Need Advice on Solar System

NathanaelA

I've read a ton of posts on a ton of sites and I'm looking at trying to build a future Grid-Tie system. Right now there is no power to the property and it might be years (or just a few months, who knows) before we can get power to the property so I'm trying to "future" proof this system to a certain degree.

Can someone double check my findings and point out any holes in my thinking...

I'm looking at a

Leviton 51120-1 Panel Protector, 120/240-Volt -- this is for when the future power from utility is put in; my understanding is the power is not really great so I would prefer to do a whole house protector on the way in from them. I haven't fully research whole house surge; but I know years ago Leviton made pretty good products, and this looks fairly decent for what I need.

That is wired to a 100Amp SquareD DU323 or 200Amp DU324 which is used as a safety from the Power Grid to my Grid so I can disable power either direction manually. I'm thinking 100Amp Capability should be plenty; but any thoughts?

Next in Line is a Sunny Boy 6048, this from everything I read can allow me to have my own island of power when the power grid goes out and in this case since I won't have access to the power grid for a while I need to be able to have my own island of power. So, as far as I can tell this is one of the few inverters that EASILY supports both Grid Tie & Off Grid w/ Micro-inverters. I really would like to use Micro-Inverters because of the shade type issues.

Next is a Sunny MultiGate Panel, and 12 Sunny Boy micro-inverters. With 12 x 250w Panels, This should produce ~3,000 watts of power or ~12 amps @ 240v.

Down the Road I might double the system and get another Multigate, 12 Sunny Boys & Panels; to be able to generate ~6000 watts of power, especially if we find that the power to our property is delayed by a really long time and it still makes economical sense and we have the need for it...

Now here is where I have a really weird requirement; I'm only really wanting it to power things during the day while there is sun. Once the sun is low enough to stop generating enough energy I expect the system to basically shutdown. However obviously the next morning when we have sun, I would like the system to power back up. So I expect I would need at least a 48volts of bank of batteries to start the system so that the Sunny Island can put voltage onto the wire so that the Sunny Boys can start up and then take the load over. I expect the battery only needs to be able to run for a couple minutes before power stabilizes and the Sunny Boys can put the 12amps of available juice on the system.

Can I get away with a 4 Concord 12v @ 84ah (PVX-840T) batteries, If I do the math, 4 of them in Series = 48v @ 84ah = ~4000 watts. This should be enough to supply startup power to all the devices, and get the system started and also maintain the 4w load of the Sunny Island for 12ish hours.

It appears the Sunny Island supports a couple ways I could have the system basically shutdown all power (except for the 4watts it draws) at night. So I could cause the system to auto-sleep power production from 7pm to 7am (or whatever times I determine are best); then by powering the system; the Sunny Boys should come alive and take over and re-charge the ~50 watts of power used over the night and whatever power it needs for restarting the system...

If my math is correct; and my understanding of the devices are correct; does any one see any gotchas?

Nathan

Cariboocoot

Re: Need Advice on Solar System

Welcome to the forum Nathan.

Can you give us your location? Some of the members may be near where you are at and have experience with the grid there. Bad utility power is never a fun thing to deal with. The frequency and length of outages may greatly influence your design.

The SMA Sunny Island is a great choice for AC coupling other inverters, although it works best with their Sunny Boy units. Are you sure you'll need micro-inverters? I have not seen any SB micros, only small ones (a micro-inverter is one per panel, not just low Wattage). The SB line seems to have dropped everything below 3kW from what I can see. Please tell me if there is a specific model you were looking at.

When you rely on GTI's for daytime power you limit yourself. If there isn't enough sun, you have no power. If you try to load the battery-based inverter for the GTI's contribution and they can't supply it the inverter will fault overload and shut down. It is not easy to avoid this, so sizing the main inverter and battery bank correctly is important.

