Solar Panels

[Sheila1947]

We are new to RVing and I've been reading about boondocking.  One of the recommendations for extending our time is the installation of solar panels.  I would like to start a discussion about this.  Who has them?  How many panels?  Is this DIY?  Are they worth it?  etc.    Any and all information would be appreciated.

Sheila

 

[robatthelake]

We have 3X 75 Watt PV Panels that we have had since 2002 . A Go Power Controller providing a charge to 4 X 6 Volt Golf Cart Batteries.

These have worked very well on 2 different Motor Homes. We often Boondock for a Month or More without using the genset. Watch Satellite TV Every Evening  and always have enough power!

These days 120 even 150 Watt Panels are cheaper than what we paid for Our 75 Watt jobs 8 1/2 Years ago!

I must point out that We spend Winters in Mexico so there is plenty of Sunshine!

 

[Tom]

Welcome to The RV Forum Sheila. In addition to responses you receive here, you could also run a search; We've had numerous prior discussions on this subject.

 

[Wendy]

We paid just under $3000 in 2006 for 2 120-watt solar panels and an inverter. We have 4 batteries. Our thinking was never that we would save money, it was that we wouldn't have to listen to our generator and neither would our neighbors. We do use a lot of power and still run the generator about an hour a day when we're boondocking. I'm glad we have the solar panels and have never tried to figure out if they've paid for themselves or not. We dd install them ourselves (with great advice from the Forum solar expert) but Mike is pretty handy. Hardest part was getting the buggers up on the roof.

Wendy

 

[Tony_Alberta]

We do use a lot of power and still run the generator about an hour a day when we're boondocking.

I've been thinking about that.  Seems to me the best time to run the generator would be earliesh in the morning before the sun gets too high.  My thinking is that up to about 70% of the charging cycle the battery takes in the most amps.  After than the chargers/charge controllers/battery decrease the amount of current going into the battery on a sliding scale.  Therefore to get the most efficiency out of your generator get the batteries up to 70% before the solar panels start to kick in.  Then let the solar panels "top up" the battery.    And at least size the batteries and solar panels so that they will top up the 30% of the batteries by the time the sun gets too low.

Of course all these numbers will be different for folks depending on their power consumption.  And if you want a microwave to run for 20 minutes during meal prep well get the generator going then.

 

[Wendy]

We are not morning people. So our thinking is to let the sun and the solar panels charge up the batteries during the day when we're not using a lot of power and then use the generator in the evening while we're watching TV. Of course, the folks who need to use their coffee makers might want to run the gen in the a.m. And all bets are off if you're in an area where you need to run the A/C.

Wendy

 

[taoshum]

I've been thinking about that.  Seems to me the best time to run the generator would be earliesh in the morning before the sun gets too high.  My thinking is that up to about 70% of the charging cycle the battery takes in the most amps.  After than the chargers/charge controllers/battery decrease the amount of current going into the battery on a sliding scale.  Therefore to get the most efficiency out of your generator get the batteries up to 70% before the solar panels start to kick in.  Then let the solar panels "top up" the battery.    And at least size the batteries and solar panels so that they will top up the 30% of the batteries by the time the sun gets too low.

Of course all these numbers will be different for folks depending on their power consumption.  And if you want a microwave to run for 20 minutes during meal prep well get the generator going then.

You raise a really interesting question...  I've always thought that an amp-hr is an amp-hr no matter where it comes from, genny, solar cells, the grid, whatever... so it wouldn't matter where it comes from... I mean the batteries don't know what is sending the amp-hrs to them...  But you raise another aspect, the genny can generate way more amps than the solar cells, even if the voltages are similar so when the batteries are low and can take more current, the genny can supply it but the solar panels are power limited to their capacity which is way lower than the genny.  So I think you're right, if you are going to run the genny, it doesn't used much more gas/diesel to provide big amps than to provide the low amps since most generators have like 8,000 watts max output but the solar cells have like 300 watts.  At 15 volts, the solar cells can generate, about, 15-20 amps depending on the sun, but the genny output could be 500 amps.  This would way overpower the batteries so the charger limits the current to 70-80 amps if they are in bulk charge mode which runs the genny at about 20%.  Same thing goes for the charger if you're running off shore power.  As the batteries charge, the charger lowers the amps so at some point the solar cells are adequate.  So the quickest way to charge the batteries is genny first, then solar.  If you need 150amp-hrs to fully charge the batteries, the solar system would need at least 10 hours or more.  With the genny, an hour or so would get most of it done and the solar can "top it off" as you say.

It works either way, but it's more efficient the way you suggest... maybe someone else has a different perspective

 

[Tony_Alberta]

BTW my thinking is based on the graph at http://www.batteryuniversity.com/partone-13.htm

 

[taoshum]

BTW my thinking is based on the graph at http://www.batteryuniversity.com/partone-13.htm

Yeah, that shows it pretty well!  Great reference.  Thx.