Solar DC water Heater - Shear madness or absolute genius?

[ExpatOilWorker]

Using solar electricity to produce hot water is breaking with tradition, but is it as crazy as it sounds?

 

Our daily shower consumption is around 150 l, so using Crossy's 0.25-0.9 kWh/m2, 8 m2 of solar panels are required to produce +15 C and ensure a warm morning shower. I take the liberty to ignore heat loss from the tank.

 

Cost: 

30,000 baht 200 l tank + shipping

12,000 baht 4 ea. 2 m2 solar panels

8,000 baht wiring and panel roof frame

Labor: Free

 

Assuming and average production of 4 kWh/day and since we pay 16 baht/kWh, payback time is 781 days or just aover 2 years.

 

It also a project with a nice fun factor and one major benefit is that the tank can be very close to the shower.

Currently we are using a gas heater, but it is a full 1 minute from the shower and does have an annoying 3-4 C temperature variation when it cycle on/off.

 

I did notice the 50 units minimum order, so I just need 49 of you guys to be in on the idea or I need to convince the vendor to send me a sample.

 

[Crossy]

Why not, if the energy isn't doing anything else heat water.

 

Do these things have smarts to get the best out of the panels or are they just a resistor?

 

Why are you paying 16Baht a unit?

 

[ExpatOilWorker]

2 hours ago, Crossy said:

Why not, if the energy isn't doing anything else heat water.

 

Do these things have smarts to get the best out of the panels or are they just a resistor?

 

Why are you paying 16Baht a unit?

 

We are connected to a community genset, shared among about 30 villas. Price fluctuate a bit, but generally stay around 15-20 baht/kWh.

Koh Tao is still not connected to the mainland grid and a battery of about 6 big gensets run the main grid on the island. The state charge 5-8 baht/kWh and subsidize every kWh produced, but we are too far off the beaten path to connect to this grid.

 

In what way can a heating element be smart and get more out of a solar panel?

[Crossy]

1 minute ago, ExpatOilWorker said:

In what way can a heating element be smart and get more out of a solar panel?

 

Maybe have an MPPT tracker to get max power, bet it's just a resistor though.

 

Got it about the genset, add more solar!! One pays the price for being in such a lovely location.

[ExpatOilWorker]

1 hour ago, Crossy said:

 

Maybe have an MPPT tracker to get max power, bet it's just a resistor though.

 

Got it about the genset, add more solar!! One pays the price for being in such a lovely location.

Actually the 200 l tank is 6 resistors, each rated at 290 W.

I am not really sure what the x2 for the peak and open circuit voltage means. You have any idea?

Bit tricky to find panels that will only produce 290 W at a 126 open circuit voltage. 4 ea. 30 V small 50W panels in series is close. Any better solution?

[ExpatOilWorker]

2 hours ago, Crossy said:

Got it about the genset, add more solar!!

It gives me immense pleasure to support my old industry when I turn on the kettle on the morning.

Every second day or so, 2 fully loaded fuel trucks roll on to the island.

But, yes solar is fun and make a lot of sense, except we can't produce back into the genset grid.

 

[driver52]

methinks this is better genius ????

 

 

[Crossy]

10 hours ago, ExpatOilWorker said:

But, yes solar is fun and make a lot of sense, except we can't produce back into the genset grid.

 

Yeah, you'd have to go hybrid if you can't export, adds the $$$ ???? 

[Crossy]

12 hours ago, ExpatOilWorker said:

Bit tricky to find panels that will only produce 290 W at a 126 open circuit voltage. 4 ea. 30 V small 50W panels in series is close. Any better solution?

 

Your earlier spec. sheet suggests that regular 300W panels should be in spec. In reality going to 340W panels (now easier to obtain) would likely be just fine.

 

The 126V is the maximum panel open-circuit voltage, never to be exceeded on pain of the magic-smoke exiting!!

 

The max power voltage is 1-150V (which actually makes no sense with an O/C max of 126V).

