LoadMaster XP - A Smart PV MPPT Solar Hot Water Controller

With 30V Vmpp and your FETs having VDS max of 100V I don't think a snubber is so important. I am operating at around 165V Vmpp and 18Amps so we have quite different setups. I'm using my first and only FET working non stop for over 4 .5 years, so i'm reluctant to remove the snubber since its power loss is small (1.5W or so) compared to the 3kW delivered. It seems that gate charge is always higher for the higher 600/650V rated MOSFETs I need to use ...The FETS you mention there are VDS =100V which are great choices for a low voltage setup but would go bang in my setup. How is it all working in your low voltage setup? I havent any experience of LM operating at that low voltage so would be interested to know how it is all performing. Cheers, Steve

Hi Greenwestern, Well, unfortunately at the moment the supply of a complete unit is not on my radar, although I fully recognise and appreciate your comments, I only have some blank PCBs. There are numerous people around the world on web and Youtube (Opera) etc who recognise PV offers a great & cost effective solution to solar hot water. There are indeed simpler solutions, especially if you have a situation/location where you really dont need to squeeze every watt out of the PV into the heating (that isn't the UK!). I've seen simple on-or-off control approaches (solid state relays or FETs etc) where a single heater load resistance is optimised at around R= Vmpp /(2/3 of Impp)... where Vmpp & Impp are the ARRAY's max power V&I values. This recognises that for most of the time the array will never be operating anywhere near to its max power point. Loadmaster tracks / reduces the effective load resistance perfectly to match any reduced solar conditions and a system can be designed to use standard cheap immersion heaters etc. Switching in different heaters may present issues of having a cylinder to accept multiple heaters and seeking non-common heating elements of appropriate R and power rating etc. Note also ,High Voltage DC and Relays are a highly dangerous No-No (DC Arcing). Your comments, and others, do make me wonder if there is scope for a very cut down kit design ....(i.e the same pcb but only populated with the absolute essentials -(i.e say single RGB LED push button switch, single temp sensor, arduino plus the power side electronics only, -Display, real time clock, multiple sensors etc could easily go). ..I feel a winter project comming on. Where are you based? Cheers. Steve

Yep, I have a 3kW 5S x 2P array of REC Solar 300W TP2 panels on my roof. In the downloads section i've included a copy of my excel design spreadsheet - one worksheet shows images of my setup plus a review of its performance based on a download of approx. one years data. Cheers, Steve

Hi Dougal & Cheers for your compliments. I also saw a similar comment on a forum somewhere suggesting you can't use a immersion heating element on DC due to electrolysis. Personally, I suggest that is ridiculous and is most definitely not a problem!. If the heater's resistance wire and its positive and negative connections were sitting in the water, then absolutely 'Yes', - you would have electrolysis plus a massive safety, corrosion & flooding risk whether AC or DC powered!. However, a heating element is fundamentally resistance wire contained inside a dry, fully water tight Incoloy or Titanium tube (you cant use a copper immersion element in a stainless cylinder due to electrolysis of dissimilar metals sitting in the same mineral filled water). You certainly wont find a resistor that can't be used on DC!. I have worked on this project for about 2.5 years and had a system running for nearly 2 years in different stages of development. I would of course say this, but honestly I am totally impressed by the performance & reliability which exceeded my best expectations, I very nearly have a years performance data logged for my system. As you probably appreciate, PV energy generation for a location, time of year etc and the energy required to heat a given volume of water by x degrees C is simply maths. In my experience the maths and reality are very close. Steve

Steve I have working systems and very interesting in your corrosion comments, can we chat please,

Thanks...That's the answer I wanted... Practical experience not theory. From those numbers I assume your using a fixed roof mounted array ? This type of design is one of 3 options I'm considering to boost my existing solar hot water. I have some panels about to be retired from one of my trackers.

The capacitor effectively sits across the PV. As it charges from the PV the volts across it will ramp up slightly. At the same time its supplying pulses of current (i.e a controlled amount of charge is removed as the output FET turns On:Off). The capacitor therefore sits at the array's Vmp DC volts but has a Volt or two of Pk-Pk ripple across it as charge is put in and then taken out. The Cap is therefore not seeing purely DC. RMS ripple current from the capacitor can be nearly half of the arrays maximum current depending upon PWM dutycyle (only when PWM is 100% ON will there be no ripple current). The capacitor must have a suitable ripple current rating, a low impedance (else that ripple current will effectively lead to power dissipation in the Capacitor and it getting hot) and good pulse handling capability. It's not just a smoothing cap but plays a key role in delivering charge and energy at the correct load impedance to extract max power from the array. You may find some electrolytics that could do the job, however this type of application best suits film type capacitors. A suitably rated film type cap will last forever, Electrolytics can deteriorate over time esp. with high ripple and high temperatures. (take a Google at 'DC link capacitors'). Cheers Steve

Hi Eidolontech. Many thanks for your comments and input. As an 'off-gridder' you obviously have an equally valid and good solution to delivering PV solar power into hot water. I am not 100% off grid and most likely never will be. I recognise your observation (and frustration!) regarding some comments & opinions on renuewable energy forums etc which appear 'blinded' that Solar thermal is the only viable approach to Solar hot water (sadly that's outdated, uniformed, narrow minded rubbish!.) Apart from PV DHW requiring more collection area, basic maths and understanding should show anyone that in 99% of applications, today PV for hot water wins hands down:- PV is now lower cost, is just wires, some minimal reliable electronics, uses standard heating components, is near zero maintenance plus spare electricity is versatile. PV hot water has no issues of anti freeze/corrosion fluids, no pumps, leaks, failed vacuum tubes, no maintenance costs etc etc). Heating water uses a LOTs of energy, typically the second a largest area of energy comsumption in the home (Space heating = No1) so, as a relatively cheap, straight forward project, in the scope of many competent electronics & DIYer's, PV feels like a no brainer solution to having lots of free hot water! I take my hat off to you for going off grid! Where? Cheers Steve

eidolontech, I am in a similar situation, off grid more panels less battery. I have been manually controlling the water heating load and want to automate this. What are you using for a controller for the heat load?

