Thursday, December 15, 2011

A Better Solar Charging Mouse Trap.PART 6

It's been a long road, but we made it! For those of you who haven't been slogging through this new fangled Solar charging install, I recommend you take a peek at the first 5(!) parts of this series. There are convenient links at the bottom of this article.

As you can see, no evidence of the solar panels from the ground!
Now that everything is working and I've had a few months to test out the system in the wild, so to speak. I learned quite a few lessons. Mostly that some behavioral modifications will be needed to get the most out of any Solar charging system. It would be nice if you could get lots for nothing. Alas..this is not the case. When you use power, it has to come from someplace. In our case it's either the sun or the batteries or a combination of both. The trick is making sure you have enough power when you need it. Let's take a look at a major power hog, the microwave. This great device is a fantastic time and effort saver for an RV. If you have a shore power hookup and/or run your generator all the time when you use it, there is no need to think about WHEN you turn it on.

Microwace/Convection Oven
GOTCHA! If you use an inverter to take your precious DC power and turn it into AC power for your microwave it uses a serious amount of juice. Take the average 1000W microwave. That 1000W at 120V which is around 8.3 Amps draw. Of course we now have to convert to 12V so times 10 equals 83.3Amps! (Really it's more because of losses and such) That's a lot to ask of 1 or 2 batteries for any length of time. So now what? Well, if you have fully charged batteries and your Solar charging system is working you should be able to offset the draw a good bit. If you are generating 25 Amps and are drawing 83.3 Amps, your batteries only have to fill the gap (58.3 Amps) and this has to happen for a short time. I mean, how long do you normally run a a microwave? 2-7 minutes? I wouldn't cook a Roast or anything, but for reheating food, or frozen dinners, go for it. You will use some battery power, but then (as long as you have sun) the panels will put it back in.

Dash Mounted Energy Monitor
The Trick is to use high load devices after your batteries are charged and you have daylight left over. Yes, you can cheat a bit and use it when the batteries are around 80% without too much trouble. Here's where a change in behavior will help you out. I wake up in the morning (sometimes early!) and want (need?) some coffee. At this point your batteries have gotten you all the way through the night (maybe using the furnace, another big draw item) without any charging from the sun. Now you want these tired guys to supply a lot of power? Naaahhhh. Let 'em rest, start charging and recuperate. Use the stove, go to a convenience store, have iced coffee or, better yet, get up later! A few hours of sunlight and you should be in a better position to run a higher draw item with ease.

Later on, as a secondary project to this, I have been looking into adding a "diversion load" capability. The MPPT controller will support this and it seems like a good idea. What is it you may ask? It's just the ability for the controller to DIVERT amps to another use after the batteries are charged ore when there is excess available. I was thinking of adding a 12V heating element to the water heater and using it to slowly bring the water up to temperature. Well, maybe.....if anyone has an idea for a use of power after the batteries are finished charging, let me know. I was also going to use a passive solar water heater on the roof. Not very big, but it would just feed water into the water heater after it is heated by the sun. Not electrically, just a black heat absorbing flat-ish bag affixed to the roof. I'd need a small pump to get water up to it, but gravity would bring it down to the hot water heater tank.....maybe next season!

Now for the big question.

How much did all this actually end up costing?

Good question. The panels were around $1980.00 Shipped via DHL from China. The MPPT 45AMP controller was around $450.00 Shipped from California, heavy cable and wire was another $300.00 from various sources. We used 5 tubes of 3M 760 adhesive at $12.00 per tube for $60.00. I had the inverter already, but it would be close to $450.00. Fuses and Fuse Holders were $50.00 all together and the remote monitoring for the Controller was $150.00. Since I already had an Energy Monitoring System, I didn't need to buy another, but if you did, figure on another $300.00 including the shunt. The grand total???


...Seems like a lot of money. Prices have come down a bit, so this could be done for around $2600.00 or so in today's' pricing. Less if you already have any of the pieces installed. Included was the Shipping from China at $500.00, so if you use an alternative method it could be brought down as well.

Remember, I did all the engineering and installation for this project, so there was no labor charges. (Well, Passenger Pete did want some food in exchange for labor so I guess I could figure that in.)