Which brings us to the batteries. There's your "gotcha". 84 Amp hours is way too small for a 6kW inverter. For one thing the usable power would only be (42 Amps hours * 48 Volts) 2kW hours DC. That's somewhat less than I use here totally off-grid with a very minimalist lifestyle. For another, the maximum load at any one time will be limited by the amount of current the batteries can supply in an instant. Even though these are AGM's (and you might want to reconsider that for an initial battery bank) with their small capacity you are restricted to maybe 25% of rating for output current. In other words a measly 20 or so Amps @ 48 Volts or about 1kW. Higher discharge rate will cause too much Voltage sag and again the system will shut down.

I think you might want to work out the cost of the SMA system versus the cost of using a hybrid inverter like the XW or Radian. Design around the idea of the battery-based inverter supplying critical loads and any AC coupled GTI's to be supplemental. And definitely a larger battery bank. If you use a hybrid and grid couple later for sell-back (if allowed) you want 100 Amp hours per kW hour of 48 Volt inverter. You won't regret having the extra power capacity.

NathanaelA

Re: Need Advice on Solar System

Cariboocoot wrote: »

Can you give us your location? Some of the members may be near where you are at and have experience with the grid there. Bad utility power is never a fun thing to deal with. The frequency and length of outages may greatly influence your design.

The location is just north of Tulum, Mexico

The SMA Sunny Island is a great choice for AC coupling other inverters, although it works best with their Sunny Boy units. Are you sure you'll need micro-inverters? I have not seen any SB micros, only small ones (a micro-inverter is one per panel, not just low Wattage). The SB line seems to have dropped everything below 3kW from what I can see. Please tell me if there is a specific model you were looking at.

The Sunny Boy 240-US Micro-inverter. Basically it generates 240v/1a power from a 250 watt panel. I _assume_ based on all the research I've done that it is similar to the enphase in that it takes a few minutes (5 minutes on the enphase) before it starts feeding power back onto the grid, but I haven't seen any concrete numbers for the Sunny Boy 240-US. I would like to use the micro inverters because cloud cover is pretty variable and I don't want one panel (being in shade) in a series killing my output of the whole series.

When you rely on GTI's for daytime power you limit yourself. If there isn't enough sun, you have no power. If you try to load the battery-based inverter for the GTI's contribution and they can't supply it the inverter will fault overload and shut down. It is not easy to avoid this, so sizing the main inverter and battery bank correctly is important.

Hmm, interesting. Thanks, that is one hole in my planning I didn't consider -- I can see what you are saying if you are having an very cloudy period of time it will fall back to the batteries; which is way undersized for any length of time as they are designed for startup purposes only...

Which brings us to the batteries. There's your "gotcha". 84 Amp hours is way too small for a 6kW inverter. For one thing the usable power would only be (42 Amps hours * 48 Volts) 2kW hours DC. That's somewhat less than I use here totally off-grid with a very minimalist lifestyle. For another, the maximum load at any one time will be limited by the amount of current the batteries can supply in an instant. Even though these are AGM's (and you might want to reconsider that for an initial battery bank) with their small capacity you are restricted to maybe 25% of rating for output current. In other words a measly 20 or so Amps @ 48 Volts or about 1kW. Higher discharge rate will cause too much Voltage sag and again the system will shut down.

Hmm, I must have missed something on the batteries, somewhere; how does 84 Amp Hours; drop to 42 amps or even only just 25% of battery power usable; are their any good threads or links that I can brush up on the batteries, as whatever I did read and processed apparently doesn't match reality. :-) My goal was still to only use the batteries to start the system and maintain the Sunny Island overnight 4w of power.

I think you might want to work out the cost of the SMA system versus the cost of using a hybrid inverter like the XW or Radian. Design around the idea of the battery-based inverter supplying critical loads and any AC coupled GTI's to be supplemental. And definitely a larger battery bank. If you use a hybrid and grid couple later for sell-back (if allowed) you want 100 Amp hours per kW hour of 48 Volt inverter. You won't regret having the extra power capacity.

Well, I was trying to avoid a battery bank as the costs just sky rocket with a decently sized bank. But I might have to rethink my plans; and consider it.