 

 

[ExpatOilWorker]

24 minutes ago, Crossy said:

 

Your earlier spec. sheet suggests that regular 300W panels should be in spec. In reality going to 340W panels (now easier to obtain) would likely be just fine.

 

The 126V is the maximum panel open-circuit voltage, never to be exceeded on pain of the magic-smoke exiting!!

 

The max power voltage is 1-150V (which actually makes no sense with an O/C max of 126V).

 

 

But, if the heating element is just a resistor,  would the 46 V open circuit not only generate 106 W of heat, effectively wasting nearly 240 W of the 340 W panel?

I am assuming the 290 W is for the nominal 126 open circuit voltage. 

 

 

[sezze]

https://www.lazada.co.th/products/40l60l10-i1824058707-s5480830729.html?&search=pdp_v2v?spm=a2o4m.pdp_revamp.recommendation_2.1.630d6401RJlpU7&mp=1&scm=1007.16389.126158.0&clickTrackInfo=7de2f2ae-e93f-4c5a-abc5-fc3bc5dfec87__1824058707__3896__trigger2i__202835__0.28__0.28__0.0__0.0__0.0__0.28__0__8__PDPV2V__251__null__null__0____5874.0__0.5771195097037793__2.0__1__2484.0__101825,122209,94498,106116,94667,95499,107629,94190,103150,105742,120657,112210,117557,97876,100116,93239,89566__null__null__null__3650.16537_3650.16544_955.3632__null__13499__null__0.0__0.0__elp.2_starplus.4__

 

Theres many more on lazada , although they arent top searches. This is a 2000 watt resistor,add solar as you please . Advantage , you solar install can still make electricity for grid or off grid use . There are many solutions , but basically making electric out of solar and changing back to heat is not the most efficient .

https://www.lazada.co.th/products/aieoo-12v-100w24v-300w36v-400w48v-600w-i2618934798-s9390421278.html?spm=a2o4m.searchlist.list.141.50f16d66bAg2z0&search=1

this 1 can use straight DC voltage , lower wattage , add tank as you please ( and a temp cut off , can look up links for that also) .

[talahtnut]

In 22 years I've never had a hot shower, save the bother and have cold showers,

like a traditional Thai.

[Crossy]

13 minutes ago, ExpatOilWorker said:

I am assuming the 290 W is for the nominal 126 open circuit voltage. 

 

The O/C voltage is usually the MAXIMUM voltage the works can handle. Exceed it on a charge-controller and the magic-smoke comes out! Simple resistors are rather more tolerant.

 

The panel you show has V_MP (max power voltage) of 38.2V and I_MP (max power current) of 8.9A giving about 340W. So the ideal resistor would be about 4.2 ohms.

 

[sezze]

Did you ever think about some DIY ,

think this ...

https://www.lazada.co.th/catalog/?spm=a2o4m.searchlist.search.9.7a5223fcmRzmtf&q=copper tube&_keyori=ss&clickTrackInfo=textId--9199461186115381833__abId--217103__pvid--254d56ed-e5c9-4bc6-871f-d76a4f965031__matchType--1__srcQuery--copper tube__spellQuery--copper tube&from=suggest_normal&sugg=copper tube_8_1

or cheaper

https://www.lazada.co.th/products/38-6-i2339990435-s7907542287.html?&search=pdp_v2v?spm=a2o4m.pdp_revamp.recommendation_2.6.77812aba8hYDu1&mp=1&scm=1007.16389.126158.0&clickTrackInfo=6ee95496-b6a8-4022-9513-4278f275f509__2339990435__5856__trigger2i__202835__0.054__0.054__0.0__0.0__0.0__0.054__5__8__PDPV2V__251__null__null__0____200.0__0.36__4.592592592592593__27__128.0__108012__null__null__null__3650.16544_955.3632_3650.16542__null__13499__null__0.0__0.0__elp.9_starplus.4__

Together with something like this ...

