Help Me With My PV Terms

[codefoster]

I'm starting to look at a rather DIY home solar solution but I'm not great at knowing all the trends yet so I don't want to pollute the forum with a poorly worded question.

I have enough south-facing roof (standing-seam metal) for 35 430W panels (15kW total). I want to use Victron components (MPPT(s), Multiplus-II, etc.).

For phase 1, I want the array and the multiplus so I can use energy from the array when it's there or from the grid otherwise. I heat with electric (6kW boiler) and have a very big, thick slab that retains heat well, so if I heat when solar is available, the slab will mostly take me through the night. My consumption is pretty frugal. I have a secondary heat source (propane).

For phase 2, I want to add a small battery bank. I would use the secondary heat source during an outage, so consumption would be pretty low.

What is this system in describing?

My main question is going to be how to tie it into my house. My multiplus would be near the array about 100' from the house panel, so if have an AC (the AC out from the multiplus) coming into my house utility room and an guessing I need to have a pro electrician help me with some part of this? Will it be allowed as I've described?

 

[sunshine_eggo]

You can't operate the MP without batteries.

 

[codefoster]

You can't operate the MP without batteries.

Good point. I think I meant that in phase 1 I'd have an array and appropriate solar controller. MP would come along in phase 2 when I installed batteries.

 

[sunshine_eggo]

Good point. I think I meant that in phase 1 I'd have an array and appropriate solar controller. MP would come along in phase 2 when I installed batteries.

What is the point of that? An array and a solar controller alone are about as worthless as you could imagine. No means of storing or extracting the energy.

I mean if you have to buy it in stages, just bank the $ until you can afford the MP and batteries.

 

[codefoster]

Yeah. Hasty response. If course I'd need an inverter. I don't know yet how to build it but I want to use the solar power when the sun is shining and the grid otherwise. Be nice. I'm new.

 

[sunshine_eggo]

Yeah. Hasty response. If course I'd need an inverter. I don't know yet how to build it but I want to use the solar power when the sun is shining and the grid otherwise. Be nice. I'm new.

If you hang around, you'll learn this is the only way I am. Blunt. This guy put it a nicer way:

Post in thread 'Phantom currents with Victron Smartshunt'

Jan 29, 2025

It happens. It's like they figure out I'm a butthole before I actually say anything along those lines...

I never think you’re being a butthole. You are just supremely forthright.

• DougfromdaUP

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"forthright"

I'm not going to mince words.

1) PV and MPPT are the cheapest
2) Inverter and Battery are the not-cheapest, but they could be used for peak shaving without #1.

You can't use #1 without #2.

Design your system and save your pennies, so you can deploy it all at once.

 

[robbob2112]

Besides being a dick the eggo is almost always right.

First, buy nothing until you have a plan. If you do you will have a pile of extra parts with no purpose. And when you do start buying always have an eye towards upgrading. So if you do buy 12v stuff make sure it will do 48v...the inverter won't be multiple voltage but many other things can be.

Do some reading and learning... I have a number of example system designs in my answer thread below. They are mostly from answering different people's questions. I tend to write novels to explain why I answer a certain way. There are many subjects to deep dive depending on what your end goal is.

My standard blurb is here.

Post in thread 'Robbob2112 Answer thread'

Jan 14, 2025

Standard Blurb

Don't spend any money, until you have planned out the entire system. An eraser is cheap, but returns can be costly.

Planning

1. Energy Audit - what do you have to power?
2. Size the inverter for your maximum instantaneous demand (including surges).
3. Size the battery for how long you want power, when the sun isn't shining.
4. Size the PV to cover the loads and recharge the battery, when the sun is shining for your area - most in the US use 4hrs or 5 hours a day of sun
5. Trying to use old equipment you already have usually costs more in design compromises than just...

• robbob2112

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[robbob2112]

Addendum - i reread your original post.

You are building a house sized install. Very doable but you have a lot of reading before you are there.

If you want to start small build an off-grid setup to power your office. The only connection to the house electrical would be to the house ground rod so that is common. For a house sized system you are looking at 48v batteries. Buying pre-made ones is simpler and easier especially when the bank is small. For a large bank you can save a fortune by building them.

Before you can connect anything to the grid you require an interconnect agreement which usually means AHJ inspections. Which means everything to code.

So starting small... figure out how much juice you need to run the office..or a shed.. build to code, keep reading and you are good. Post your plans and ask lots of questions.

 

[codefoster]

Thanks, all.

 

[Supervstech]

Yeah. Hasty response. If course I'd need an inverter. I don't know yet how to build it but I want to use the solar power when the sun is shining and the grid otherwise. Be nice. I'm new.

Welcome to the forum!

There are inverters available that operate directly off pv, but most find that option very limiting.

Maybe we should take a step back and discuss your goals.

What do you want to power?

How much usage do you have?

What are you trying to accomplish?

Very few options are less than the grid, lets discuss how best to spend the money.

 

[codefoster]

Welcome to the forum!

Thank you so much.

There are inverters available that operate directly off pv, but most find that option very limiting.

Great to know.

Maybe we should take a step back and discuss your goals.
What do you want to power?

I have a house and a "studio" (like a detached garage) on separate 200A meters. Both are shed roofs. The house roof (the footprint of the house is 52' x 32') isn't ideally oriented - it's facing ENE. The studio, however, is facing SSE.

How much usage do you have?

We use 800-1800kWh per month on the house and 300-500kWh on the studio. About 45% of the house load is heating (electric boiler) and heating water (heat pump) is 14%. Lights are all LED.

What are you trying to accomplish?

I had a local solar company come out and give me an estimate. Their plan was 35 (arranged 7 x 5) 430W panels for a total of 15kW of solar. Plan was to grid tie and rely on net metering. I almost went ahead with that, but I am wondering if I could do something more home grown. In my state (Washington) if I go this way by (at least) the end of 2025 I'll get the one-to-one net metering. I think that's still a pretty good way to go. I don't have to have a battery bank at all. But I also don't have the ability to power from battery in the case of a power outage, although that's not a huge use case for us - easily worked around by running a generator for a few hours per year we lose grid power. Mostly I just like the idea of avoiding rising power costs over the years.

Very few options are less than the grid, lets discuss how best to spend the money.

Agreed, and furthermore our electricity is pretty cheap (~$0.13/kWh) so none of this is super necessary. Just something to spend my time on and learn.

Thanks!