Tools for solar/off-grid system

Hi all,

I'm soon going to be a position where I can start thinking about an off-grid solar system to power a small workshop - really just enough for some lighting, charging for phones/laptop/tool batteries and to run the bench grinder or belt sander (both low-powered versions of those tools) to sharpen up chisels. I've done the math and I need 1-2kWh of energy and around 800w continuous (say 2kW surge) for the charging, lighting and the saw.

Anyway, my question is about tooling for setting up the system. I have a set of cheapo wire snips that have crimps built into them but they are not very good and I doubt they would cope with the larger wire gauges for the battery cables (say 25mm2/4 gauge or even 50mm2/1 gauge). I also have a set of slightly less cheap wire strippers that I never use - I tend to use some side-cutters or a utility knife and do it manually. I do have a heat gun that I can use for the heatshrink insulation, however. Finally, I have a decent (Fluke brand) multimeter; my unbranded one finally gave up so I upgraded to something decent and reliable.

Does anyone have any recommendations for crimps, in particular, or other good tools that I can consider purchasing?

Many thanks

I set up a 2 KW homestead system with just basic tools...snips, pliers, etc.  Stripped wires with a pocketknife.  I did have a pretty good multimeter, useful for testing voltages etc. and checking over your work.  Batteries in the system (assuming lead-acid batteries that need maintenance) require special things like a hygrometer, funnels etc. for topping them up (that are not your kitchen funnels!) and heavy rubber gloves, and pliers/wrenches with rubber wrapped handles to avoid the dangers of an accidental short.

Rather than focusing attention on crimping right now, I'd recommend you focus more attention on overall system design, and worry about crimping later.

The grinder or sander will be your biggest loads, and I focus on supplying those first.  Other stuff is trivial compared to the draws those two will need.  If you focus your attention on those, the rest will be easy.

A good rule of thumb I follow is to have about 2X your largest load as for how many solar Watts you need.  So with a 800W load, maybe 1600W of solar panels.  The good news is that high-voltage residential panels are getting dirt-cheap right now, and you can find 30V/250W panels for 40-50$ right now.  So, six of those would be close to perfect in terms of meeting your wattage needs.  That's about 300$ right now in the cash and carry market.  Don't order panels online!  You will pay outrageous shipping fees.  Shop locally on Craigslist, with cash and carry purchases.

The amperage to handle 1600W is a bit too high for a basic 12V system, so I'd recommend going with at least 24V.  That's what I have in my workshop right now.  In terms of a budget charge controller, take a look at Epver's new XTRA Series MPPT Solar Charge Controller.  40A of current at up to 150V, for only 120$.  40A would be good for more than 1000W of panels.  In general, it's OK to exceed the recommended amps of a unit.  Under no circumstances though should you ever exceed the voltage.  Remember though that the voltage of panels goes up as the temperature goes down.  A good safety margin is ~20-25%.  So, for a 150V controller, never surpass ~120Voc.  That should be good for three 30V panels in series.  Their Voc at freezing is going to be ~40Voc.

I have a clamp meter with "inrush current" capability.  What I've found is that the brief starting surge for motors that start under load is ~4X.  So, for that grinder or sander that needs 800W to run, expect them to need up to 3200W for less than 1 second to start.  So, I'd suggest shopping for at least a 3000W 24V inverter.  Get Sine-Wave for anything that will be running an electric motor.  Cheaper modified sine-wave models are well-known for burning out electric motors in short order.

Lastly, you'll need batteries.  You might want to take a look at CostCo's 210Ah 6V golf-cart battery.  At 110$ right now, you'd need four of them in series to make a 24V battery bank.  That would be 440$ plus tax and core charges.  Assuming you don't drain these lead-acid batteries more than 50%, you'd have 2.5kWh of available power.

If you built a rotating array frame like I have, you could reduce your panels needed to down to 1000W.  My frame easily holds four large residential panels in portrait, but can hold as many as six oriented in landscape.  I just sunk a 3.5" schedule 40 pipe in concrete, and slipped a 4" schedule 40 pipe on top of it.  The array frame is welded to the top of the 4" pipe.  This will allow you to rotate (by hand) East in the morning, South around noon, and West in the afternoon.  That will basically double the number of watthours you can make in a day.

BTW, I've made excellent terminals for my solar wire with cut lengths of copper tubing.  For my 000 battery wire, I belled 1/2" copper tubing, slid the wire halfway inside, then flattened the other end.  Once flattened, I soldered the wire to the tubing.  I then drilled 5/16" inch holes in the flattened ends to accommodate that stainless steel mounting bolts I used to attach the batteries to the inverter.

