Hi Im Greg and I need some solar questions answered

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GBC

2 posts

Wannabe Geek

#91434 13-Oct-2011 11:35

Hi Guys and Girls

I have been directed to this website and I am hoping someone might be able to help.

I am going camping to a DOC campground with no power and no generators allowed.

I am hoping to do a solar panel to battery to inverter to power the fridge, a light, and charger for my ph and marine VHF radio.
Where can I find out what I need

LookingUp

411 posts

Ultimate Geek

#532794 13-Oct-2011 12:11

First you need to do a power budget, which is simply a calculation of how much power you'll need. It's best to work this out over a 24hr period.

eg. (Fridge = ?? watts average x 24hrs) + (lights = ?? watts x ?? hours) + (radio = ?? watts x ?? hours) + ....

... to give a number of watt hours you'll need over a typical day.

Then look at the inverter to see what it's efficiency is, as power will be lost in conversion from battery to 230VAC. If it's 80% (a number I've just plucked out of the air) then the amount of battery storage you need is (required watts hours / 0.8) = the amount of battery storage needed in watt hours, or divide this by 12 to get the storage required in Amp hrs, which is what batteries are commonly rated in. In reality you'll need a much bigger battery, as you can't always assume it'll be sunny and you'll get a full daily charge.

You'll also have to check that the inverter will provide enough power for the maximum load you'll have, which I assume will be with the fridge + lights + radio on.

Next, size the solar panel. As a rule of thumb, I'd normally allow a 10~20x factor - if your average load is (for eg.) 10Watts, you'll need a 100-200Watt solar panel.

You'll also need a solar regulator, which controls the charging of the battery from the solar panel. You'll need to ensure that the regulator can cope with the output of the solar panel in terms of the number of amps it can provide.

I'm sure you must be able to provide kits that include all the bits (?) The key is knowing what the maximum load will be.

Things are LookingUp.... A photo from my back yard :-)

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wellygary

8171 posts

Uber Geek

#532804 13-Oct-2011 12:29

You probably also need to consider if you actually need a solar panel as a charger,

How long are you going to be at the campground? -If it is only for a couple of days, could you get away with spending your solar panel money on a bigger battery and just charge that before you go?

Also you could also consider looking at getting a 3 way fridge that would run on either directly of 12 V, or even better on LPG, - then all you would have is a light a phone charger and a VHF all which are pretty low in draw, and would reduce the size of any panel and inverter you need.

Your fridge is the biggest driver of the size of the power system you will need,

GBC

2 posts

Wannabe Geek

#532807 13-Oct-2011 12:32

Thanks for the replys so far. They are making sense.

We will be there for at least 10 days. I cant go that long with out a cold beer.

the 3 way fridge is not an option at this stage as we normally go to powered sites for camping and we have a nice little fridge that does the job. It says on the label it draws 68w so it is only small.

alexx

867 posts

Ultimate Geek

#532823 13-Oct-2011 13:12

GBC: Thanks for the replys so far. They are making sense.

We will be there for at least 10 days. I cant go that long with out a cold beer.

the 3 way fridge is not an option at this stage as we normally go to powered sites for camping and we have a nice little fridge that does the job. It says on the label it draws 68w so it is only small.

Is that 68W an average or peak?

If we go to the www.jaycar.co.nz site and look for solar panels, we can see a 120W panel for $625 dollars. Perhaps there are better deals, but lets take that one to start with. Now given the loss in your DC-AC converter, 120W might just do the trick.... during the day, when the sun is shinning and the panel is almost perfectly aligned.

However, if you want reliable charging over the course of the day, even with a few clouds and with a enough excess capacity to power the fridge and charge the battery, so the fridge runs overnight, then we might need to scale the panel capacity vs the total DC load, by a factor of maybe 4 to 8. For long term 365 day reliability, a factor of 12-15 might be used. Even if we go for 4 panels or even just 2 (let's hope the sun shines a lot), that's going to be a really expensive cold beer after you get those panels and a suitable standby battery system.

#include <standard.disclaimer>

mattRSK

822 posts

Ultimate Geek

Trusted

#533033 13-Oct-2011 18:30

Hi

When looking at an inverter you will find there are two types. One that outputs a pure sine wave and one that doesn't. If you are going to be running a fridge you will need the pure sine wave type.

oxnsox

1923 posts

Uber Geek

#533104 13-Oct-2011 21:50

What type of fridge is it?
Compressor or electronic (peltier effect)?

With what you're looking at adding to your camping kit, weight wise, to achieve this I'd guess that you aren't walking far from your vehicle? Would it be possible to simply run the car engine to recharge that battery?