https://www.lazada.co.th/products/220v-100w-g3-4thread-i1788484488-s5243482557.html?&search=pdp_v2v?spm=a2o4m.pdp_revamp.recommendation_2.10.546862a9XBTulh&mp=1&scm=1007.16389.126158.0&clickTrackInfo=70e2130d-53e8-481d-8314-4b0721771fc3__1788484488__10100199__trigger2i__202835__0.227__0.227__0.0__0.0__0.0__0.227__9__8__PDPV2V__251__null__458814850__0____1656.0__0.572463768115942__4.333333333333333__3__708.0__89564,89566,92323,93239,95354,97766,100048,101411,101825,102652,103150,105742,106116,106117,107289,107629,110079,110142,110278,110570,111385,112107,112210,112638,113003,114584,115501,116778,117557,117559,117607,118008,118208,119232,119328,120159,120533,120657,120722,121085,121756,121868,121951,122209,122213,122650,122799,122877,125411,128280__null__null__null__3650.16544_955.3632__null__13499__null__0.0__0.0__elp.7_starplus.10__

Have cheaper or more expensive , all to your likes .

Add a black painted box , plenty of examples on internet around to make some kind of black box to put on your roof . The pump in lowest setting is about 30Watt is i read correct , and its a circulation ( like central heating ) pump .

[sezze]

44 minutes ago, talahtnut said:

In 22 years I've never had a hot shower, save the bother and have cold showers,

like a traditional Thai.

I've done cold showers from standard toilet big buckets ( used for all water in toilet , bathroom , shower .... )  . But after toilet paper ( yep done that also ) , it was the 1st thing i missed and changed when possible . I do not need much ( i can live very easy ) , but if i got the choice , toilet paper and hot water are very high on the list ( toilet paper being nr 1 ) .

[BE88]

Inexpensive solar system with no guarantee of hot water every day but almost

 

[BE88]

But if you want a perfectly functioning system with a lot of hot water in reserve

[pagallim]

I thoroughly recommend having solar hot water heating.   It's not only for showers of course, but for sinks i.e. shaving and washing dishes.   We have three bedrooms, all with en suite, and a downstairs cloakroom/shower room where a few years ago I installed an electric shower for those very odd occasions where we've had no sun for a few days and the hot/warm water has gone.   The system was already installed when I bought my house just over 13 years ago, and the house was approximately 7 years old then, so the solar system has been good for 20 years and never any maintenance.

 

A photo of my system.

 

 

[Damrongsak]

1 hour ago, talahtnut said:

In 22 years I've never had a hot shower, save the bother and have cold showers,

like a traditional Thai.

43 years ago I had a big plastic washtub that I filled up each morning from the cement ang and covered with an old side window from a bus.  By 4 p.m. it warmed up in the sun enough to be bearable.  It gets cold at night in the winter in Loei and there wasn't enough water pressure for any kind of shower. 

[BE88]

48 minutes ago, Damrongsak said:

43 years ago I had a big plastic washtub that I filled up each morning from the cement ang and covered with an old side window from a bus.  By 4 p.m. it warmed up in the sun enough to be bearable.  It gets cold at night in the winter in Loei and there wasn't enough water pressure for any kind of shower. 

Like everywhere in Issan, but with a pump and a tank my shower works great LoL

 

[ExpatOilWorker]

7 hours ago, Crossy said:

 

The O/C voltage is usually the MAXIMUM voltage the works can handle. Exceed it on a charge-controller and the magic-smoke comes out! Simple resistors are rather more tolerant.

 

The panel you show has V_MP (max power voltage) of 38.2V and I_MP (max power current) of 8.9A giving about 340W. So the ideal resistor would be about 4.2 ohms.

 

I got a reply from the vendor. Bit of a Chinese partial answer, but better than nothing. 

 

1) for single solar panel voltage suggest to b 36V and 2 pcs or 3pcs in serial connection.