Good Morning Steve, Thanks for your reply. Please excuse my ignorance, as I am not an electronics or electrics expert, but can the loadmaster drive a DC immersion heater or does it have to be AC? I currently have an AC immersion heater available but my have to change my tank in a while and was just wondering which way to go. Can you let me know the price of one of your Loadmaster PCBs? Once again thanks, Regards, Graham Willsher

Hi Graham & thanks for your interest. Well DC heaters and AC heaters are just resistance wire in a metal tube, they are essentially the same thing. A resistor will dissipate the same power if you put 12V DC across it or 12VAC RMS. My understanding is 'DC' ones get named 'DC' as they are designed to have a certain power output rating when targeting a common DC setup market place - i.e 12V, 24V, 48V DC etc. Ultimately the Volts and Power rating of a heater relates to it having a specific resistance value. Yes, a key LoadMaster attraction is DIY, - avoiding an expensive MSC approved PV & inverter install, no requirement to register a PV setup with your electricity (DNO) provider, no expensive immersion diverter device etc. PLUS, if you do have a PV grid tie system, (which in many instances in the UK are limited to less than 16A / 3.68kW), then having a totally stand alone, grid isolated PV hot water setup effectively typically removes the 2nd highest domestic consumption load away from your AC inverter, thereby freeing up more solar AC KWhr for other loads. LoadMaster could allow you to benefit from say 6kw of PV on your roof whereby only 3.6kw of it has any connection to AC grid bureaucracy. Cheers, Steve

Hi Graham. Please see above for AC - DC heater comments, for PCB please contact me PVhotwater@btinternet.com. Cheers Steve

Well Done Peter! Great job. Not only have you played a small part in reducing CO2 but you will also save a load of money!. 'Switching excess PV to an Inverter input' - Around line 332 in V95 code you will see you can set the mode for the 2nd Output FET;- Output2 = NotFitted; (the default 'single output mode' with Q4 FET 'NotFitted), or Output2 = Switch; (i.e Once the primary output reaches its set temperature, Q4 is simply turned fully on - switching the low side of PV to say a small G.T inverter /charger etc. or Output2 = MPPTHeater; (i.e the 2nd output FET Q4 drives a 2nd resistive heating element for water or space heating using MPPT to deliver max power. An extra AuxTemp sensor is used to temperature control this 2nd output. I have used 'Output2 =Switch' to switch excess PV to the input of a Solis Mini 2.5kw inverter. This worked fine, - having the capacitor effectively across the inverters input had zero effect, I really can't comment about other inverters but doubt it should be a problem. "Wire Inverter to Consumer Unit or fused Spur etc"?..umm. Most guidance say's directly to C.U via AC isolator etc -but i've seen all sorts! Perhaps look at Pluginsolar.co.uk. In the UK all Grid connected inverter installs should be registered with your D.N.O (SSE etc). What I can say is that once you have gone to all the effort of installing an inverter, then rather than just switch any excess from the 'PV Hotwater' array to to it (which will be small to zero excess across a number of months), you will just wish you had a second array dedicated to the AC inverter!. (see earlier comments about 3.68kW microgeneration limit in the UK). Cheers Steve

Hello, Built my Loadmaster system earlier this year, located midlands UK using 4 x 270w series panels to a 240v immersion heater. Worked fine but recently upgraded ro 5 x 265w series panels which according the Loadmaster notes is a pretty good match to a 240v immersion heater. The improvement is immense and in the recent sunny days have achieved a blue led and my 150L tank at 60C. Eventually plan to upgrade to 2 parallel arrays of 5 panels which will double my output. I'm assuming when 60c is hit the Loadmaster output can be automatically connected to a small grid tie inverter and onto 240v. Does the grid tie inverter need wiring to my main distribution board or can it be plugged into a switched 13A socket? Keep reading but getting confliction answers! Regards Peter

Hi Craig Thanks for your interest in the project. You will most definitely see a benefit from using mppt in winter months. At the moment I am holding back a little from publishing the PCB gerber data. There is now a growing number of systems working and being made around the world and I wish to collated any feedback from those prior to releasing artwork etc. I have some PCBs which I can supply. Please drop me an email to pvhotwater@btinternet.com, Cheers Steve

Hi, At the current time I can only supply PCBs and support for interested project builders with suitable skills.

Hi Isdeekelis Many thanks for your interest and compliments. It sounds like you also have a very interesting project going on there. Why 5Khz...(its currently at 3.9kHz), well, initially I had problems getting high PWM frequencies and reasonable PWM resolutions on a Nano, however that's now achievable. As the basic principle is Capacitive energy storage I was aware dielectric and switching losses could rise with freq (but probably still unimportant - just couldn't find data for many caps etc), There is some audio noise (see assembly doc) but its really minimal. I modelled the cct in TI tina and then ended up at a common cap value and freq giving only a few Volt ripple in the PV Vmp volts. Basically! i haven't had a major need to try higher frequencies - maybe one rainy day i will test it out. Use a pre-set range etc for Vmp? - Well up until 2 days ago! I had never seen a problem of multiple peaks in an arrays power output - a project builder having an array of mixed panel types reported an issue were it could lock on to a lower power level peak. In many systems, with an array comprised of the same panels and with no major shading issues then there has been no sign of an mppt tracking problem. Adding some Vmp acceptance window in the P&O mppt code could definitely be an option to fix that. As far as I am aware many Mppt routines just assume a normal V-I curve and single power peak. (if you see any code for that I would love a copy) All the best for your project, Steve

