Complete Beginner - Installing a Renogy 20amp MPPT in caravan with 300W solar panels

[ConorN]

Hi all,

So I know pretty much nothing about solar power, to make it worse I know pretty much nothing about electricity either. Nevertheless, As I need a CPAP machine to sleep and have to camp off-grid in my caravan at a music festival in mid July, I've decided to dive in head first. However I think I may have screwed up with what I bought. My CPAP adapter says it needs Input: 100-240 Volt, 2.0-1.0 Amps, outputting 12v 6.67 amps to the machine. So I should have no trouble with a 100ah AGM leisure battery, as long as it's charged each day.

So I picked up 2 x 150Watt 18volt ETFE Monocrystalline Photovoltaic Panels, then I bought a Renogy 20A 12/24V MPPT Bluetooth Solar Panel Charge Controller.
The Solar Panels page on amazon described them as for 12volt Caravans, Motorhomes etc. But now that I'm actually looking to install them, I'm seeing a discrepancy, the MPPT Controller states: Max. PV Input Power 12V/260W. But the panels are 18volt and 300 watts. So, can I reduce the power of the panels before the controller? Or did I badly screw up and need to get different panels? I have about 4 weeks to get this all up and running so I'm starting to panic!

Any advice, greatly appreciated!

 

[mikefitz]

You are missing reading the controller specification, it recomends for a 12 volt battery system to use a maximum of 260 watts, that's the 12v/260 you are seeing in the specification.
It's very unlikely your panels will generate 300 watts, typically in good conditions at midday expect about 250 watts. If the panels exceed 260 the controller will limit the power to the battery, nothing bad will happen.
The panels can be connected in either series or parallel to the controller, series may be easier wiring up.
When commissioning the system connect the battery first to the controller then the panels.

Your CPAP needs 80 watts at 12 volts, if using an inverter to power the 240 to 12 converter, due to inverter efficiency you will need around 100 watts. Assuming 8 hours use that's 640 watt hours at 12v or 800 watt hours a AC 240 v.

Panel power with good solar conditions, ( do they occur in your country ?) in summer with long daylight hours should exceed 1000 watt hours. A full battery holds around 1200 watt hours.

It's recomended for long battery life, to only use 50% of the battery capacity. However over several days use there should not be serious issues discharging further.

If using an inverter connect direct to the battery via a fuse and only switch on when needed. What model of inverter are you using or can you power the CPAP direct from the battery?

Mike

 

[ConorN]

You are missing reading the controller specification, it recomends for a 12 volt battery system to use a maximum of 260 watts, that's the 12v/260 you are seeing in the specification.
It's very unlikely your panels will generate 300 watts, typically in good conditions at midday expect about 250 watts. If the panels exceed 260 the controller will limit the power to the battery, nothing bad will happen.
The panels can be connected in either series or parallel to the controller, series may be easier wiring up.
When commissioning the system connect the battery first to the controller then the panels.

Your CPAP needs 80 watts at 12 volts, if using an inverter to power the 240 to 12 converter, due to inverter efficiency you will need around 100 watts. Assuming 8 hours use that's 640 watt hours at 12v or 800 watt hours a AC 240 v.

Panel power with good solar conditions, ( do they occur in your country ?) in summer with long daylight hours should exceed 1000 watt hours. A full battery holds around 1200 watt hours.

It's recomended for long battery life, to only use 50% of the battery capacity. However over several days use there should not be serious issues discharging further.

If using an inverter connect direct to the battery via a fuse and only switch on when needed. What model of inverter are you using or can you power the CPAP direct from the battery?

Mike

Solar conditions are hard to gauge. This week for example, We've had blazing full sun for 14+ hours a day. Starting today, we have a week of overcast skies and light rain. Long range forecasts are dodgy at best, but suggest dry, sunny weather for the weekend I'll be away.

I am considering buying a second 100ah AGM battery, and charging it up before I go with my CTEK charger at home. To have as a spare if I'm short one night.

I have yet to buy an inverter for it. I'm considering this one: http://www.amazon.co.uk/dp/B00RV69O0I . It should be powerful enough to handle the CPAP with ease.

Really appreciate your answer! Thank you!

 

[mikefitz]

Low cost inverters rarely operate to specification.
Consider a Brand known for quality,

Victron Phoenix Pure Sine Wave Inverter - 12V 250VA (VE.Direct-enabled)

Victron Energy 12V 250VA professional, high efficiency, pure sine wave inverter with VE.Direct interface. For caravans, motorhomes, campervans, boats.

www.12voltplanet.co.uk