Solar Panels

Power is addictive. My best advice to anyone considering solar panels is use every square inch and cover your roof with solar panels. The more power you have the better off you'll be.

I started my RV project with the idea that I would have six identical 105 watt solar panels connected usig MC4 connectors. However I started with four. Four panels worked great for me on sunny days,. However, I discovered that on overcast days I could not fully recharge my battery. As a result I decided to upgrade to two more panels to bring it to my goal of six panels toyalling 630 watts.  

Six panels is overkill on a sunny day, but it will also top off my batteries on a cloudy day. I can still recover hundred percent about power unless it's a very dark day. It is rare to have two really dark days in a row. The next day is usually enough to bring it back up to full charge. To date I have never gone more than one day with fully recharging my batteries. 

My first battery was one 165 lb 8D Gell Cell battery. It was used battery that had some problems and had lost much of its capacity.  While it was rated for 300 AH, it could only provide 80-90 AH depending on the discharge rate. 

 I decided to buy two new MasterVolt Slim Line batteries.  Each of these was 200 amp hours. So my total capacity was increased to 400 amp hours.

Typically, one watt of solar panel charging capacity is needed for every amp hour of battery storage.  Here in New England, where I live, the number of overcast days is high enough that the relationship should be 1.5 W of solar panel charging capability for every half-hour of battery storage.

An MPPT charge controller take the power provided my the solar panels and converts it to the ideal voltages for charging batteries.  These cost a bit more but are more suitable for daily cycling of batteries.  If you were charging a boat used only once a week, a cheaper charge controller would be fine. In my case I wanted my camper to be off grid capable for extended periods with daily power cycling. 

A large capacity solar array coupled with a large battery bank gives you more flexibility. For example on sunny days I might be fully charged by 1 pm and I can then use the solar panels to run my inverter and direct this surplus power into operating my refrigerator, a small heater, an electric blanket, TV, or other AC devices.  

My charge controller takes the solar power converts it into the maximum current at the ideal voltage to charge my batteries. This means that the charges tapered as time goes on so much of the solar generated power is wasted as the batteries get fully charged.  In fact my batteries could tolerate much deeper discharges and I would still probably be fully charged the next day if it was sunny.

This means I can deliberately choose to use more power and I now do. I run an electric blanket at night. I have stopped worrying about my energy consumption. I start my blanket on high to warm up to bed, and then dial it down to a lower temperature. This allows me to avoid or reduce my furnace use at night. 

Many nights I can turn the furnace off completely and use electric blanket to stay warm. That reduces my propane usage considerably. Additionally the furnace fan blower motor uses a fair amount of electricity.  I have found I can use the electric blanket more than I expected without worries about drawing my battery too low as the drain from the furnace is reduced or eliminated. 

I use a LinkPRO battery monitor.  It gives me accurate information on my state of charge.  To date I have never drawn the batteries below 75% charge.  I have never used more than 100 amp hours discharge in a day.  Typically I use 40-70 AH.  I have not had to be cautious with my power use. However if I am  cautious with power use  I can reduce my consumption to about 37 AH 's.

I estimate that my system could last 5 to 6 days in serious overcast conditions.  My goal is to make this a true four-seasons camper that could be used in the winter with my water systems in operation.  In an emergency I can stay warm even if I run out of propane.

To test out my camper I started living in it on March 10 of this year. I activated the water around March 15. I had a few nervous moments when it got extremely cold. I saw nights with temperatures as low as 13° and high winds.  On a few nights my furnace stopped working because of a pressure gauge that restricted the flow at lower pressures.  Nothing froze. I fixed that issue and my tanks remain well above freezing.

I monitor inside, outside,  refrigerator, and two holding tank area temperatures all with one instrument above my dinette and four remote wireless sensors. 

Propane usage usage is a concern. I will discuss that on a future blog entry.

I will add a few photos of my system later.