Where to begin advice

Runningwater

Hello, I'm new to the forum. I have a little cabin in Northwest Nebraska that has no electric service. It has wood heat, and we use Coleman gas lanterns for light, and a battery jumper/charger pack to power a radio/dvdplayer/fan as needed. We also have a cheap generator to use when needed for power tools, vacuum, etc. Have been interested in putting in a limited solar power setup to provide lighting, fan/radio/dvdplayer use, and possibly also run a vacuum (for say 10 or 15 minutes). We typically only stay at the cabin a couple days at a time, a couple times a month. It doesn't need to be 100% available under any circumstances, we generally get by just fine the way it is. I know this will be some pretty pricey $/kwh, but (1) need another hobby/project, (2) would like electric light, especially in the summer to reduce the heat byproduct of mutliple gas lanterns, (3) would use the vac more if it didn't involve dragging the old load generator out of the outhouse.

So I'd prefer to be able to run about 8 13.5W LED bulbs for up to 6 hours a day, run a fan (not sure of a decent little window fan wattage) for up to 6 hours a day, a 4 hours a day of a dvd player or boombox (say 50W?) and a vacuum (think I can find some in the 1000W range?) for 10 or 15 minutes once a trip. Don't need to have everything on at the same time, and isn't a crisis if under some usage or weather conditions everything isn't available. In the summer the lighting hours will be only half this and in the winter the fan won't be used much.

Here's the VERY rough spot I was starting from. Was thinking of having a 12V system, a couple 250W panels (was looking at Grape), a 45A MTTP battery charger/controller(perhaps Morningstar TriStar 45 Amp MPPT Solar Charge Controller), and a 1500W inverter (perhaps/such as Ramsond Sunray 1500 Pure Sine Wave Intelligent DC to AC Inverter (12 Volt) ), and was orginally looking at about 220-ish ah worth of AGM battery (a single a a couple smaller ones) - but in perusing this forum am now open and/or leaning toward some sort of golfcart/forklift battery setup.

I know there is a heck of a lot of devil in the detail here, but can anyone tell if I'm widely off already on a workable setup? Any recommendation on the setup, advice, or specific recommended brands/models of equipment are very appreciated. Don't plan on pulling the trigger on anything until after I have a good plan.

Thanks so much - and I apologize in advance for my ignorance!8)

icarus

Re: Where to begin advice

Look at my signature.

We live with 400 watts of PV, 450 ah of battery, into a 300 watt inverter.

If you just run the vacuum in the genny, you would be golden with a system about this sized.

Just remember, as y have p ower available, you will use it, and your use WILL grow with time.

The basic design criterion starts with the loads. The loads determine the battery needs, the battery needs determine the OV requirement, and that in turn determines the CC needs. Determine the daily loads, both total and peak, the number of days of autonomy and move from there, remembering that those loads will grow with time.

My simple rule of off grid PV is this. Take the name plate rating of the PV, divide that in half to account for all cumulative system loses, then multiply that number by 4 to represent the average hours of good sun you can expect, per day over the course of the year..

So a 500 watt PV system for example might look like this: 500/2=250*4=1000 WH/day.

Welcome to the forum, good luck and keep in touch,

Tony

westbranch

Re: Where to begin advice

Just to prove a point to yourself, take Tony's formula and look at what it will take to run that vacuum, which is probably in the 800 - 1000W for a load figure, and you will need an inverter, TSW of about 1500 watts to start and run the vacuum... I'll leave the rest to you for todays homework...;)

icarus

Re: Where to begin advice

I forgot to mention, that we use between 500-800 WH/day on averge. If you use my formula you will see that it works quite well. On an ideal day we can harvest nearly 2kw, which is 3 days of load. Rarely do we ue a genny except to vacuume (or to run the shop tools,). We have a minimum of three days of autonomy with no sun. That said however, there are relatively few days (Except in Nov when we hanve no snow or ice to reflect) that we get no harvest at all. In the " real world", we probaby have a week of autonomy before the batteries drop to 50%. In those cases, it is a simple batt to add some bulk charge from the genny, or mange loads (like computer charging, tool charging and even water pumping, trying to anticipate the coming likelyhood of getting a good charge day, and when.

Tony

PS. In addition to Eric's point about needing bigger (read less efficient) inverter, a 1000 watt vacuum run for 12minutes (.2 hours) will draw 200 WH, about 1/3 of our daily total! 12 minutes of genny time will burn...almost no fuel. Couple that with vacuuming when you are running the genny for charging and the energy cost is now nearly " free".

Living off grid is not that hard, , but it does require some subtle changes in habits, like load time shifting. For example, we often turn the water pump off in the evening (the is plenty of water in the tank) in favor of running it in the morning when the panels are putting out thier greatest, or ideally in the afternoon when the batteries hve gone into float, thus saving ~ 20%, because every WH taking out of the battery requires ~ 1.2 ah of power to get back even.

T