Help with a small off grid system

System

I'm looking to build a small system for power outages and was wondering if I could get some guidance. I live in Richmond, VA. Right now I'm looking at a Photowatt PW100 (100 watt panel, UL listed? Couldn't find any info on that), a Morningstar Prostar 15M charge controller, a MK 8A27 Sealed AGM battery (92AH) and a Xantrex Xpower 1000 watt inverter. What I'd like to power is two 13 watt CLF bulbs for about 4 hours and a TV for about an hour a day. I need to start small due to money, but will likely add on when I'm able. What else am I going to need for this small system? Will I need fuses with a system this small? At them moment I think I will roof mount the panel, but may consider pole if I can find a location close to the sun porch where the battery, inverter and charge controller will live. How about grounding, what is recommended?

niel

Re: Help with a small off grid system

sounds like what you have will work ok. as to fuses and switches i'd recommend them for protecting the battery from shorts on the inputs and outputs with the switches able to isolate or turn things off to the battery. it may be a good idea to ground the pv frame to an independant ground rod, but nothing else needs grounded. just be sure you have the right gauge wire for the current you'll need (even in the future as you don't want to rewire) at whatever distance by using the voltage drop calculator in the general solar topics sticky.

BB.

Re: Help with a small off grid system

You can use this link to estimate the amount of power per day/month/year your system will generate (note: it does not go down to 0.1 kW panel size--so you will have to enter 1.0 kW panel and divide all the results by 10).

OK, Richmond VA, 0.1 kW panel (100 watts), use a 0.50 derating factor because you are "designing" an off-grid system and there are battery+inverter losses.

You will generate, roughly 5 to 7 kW hours per month (depending on season) or (divide by 30) 167 to 233 Watt*hours per day (useful energy from inverter to your AC load).

Load is 2 x 13watt x 4 hours per day = 104 Watt*hours for lighting.

Remaining power for TV, roughly 63 to 129 watt*hours per day for your TV.

The 1,000 watt inverter is probably way overkill for this system. Also, an inverter that large is probably a modified sine wave (really mod. square wave) inverter... Most loads will sort of work OK--some will either fail from overheating (motors) or have nasty RF interference (some TV's, radios, etc.).

You would be better off all the way around looking for a smaller "true sine wave inverter" sized closer to your load (in this case, roughly 2x times your normal rated load--unless you are planning on using electric motors--but this is a pretty small system to even run one of those for any length of time).

Exeltech is one brand that has been mentioned several times here as a good true sine wave inverter.

The other thing you did not ask about was the type/size of battery you would like to run this system... If you can justify it, an AGM type sealed lead acid battery, roughly 3-6x your daily power requirements would be a good fit.


233 watt*hours / 12 volts = 20 amp hour... Or ~60-120 amp*hour rated 12 VDC deep cycle storage battery would be fine.

You could also use regular wet cell batteries. More maintenance, cheaper to purchase (and mess-up with if this is your "training" solar PV system).

You do want to not try and drain your system to less than 50% state of charge for best battery life. If you drain it deeper than that, the battery will not last near as long (and wet cell batteries may fail in weeks or a few months if discharged that deeply).

On the other hand, AGM batteries don't like over charging at all because you cannot replace water if they over charge and vent. Wet cell lead acid can have water replaced (using distilled water).

-Bill

System2

Re: Help with a small off grid system

Thanks for the great info! As for switches and fuses, what would you recommend? Can you link to something that would be good for this purpose? I'm thinking automotive fuses would work best, correct? As for the inverter, do I really need a true sine wave for CLF lighting and a small TV? Could the inverter I have damage my TV over a long period of time? I was only going to use this inverter because I have it already, I can purchase something else if I NEED to.

Also what is code for outdoor wiring, do I need to run all wires in PVC or metal housing?

System2

Re: Help with a small off grid system

Yeah, I agree, the 1000 watt inverter is way overkiill. And generally, the larger inverters have greater idle power usage, the power required just to run it, so with a relatively small system, that's something to think about.
One inverter I've found really good, very well made for smaller loads is the Prosine 300, by Morningstar. 300 watts continuous, it can handle a 600 watt surge for 15 minutes @25C, is true sine wave so you won't have to worry about smoking your TV or other delicate electronics, remote on/off capable, can handle up to 15.5 volts before shutting down which is great for use while batteries are charging, and selectable auto start/ always on/ remote start features. AND no cooling fan to fail, make noise, or use power, it's convection cooled. Humidity to 100% non condensing, Temp range -40C to +45C. THD 4%. In short a real quality unit, not all that expensive and you won't regret not buying a better inverter. Plenty of power for what you want to run and room for expansion.
Cheers
Wayne

System2

Re: Help with a small off grid system

If you haven't already smoked your TV, then you probably are lucky and have a TV that can handle MSW and won't have problems. As to CF lamps, I've run them for years on MSW with no problems except they buzzed a bit, but now all that stuff, including this computer, I run off the Prosine 300.

