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Author Topic: Home Solar Powered Station (Long Post)  (Read 4991 times)
KF7Z
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« on: March 24, 2013, 02:55:43 PM »

While this thread only pertains to a small part of EMCOMM details (that of station primary power), I hope that some readers will find it interesting and worth the bandwidth here consumed.

Just two weeks ago I finished getting my home solar powered station up and running.  I’ve been licensed continuously since 1966, but haven’t had an operable station since the early 1990’s.  While I’m not at this time planning to join any EMCOMM organizations, setting up provisions for being able to operate off-grid is part of our larger plan for off-grid independence.  We are fortunate to live in a rural location, and an important part of our retirement planning has been to provide for a reasonable quality of life with very little monthly cash spending, if necessary.  (One negative of our rural location is that we are near the end of a long power line, fed from only one direction, which means we have a lot of interruptions of service. This solar system is really nice to have when the grid power goes out.)  I offer this long description of how I have provided for our power needs in case that it might give others some ideas for cost-effective off-grid power planning.  After much reading and study, all of the system components were selected and installed by myself.

The core of our power plan is 4.4 kW of solar panels mounted on our roof, powering a 24-volt DC system.  This is 20 solar panels of 220-watts capacity each.  The panels are all wired in parallel through a pair of Midnight Solar combiner boxes in the attic space.  The parallel configuration necessitates more wiring than would a series-parallel scheme, but each panel puts out 52 volts (open circuit) which is near the optimum input voltage for our charge controllers when feeding a 24-volt system.  Wiring the panels in series-parallel pairs to put 104 volts to the charge controllers would lower the charge controller efficiency a few percent as the controllers would waste more power in the step-down conversion.  Each combiner box, handling ten panels, is connected to one of a parallel pair of Outback Power MX80 charge controllers.  When power demand is low relative to panel power output, one charge controller and the associated panels are automatically idled.

The Outback Power charge controllers connect both to pair of 2400-watt DC to AC inverters, and to 5500 amp-hours of Rolls-Surrette AGM storage batteries.   These are a total of 12 batteries, of 6-volts and 420 amp-hours capacity each, connected in series-parallel in three strings of 24 volts each.  Each of the three battery strings is connected through a 125-amp DC breaker to the main 24-volt buss in the Outback panel.  With these expensive storage batteries, long life is a matter of optimizing depth-of-discharge and lifetime charge/discharge cycles.  Having each string tied through a DC breaker allows me to easily optimize the in-service battery capacity to the daily load. Rather than using flexible cable to interconnect the batteries, which would typically be 2/0 welding cable, they are interconnected using 1/4-inch thick solid copper buss bars that I fabricated myself.

I could have chosen to configure a 48-volt DC system.  That would have been a wiser choice for a grid tied system. However, I am not attempting to sell power back to the grid.  While the DC to AC inverters built into the Outback panels can generate 120 or 240 volts for home appliances, and are capable of being grid-tied, in the interest of efficiency I have set up our home to operate nearly entirely on DC power when we are off-grid.  Even then a 48-volt system would reduce IR losses in distribution wiring, but there are very few 48-volt home appliances and conveniences available.  I have been able to buy step-down converters from 24 volts to 12 volts at very reasonable cost.  Step-down converters for 48-volts to 12-volts are much less common, and more expensive. Keeping loads small is the goal of any off-grid system, which simultaneously reduces distribution wiring IR losses.  Our small off-grid refrigerator and freezer each operate directly off of 24 VDC.

About the only AC loads we will run from the inverters is when my wife wants to do her sewing, and to treat the grandkids to watching a DVD in the evening on our large screen television.

I have 24 VDC wired to each room of our house, and to two places each in a couple of the larger rooms.  These DC  power outlets are a pair of high quality “banana jacks” in red and black pairs installed into standard blank brushed stainless steel outlet box covers.  Each pair of jacks is connected by way of a 10-gauge stranded wire pair to a 15-amp breaker in a DC distribution panel mounted on the wall above the batteries, and next to the Outback controller/inverter panel.  This DC panel is a standard Square D box from Home Depot, selected to allow the use of Square D QO series breakers.  The QO breakers are an inexpensive solution as they happen to have a 48 VDC voltage rating.  Wiring to the room with the ham station is through a 30-amp breaker by way of 4-gauge wire to a pair of insulated terminal buss bars mounted low on the wall, to which are connected several 24-volt to 12-volt converters.

For everyday living, this DC system can power lighting, a home music system, radios, laptops computers, and of course, the ham station, plus the refrigerator and freezer.

