Proposed small system

ScottBarMtn

Here's the situation: The solar project that I am planning is for a workshop that is not grid connected. It is across the creek and down a ways from my house (which is connected to the grid). For a number of reasons, it is not feasible to run grid power to the workshop. I would call it a small system, with the goal of being able to run lights inside for working, and a few small power tools. For those times when I need to power heavier equipment or I have a big project going, the fall-back plan will be to fire up a generator for power.

Typical power needs, on a daily basis. If I need more power than this, I would plan to run a generator:
- Two 55 watt 12 volt halogen light fixtures running 6-8 hours per day (no inverter needed for these...)
- Occasional use of small tools (drill, etc.) during the day. Maximum 7 amp 120 volt motor for one hour per day. I would turn on the inverter only when I use a tool.

Proposed system:
- Solar Panel: One of Kyocera KD135SX-UPU - 135 Watt, 12 Volt Solar Panel (Junction Box)
- Charge Controller: Xantrex 12 Amp, 12 Volt Charge Controller
- Batteries: Two of Trojan T105-RE 6 Volt, 225 AH Deep Cycle Battery
- Inverter: Samlex 1500 Watt Pure Sine Wave Inverter 115 volt AC output, 12 volt DC input
- Charger: Xantrex Truecharge2 12-Volt, 20-Amp Battery Charger
- Battery sensor: Xantrex Battery Temperature Sensor, 15 foot cable
- One kill-a-watt meter for AC
- Two DC amp-hour/watt-hour meter (one between panel and battery, one between battery and inverter)
- Generator: Existing Dayton 3000 watt generator (may buy a generator/welder as backup)
- Estimated cost: A little less than $2000

Questions
- Do you see any weak links in this configuration?
- What is the difference between an electronic-based inverter like the Samlex, and a transformer-based inverter like the Outback? Will I regret buying the Samlex?
- Could I get by with a 1000 watt inverter?
- Any other suggestions? Cost is a consideration...

BB.

Re: Proposed small system

ScottBarMtn wrote: »

Typical power needs, on a daily basis. If I need more power than this, I would plan to run a generator:
- Two 55 watt 12 volt halogen light fixtures running 6-8 hours per day (no inverter needed for these...)
- Occasional use of small tools (drill, etc.) during the day. Maximum 7 amp 120 volt motor for one hour per day. I would turn on the inverter only when I use a tool.

Lets call it:

• 2x55 watts * 8 hours per day + 120 volts * 7 amps * 1 hour per day = 1,720 Watt*Hours per day

That is actually a fair sized system for an off-grid cabin. If possible, I would suggest looking for alternatives for the Halogen lamps.

Anyhow--Assuming you are sort of near Medford Oregon (weather wise inland a bit), using PV Watts website, 1kW panel (even number), 0.52 system efficiency, fixed array:

"Station Identification"
"City:","Medford"
"State:","Oregon"
"Lat (deg N):", 42.37
"Long (deg W):", 122.87
"Elev (m): ", 396
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 42.2"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 7.2 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 2.33, 34, 2.45
2, 3.43, 47, 3.38
3, 4.99, 74, 5.33
4, 5.53, 78, 5.62
5, 6.35, 92, 6.62
6, 6.42, 87, 6.26
7, 7.25, 99, 7.13
8, 7.14, 98, 7.06
9, 6.34, 86, 6.19
10, 4.91, 72, 5.18
11, 2.44, 34, 2.45
12, 1.92, 28, 2.02
"Year", 4.93, 828, 59.62

Assume that you want at 9 months of the year solar power only--and the other 3 months of the year you will use a backup genset... That makes February at 47 kWH per month:

• 47 kWH per month / 30 days per month = 1.567 kWH = 1,567 WH per day
• 1,720 WH per day loads / 1,567 WH per day per 1,000 Watt of panels = 1,098 watts of panels

So that will meet your load for ~9 months of the year.

Battery bank wise, we recommend 3 days of no sun, and a maximum of 50% discharge--For a work shed (not used every day)--You might go as low as 1 day of no-sun and 50% maximum battery discharge (assume 12 volt battery bank):

• 1,720 WH * 1/12 volt battery bank * 1/0.85 inverter efficiency * 1 day of no sun * 1/0.50 max battery discharge = 337 AH minimum @ 12 volts
• 1,720 WH * 1/12 volt battery bank * 1/0.85 inverter efficiency * 3 day of no sun * 1/0.50 max battery discharge = 1,012 AH maximum @ 12 volts

If much of your power is not using the inverter and using most of your power during the day (when the sun is up)--you could get away with less battery and a bit less solar panels (again, just a starting rule of thumb).

