modest PV system for a renter

nature.boy · August 2014

Greetings to all,

I've had emergency preparedness in mind for a while; I see how people have become so dependent upon electricity and/or gasoline. (Not many people could so much as drill a hole in a piece of wood without firing up a generator if the grid should fail, right?) This region is due for a large earthquake, and I'd like to be better-prepared if the electrical grid should be unavailable for days or weeks. I'm renting a small house, and I work from home. I have a workshop in an attached garage.

I've been thinking about a small PV system. I analyzed my electric usage, and I estimated what I'd need to run a laptop computer for four hours a day, and my workshop for four hours a day, plus a few lights, fans, radios, accessories, and such. I left out luxuries such as the refrigerator, the air conditioner, and the washing machine. According to my figures, I could get by with 100 W or less at any given time. My requirements, according to my rough calculations, would be about 200 W of solar panels and 50 Ah @ 12 V of batteries. This seems affordable. Given that a battery pack shouldn't be added onto later, I'm thinking about buying twice as much battery capacity; I could always add more solar panels later.

So my question is, can I install such a modest system in my rented house on a "temporary" basis, without tying into the breaker box, and do so reasonably safely? I'm thinking I'd put the panels on the roof if the landlord consents, or in the back yard if not. The batteries, charge controller, and inverter would go in the attached garage/workshop. Under normal circumstances I'd plug one or two devices into the inverter (the refrigerator perhaps). If the grid failed I'd run heavy-duty extension cords from the inverter to the living room and the office. I know the PV system would need to be grounded to the house's safety ground no matter what. (The house was built in the fifties, and the safety ground seems to be the cold-water pipes.)

Does this seem to be a reasonable plan? I'd rather invest in a solar system than a generator, because a solar system would keep working no matter how long the grid goes down.

ILFE · August 2014

Re: modest PV system for a renter

Hi, and welcome to the site.

I am renting a home in Cambodia. We have power cuts here about once per week, usually from about .5 to 3 hours. I wanted something to keep my laptop, external monitor and other hardware running during that time, or any other power cuts that may start here at any given time. (In SE Asia, you never know what is going to happen. So, it's best to always be prepared for the worst.)

Anyway, I recently purchased 2 - 135 watts panels, had a pole mount built and installed, and a Midnite Kid controller and 120AH battery put in the house under a stairwell. (The battery is flooded lead acid. But, venting isn't a problem here, because all windows are left open 24 hours per day.)

The pole mount is easy to cut, or even dig up, if I wanted to take it with me at the time I choose to leave here. Pull four anchor screws from the concrete wall to remove the controller, pick up the battery off the floor - and away we go.

nature.boy · August 2014

Re: modest PV system for a renter

Hi Paul, and thanks for your reply! Are you happy with your PV system?

- Rob

BB. · August 2014

Re: modest PV system for a renter

You really need to measure and define your loads using a Kill-a-Watt type meter (for AC loads). And then define what is a "critical load".

For example, a computer may not be worth much past 12 hours of power failure when the batteries and propane generators that run the cell towers and cable system run out of energy/fuel. If you still have a dial up account, you can probably go longer (assuming the phone company lines are still there and have not been pulled for copper scrap).

Anyway--think of it more as a camping trip and what you will need for that. There is the old saying about how quickly you will die:

3 minutes without air
3 hours without shelter (assuming you life in a harsh climate)
3 days without water
3 weeks without food

Certainly, it can be very nice to have some source of backup electricity... But very few people have any idea of how much electricity they use and how much they can store/generate.

We measure the loads (and generation) in Watt*Hours (I.e., 100 watts * 8 hours of use = 800 Watt*Hours = 0.8 kWatt Hours). Or Amps*Hours at what voltage (10 amps * 8 hours * 12 volts = 960 Watt*Hours or 80 Amp*Hours on a 12 volt battery bank).

To give you a rough idea of power usage:

1,000 Watt*Hours per day (1 kWH per day): Cabin Lights, Laptop, Radio, charging cell phone, etc.
3,300 WH per day: Add a refrigerator, efficient well pump, clothes washer (a very efficient small home/cabin, near normal life)
10,000 WH per day: Add central heat, more power usage, very efficient city home
33,000 WH per day: Average North American Home. Some A/C, not very energy efficient, some A/C, lots of power
100,000 WH per day: Home in Texas/Florida/etc., using lots of A/C, electric heat, etc.

Even a 3.3 kWH per day solar system is not cheap--Probably $5,000 to $10,000 worth of parts and labor.