BB.

Re: Help with a small off grid system

The issue with Mod Sine Inverters is that probably 90% of your electrical loads will work OK (may be a bit more buzz and a bit more heat). And 10% will fail within minutes or hours of use...

Problem is you don't know which device will fall into the 90% or 10% bucket...

Fridge/freezers and other consumer items with motors generally will run hot and can fail sooner than expected.

Cheap/mass produced consumer electronics can fail with Mod Sine (somebody here said their Black and Decker cordless drill battery charger died quickly--and I think somebody else said their B&D worked fine).

If you need cheap, portable power, and don't care too much about what you are powering (flood lights, resistive heating elements like ovens, hand tools, etc.)--mod sine is fine.

However, if this is going to be for ongoing use (like a solar powered home), bite the bullet and get a real sine wave inverter.

The smaller inverters are not that expensive and the cheap but large mod sine units are usually way to big for most people's applications--and frankly, way too big to clip onto a 12 volt car sized storage battery (running a 1kW 12 vdc input inverter will probably completely flatten a standard sized storage battery in 10 minutes +/-... This is pretty much the equivalent of sitting in your driveway and cranking your car engine with the coil disconnected--a continuous 100+ amp load at 12 volts).

For outdoor wiring, you should look at the NEC (National Electric Code)... But basically, most wire should be in conduit when exposed to sun and weather. You can get cable/wire that is rated for UV/outdoor use to wire solar panel to solar panel.

-Bill

niel

Re: Help with a small off grid system

i did not say anything about the inverter as you indicated you would expand later, but the points of some items failing on modsine inverters and more idle draw are good ones. staying away from items with motors and some wall wort items like bb mentions and you will be fine using modsine. most tvs and lights work with modsine, but i'm not sure on all of the lcd tvs.
yes wire the pv in conduit or any approved wiring arrangement as specified by the nec and that's my official advice, but for 1 pv i'd only be concerned with the proper wire gauge to keep losses down and grounding the pv frame. i say this because you intend to upgrade later with more for your system and then you can go whole hog with conduit and such.
i say the same about your inverter, but if you want to keep losses lower due to the small draws then by all means by another inverter and it could be a small 300w modsine as long as you know what it's powering is not sensitive to blowing out from it. do by all means get a good sinewave inverter later down the road when and if you need it with a bigger system.
also, for a small system like this one you had speced, the older style automotive fuses will do better as you can mount them easier and apply larger wires to them. you could skip the switch if you have easy access to the fuses and you can pull them to shut things down. eventually, when your system gets bigger, you can opt for switches.
all of this is considered a temporary setup for future expansion and planning is a necessity in this. do note that it isn't a good idea to go very long without adding more batteries, say maybe a year if they aren't abused or cycled deeply. in your expansion it's also not good to go with different batteries as they should be identical.

SolarJohn

Re: Help with a small off grid system

Congradulations on your decision to build a back-up system. It's great fun to put lights all over the house when the rest of the neighborhood is using candles.

Like you, I started out with a MSW inverter. It produced an annoying buzz in my radio and tv sound, and it produced streaks in the picture of my tv. Motors didn't run right, and I was always worried that I would fry something. As others have suggested, you'll be much happier with a true sine wave inverter that is not excessively big when considering the loads you intend to power. For your application, the Exeltech 300w model would be a good choice.

John

System2

Re: Help with a small off grid system

Thanks for all the great information! Right now I'm still building my parts list, it seems to change daily. Once I have everything ordered and in hand I'm sure I will have more questions. Thanks again for all the feedback!

System2

Re: Help with a small off grid system

Have you looked into grabing up an old used APC true sine wave UPS and use a 24V bank (I think there is a 12V True sign wave but hard to find).

I have been using a 4 cell golfcart batt set up with 3 EG 190's+ MX-60 to renew and charge the bank that powers an APC 1400. I have used it 3 times and ran a Refer, fridge, laptop and small AA batt charger for at most 8 hours during an outage and bairly touched the banks capacity.