Michael Qulek wrote:Rather than focusing attention on crimping right now, I'd recommend you focus more attention on overall system design, and worry about crimping later.

Thanks for the advice. I am pretty confident with my system design, although I didn't go into too much detail in my first post. I was hoping to get some info about what tools worked well and what to avoid so I don't buy something I later have to upgrade as I've already made that mistake with a soldering iron and my wire strippers.

Michael Qulek wrote:
The grinder or sander will be your biggest loads, and I focus on supplying those first.  Other stuff is trivial compared to the draws those two will need.  If you focus your attention on those, the rest will be easy.

Agreed. The bench grinder runs at 340W so I'm expecting a surge of ~1200W. I don't have a way of accurately measuring that, however.

My fast charger for the tool batteries is 265W.

Michael Qulek wrote:
A good rule of thumb I follow is to have about 2X your largest load as for how many solar Watts you need.  So with a 800W load, maybe 1600W of solar panels.  The good news is that high-voltage residential panels are getting dirt-cheap right now, and you can find 30V/250W panels for 40-50$ right now.  So, six of those would be close to perfect in terms of meeting your wattage needs.  That's about 300$ right now in the cash and carry market.  Don't order panels online!  You will pay outrageous shipping fees.  Shop locally on Craigslist, with cash and carry purchases.

I've been advised to consider the peak sun hours (1kW/h/m3) for my location. This works out at about 1 hour during the winter and 8 hours during the summer. From this, and knowing that my daily usage will be <= 1.2kWh, I'm aiming for 1.2kW of panels or above to keep the batteries topped up over the winter. I appreciate that this won't be foolproof as there will be multiple days without sun but I do not need to use the power there in that case, I'll just leave it until the batteries reach a good level of charge.

As for panels, I'm going to buy new 425W 36V panels as they are going for very cheap right now (£60/$80 including delivery). I'm going to start with 3 of those in series and use a 150v 35A MPPT charge controller.

Michael Qulek wrote:
The amperage to handle 1600W is a bit too high for a basic 12V system, so I'd recommend going with at least 24V.  That's what I have in my workshop right now.  In terms of a budget charge controller, take a look at Epver's new XTRA Series MPPT Solar Charge Controller.  40A of current at up to 150V, for only 120$.  40A would be good for more than 1000W of panels.  In general, it's OK to exceed the recommended amps of a unit.  Under no circumstances though should you ever exceed the voltage.  Remember though that the voltage of panels goes up as the temperature goes down.  A good safety margin is ~20-25%.  So, for a 150V controller, never surpass ~120Voc.  That should be good for three 30V panels in series.  Their Voc at freezing is going to be ~40Voc.

Agreed! I'm going to use a 48v system. This might be overkill for such a small system but I'd like room to expand in the future. Plus, more voltage = less current going through the wires = less copper needed!

As I mention above, I'm planning on using a 150V 35A charge controller for the batteries. The 3x 36Voc panels shouldn't exceed this, although there will be a slightly lower safety margin than you suggest. The figures I was given are to expect a ~5% increase in Voc from 25C to 0C but, even at 10%, I'm still under 120V. It also rarely gets that cold where I live, most of the time we hover just above zero (or as high as 8C) during the daylight in mid-winter.

Michael Qulek wrote:
I have a clamp meter with "inrush current" capability.  What I've found is that the brief starting surge for motors that start under load is ~4X.  So, for that grinder or sander that needs 800W to run, expect them to need up to 3200W for less than 1 second to start.  So, I'd suggest shopping for at least a 3000W 24V inverter.  Get Sine-Wave for anything that will be running an electric motor.  Cheaper modified sine-wave models are well-known for burning out electric motors in short order.

~4x is a bit more than I was expecting! At 340W, the grinder will pull ~1400W during the surge. I don't know how much power the belt sander uses off-hand but I suspect it will be a little more. The inverter that I am planning to buy is rated for 1200W continuous / 2400W surge so it should cope. I'm looking exclusively at Victron kit by the way, they are very popular here.

Michael Qulek wrote:
Lastly, you'll need batteries.  You might want to take a look at CostCo's 210Ah 6V golf-cart battery.  At 110$ right now, you'd need four of them in series to make a 24V battery bank.  That would be 440$ plus tax and core charges.  Assuming you don't drain these lead-acid batteries more than 50%, you'd have 2.5kWh of available power.

