Open Source Solar Inverter - Page 1
Forum section: electronics / projects

author: DG2MMT
author_rank: Newbie
timestamp: March 23, 2015, 07:51:52 am
content: Hi Guys!Last week I decided to start my project on Sourceforge.You can find it here:https://sourceforge.net/projects/os-si/I'm a hardware guy mainly in embedded electronics, not so much in power electronics or software or mechanics. I know my way around in those topics but I'm not an expert in those. However I'm a professional in this industry and know what I'm talking about.As a project in this complexity I'm pretty sure it would take at least one years to have a (somehow) working prototype. Additionally it is not a project for the average hobbyist because it requires experience working with high voltages and high currents.I just want to collect some input on this.What do you think? Does this sound as a fun project? Or is this just plain stupid?Best Regards,DG2MMT

author: Seekonk
author_rank: Super Contributor
timestamp: March 23, 2015, 11:50:25 am
content: I think you got your answer. I've been in solar for more than a dozen years and build all my own equipment. Still, I have absolutely no idea what you are taking about, inverting up, down, sideways, what. This is a multinational forum and something like solar inverter probably doesn't translate well. I build my stuff with everyday objects and certainly wouldn't want to post it on the internet. Retail power parts are neither common or cheap. Everyone will want something different. I build my stuff because the commercial stuff doesn't do what I want.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: March 23, 2015, 01:08:12 pm
content: So if you are saying 'solar inverter' then it seems to me to be a grid tie inverter.I can imagine a whole world of regulatory pain if you want to do a grid tie inverter.Unless you have built a solar battery charger then you don't want to be building a grid tie inverter.If you want to do off grid then you probably want a solar battery charge controller, with possibly an inverter output.In short, the first step would be a solar battery charger.I assuming you haven't already done this.

author: Scrts
author_rank: Frequent Contributor
timestamp: March 23, 2015, 01:59:05 pm
content: If you'd need help from guy like you with microcontrollers and FPGA experience - I am interested in this

author: richard.cs
author_rank: Super Contributor
timestamp: March 23, 2015, 05:22:13 pm
content: I looked at making a grid-tie inverter. In the UK the regulatory side isn't impossible, just awkward - it seems to be you produce some technical documents and self-certify a bit like CE marking, then you submit your paperwork to get the design approved just like any other manufacturer. Similar in some ways to the scheme for getting home-built cars on the road.I was going for something like Roman Black's design where you mimic a resistive source, it's a neat way of generating a good waveform and avoiding islanding.http://www.romanblack.com/micro_gt.htmI was however going to make it full wave.

author: eneuro
author_rank: Super Contributor
timestamp: March 23, 2015, 05:39:04 pm
content: Quote from: richard.cs on March 23, 2015, 05:22:13 pmI'm going to 3 phase full wave of course-3 wires makes available power more usable

author: wiss
author_rank: Frequent Contributor
timestamp: March 23, 2015, 05:42:05 pm
content: Feeding DC to the grid sound like a very bad idea! (Lawsuit waiting to happen...)Why not just feed a 9 V mains transformer? They come in push-pull etc...

author: mtdoc
author_rank: Super Contributor
timestamp: March 23, 2015, 05:48:27 pm
content: In the US, UL 1741 and IEEE 1547 are the required standards. Use of a grid tied inverter that does not meet these is both illegal and dangerous.

author: eneuro
author_rank: Super Contributor
timestamp: March 23, 2015, 09:03:11 pm
content: Quote from: mtdoc on March 23, 2015, 05:48:27 pmhttp://en.wikipedia.org/wiki/Grid-tie_inverterProperly configured, a grid tie inverter enables a home owner to use an alternative power generation system like solar or wind powerwithout extensive rewiring and without batteries. If the alternative power being produced is insufficient, thedeficit will be sourced from the electricity grid.Since selling alternative produced power at a few times lower price than sourcing from grid doesn't makes any sense and probably better store this energy as a heat to reuse in next days and save gas bill, grid-tie inverters are creating more hazadous scenarios especially when mains grid is powered off for maintenance or in the case of other disaster by its operators, that failure of detecting this event in home grid-tie ineverter can be very dangerous, so probably better do not mess with such types of inverters in made @ home instalations while return of investment (ROI) in alternative green energy will be longer and even using commercial grid-tie inverters with 10 years waranty and 7 years return of investment doesn't look great, since our expensive comercial inverter will usually die shortly after waranty period is over and destroy our ROI we were looking for when made jump into alternative "green" energyMuch more money can be saved charging and driving small electric car, while petrol bills are much higher than home electricity usage, so traveling for free is very exiting alternative when we have both free alternative electricity and electric vehicles -no need to give away to grid any produced green power for "free" and risking lawsuits for mailfunctioning grid-tie inverter