To give you some sizing--Say 24 volt battery bank, 2 days of storage, and 50% maximum discharge, 120 VAC power, and 4 hours minimum hours of sun per day (maybe ~9 months a year minimum):

3,300 WH per day * 1/0.85 inverter eff * 1/24 volts * 2 days storage * 1/0.50 maximum discharge = 647 AH @ 24 volt battery bank
3,300 WH per day * 1/0.52 end to end system eff * 1/4 hours of sun = 1,587 Watt Array minimum

Add a ~1.5 to 2 kWatt AC inverter, minimum 45 amp MPPT charge controller, wiring+breaker/fuses, racking for panels, etc.

To give you an idea of what a smaller system can look like:

BB. wrote: »

Add this link to our Solar Beginner Post:

Emergency Power

Basically a very long thread that starts from the beginning with a few vague requirements through design and assembly for a "portable" solar RE off-grid power box.

And here is another example by Mike90045 called the Solar Monolith:

Update pictures/information here.

If you are looking for short term backup power (say less than 2 weeks), a smaller genset (Honda eu1000i or eu2000i -- 900 watt or 1,600 watt generator) plus stored fuel (gasoline, propane, natural gas, etc.) will usually give you a more practical backup (less upfront costs and long term maintenance--and can run your refrigerator for a couple of weeks on 10-20 gallons of gasoline).

-Bill

ILFE · August 2014

Re: modest PV system for a renter

nature.boy wrote: »

Hi Paul, and thanks for your reply! Are you happy with your PV system?

Yeah, I'm happy with it. I have only had it up and running a few days. But, so far, no worries. The landlord was very easy to work with, which is not surprising in SE Asia. They don't mind you making even major changes to a home, typically. I gave him my word that I would repair the holes (that he drilled by the way) and repaint the entire room the system is mounted in, prior to leaving. He had no problem with me choosing the location for the pole mount. Honestly, I could have moved it a bit closer to the house (not the one behind it in the photo), because the array will only tilt a maximum of ~50 degrees throughout the year. (I took the photo of the pole mounted array from the front porch of the home I rent.)

Of course, the difference between Cambodia and the US is, here, if you agree to something, you will do it - and they expect you to. In the US, and considering I do not know you or your landlord, you probably should have some sort of addendum to your lease agreement, if you are going through with this. Make sure it is something both you and your landlord sign. So that, when you leave, it is not expected to remain part of the property.

Once something is attached to a home in the state of Georgia, where I am from, it becomes part of that home. So, do check on your laws there. Probably a good reason to use a pole mount. Worst case, you can walk away from the pole when you leave, taking your panels with you.

Typically, I don't use the system but one day per week. I am pondering the idea of buying one or two more panels, adding a second 120AH battery (that I already have), and running the electronics off it 24 / 7 / 365. Here, I pay about $1.30 per watt, for panels. I have $410 USD, all in, for the panels and the pole, installed. (One more panel would actually max out the controller. But, I learned this controller can be overloaded with PV with it not being affected.)

nature.boy · August 2014

Re: modest PV system for a renter

ILFE wrote: »

Typically, I don't use the system but one day per week. I am pondering the idea of buying one or two more panels, adding a second 120AH battery (that I already have), and running the electronics off it 24 / 7 / 365. Here, I pay about $1.30 per watt, for panels. I have $410 USD, all in, for the panels and the pole, installed. (One more panel would actually max out the controller. But, I learned this controller can be overloaded with PV with it not being affected.)

Hi Paul, I like your pole mount! Do you just run an extension cord from your inverter when you want to use the power? By the way, I sent you a private message, so please check your inbox.

- Rob

nature.boy · August 2014

Re: modest PV system for a renter

BB. wrote: »

You really need to measure and define your loads using a Kill-a-Watt type meter (for AC loads). And then define what is a "critical load".

Hi Bill,

First, wow! Thank you very much for the detailed response, the sage advice, and the links to other sage advice! I'm impressed by this particular online community.

I have a Kill-A-Watt, and I've done a fair amount of homework already. In case it helps someone else I'll share a bit of it:

Device                                                W  hours/day  W&#8901;h
---------------------------------------------------  --  ---------  ---
DSL router                                            7   3          21
netbook                                              14   2          28
desktop computer                                     36   2          72
monitor                                              22   2          44
laser printer, 25 sheets printed over 1 hr           20*  1          20
soldering iron                                       20*  4          80
soldering fan                                        15*  4          60
LED soldering lamps, qty 2                           10   4          40
pedestal fan, on medium                              37   4         148
reading lamps, qty 2, CFL bulbs                      30   4         120
transistor radio                                      1   8           8
ham radio HT, 20% duty                                3   8          24
ham radio 2m mobile rig, 50 W out, 50% duty          42   1          42
mobile phone charger (for 3 phones)                   4   3          12
small battery chargers (MP3 players, NiMH AAs, etc)  10   4          40
                                                                    ---
*: guess                                                            759

The wattages with (*) are guesses; every other wattage is either measured with the Kill-A-Watt or taken from manufacturer's specifications.

