Constructing a basic 1kw off grid system - Can you point me in the right direction?

[lpolson07]

Hey everyone, I am new here but have been doing quite a bit of reading on solar panels both here and on the internet in general. I think I would like to start purchasing components to get a 1kw system up and running this coming spring. I live in Des Moines, Iowa and we are fairly close to our first snowfall which will last into late march or possibly early april of 2015. At this point I will begin constructing my new system.

The usage of the solar panels would ideally be to run my household lights (led), TV and other miscellaneous items such as cell phone chargers, laptop chargers, roku, dvd players, game consoles (seldom used) and whatever else is in the area where I install an outlet. I do not plan on running my desktop computer, refrigerator or any other large appliance on this size system.

I would like opinions on the direction I am going and recommendations as to what looks OK or what could be done better. I know there is always room for improvement. Here's what I am thinking:

250 watt polycrystalline panels x 4

6v golf cart batter x 4 (wired 2 in series for 12v and then in parallel ---> :: ) (not entirely certain if this size battery bank matches my 1kw system or not)

MPPT Charge Controller - This one has be a bit confused, From what I understand these are more efficient/worthwhile than a PMW Charge Controller, is this correct? I am not against spending the money necessary to get a decent one (MPPT) but much more than $175 might not be feasible for me at this point in time.

Brackets - I haven't found affordable brackets yet - guidance here would be awesome!

Wiring - this I am also clueless on - have an electrician to help make sure everything looks good but I am a plug-n-play person that likes to have all the appropriates on hand before starting the task. What gauge wiring do I need for each part of the system?

Power Inverter - I have limited experience with these but I know we need to convert DC to AC for my 120v appliances to actually work. I am thinking 2-3kw inverter would suffice but would prefer to buy the right gear upfront rather than upgrade later.

I would also like to be able to expand this system later to 2-3kw if that is possible.


Panels I am looking at seem affordable and have ok reviews from the few I have found - any personal stories out there in regards to these?

http://www.gogreensolar.com/products/suntech-power-stp250-20-wd

What are your recommendations in these areas? I look forward to hearing from you guys - the posts I have read thus far have been very beneficial.

-Larry

[Mike90250]

....
The usage of the solar panels would ideally be to run my household lights (led), TV and other miscellaneous items such as cell phone chargers, laptop chargers, roku, dvd players, game consoles (seldom used) and whatever else is in the area where I install an outlet. I do not plan on running my desktop computer, refrigerator or any other large appliance on this size system........

What are your recommendations in these areas? I look forward to hearing from you guys - the posts I have read thus far have been very beneficial.

-Larry

I recommend, that for 25% of the cost of installing a 1Kw system, you should spend on electrical appliance upgrades (Fridge, HVAC system motors, Lighting updates). Since you are "on-grid" it makes no sense to spend thousands of dollars to move some low wattage appliances off grid to save $80 a year.
If you are in an area that often looses power for days at a time, maybe a backup generator and transfer switch are worth looking into also.

[Sunking]

Need to poke some hole sin your plans. First one you need to ask yourself why you want to take anything off-grid? Don't tell us to save money or the earth because that is impossible. Anything you take off grid is going to cost you roughly 10 times more for power than what you pay the power company for the rest of your life.

Moving on. 12 volts is for toys and RV's, and at 1000 watt panel power is no toy and at least a 24 volt and 48 volt battery system. It is possible to have a 1000 watt 12 volt system but will require no less than a 80 amp MPPT controller. Use 24 volts and that drops to a 40 amp MPPT controller, and 20 amps at 48 volts.

With 250 watt panels means they are grid tied panels and thus require that you use MPPT controllers. PWM is for toys and folks who do not know the difference. If you used 250 watt panel with a PWM controller would result in turning your 1000 watt panel into roughly 300 watts. Just as well throw 3 of the panels away and use a MPPT controller on the one panel remaining.

Lastly if you use 1000 watts on a 12 volt 440 AH is to small. It would require a 3rd battery string to get to the minimum 660 AH to handle 80 amps of charge current. That brings us to the next battery issue. You never want to use parallel string sof batteries unless absolutely necessary, and in your case there is no reason to use parallel batteries. If you need 660 AH, buy 660 AH batteries. What you could do is buy 8 of the golf cart batteries wire them in series to make 48 volts 220 AH. With a 20 amp MPPT controller would be nicely matched up and cost a whole lot less than you have planned so far.

[lpolson07]

Need to poke some hole sin your plans. First one you need to ask yourself why you want to take anything off-grid? Don't tell us to save money or the earth because that is impossible. Anything you take off grid is going to cost you roughly 10 times more for power than what you pay the power company for the rest of your life.

Moving on. 12 volts is for toys and RV's, and at 1000 watt panel power is no toy and at least a 24 volt and 48 volt battery system. It is possible to have a 1000 watt 12 volt system but will require no less than a 80 amp MPPT controller. Use 24 volts and that drops to a 40 amp MPPT controller, and 20 amps at 48 volts.