I'm looking at LiFePO batteries as, at least at the suppliers I've looked at, they work out cheaper per Wh than lead-acid and have a much deeper DoD too (95% vs. 50%). They are still expensive as the smallest size I can buy is 2.4kWh @ 48v but they should outlast the lead-acid batteries, plus they have a 10 year warranty on them.

Michael Qulek wrote:
If you built a rotating array frame like I have, you could reduce your panels needed to down to 1000W.  My frame easily holds four large residential panels in portrait, but can hold as many as six oriented in landscape.  I just sunk a 3.5" schedule 40 pipe in concrete, and slipped a 4" schedule 40 pipe on top of it.  The array frame is welded to the top of the 4" pipe.  This will allow you to rotate (by hand) East in the morning, South around noon, and West in the afternoon.  That will basically double the number of watthours you can make in a day.

That is super nice! Well done. Are there any bushes or bearings between the two pipes?

Michael Qulek wrote:
BTW, I've made excellent terminals for my solar wire with cut lengths of copper tubing.  For my 000 battery wire, I belled 1/2" copper tubing, slid the wire halfway inside, then flattened the other end.  Once flattened, I soldered the wire to the tubing.  I then drilled 5/16" inch holes in the flattened ends to accommodate that stainless steel mounting bolts I used to attach the batteries to the inverter.

Also nice to read that you can make connectors like that. Do you have any idea how much current they can cope with?

Thanks for taking the time to reply

I'd suggest that only a 5% overvoltage estimate is too low.  Midnight Solar recommends 12% for 0C (freezing).  To be really safe, I'd suggest you plug your panel specifications into Midnight's string calculator.  That will give you an accurate Voc at whatever your winter low is.

http://www.midnitesolar.com/sizingTool/index.php

For my own arrays, with three panels in series, I went with Midnight's 200V controller.  That gives me a very broad safety margin.  If you haven't gotten your charge controller yet, I'd really recommend you get a higher voltage model, and also higher amperage.  If you plan on going with 48V, which I think is a good idea, you'll most likely want to upgrade your system in the future.  Limiting yourself to only 35A is going to hobble yourself.  In terms of those home-made terminals, I was daily passing 60-65A through them with no issues.

1275W of solar is quite small for a 48V system.  I really think you should plan for upgrading your system in the future.  For my own cabin, I've got a 48V system that can make American split-phase 120/240VAC, which I use to power my well-pump.  That's a monster that needs ~9200W at startup, and 2000W to run.  I understand you don't need that much power, but who's to say what you will want in the future.  Make sure you have a clear path to future upgrades.

One thing you can do now with that idea in mind is going a gauge or two thicker in copper wire than what you need today.  Besides the extra safety margin, you'll save money in the long run because you won't have to rip out thinner wire when you decide you want to upgrade.  Believe me, I know.  I've upgraded my cabin system three times since I installed it in 2017.  I've added an additional 1000W with each upgrade whenever I got good deals on Craigslist panels.  I've got 4 gauge between the charge controller and batteries, and 0000 wire between the batteries and the inverter.

I'd encourage you to get a clamp meter that can read inrush.  I started out with an expensive Fluke meter, but found a much cheaper alternative that I use routinely now, a UniT-216C  I can read both AC and DC amps, AC inrush, and regular volts and ohms.  In the US, it's about 75$ on Ebay right now.

One last thing.  Don't believe the salesman hype about the deep discharges of Li batteries.  Although they do have a deeper discharge curve than lead-acid, very deep discharges shorten their lives almost as much as lead acid.  If you want to have long battery life, plan on never discharging them more than 50-75% on a daily basis.  You would be wise to double your battery capacity right now in anticipation of lower discharges.

Hi Luke,
Fun problems to solve! Going back to your question about crimping, it depends on how often you might do this. I have a $50 crimper from Amazon/China that has a rotary die at the tip, and can do from like 8awg to 0awg (but I have popped one at the high gauges, so really it tops out at 2awg or 4awg, and I use my hydraulic one above that).

I don't know how game you are to solder, but filling your crimped terminal will guarantee no relaxation over time, especially on battery terminals. Your heat gun may allow you to do this without new tooling, depending on how toasty it gets.

Michael makes a good point about your cold overvoltage case, but just do the math with the datasheet, and remember that panels can get many degrees cooler than air temperature if the sky is clear, due to radiative loss to space, so leave margin.

