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Newbie solar idea - Pahrump, NV

mgoswald

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Joined
Jan 9, 2022
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9
Hello all,

I am literally a zero experience newb. I do have experience working in power generation, but I've never set up a solar system - ever.

I live in Pahrump, NV where the price per kw/h is about 12.5 cents - regardless of time of day. Also the local power utility will not allow solar systems to exceed 75% of the average annual usage of the customer.

I live on an acre and have a 50' x 30' shop in my back yard on a dedicated 60 amp circuit (with nothing but led lights inside). I would install my solar array on the roof of this shop.

Here's a concept design I have been thinking about:

Sizing a solar array to be significantly larger than 100% of my grid usage. The array would feed the grid during day, but would also charge a battery stack so that the house could run off of battery during the night. Without going into a deep dive of all the details . . . this was my initial thought.

I know many calculations would need to be done regarding demand and size/scope of the system, but this is my way of maximizing my system and to somewhat avoid the 75% cap set by the utility.

Any thoughts or advice would be appreciated.

Thanks!

Mike
 
I'm a bit fuzzy about this 75% cap your utility puts upon you?

Say you consume on average 50kWh of power each day, so annually you'd consumer 50kWh X 365days = 18250kWh.

Are they saying that you can not install a system that would make more than 75% of that annually? That would be 18250kWh X 0.75 = 13,688kWh. Is that the correct logic? That would mean you can not make a system that makes more then 37.5kWh of power per day?

Assuming you get 5sunhours in Pahrump in the summer, that works out to be a 7500W solar array? That is a really big array! 100% would be 10,000W array!

More details about your contract would be very helpful.
 
Sorry for the late reply. Yes, our utility will not allow solar builds to exceed 75% of the average annual usage. So, my thought initially was simply to build a stand alone system that would support our house with a backup grid connection (fail-over) which costs $25.00 per month - or something similar. I have a large home (3500 sq/ft) so the system would need to be . . . robust.

My current concept (as I previously referenced) would be to do a grid tie so the solar would feed the grid during the day and run off batteries during the night . . .? This concept would require more solar than what we use during the day to charge the batteries - as they would be drawn down from the previous night. We have 8 tons of HVAC.

Any thoughts about all of this would be really appreciated. Again, I am a total newbie at this. . . .

Thanks!
 
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I suppose this could be managed by the proper programing of a hybrid inverter.

Your first step would be an itemized list of what needs powering and when. I'm assuming in Pahrump, that will be night-time air-conditioning and refrigeration. Intuitively, this doesn't seem like the best strategy, because you are storing very expensive electricity for use at night when electrical rate are lowest. You need to remember that battery storage electricity is the single most expensive way to make electricity.

Economically, I would think it would be more economical to use your solar power to run your air-conditioners in the daytime, and then use cheaper grid power at night to keep them running.

But, let's suppose you do want to run the air-cons at night off your own batteries. Let's do some simple math to outline what you need. I throw out some simple numbers just to do the math. You can change the numbers to fit your situation, though the calculations themselves stay the same.

Let's say you are consuming ~2500W per hour for 8 hours each night. That's 2500W X 8hr = 20,000Wh of power, or 20kWh.
Let's say you want to consume only 1/3rd of your battery, so that means you want 60,000W of battery storage. At 48V that would be a 60,000/48V= 1250Ah battery. That's a common battery size for 2-4V batteries. Take a look at this one. https://www.rollsbattery.com/battery/4-ks-25p/

You would need twelve of those, that I guestimate would run you ~14k$.

To keep a 1400Ah battery charged, assuming a charging rate of 1/8th C you need (1400Ah/8) X 50V charging = 8750W of solar. That would be 6 of the single-pole rotating solar arrays like what I built. With 250W panels running 75$ right now, that would be 36 panels X 75$ = 2700$ for panels.

With 175A of charging current, you'd need 2-3 high-voltage MPPT controllers in parallel to charge the bank. I like Midnight, which at 600$ each would run you 1800$+.

To handle the big surge currents of air-conditioners starting, I'd think you'd need a pair of large hybrid inverters, say Schneider's XW6848, or Outback's Radian 8048. Those are running 3400$ and 3900$ each right now, so 6800-7800$ for the inverters. Thrown in another 2000-3000$ worth of wire, AC and DC power centers, an dodads like breakers, lightning arrestors, and stuff.
 
So this is my fault. I didn't really communicate this well, but . . . the electricity rates are static here. It's always 0.12 kw/h - 24 hours per day. So there's no reduction in the rate at night - as there would be in larger cities.

I will certainly check out the equipment you suggested. Thank you very much!