author: free_electron
author_rank: Super Contributor
timestamp: March 23, 2015, 10:13:27 pm
content: I think you seriously underestimate such a design.you need to deal with two things1: charging a pack from the PV system. PV is essentially a current source.2 : converting the pack to AC.a direct convertor is very difficult as you need to work from hugely varying input voltage. you are better off stabilizing this into a packST microelectronics has a sample design for such a converter using an STM32 and their line of products designed specifically for such converters.Be prepared to design your own magnetics though. They use high frequency switchers followed by a 3 phase H bridge driven in PWM followed by a gigantic filter bank to make it compliant. But it does produce a clean 50Hz 3 phase signal.I thnink the demo design is like 2 kilowatt.

author: Phoenix
author_rank: Frequent Contributor
timestamp: March 24, 2015, 02:03:22 am
content: You're nuts.TI do have some evaluation inverters if you just want to play around with the embedded control and have the electronics as a given:http://www.ti.com/tool/TMDSSOLARUINVKIThttp://www.ti.com/tool/tmdshv1phinvkitChallenges you will face:Topology design/selection100Hz/120Hz power flow into grid vs DC in solar panelController selection, control scheme selection, programming, gain selection/tuningPower stage design, circuit layoutMagnetics designEMI (internal and external)did I mention EMIMains voltage hazard

author: free_electron
author_rank: Super Contributor
timestamp: March 24, 2015, 02:26:38 am
content: http://www.st.com/st-web-ui/static/active/cn/resource/sales_and_marketing/presentation/product_presentation/stforsolarenergy_marketing_pres.pdfthe above one has info on a 3Kw inverter that has a dc/dc for input stabilisation and a dc/ac to create power.

author: DG2MMT
author_rank: Newbie
timestamp: March 24, 2015, 05:50:39 am
content: Thank you all for your input so far.Why not battery: to keep the (first) design simple. It involves an additional circuit with additional safety risks to implement a battery in an inverter. (I already did this in my professional job…) And you need to decide up front what will be the kind of battery you want to support and so on.The first implementation will not be grid tied. Out of the reasons some of you mentioned. I know the involved standards (they are also listed on the project pagehttps://sourceforge.net/p/os-si/wiki/The%20Requirements/…)Yes stabilization is needed. That is standard in inverters for solar systems. Only some special builds for big solar plants with very tight specification for the solar generator work without a booster circuit.And there are applications where it is sufficient to only have the generator running when the sun is shining like e.g. a water pump that fills a reservoir.And as I wrote in the initial post: I know that solar inverters are very complex designs and have a lot of challenges.But the idea is to design one and therefore give people the opportunity to learn not only how to build a solar inverter but also a lot about design challenges and how to decide what components go into the device.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: March 24, 2015, 06:18:25 am
content: QuoteIt's just your terminology I was querying. I wasn't sure what you were wanting to make.If it is running off a battery then its just an inverter.I guess what you are making is a combined solar battery charger and inverter.You would be too late for this but it's worth a look.https://www.littleboxchallenge.com/

author: DG2MMT
author_rank: Newbie
timestamp: March 24, 2015, 07:04:52 am
content: Quote from: HackedFridgeMagnet on March 24, 2015, 06:18:25 amI know this project. But: if you want to develop an innovative high volume robust inverter for solar systems in a short time frame 1 million will not pay for it.Our latest product took a lot more to develop, packs a lot of power in a (quite) small package (I think the smallest for its power currently on market), but we were not able to achieve the goal of 50 Watts per cubic inch.We did not even get near. Stripped down to the barest enclosure size (no "design" overhead) it still would not produce more than 4.5 W/cubic inch. Because you need a lot of components to achieve a stable system. And you need size to cool your circuits if the inverter should run not only in cool(ed) environments…But I will definitely look on the results of that challenge. Thanks for the reminder.

author: Phoenix
author_rank: Frequent Contributor
timestamp: March 24, 2015, 10:05:45 am
content: Quote from: DG2MMT on March 24, 2015, 07:04:52 amI want to see the results too! My team was targetting 25in^3, but due to time/money constraints it's looking more like 30in^3 if we even get it finished in time (4 people isn't enough, especially when only 2.5 do the work). 50in^3 won't win if someone makes one 49in^3, smallest wins! Fortunately it doesnt have to be robust - 100 hours isn't very long.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: March 24, 2015, 10:20:35 am
content: It would certainly make an interesting project and there will be plenty there to keep you busy but like a lot of these open source projects I'd have to ask....why?Even if you'd spent years working on the design to get the project fully complete you wouldn't be able to make an inverter as good as these for less than their retail price:http://www.windandsun.co.uk/products/Inverters/SMA-Inverters/Sunny-Boy-Inverters#.VRE5F_msXToThe parts alone would cost you more than the off-the-shelf retail price.