We have a couple of dozen 24-volt “table lamps” that are home built units, each incorporating a series pair of warm-white 12-volt LED automotive tail-light bulb assemblies.  These LED bulbs can be purchased off Ebay direct from distributors in China at very low bulk prices.  We built the bulb sockets into small attractive ceramic flower pots that are filled with plaster of paris for weight and stability.  These LED table lamps are hugely more convenient than any kerosene lamps, or candle solution to off-grid lighting, and they are tremendously efficient light sources.  I have also built several small 24-volt powered power supplies and chargers that output a variety of lower DC voltages for to run various computer and solid state devices.

In the winter months, we “harvest” any excess daytime solar capacity, beyond what is needed to recharge batteries, in the form of space heat.  For this I have built a number of 350-watt DC-powered “space heaters” with each one simply being a 2-ohm 500-watt resistor mounted on a simple aluminum heat sink that keeps the resistor surface from getting hot enough to scorch anything.  I also purchased those high-quality resistors direct from a Chinese distributor on Ebay at very reasonable cost.  While a wood stove is our primary heat, these small “space heaters” are nice supplemental heat for the rooms that are farthest from the wood stove.

During daytime solar hours, once batteries are recharged (which usually only takes a couple of hours since our night-time system loads are usually small) the system rides along at about 27 volts, which is determined by the battery float charge voltage setting.  Once the sun goes down, system voltage drops to the 25.5 volt level determined by battery charge state.

All in all, I am very pleased with the way the system is performing.  Because I only completed it a few months ago, I don’t yet have a lot of data on how much power our solar panels will put out on an overcast winter day.  However, I have been pleasantly surprised by the significant power that they generate even during hours of low sun angle, and even during periods of heavy overcast.

Maybe I should have opted for a grid tied system in order to qualify for the tax subsidies, and the revenue to offset or normal electric bill.  However, such a grid-tied system would have probably been twice as expensive to install.  This is because such an installation must be completed by a certified installer, and would need to incorporate many expensive system details that I was able to forego.  By building it myself I not only save a lot of money, but I have a system that I know intimately, and can optimize and repair with ease.  It’s assembled with all appropriate provisions for safety, to a high level of craftsmanship.

This has been a very interesting project for me, and it’s very satisfying to now be able to operate my ham station through a solar power system that I designed and installed myself. Every component of my station is selected to operate directly from 12VDC – and I don’t need to buy any 120-volt power supplies. I don’t have any antenna rotor to operate yet, though I am considering that.  For that I might need to install a small 24-volt inverter under the desk that I could switch on when the beam needs to be turned.

There are a lot more details pertaining to how I solved many of the challenges of how to install the complete system at the most reasonable cost, and how to be grid-independent.  I would be happy to exchange emails, or on-air contact, with anyone else contemplating a home solar system.
« Last Edit: March 24, 2013, 03:43:28 PM by KF7Z » Logged
K5LXP
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« Reply #1 on: March 25, 2013, 07:33:59 AM »

Thanks for the detailed description of your setup.  You clearly went through a lot of investigation, work and expense to get this far.  Even if you decide to change it up you have a lot of the building blocks already.

Some utilities won't let you grid tie with a battery backup.  I guess they don't want you to get the energy credit *and* be energy independent at the same time.

You didn't mention if you have a genset or not.  I think this is a pretty important feature as it allows flexibility to operate large loads when needed, allows you to have a smaller battery bank and gives you an option to easily ride through an extended outage or series of overcast days.  Doesn't have to be a big one, say 5-6kW with appropriate transfer switch.  If you have propane at your QTH you have a ready source of stored fuel for it.


Mark K5LXP
Albuquerque, NM


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KF7Z
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« Reply #2 on: March 25, 2013, 08:42:43 AM »

Hi Mark,

Thanks for the comments. Yes, in the interest of some brevity, I didn't mention some parts of the integrated system.  I have two generator sets, both diesel powered because we have all diesel powered vehicles and tractors.  One generator is a very nice modern 10kW Perkins 3-cylinder.  For further backup, we also have a smaller, old Lister ST1 that I rebuilt.  It will put out about 4 kW.  They are intended for potential use during extended periods without sun, or for occasional large AC loads.  Also, because of the high cost, in terms of reduced life span, of allowing batteries to deep discharge, it seems important to have some back up means for recharging.  Wind power would be nice, but we don't have enough reliable wind.

We keep a fair bit of winterized diesel on hand. 