So I came up with 759 Wh daily usage in my scenario. Other assumptions: 77% efficiency for the combination of charger, battery, and inverter; twelve hours a day of sunlight; partly-cloudy skies resulting in the panels only putting out 60% of their rated output; maximum battery discharge 50%. Then I really geeked out, and I simulated the hour-by-hour production of the panels assuming a sinusoidal pattern, and I also simulated my power usage hour-by-hour, and from that data I was able to estimate how much battery capacity I'd need. So I have good confidence that my numbers are at least in the ballpark, given my scenario. The likelyhood of my scenario is, of course, open to debate

BB. wrote: »

If you are looking for short term backup power (say less than 2 weeks), a smaller genset (Honda eu1000i or eu2000i -- 900 watt or 1,600 watt generator) plus stored fuel (gasoline, propane, natural gas, etc.) will usually give you a more practical backup (less upfront costs and long term maintenance--and can run your refrigerator for a couple of weeks on 10-20 gallons of gasoline).

I've been weighing the pros-and-cons of a PV system versus a generator.

PV system pros:
* will partly pay for itself; at 15¢/kWh, will generate some $400 worth of power in 10 years
* clean, quiet
* better for the environment? (must weigh impact of solar panel fabrication)
* in a long-term emergency, would keep working day after day

PV system cons:
* expensive
* fragile
* not very portable

generator pros:
* cheaper, more powerful than PV
* more portable than PV
* useful for camping and such

generator cons:
* more greenhouse gases
* more easily stolen
* gasoline storage issues

In particular I'm thinking about the gasoline storage issues. I'd want at least 20 gallons (75 liters) of gasoline in reserve, and the only place I'd be able to keep it would be a shed in a tiny back yard, close to other houses. If that shed caught fire, watch out! I drive an economy car with an 11-gallon tank, so I couldn't count on that as my storage location. Also, if I had 20 gallons of gasoline stored then I'd be perpetually filling fuel containers and pouring the old fuel into my car's fuel tank. I could mitigate those issues somewhat with a fuel drum and a pump, but it's illegal to store gasoline in anything other than a portable container here, and I can see why: a drum could leak and/or vent a lot.

I have plenty of issues to sort out!

- Rob

ILFE · August 2014

Re: modest PV system for a renter

nature.boy wrote: »

Hi Paul, I like your pole mount!

Thanks! For $60 USD, I don't think I can complain, although - it wasn't exactly what I wanted. (You get accustomed to this, though, after living abroad for a long time.)

nature.boy wrote: »

Do you just run an extension cord from your inverter when you want to use the power?

Everything I wish to run when mains power has been cut, I keep plugged in to one power strip. When the power fails, I just unplug the strip from the wall and plug it into the inverter. The inverter is always wired to the battery. (I need to sort out an automatic switch, so I don't have to wait for the network to reconnect when the mains fail. But, it isn't too much of an inconvenience.)

nature.boy wrote: »

By the way, I sent you a private message, so please check your inbox.

Got it. Replied. Hope you are sitting down with some popcorn to read it.

Plowman · August 2014

Re: modest PV system for a renter

nature.boy wrote: »

So I came up with 759 Wh daily usage in my scenario. Other assumptions: 77% efficiency for the combination of charger, battery, and inverter; twelve hours a day of sunlight; partly-cloudy skies resulting in the panels only putting out 60% of their rated output; maximum battery discharge 50%.

Annual average sun hours per day in Medford is 4.51. Winter average is 2.02. In my part of Oregon it's 1.9.

Using the calculations I've done for my little system, for your 759 Wh/day, you'd need roughly 770W of panels + ~250 ah of batteries (if only run down to 75%). This is for a system sized for winters in northwestern Oregon.

I wouldn't count on hour-by-hour assumptions for running your loads "directly" off solar during the day. Weather varies too much for that. If most of your loads are during the day, I'd imagine you could reduce my solar and battery estimates somewhat.

Still, I don't see how you can power these loads with 200W of panel and 50 ah of battery.

BB. · August 2014

Re: modest PV system for a renter

If you want to "play" with solar--Go for it.

If you want it to "pay for itself"--Sometimes hard to make that happen.