Depending on the motor, surge can indeed be large as Michael also noted. A good inverter (with adequate internal inductance & capacitance) will act like a soft starter and be ok. A cheap one will trip and you will never start your tool. I would consider whether you can parallelize the inverters you have, or go a bit bigger. Running 240v tools is actually much kinder to a solar system than 120v, because of the balanced load and lower running and surge amperage, but that may not be an option. I like to have 240v available for many tools, but you know your needs.

Good luck!
Mark

Michael, thanks again for the helpful comments.

Michael Qulek wrote:I'd suggest that only a 5% overvoltage estimate is too low.  Midnight Solar recommends 12% for 0C (freezing).  To be really safe, I'd suggest you plug your panel specifications into Midnight's string calculator.  That will give you an accurate Voc at whatever your winter low is.

http://www.midnitesolar.com/sizingTool/index.php

I have plugged the specs for the panels I plan to use into this and it came out with a max Voc of 120.1 @ -30C. I doubt I'll ever get that cold so I think I'll be safe with a 150V charge controller. Thanks for the link though, it was helpful.

Michael Qulek wrote:For my own arrays, with three panels in series, I went with Midnight's 200V controller.  That gives me a very broad safety margin.  If you haven't gotten your charge controller yet, I'd really recommend you get a higher voltage model, and also higher amperage.  If you plan on going with 48V, which I think is a good idea, you'll most likely want to upgrade your system in the future.  Limiting yourself to only 35A is going to hobble yourself.  In terms of those home-made terminals, I was daily passing 60-65A through them with no issues.

1275W of solar is quite small for a 48V system.  I really think you should plan for upgrading your system in the future.  For my own cabin, I've got a 48V system that can make American split-phase 120/240VAC, which I use to power my well-pump.  That's a monster that needs ~9200W at startup, and 2000W to run.  I understand you don't need that much power, but who's to say what you will want in the future.  Make sure you have a clear path to future upgrades.

I have toyed with getting a higher amperage model and may yet decide to do so. I will undoubtedly upgrade my system in the future but it might be for a different building, or with a separate charge controller and a new array (for redundancy, plus the option of facing a different direction). Right now budget is a big concern and it's definitely limiting my options. As money allows, I'll probably try and install another solar array and add to the system that way.

Michael Qulek wrote:One thing you can do now with that idea in mind is going a gauge or two thicker in copper wire than what you need today.  Besides the extra safety margin, you'll save money in the long run because you won't have to rip out thinner wire when you decide you want to upgrade.  Believe me, I know.  I've upgraded my cabin system three times since I installed it in 2017.  I've added an additional 1000W with each upgrade whenever I got good deals on Craigslist panels.  I've got 4 gauge between the charge controller and batteries, and 0000 wire between the batteries and the inverter.

I absolutely agree with this. I am pretty safety-conscious anyway and tend to 'overbuild' things. Thicker timbers, thicker wires, larger fixings. I'd rather spend a bit more today and not have to redo or repair something down the line.

I just looked up the cross-sectional area of 0000 wire - it is huge! I am planning to use 0 gauge (50mm2) between the batteries and a bus bar and then 4 AWG (25mm2) or 6 AWG (16mm2) between the bus bar and the charge controller/inverter. The fittings for solar panels over here only allow for 12 AWG (4mm2) or 10 AWG (6mm2) so I'll use the larger of the two.

Mark Miner wrote: Going back to your question about crimping, it depends on how often you might do this. I have a $50 crimper from Amazon/China that has a rotary die at the tip, and can do from like 8awg to 0awg (but I have popped one at the high gauges, so really it tops out at 2awg or 4awg, and I use my hydraulic one above that).

I don't know how game you are to solder, but filling your crimped terminal will guarantee no relaxation over time, especially on battery terminals. Your heat gun may allow you to do this without new tooling, depending on how toasty it gets.

Cheers Mark! Exactly the answers I was looking for. It sounds like I might need to buy or borrow a hydraulic crimper for the lugs on the battery wires. I'll try and get something for the smaller stuff and I guess Amazon might be a good place to start looking, as much as I'd rather avoid it.

As for soldering the crimped terminal, that's a great shout and not something I would have thought of. It's a pretty entry-level heat gun but I think I can borrow a big soldering iron or a blow torch from a friend.

Thanks

I have plugged the specs for the panels I plan to use into this and it came out with a max Voc of 120.1 @ -30C. I doubt I'll ever get that cold so I think I'll be safe with a 150V charge controller. Thanks for the link though, it was helpful.