Proposed system:
- Solar Panel: One of Kyocera KD135SX-UPU - 135 Watt, 12 Volt Solar Panel (Junction Box)

Probably not big enough solar panel... Assuming February and 3.43 hours of "full sun" average, with 0.52 end to end efficiency:

• 135 Watt panel * 3.43 Hours of sun * 0.52 system eff = 241 WH per day (February)

So, that would only be 241/1,720 = 1/7th of your daily loads (February).

- Charge Controller: Xantrex 12 Amp, 12 Volt Charge Controller
- Batteries: Two of Trojan T105-RE 6 Volt, 225 AH Deep Cycle Battery
- Inverter: Samlex 1500 Watt Pure Sine Wave Inverter 115 volt AC output, 12 volt DC input
- Charger: Xantrex Truecharge2 12-Volt, 20-Amp Battery Charger
- Battery sensor: Xantrex Battery Temperature Sensor, 15 foot cable

May change depending on how much power you will need.

- One kill-a-watt meter for AC
- Two DC amp-hour/watt-hour meter (one between panel and battery, one between battery and inverter)

For the DC Amp-Hour Meters--I would suggest one Battery Monitor instead. Bi-directional measurement of AH/WH into/out of the battery bank. I think it will be easier to use and give you more information on the health of the battery bank.

- Generator: Existing Dayton 3000 watt generator (may buy a generator/welder as backup)

Take a look at a Honda eu2000i or eu1000i for your solar assist loads (charging battery bank, running small tools--The TrueCharger should run fine on the smaller eu1000i if you want a smaller genset). Tend to be much more efficient (fuel wise) vs the average 3-5 KWwatt gensets (the Honda eu2000i runs almost 10 hours on 1.1 gallons of gasoline).

- Estimated cost: A little less than $2000

Depending on what your actual sun availability and power needs (I may be 20% on the conservative side)--Your panels may cost you $2-$3+ per watt--so that would be $2-$3k+ just for solar panels. Obviously, for ~7 months of the year, a system with 1,100 watts of solar panels will generate way more than 1,098 WH per day.

Questions
- Do you see any weak links in this configuration?
- What is the difference between an electronic-based inverter like the Samlex, and a transformer-based inverter like the Outback? Will I regret buying the Samlex?
- Could I get by with a 1000 watt inverter?
- Any other suggestions? Cost is a consideration...

Revisit loads and power needs. Set against the amount of sun/season that you will be working out there (if summer only, only need 1/2 the size of solar array).

Not sure which inverter to recommend yet--Need to understand AC loads more. Certainly, you are comparing less expensive against more expensive inverters--It sounds like the less expensive inverter would meet your needs.

-Bill

ScottBarMtn

Re: Proposed small system

Wow - Excellent information that you have provided! I will take some time and rethink both my power needs, time of year, expected costs, etc, and will come back to this forum when I have a revised plan.

Thanks,

Denver

ScottBarMtn

Re: Proposed small system

After giving this some thought, I am coming to the conclusion that solar may not be a good solution for what I need.

Most of the work that I do in the workshop is typically done with these new generation of rechargeable tools using lithium batteries (e.g. Makita). They last a long time, and when recharge is needed it only takes about 20-30 minutes. When I need to use something like a drill press or table saw occasionally, it is no big deal to fire up the generator.

So that leaves indoor lighting as my main need for solar power. Unfortunately, the time that I need this most is in the winter when it is too stormy or cold outside to open the doors and let in the light, but this is exactly the same time when the solar potential is at its lowest where I live. The place does have creek running through it, which runs strong in the winter, so for my case some type of mini-hydro might be a better renewable source of power.

As a result, for the short term I am leaning toward simply purchasing the Makita work lights that use the same type of lithium battery. And perhaps one of these new breed of economical generators (e.g. Honda eu2000) for when I need the extra light or power.

Anyway, I appreciate the outstanding advice that is given on this forum - it saves a lot of wasted effort and money to say the least, and it is a pretty good way to learn all about solar.

Denver

BB.

Re: Proposed small system

Welcome to the solar forum anyway.

Hope to hear more about a hydro project from you... We do not get a lot of those here and it would be neat to see what you come up with.

Sorry about the solar--Lots of power requirements in the winter really does make solar pretty difficult to justify.

-Bill