Small PV Systems

[John Dalhaus]

Because I like to tinker, I put together a small PV system about a year ago. Then, a couple of extended power outages showed us just how valuable a small system can be. The latest outage occurred in the winter, and the system helped to keep us warm that first night. We were able to provide power to the motors of our bio-fueled stove. We're now enlarging the system so that it can better meet our needs in the future.

If you've installed a small system, I'd like to hear about it, and how you use it. You can use my format (below) if you wish.

At the present time my system consists of:

3 - 85 watt Kyocera panels
1 - Morningstar 20a Charge Controller
4 - 105ah Marine Deep Cycle Batteries connected in parallel
1 - Exeltech 110-Watt inverter

I consider my system a backup to grid-supplied electricity. When the power fails, I use power from my system to keep a small chest freezer running, and I'm able to run several CF lights. We also use the system to charge cell-phone batteries, and to cook meals. Powering a radio and TV helped us to keep track of a recent storm's progress when our power was out.

I don't like the idea that unused power is just going to waste, so in the near future I plan to connect the chest freezer on a continuous basis. I write about my experiences on my blog: http://solarjohn.blogspot.com

Tell us about your system, and what you use it for.

[Joe Blake]

My current system consists of

2x64 Watt Uni-solar panels
16x2.4 Watt Uni-solar panels
2x regulators. (1xArrid, 1xSolarex (ancient))
2x6v deep cycle batteries, 120(?) A/h (series)
2x12v car batteries (520CCA) (parallel)
2xSEA 12v/240 inverters (1x150W, 1x500W)
Engel 40 litre 12 v/24 v/240 v AC chest freezer.

The freezer has been running off the sun since December 2005, and feeds directly off the batteries.

The 500 W inverter runs my office, 1 computer, screen, audio transcriber. The office actually runs off a UPS with about 5-10 minutes capacity, which is plugged into the 240v mains. If the mains power goes down, then I just unplug the UPS from the mains, and into the inverter without losing anything. Plus the UPS is very good for supplying the "Start up current" for the computer's hard drive. I CAN run the office UPS off the 150 w inverter, but it just doesn't supply quite enough power to keep it charged, and after about 4-5 hours the UPS battery goes dead and the whole system shuts down. The 150 w inverter won't supply enough grunt to reboot the system.

When the sun is in the optimal position, the PV array has sufficient power to keep the batteries at above 12 volts. ie fully charged.

I cheat a little bit and have a trickle charger on mains power to get the batteries back up to full capacity overnight, but for most of the day it draws negligible power, and I could quite easily run without the charger on.

The 150 W inverter handles stereo/DVD/TV if necessary.

I have a 7 w fluoro camping lantern permanently attached to the main batteries, so in the event the power goes down at night time, the little green charging light will lead me to the lantern and I have sufficient light for about 7 hours.

Other auxiliary lights include a wind up/solar torch/radio and another similar, but runs of 4xD cell rechargeables, with two metered solar battery chargers (max 2xD cells capacity.).

In an emergency, I can plug my motorcycle into the circuit through the accessories plug, but it only has a 400 w generator.

The system proved its worth last year when, due to winter storm damage, my house was without mains power for about 4 days, and I was able to keep working and earning money despite this. I didn't lose any food due to spoilage and I was able to give my neighbour in the other half of our duplex unit some ice to keep his food cool, if not actually cold. It rained for 2 days, so the PV panels weren't getting very much power during the day.


Regards,

Joe

[Larry Hollenberg]

I recently replaced my deep cycle marine type battery that runs some 12 volt lines in the house. I did it to get back in touch and hopefully get to adding a solar panel or so this year, I think for what little use I make of that part of my home system it wouldn't take much to keep it ready for say, "ice storms" or other outages and supplement a bit of house lighting with solar.

What I am concerned with at the moment is now that I have this full battery and replaced some standard 12 v. light bulbs with the new florisant type sprial bulbs for energy conservation, I am not draining the battery much though infrequent use.. It still says 12.5 on the meter after three weeks. I have a regular battery deep cycle electric charger to replenish it with but so far haven't tried more than once. That time it didn't take any power yet. I always end up killing a perfectly good battery through neglect with this set up. Till I can get it on to a solar system how often and at what point should I be recharging this battery?

[Joe Blake]

Although you didn't say so, I presume your charger has a regulator which cuts out when full voltage is reached? If not, then that could be a source of problems. Unlike Ni-Cad batteries, lead acid batteries, whether deep cycle or standard, get best "mileage" when kept fully charged but not over charged, as well as acid level kept over the tops of the plates (in those batteries that can be opened - sealed batteries are a different kettle of fish.)


Regards,

Joe

[Larry Hollenberg]

Yes the charger is supposed to sense the full load and cycle back at the end. My real question I may not have made too clear is how often would you recommend charging the battery if its not getting much use. I think I have read that they work better when used about half, then refilled. Seems that suggested it should be done frequently to maintain the battery rather than waiting too long.. but since I am not drawing the battery down much right now I wondered how often to top it off.

