Ignorant and seeking wisdom

solarnovice

I am new to solar and would like any advice you care to give.

I am currently in the process of setting up my system which will consist of:

600w PV array
TriStar 60 MPPT Charge Controller
Power Bright 12V 6000W Power Inverter (I know, but the price-point is too good to resist starting out)
800ah battery bank

Questions I have include:

1. Will this system work, and if not, what do I need to make it work?

2. Can I mount my PV array in my back lot and run cable to my controller (approx. 100 ft. run) without sacrificing power, and if so what wiring should I use?

3. Is it necessary to run the array through a disconnect box? (Seems like a good idea from what I've read)?

4. Am I completely off the mark on this setup and need to think this through again?

Any comments or suggestions would be greatly appreciated.

Thanks, the new guy on the block.

waynefromnscanada

Re: Ignorant and seeking wisdom

Welcome to the forum!
First, and I won't be the only one to say this I'm sure - - forget that beast of a 6000 watt 12 volt inverter!
Second, what will your loads be? Once you have a good handle on your daily kwhr loads, the next step is to use that info to determine what you'll need for batteries, and then what you'll need for panels to properly charge the batteries. Finally comes the charge controller and the inverter.

Cariboocoot

Re: Ignorant and seeking wisdom

Welcome to the forum.

You have the basic ingredients, but the mixture is a little off.
The first question would be: What are you intending to do with this? Off-grid systems are designed around loads, and without knowing what you want to power it's random chance on picking equipment.

For example your 800 Amp hour 12 Volt battery bank would supply up to about 4.8 kW hours DC. That's quite a bit of power for most systems and usually would be fulfilled by a 24 or even 48 Volt system. Why? Because of the problems in making up that size battery bank. See this bit on equivalent power: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

The second question would be how did you size the array and charge controller? An 800 Amp hour battery bank would like 80 Amps of peak charge current, and the 600 Watt array is capable of about 38 Amps whereas the controller couldn't pass 80 Amps even if the array could produce it. As a result you would have a maximum charge rate of <5% which is below the minimum for a system with no simultaneous loads.

This is not a balanced set-up and would not work well at all.

As for running your array output through 100 feet of wire, that will require a pretty high array Voltage to overcome the resistance even with fairly large wire and low current. This will move the array Vmp far away from the system Voltage further reducing efficiency. You are looking at quite a bit of power loss here.

Whether or not you use a disconnect on the array will depend mainly on its configuration. You'd need to work out the rest of the system specs precisely first.

You should definitely think this through again before spending any money, no matter how cheap the equipment deal seems.

SolInvictus

Re: Ignorant and seeking wisdom

A 12 V, 6000 W inverter is a bad idea because it would draw over 500 A from the batteries to output 6000 W. 4/0 gauge copper wire is not large enough for 500 A continuously. You should consider a 24 V or 48 V battery array which would reduce the current and allow you to use smaller diameter and less expensive wire and possibly a less expensive charge controller rated for less current.

1. I can not answer this question until I know how much power will you be using on an average day in kilowatt hours / day (kWh/day) and the insolation at your site. NREL PV Watts can help you determine the insolation. Also what are your highest power loads and their power ratings?

2. All cable runs sacrifice power. The longer the run, the more power is lost and the more money you spend on larger diameter wire trying to minimize the loss. The Morningstar TriStar 60 ampere MPPT charge controller allows a maximum input voltage of 150 V. Assuming you are planning to use two 300 W PV panels, the specifications would be similar to:

Vmp = 40 Volts DC
Imp = 8 Amps DC
Voc = 49 Volts DC
Isc = 8.5 Amps DC

If they are connected in series, you have an open circuit voltage of ~100 V, an operating voltage of ~80 V and an operating current of ~ 8 A at the input side of the charge controller. Using 10 gauge copper wire for the 100 foot run:

Resistance of wire: 1.018 Ohms/1000 feet * 100 feet * 2 = .2 ohms
power loss in wire: I^2 R = 12.8 watts
Voltage drop across wire: 1.6 volts

Is a 2% loss of power acceptable to you?

3. Do your local building codes give you a choice?

Are you planning to include a generator for extended cloudy days?

vtmaps

Re: Ignorant and seeking wisdom

solarnovice wrote: »

I am new to solar and would like any advice you care to give.

As the others have said: Define your loads.

Building an off-grid system is like buying a truck. When you choose a truck you choose it based on the intended loads. Buying a half-ton truck is an expensive mistake when you need a one-ton truck, and vice versa.

Another way solar systems are like trucks: Its not possible to convert one truck to the other if you make a mistake, and you will be surprised at how little of your proposed system is usable in a properly designed system.

One more question: why are you building this system? Is the grid unavailable where you are building it?