Nathan

Cariboocoot

Re: Need Advice on Solar System

NathanaelA wrote: »

The Sunny Boy 240-US Micro-inverter. Basically it generates 240v/1a power from a 250 watt panel. I _assume_ based on all the research I've done that it is similar to the enphase in that it takes a few minutes (5 minutes on the enphase) before it starts feeding power back onto the grid, but I haven't seen any concrete numbers for the Sunny Boy 240-US. I would like to use the micro inverters because cloud cover is pretty variable and I don't want one panel (being in shade) in a series killing my output of the whole series.

I have not yet seen any info on these. But SMA is a reputable manufacturer so I would be confident in them being good units and working well with a Sunny Island.

Hmm, interesting. Thanks, that is one hole in my planning I didn't consider -- I can see what you are saying if you are having an very cloudy period of time it will fall back to the batteries; which is way undersized for any length of time as they are designed for startup purposes only...

Yes. And with the size of your proposed battery bank you may not have enough to get through the night. First part of the day would be the most likely overload time.

Hmm, I must have missed something on the batteries, somewhere; how does 84 Amp Hours; drop to 42 amps or even only just 25% of battery power usable; are their any good threads or links that I can brush up on the batteries, as whatever I did read and processed apparently doesn't match reality. :-) My goal was still to only use the batteries to start the system and maintain the Sunny Island overnight 4w of power.

You're not taking into account maximum Depth Of Discharge. Usually you don't want to go below 50% as it shortens battery life - down to nothing if you try for 100% DOD. So whereas 84 Amp hours * 48 Volts is 4032 Watt hours only half of it is really available, so the real power available is only about 2kW hours DC (convert to AC and you lose more do to inverter consumption and efficiency).

The 25% figure is maximum current draw at any one time. Batteries aren't linear; the greater the rate of discharge the smaller the real capacity is at that moment. When we look at the 20 hour rate that's is a figure for a low, consistent current draw over 20 hours. Increase the rate of draw, decrease the capacity. A battery of any given size can not produce a large current without suffering significant Voltage drop. Hence the 25% figure. Pull greater than that (even the AGM's are better than FLA's at current handling) and the Voltage can drop so much that the inverter "see" low Voltage on its input and shuts down.

Well, I was trying to avoid a battery bank as the costs just sky rocket with a decently sized bank. But I might have to rethink my plans; and consider it.

Nathan

I understand completely. Solar has switch from expensive panels and cheap batteries to cheap panels and expensive batteries. But battery costs go even higher if you use them to the point where you have to replace them every two or three years rather than ever five or six. As a rule we try to plan on average daily DOD of 25% which gives another 25% 'reserve' for bad weather day and has a fairly good cost/life cycle return for most batteries. The lifespan goes down as the DOD goes up. So you might save money short-term with a small bank, but if it can't handle the service you end up spending more.

animatt

Re: Need Advice on Solar System

Not sure how long you have been in mexico but i would recommend keeping setup easy.
Things to consider.

Are you going to import everything or buy locally. A good bit of money can be saved by importing, but can be a real pita. Always fun. Unless you drive it material would probably be shipped to port of puerto morelos or less likely progreso yucatan.

Depending on answer to above you may want to see what is locally available. Last time i checked it was heavily outback based products in cancun and playa del carmen area. But then solar i see here is heavily offgrid. I have not noticed grid tie solar installs.

Are you personally going to maintain the system? I ask this as straying to far from standard products and designs here may make it harder for a local to actually maintain, and could make it easier for well intentioned person mess something up.

I would reflect on those question before getting product specific.
You may even want to stop into a solar installers office to get an idea of what they want to charge you and the products they use. But go in informed as to what you want.

Animatt
Did an offgrid house between cancun and puerto morelos. I do not have access to house anymore.
Bought by Natalya Andrejchenko

animatt

Re: Need Advice on Solar System

Also not sure of exactly where you are, but you want to think about theft prevention especially if property will be left alone for any length of time. I have expirenced the mexican ingenuity down here. They are magicians. They can make anything grow legs and walk off. Look at making install that makes it a real pain to get at later.