[Joe Blake]

I've described my system earlier up the thread and I have the solar panels constantly feeding the batteries (via regulators), plus I always have a regulated charger for maintenance of charge overnight. Admittedly I'm always drawing against the batteries, day or night, with my 12 volt freezer but even if I weren't drawing anything, I'd not bother about turning the charger off. As long as the regulator is working properly, there should be no worries.

I think what you read about using "half" and then refilling may actually have been referring to using "no more than half" and then refilling. In other words it's best not to discharge wet cell batteries too far or too often, even deep cycle ones.

One suggestion which I can recommend is to buy one of the small solar panels used for maintaining car/boat batteries. They are designed specifically for the task of trickle charging batteries and even leaving them on day and night, they generate so little power they can't really overcharge the batteries, since PV cells can manipulate their own voltage, so to speak. (However, you can have some problems if you have too many PV panels hooked up.)

http://store.sundancesolar.com/trchforcatrr.html

Something like this.

If you have a larger than usual drain on your batteries and the voltage drops significantly, then you can use your mains charger, but I think the PV car charger would suit your needs perfectly.

Regards,

Joe

[Larry Hollenberg]

Thanks for the advice and source.. The battery charger I have is a regular over the counter charger that once it gets to the full point the pointed swings back and forth rapidly from it shutting on and off. I don't think that must be the kind of charger your using? Probably what little I am using the power at the moment the small panel might be a good Idea.

When I get ready to purchase say two larger panels though I will need to get some kind of regulator in the line, (how ever they connect). I have a gas servel and wood and oil cook stoves, I could fairly easily do without the power from the company but then I got into this computer thing, and I would guess it would demand quite a bit of extra power to operate, not to mention and inverter. My system so far is made to operate things on 12V.

[Joe Blake]

Larry,

If you are wishing just to run your computer(s) from a solar array, have a peeky-boo here.

http://www.motium.com.au/products/index.html

They do a nice line in computers (and screens) which are designed to run directly off 12 volts. I have the 7" screen for jobs when I went "mobile" and am investigating purchasing the "fanless" computer to complement it.

I use a 3-burner gas stove for my cooking and have a small electric toaster oven which I find I am able to do without, for at least a couple of day.

Probably these days, since installing a solar hot water system most of my (grid) power goes in my big refrigerator and my water-from-air condensing machine (which has been off now for nearly 2 days straight, as I have ample water stored.)

However, I think having a 500 watt inverter would probably be a nice "comfort" investment for later on when you get more solar panels on your array. Handy for stuff which you can't buy that runs off 12 volts.

In Perth we are blessed with a shop dedicated to 12 volt gear. It's like walking into a candy shop as a kid.

http://www.12volt.com.au/

Regards,

Joe

[Larry Hollenberg]

Joe,

Thanks for those sites, they are really interesting.. I have looked them a bit but will come back for more.

Larry

[Aaron Menzies]

Our system consists of:

10 x 55 Watt panels
6 x 2 volt 1000 Ah batteries
40 Amp charge controller (xantrex c40)
300 Watt inverter,
2000 watt inverter
5.7 KVA diesel Generator
1.7 KVA petrol Generator

This system is for powering a small cottage that has to accsses to the grid.

We are still builing another small cottage that will also use the system. because we have more power than we need!

[Jordan Hazen]

I've been operating computers from 12V for several years.

Laptops are the easiest case, since car/air adapters are readily available and can be simply plugged in with no hardware changes. The adapters contain a step-up DC-DC converter that generates (usually) 16V or 18V from a 10-15V input. Efficiency varies from model to model, but should always be significantly better than using an inverter to feed the laptop's AC supply.

For a few more efficiency points, especially in off/standby state, some laptops will accept 12V on their internal battery terminals (older IBM Thinkpads, for instance; this is with the LiIon battery removed, of course). I do this on one computer that runs 24/7 as a router/firewall/server. Before attempting, it's best to open up the machine and check its circuit layout, to be extra sure of the pinout and acceptable voltage range-- any mistakes can cause major damage! The external adapter is a much safer way to go, and standby losses can be avoided by simply disconnecting it on the 12V side when not in use.

For desktop computers, there are some commercial DC-DC ATX PSU's on the market, intended mostly for mobile applications (car PC). I've had good results with the M2-ATX, as sold at short-circuit.com ... one is powering the computer I'm typing on.

Note that these DC-DC supplies put out very limited current, especially on the +12V rail, and unless carefully designed for efficiency, most PCs are too power-hungry to accomdate one. Common watt-hogs include high end video cards, and pre-"Core" series Intel CPUs (Pentium 4's). Best to take a quick Kill-a-Watt reading before even considering a DC retrofit.

