How much of a markup do high end inverters and stuff for solar panels have?

[CopperCone]

How much can you save doing the engineering of the inverter yourself?

Is it a typical ~400% materials markup? Or do economies of scale bring it down some?

I would like to consider electrical solar power (I use solar thermal water heating, which has actually paid off), but the margins are kind of slim where I live.

I think I can handle doing the roofing work, building/designing load bearing wind and seismic resistant fixtures and mounting the panels by myself to save labor costs, but decent inverters are kind of pricey.

How would a DIY job (assuming you buy the appropriate water proof connectors and don't make ghetto fixtures) save vs just paying the company?

And, another reason for this is because I very much like the Tesla Powerwall, but I know that in terms of making money, it basically prevents the system from ever breaking even (I never did the calculations but I assume it would take at least 20 years to pay itself off and its a battery that will degrade). I don't really enjoy using generators and there are power outages here.  Most are under 24 hours, and I don't mind using some chinese shit generator for longer ones, as its basically a state of emergency, but I would prefer a tesla wall to some kind of monster standby generator which I see as a complete pain in the ass high maintenance investment, for at least 3000$.

I don't feel too comfortable making some kind of home made power wall or battery maintainer at this point, unless I figure out a way to make some kind of underground storage unit for the battery bank away from my house), which would have its own challenges of moisture proofing, temperature control, etc.

[David Hess]

Designing an inverter is a losing economic proposition although you would learn a lot about the various failure modes of line connected power equipment.  The only reason I would suggest doing it is to learn the details of power inverter design.

[CopperCone]

why? manufacturers get crazy bulk IGBT discounts?

What does the volume look like for the industry? What kind of wheeling and dealing is going on do you think? Like what order quantities do they use on their assembly line. I figure between 1000-10000 units? Or is it even bigger then that? So like 30% cost reduction on the power components? Or more?

[David Hess]

why? manufacturers get crazy bulk IGBT discounts?

No, the parts cost is a small fraction of the investment if you are only building one or a couple.  The bulk discount for parts is better than 75% but the investment in design time is considerable.

To put it another way, there are many more ways for a line connected inverter to fail than to work.  The parts cost during the design and testing phase increases as the parts are lost to explosive disappearance.

What does the volume look like for the industry? What kind of wheeling and dealing is going on do you think? Like what order quantities do they use on their assembly line. I figure between 1000-10000 units? Or is it even bigger then that? So like 30% cost reduction on the power components? Or more?

I suspect that is about right for the larger players.  Remember that there are multiples of the big ticket items like power transistors so the bulk discounts are better.

[CopperCone]

my idea was to use big reactors to control the peak currents to hopefully prevent really big explosions but I forgot that you need to basically make some kind of high powered boost converters.

The efficiency of a stepup converter seems hard.

I also see myself wanting microconverters, which may or may not complicate things. Single big inverter seems dumb.

Im guessing these microconverters use phase shifting ? The control loop seems kinda odd, im guessing fast control on the phase shift and slow control on the boost converter voltage adjustment (so you rather loose power through cancellation for a short duration then trying to adjust a buncha DC DC converters all fast? Seems like the inductor would be easier to deal with doing that?

[james_s]

It sounds like you are in way over your head. Designing a good inverter that will be safe and reliable while offering good performance is far from trivial. There's a reason they are expensive, and the cheap Chinese ones tend to blow up.

[NiHaoMike]

I'm pretty sure he's talking about standalone inverters, not grid tie. Most grid tie inverters cannot be used for backup power.

At that point, the power requirements and target runtime will determine what would be the best solution.

[james_s]

With standalone there's even less incentive to try building something, reasonably good inverters are cheap, even true-sine units have come down in price a lot in the last decade or so. There's no way you could build one from scratch that would be half as good for twice the price of just buying one.

If you want really cheap, pick up an old UPS, even the big enterprise grade units can be had for little or nothing once the batteries have failed.

[CopperCone]

No i meant a line feedback one.

How are these guys typically structured?

Does each panel get stepped up to hv dc, then the boost converters put in parallel to create something like a stable 170vdc rail? Then that rail is connected to a h bridge and a filter to make the output sine?

Then i imagined you use a phase lock to track the line frequency, perhaps sampling through a high order 60hz bpf ?

Also i had completely forgotten about maximum power point tracking. Im not that clear on it actually.

The idea is to somehow hunt down a favorable point in the iv curve then run a converter circuit, which is basically a current to voltage converter with some kind of reasonable output voltage range, which is then considered low impedance, then to use a voltage to voltage converter to make a dc rail, which can either be networked to form a bigger rail or have individual dc to ac converters which somehow track each other?

Do they use some kind of fancy single stage converter to do variable impedance fixed voltage output?

I think that having a bunch of dc to ac converters seems like a bad idea since you have more crap and control systems connected to the power grid.

[Photon939]

The professional micro-inverters I've seen are all mains AC output. You slap a little ~300W complete DC->AC grid tie inverter in a box and attach them to each panel. Then you just have a 240vac bus that daisy chains across the micro-inverters.

Each solar panel then has its own MPPT tracking along with the AC grid tie logic. Each one does its own thing and feeds as much power to the grid as it can. Usually they have some kind of communication interface that allows you to monitor the group of inverters via some PC software.

[David Hess]

There are many examples online which show what is involved and lots of different topologies depending on the required power level.  It usually comes down to a boost converter to produce a high voltage DC bus and then an inverter suitable for generating a controlled current output:

http://solar.smps.us/grid-tie-inverter-schematic.html
http://www.st.com/st-web-ui/static/active/en/resource/technical/document/application_note/CD00253868.pdf
http://www.st.com/resource/en/application_note/dm00050692.pdf

TI and Microchip have micro-inverter examples which use one current output switching stage with an SCR bridge on the output to produce AC:

http://www.ti.com/lit/an/sprabt0/sprabt0.pdf
http://www.microchip.com/stellent/groups/SiteComm_sg/documents/DeviceDoc/en550277.pdf

[woodchips]

Wouldn't it be easier as a one off to simply get a large DC motor driving an induction motor as an induction generator?

Sure, the efficiency will be 80% but it is all very simple technology, and the parts are both easily obtained and cheap.

[CopperCone]

Yea i thought about that but over a decade that 15% per year starts to eat away at your soul a bit