LIVING WITH SOLAR AND A BIG BATTERY PACK
We added solar panels and redid the electrical system of the old coach, our 19 year old Foretravel. The up date was prompted by two factors. One, we were about to embark on a six month odyssey and second we wanted the option of operating the micro wave and coffee pot without firing off the generator. The question was, is it worth it?
This was more than just adding a couple of solar panels to the roof and some wiring. A good system will include:
- Solar panels
- A voltage regulator for the solar input
- A converter/inverter/charger
- A control panel for the converter/inverter/charger
- A decent sized battery pack
The system provided us from RV Solar Electric in Phoenix AZ included two solar panels rated at 160 watts, a Magnum 2000 watt converter/inverter/charger, the control panels and the 12 volt wiring. For the battery pack there was six Trojan T 105 batteries sitting in my golf cart that would only be sitting at home while we were on our trip. They ended up in a battery bank that also included an 8-D series heavy duty truck battery raising the battery capacity for the house side of the system from 250 amp hours to 1000 amp hours.
This means that we can draw one amp for 1000 hours or 1000 amps for one hour or any combination in between before the batteries are run down to a point that they will not safely operate the equipment. That is about 9.6 volts. The lower the voltage gets in a system, the higher the amperage draw is to operate a unit. It is the flow of amperage through a circuit that creates heat and increases the chance of an electrical fire.
INVERTER/CONVERTER/CHARGER
The heart of the unit is the Magnum inverter/converter/charger. The unit has three distinct functions:
- First, it will take 12 volt direct current and turn it into 120 volt alternating current.
- Second, it will charge your batteries with first a fast or bulk charge rate of up to 100 amps, and then drop off to a float charge that will keep the batteries fully charged.
- And third it will take 120 volts, either from shore power or the generator, and provide 12 volts to maintain the batteries and support all of the 12 volt loads in your coach. A good inverter/converter/charger will have automatic switching that will kick in when running the generator or plugging into shore power.
WATTS, VOLTS, AND AMPS
Volts is the electrical pressure in a system, just like the PSI in a hydraulic system. Volts is the push. Amps is the flow of electricity in the system and is like gallons per minute flow in a hydraulic system. Watts is a unit of measure that is volts times amps. Lets just say that the electric toaster on your kitchen counter is rated at 500 watts of power needed to operate. If you divide the watts, 500, by the voltage, 120, you find that the toaster will draw 4.1 amps. In electricity if we are going to draw 500 watts out of one end then we must put 500 watts into the other end. There is a small operating loss but not enough to bother with for these calculations. So, on the 12 volt side again divide the 500 by 12 volts and it comes out to 41.6 amps going in.
In the inverter mode it will run any 120 volt unit that has a current draw of less than 2,000 watts. That equals about 16 amps.
On top of this the solar system will add to the charge rate when ever the solar gain is high enough to raise the voltage above other charging inputs.
DOES IT WORK THAT WAY?
On this trip we just finished 4 days of dry camping in a row as our Thousand trails membership is the 14/7 plan. That means 14 days in a TT park and 7 days out of the system. We did not economize on the use of electricity using the coffee maker and microwave as needed. We watched TV and ran lights and both furnaces at night as the temperatures are in the 40’s overnight. The solar panels are rated at 160 watts under ideal conditions. This 4 days of dry camping occurred in the Sequim Washington area and the conditions were less than ideal. The sun was low in the southern sky and the days were 30% cloud covered. Instead of getting an output of 13 amps from the solar we were lucky to get 5 amps and for only 7 hours a day. That figured to 140 amp hours of power from the solar for the four days which covered the complete needs of the two furnaces, or about an hour of micro wave time, or any combinations, but you get the point. In case you are wondering what happened to the other three days, well we sat those out in Tall Chiefs Resort in Fall City, WA. waiting for flood waters to recede so that we could get to Sequim, but that is another story.
In this latitude this size solar will act to help lengthen the time that you can dry camp but will not comfortably solely support the coach without really conserving use. The thing that appears to be important at this point is to have enough battery capacity to support your system.
After the four days of boondocking, it took a combination, of first three hours of driving and two and a half hours of battery charging with the coach plugged into shore power to bring the batteries back up to snuff. This would have been the equal of five and one half hours of generator time.
How does that compare to the old system that had no solar and only one 8-D battery to support the coach and a 45 amp converter? Before the new system we would have run the generator two hours in the morning to make breakfast and charge batteries and two to three hours at evening meal time to make diner and watch TV making sure that the batteries were up in case we needed heat during the night. That adds up to four to five hours of generator time a day compared now to one and one quarter hours a day average.
On the road we keep the inverter on full time providing 120 volts in the coach keeping the lap top running with Streets & Trips, charging Lucy’s camera batteries, and running the refrigerator on electricity instead of. We switch over to propane when we stop for the night. The alternator on the engine supplies the current needs and provide us with fully charged batteries when we stop for the night, usually around 4 PM.
Even with the limited sun the system has worked and cut our generator use by at least 60%. And at 3 bucks a gallon for propane, run the numbers, it works. Not counting the convenience of coffee without the noise. While it is true that the system, as configured, will not support the entire load and keep the batteries charged but it is better than what we had.