--vtMaps

solarnovice

Re: Ignorant and seeking wisdom

Thanks for the input guys.

Sorry I didn't mention what I planned to do with this setup.

Starting out, I would like to be able to power my work shop with my configuration, and later add on to cover not only the work shop but my house as completely off-grid as I can make it.

In the workshop, I'll be running everything from lights to tablesaw, drill press, lathe, dust-collection system, circular saw, cut-off saw, planer, router, etc. Pretty much everything you would find in a work shop where I would be building anything and everything I could with wood. Most of these items I know have high inductive loads when they crank up, one of the reasons I had planned on the 6000v inverter.

When I upgrade to cover the house, that would mean everything in the average household. Lights, ceiling fans, refrigerator, stove, washer-dryer, tvs, radios, computers, microwaves, and any number of different items you normally find in the home.

I know this is an ambitious (and possibly unrealistic) endeavor, but I would like to push this as far as I could.

Does that help at all in trying to determine what system I would need in place?

Again, thanks for the help so far, and look forward to hearing more.

The new guy.

vtmaps

Re: Ignorant and seeking wisdom

solarnovice wrote: »

I know this is an ambitious (and possibly unrealistic) endeavor, but I would like to push this as far as I could.

Does that help at all in trying to determine what system I would need in place?

Again, thanks for the help so far, and look forward to hearing more.

The system you need in place is Lots of Money. Off-grid is MUCH more expensive than grid-tied, and grid-tied makes economic sense only when there are tax breaks and subsidies. Why do you want to go off grid? Are you trying to make a statement? Is your grid power so unreliable that it's not worth having?

I don't know where you are located, but most off-grid homes and workshops use generators quite a bit depending on the season. Are you planning to run a generator to charge your batteries?

--vtMaps

solarnovice

Re: Ignorant and seeking wisdom

Thanks vtMaps.

I guess in answer to why I want to do this: I just thought it would be a good way to run my workshop instead of having to run power from my house to the shop. It is located about 125 ft. from my meter on the house. I didn't want to have to trench, purchase conduit suitable from underground use, etc. Just seemed to be an easy solution to hook up solar panels with a charge controller and inverter and tie it to a panel I install myself (that part of the equation I know I can handle). Thought it might save me some money on my electric bills in the long run.

Same with upgrading and putting solar to use in the house. Just trying to cut down on money I seem to be throwing away to the utility company when I can generate some power with solar.

Make sense?

Thanks.

Cariboocoot

Re: Ignorant and seeking wisdom

Almost impossible to determine the Watt hour consumption of a workshop as it will vary with the work being done. A household on the other hand has fairly consistent power consumption averaged day to day.

If you've got grid, use it. Off-grid power is very expensive with the best of deals and as vtMaps said the stuff needed to power a workshop is très expensive. All those motors are not going to enjoy cheap MSW power, for example. A length of wire from the house is going to be far less expensive, even large wire professionally installed.

I have an $8,000 2.4kW hour OG system at the cabin. Last year I reroofed the place. To do so I fired up the gen first thing in the morning and bulked up the batteries. The panels were then able to take over and keep the compressor and saws running as-needed throughout the day. Sometimes, if I was really productive, I had to fire up the gen at night too.

So far off-grid doesn't save any money if the grid is there. The way things are going this may change in the future.

If you want to experiment with how effective solar is, built a small "lights only" system for the shop. It could also recharge battery tools. When you need the big power, start the gen or run a cord from the house.

SolInvictus

Re: Ignorant and seeking wisdom

To give you an idea of the PV system need for your situation:

Your battery array should be at least 24 V to power the shop tools and accommodate the future expansion to power the house.

With a 24 V system, the Morningstar TriStar 60 MPPT Charge Controller could handle up to 1,600 W of PV panels pointed in the same direction. If you have great insolation, you could get ~8 kWh/day of electricity, but your workshop and house might need more. Expansion might require an additional 2 to 4 charge controllers.

If you have a 48 V battery array, then the TriStar could handle up to 3,200 W of PV panels yielding about 16 kWh/day if you have good insolation. Expansion might require one additional charge controller.

A 12 V, 800 Ah battery array is a bit small to start your shop tools. I think your battery array should be doubled to 24 V, 800 Ah. My 12 V, 1580 Ah battery array with power from the PV panels can start and run my air compressor with a 3/4 hp motor. You would need to expand your battery array more to power your house too.

You should use 4/0 gauge copper wire between the battery array and inverter (even with a 48 V battery array) to minimize the voltage drop when high surge currents are needed to start your motors and accommodate expansion to power the house.