With 250 watt panels means they are grid tied panels and thus require that you use MPPT controllers. PWM is for toys and folks who do not know the difference. If you used 250 watt panel with a PWM controller would result in turning your 1000 watt panel into roughly 300 watts. Just as well throw 3 of the panels away and use a MPPT controller on the one panel remaining.

Lastly if you use 1000 watts on a 12 volt 440 AH is to small. It would require a 3rd battery string to get to the minimum 660 AH to handle 80 amps of charge current. That brings us to the next battery issue. You never want to use parallel string sof batteries unless absolutely necessary, and in your case there is no reason to use parallel batteries. If you need 660 AH, buy 660 AH batteries. What you could do is buy 8 of the golf cart batteries wire them in series to make 48 volts 220 AH. With a 20 amp MPPT controller would be nicely matched up and cost a whole lot less than you have planned so far.

Alright, here is my check on learning...Let me know how it looks.

1. Why take anything off-grid...saving money is secondary and saving the earth not a concern although nice thought. Some people like to party, do drugs or drive expensive cars. I prefer other hobbies such as metal casting, 3-D printing or possibly managing a mini-solar array that can provide some level of ROI for me (metalcasting and 3-D printing do not, can you believe it?). While the overall cost isn't likely to save me anything long term, solar energy has peaked my curiosity which is enough to motivate me to push forward.

2. 12v is rubbish - check, voltage up = charge controller down - check. The higher the voltage, i.e. 24, 36, 48 the less energy losses I will realize from panel to outlet or battery to outlet? I think I understand this part.

3. MPPT vs PWM - now I know the diffs, kind of, and thank you. PWM = inneficient and a waste of mucho wattage. PWM is childs play and a 1kw system has surpassed childs play.

4. Batteries in series are the way to go (........) - check, batteries in parallel ( ::: ) should be a last resort - check


I appreciate the feedback that you have both provided!

Any input on power inverters or gauge of wire?

[SunEagle]

Alright, here is my check on learning...Let me know how it looks.

1. Why take anything off-grid...saving money is secondary and saving the earth not a concern although nice thought. Some people like to party, do drugs or drive expensive cars. I prefer other hobbies such as metal casting, 3-D printing or possibly managing a mini-solar array that can provide some level of ROI for me (metalcasting and 3-D printing do not, can you believe it?). While the overall cost isn't likely to save me anything long term, solar energy has peaked my curiosity which is enough to motivate me to push forward.

2. 12v is rubbish - check, voltage up = charge controller down - check. The higher the voltage, i.e. 24, 36, 48 the less energy losses I will realize from panel to outlet or battery to outlet? I think I understand this part.

3. MPPT vs PWM - now I know the diffs, kind of, and thank you. PWM = inneficient and a waste of mucho wattage. PWM is childs play and a 1kw system has surpassed childs play.

4. Batteries in series are the way to go (........) - check, batteries in parallel ( ::: ) should be a last resort - check


I appreciate the feedback that you have both provided!

Any input on power inverters or gauge of wire?

You got everything right except for part that a "mini-solar array will provide you with some level of ROI". Unfortunately just like the metalcasting and 3-D printing a solar off grid system will cost you more and you will never get back what you put into it.

Now a Grid Tie solar system fully sanctioned and approved by your local inspector and POCO can have an ROI depending on where you live, how much electricity you use and what your POCO $/kWh rate is. Places like CA (very high $/kWh charge) have shorter paybacks then places like Texas (very low $/kWh charge).

If you are interesting in building a small off grid system to learn about the technology then go ahead but once you get past the 250 watt point the system gets expensive and will become extra work to keep those batteries healthy.

Oh almost forgot. With any off grid battery system you need to have a generator in case you do not get enough sun to charge those batteries as well as being able to EQ them every once in a while.

[Mike90250]

....Oh almost forgot. With any off grid battery system you need to have a generator in case you do not get enough sun to charge those batteries as well as being able to EQ them every once in a while.

He has grid, so a plug in 12V smart charger that fits the battery profile and has an EQ cycle, would work for battery pairs AND his vehicles.


As to the size of the inverter, and the wire gauge, now the home work begins. You get to figure your loads, in excruciating detail, into watt hours used.
Fan 90 watts 14 hours = 1260 watt hours

Add all your loads up for total wh used in 1 day/night
These are "fun" loads, and you can always use the grid instead, if you get a cloudy week, unless you want to scale it for a SHTF scenario.
so for fun, your battery bank Watt Hours should be 3x the daily calculation, but no smaller than (big math calculations) 10% of your battery charge current in Amps:AmpHours
PV controller produces 40 amps, needs a 400ah bank to not be BBQ'd by the charge current.

Wires need to be large enough to carry that amperage with less than 3% loss (calculator link in my .sig)

Inverter needs to be sized to seldom be loaded more that 80% of it's rating..

[SunEagle]

He has grid, so a plug in 12V smart charger that fits the battery profile and has an EQ cycle, would work for battery pairs AND his vehicles.