Wow, it has been a long time since I've been here. I use a fixed Vmp on my heater control though it is capable of tracking via temperature from that set point. The main reason is the water heater control operates in parallel with the charge controller to harvest excess energy when the battery nears full charge. Lead batteries have charge cycles which reduce maximum charging. At 8am I'm still able to divert some current to heating. A fixed voltage also allows prioritizing certain loads. I have a second 40gal water heater in my detached garage just for laundry set to a slightly higher voltage that kicks in when the house tank is up to temperature. Typically 1-2.5KWH gets diverted which is enough to heat the upper 15gal of water. Capacitor bank must be isolated with diode when used with charge controller. The Polish ACTii had fixed voltage capability option besides IV tracking. The newer ACTii/PL although better hardware design does not. I should add that my location has intense shading with over 75% of panels shaded at any time and my charge controller gets lost quite often. A circuit disconnects the charge controller when that happens to reset it. I wish the controller had the option od selecting a normal operating voltage band. I gained water heating capability without adding any extra panels to my system. So many off grid are looking to add diversion capability to heating water without consuming charge controller, inverter and battery capacity. Fixed voltage is certainly a valuable option to have. With solar thermal, it just becomes junk on your roof one the tank is up to temp. PV can always find another use for that energy.

Hi John ...we have now exchanged messages via email, however just to say I'm pretty sure the photos you sent point to issues of dissimilar metals. Cheers, Steve

Hi Judesanson, Roger and that's great news. Let me look at cost and shipping logistics over the weekend and i will get back to you ASAP. I'm also trying to work out how to contact you without putting emails and paypal info all over this comments section!. Cheers for now, Steve

Hi Stevetearle, I totally agree we need more and more properly thought out DIY projects that can help those in the maker community do their bit to reduce CO2 and build something thats very cool. I would be very happy to buy one or two of the PCB's for my house and my rental property. I'm located in Winnipeg, MB, Canada. Could I order that from you directly and pay with PayPal? Thanks

Hi Judesanson, Thanks for the comments and its really great to know this project has motivated you. I've seen lots of 'half baked' projects on Youtube etc but i really felt this application and our warming planet could benefit from a solid, open project like this. I do have some extra (blank) V4 PCBs (thats my final 'perfect! PCB made by JLC, 2 Oz copper). Where are you based? I may be able to put these on ebay etc

Steve, Would you happen to have a PCB available for this project? My email is trwells71@gmail.com. This would be for a PV array intent on heating water to radiate through a floor system in a utility room. This is to keep the room above freezing year round at 8800' in Colorado. The room is not built yet but when built it will be heavily insulated, have hot water radiant running through the floor with a tank heated by PV panels. There will also be an oil immersion electric radiator plugged into the grid for backup or a second grid connected heating element in the tank. At least that is the current plan. This cabin is a summer cottage that gets snowed in during the winter months. My wife and I like to ski to it a couple times in the winter. It is heated with a wood burning stove and I would like to set up a utility room for the water well related tank and accessories to be kept from freezing. Otherwise that all gets drained for the winter and we melt snow for water. It is no problem for the rest of the cabin to be frozen but ultimately if I can keep the whole place above freezing that would be cool too. Thanks Thaddeus

Hi Alex. Ì am pretty sure I have a few spare blank pcbs still available but need to confirm when I'm back on the weekend, I will also check postage cost etc. In the mean time please can you drop me an email to pvhotwater@btinternet.com. Cheers Steve

Hi GreenWestern Well LoadMaster effectively has two outputs that can be used sequentially, I have just updated firmware such that when the main water store has reached temperature, the primary FET output is disabled and the second FET output will either, A) divert power (using MPPT) to a different load (say a 2nd hot water store, resistive space heating etc), or as in my case, B) simply switch the PV supply (i.e fully ON, no MPPT) to the input of a small (2kW) GTI. The reality i find is that the times when you you would benefit from space heating ocurr at the time of the year having the lowest excess kWHr of solar energy. Summer months have WAY more excess in PV kwhrs, so for me, transferring this large amount of summer excess into to a Grid Tie Inverter for daytime load consumption ...washing machine, freezers, small battery store, etc gives me the biggest opportunity to maximise useage of my annual generated PV kWhrs. Anyway with renewables and PV etc there is no single golden or perfect solution. Cheers Steve

Hi Alex - Well, nobody has ever said that to me before! Thank you for your comments! All the best, Steve

Hi Ilyyes My design notes spreadsheet is in the downloads section - its a bit spurious but covers snubber and various parts of cct. However, the typical storage Capacitor values were initially confirmed by modelling the circuit in the 'Ti Tina' spice app (other people were already doing this type of control way before I started this project so I just wanted to understand waveforms / ripple current etc). The Cap value, PWM freq & duty cycle determine how much Pk-Pk ripple there is in the PV voltage as the capacitor charges and then releases some charge. The bigger the cap, the lower the ripple. As mentioned the inductor simply lowers di/dt which reduces emc switching noise- again that was in Spice. I would say switching losses of this design approach are very low and way smaller than potentially hundreds of watts you could be loosing due to an impedance mismatch between heater load R and the current PV solar conditions. Cheers. Steve

Hi Peter & thanks for your feedback,- it's great to hear that it is all going well. My LM system has been running in excess of 3.5 years now with not a single issue or part failure. It's saved a fortune in LPG and given today's insane energy prices and global instabilities it will continue to deliver even more savings & benefits. Thanks again, Steve

Hi Leonard Glad that you liked the project. Drop me a mail on pvhotwater@btinternet.com Cheers for now, Steve

Hi Coopercompany, If you look at the 'Basic Architecture' diagram above you should see that the negative side of the storage cap 'C-' is taken as the ground reference for the entire circuit, the Arduino measures the PV volts relative to that rail and also the PV current is measured in the PV negative lead with respect to that ground ref. I hope your build goes well, just be really careful on the layout - switching high currents and volts in a product like this needs a lot of care in the layout, keep the power side and digital sides clearly separated with just one small joining point (the net star point in cct diag). My final 100% reliable PCB when I published this project was at PCB revision V4.0 which tells a learning curve story! All the best and let us know how it all goes. You will be really happy to get free hotwater!. Steve