The neighboring property about a month before i started house had its entire solar system taken.

NathanaelA

Re: Need Advice on Solar System

You're not taking into account maximum Depth Of Discharge. Usually you don't want to go below 50% as it shortens battery life - down to nothing if you try for 100% DOD. So whereas 84 Amp hours * 48 Volts is 4032 Watt hours only half of it is really available, so the real power available is only about 2kW hours DC (convert to AC and you lose more do to inverter consumption and efficiency).

The 25% figure is maximum current draw at any one time. Batteries aren't linear; the greater the rate of discharge the smaller the real capacity is at that moment. When we look at the 20 hour rate that's is a figure for a low, consistent current draw over 20 hours. Increase the rate of draw, decrease the capacity. A battery of any given size can not produce a large current without suffering significant Voltage drop. Hence the 25% figure. Pull greater than that (even the AGM's are better than FLA's at current handling) and the Voltage can drop so much that the inverter "see" low Voltage on its input and shuts down.

Thanks, that is what I didn't understand. So basically in summary I should size the bank to assume only 25% of the amp hours are available.


Nathan

NathanaelA

Re: Need Advice on Solar System

Also not sure of exactly where you are, but you want to think about theft prevention especially if property will be left alone for any length of time. I have expirenced the mexican ingenuity down here. They are magicians. They can make anything grow legs and walk off. Look at making install that makes it a real pain to get at later.
The neighboring property about a month before i started house had its entire solar system taken.

Ouch, that has to hurt. Not too concerned about that -- we will be permanently living on the property.

animatt wrote: »

Not sure how long you have been in mexico but i would recommend keeping setup easy.
Things to consider. Are you going to import everything or buy locally. A good bit of money can be saved by importing, but can be a real pita. Always fun. Unless you drive it material would probably be shipped to port of puerto morelos or less likely progreso yucatan.

We are looking at importing it all; that is why I'm trying to nail things down now.

Depending on answer to above you may want to see what is locally available. Last time i checked it was heavily outback based products in cancun and playa del carmen area. But then solar i see here is heavily offgrid. I have not noticed grid tie solar installs.

We were originally thinking about fully off-grid; but if I don't have to deal with the expense of Batteries and life of batteries because I can become Grid-Tied then I'll be a lot happier. :-) But maybe what I need to do is plan the initial system for being totally off-grid for until the batteries have exceeded their usefulness and then look at becoming grid tied somewhere around that point...

Are you personally going to maintain the system? I ask this as straying to far from standard products and designs here may make it harder for a local to actually maintain, and could make it easier for well intentioned person mess something up.

Yep, The system will be maintained by me.

Did an offgrid house between cancun and puerto morelos. I do not have access to house anymore.

How did the random could cover the PV array? How much usable solar energy did you have -- based on research the shortest sunlight day is 10 hours; the longest is 12. So I'm guesstimating 8 usable hours; but some real data for that area would be awesome.

What size was the system?

Any other specs you can share?

Are you still in Mexico?

Nathan

animatt

Re: Need Advice on Solar System

Yeah still in mexico. I bounce between a place i am setting up for myself near tizimin yucatan, and puerto morelos. I am mostly in puerto.

The house really was setup for efficient use of energy but that was thrown out the window with who bought the place. A large propane generator was installed to help when owner wanted everything on. She had electrically heated hot tub installed, as well as 8 mini split air conditioners. There was no real data collection on this house. She wanted privacy and wanted to use tons of electrity.

I did live in the house which was robbed for about 4 months on a small replacement system. Basically i was watching the house for the people. The system consisted of 6 evergreen solar panels which were 190w each. So 1140 watts of panels. These were summer months. With panels mounted facing south at a fairly low angle. I would guess around 20 degrees away from being flat.

These panels produced about 5000 to 5500 watts on good days when batteries were in bulk charge all day.


I would calculate 5 hrs of good sun for your calculations. If planning air conditioners insulate well. Maybe have a bedroom cooled.

