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jockmacrea avatar image
jockmacrea asked

Do I have Enough power?

img-0378.jpegI have completed building my garden autotracking solar system Which tracks the sun from morning to evening therefore maximising on my investment.

It comprises, 1x 435w solar panel, 1 x Victron Smart Solar charge controller MPPT 100/15, 1 x 100ah Renogy lifepo4 self heating battery. 1 x 1Kw pure sine wave inverter.

My ambition is to supply a garden outhouse with 240vac to run a washing machine and a tumble dryer. These would be used about 3 maybe 4 times a week.

My question is, am I generating enough power, should I add another 435w solar panel? What fuses and disconnects should I use?

A hookup schematic would be a great help. Many thanks

MPPT SmartSolar
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4 Answers
lucapif70 avatar image
lucapif70 answered ·

Buongiorno. Anche il regolatore Mppt non è sufficiente. Ti serve almeno Mppt 100/30 con quel pannello.

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matt1309 avatar image
matt1309 answered ·

HI @Jockmacrea

Cool project!

It's really hard to say without some solar data. Your best bet is to run the system for a week and just use that data. Most folk wont have tracking system (a lot of the time a large daily tracking systems cost is expensive and the cost/benefit is usually quite close so most folk dont bother) so using other peoples data might not be accurate.


However given your description I dont think you'll have enough peak power for your use case. A tumble dryer can draw quite a bit of power, your battery is 100ah 12v?

If so that'll probably be able to provide max 1.2kw (1C draw). Which might not be enough for the tumble dryer.

I'd probably suggest 3 maybe 4 of those to be safe just to cover the peak draw.

In terms of energy (as a pose to peak power). If you've got 900w of solar, south facing my guess would be in summer you'd get 4kwh a day in summer.

If I guess a washmachine uses 1.5kwh and a tumble dryer say 4.5kwh. That would be 6kwh per wash. And say you need solar to charge that up every 2 days. In summer you'd probbaly be fine, but winter you'll probably need some more panels as well.



EDIT: and of course you'll need an inverter. 3000kva model might manage it, if you've got grid for power assist just in case it isnt.

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gazza avatar image gazza commented ·
....what @matt1309 said!! Your 1kW inverter will most likely not be powerful enough. A washing machine alone can peak over 2kW while heating the water and the tumble dryer is probably more hungry! For a 12V system your going to be pulling peak currents of 180A or more. So, I think the max discharge rate of your battery is going to be challenged. You will need a couple in parallel, check the spec of your battery? Maybe also consider a 24V system to keep the cable dimensions sensible?

Love the concept of the tracker though, nice project!

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jockmacrea avatar image jockmacrea gazza commented ·

img-0379.pngThanks Gaza, you’ve worried me now, it looks like I built a ‘dead duck’ and moving to 24v is out as I’ve just paid nearly £400 for my new battery. I could add another panel and perhaps purchase a much larger inverter. Now then, tell me about ‘sensible’ cable sizes you mention.

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jockmacrea avatar image jockmacrea commented ·
Oh dear, seems I have may have been a tad over enthusiastic. I’m a raw beginner and thought I’d bought all the best parts. I just paid almost £400 this week for a nice battery, sadly I can’t afford another one. I could add another panel if that would help. A 2kw inverter is within reach at the moment. i have a household 4kw installation but no battery so everything is going to the grid. Is it possible to supplement this with the power from my new tracking system ?
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gazza avatar image gazza jockmacrea commented ·

It is a nice battery and inverter... Renogy gear is perfectly useable but I reckon you are going to need at least 2x 12V batteries in parallel to get 200A discharge rate. Interestingly that spec says "NOT to put them in series", I guess that is to do with the built in BMS? So that rules out a 24V system with that battery. Would it be possible to go back to your supplier and see if they can recommend a battery set up to deal with the higher expected load? Additionally I would try and get a bigger inverter, or at least save up for one, maybe you could get a refund for that? The thing is a 1kW inverter is only really ever going to be big enough for a "camping" type AC power source. Any home "utility" inverter should ideally be up around the 3kW+ region. Hence home systems tend to go for 48V battery set ups to keep the current manageable.

Regarding your household system I would go back to the company that installed it as they will have all the design details and they would be able to tell you what would be required. Generally, however, domestic "grid tied" systems rely on a string of identical panels, I am guessing the panel you have on your tracker is not the same as for your home....?

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matt1309 avatar image matt1309 gazza commented ·

Hi @Jockmacrea


I'd do what @Gazza suggests and reach out to the folk you purchased the battery from. They may just offer you something larger if you return the other two. It is a shame you can't run them in series. (I've had some surprising success on returns in this market when I've ordered something by mistake)


As gazza said check with your originally house installer however one potential option if it's supported/in budget would be to get a Victron inverter and run it in parallel with your current system/grid and have bulk of your loads in ACIN (grid tied) side.

And then critical loads on ACOUT2 side (maybe the washing machine). Maybe the washing machine etc on AC out side. You could then use you tracking PV into the battery connected to Victron inverter, and also have excess house PV go into the battery. You could potentially get a smaller victron inverter/charger (although still expensive) and have washing machine on ACOUT2 and use power assist to use battery + some grid if the washmachine power peaks above what the inverter can handle.