Hi Steve, Thank you very much for your comments! First of all i Pm-ed you and wrote you an email about buying 2 Loadmaster XP PCB-s. Please respond when you can. I got your point about resistance. I am not in hardware at all and i may say something stupid but I have side question about cap(s) and RMS currents: From the opera videos on youtube he is using at lest 6-10 caps electrolytic around 6000uF - 10000uF in total and PWM freq 100-120 Hz from memory You are using one 200-400 uF film type at 3.9-5 Khz Pwm. His explanation is that each cap should see no more than 1 Amp and his total voltage swing around capacitor bank is about 2 volts. So that difference in capacitors is due to Loadmaster XP Higher pvm frequency or due to the fact that film type suggested film type cap can take 15A RMS current? Some of the Loadmaster Xp photos (Mike in Wisconsin) showed folks using three film caps. My question is what would be the best setup to achive 10+ years capacitor life Maybe 2-3 200-400 uF film type in parallel or this is over kill? Cheers Hristo

Hi, I theory it is true BUT then there will be much more stress on CAPacitor (bank). Pwm% will never reach 100% and much more energy will be taken from caps. Not to mention that after years when PV array degradates this resistance mismatch will become worst.

Hi Hristo, Perhaps best drop me an email (pvhotwater@btinternet.com). Capacitors:- If you do a specification filter search of Ali Electrolytic capacitors on say Digikey with ripple current ratings >say 24A and 350V capable, the resulting caps tend to be very large capacitance values and $$. That is probably the primary reason he is using large uF values, - to get the ripple current rating and life expectancy, not for the peak to peak ripple voltage across the capacitor. 300uf Film cap is fine for peak to peak ripple and take a look at there pulse & ripple current ratings. A google for DC-Link capacitors will show the advantages of Film vs Electrolytic and explain how they perfectly target an application such as this. Cheers for now, Steve

Hi Ioshia That is a good question.... Refreshing myself from the web:- “ PV N.O.C specs are an approach to mirror real-world conditions… closer to representing real available peak wattage on an average day, NOC values are probably more realistic than STC”. So yes, it would seem more appropriate to consider NOC specs although by ‘average’ conditions it of course means sometimes you will see slightly higher outputs under REALLY perfect conditions , - i.e with full sun, at correct inclination, maybe with colder conditions, clean panels, no aging etc etc. As Isdeekelis says, LoadMaster can always make a too low resistance look a bit higher so it could cope with the lower resistance & my thinking is that the specs of many DC-link film capacitors would suggest they are under little stress. From memory, the highest RMS currents in the capacitor occur closer to 50% PWM, at near 100% PWM the capacitor actually delivers no energy. My pragmatic thoughts:- The number of times I see my panels delivering close to their nameplate STC power is very infrequent, they do, but that’s like a lottery win compared to the other 99% of the times of the day / year when the it operates significantly below peak STC output. So achieving a perfect match at 100% PWM doesn’t exactly have a huge impact on the systems overall contribution. My system is sized to give the best as practical ‘widest’ coverage of the year (i.e deliver near 100% PV hotwater from March to Mid- Oct, UK). This means that in summer (i.e when you are most likely to see the 100% PWM matching issue) I have a huge PV excess anyway!, thus any small mismatch at 100% PWM at that time of year doesn’t matter since by 1pm the water is hot and it turns off!. Also! in reality to find a ‘Standard heater’ who’s resistance perfectly matches the arrays V/I specs (whether STC or NOC) is near impossible. Perhaps assume a nominal Resistance midway between the calculated NOC & STC values and then if you can then get a heater resistance within say +-10% , even 15% or so of that figure it will be fine. I hope that makes some sense!? Cheers, Steve

The Opera version uses large electrolytic capacitance to reduce the voltage sag to a minimum. The lower the differential voltage, the higher the efficiency. That circuit also imitates line frequency of 50Hz forming an arc interrupt which allows existing mechanical thermostats to operate without damage due to arc over. This allows heating elements to be daisy chained as typically found in US water heaters and even multiple tanks. During the off time of less than a ms all panel power has to be stored in the capacitor to remain efficient. That takes a lot of capacitance. Unknown consumer grade capacitors should not be expected to handle more than 1A. Commercial grade can easily handle considerably more at line frequencies. Capacitors have internal resistance which causes heating and many parallel capacitors will reduce the current each capacitor sees. The welds and crimps in a capacitor are a common failure point with high currents. Reducing currents with parallel capacitors insures long life.

Use lower one. Loadmaster can make it higher, but not vice versa.

Hi Tgrauss Well from your description it sounds you have plans for a large system,...12kw, dual inverters, battery storage etc. With such a large investment in an 'AC electrical' type system already, my thinking is that you are probably best to simply use 240vAC and a say a PV immersion heater diversion type controller (immersun, iboost etc). Load master targets at a much simpler and cheaper approach to capturing and storing as much PV energy into hotwater, or space heat and then maybe switching any excess, mostly in summer to a small GTI inverter. It also suits 2Px5S or 2Px6S, 2.5kW to 4kW array configs..large inverters will generally require higher voltage PV configurations Cheers Steve

Hi Hopihalido, Many thanks for your feedback - it's always good to hear the project has been successful and delivering good results, saving energy & CO2 etc - it's my motivation for the project!. Once you establish your gas saving data it would be great if you can share it on here - I'm sure others would be very interested to see that. This year we (2 adults ) used 100% PV heated water from Mid march to Mid Oct - I can't quantify this in terms of our LPG gas this saving, however in electrical terms those 7 months alone represented over 1,200kWHrs delivered into our hot water. Cheers, Steve

I am rather up to my neck in stuff at the moment! but would be very interested to hear about your project. Feel free to drop me a message on PVHotwater@btinternet.com Cheers, Steve

Hi Jupet, I do have some PCBs available. Please drop me a mail to PVHotwater@btinternet.com. Cheers Steve