Can you please post the actual specifications of those panels?  I am a bit suspicious, and I think there might be some mistakes here?  With three 72-cell panels in series, I routinely see 120-125VDC on regular summer days, not the winter.  To me that 120V reading at a frigid -30 doesn't seem right?  I want to make sure you are not getting advice that could result in a fire at your place.

Of course. The panels are here.

The specs are posted in "STC" (standard test conditions) and "NOCT" (nominal operating cell temperature). I used "STC".

Parameter	Value
Vmpp	31.42v
Impp	13.05A
Voc	37.4v
Isc	13.84A
V temp coeff	-0.265%/°C
I temp coeff	+0.05%/°C

Plugging those values in again, I get 128.7v @ -30°C. I think I must have accidentally used a "NOCT" value for one or more parameters previously, which would explain the difference of 8v in my two numbers.

If you think I'm doing something wrong, please do let me know!

OK, those numbers appear better.  I think you are good to go.

Michael Qulek wrote:Rather than focusing attention on crimping right now, I'd recommend you focus more attention on overall system design, and worry about crimping later.

The grinder or sander will be your biggest loads, and I focus on supplying those first.  Other stuff is trivial compared to the draws those two will need.  If you focus your attention on those, the rest will be easy.

A good rule of thumb I follow is to have about 2X your largest load as for how many solar Watts you need.  So with a 800W load, maybe 1600W of solar panels.  The good news is that high-voltage residential panels are getting dirt-cheap right now, and you can find 30V/250W panels for 40-50$ right now.  So, six of those would be close to perfect in terms of meeting your wattage needs.  That's about 300$ right now in the cash and carry market.  Don't order panels online!  You will pay outrageous shipping fees.  Shop locally on Craigslist, with cash and carry purchases.

The amperage to handle 1600W is a bit too high for a basic 12V system, so I'd recommend going with at least 24V.  That's what I have in my workshop right now.  In terms of a budget charge controller, take a look at Epver's new XTRA Series MPPT Solar Charge Controller.  40A of current at up to 150V, for only 120$.  40A would be good for more than 1000W of panels.  In general, it's OK to exceed the recommended amps of a unit.  Under no circumstances though should you ever exceed the voltage.  Remember though that the voltage of panels goes up as the temperature goes down.  A good safety margin is ~20-25%.  So, for a 150V controller, never surpass ~120Voc.  That should be good for three 30V panels in series.  Their Voc at freezing is going to be ~40Voc.

I have a clamp meter with "inrush current" capability.  What I've found is that the brief starting surge for motors that start under load is ~4X.  So, for that grinder or sander that needs 800W to run, expect them to need up to 3200W for less than 1 second to start.  So, I'd suggest shopping for at least a 3000W 24V inverter.  Get Sine-Wave for anything that will be running an electric motor.  Cheaper modified sine-wave models are well-known for burning out electric motors in short order.

Lastly, you'll need batteries.  You might want to take a look at CostCo's 210Ah 6V golf-cart battery.  At 110$ right now, you'd need four of them in series to make a 24V battery bank.  That would be 440$ plus tax and core charges.  Assuming you don't drain these lead-acid batteries more than 50%, you'd have 2.5kWh of available power.

If you built a rotating array frame like I have, you could reduce your panels needed to down to 1000W.  My frame easily holds four large residential panels in portrait, but can hold as many as six oriented in landscape.  I just sunk a 3.5" schedule 40 pipe in concrete, and slipped a 4" schedule 40 pipe on top of it.  The array frame is welded to the top of the 4" pipe.  This will allow you to rotate (by hand) East in the morning, South around noon, and West in the afternoon.  That will basically double the number of watthours you can make in a day.

BTW, I've made excellent terminals for my solar wire with cut lengths of copper tubing.  For my 000 battery wire, I belled 1/2" copper tubing, slid the wire halfway inside, then flattened the other end.  Once flattened, I soldered the wire to the tubing.  I then drilled 5/16" inch holes in the flattened ends to accommodate that stainless steel mounting bolts I used to attach the batteries to the inverter.

I disagree with the recommendation for the golf cart batteries. 5kwh of lithium with full usable capacity can be had for about $800 if you play your cards right. Lifespan is 3-4x that of lead acid and it performs better to boot. It’s straight up cheaper over the life of your system if you plan to use it longer than 7 years.

Also, just buy crimp cable lugs. They’re UL listed and chances are your local electrical supply house will let you borrow or rent a hydraulic crimper. Don’t DIY something that will be carrying big amps. Don’t be afraid of big amps but build appropriately for them.

Otherwise I think this advice is good.