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Get Powered Up! Certified Energy Manager Jeff Yago answers your alternative energy questions

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Sorry. Jeff no longer answers questions online.
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Archive for the ‘Motor home’ Category

 

Battery hookup

Wednesday, December 24th, 2008

I hope this is a easy question.

I have a motor home that has 3 deep cycle 12 volt batteries.

I want to keep them charged with solar as much as possible.

Will connecting 2 or more 45 watt separate systems charge them better than just one?

As they are all the same watt I am not sure adding 2 or more same watt systems will charge any more than 1.

Help Please.

Thank you

Att: Help Please:

I assume you mean connecting each battery to its own solar module and charger verses connecting one solar charging system to all three batteries. For good battery voltage balance, its better if you connect one solar charger to all batteries wired in parallel. I don’t know how you could do this separately unless each battery can be disconnected from the others, since normally they all are wired to the same 12 volt positive and negative mains. Assuming you could separate them from each other, as soon as you connected a battery that was at a higher charge than the others, current will flow from one to the other until they are equal in voltage.

Keep it simple,

Jeff Yago

 

Going solar on our RV

Thursday, September 25th, 2008

We would like to go totally solar on our RV. Any suggestions on the least expensive route to go?

Katrina

Katrina:

This is not easy to do unless you have lots of roof area not obstructed by antennas, vents, skylights, and AC units as most solar RV systems are only large enough to meet full-time power needs. Also, powering your air conditioner unit is out of the question, so I hope your camping will be in an area that has mild weather.

If still interested your first problem to address is increasing your battery capacity. Most RV batteries can only store about one day’s electric requirements as they assume you will be connecting to the RV park each night for re-charge. I suggest replacing your single 12 volt RV battery with two (2) 6-volt golf cart batteries which will provide more storage capacity and will stand up to the heavy daily charge-discharge cycling. Next, since your RV’s battery system is not wired to any of the 120 volt outlets, you will need to add an inverter unless you will not be using any 120 volt AC appliances like a TV, computer, DVD player, or micro-wave. I STRONGLY suggest buying an inverter having a pure sine-wave output as it will provide much better service and have less risk of damage to some types of electrical loads than lower-cost modified sine-wave inverters. You will need at least 800 watts capacity to power all the electronics you may have, but you will need at least 1800 watts output to power most micro-wave ovens.

Lastly, if you stay with only the DC circuits in your RV and do not need an inverter, your RV roof may provide enough free roof area for the solar modules. However, regardless of mounting, there will be times the RV will not be oriented properly or will be in a shaded area. Since I wanted much more solar power than I could get on the roof of my RV, I have four (4) larger 75 watt size solar modules and folding ground mounting rack that I keep in the rear truck bed. It is pre-wired with a 50-foot cable and if I need to dry-camp, I can remove them and position the rack on any side of the RV to face south. If my batteries are really low, I can re-position the solar array several times during the day to always face the sun. Since solar modules are available in different sizes, you can find a size that is not too large for you to handle by yourself, but will fold up as needed to fir the storage area you have. There are several firms now providing roof mounts for solar modules that can be remotely raised and lowered or even rotated, but your power requirements may exceed the amount of solar array these can handle.

Good luck,

Jeff Yago

 

Solar water heating for camper vans, motor homes and RVs

Sunday, July 20th, 2008

Dear Jeff,

I’m hoping to develop a low tech, low cost solar water heater for use in a camper van. As such, it needs to be capable of supplying sufficient hot water for showering and dish washing for a family of four.

Assuming two daily wash-ups, and each family member showering perhaps every other day (we are roughing it in the great outdoors after all), daily water usage should be fairly small. I’ve seen the commercially available ‘Solar Shower’ bags, and have read about water-filled truck inner tubes and the like, but I’d like to develop something a little more sophisticated, if only to impress my (slightly more smelly) campsite neighbours!

Initially, I planned to make an open thermosiphon type system, utilising an insulated ground level collector, incorporating a secondhand refrigerator matrix, with a suitably sized storage tank sited on the van roof. This would be fine assuming we’re pitched up for a day or two- more often than not, we’re on the move for much of the day, and pitch camp in the evening- so any system would need to be permanently installed in/on the van and capable of making use of the sunshine on the move during the day.

Due consideration would have to be given to reducing the effect of cooling air passing over the collector while driving, but would a closed, pumped glycol based system, with a heat exchanger and on-board storage tank be feasible?

What precautions would I have to take regarding temperature and pressure build up, and how would one calculate the various capacities involved?

As you may have guessed, this idea hasn’t even reached the drawing board yet, but I’d be keen to hear your views, even if it’s to dismiss it out of hand!

Thanks for your time.

Jonathan

Jonathan:

You may want to check out the next issue of Backwoods Home Magazine (#108) as I show how to mount solar electric modules on a trailer which can tilt up.

Back in the 1920’s and 1930’s Florida did not have any piped natural gas or propane, and those homes with electricity back then usually only had one or two 15 amp fuses for lights and the radio. The did not wire homes for large electric hot water heaters. Therefore, almost every family home in Florida during this period had commercially made solar hot water heaters. They located the solar panel at the lowest part of the roof just up from the roof eve, then they cut a hole in the roof at the peak and stood up a hot water storage tank. They piled insulation around this tank which stuck up above the roof eve then fabricated a fake chimney around it to hid it. They did this so the tank would be much higher up than the solar hot water panels which allowed thermo-syphening and did not require a pump. Back in the late 1970’s we removed one of these old solar hot water heaters from an older Florida home that was still operational and replaced with a new system.

If you also want to use a thermo-syphen system, you must have the solar module as low as possible and the storage tank as high as possible. If you operate in colder locations you will need some type of anti-freeze. However, commercial solar hot water heaters are required to use a double-wall heat exchanger due to the danger of the heat exchanger getting a leak inside the storage tank and letting anti-freeze leak into water you could be drinking. Ethylene-glycol (automobile anti-freeze) is very poisionous, but propolene-glycol (red food coloring) is not poisionous and this is what they sell in RV stores for winterizing an RV. The problem with any system that uses anti-freeze is this reduces the heat transfer efficiency of the water mixture, so there is a down-side if you must prevent freezing.

If you can utilize a small DC powered pump, you will not need any anti-freeze. You have a small insulated non-pressurized holding tank just below the elevation of the solar panels. When the sun starts heating the panel, the pump is turned on and moves water up into the solar panels flowing from the bottom to top. When the sun goes down the pump shuts off and all the water drains back into this small holding tank, which is NOT the hot water storage tank. Your hot water storage tank will need a heat exchanger for this heated water to pass through as it moves back down from the top of the solar panels through the heat exchanger then into the small drain-back tank.

They also make special controllers that you connect a temperature sensor on the solar panel and the other in the hot water storage tank and it will turn on the pump anytime the solar panel is hotter than the water in the tank.

Since the solar panels are empty when the pump shuts off, there is nothing to freeze.

There are lots more to the design of these systems, but this should get you started.

Good luck,

Jeff Yago

 
 


 
 

 
 
 
 
 
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