As to the size of the inverter, and the wire gauge, now the home work begins. You get to figure your loads, in excruciating detail, into watt hours used.
Fan 90 watts 14 hours = 1260 watt hours

Add all your loads up for total wh used in 1 day/night
These are "fun" loads, and you can always use the grid instead, if you get a cloudy week, unless you want to scale it for a SHTF scenario.
so for fun, your battery bank Watt Hours should be 3x the daily calculation, but no smaller than (big math calculations) 10% of your battery charge current in Amps:AmpHours
PV controller produces 40 amps, needs a 400ah bank to not be BBQ'd by the charge current.

Wires need to be large enough to carry that amperage with less than 3% loss (calculator link in my .sig)

Inverter needs to be sized to seldom be loaded more that 80% of it's rating..

Mike

All good points. I should have added "if you have power outages then a generator is a must for a solar off grid system".

One area that concerns me is that he wants to buy 1000 watts of panels and wants a 12volt battery system. That requires an 80Amp CC and a 800Ah battery.

Sure if he wants to build a "fun" system then fine. But he doesn't need to start with those 1000 watts of panels.

[lpolson07]

Mike

All good points. I should have added "if you have power outages then a generator is a must for a solar off grid system".

One area that concerns me is that he wants to buy 1000 watts of panels and wants a 12volt battery system. That requires an 80Amp CC and a 800Ah battery.

Sure if he wants to build a "fun" system then fine. But he doesn't need to start with those 1000 watts of panels.

I think you may have misunderstood the 12v system idea...its not that I "want" that but rather I wasn't aware of the alternative until sunking provided some valuable insight....

I do currently have a generator as well.

[Sunking]

Only thing I can add, is 1000 watt system is not an experiment or toy to learn with. Just remember ROI is impossible with a off-grid battery system. So if you think there is one I got a great investment for you that will make us both tickled pink. For every $1 you invest into my mutual fund , at the end of 5 years I will give you 10-cents and call it even. I think you wil be so happy you will beg me to do it again which I will be more than happy to do.

[lpolson07]

Only thing I can add, is 1000 watt system is not an experiment or toy to learn with. Just remember ROI is impossible with a off-grid battery system. So if you think there is one I got a great investment for you that will make us both tickled pink. For every $1 you invest into my mutual fund , at the end of 5 years I will give you 10-cents and call it even. I think you wil be so happy you will beg me to do it again which I will be more than happy to do.

It appears you as well have misunderstood what I was attempting to say when I made the comparison of other hobbies in relation to a solar setup.

I came here for information and guidance, not to be told how I should spend my money on other things because its the choice each of you would make personally.

Furthermore I chose this size system because I believe it will suit its immediate purpose. As I was taught in the Army, you train how you fight and that is what I'm attempting to do in this instance. I am not going to construct a useless 50-100w system when I know its not for me...

Thanks for the insight that was provided...have a good one.

[SunEagle]

It appears you as well have misunderstood what I was attempting to say when I made the comparison of other hobbies in relation to a solar setup.

I came here for information and guidance, not to be told how I should spend my money on other things because its the choice each of you would make personally.

Furthermore I chose this size system because I believe it will suit its immediate purpose. As I was taught in the Army, you train how you fight and that is what I'm attempting to do in this instance. I am not going to construct a useless 50-100w system when I know its not for me...

Thanks for the insight that was provided...have a good one.

Ok. So forgetting the cost and why you want to build your system I will try to give you an idea of what components you will need.

First off with an off grid system you can't start small and grow. Adding new batteries to an old set just hurts the new batteries. Getting a PWM charge controller or a small MPPT in the beginning means you will have to replace it with a bigger one.

So for a 1000 watt ( 4x 250watt) solar panel 24volt system you should get an MPPT charge controller rated 45amps. 4 x 6volt batteries rated about 800 to 1000AH. A 24volt inverter rated no more than 2000watts max. You will wire the panels in series to the charger controller (make sure that CC is rated for the total Voc of the 4 panels plus a little more). The wire between the panels and charge controller need to be rated about 1.25% greater than the Imp rating of one of those panels, and sized not to exceed a 3% voltage drop. The wire between the charge controller and batteries (depending on the length) should be rated 50Amps and have a 50amp fuse.The wire between the batteries and inverter needs to be rated about 100amps with a 100 amp fuse. This system should get you about 5000 to 6000 watt hours a day if you don't discharge your batteries more than 25%. I do not know if that is enough or too much since you haven't determined your actually daily watt hour needs.

You can go to a 48volt system which requires 4 more 6 volt batteries. This will reduce the size of your wires and fuses due to the higher voltage as well as your Charge controller amp rating. The area you have to watch out for is that you will still need enough amp output for that CC to keep that battery system happy with a C/8 to C/12 charge rate where C = Battery system AH.

Hope that helps you.

[lpolson07]

It most certainly does. Thank you for all of the good advice