The inverter will have to be a good, expensive one with a big, heavy transformer to handle those inductive loads. I have a cheap 2,000 W inverter with surge of 4,000 W that surprisingly can not start the 1/3 hp (420 W) split phase motor on my grinder. From your list of tools in the shop, it seems like you would run the lights, dust-collection system and one power tool simultaneously. Expansion to the house would mean the fridge and at least one other major appliance (stove, washer-dryer, microwave oven) running simultaneously too. The 12 V, 6000 W inverter could not handle all these loads. You will need something like Schneider Electric Conext SW 4,000 Watt, 24 Volt Inverter/Charger with a price of $1,440.

You will need a generator for the cloudy days.

My use of power tools is intermittent which allows the PV panels to recharge the batteries when they are off. Cariboocoot's example of reroofing his cabin included a compressor (very inefficient) which probably ran frequently making it hard on his PV system. I built a garage with only 350 W of PV panels and the principal power tools being a drill and circular saw without discharging my batteries significantly and did not use a generator. I cut firewood from 8 am to 1 pm with 600 W of PV and a 1440 W electric chainsaw while the batteries stay charged due to the intermittent operation and the day being sunny.

Your PV array will definitely need to be larger to power the house too. If the PV array needs to be much larger than 600 W, the 100 feet cable run from the PV array to the charge controller could be a problem. If you double the current to 16 A on a 10 gauge wire, the power loss will be 51 W. Tripling it to 24 A makes the power loss 115 W. You would need larger diameter wire to conduct more than 30 A. I think this cable would need to be buried requiring you to dig a trench anyhow.


If you want to reduce the price tag of the off-grid PV system, then do demand side management:

Replace the drier with a cloths line;

The electric stove will need to be gas or induction;

Use the lowest powered microwave oven possible. To establish a lower bound, I have a compact one, .7 cubic feet, 700 W magnetron and consuming 1,050 W of electricity;

Computers will have to be laptops;

Run the fridge on a timer that only allows it to operate during the day;

Run high powered loads, except cooking, only on sunny days;

Coordinate your power use, for example, do not cook with electricity at the same time you run the shop tools;

and more is possible, but I hope these suggestions give you an idea of the level of sacrifice.

waynefromnscanada

Re: Ignorant and seeking wisdom

SolInvictus wrote: »

Run the fridge on a timer that only allows it to operate during the day.

Of all the points you make, this is the only one that I have trouble with. I totally agree with everything else you pointed out.
Standard fridges, if turned off, don't take long to reach temperatures which allow the growth of bacteria.
A better solution might be to convert a freezer for fridge use. My 10 cu ft converted upright uses roughly 0.3 kwh per 24 hour day AND that's with the temp set as close to the freezing point as possible. The difference in how long food stays fresh at those temps compared to a "normal" fridge is nothing short of amazing.
For that last reason alone, I'd never want to go back to using a "normal' fridge.
The only downside can be moisture buildup, as unlike a normal fridge, a converted freezer doesn't dry out the air or the products kept in it. On the + side of moisture, veggies kept in the converted freezer never wilt.
Food for thought.

solar_dave

Re: Ignorant and seeking wisdom

Look at going grid tie and use the grid with net metering as your "battery". Much more cost effective. Much easier to expand as well. Just add panels and GT inverters as money allows. Lots of people do that with micro inverters a few panels at a time.

SolInvictus

Re: Ignorant and seeking wisdom

waynefromnscanada wrote: »

Standard fridges, if turned off, don't take long to reach temperatures which allow the growth of bacteria.

Certainly converting a freezer to a refrigerator is an option for creating an efficient refrigerator. I was being brief and omitted the part about adding thermal mass (ice and brine bottles) to the fridge. There are two main advantages to running the fridge on a timer during the day:

1. maximize the use of power from the PV panels and minimize the discharge of the batteries to prolong battery life; and

2. setting the fridge controls to maximum cold causes the fridge to turn on only once per day at the time specified by the timer minimizing the frequency of two or more motors starting simultaneously. You know not to start a shop tool or electric range when the fridge is scheduled to start. Otherwise the fridge will start about every 30 minutes as shown in Do the Math: Death of a Battery, Tom Murphy (scroll down to the chart with the date of 2012-08-29). The cyan curve is the load clearly showing his fridge cycling on and off. If you minimize the probability of two or more high powered loads starting simultaneously, then one can use a lower powered inverter and smaller battery array.

Cariboocoot

Re: Ignorant and seeking wisdom

Or you can buy a refrigerator that fits your needs and design the power system to meet its needs. Much easier, less hassle, very practical.

SolInvictus

Re: Ignorant and seeking wisdom

and more expensive.

Cariboocoot

Re: Ignorant and seeking wisdom

SolInvictus wrote: »

and more expensive.

Only if you place no value on your time and convenience.