I would do it again in an instant. The whole system weighs less than a single large conventional panel, including all the pieces and parts. It puts out more than I need Watts-wise and fit on what real estate my tiny roof had available. As it is, I haven't run my generator at all last season (except to exercise it) and am enjoying the peace and quiet (not to mention fuel savings!) that this Solar Charging system brings. I highly recommend it!

Periodically, I will be updating the this system to make it more user friendly and transparent. Next will likely be Lithium Phosphate (LiFePO4) batteries. I'll be writing an article all abut my research into them and whether it's going to be doable.

Stay tuned to this space for more technical project information as well as some lighter-side moments as I go...

Down The Road...

Rich "The Wanderman"

Read Part 5 of this series.
Read Part 4 of this series.
Read Part 3 of this series.
Read Part 2 of this series.
Read Part 1 of this series.


  1. I have just recently finished my own installation, albeit a different philosophical bent. I decided on flex-amorphous panels for their shade and angle tolerance and (of course) ease of mounting - - peel-and-stick. With a limit of only 10 amps (2 68W panels), my installation overall cost was about $1000. A very comparable price ratio-wise. No, I can't be lavish with the microwave or hair-dryer, but normal daily use is pretty nicely covered, and I run out of water LONG before the batteries drop to 50%.

  2. I completely agree! You took the time to figure out your usage and designed a system around it. Way to go! I looked long and hard at the UNI-Solar style panels, but the large ones are longer than I had roof space for!

    Rich "The Wanderman"

  3. We have a 2 123 watt per panel, 240 watt controller, 2 Trojan 6 V batteries and 1250 watt inverter. Don't use microwave. Do use a 20 inch flat screen satellite box controlled TV and all 12 volt items in system without any troubles. Just be frugal.

  4. Outdoor Activities,
    That's the key! Modify your behavior to fit in with your capacity. Most folks will find it's not a problem at all and it isn't even an inconvenience.

    Rich "The Wanderman"

  5. I have a 6 panel set up of 500 watts. I use my diversion to maintain a good charge on my starter batteries. I have a "Lighting rod" installed to heat my water heater which uses current off my solar panels (house batteries), alternator, or when plugged in. My advice to anyone doing solar... you can't have too much solar power.

  6. That's great! The lightning rod is a 120V device, are you running it at 12V as a diversion load??

    Yes, power is good!

    Rich "The Wanderman"

  7. Rich, Yes the lighting rod is 110v and it pulls about 5 amps. In typical sunlight my solar panels will charge at 12 to 20 amps, in direct sunlight they will charge up to 25amps. I have 4 house batteries (thinking about adding 2 more)and I have no trouble keeping them charged. The solar panels at 24v are converted to 12v to charge my house batteries. My 2000 watt inverter converts the 12v to 120v which then is used to power the Lighting Rod and all other 120 circuits. This setup has reduced my propane heating of water by about 90%. My diversion is wired to my 2 starter batteries (a Cat. diesel) as some of my other systems have a slight drain on them so the diversion maintains them at a good level.

  8. I see you have the Morningstar MPPT 45 but did not see any Rs232 connection to the controller. Just wondering if you were taking full advantage of the wonderful Morningstar offerings. Did you program your controller via a PC or simply set the three or four on-board switches and call it good. Morningstar very often comes up with firmware upgrades for that specific model, suggest you take a look at your firmware version. They also offer free MsView and MsLoad applications which are actually very good. Did you consider installing any proactive warning / alarm systems? The Morningstar Relay Driver would compliment your system nicely. I have used it many times to monitor the separate battery banks both high and low voltage conditions and durations then drive a sonalert and warning lamps.


  9. Excellent. I am going to look into water heating as a diversion load. I believe I will still stick with a 12V load, since I'd like to avoid the inverter losses.

    Saving propane with the sun is a great thing indeed!

    I wish I could find space for additional batteries, but I really have nowhere for them at the moment. In an article I am writing now, I'm exploring battery options for right now and a bit into the future. Stay Tuned!


    Rich "The Wanderman"

  10. Ken,
    I definitely have the RS232 port in use! I have an old 486 notebook that I use exclusively to monitor and program the Morningstar controller. It's invaluable for tweaking the system and really knowing what's going on!

    I just wish the Morningstar software was a bit more user friendly. Their "GUI" is awful.

    Rich "The Wanderman"


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