Either way, do several paper designs to check the costs and other issues between solar, genset, etc...

A small genset like the Honda eu2000i will generate around 4 hours @ 1,600 watt load or ~9+ hours on a 400 Watt load per ~1.1 gallons of gasoline.

Costco is currently selling a Champion 7 kWatt gasoline/propane generator for ~$850:

http://www.costco.com/Champion-7000W-Running--9000W-Peak-DUAL-FUEL-Generator-wElectric-Start.product.100112008.html

Champion appears to be a reasonably reliable and rugged genset for the price (based on earlier models talked about here). And propane is a really nice fuel for long term storage... But look at the fuel usage:

Generator will run 8 hours on a full tank (6.1 gallons) of gasoline or 5 hours runtime off a 20#/5 Gallon Propane-LP gas tank (propane tank not provided) at 50% load.

3.5 kWatt output and 8h/6.1 gal = 1.3 hours per gallon of gasoline and probably ~1 hour per gallon of propane (again, at 1/2 rated power)

Vs the Honda which will give you around 4-9+ hours per gallon of gasoline (at 1.6 to 0.4 kWatt output power).

For me--At least during emergency usage--using as little power as possible is the goal... Less noise, fuel usage, less cost tied up in equipment/batteries/etc. Trying to find many gallons of gasoline per day (using close to 4-12 gallons of gasoline with the 7 kWatt genset) can be a huge pain if there are regional power outages (no power for gas stations, depot delivery issues, etc.)... At least with something running ~4-9+ hours per gallon--10 gallons will last you some time (I use a gas stabilizer and recycle the fuel into the car once a year--Some folks here say I should really be doing it 2x per year--small generators have small jets that are easy to plug up).

You did a nice job measuring your loads... But many of them are not going to be running every day--So, your daily "emergency/backup" AC power may be much less (give you some more head room for power in winter, or on the occasional days when you need a lot of power).

Say you are happy with a 1 kWH per day system and minimum of 4 hours of sun per day (usually true for ~9 months a year).

You start sizing the system. Stick with 12 volts (sounds like you have some 12 VDC native loads possible):

1,000 WH per day * 1/12 volts * 1/0.85 inverter eff * 2 days of backup power * 1/0.50 maximum discharge = 392 AH @ 12 volts

You should charge around 5% to 13% rate of charge:

392 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 369 Watt array minimum
392 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 738 Watt array nominal
392 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 960 Watt "cost effective" maximum

Using PV Watts for Medford OR, fixed array, tilted to latitude:

Month Solar Radiation
(kWh/m 2/day)
1 2.33
2 3.43
3 4.99
4 5.53
5 6.35
6 6.42
7 7.25
8 7.14
9 6.34
10 4.91
11 2.44
12 1.92
Year 4.93

Not a lot of sun in the winter there---Toss the bottom three months and get 3.43 Hours of average sun for February:

1,000 WH * 1/0.52 solar 120 VAC system efficiency * 1/3.43 hours of sun = 560 Watt array "break even" for February

If this is a rarely used system, or weekend use (camping/weekend cabin, etc.)---You could get away with 5% rate of charge (charge during the day, use some power at night). If you are going to use power daily (full time cabin, etc.), then you probably would be better at 10-13%+ array sizing...

4x 6 volt ~200 AH golf cart batteries setup in 2 in series/2 parallel strings would be a nice start. Something between a 300 watt and 1,000 Watt TSW (recommended) inverter would be nice... If you can keep your peak loads low--The MorningStar 300 Watt TSW 12 volt AC inverter is pretty nice for the job--and includes remote on/off and "search mode" (low power standby until >6 watts of 120 VAC power is needed.

-Bill

nature.boy · August 2014

Re: modest PV system for a renter

BB and Plowman, thank you so much for your expert advice. I'm awed by how much expert advice is available for free on online forums like this one. (Assuming of course that the questions are asked respectfully and not lazily, and that the person asking has done his or her homework.)

I'm especially grateful for your having looked over my calculations. I assumed that a derating factor of 60% for the solar panels would yield a system design that would be good enough maybe nine months of the year. Your real-world experience must tell you two that I was way overestimating how much power I'd get from the solar panels on cloudy days.

As a side question, what do you think would be a reasonable estimate of solar panel output on a November day that is 100% overcast with five hours of drizzling rain? 20% of rated power?

By the way, I wasn't trying to take my hour-by-hour usage estimates too seriously, I was just trying to see how much less battery I'd need if I reasonably tailored my power usage to match the output of the solar panels as much as possible. It made quite a difference: according to my calculations, if I used all the power at night then I'd need 160 Ah, but if I used the power in a reasonable way, powering the biggest loads when the panels are generating the most, then I'd need only 47 Ah. (Assuming 12 V batteries.) That's 70% less!