Mike
 
Just a big picture view here.

I would suggest you try to build a system that runs your house and shop during the day. If big enough it can charge your batteries for some night time use. That would be your max benefit IMHO.

You will likely find that when you sell power your power company will pay you a fraction of the 12 cents they charge you to buy power. They make the rules so of course it benefits them. And of course they can change the rules whenever they want.

Probably not in your favor.

There is also the matter of rules to connect to their grid, which they also make.

Until you are certain you can generate more power than you need, which I will guess is unlikely given the size of your house and shop, I would concentrate on using what you generate and leave the POCO out of it.

That’s what I’ve done. And I now have a few days of autonomy for my critical loads in a grid down scenario.

Just one opinion to consider.
 
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Just a big picture view here.

I would suggest you try to build a system that runs your house and shop during the day. If big enough it can charge your batteries for some night time use. That would be your max benefit IMHO.

You will likely find that when you sell power your power company will pay you a fraction of the 12 cents they charge you to buy power. They make the rules so of course it benefits them. And of course they can change the rules whenever they want.

Probably not in your favor.

There is also the matter of rules to connect to their grid, which they also make.

Until you are certain you can generate more power than you need, which I will guess is unlikely given the size of your house and shop, I would concentrate on using what you generate and leave the POCO out of it. That’s what I’ve done.

Just one opinion to consider
 
I appreciate your thoughts here. Also, our property is 4.2 acres . . . so I have a lot of room. It's Nevada . . . and sunny almost every day. If I went stand alone, I was thinking a propane generator as backup might be the way to go?
 
I suppose this could be managed by the proper programing of a hybrid inverter.

Your first step would be an itemized list of what needs powering and when. I'm assuming in Pahrump, that will be night-time air-conditioning and refrigeration. Intuitively, this doesn't seem like the best strategy, because you are storing very expensive electricity for use at night when electrical rate are lowest. You need to remember that battery storage electricity is the single most expensive way to make electricity.

Economically, I would think it would be more economical to use your solar power to run your air-conditioners in the daytime, and then use cheaper grid power at night to keep them running.

But, let's suppose you do want to run the air-cons at night off your own batteries. Let's do some simple math to outline what you need. I throw out some simple numbers just to do the math. You can change the numbers to fit your situation, though the calculations themselves stay the same.

Let's say you are consuming ~2500W per hour for 8 hours each night. That's 2500W X 8hr = 20,000Wh of power, or 20kWh.
Let's say you want to consume only 1/3rd of your battery, so that means you want 60,000W of battery storage. At 48V that would be a 60,000/48V= 1250Ah battery. That's a common battery size for 2-4V batteries. Take a look at this one. https://www.rollsbattery.com/battery/4-ks-25p/

You would need twelve of those, that I guestimate would run you ~14k$.

To keep a 1400Ah battery charged, assuming a charging rate of 1/8th C you need (1400Ah/8) X 50V charging = 8750W of solar. That would be 6 of the single-pole rotating solar arrays like what I built. With 250W panels running 75$ right now, that would be 36 panels X 75$ = 2700$ for panels.

With 175A of charging current, you'd need 2-3 high-voltage MPPT controllers in parallel to charge the bank. I like Midnight, which at 600$ each would run you 1800$+.

To handle the big surge currents of air-conditioners starting, I'd think you'd need a pair of large hybrid inverters, say Schneider's XW6848, or Outback's Radian 8048. Those are running 3400$ and 3900$ each right now, so 6800-7800$ for the inverters. Thrown in another 2000-3000$ worth of wire, AC and DC power centers, an dodads like breakers, lightning arrestors, and stuff.
Would you have a non-lead acid battery solution? Like LiPO would be great. I'd like to stay away from lead acid batteries. . . . Thank you!
 
where the price per kw/h is about 12.5 cents - regardless of time of day.
If you are trying to save money with solar, this price per kWh is VERY hard to beat. You'd need to shop around to get bargains, do all the work yourself and be lucky not to have any major failures (or good warranties) during the 10-15yr break even period. Yes, that long just to break even (at your current electricity rate).
 
If you are trying to save money with solar, this price per kWh is VERY hard to beat. You'd need to shop around to get bargains, do all the work yourself and be lucky not to have any major failures (or good warranties) during the 10-15yr break even period. Yes, that long just to break even (at your current electricity rate).
I'm spending $400 per month on electricity whether I have solar or not. I'd rather pay myself than the utility (in my current house). I will be building a new home here in Pahrump in the next year or so and will be installing a complete off-grid system . . . because the cost to get power to this property is $50k (per the utility). I can build and install a bitchin system for $50k.
 
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