My main workstation, slightly underpowered by modern standards:

- MSI MS-7030 motherboard (Socket 754) w/ onboard NIC & audio
- AMD Turion MT-37 CPU, 2 GHz (a laptop CPU; but older ones would fit certain desktop boards. New "socket S1" Turions won't. Some of the more mainstream AMD Athlon64 and Intel Core2 CPUs are now nearly as power-efficient, though)
- nvidia Geforce 6200 video card (no fan, passively cooled; onboard motherboard video could save even more power, at the cost of poor performance)
- one 500 GB SATA hard drive (Samsung HD501LJ; nice and quiet)
- DVD-RW
- "PCHDTV" tuner card
- M2-ATX 12VDC power supply (this needs to be custom mounted, btw; it comes as just a bare circuit board)

This machine pulls about 44W (3.3A @ 13.3V) when lightly loaded, 10-12W more at full load. (I could save a few more watts by adding some sort of switch to power down the tuner part of that HD card when it's not in use).

The Samsung 216BW 22" LCD monitor draws another 18-40W, (1.4-3A) depending on brightness setting (minimum is usually plenty bright!). It runs from 150V DC. I modified a small ~100W MSW inverter, bypassing its final output-stage H-bridge MOSFETs, the ones that normally alternate +/0/- at 60Hz-- no more annoying buzz! It's slightly more efficient this way as well.

That 150VDC circuit also runs a satellite receiver, some CFL lights, and several other AV/computer/network components, those that can't accept 12V directly. Anything with a switching power supply (not linear!) and no voltage-doubler on the input is usually quite happy to run on DC in the 120-170V range, because input power gets immediately rectified anyway, and a normal 120V RMS sinewave already reaches 170V at its peak. If anyone tries the same mod, be sure to fuse the stepped-up DC output appropriately, to reduce the risk of damage if you accidentally plug in something with a linear (transformer) supply, or an AC motor, either of which would appear as a short circuit at DC.

Well, this is getting long, so I'll describe the rest of my system later.

[Jens Naumann]

In 1999, I just got the urge to buy 2 Seimen's 100W panels , well, because they looked so good. I hooked them in parallel and to 4 traditional 6v 220amp/hr golf-cart batteries with proper 12V configuration (2 parallel, then the 2 groups in series) ...) and I got a 12V 1500W inverter - OH, what fun - free power... I just put 3 wall sockets in my office and ran my computer/printer/fax... well, in no time I got another 2 panels, another 4 batteries... Kind of lost self-control when I bought another 4 PV panels (100W again) and next thing I had extension cords running through the house so I could plug in the fridge, freezer...
It was only 3 months later that I went all the way and doubled the station to 16 - 100W panels, added a couple turbines (small ones) and a bigger and better inverter. With 32 batteries, I thought I had it made and called in Ontario Hydro to cut my services...
"What do you want us to do?" asked the hydro man in disbelief... well, I figured the investment only made sense if I got off the grid with a statement - to still have the service connected, even if not in use, would not serve to prove this actually works as most onlookers may think I am secretly using the grid when no one's looking...
Oh, yes, I did run into overcharging problems. The inverter would quit - the batteries bubbling audibly and I tiptoed aroun them so as not to cause a spark - sending myself and the system into the next galaxy with the perfect buildup of hydrogen/oxygen for some disastrous explosion.
I searched out charge regulators - all of which claimed efficiency but had terrible voltage drop between battery and PV panels during charging cycle, and an equal waste when on cloudy days they still needed that precious power just to close the connection between PV and batteries - so... I built my own... no consumption whatsoever until the battery is at the set voltage of 14.5 or whatever I prefer to set it at with a pot - nope, no screen with menu, just a knob... even my growing kids knew how to set these ones...

I think my system is still small - but lots of fun, and never a shortage of power. I use coffee machines, regular freezers and fridges, computers galore, and on the regulators there's an audible "beep" that once the batteries are full, they indicate to all that we can... Waste Power...!
I went to a green home convention hosted by the Prince Edward County and many green enthusiasts I spoke to said..."I want to get off the grid ... once my kids move out..." I retorted..."I had 8 kids in the house when I got off the grid, and at the time it was more fun than ever as all those growing minds that watched me do it and then reaped the benefits now are fully convinced that green power is indeed a good way to go..."
Now 3 kids remain - the others moved on with their own lives, and there's far too much power kicking around here - usually I'm running on only 9 panels...
My first 2-panel system was just as fun as is my current 1.6kW system - its all about budget, what you want and what you can do. Even a 50W panel, single 12V battery and $75 inverter can be fun - there's something about free power that's intriguing.

[John Dalhaus]

Jens,

I can't help but wonder why you would choose not to use a charge controller????? For safety reasons, and to protect your batteries from damage, I hope you decide to add one soon.

John