So I've come to some conclusions:

* My numbers are somewhat reasonable for the sunny months of the year, June through October, and probably good enough for April and May also. (Our weather in Southwestern Oregon is more like Northern California's than Portland's or Seattle's; cloudy days in the summer are almost unheard-of.)
* My numbers would result in an underdesigned system because of real-world variations in load usage and power generated, etc.
* The system I designed would be minimally useful in the rainy season.
* It would be much cheaper to include a generator in my plans than to design the PV system to meet the requirements year-round.

I'm still pondering the generator question, because of the fuel storage issue. I like the Honda generators for being very fuel-efficient, but I'm also considering a dual-fuel generator (thanks for the idea Bill), since propane stores for years. If I were a homeowner I could install a 120-gallon or 250-gallon propane tank, which would solve the problem nicely. But being a renter I'll need to be more modest in the short run, and think about five-gallon containers of propane or gasoline. If I just used the generator to recharge the batteries on cloudy days, then I could make 20 gallons of fuel last a long time.

Thanks again folks!
- Rob

BB. · August 2014

Re: modest PV system for a renter

nature.boy wrote: »

BB and Plowman, thank you so much for your expert advice. I'm awed by how much expert advice is available for free on online forums like this one. (Assuming of course that the questions are asked respectfully and not lazily, and that the person asking has done his or her homework.)

Our pleasure... The sticking point with forums are arguments. We all started out at ground zero with zero knowledge until our parents/teachers/mentors helped us with the answers to our initially "dumb" questions.

The arguments are sometimes difficult to differentiate with respect to discussions. No body language or voice inflections here.

Anyway, the reason I like to use the equations is so that "you" can see all of the assumptions I have made. There are multiple areas for deratings (solar panels+charge controllers~77% efficiency, flooded cell battery charging ~80%, AC inverter ~85%, hours of sun, tilt of array, seasonal usage, etc.)... You are the only one that has enough knowledge of your needs/location where you can tweak our assumptions to better meet your needs.

I'm especially grateful for your having looked over my calculations. I assumed that a derating factor of 60% for the solar panels would yield a system design that would be good enough maybe nine months of the year. Your real-world experience must tell you two that I was way overestimating how much power I'd get from the solar panels on cloudy days.

The 52% derating is from the Solar panel "marketing number" through the charge controller, battery bank, AC inverter, and to your AC loads for a "typical" system with a "typical" person running it. For example, if you use DC only power, you save the 85% for the inverter. If you use AGM batteries, you can get 90+% efficiency, higher elevation will give you a few percent more solar panel output, etc...

However--At this point, solar panels are relatively cheap--so adding more panels is usually a good way to make for a robust and reliable system with relatively long battery life. Trying to get any better than +/-10% between estimates and "real life"--Is hard to justify. Year to year weather can vary your hour of sun that much, and 2 weeks of bad weather--Nothing but a generator or burning candles will help that.

As a side question, what do you think would be a reasonable estimate of solar panel output on a November day that is 100% overcast with five hours of drizzling rain? 20% of rated power?

It all depends... The PV Watt numbers assume a "20 year average" of November conditions--So weather is taken into account. However, a dark/rainy day, my GT system will only produce 5% of its rated energy for the full day.... Any light overcast, and you can be looking at 50% of sunny weather power. Solar panels need full sun--Anything that limits that sun, and the output tanks.

By the way, I wasn't trying to take my hour-by-hour usage estimates too seriously, I was just trying to see how much less battery I'd need if I reasonably tailored my power usage to match the output of the solar panels as much as possible. It made quite a difference: according to my calculations, if I used all the power at night then I'd need 160 Ah, but if I used the power in a reasonable way, powering the biggest loads when the panels are generating the most, then I'd need only 47 Ah. (Assuming 12 V batteries.) That's 70% less!

We spend much of our time having forest vs trees discussions here. We try at least once in every thread of this type to mention the "big picture" stuff to make sure that people do not end up with a 4x larger system than they really need.

Obviously, we are not there and talking to you directly--So we do sometimes sound a bit repetitive. Dangers of the forum.

So I've come to some conclusions:

* My numbers are reasonable for the sunny months of the year, June through October, and probably good enough for April and May also. (Our weather in Southwestern Oregon is more like Northern California's than Portland's or Seattle's; cloudy days in the summer are almost unheard-of.)
* The system I designed would be minimally useful in the rainy season.
* It would be much cheaper to include a generator in my plans than to design the PV system to meet the requirements year-round.