I doubt if it will ever be economical to go back and grid tie my system - but things can always change.
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K5LXP
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« Reply #3 on: March 26, 2013, 12:20:45 PM »

Grid tie only makes economic sense when there's a fat subsidy to go with it, and then only barely.  The solar outfits here are in cahoots with banks to create these turnkey grid tie systems and all you do is write a check to the bank once a month for incrementally less than what you'd normally send to the local utility.  I don't think they take into account lost opportunity and it's a good bet there's upkeep/insurance/repairs they're not factoring in.  It seems the only goal is to see the meter turn backwards and not look at all the costs and effort involved.  The cheapest kWh you'll ever buy is direct from the utility I don't care how cheap solar panels ever get.

FB on your gensets, you're covered there.  I had a colleague at work who lived off the grid for years on a basic solar system plus a modest genset to periodically run the wash machine and other heavy loads.  Here the climate is pretty temperate so swamp coolers suffice for A/C and he heated with wood.  Not sure how he ever got his XYL to buy into that lifestyle but I you gotta respect the fact he persevered and made it work.

I have another buddy who bought a grid tie system but gets around the battery bank issue by charging his EV off of his inverter.  Technically he can say is EV is solar powered.  So while not a solar-battery setup he's got 30kWh or so of DC he can use to light lights and keep the fridge running when the hurricanes come through (he's in Florida).  I've used my EV for power outages here a few times as well.  One year I ran a 2A Field Day setup entirely off the EV which was a fun exercise.  No genset noise to listen to all night long.

In keeping with the Emcomm theme here I don't have any solar power at the house, just a large capacity UPS that will run the station from hours to days depending on what I've got turned on.  No issues then with having AC only equipment as that's what the UPS puts out, so the antenna rotator, desktop PC, wall warts, etc all operate per usual.  With few real Emcomm events here in New Mexico, this degree of backup has proven sufficient.  My backup genset is a large  inverter connected to a running vehicle - not the most efficient way to go but convenient and pretty effective.

Looks like for you the fun part is just beginning - data gathering, trend watching, tests and tweaks. 


Mark K5LXP
Albuquerque, NM
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W8JX
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« Reply #4 on: March 26, 2013, 12:33:12 PM »

If I was going to play with renewable energy, it would be with wind power because it is more cost effective and meter back potential. Granted there are days with no wind but solar does not work at night and poorly during cloudy or stormy days when wind is usually present. Solar is still pretty pricey.
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K5LXP
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« Reply #5 on: March 27, 2013, 06:38:31 AM »

To get to useful wind for power you have to be pretty high up.  If you think getting a ham tower up in a city is tough, you should see what the alternative energy guys have to go through.  I had a guy in my neighborhood that wanted to put up a modest windmill and stopped by to talk to me about tower permitting.  He had to apply for a variance and was shot down by all his neighbors, "NIMBY".   A few kW of solar panels on the roof are low profile, make no noise and work most of the time.  It takes a sizeable windmill on a beefy tower to generate that same kind of power and something that size will definitely be visible and audible.

Of course it'd be great to have both - they tend to complement each other based on the weather.  Great idea if you have the space and money.  Knowing several people that are 100% off the grid and how they go about it, wind is pretty low on the list of practical options.


Mark K5LXP
Albuquerque, NM
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KF7GFL
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« Reply #6 on: March 27, 2013, 10:32:09 AM »

Regarding wind vs. solar, I bought my son a small solar kit for Christmas a few years ago. It came with a solar cell (about 3 inches by 5 inches), a few wires, and an electric motor. The idea is to use the solar cell to power the motor which is then used as a fan. It was an eye-opener to me to see how fast that motor runs with such a small solar cell. Trying to create the same amount of energy in reverse (having wind turn the electric motor) would require a lot of gearing and a huge fan blade.

As a sailor, I read a lot of stories about people harnessing the wind to charge batteries on their sailboats as places to mount solar panels can be tough to find on such a relatively small vessel. One thing you have to worry about with wind is the speed. Once the wind starts blowing really hard, you have to have a mechanism to slow fan blade down or you will burn out the generator. Some sailors end up lashing the fan blade so it won't move during such wind storms, which generates no electricity. There are also quite a few moving parts that require constant attention. Personally, I like the idea of putting something on my roof and never having to worry about it and so that gives solar the advantage in my book. However, both could be a part of any off-the-grid strategy as solar doesn't work at night or on rainy days.

I hope this helps as I once believed wind was a better source of electricity than solar.

