playing around with some ideas

rcmatt007 · October 2015

I have been thinking of adding a back up system to run a few things in case of an outage, but also wiring it into an small "add on room" to provide some heating and cooling so the system will not be sitting there doing nothing. In Oklahoma we get a lot of sun, but have weather related outages

I have decent experience with construction and wiring, but this whole solar thing is new. I am also looking at ways to get the parts I need without paying a fortune for shipping (picking up at home depot and northern tool e.g.). I also understand that by running things in series I can eliminate a lot of redundant wires and keep the amperage down and reduce loss.

Here is what I am looking at:
4 grape solar 265W panels run in series which would give me approximately 124 volts (30.96 each) @ 8.56 AMPS (in series allows me to run only one line into the system from outside)
Midnight classic MPPT 250 charge controller
2 UPG 12v 250 amp batteries in series (24 volts)
magnum RD1824 inverter

My questions:

1: do I have any big mismatch?
2: I understand that in series it is best to use diodes, what should I use and where do I get them?
3: With one line coming into the charge controller I can use one disconnect. Any suggestions on what I should use?
4. I plan on running 3 or 4 lines to various places for back-up needs and the add on room. Is it okay to simply run the line from the inverter to a panel with four circuit breakers and then distribute from there

inetdog · October 2015

rcmatt007 said:

I have been thinking of adding a back up system to run a few things in case of an outage, but also wiring it into an small "add on room" to provide some heating and cooling so the system will not be sitting there doing nothing. In Oklahoma we get a lot of sun, but have weather related outages

I have decent experience with construction and wiring, but this whole solar thing is new. I am also looking at ways to get the parts I need without paying a fortune for shipping (picking up at home depot and northern tool e.g.). I also understand that by running things in series I can eliminate a lot of redundant wires and keep the amperage down and reduce loss.

Here is what I am looking at:
4 grape solar 265W panels run in series which would give me approximately 124 volts (30.96 each) @ 8.56 AMPS (in series allows me to run only one line into the system from outside)
Midnight classic MPPT 250 charge controller
2 UPG 12v 250 amp batteries in series (24 volts)
magnum RD1824 inverter

My questions:

1: do I have any big mismatch?
2: I understand that in series it is best to use diodes, what should I use and where do I get them?
3: With one line coming into the charge controller I can use one disconnect. Any suggestions on what I should use?
4. I plan on running 3 or 4 lines to various places for back-up needs and the add on room. Is it okay to simply run the line from the inverter to a panel with four circuit breakers and then distribute from there

1. You have more panel power than you need. With FLA batteries the rule of thumb would have 530AH of battery at 24V. You will have to limit the charging current in the CC to no more than 250/8 = 31.25A.
If you used AGM batteries the charging rate corresponding to the full panel power would be OK.
2. You do not need blocking diodes when using a CC. And bypass diodes will already be built into the panels. So, no.
3. No suggestion. But make sure that it is DC rated for the voltage and current and that it can be safely opened with current flowing.
4. Yes, in principle. Will this be subject to a building permit and inspection? If not, it would be a good idea to have a local electrician check your plans and your work if possible.

rcmatt007 · October 2015

thanks for the reply.

I was looking at 4 panels because they come in a four pack. I figured 265 w panels were more cost efficient than smaller 100 w panels. Would it be best then to use only 2 panels?

I suppose I could add more batteries but yikes $$$$

Any other suggestions on how I might configure this? Maybe I was going for over kill-LOL

What I was planning was something big enough to run a full size refrigerator when needed. Or run the fan part of a NG heater (we are in the country and ice storms take out power) and when not needed for back up, a window AC unit or baseboard heater for the add-on room ( about 120 square feet).

What I was looking to do was build something that could stay under $4-5000. I see now that the store is in Flagstaff and we are out there a couple of times a year visiting familt

animatt · October 2015

Not sure why you would go with that charge controller. Would think the midnite 150 or 200 would be a better fit and cheaper. But does depend on certain other factors. Possible future expansion of the series string.
And does not even need to be the midnite line. All depends on what you need/ want.

I particularly like morningstar controllers, but they do have less bells and whistles compared to midnite.

___Edit______

Forgot to mention if funds are real tight I may recommend going with a less expensive mppt controller

And getting a sine wave inverter. Either way funds tight or not sine wave is something to think about

rcmatt007 · October 2015

am trying to figure out how best to do this. You are right in that the CC is too big. It did not appear the prices were much less for smaller ones. When I looked in the store for this site, all their prebuilt systems were larger and more expensive than I wanted to go. Maybe it would best to ask them to size something for what I want to do. As I mentioned I go through Flagstaff once or twice a year and so could actually pick up what I need. When I looked at other websites, it was the shipping that made this way too expensive

animatt · October 2015

The midnite 250v is not any bigger it just accepts a higher input voltage. The ONLY reason to go with it is if you needed higher inout voltage, The maximum output of the 250 is actually lower then both the 150 and 200. 150 having the highest output

rcmatt007 · October 2015

good to know, thanks

rcmatt007 · November 2015

I am finding all the tutorials on this site incredibly useful! It looks like this would be a lot more manageable thinking 48 volts not 24. Also, it looks like I could get made in USA panels from the store in flagstaff (I drive through there at least once a year) and not be killed with shipping as well as picking up better batteries.

WaterWheel · November 2015

My old solar system was similar but smaller. Year round I used it to run a chest freezer and during the summer I used it to run a window AC unit... It provided some power for power outages and by using if to run some things year round I was able to half way justify the expense of building it.

jcheil · November 2015

That may not be "too much" solar if he has a bunch of base loads. I myself have "considerably more" solar than I would need for my battery bank if you just looked it at face value. But in reality I have a constant 1.0kw (AC) load 24/7 and an additional 2.0ish kwn in the daytime when the AC is running so the additional/extra solar panels are needed to take that into consideration.

playing around with some ideas

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