Yep. Unless you can justify a 3x larger solar array for use during the dark months of winter. Usually, the generator is a better solution. Of course, there is always the ability to modify your power usage and cut back to the minimum during the week or so of bad weather. But using a generator to bump the battery bank from 50% to 80% state of charge is relatively fuel efficient and worth a gallon or two a day (if the power is needed).

I'm still pondering the generator question, because of the fuel storage issue. I like the Honda generators for being very fuel-efficient, but I'm also considering a dual-fuel generator (thanks for the idea Bill), since propane stores for years. If I were a homeowner I could install a 120-gallon or 250-gallon propane tank, which would solve the problem nicely. But being a renter I'll need to be more modest in the short run, and think about five-gallon containers of propane or gasoline. If I just used the generator to recharge the batteries on cloudy days, then I could make 20 gallons of fuel last a long time.

There are a few kits and even vendors that will modify a Honda eu2000i (or other genset) to use propane--A few people here (I think) have done that and are very happy with the results.

Propane's big downside can be problems running in cold/subfreezing weather. Small tanks can ice up (vaporizing fuel) pretty easily. And cold weather (sub zero F) starting can be an issue too.

https://www.google.com/search?q=site%3Aforum.solar-electric.com+honda+eu2000i+propane+conversion

-Bill

nature.boy · August 2014

Re: modest PV system for a renter

Hi Bill,

Right right, your comments about forums and interacting via text over the internet are spot-on. Personally I've gotten lots of useful nuggets from your off-the-cuff comments in other threads, so please feel free to make "big-picture" comments and repeat yourself as often as you like; lots of people will benefit.

By the way, you were right about my having 12 V native loads: I'm a ham radio operator, and all my ham gear can run on 12 VDC (except the computer). Ham radio is a big part of my scenario, because with just 5 to 100 watts output from my HF radio, I can talk to other ham operators across North America fairly easily. Similarly, with VHF I can keep in touch with the locals. Better still, I can send and receive small emails if I also have the use of my computer. I imagine that the ability to relay emergency and health-and-welfare messages by the hundreds would be incredibly useful in a major disaster. (I'm a part of the local Amateur Radio Emergency Service group, so I'm coordinating with others and not trying to save the world solo.)

I didn't know that there are aftermarket kits to convert Honda generators to tri-fuel (gasoline, propane, or natural gas). Central Marine Diesel even sells new Honda eu2000i generators with the tri-fuel kit already installed. That's the best generator option for me so far, I think.

So your PV system generates only 5% of rated output on a really cloudy, rainy day? Wow.

I can't pay for the entire system at once, so I've decided this is a reasonable order to put a system together:
1) Batteries, insulated plywood battery box in the garage vented to the outdoors, a good AC charger, and a fat DC cable to connect to my ham radio: allows me to run the radio, charge my phone, etc. for a few days
2) Inverter: allows me to power other loads (and operate my business)
3) Generator: allows me to survive longer power outages
4) Solar panels, charge controller: daily electricity no matter what (unless things get really bad, which is not my focus)

A few days ago I just had a vague notion, and now I have much more concrete plans. Thank you again!

Best regards,
- Rob

BB. · August 2014

Re: modest PV system for a renter

Your 4 steps to solar. ... that is what I would recommend.

And another big picture warning. 12 volt HAM gear (usually the higher power he gear is rated at 13.8 volts. And most car 12 volt devices are designed for around 12.0 to 14.4 volts or so.

A true off grid deep cycle battery bank+loads can expect to see from 10.5 to 15 or even 16 volts. There is not a lot of 12 gear that will happily take that wide of voltage range.

You could install a buck-boost 12 to 13.8 volt power converter. Or just get a good quality tsw ac inverter and run everything from 120 vacation and just use a transfer switch to run from utility, generator, or inverter.

There are also nice inverter chargers with internal ac transfer switches so your solar power system becomes a ups.

-Bill

Plowman · August 2014

Re: modest PV system for a renter

nature.boy wrote: »

I can't pay for the entire system at once, so I've decided this is a reasonable order to put a system together:
1) Batteries, insulated plywood battery box in the garage vented to the outdoors, a good AC charger, and a fat DC cable to connect to my ham radio: allows me to run the radio, charge my phone, etc. for a few days
2) Inverter: allows me to power other loads (and operate my business)
3) Generator: allows me to survive longer power outages
4) Solar panels, charge controller: daily electricity no matter what (unless things get really bad, which is not my focus)

That's the order in which I cobbled my off-grid system together. But I did #1-3 all at once. You kind of have to unless you can charge the batts from grid power. You also need a quality multi-stage battery charger, assuming you don't have an inverter with built-in charging capability.