Have a gander through this, might give you some ideas:

1. ESS Introduction & Features (victronenergy.com)

You would "AC couple" your house PV on the ACIN side if supported, most are supported you might just need to add an additional energy meter to it so that victron system can see how much is being produced.

AC-coupling and the Factor 1.0 rule [Victron Energy]


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grahamwood avatar image
grahamwood answered ·

The first thing that I would do is buy one of these:- https://www.amazon.co.uk/dp/B0BZYN6544?ref=ppx_yo2ov_dt_b_product_details&th=1

Use it on the devices that you want to run on your system. A full 90 degree cycle on your washing machine (wash some sheets or something) and a full cycle on the Tumble dryer. This will then give you the data so you know exactly what your power requirements are.... and then add 20%.

Once you have the power requirement data, then you can work out what you need solar wise to satisfy the requirement.

Always know what your dealing with. At the moment with 1 panel you are going to need a shed load of batteries. The more panels you add, the more strain on your tracking system. Get the power usage data first, and then decide whether it's doable.

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jockmacrea avatar image jockmacrea commented ·
Thanks Graham, good advice. If I purchase another 12vb 100ah battery and use it in parallel with existing one, do they have to be the same make? the second battery may not have a BMS as does the first.
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matt1309 avatar image matt1309 jockmacrea commented ·
Hi @Jockmacrea it'll depend on the manufacturer but most usually specify it's got to be the same. I'd recommend reaching out to place you purchased it from. If you're asking for an upgrade they might just swap the units with minimal/no extra charge.


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grahamwood avatar image grahamwood jockmacrea commented ·
I know hindsight is a wonderful thing but this type of project really lends itself well to building your own batteries. Eve grade A 280Ah prismatic LiFePO4 cells with JBD BMS's is a value for money option. You could build 3 12v battery units and hook them up in parallel for a lot less money then ready built. That would give you all the power you need.

With your MPPT CC you would be looking to have a series array to produce higher voltage. This makes the CC a lot more efficient. I'm assuming your panel is 12v. If you get another panel then connect it in series.

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jockmacrea avatar image jockmacrea grahamwood commented ·

Thanks Graham, and everyone else for your valued input. I have now asked my retailer to cancel my order for the two batteries. (not yet despatched) I will now buy 4 EvE Grade A 280Amp prismatics and a BMS with Balance. (recommend one please) The tests results show washing machine 1 h 45 min with a max of 2.05Kw and the dryer 48 mins and a max of 2.6Kw so I’m considering a 2.5 to 3Kw inverter (cont rated) As to my location, I’m situated in a wee quiet village of Denholm in the Scottish Borders. Anyone for Haggis ?

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matt1309 avatar image matt1309 grahamwood commented ·
I can't help but agree with @Grahamwood, especially give you've already created a cool DIY project. (although I prefer the JK BMS if you can fork out a little extra for it).



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jockmacrea avatar image jockmacrea grahamwood commented ·

Well Graham, i bit the bullet and bought a second identical battery. That in parallel gives me 200Ah I spoke to Ivy Watts and she says that's 2.5Kw. My inverter is a 1Kw pure sinewave. I will now search for a larger one. Would I get away with 2k continuous with 4Kw peak? No going back from there. My panel output is 435Watt at 45V. Tomorrow I will test the washing machine with the power monitor in line. We'll see how much power it consumes. More to follow.

George

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gazza avatar image gazza jockmacrea commented ·

With a pure sine wave inverter you might get away with that.... With the power monitor watch for the transients, and try on say 40° temp to see what it uses to heat the water.
In terms of "overall" power storage it is difficult to give accurate estimates of what solar you will generate each day due to your cool tracker system.... time will tell. Not sure of your exact location but you can look up "average" sun hours in solar maps on the internet. For example southern UK is around 3.2. So, what tends to happen is that in the winter you might get the equivalent of 1hr a day (or less in heavy overcast) but in the Summer you may get 6hrs a day. Most of us don't get enough in the Winter and make more than we can use in the Summer!! Good decision on adding the second battery, both for discharge rate and storage capacity!

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gazza avatar image gazza jockmacrea commented ·

Actually @lucapif70 is correct in the sense that your output current will be limited by the MPPT. Just looked up the max PV recommended is actually 220W for a 12V system. You have the input voltage headroom but that MPPT will not get the best out of your panel.


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jockmacrea avatar image
jockmacrea answered ·

Sorry to be a bore on this one guys but here is what I now have.

MPPT 100/30 with the option of getting a 100/50. A 3Kw Continuous 5Kw peak 12 to 240Vac pure sine wave inverter and 1 x 12V Eve Grade A 280 Ah prismatic life Po4 battery with Active BMS.

Washing machine time was 2.0Hrs with max of 2Kw

Dryer was 45 Mins with max of 2.6Kw

Am i getting there yet. My. Pockets are now empty!

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gazza avatar image gazza commented ·
:) You're doing good!! Definitely in the ballpark now. The thing is about renewables, which you learn when you start to set it up, is that it ain't cheap...!

So, you definitely have a decent sized inverter and a good match of MPPT to the panel you have chosen. Once you get it hooked up and the BMS sorted then it should be good for ~ 3kWH... ish?? A typical wash cycle is around 1.5kWH (don't know about the dryer cycle?). Do follow manufacturers instructions on the battery charge values and recommended discharge state for long life.
The exciting bit will be to see how much "extra" you can harvest over and above a fixed panel! Keep us updated.

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