What is motivation being offgrid? I would look at cost of having grid power installed. Offgrid power costs about $1kwh where grid power here costs much less. In non turist area i pay less and 6 cents per kwh. In turist area i have paid high around 20 cents. Both much less then offgrid. Something to consider. You can run numbers and see where that leaves you. Being air condition would probably highly desired during hot summer months grid helps alot.

I would highly suggest thermosiphon hot water heater for your hot water needs. Grid power or not. Very simple to do here

zoneblue

Re: Need Advice on Solar System

NathanaelA wrote: »

I would like to use the micro inverters because cloud cover is pretty variable and I don't want one panel (being in shade) in a series killing my output of the whole series.

String shading only becomes an issue if you have trees or buildings. Clouds are not a convern. SB micros are brand new out, and so dont yet have extensive field experience.

Well, I was trying to avoid a battery bank as the costs just sky rocket with a decently sized bank. But I might have to rethink my plans; and consider it.

In case you hadnt noticed SMA gear is right pricey too. (good though)

This scheme of yours to avoid batterys is not going to work. Rainy day= no power. Night = no power. If your need of power is that minimal, what do you need power for at all?
Your problem like all who attempt to tread this route, is that, youre trying to build and fund two complete seperate systems, based on vague notions of security, independence etc.

What you need to do is accurately assess the reliability , Net meter (NEM) viability, and the costs of the grid connection.

- If the cost and reliabily are good enough, then thats likely your best route forward. Small honda for power cuts and your good to go. If you have an interest in solar, add straight grid tie, assuming the NEM program is viable.

- If the local power is pricey (like it is here 30c/kWh +) , and/or your connection charge is pricey (10K+), then a full off grid setup quickly becomes the most attractive option. Total cost wont be too much more than grid, or even less. Plus you get your hobby and security of supply.

- If grid connect charge is cheap/free, and monthly charge cheap, then you can design an off grid system that uses the grid as a backup. Thus keeping your bank size down.

- If the unit rate and monthly charges are ok, but no viable NEM plan, and real bad grid reliability (1+ outage per week) you can design a small redundant off grid system to cover backup of key loads. With or without solar. Basically bank+off grid inverter and transfer switch. Grid charge batterys between outages.

This whole redundant head trip. If you are made of bucks and really want to do it, then these are some thoughts.
- AC coupling is expensive and better suited to bigger more complex mini-grid systems, or systems involving multiple buildings. You are essentially buying two inverters where off grid you only need one.
- If you do it you need SB/SI. Thats pretty much the king of AC coupling. Check is SMA micros will talk to the SI.
- many recent SBs have a batteryless sun hours backup feature, which may be enough for you
- full hyrbid setup. Dont skimp the batterys. Design it, as Coot said, as an off grid setup with a hybrid inverter with decent sell, backup, grid zero etc features. That limits you to about 3 products. SI, XW, and radian. All more epensive than most std off grid iverters.
- Having said that, it depends on your loads. If you need a 6-8kW inverter then your into the 4K plus bracket for inverters anyways.
- ponder long and hard how a genset can meet your redundancy needs, for lots lots cheaper.

stephendv

Re: Need Advice on Solar System

I really like my Sunny Island, but don't think it's the right choice in your case. Firstly, the SMA microinverters are 240V right? And the US versions of the Sunny Island is 110V output, so you'd either need 2 x Sunny Islands or a transformer, which significantly increases the cost.

When you say "grid tie" system, do you mean a system that pulls power from the grid when needed- or one that sells power back to the grid? Normally, "grid tie" means the latter, i.e. selling power back to the utility. If you don't plan to sell power back, then there's really not a very good case for using micro-inverters or any kind of grid tie inverters. It would be cheaper and more efficient to use a DC based system using charge controllers and a standard inverter/charger which can later be connected to the grid to supply charge the batteries when solar isn't available.
The Xantrex XW provides 110V/220V split phase in one unit and is substantially cheaper than a Sunny Island + transformer combination. I think the Outback Radian provides similar functionality.