This has been our experience in the northern part of the country in late fall when the sun is low on the horizon and we are approaching the shortest day of the year. After we leave the Seattle area we are heading south and we will keep the log going to see how the system works when we get more sunlight.
Brad
nomore TV
What was the weight of the batteries and entire systems, as weight does eventually start to impact MPG, tires etc. How do those things mount on roof as seems like they will create some drag as well as lift if wind gets under panels going down the road. could also move the roof structure (leaks) a bit? Not knocking it..but curious as to tolat installation pros and cons.. very concerned about going through roof for boltung down the panels and what actual wind speed they are certified to handle, that is appant wind, not just what the speedometer shows..Seems like on long tirps at 60-70 with local winds cranked in, might need some real thought as to how installed.. warranty etc.
Roger
WARNING
If tou a Google search on solar energy or similar there may be ads on the side of your results page presented by “Google ads”. What you will see appears to be a series of reviews on a couple of different “courses”. If you click a different advertisement you will find similar page designs with glowing “reviews”.
Wile I could only reasearch a few of these “review” pages what I found was that there were direct contact information on these “review” pages just links to a place you could purchase their products.
After trying to trace who was posting these “reviews” I found
“How to build a solar panel” liks to Earth4energy.com an homemadeenergy.org
were registered to
DomainsByProxy.com
I also discovered a web site that generated “review” web sites which would allow someone to generate what looks like many different sites t all seem to give similar glowing reviews.
I think Solar has some very good possibilities. Just be sure you are dealing with a reputable company not someone that posts reviews of their own products.
G Shea
Or, you can wait for the new free-thinking government to start being aggressive toward solar and wind…..
Going to be waiting awhile. This administration is no more “free thinking” than any in the past (in my opinion). I will predict that 4 or 8 years from now, the US will be just as dependent on oil, We will not be driving CNG cars (as we sould and could), and that will won’t be any better off than before. Every admin since Carter has promised to “get us off middle east oil” and not one has. After being lied to over and over, I fail to see why folks think the next admin will be somehow different. Must be marketing….
Duff Jolly
A lot of good points for and against. Last year in the deasert North of Los Algadonas we met lots of campers with various combinations of solar systems. One comment I heard frequently was the low output of the solar panels due to the low angle of the sun were not doing a great job of keeping the batteries charged and the generator was being used on a regular basis. I spoke to one fellow who spent $6000.00 for a complete system and still had to use his generator. We stayed in the desert for 4 weeks and used the generator twice a day for about 1 hour each time. We could buye a lot of propane for $6000.00 so unless 2 hours a day of generator noise is too much for me I’ll stick with what I’ve got
Sheldon Dedek
If you are traveling through less than ideal locations and conditions, you can still boost your charging effectiveness of your solar panels using a MPPT charge controller. MPPT is short for Maximum Power Point Tracking.
Basically, it is a controller that changes the way the load appears on the solar panels. Lets say that in full sun, your panels are producing rated voltage and current. But, in partial cloudiness, the solar panel doesn’t do much charging because the voltage is not high enough. As an example, lets say that a panel is capable of producing 12 volts at 12 amps through a typical controller. A potential of 144 watts. If the battery pack is lower than this voltage, the pack charges. If the pack voltage is above 12 volts, then very little, if any, charge occurs. The way a MPPT controller works is that the load as seen by the solar panel is optimized so that a load (current draw) of 8 amps is present, then voltage from panel will rise to 18 volts. With the voltage now higher than the pack, charging will commence.
It is complicated to understand, but it works fantastic. The downside of the controllers is their price, and they need to be matched to the panels as they controllers do have limits.
What they are:
http://en.wikipedia.org/wiki/Maximum_power_point_tracker
How they can be used:
http://www.solar-facts.com/controllers/mppt-controllers.php
Ron
In 98 was able to pickup 4 90 watt panels, 6 T105s and Prosine 2500, replaced inverter with a 3000 due to storm but panels were no problem. Replaced all batteries at the same time also. Two points with the batteries. Should try not to discharge over 50%, more will shorten the live of batteries. Also best to replace all at the same time, battery bank only as good as the weakest batteries.
Sparky Jim
WHOA UP A MINUTE!!!! If you back off your AC power use on the fridge, TV etc. and spend more time outside you will realize the beauty of living green. We have two 180 watt panels, a 400 watt wind generator, four 6 volts and a 2000 watt inverter. Using this system for the past 5 years we have run for over a year without shore power or generator.
We use our microwave and coffee machine and toaster each morning, an hour or so of TV news after supper. And I am a Ham operator and computernut with Hughes satellite internet. We also have a solar oven that offsets the propane use in the fridge.
We are totally independent of RV parks and hookups, only needing to water and dump every 10 to 14 days, dump trash and buy groceries.
It is definitely worth the effort and expense if you live within its limitations.