I do have PCBs available. Please drop me an email to PVHotwater@btinternet.com. Cheers, Steve

Hi Coopercompany, If you look at the 'Basic Architecture' diagram above you should see that the negative side of the storage cap 'C-' is taken as the ground reference for the entire circuit, the Arduino measures the PV volts relative to that rail and also the PV current is measured in the PV negative lead with respect to that ground ref. I hope your build goes well, just be really careful on the layout - switching high currents and volts in a product like this needs a lot of care in the layout, keep the power side and digital sides clearly separated with just one small joining point (the net star point in cct diag). My final 100% reliable PCB when I published this project was at PCB revision V4.0 which tells a learning curve story! All the best and let us know how it all goes. You will be really happy to get free hotwater!. Steve

Hi Peter & thanks for your feedback,- it's great to hear that it is all going well. My LM system has been running in excess of 3.5 years now with not a single issue or part failure. It's saved a fortune in LPG and given today's insane energy prices and global instabilities it will continue to deliver even more savings & benefits. Thanks again, Steve

Hi Ilyyes My design notes spreadsheet is in the downloads section - its a bit spurious but covers snubber and various parts of cct. However, the typical storage Capacitor values were initially confirmed by modelling the circuit in the 'Ti Tina' spice app (other people were already doing this type of control way before I started this project so I just wanted to understand waveforms / ripple current etc). The Cap value, PWM freq & duty cycle determine how much Pk-Pk ripple there is in the PV voltage as the capacitor charges and then releases some charge. The bigger the cap, the lower the ripple. As mentioned the inductor simply lowers di/dt which reduces emc switching noise- again that was in Spice. I would say switching losses of this design approach are very low and way smaller than potentially hundreds of watts you could be loosing due to an impedance mismatch between heater load R and the current PV solar conditions. Cheers. Steve

Hi, At the current time I can only supply PCBs and support for interested project builders with suitable skills.

Hi, I theory it is true BUT then there will be much more stress on CAPacitor (bank). Pwm% will never reach 100% and much more energy will be taken from caps. Not to mention that after years when PV array degradates this resistance mismatch will become worst.

Hi Ioshia That is a good question.... Refreshing myself from the web:- “ PV N.O.C specs are an approach to mirror real-world conditions… closer to representing real available peak wattage on an average day, NOC values are probably more realistic than STC”. So yes, it would seem more appropriate to consider NOC specs although by ‘average’ conditions it of course means sometimes you will see slightly higher outputs under REALLY perfect conditions , - i.e with full sun, at correct inclination, maybe with colder conditions, clean panels, no aging etc etc. As Isdeekelis says, LoadMaster can always make a too low resistance look a bit higher so it could cope with the lower resistance & my thinking is that the specs of many DC-link film capacitors would suggest they are under little stress. From memory, the highest RMS currents in the capacitor occur closer to 50% PWM, at near 100% PWM the capacitor actually delivers no energy. My pragmatic thoughts:- The number of times I see my panels delivering close to their nameplate STC power is very infrequent, they do, but that’s like a lottery win compared to the other 99% of the times of the day / year when the it operates significantly below peak STC output. So achieving a perfect match at 100% PWM doesn’t exactly have a huge impact on the systems overall contribution. My system is sized to give the best as practical ‘widest’ coverage of the year (i.e deliver near 100% PV hotwater from March to Mid- Oct, UK). This means that in summer (i.e when you are most likely to see the 100% PWM matching issue) I have a huge PV excess anyway!, thus any small mismatch at 100% PWM at that time of year doesn’t matter since by 1pm the water is hot and it turns off!. Also! in reality to find a ‘Standard heater’ who’s resistance perfectly matches the arrays V/I specs (whether STC or NOC) is near impossible. Perhaps assume a nominal Resistance midway between the calculated NOC & STC values and then if you can then get a heater resistance within say +-10% , even 15% or so of that figure it will be fine. I hope that makes some sense!? Cheers, Steve

Hi Hristo, Perhaps best drop me an email (pvhotwater@btinternet.com). Capacitors:- If you do a specification filter search of Ali Electrolytic capacitors on say Digikey with ripple current ratings >say 24A and 350V capable, the resulting caps tend to be very large capacitance values and $$. That is probably the primary reason he is using large uF values, - to get the ripple current rating and life expectancy, not for the peak to peak ripple voltage across the capacitor. 300uf Film cap is fine for peak to peak ripple and take a look at there pulse & ripple current ratings. A google for DC-Link capacitors will show the advantages of Film vs Electrolytic and explain how they perfectly target an application such as this. Cheers for now, Steve

The Opera version uses large electrolytic capacitance to reduce the voltage sag to a minimum. The lower the differential voltage, the higher the efficiency. That circuit also imitates line frequency of 50Hz forming an arc interrupt which allows existing mechanical thermostats to operate without damage due to arc over. This allows heating elements to be daisy chained as typically found in US water heaters and even multiple tanks. During the off time of less than a ms all panel power has to be stored in the capacitor to remain efficient. That takes a lot of capacitance. Unknown consumer grade capacitors should not be expected to handle more than 1A. Commercial grade can easily handle considerably more at line frequencies. Capacitors have internal resistance which causes heating and many parallel capacitors will reduce the current each capacitor sees. The welds and crimps in a capacitor are a common failure point with high currents. Reducing currents with parallel capacitors insures long life.

Use lower one. Loadmaster can make it higher, but not vice versa.