2) each different capacity resistor is different according to the water tank capacity and transfering effiency.

Waiting for your reply. you can test some samples for more understanding .

 

My question:

Thanks for the quote and product information.

Why do you recommend to use 36-40 V open circuit panels, but in your tank spec sheet you have the open circuit voltage listed at 84 V and 126 V?

Is that heating element just an resistor type or does it have a MPPT tracker?

How many ohms is the resistor for the heating element?

[Crossy]

Oooh, you might be able to buy a "sample" or two.

 

The big plus of going this less-efficient way is that you can put the panels and tank where you like, running electical cable is far easier than running water pipe.

[ExpatOilWorker]

28 minutes ago, Crossy said:

Oooh, you might be able to buy a "sample" or two.

 

The big plus of going this less-efficient way is that you can put the panels and tank where you like, running electical cable is far easier than running water pipe.

Buying a sample is a nice way to purchase direct from the manufacturer in China at wholesale price. From the company profile, it could be a nice product, they also do water heaters that capture the heat from air conditioner. 

I suspect the heating element is just a resistor with about 4.2-4.5 ohms as per your earlier calculation. The 6x290W heating element for the 200 l tank is probably a roundabout Chinese way of saying it has two DC heating elements, each generating 290 W, 580 W or 870 W, depending if 1, 2 or 3 panels are in series. 

[Netease]

18 minutes ago, ExpatOilWorker said:

Buying a sample is a nice way to purchase direct from the manufacturer in China at wholesale price. From the company profile, it could be a nice product, they also do water heaters that capture the heat from air conditioner. 

I suspect the heating element is just a resistor with about 4.2-4.5 ohms as per your earlier calculation. The 6x290W heating element for the 200 l tank is probably a roundabout Chinese way of saying it has two DC heating elements, each generating 290 W, 580 W or 870 W, depending if 1, 2 or 3 panels are in series. 

 

[ExpatOilWorker]

7 minutes ago, Netease said:

 

Holy smoke! You have taken water and heat management to the next level. 

Do you have an aircon heat recovery system from Shintaeki?

I noticed your isolated PVC piping, what is that for?

I see you use the correct green pipes for your hot water.

 

A 60 KW electric pool heater, now we are talking. A gas heater would make much more sense.

 

[Crossy]

16 minutes ago, ExpatOilWorker said:

A 60 KW electric pool heater, now we are talking.

 

Our condo in KL had a cooled pool, very nice to plunge into after a good toasting in the sauna.

 

The locals didn't really like it "too cold". Tough!

 

[Netease]

1 hour ago, ExpatOilWorker said:

Holy smoke! You have taken water and heat management to the next level. 

Do you have an aircon heat recovery system from Shintaeki?

I noticed your isolated PVC piping, what is that for?

I see you use the correct green pipes for your hot water.

 

A 60 KW electric pool heater, now we are talking. A gas heater would make much more sense.

 

Separate heat exchanger and hot water tank. isolated PVC piping is town water in. stainless steel tank stored town water

[ExpatOilWorker]

Ups, this guy just killed the DC water heater industry (6:00 minute), and the key word is "solar diverter".

The idea is to have a big array of solar panels connected to one DC-AC converter and whenever the panels produce more than consumption and batteries are fully charged, the converter will divert the excess power to your EV car, boiler, etc.

 

This is the perfect solution and a perfect way to smooth out production variations, except apparently it is a future feature, so need to wait a year or two.

 

 

[tjo o tjim]

For Koh Tao, solar thermal is the smartest move if you like hot showers year round. For me, hot water was nice in November-December, but I wanted it as cold as I could get the rest of the year. 
 

The next best thing is a heat pump hot water heater connected to solar, if you have money to burn. 

[ExpatOilWorker]

13 hours ago, Netease said:

Separate heat exchanger and hot water tank. isolated PVC piping is town water in. stainless steel tank stored town water

You need a gadget like this:

 

https://s.lazada.co.th/s.ewrK9