author: diyaudio
author_rank: Frequent Contributor
timestamp: March 24, 2015, 01:06:14 pm
content: Quote from: Phoenix on March 24, 2015, 10:05:45 amI was looking for members in South Africa (found none) as I actually work as software engineer that builds solar monitoring tools that interfaces with intelligent solar smart meters, I might have been able to do participate in doing the power electronics with firmware as a digital converter probably as a PID system, but no man is an island and for the time constraints almost impossible..Why no talk on building open-source micro-inverters?

author: DG2MMT
author_rank: Newbie
timestamp: March 24, 2015, 01:58:37 pm
content: Quote from: diyaudio on March 24, 2015, 01:06:14 pmIt could become one. As I'm just now collecting ideas and input there is currently no set target size. The only thing I'm currently not willing to chang is the requirement not connecting to a grid.If the design is done with scalability in mind the core software then only needs to be tweaked for higher power when starting small.

author: eneuro
author_rank: Super Contributor
timestamp: March 24, 2015, 05:30:06 pm
content: Quote from: Phoenix on March 24, 2015, 10:05:45 amDo you mean requirement is it have to survive at least ONLY 100 working hours?Those things will be useless exception maybe in military PSU which will be destroyed at missle impactLet's calculate 10kW in box 0.5mx0.5mx0.5m which can be easy hidden somewhere in house with additional 10cm thermal insulation to control its internal temperature, than we have 8000 in^3, so we need achieve ONLY 1.25W/in^3, so aorund 50 times lower power density than those "winning" perfect "best" in the "world" inverters.Why I do not care about this challenge-because of I do not need huge power for another crappy cell phone or tablet and can easy put somewhere in the house 0.125m^3 (125 L) black box inverter and while no plans to connect it to outside mains grid it can last for years and easy to repair since Made @ Home with full MPUs source code and schematics

author: mtdoc
author_rank: Super Contributor
timestamp: March 24, 2015, 05:57:23 pm
content: Quote from: DG2MMT on March 24, 2015, 01:58:37 pmI'm confused - you say it will not be grid tied. If so why doesyour posted requirementsinclude meeting UL1741 which is all about tying to the grid?Also why is one of your requirements "The inverter should run with small solar panels starting with 100 W output power"? this makes no sense to me since if you are not grid tied you will need to be battery based. Solar panel wattage will be independent of any inverter requirements since the DC input to the inverter will be the battery bank, no?Similarly the requirement "The inverter should be able to accept up to 600 V input voltage (market standard)" would also be applicable to a grid tied (battery-less) system, unless you anticipate 600V battery banks being used.It's true that companies are starting to make grid tied inverters that have some limited ability to provide power from solar PV without batteries when the grid is out - but these are still basically grid tie inverters with very limited power production capability without grid tie.

author: Seekonk
author_rank: Super Contributor
timestamp: March 24, 2015, 06:16:08 pm
content: Grid tie is a dead issue. Meeting UL1741 isn't certified UL1741, so it would only be an academic effort. Stick with something useful.

author: Phoenix
author_rank: Frequent Contributor
timestamp: March 24, 2015, 10:01:51 pm
content: Quote from: eneuro on March 24, 2015, 05:30:06 pmYup, maximum test is 100 hours. Means you can stress some of your components. I'm not doing it to build something useful as such, I'm doing it for fun, to play with cool new toys and to learn something. How many people can say they've designed a gate driver for a stupidly fast switching GaN FET.

author: DG2MMT
author_rank: Newbie
timestamp: March 25, 2015, 05:49:08 am
content: Quote from: mtdoc on March 24, 2015, 05:57:23 pmLet's start from the back:- Running from a battery may be possible, but requires a different approach regarding "MPP". Could be easy to be done, but where's the fun in it?could really easily be done with a design that meets the solar DC input with just a change of the controller software.- The project is all about getting the knowledge how to design and build a solar powered inverter with all the challenges in the open. There is no restriction to improve it further when the basic building blocks are there.- The UL requirement is also because there are some restrictions in it regarding how to connect to a high voltage device, what insulation requirements need to be addressed and some other safety related issues… If someone from the U.S. wants to build it, he may not worry that it is regarded "unsafe" in his country.

author: mtdoc
author_rank: Super Contributor
timestamp: March 25, 2015, 06:08:59 am
content: Quote from: DG2MMT on March 25, 2015, 05:49:08 amSounds great!I'll follow with interest since i'd love to learn enough about inverter design to repair mine if needed!