Hi Steve, Thank you very much for your comments! First of all i Pm-ed you and wrote you an email about buying 2 Loadmaster XP PCB-s. Please respond when you can. I got your point about resistance. I am not in hardware at all and i may say something stupid but I have side question about cap(s) and RMS currents: From the opera videos on youtube he is using at lest 6-10 caps electrolytic around 6000uF - 10000uF in total and PWM freq 100-120 Hz from memory You are using one 200-400 uF film type at 3.9-5 Khz Pwm. His explanation is that each cap should see no more than 1 Amp and his total voltage swing around capacitor bank is about 2 volts. So that difference in capacitors is due to Loadmaster XP Higher pvm frequency or due to the fact that film type suggested film type cap can take 15A RMS current? Some of the Loadmaster Xp photos (Mike in Wisconsin) showed folks using three film caps. My question is what would be the best setup to achive 10+ years capacitor life Maybe 2-3 200-400 uF film type in parallel or this is over kill? Cheers Hristo

Hi Alex - Well, nobody has ever said that to me before! Thank you for your comments! All the best, Steve

Hi Graham. Please see above for AC - DC heater comments, for PCB please contact me PVhotwater@btinternet.com. Cheers Steve

Hi Graham & thanks for your interest. Well DC heaters and AC heaters are just resistance wire in a metal tube, they are essentially the same thing. A resistor will dissipate the same power if you put 12V DC across it or 12VAC RMS. My understanding is 'DC' ones get named 'DC' as they are designed to have a certain power output rating when targeting a common DC setup market place - i.e 12V, 24V, 48V DC etc. Ultimately the Volts and Power rating of a heater relates to it having a specific resistance value. Yes, a key LoadMaster attraction is DIY, - avoiding an expensive MSC approved PV & inverter install, no requirement to register a PV setup with your electricity (DNO) provider, no expensive immersion diverter device etc. PLUS, if you do have a PV grid tie system, (which in many instances in the UK are limited to less than 16A / 3.68kW), then having a totally stand alone, grid isolated PV hot water setup effectively typically removes the 2nd highest domestic consumption load away from your AC inverter, thereby freeing up more solar AC KWhr for other loads. LoadMaster could allow you to benefit from say 6kw of PV on your roof whereby only 3.6kw of it has any connection to AC grid bureaucracy. Cheers, Steve

Well Done Peter! Great job. Not only have you played a small part in reducing CO2 but you will also save a load of money!. 'Switching excess PV to an Inverter input' - Around line 332 in V95 code you will see you can set the mode for the 2nd Output FET;- Output2 = NotFitted; (the default 'single output mode' with Q4 FET 'NotFitted), or Output2 = Switch; (i.e Once the primary output reaches its set temperature, Q4 is simply turned fully on - switching the low side of PV to say a small G.T inverter /charger etc. or Output2 = MPPTHeater; (i.e the 2nd output FET Q4 drives a 2nd resistive heating element for water or space heating using MPPT to deliver max power. An extra AuxTemp sensor is used to temperature control this 2nd output. I have used 'Output2 =Switch' to switch excess PV to the input of a Solis Mini 2.5kw inverter. This worked fine, - having the capacitor effectively across the inverters input had zero effect, I really can't comment about other inverters but doubt it should be a problem. "Wire Inverter to Consumer Unit or fused Spur etc"?..umm. Most guidance say's directly to C.U via AC isolator etc -but i've seen all sorts! Perhaps look at Pluginsolar.co.uk. In the UK all Grid connected inverter installs should be registered with your D.N.O (SSE etc). What I can say is that once you have gone to all the effort of installing an inverter, then rather than just switch any excess from the 'PV Hotwater' array to to it (which will be small to zero excess across a number of months), you will just wish you had a second array dedicated to the AC inverter!. (see earlier comments about 3.68kW microgeneration limit in the UK). Cheers Steve

Hello, Built my Loadmaster system earlier this year, located midlands UK using 4 x 270w series panels to a 240v immersion heater. Worked fine but recently upgraded ro 5 x 265w series panels which according the Loadmaster notes is a pretty good match to a 240v immersion heater. The improvement is immense and in the recent sunny days have achieved a blue led and my 150L tank at 60C. Eventually plan to upgrade to 2 parallel arrays of 5 panels which will double my output. I'm assuming when 60c is hit the Loadmaster output can be automatically connected to a small grid tie inverter and onto 240v. Does the grid tie inverter need wiring to my main distribution board or can it be plugged into a switched 13A socket? Keep reading but getting confliction answers! Regards Peter

Good Morning Steve, Thanks for your reply. Please excuse my ignorance, as I am not an electronics or electrics expert, but can the loadmaster drive a DC immersion heater or does it have to be AC? I currently have an AC immersion heater available but my have to change my tank in a while and was just wondering which way to go. Can you let me know the price of one of your Loadmaster PCBs? Once again thanks, Regards, Graham Willsher

The capacitor effectively sits across the PV. As it charges from the PV the volts across it will ramp up slightly. At the same time its supplying pulses of current (i.e a controlled amount of charge is removed as the output FET turns On:Off). The capacitor therefore sits at the array's Vmp DC volts but has a Volt or two of Pk-Pk ripple across it as charge is put in and then taken out. The Cap is therefore not seeing purely DC. RMS ripple current from the capacitor can be nearly half of the arrays maximum current depending upon PWM dutycyle (only when PWM is 100% ON will there be no ripple current). The capacitor must have a suitable ripple current rating, a low impedance (else that ripple current will effectively lead to power dissipation in the Capacitor and it getting hot) and good pulse handling capability. It's not just a smoothing cap but plays a key role in delivering charge and energy at the correct load impedance to extract max power from the array. You may find some electrolytics that could do the job, however this type of application best suits film type capacitors. A suitably rated film type cap will last forever, Electrolytics can deteriorate over time esp. with high ripple and high temperatures. (take a Google at 'DC link capacitors'). Cheers Steve