The beep was a bit anoying but I can remove it if I can find a programing cable.

It is even auto sensing to kick on.

n3qik

Re: Help with a small off grid system

The one thing to remember is that a UPS is design to run short durations. You must watch how warm/hot they get when running long term. The UPS I was using, I drilled 50+ 1/4" vent holes in the case. Other than that, they make great inverters.

System2

Re: Help with a small off grid system

The ones I use have a fairly big batt pack and active ventilation via a 90mm Fan.

I will be swapping in a better more eff fan and I might drill some more holes...

Not bad for free though!!!

2manytoyz

Re: Help with a small off grid system

I have a small solar setup, not much different that what you're looking to build.

I have 65 Watts of my 140 Watt array on the roof at the moment. I'll be installing more this week. But the 65 Watt array has been serving my needs for the past year.

I'm using a MorningStar 10 Amp controller, which also controls my lighting. When the sun goes down, the panels stop producing power, and the controller then turns on the lights. No need to ever set a timer, or worry about DST.

Each night for 6 hours (adjustable), it turns on my low voltage garden lights which have been converted to LEDs: http://2manytoyz.com/gardenlights.html

At the same time, a 400 Watt MSW Vector inverter is powered up. This runs two CFL bulbs on each side of my driveway.

The total draw on my batteries with the garden lights, inverter, and two CFL bulbs, is under 2 Amp/hr. My small array quickly recharges the batteries that had a light load the night before.

TV and cable box power varies. It pays to put these on a strip and turn them off when not in use. While my TVs draw next to nothing when off, my cable box is a pig! 32 Watts on or off. My bedroom 32" HDTV draws close to 100 Watts, the 42" living room HDTV is closer to 200 Watts (cable box included in this figure).

Since I'm in FL, marine stores are everywhere. I bought heavy duty fuses, and a battery switch, through West Marine.

I am using four 6 Volt golf cart batteries in my system so far. Before hurricane season starts again, I'll double my capacity. My system is setup for 12 Volts, so I currenty have 452 AH of capacity.

I have had great success with MSW inverters. Details about my experiences here: http://2manytoyz.com/inverters.html

Info about my small scale solar setup here: http://2manytoyz.com/solarpanels.html

Seems like most on this forum are large scale. If I had the budget, I'd probably jump in with both feet too. Don't know if there are many "tinkerers" here.

System2

Re: Help with a small off grid system

So far I've purchased 3 Solarex MSX77 solar panels (used, 77 watt each, couldn't pass up the deal at $2.38 a watt), one Deka Solar 106 Ah AGM battery and I have a Xantrex 400 watt mod sine inverter, will upgrade later. I'm looking at the Morningstar Prostar 30M charge controller or the Xantrex C35, does anyone have any experience with either one of these controllers? I like the Morningstar since it has the digital meter, but it's not UL listed. The Xantrex is UL listed and has a meter that can be added for about $70 more. Is there another choice out there that might be better for this small of a system?

Thanks everyone for posting great info so far, this is all new for me so every little bit is very helpful and encouraging!

westbranch

Re: Help with a small off grid system

you might try looking at the BlueSky controllers as well. try looking here
http://store.solar-electric.com/chco.html
or here
http://www.blueskyenergyinc.com/products.htm

Cheers
Eric

2manytoyz

Re: Help with a small off grid system

The Xantrex C40 is very popular. Takes a wide range of inputs, and will work on several battery configurations (12V, 24V, 48V). I know a few people who have these. The C35 is very similar, but not quite as many features.

But I don't need a load controller, and would like a digital display. I have a couple of MorningStar controllers (one on the house, one on the boat), and have been very impressed with their quality. So it looks like a Prostar 30M will likely be my purchase as my array increases. Little less expensive than the C35 or C40 by the time you add the optional display.

As for UL listing, that means less to me than it once did. We had a big problem at work with UL listed surge protectors melting/catching fire. Turns out there are two versions of UL 1449. The second edition is much more stringent, and makes for a safer product. UL did not recall first edition products, nor did they create a new code. So many products are available even today, that only meet the first edition. Very difficult to tell which surge protectors meet the second one. Google "metal oxide varistor fires". Serious stuff. UL dropped the ball on that one. I now only buy surge protectors that have a metal case, and use thermal fuses.

The Prostar comes with a 5 year warranty, and meets the European Standard, which many times is tougher to meet than USA standards.

Either way, I fuse everything on my system. Anything goes wrong, a fuse will pop before things get ugly.