Solar with a residental fridge
All, I have a question about solar panels for my new (to me) RV. I have a 2016 Thor Outlaw Gas Class-a. I have three main concerns regarding power when not plugged in and not running the generator ...
Forum Discussion
What is the wattage/amperage of the fridge? Let's assume 100w (no idea what it really is for your fridge but 100w makes the math simpler, update the calculation for the real value) For a hot desert use in an RV that isn't air conditioned, I would assume 100% duty cycle (what percentage of the day the compressor is running).
If you have anything else using power, you need to do a similar estimate and add it in.
That means you need 2400w-hr of energy generated to replace what the fridge uses each day.
Solar panels will typically produce around 4 time their rated wattage in w-hr (ie: a 100w panel will generate around 400w-hr per day) So in our example, you would need about 600w of panels assuming no other loads.
You also need to figure out how much the batteries will need to hold. As mentioned, 20amp-hr would be something like a lawn tractor battery. (Find the real amp-hr ratings). Since you have a generator, let's assume if you get an overcast day, you can run the generator for a short period to make up the difference (if you really don't want to run the generator, you need to decide how many overcast days you want before you resort to generator and increase the system size to account for it). Let's assume the longest period you will go without sun is 18hr (late and early day solar isn't generating much of anything)...So the batteries need to hold enough to cover 3/4 of a day or 1800w-hr. 1800w-hr at 12v = 150amp-hr. Of course, you can't use 100% of the ratings on a lead acid battery or they won't last long. Usually, people assume 30-50% is available to use, so you need somewhere around 300-450amp-hr of battery to support the system.
Since the batteries are 6V, you calculate the amp-hr rating by multiplying the rating by the number of batteries and divide by 2 for 12V. (assuming you have 6v golf cart batteries, good chance you have around 400-450amp-hr in your current bank if they are in good condition).
A couple of side issues:
- If you have other electrical draws and they are heavy, you need to account for the Peurkert effect. Under heavy draw, the amp-hrs available are reduced...unlikely to be an issue if it's just the fridge.
- Similarly batteries absorb power more slowly as they near full (why some suggest assuming 30% available as you go from 50-80% charge and back each day). 100% charge can be difficult to achieve. If you do start the generator to give it a boost, do it early in the day so the solar can slowly fill that last part.
If you have anything else using power, you need to do a similar estimate and add it in.
That means you need 2400w-hr of energy generated to replace what the fridge uses each day.
Solar panels will typically produce around 4 time their rated wattage in w-hr (ie: a 100w panel will generate around 400w-hr per day) So in our example, you would need about 600w of panels assuming no other loads.
You also need to figure out how much the batteries will need to hold. As mentioned, 20amp-hr would be something like a lawn tractor battery. (Find the real amp-hr ratings). Since you have a generator, let's assume if you get an overcast day, you can run the generator for a short period to make up the difference (if you really don't want to run the generator, you need to decide how many overcast days you want before you resort to generator and increase the system size to account for it). Let's assume the longest period you will go without sun is 18hr (late and early day solar isn't generating much of anything)...So the batteries need to hold enough to cover 3/4 of a day or 1800w-hr. 1800w-hr at 12v = 150amp-hr. Of course, you can't use 100% of the ratings on a lead acid battery or they won't last long. Usually, people assume 30-50% is available to use, so you need somewhere around 300-450amp-hr of battery to support the system.
Since the batteries are 6V, you calculate the amp-hr rating by multiplying the rating by the number of batteries and divide by 2 for 12V. (assuming you have 6v golf cart batteries, good chance you have around 400-450amp-hr in your current bank if they are in good condition).
A couple of side issues:
- If you have other electrical draws and they are heavy, you need to account for the Peurkert effect. Under heavy draw, the amp-hrs available are reduced...unlikely to be an issue if it's just the fridge.
- Similarly batteries absorb power more slowly as they near full (why some suggest assuming 30% available as you go from 50-80% charge and back each day). 100% charge can be difficult to achieve. If you do start the generator to give it a boost, do it early in the day so the solar can slowly fill that last part.