Hi Vladimir. This sounds like PWM switching noise is somehow getting into the digital ground or being picked up in cabling. How have you assembled the circuit? - made a PCB,? used 2oz copper, stripboard etc? The layout is critical and requires a good attention to the segregation of Power Gnd and Digital 0V with only a single point of them joining at the current sense resistor. No PV switching currents must find their way into the digital side of the circuit. The Inductor, Capacitor and Diode on the output side are key to slowing dV/dt and dI/dt and this reduces the radiation of switching noise which could potentially corrupt sensor comms (are they fitted?). Loadmasters Power (PV) Gnd & digital 0V must remain isolated from earth. Have you seen the sensor wiring notes in the 'External wiring diagram' of the 'Assembly notes' document in the downloads section? (i.e using twisted pairs in ethernet cable with the cables shield connected to PCB main ground point (U12) at loadmaster end only). Does the Water cylinder have a good earth connection? and are all sensors & sensor cables isolated from earth at the cylinder? Avoid running the sensor cable adjacent to the Heater power cable. If you still have problems, please drop me an email PVhotwater@btinternet.com. Cheers Steve

I had issues with dallas sensors too... So i started using TMP36 sensors measured by ADS1115 DAC. My "PCB" is a mess :) , so i have a lot of noises around which are not good for digital temperature sensors. Analog sensors pick that noise too, but it can be reduced by using small capacitor ant resistor.

Hi Isdeekelis Many thanks for your interest and compliments. It sounds like you also have a very interesting project going on there. Why 5Khz...(its currently at 3.9kHz), well, initially I had problems getting high PWM frequencies and reasonable PWM resolutions on a Nano, however that's now achievable. As the basic principle is Capacitive energy storage I was aware dielectric and switching losses could rise with freq (but probably still unimportant - just couldn't find data for many caps etc), There is some audio noise (see assembly doc) but its really minimal. I modelled the cct in TI tina and then ended up at a common cap value and freq giving only a few Volt ripple in the PV Vmp volts. Basically! i haven't had a major need to try higher frequencies - maybe one rainy day i will test it out. Use a pre-set range etc for Vmp? - Well up until 2 days ago! I had never seen a problem of multiple peaks in an arrays power output - a project builder having an array of mixed panel types reported an issue were it could lock on to a lower power level peak. In many systems, with an array comprised of the same panels and with no major shading issues then there has been no sign of an mppt tracking problem. Adding some Vmp acceptance window in the P&O mppt code could definitely be an option to fix that. As far as I am aware many Mppt routines just assume a normal V-I curve and single power peak. (if you see any code for that I would love a copy) All the best for your project, Steve

Wow, it has been a long time since I've been here. I use a fixed Vmp on my heater control though it is capable of tracking via temperature from that set point. The main reason is the water heater control operates in parallel with the charge controller to harvest excess energy when the battery nears full charge. Lead batteries have charge cycles which reduce maximum charging. At 8am I'm still able to divert some current to heating. A fixed voltage also allows prioritizing certain loads. I have a second 40gal water heater in my detached garage just for laundry set to a slightly higher voltage that kicks in when the house tank is up to temperature. Typically 1-2.5KWH gets diverted which is enough to heat the upper 15gal of water. Capacitor bank must be isolated with diode when used with charge controller. The Polish ACTii had fixed voltage capability option besides IV tracking. The newer ACTii/PL although better hardware design does not. I should add that my location has intense shading with over 75% of panels shaded at any time and my charge controller gets lost quite often. A circuit disconnects the charge controller when that happens to reset it. I wish the controller had the option od selecting a normal operating voltage band. I gained water heating capability without adding any extra panels to my system. So many off grid are looking to add diversion capability to heating water without consuming charge controller, inverter and battery capacity. Fixed voltage is certainly a valuable option to have. With solar thermal, it just becomes junk on your roof one the tank is up to temp. PV can always find another use for that energy.

Hi Craig Thanks for your interest in the project. You will most definitely see a benefit from using mppt in winter months. At the moment I am holding back a little from publishing the PCB gerber data. There is now a growing number of systems working and being made around the world and I wish to collated any feedback from those prior to releasing artwork etc. I have some PCBs which I can supply. Please drop me an email to pvhotwater@btinternet.com, Cheers Steve

Hi Leonard Glad that you liked the project. Drop me a mail on pvhotwater@btinternet.com Cheers for now, Steve

Hi John ...we have now exchanged messages via email, however just to say I'm pretty sure the photos you sent point to issues of dissimilar metals. Cheers, Steve

Hi Alex. Ì am pretty sure I have a few spare blank pcbs still available but need to confirm when I'm back on the weekend, I will also check postage cost etc. In the mean time please can you drop me an email to pvhotwater@btinternet.com. Cheers Steve

Hi GreenWestern Well LoadMaster effectively has two outputs that can be used sequentially, I have just updated firmware such that when the main water store has reached temperature, the primary FET output is disabled and the second FET output will either, A) divert power (using MPPT) to a different load (say a 2nd hot water store, resistive space heating etc), or as in my case, B) simply switch the PV supply (i.e fully ON, no MPPT) to the input of a small (2kW) GTI. The reality i find is that the times when you you would benefit from space heating ocurr at the time of the year having the lowest excess kWHr of solar energy. Summer months have WAY more excess in PV kwhrs, so for me, transferring this large amount of summer excess into to a Grid Tie Inverter for daytime load consumption ...washing machine, freezers, small battery store, etc gives me the biggest opportunity to maximise useage of my annual generated PV kWhrs. Anyway with renewables and PV etc there is no single golden or perfect solution. Cheers Steve

Hi Tgrauss Well from your description it sounds you have plans for a large system,...12kw, dual inverters, battery storage etc. With such a large investment in an 'AC electrical' type system already, my thinking is that you are probably best to simply use 240vAC and a say a PV immersion heater diversion type controller (immersun, iboost etc). Load master targets at a much simpler and cheaper approach to capturing and storing as much PV energy into hotwater, or space heat and then maybe switching any excess, mostly in summer to a small GTI inverter. It also suits 2Px5S or 2Px6S, 2.5kW to 4kW array configs..large inverters will generally require higher voltage PV configurations Cheers Steve