I lived all of last winter using a generator to charge a deep cycle battery system. It was expensive and bothersome, not to mention polluting and noisy. It motivated me to really focus on expanding and improving my little solar electric system. It's been working great thus far.

I'll still have the generator to get me through really cloudy spells during the winter, but my goal is to reduce its use to as little as possible, preferably zero when it comes to my general household electricity.

nature.boy · August 2014

Re: modest PV system for a renter

BB. wrote: »

And another big picture warning. 12 volt HAM gear (usually the higher power he gear is rated at 13.8 volts. And most car 12 volt devices are designed for around 12.0 to 14.4 volts or so.

A true off grid deep cycle battery bank+loads can expect to see from 10.5 to 15 or even 16 volts. There is not a lot of 12 gear that will happily take that wide of voltage range.

You could install a buck-boost 12 to 13.8 volt power converter. Or just get a good quality tsw ac inverter and run everything from 120 vacation and just use a transfer switch to run from utility, generator, or inverter.

Ah, another wrinkle to consider

I'll have to give that careful consideration. I have a much smaller boost/buck regulator, and its efficiency is something like 87%. Maybe a more expensive one would do better, or then again maybe it's just another factor I need to include in my calculations. But the ability to charge batteries and operate at the same time could be very valuable, so I'll try not to use a transfer switch if I can help it.

BB. wrote: »

There are also nice inverter chargers with internal ac transfer switches so your solar power system becomes a ups.

Interesting! Would you please give me an example of a model that does that, so I can research that further?

- Rob

nature.boy · August 2014

Re: modest PV system for a renter

Plowman wrote: »

I lived all of last winter using a generator to charge a deep cycle battery system. It was expensive and bothersome, not to mention polluting and noisy. It motivated me to really focus on expanding and improving my little solar electric system. It's been working great thus far.

I'll still have the generator to get me through really cloudy spells during the winter, but my goal is to reduce its use to as little as possible, preferably zero when it comes to my general household electricity.

That must be quite the challenge to live off the grid, Plowman! I hope you live somewhere spectacular that makes the extra effort worthwhile

- Rob

BB. · August 2014

Re: modest PV system for a renter

You can go with:

Manual Transfer Switch: Midnite Solar 30 Amp 240 Volt Dual AC Manual Transfer Switch
Simple Relay based AC Transfer switch: PowerMax PMTS-30 Automatic Transfer Switch

Or AC inverter/chargers that can be really sophisticated in their power management:

Magnum Energy Sine Wave Inverters & Accessories
Schneider Electric Conext SW Pure Sine Wave Inverters and Accessories

And Outback makes a GFX series--I am not sure how or where to get it--The version that does generator support very nicely may not be UL/NRTL Listed for use in the US (i.e., 230 VAC 50 Hz units, 120 VAC 60 Hz units may be special order???).

Big long thread here about Generator Support:

Demonstration of Generator Support

It is a really nice way to use a smaller AC genset (like a Honda eu2000i 1,600 Watt generator) where the Inverter/Charger only draws rated power from the generator (for pass through AC loads and battery charging from AC input)--And the inverter/charger can switch around and use battery+inverter power to support AC loads that are larger than the generator can support by itself.

-Bill

Vic · August 2014

Re: modest PV system for a renter

Hi n.b

BB Bill has covered many of the issues in trying to operate 12 V Ham HF Transceivers directly from batteries that are not being charged at the time. Most of these 100 watt radios are speced with 13.80 VDC input, and even large Flooded batteries would do well to have off-charge terminal voltages much above 12.5 V at 25 degrees C, for long, at 23-ish Amp (or greater) loads. And there is that pesky drop in the 12 VDC power cable to the radio.

Some Mobile HF radios may do better at lower DC input voltages ... perhaps.

Inverting the DC to AC and converting back to DC avoids these problems (yes, at some efficiency cost), and allows placing the radios almost anywhere, without concern for DC voltage drops when distributing the power

Furthermore, most MPPT Charge Controllers, Inverters, DC/DC Converters/Buck/Boost devices, and Inverter-Generators create (usually a lot) of RF Hash, birdies etc. Many of these devices respond well to Common-Mode and other filtering techniques. In general, for HF, the NOISE is line-conducted. There have been some testing of some of these devices published by the ARRL.

Generally, separating the antennas from the noise sources works well. For the lower frequencies -- 160 - 40 M --, substantial separation may be required.

