PV system with an array of 1500 watts

[James Osbourne]

Hello all,

I am in deep water here based on my very fundamental understanding of physics generally and solar design specifically.
I am 83 years, homeless, and have access to land with one building, wood heat, non-potable site water, and nothing else.

I want to make a PV system with an array of 1500 watts or slightly more, I have so far tentatively selected 6 Surette s480 batteries; each 375 nominal AH. I would like to make the system higher voltage than 12, to reduce losses wire size and the only one I can make with that bank is 36 V. I have searched for basic design info on that voltage system and have found none. Yet I see many charge controllers and inverters with that input. To go to 24 or 48, will raise the cost of the bank and the array. I intend to use a single pole mount that will rack 6 large modules.
I live on <1500/month and have saved about 3K so far.
I seek advice and literature that I can understand and use.

 

[Tom.G]

Hi James and welcome to PF!

It sounds like you have chosen the solar panels, can you tell us which ones they are, make and model so we can look up their characteristics?

Mechanics is not my field but I am concerned about mounting 110 to 160 sq.ft. (10 to 15 square meters) of panels on a single pole. To stay together in a wind storm, that would be a rather substantial structure. What part of the World are you in and what is the worst-case weather there?

Hopefully some others here can jump in with some real expertise. Answers to the above would help them get started.

Cheers,
Tom

 

[anorlunda]

Many panels put out up to 19 V. Putting two in series gives 38V.

It is important that you choose a MPPT charge controller. They adjust current and voltage for maximum power.

You will also need an inverter to convert battery DC to household AC.

If you plan to connect to the power grid at the same time, you will need an interface box provided by the local utility. That is not optional, it is mandatory.

Based on what you said about your resources, I think you need help designing the system. If you make a mistake, the money you spend could be wasted, and it sounds like you can't afford that. Do you have anyone local who could help you?

 

[jim hardy]

inverters are a power loss. Use 12 volt appliances and lights wherever you can, and propane for heat.

 

[James Osbourne]

Hi James and welcome to PF!

It sounds like you have chosen the solar panels, can you tell us which ones they are, make and model so we can look up their characteristics?

Mechanics is not my field but I am concerned about mounting 110 to 160 sq.ft. (10 to 15 square meters) of panels on a single pole. To stay together in a wind storm, that would be a rather substantial structure. What part of the World are you in and what is the worst-case weather there?

Hopefully some others here can jump in with some real expertise. Answers to the above would help them get started.

Cheers,
Tom

I am in Northern New Mexico at 6400 ASL. Winds of up to 80 MPH have been recorded in the area, but the location is somewhat shielded by being in the lee of a cliff facing the prevailing wind. See attached PDF for pole mount specs.
35° 25' 16" N / 105° 33' 32" W
I have 4 modules from the prior defunct 12 V system. 4 x 4.5 A. 15 years old. I am assuming a loss of 20% and I intend to measure the actual output. I intend to add two +/- 250 Watt modules. Provisionally 6 Rolls Surette s480 in series; 125 A MPP controller. No inverter seleccted. One bedroom. All I need is light, electronics, and a small ref/freezer. The 12 V system with 4 similar batteries supported a 2,500 W inverter. I can use a gasoline generator for occasional use of heavier electric tools.
Thank you for all responses.

 

[anorlunda]

Your MPP controller will dictate what voltage it wants and thus how many panels to series/parallel.

Consider what @jim hardy said, 12VDC lights, fridge, and digital device chargers will use far less power than an inverter and 120VAC appliances. I assume that when you say electronics, that does not mean a TV.

Those GPS coordinates are not wilderness. May I assume that you will not be connected to the power grid?

 

[James Osbourne]

"Many panels put out up to 19 V. Putting two in series gives 38V." That is the kind of info I need. Thank you anortunda. One of my questions is how to series/parallel wire the modules for 36 V into the charge controller.
Using 12 V appliances means wiring the house for 12 V: much larger wire, DC breakers and special receptacles and buying all new expensive appliances. When the grid comes, the system has to have a major conversion. I prefer to size the PV system slightly larger to compensate for the inverter conversion inefficiency.
The site is not in the wilderness but is very remote. The grid is 10s of thousands of dollars away. Denial of a connection to the grid is the way you are forced to contract with the de facto corporation posing as a government and you are made to pay, pay, pay, and submit. No thank you.
Electronics is a computer and an SW radio. I have not had a TV nor watched broadcast TV for 15 years; I don't do bad drugs. I do like big displays.

 

[anorlunda]

One of my questions is how to series/parallel wire the modules for 36 V into the charge controller.

You said MPP controller. The controller documentation should include wiring diagrams showing how you should connect your panels in series/parallel. Just follow the recommendations.

I lived 12 years full time on a sailboat. All my lights, and fridge and SSB radio, and other electronics were 12V. But I used propane for cooking. I got along fine with 250 w of solar panels, and two 220 AH 12V batteries. The wiring was lightweight, and I had switches instead of breakers. I could get away from that because everything was low power. The biggest draw was 4A to start the fridge.

The advantage of 12V stuff is not the voltage per se but the low power. When you're living on solar, you must learn to think low power, low energy.

I know you're not near the ocean, but if you could manage to find a boat ruined in a hurricane, you could salvage all the things you need inexpensively. Ditto salvaging from a wrecked RV. (RVs use propane fridges, not 12V.)

 

[James Osbourne]

Thank you for the good suggestions. I am being given a propane refrigerator to use until I can get the solar working. It needs some work on the pilot safety. I have used them for years in the past, RV types are very small, and when they have a problem are very difficult to repair if you are not an expert in a specific brand. You have a good point. The former system was adequate for everything but electric refrigeration. I dislike lugging around small propane tanks and having to change them at always inopportune times. If I do not enlarge for the fridge, I can use my old charge control and other gear. Hummm...

 

[jim hardy]

Electronics is a computer and an SW radio. I have not had a TV nor watched broadcast TV for 15 years; ... I do like big displays.

So you can get started with low voltage and 'temporary' wiring.
Beauty of low voltage is code is way more permissive. Just keep it away from your 120VAC wiring, don't share conduits or receptacles.

A friend built his house right in town with a separate 12 volt system - a light and receptacle or two in every room.
When power fails he's not in the dark. His shortwave is 12 volt and he has a small inverter for the computer and one TV.

 

[James Osbourne]

Many panels put out up to 19 V. Putting two in series gives 38V.

It is important that you choose a MPPT charge controller. They adjust current and voltage for maximum power.

You will also need an inverter to convert battery DC to household AC.

If you plan to connect to the power grid at the same time, you will need an interface box provided by the local utility. That is not optional, it is mandatory.

Based on what you said about your resources, I think you need help designing the system. If you make a mistake, the money you spend could be wasted, and it sounds like you can't afford that. Do you have anyone local who could help you?

Thank you for your help.
I have joined NM Solar Association. No response from inquiries similar to the ones I have made here. I have enough knowledge to do hookups and wire sizing. I have decided to not size the system for electric refrigeration and instead use propane for that. That means that I can put 4 6V batteries in series and use my existing charge controller. I do not have the existing inverter data with me now but it may also accept 24 V.
Question; do batteries in series discharge and charge uniformly?

 

[anorlunda]

Question; do batteries in series discharge and charge uniformly?

Lead acid batteries can be used in series. But you need to be careful that the condition, age, temperature, level of water, and state of charge are pretty much matched.

https://batteryuniversity.com
Has a wealth of information, including operation of many kinds of batteries. That would be a good source for you.