Hi Greenwestern, Well, unfortunately at the moment the supply of a complete unit is not on my radar, although I fully recognise and appreciate your comments, I only have some blank PCBs. There are numerous people around the world on web and Youtube (Opera) etc who recognise PV offers a great & cost effective solution to solar hot water. There are indeed simpler solutions, especially if you have a situation/location where you really dont need to squeeze every watt out of the PV into the heating (that isn't the UK!). I've seen simple on-or-off control approaches (solid state relays or FETs etc) where a single heater load resistance is optimised at around R= Vmpp /(2/3 of Impp)... where Vmpp & Impp are the ARRAY's max power V&I values. This recognises that for most of the time the array will never be operating anywhere near to its max power point. Loadmaster tracks / reduces the effective load resistance perfectly to match any reduced solar conditions and a system can be designed to use standard cheap immersion heaters etc. Switching in different heaters may present issues of having a cylinder to accept multiple heaters and seeking non-common heating elements of appropriate R and power rating etc. Note also ,High Voltage DC and Relays are a highly dangerous No-No (DC Arcing). Your comments, and others, do make me wonder if there is scope for a very cut down kit design ....(i.e the same pcb but only populated with the absolute essentials -(i.e say single RGB LED push button switch, single temp sensor, arduino plus the power side electronics only, -Display, real time clock, multiple sensors etc could easily go). ..I feel a winter project comming on. Where are you based? Cheers. Steve

Hi Eidolontech. Many thanks for your comments and input. As an 'off-gridder' you obviously have an equally valid and good solution to delivering PV solar power into hot water. I am not 100% off grid and most likely never will be. I recognise your observation (and frustration!) regarding some comments & opinions on renuewable energy forums etc which appear 'blinded' that Solar thermal is the only viable approach to Solar hot water (sadly that's outdated, uniformed, narrow minded rubbish!.) Apart from PV DHW requiring more collection area, basic maths and understanding should show anyone that in 99% of applications, today PV for hot water wins hands down:- PV is now lower cost, is just wires, some minimal reliable electronics, uses standard heating components, is near zero maintenance plus spare electricity is versatile. PV hot water has no issues of anti freeze/corrosion fluids, no pumps, leaks, failed vacuum tubes, no maintenance costs etc etc). Heating water uses a LOTs of energy, typically the second a largest area of energy comsumption in the home (Space heating = No1) so, as a relatively cheap, straight forward project, in the scope of many competent electronics & DIYer's, PV feels like a no brainer solution to having lots of free hot water! I take my hat off to you for going off grid! Where? Cheers Steve

eidolontech, I am in a similar situation, off grid more panels less battery. I have been manually controlling the water heating load and want to automate this. What are you using for a controller for the heat load?

Steve, Would you happen to have a PCB available for this project? My email is trwells71@gmail.com. This would be for a PV array intent on heating water to radiate through a floor system in a utility room. This is to keep the room above freezing year round at 8800' in Colorado. The room is not built yet but when built it will be heavily insulated, have hot water radiant running through the floor with a tank heated by PV panels. There will also be an oil immersion electric radiator plugged into the grid for backup or a second grid connected heating element in the tank. At least that is the current plan. This cabin is a summer cottage that gets snowed in during the winter months. My wife and I like to ski to it a couple times in the winter. It is heated with a wood burning stove and I would like to set up a utility room for the water well related tank and accessories to be kept from freezing. Otherwise that all gets drained for the winter and we melt snow for water. It is no problem for the rest of the cabin to be frozen but ultimately if I can keep the whole place above freezing that would be cool too. Thanks Thaddeus

Hi Judesanson, Thanks for the comments and its really great to know this project has motivated you. I've seen lots of 'half baked' projects on Youtube etc but i really felt this application and our warming planet could benefit from a solid, open project like this. I do have some extra (blank) V4 PCBs (thats my final 'perfect! PCB made by JLC, 2 Oz copper). Where are you based? I may be able to put these on ebay etc

Hi Judesanson, Roger and that's great news. Let me look at cost and shipping logistics over the weekend and i will get back to you ASAP. I'm also trying to work out how to contact you without putting emails and paypal info all over this comments section!. Cheers for now, Steve

Hi Stevetearle, I totally agree we need more and more properly thought out DIY projects that can help those in the maker community do their bit to reduce CO2 and build something thats very cool. I would be very happy to buy one or two of the PCB's for my house and my rental property. I'm located in Winnipeg, MB, Canada. Could I order that from you directly and pay with PayPal? Thanks

Steve I have working systems and very interesting in your corrosion comments, can we chat please,

Hi Dougal & Cheers for your compliments. I also saw a similar comment on a forum somewhere suggesting you can't use a immersion heating element on DC due to electrolysis. Personally, I suggest that is ridiculous and is most definitely not a problem!. If the heater's resistance wire and its positive and negative connections were sitting in the water, then absolutely 'Yes', - you would have electrolysis plus a massive safety, corrosion & flooding risk whether AC or DC powered!. However, a heating element is fundamentally resistance wire contained inside a dry, fully water tight Incoloy or Titanium tube (you cant use a copper immersion element in a stainless cylinder due to electrolysis of dissimilar metals sitting in the same mineral filled water). You certainly wont find a resistor that can't be used on DC!. I have worked on this project for about 2.5 years and had a system running for nearly 2 years in different stages of development. I would of course say this, but honestly I am totally impressed by the performance & reliability which exceeded my best expectations, I very nearly have a years performance data logged for my system. As you probably appreciate, PV energy generation for a location, time of year etc and the energy required to heat a given volume of water by x degrees C is simply maths. In my experience the maths and reality are very close. Steve

Yep, I have a 3kW 5S x 2P array of REC Solar 300W TP2 panels on my roof. In the downloads section i've included a copy of my excel design spreadsheet - one worksheet shows images of my setup plus a review of its performance based on a download of approx. one years data. Cheers, Steve

Thanks...That's the answer I wanted... Practical experience not theory. From those numbers I assume your using a fixed roof mounted array ? This type of design is one of 3 options I'm considering to boost my existing solar hot water. I have some panels about to be retired from one of my trackers.