Putting together a solar system

Cariboocoot wrote: »

Okay, there are some things an MSW inverter won't run and a lot of others it will run poorly. Like AC induction motors as found in refrigerators, washing machines, and some water pumps. Other things that "don't like" MSW include certain battery chargers and UPS units. It can be a bit of a crap shoot finding out if your devices will actually function with MSW, or function without significantly shortened life.

As to the size of the battery bank ... This is where we start playing the broken record about getting a firm grip on loads. I know it's tough to do, but you need some kind of "ballpark figure" on how many Watt hours you'll use in any given day. There's no sense buying too much battery and having to spend even more to keep it charged and there's unpleasantness in suddenly running out of power and having to start a generator at 10:00 PM.

Take a look at the equipment in my sig. It manages to run a refrigerator, plus the computer/satellite set up and lights as well as water pump (1/3 HP) digester pump (septic - 1 HP) and microwave. The last three are only run under full sun, fully-recharge battery conditions. The 700 Watts of panel supply approximately 2.4 kW hours of power on a good Summer day. But it's cooler up here, I'm at 3000 feet (clearer air), and our Summer days are up to 16 hours long so our sun exposure can be 5-6 hours of 'good' light.

That said, if you put all those panels together I wouldn't be surprised to see better than 3 kW hours harvest per day in Baja, despite the heat. It would be enough panel to recharge about 600 Amp/hrs of battery bank, so perhaps you might want a parallel set of L16's @ 320 Amp/hrs (640 total) or 2-3 sets of T105's (450-675 total). The L16's would give you approximately 3.6 kW/hrs per day to work with max (50% DOD), and the T105's would run either 2.7 or 4.0. Any of these configurations is potentially feasible with the total panel count (all 915 Watts). Heat derating I'm not sure of, nor any other losses that would be inherent in your particular system.

BB. wrote: »

For battery sizing--a reasonable starting point is to plan for 3 days of no sun and 50% maximum discharge--or 6x your daily load (don't forget inverter efficiency of 80-85% if you want to account for all loads).

A bigger bank is more expensive and requires more panels/charging current to keep happy. A smaller bank may cause you to run the genset more during strings of bad weather...

A bigger than 6x battery bank is probably a waste of money--below 4x your daily load may be a bit on the small size.

Also, check out your maximum power (surge power/current)--too small of bank may not start your well pump without browning out the rest of the inverter AC loads.

If you are looking at spreading out your costs--probably a 6x battery bank and 5% set of solar panels--run for a few months or a year--then look at how many panels you would like to add to reduce genset run time.

Another thing I like to look at is genset / AC battery charger sizing... For Diesel motors, you generally want to run them at 50-60% load.

For gasoline based gensets, running them below 50% load can be waste of fuel--For below 50% electrical load, the generator fuel flow hardly drops any further...

A few gensets, like the Honda eu2000i family, can run pretty fuel efficient down to 25% load or a bit less...

So, I like to look at the battery bank to generator load ratios too when sizing a system... Many people put a 7-12 KW, very nice prime mover, genset in--and run it at 3kW or less loading when charging the battery banks. A second small genset dedicated to battery bank charging may be worth the time and money (and fuel saved). And keep the big guy to run the shop and pump water once a week. There are not that many reliable/quite/cost effective small gensets out there--so that can be a issue trying to find one too. Sometimes getting a smaller Onan or equivalent from an RV wreckers can be a good source.

A properly sized genset my use 1/2 the fuel (or even less) vs what many people started there initial off-grid experiences with.

-Bill

Photowhit wrote: »

Lots of things here;

On the battery bank for a first time solar electric system, I would rather see you NOT invest in a big AmpHour system. The mistakes you learn in the first couple years may cost you a lot less.

If your running a home, not a weekend cabin in the woods, I'd go with a 24 volt system minimum.

With a generator back up for long periods of cloudy days, particularly in a 300+ sunny day area. I would go with a somewhat undersized battery back. Try to load shift as much as possible (running things during those sunny days, this will save you 15-25% as storing cost's you watts)

Areas with 300 sunny days are often hot, you won't need AC?

Ananda went out of business in the mid '90's, I love the Pulse power center I have from about 2000, but in a year or so, when I finally replace the PWM charge controller (there is a recent thread about my trying to replace the charge controller), it will just be an AC and DC breaker box. Indeed, I think Ananda only used a fuse on the Battery disconect.

Power centers make life setting up easier. If the Ananda is setup for a generator it might be worth a trying to use for your initial setup, but it's value I would find no more than the $250 I paid the the Pulse PC250 Power center, New Old Stock 3 years ago(a good deal). The inverter might be worth something as a backup, but thats all. 10 year old Quality solar panels might be worth as much as $2 a watt, you can get new for $2.50-3.

icarus wrote: »

16 T-105s and only 400 watts of panel?

Talk about under charging! Something like 2000ah of battery (12 volt) with ~20 amps of charge current! 1%,, just barely enough to keep in float!

Tony