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 25, 2015, 06:20:55 am
content: What about a grid tie inverter that interfaces via a commonly available low voltage transformer, so that the entire board is low voltage? If the transformer is of the type that already has a plug attached (e.g. wall wart), the user won't even have to deal with any high voltage wiring apart from plugging it in. Of course, AC wall warts are typically too small and inefficient to make the whole idea useful for more than testing purposes, but maybe something like a (mains frequency) halogen lighting transformer could be used? Something like one of those:http://www.amazon.com/gp/product/B002PNAJL0

author: mtdoc
author_rank: Super Contributor
timestamp: March 25, 2015, 06:45:07 am
content: FWIW theEG8010 sine wave inverter ASICis fairly inexpensive. You can find driver boards using that chip for sale on alibaba, ebay, etc and DIY inverter kits using those driver boards.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: March 25, 2015, 08:41:01 am
content: I don't mean to be rude,but I am still confused.So it's not grid tie and not charging a battery.Therefore that means it cant deliver any more than 10% reliable amount of power in the day nor any power at night.I don't see the use in it.IMO even though it might be a learning project you may as well make something useful.Obviously I am misunderstanding so something please let me know what it is.Or just tell me to go away and I wont post in your thread again.

author: eneuro
author_rank: Super Contributor
timestamp: March 25, 2015, 10:32:47 am
content: Quote from: mtdoc on March 25, 2015, 06:45:07 amLooked in its datasheet, but unsure if is it possible run 3 such 1 phase inverters synchronized with 120 DEG phase offsets for 3 phase?Quote from: HackedFridgeMagnet on March 25, 2015, 08:41:01 amSimple inverter can let store unused energy during a day as thermal heat anduse it at night and next days, so PV solar can be stored and integrated with thermal solar CSP systems, as well as charge a small 12V baterries to be independent of grid power for small PSU, eg. as bigger UPS to power up needed control electronics, etc, so storing some amout of PV energy in battery is a must, while we do not want relay sometimes on mains grid especially at winters when more often maintainance a few hours switch off grid windows can happen, so we do need charge small set of cheap batteries too to be ready for such events.Anyway more interested in thoseMIL-STD-704MIL-STD-704F is the specification that covers Aircraft Electrical Power Characteristics for US military aircraft, and covers in detail all aspects of the requirements.Power Supply Operation on a 400 Hz Sourcehttp://www.digikey.com/en/articles/techzone/2014/apr/power-supply-operation-on-a-400-hz-sourceThe reason 400 Hz was chosen over the traditional 50/60 Hz is because of weight. A 400 Hz generator is much lighter, thus saving fuel, and the need to support a heavier unit making the airframe lighter

author: DG2MMT
author_rank: Newbie
timestamp: March 25, 2015, 01:26:24 pm
content: Quote from: HackedFridgeMagnet on March 25, 2015, 08:41:01 amFor the start it should only be able to produce AC out of solar DC.Thats the biggest challenge here, because the source is very variable and has an optimal operation point that changes too.To charge a battery is simple.In most cases you would just need a boost or buck converter depending of your combination of DC source and battery. Then you monitor the battery voltage limit the current into the battery and stop charging if the battery is full.To operate out of a battery is simple too.You boost the battery voltage, generate your AC voltage according to load (maybe more or less sinusoidal) and stop operation when the battery is empty (= shut off voltage is reached.)There are a lot of solutions out there that accomplish that and I see no challenge in doing that.@NiHaoMikeThe design should not operate with a transformer because this adds weight, cost and eats efficiency. All current inverters for solar systems operate without a transformer out of these reasons.But they need to monitor and limit the DC current that goes into the grid. A transformer would help to prevent that.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 26, 2015, 06:42:40 am
content: I suggested the transformer solution as a workaround to the experimenter having to deal with high voltage electronics. As in small scale DIY grid tie done for educational purposes or for a beginner's solar setup. Add a relay and it could even be marketed as a kit to convert low voltage wired garden lights to batteryless solar lights.Quote from: HackedFridgeMagnet on March 25, 2015, 08:41:01 amIf it's a motor load (V/Hz control) or a resistive load, the output power can be varied to match the input. It's going to lose efficiency up high and down low, but even that can be managed with proper design. With motor loads in particular, adding just a little bit of battery or supercap can make a lot of sense to make good use of power below the level where the motor could operate effectively.