And, a bit surprisingly to me, Charge Controller's EMI/RFI testing for FCC Class B, begins at 30.0 MHz, leaving the entire HF (and MF) spectrum untested, and quite possibly unsuppressed. MPPT CCs can have very significant emissions in the lower frequency ranges of the HF spectrum. Guess, since these devices are not connected to the AC line testing below 30 MHz is not required.

FWIW. YMMV. 73, GL, Vic

BB. · August 2014

Re: modest PV system for a renter

There are limits below 30 MHz... For FCC it is between 450 kHz and 30 MHz for conducted emissions (power, data, other cables). For CISPR it starts at 150 kHz.

http://www.cclab.com/engnotes/eng290.htm

It is just not very efficient or easy to measure low(er) frequency emissions with an antenna. Using a current transformer clamped on the I/O and Power cables is very easy.

The lowest HAM band (that I am aware of) is 160 Meter or 1.8 to 2.0 MHz... (Old Loran navigation RF band)

Not to say there is not a lot of "hash" in the 160 Meter band from our electricity based civilization.

http://k9la.us/An_Introduction_to_Operating_on_160m.pdf

-Bill

Vic · August 2014

Re: modest PV system for a renter

Hi Bill,

Well, this came up on this Forum a couple of years ago ... My take on that discussion was that, since battery-connected Charge Controllers are NOT connected to the AC line, there is nothing to measure, with the standard setup -- a receiving device connected to a LISN on the AC line ...

From the header above the Tables in the Link that you provided,

"Limits on AC Powerline Conducted Emissions"

Will look for that part of a previous Thread, wherein, boB of MidNite Engineering mentioned that battery CCs were only required to be tested from 30.00 MHz up.

Yes the lowest HF Ham band is 160 M. There Experimental bands below the BC band, where some Hams play.

FWIW, Vic

Vic · August 2014

Re: modest PV system for a renter

Here is one reference to FCC B and battery-connected CCs:

http://forum.solar-electric.com/showthread.php?16884-Help-Me-Choose-A-Charge-Controller-for-My-Somewhat-Unusual-Application/page3&highlight=fcc+class+b

YMMV, Vic

BB. · August 2014

Re: modest PV system for a renter

Yea... I guess it does read that way.

When I was doing -48 VDC telecom systems, we did measure the DC conducted noise to make sure it did not exceed specifications. Too many decades ago to remember if this was how we interpreted the FCC regulations or if it was our customer's requirement (Bell Telephone companies).

30 MHz is about 8' for the 1/4 wave length. The assumption is that to radiate below that figure, the cabinent/computer would have to have a dimension >8' for below 30 MHz.

As I recall, we usually tested with about 10' of I/O cable or rolls of cable wrapped in a figure 8. Cables generally did not radiate that much more energy even if they were longer than 10 feet, and wrapping cables in figure "8"s would cancel out the "loop antenna" currents (1/2 of the "8" would cancel out the other 1/2 of the "8").

In the end, if you need quiet power--An MPPT controller may not be the best. And if you use shielded cable and/or run it in conduit for at least 10', this will block or drain common mode current back to the metal chassis of the computer (shielding should usually be bonded at the source of the noise to the equipment chassis).

Using Ferrite Beads and filter capacitors can help reduce common mode noise too.

Differential noise on DC power lines (and high speed signals) are a different issue. DC Power will saturate most Ferrite materials at relatively low current--Something like couple of amps??? (AC current will not saturate until you get much higher current flow).

And filtering differential signals--That just kills the signals (filter out to zero amplitude).

-Bill

Vic · August 2014

Re: modest PV system for a renter

Hi Bill,

Thanks for your perspective on Emissions and reduction techniques.

Have used EMT and/or Rigid pipe on all above-ground wire/cables, here (except for battery interconnects), plus Common-Mode chokes, and a bit of Differential filtering. The only PVC conduit used is buried about 30 inches below grade. This works very, very well, and the RFI environment is quite acceptable, even at high levels of power delivered.

One of the newer CCs in use here, has a considerably higher RFI output, when it was swapped into a position which had been occupied by an older MPPT CC. The old CC was easily suppressed with CM chokes, but the new one had a much greater noise footprint at HF. This situation, still, is not a real problem for the operating style, at this location, at this time.

The absolute worse noise "generators" are Inverter Generators -- horrible HASH, but even these sources respond quite well with CM filtering, and AC cabling in EMT (when necessary).

FWIW. I used to be responsible for EMI/RFI testing/compliance for our small company, and always tried to take the conservative approach to RFI suppression.
Thanks again, Bill for your thoughtful wisdom. Vic

modest PV system for a renter

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