
  • Moduie dimensions: 2172 x 1303 x 35 mm
  • Weight:35kg

We have surface right - as above is about 2.2 x 1.3 meters (2.86m2 for 585W) - but more important bit is that it weighs in at 35Kg.

 

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3 hours ago, Stuart1971 said:

would like to fit a small solar panel to power a battery for this 12v heater

To answer the question directly............

A small solar panel will just not put out enough power to recharge the battery in wintertime

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Agreed, my small 12v solar panel used to charge the dome 14Ahr battery that runs the dome rotation and shutter, is really struggling to keep the battery fully charged now that the days are shorter and the sun is lower in the sky.

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I looked at solar for my obsy instead of having mains installed from the house. The array soon became too big to be practical if I wanted to take advantage of the long winter nights. So I paid to have a mains cable laid. It was much cheaper than a solar installation, and I can take advantage of the solar on my house.

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2 hours ago, old_eyes said:

I looked at solar for my obsy instead of having mains installed from the house. The array soon became too big to be practical if I wanted to take advantage of the long winter nights. So I paid to have a mains cable laid. It was much cheaper than a solar installation, and I can take advantage of the solar on my house.

Yes I already have mains to my obsy, my initial question was just to run a 12v, 30w heater for 8-10 hours overnight,  not my whole kit….👍🏻

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  • 4 months later...

Sounds like a cool project! You'll want to get a solar panel that can charge a battery, which can then power your heater. The wattage you need will depend on how much power your heater uses and for how long. You can find calculators online to help you figure this out.
For buying the solar panel, I recommend checking out this page  for a good selection of panels. Be sure to read the reviews and product specs to make sure you're getting the right one for your needs. Also, don't forget to get a charge controller for your battery, which will regulate the charge from the solar panel and prevent overcharging. You can find these on Amazon as well.

Edited by perryjanie
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Solar panels from the like of Amazon are very much over sold on their abilities.

In practice your home panel is fixed so it only faces the sun head on, once each day.
At all other daylight time, it has lower output.
Then there are clouds.
Then they degrade with time - a few years.
Then there is risk of seals failing and letting in rain on cheap panels.

Whatever panels you buy, talk to a specialist company. They will offer you choices and know to avoid product that causes problems after sale.
A bit like the advice about buying astro kit from amazon and the like, or an astro retailer.

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Rather than go for an electric heater could you make use of other technology.?  For example, if you have a sun facing roof you could cover it with black pipes full of water and find some means of tapping off the heat from the water.  I bought a 100W panel from Amazon and fixed it to the roof of my car port.  On a more non-cloudy day it is sufficient to keep my car battery nicely topped up, but I don't know if could top the whole battery up in a day's sunshine if it were to be completely drained.

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