Matt - KF7GFL
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W8JX
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« Reply #7 on: March 27, 2013, 03:13:01 PM »

Where you live is a big factor too. If you live in north where winter days are short and often cloudy and snow can cover solar panels on roof, it can be a poor investment while wind power can still be viable. Also as far as tower size to make 5kw to 10kw so does not take a lot of tower nor a massive wind load. If you live is a rural area you can go a lot bigger and pay for it metering back.
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K5LXP
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« Reply #8 on: April 01, 2013, 03:06:03 PM »


as far as tower size to make 5kw to 10kw so does not take a lot of tower nor a massive wind load.

I guess it depends on your definition of "massive" but it's a good bet you're not going to hold up a 5kW turbine 30 feet above the nearest obstruction with Rohn 25.


Aeolos Wind Turbine 5kw Specification

Rated Power    5 kw
...
Rotor Blade Diameter    6.4 m (21 ft)
...
Turbine Weight    380 kg (836 lbs)


Mark K5LXP
Albuquerque, NM
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W8JX
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« Reply #9 on: April 01, 2013, 03:41:35 PM »


I guess it depends on your definition of "massive" but it's a good bet you're not going to hold up a 5kW turbine 30 feet above the nearest obstruction with Rohn 25.


Aeolos Wind Turbine 5kw Specification

Rated Power    5 kw
...
Rotor Blade Diameter    6.4 m (21 ft)
...
Turbine Weight    380 kg (836 lbs)


Mark K5LXP
Albuquerque, NM

Most come with their own pedestal and besides I would never consider Rohn 25 here. 
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LA9XSA
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« Reply #10 on: April 06, 2013, 06:30:29 AM »

Actually solar panels can be a viable option for summer houses and cabins in the high north, like in Alaska or northern Norway, since there's almost 24 hours of sunlight. It's not economical if grid power is available though, since we don't have net metering and electricity prices are the lowest in summer anyway.

Here's a neat idea that I've seen Bob WB4APR use in his grid-tied solar system: His system of panels is wired to deliver about 300 volts DC to the grid-tie inverter. If grid power goes out, the grid-tie inverter stops delivering AC power, but the DC from the panels is still available. Since many consumer switch mode power supplies will work on DC input power, and are made for both 110V and 230V rms systems, he has wired a couple of DC outlets so that he can plug his electronics in and use them straight from solar if the grid goes out. Of course he won't be running any linear power supplies or AC motors without an inverter, but it's something people planning a grid-tie system might consider.
« Last Edit: April 06, 2013, 07:12:18 AM by LA9XSA » Logged
KF7Z
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« Reply #11 on: April 08, 2013, 12:54:18 PM »

Actually solar panels can be a viable option for summer houses and cabins in the high north, like in Alaska or northern Norway, since there's almost 24 hours of sunlight. It's not economical if grid power is available though, since we don't have net metering and electricity prices are the lowest in summer anyway.

Do you typically use a tracking mount in such locations?

Those 24 hours of sunlight sound good, but it seems that the very low sun angle, and very large changes of azimuth angle during those 24 hours would necessitate a tracking mount to take advantage.  Tracking mounts are expensive and complicated, and add a lot of complexity. 

Before settling on my roof mounted option, I ran a simulation comparing roof mount at my less than ideal azimuth (14 degrees west of south), and less than ideal pitch, with four increasingly complex alternatives:
1.  Roof mount that would allow change of tilt angle through the seasons.
2.  Ground mount at fixed best-year-around tilt angle, at ideal azimuth (due south).
3.  Ground mount that would allow change of tilt angle through the seasons.
4.  Ground mount with both one and two axis tracking.

The simulation program is free here:  http://www.builditsolar.com/Tools/RadOnCol/radoncol.htm
The program is adequate, but does not easily handle the simulation of tracking mounts.
That required some approximations and fussing to estimate.

In my case, I ended up with the very certain conclusion that I was best off installing panels on my roof at the default azimuth angle, and my 2:1 roof pitch.  It was least costly to overcome the reduced efficiency by just installing extra panels.  Keeping the panels on one plane, parallel with the roof, also has the advantage of snow sliding off the panels much easier.  Ground mount would be nice for servicing, but introduces some other problems and costs.
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LA9XSA
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« Reply #12 on: April 09, 2013, 05:36:16 AM »

Do you typically use a tracking mount in such locations?
No, due to cost and weather. The panel is typically mounted on a south facing wall or on a roof mount that points almost vertically to the south. This means that the system produces less total power through the year, but is optimized for producing as much power as possible in the Easter holiday and the autumn hunting season. Since the summers are so bright, you won't need much lighting in the summer anyway, so all the power can be used for TV and radio, and perhaps refrigeration. Refrigeration is not needed in winter, since it's freezing outside anyway.
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