Peyton Yon
Our ’08 bus has a fully automated system with solar and automatic generator start.. BUT… when dry camping our experiences have found it’s best to turn off the automatic inverter before we go to bed which typically resulted in higher battery voltages in the morning of 12.2V instead of 10.9V
Even with the automatic generator start we found at the end of quit time (7am) the generator did not have enough house battery to even fire off the generator if we let the system manage the power loads with the inverter running full time.
We also found it cheaper to run the main engine (125 amp) to recharge the house batteries (30 minutes) as opposed to the generator running for 1.5hrs with an output of 30amp from the inverter/charger.
Fred
I have a 400 watt solar system and have dry camped over 600 days during the 12 years that I have had it. At $10 a night saved, the $3,000 solar system has paid for itself many times over, and I get to enjoy peacful campsites in the forest, with no neighbors for at least 100′ or more in most cases.
Because I can sell my solar system for almost what I bought it for, and I plan on transferring the whole system to my next RV, I have not really spent all the money on the system, because it is like putting $3,000 into a investment, and in 10 years it wil still be worth $2,000 – $2,500, so I only “Lost” about $500 for installing the system, and get to use it and save $1,000 or more per year while it is installed on this motorhome.
I would not recommend the 6 golf cart batteries, 4 is plenty and will store 5 KW of power. 6 is about 400 pounds, to much weight for a normal coach, but my guess is yours is diesel, with a little more than the average cargo rating.
320 watts of solar is a little marginal for dry camping weeks at a time. During the winter, I still need to run my generator about a hour a week, if I watch to much TV and run the batteries down.
You are much better off running the refrigerator on propane if you are not connected to shore power. The load on the alternator is significant, – about 40 amps, and will tend to overheat the wiring, or the alternator or both.
If you have a solid state battery isolator, be sure to check the voltage drop across it when the batteries are under load. Many solid state isolators have more than 1 volt drop across the terminals when under a 30 amp load.
Happy Camping !
Roger
I have two questions please. What was the cost of the system and what is a 45 amp converter? In my experience most converters produce no more than 3 to 5 amps.
jerry dean
Good article., quite detailed and supplied a lot of basic info for the laymen. However, there nee4ds to be an initial cost figure. Both for the cost of the equipment and other installation costs. Solar power does work. Does have a future. Big issue is the payback. Batteries are an issue; these are getting better and one day they will be “reasonably” priced and will last longer. Again, good article, thanx to the author.
Fred
Solar electric and wind-turbine electric are two of those alternative energies that desparately need to be priced for home and RV affordability.
The biggest reason I have seen to this point that everyday people with normal income want to go to alternative energy is to lower their utility costs and to be independent. Right now the high cost is the trade off for independence.
To boondock for any amount of time more than two or three days is going to cost you – and the manufacturing companies know that.
Also the effeciency of good solar panels tops out at about 20%. That means for every 100 watts input from the sun the panels only put out 20 watts.
To buy solar panels currently available retail will cost you about $12 per Kilowatt. You pay about 10 cents per Kilowatt to your electric company.
There is limited research going on right now to improve efficiency and reduce manufacturing costs. But, they lack money to scale up that research. We need the government to favor solar and wind energy and quit favoring big oil. Government subsidies to the solar industry for research has been almost non-existent for nearly forty years.
If you want to spend the money right now, you need not even consider payback. Just consider freedom instead.
Or, you can wait for the new free-thinking government to start being aggressive toward solar and wind. That action will take a couple of years research, then another couple years to put the new low-cost, hi-efficiency panels on the retail store shelves. That seems like a long time, but it is a whole lot shorter than the forty years solar panels’ costs and efficiencies have stagnated.
What really hurts is that at least two major American solar cell manufactures are now producing lower-cost, higher-efficiency panels right now. But, you can’t buy them.
They are for big solar installation companies only. Those big rich intallers are buying tens of thousands of panels and installing them in remote desert areas for producing big time megawatts to sell to the electric power companies.
I have 500 watts in four panels, a 2000 watt inverter, all the meters and regulators, heavy wiring and 450 AmpHours worth of batteries. I installed all of it myself to save labor. The panels on the roof can be turned like a carousel and tilted to follow the sun. The materials cost around $4000.
I am paying big time for my freedom! But, I won’t wait any longer for prices to go down, I’m seventy-two years old.
Bill Mann
Great article Brad. You covered the topic with enough technical info but not too much to cause confusion. I will watch for your updates on this. Thanks.
Adrian
Last winter we were in Quartzsite, AZ and looked into solar. We do some dry camping and thought we could expand our scope if we installed solar. We priced out 2- 120 watt panels, wires, brackets that allow for different angles and labor for $2000. We ended up not doing it because we really could not justify “cost = use”. I still think of it as an option at some point. I guess I just can’t wrap my head around the concept.
Rob Robinson
9.6 Volts………..you need help……..Please read something like
http://www.phrannie.org/battery.html
Linda Gillespie
I also am wondering is it worth it? How long will it take to make up the cost of the panels? Also did you install them or have them installed? We are going full time next year and plan on doing alot of dry camping. Is the cost really worth it? When I first heard the cost of them I didn’t think it would be, but now I’m not so sure. Thanks for the article and your imput. Linda
Connie
Yes, it works. But how long will it take to save enough to cover the cost of the solar system?