Free hot water with a solar water heater

[Zasso Nouka]

Around this time last year we installed a solar water heater and have been running it for the last 12 months. Over that time it has really made some significant savings on our gas bill, we've gone from spending around 8,000円 a month down to 2,000 - 3,000円 and on a really sunny month it has even dropped below the 2,000円 mark. So that's just gas for cooking and the hot water is pretty much free.

We opted for an evacuated tube system from MMC Solar rather than the typical flat panel system you see installed on many houses because some of our neighbours have this system and they said it is easy to install at ground level or roof mounted if desired. Apparently the evacuated tube systems are somewhat more efficient than the flat panel systems and the MMC unit was cheaper than any of the other options.

Assembly is pretty straightforward, you put the frame together first and then mount the tank on top of that.



I will say that the frame could perhaps be somewhat better made, it will do the job but could be a little more sturdy. Next up you screw the evacuated tubes into the tank

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Luckily my father was visiting at the time and able to lend a hand, once all the tubes are in place it's time to connect the heater up into your hot water system, be it boiler, eco cute or whatever. The key to the whole thing is this neat thermostatic mixer valve.

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That controls the temperature of the water delivered to your boiler/eco cute or house. Some gas boilers will throw up an error if you set the valve over 38C so it's best to start there and slowly increase it to see how your boiler copes. Many boilers will be fine with a higher setting and won't fire up the gas when they detect the incoming water is hotter than the temperature they are set at. If you are using an eco cute just set the valve at the same temp as your eco cute and it will work fine and if you are delivering the water straight to your bathroom set the valve at whatever temp you desire. MMC provide some simple pipping diagrams here

MMC pipe diagrams

When inserting the evacuated tubes into the tank don't open up the box and lay the tubes out because if it is a sunny day the ends of the tubes get really hot and can burn your hands. Take each tube out of the box as it is needed.

Here we all are at the end of the day with a functioning solar hot water heater.

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What really sealed the deal for us, apart from free hot water, was the installer chap brought his mother along and she spent the day weeding our hatake. It has never looked so clean We managed to get this put together and installed in a single day but we did have the help of a professional as neither myself or Mrs N are licensed to work with gas boilers. The system should have paid for itself after 4 - 5 years and from then on it's almost totally free hot water.

[Makichan]

Hi Zasso Nouka,

Free hot water sounds very nice, I try to be as eco as I can and if that means saving some money as well we'd like to try it. When you say easy to put in how easy is that ? Can you put it all in yourself ? We already have an eco cute so can we fit it to that ?

[Ian]

Makichan - Just finished a DIY on the same size unit as ZN - Thanks for all the great advice!

Too early to give much feedback on performance at our location (mountainous with very changeable weather), but do like the design and materials a lot, other than as ZN says the frame could be better e.g. if in stainless steel, like the tank, I’d be happy to pay extra.

Took much longer than I expected to get ours up and running, mainly due to building a frame to support the unit above one of our water storage tanks, concrete cutting etc. Would have been much easier and faster if it was on the ground and closer to the house.

Looking forward to using the hot water produced in the coming months and years and seeing the kiwifruit grow up the front of the main frame too.
Pic of the water temperature (68C) inside the tank at around noon yesterday.

Re. using it with your Eco Cute. MMC has a diagram of that at the link ZN has in his post. Should work okay.

[Ian]

Seems like I can only attach three pics to a post. Here are a few more.

[Zasso Nouka]

Assembling the heater itself is very easy Makichan, and running the pipes isn't difficult either if you are using solvent weld joins. Make sure you bury them deep enough to be below the frost line and put plenty of insulation on. To save on costs I did all the labouring for the installer and he made the connections to our cold water and hooked it all up to the boiler.

As Ian says it should work fine with your eco cute and I think it is probably easier than using a gas boiler. On their diagram page MMC show mixing the water after the eco cute but I think it might be possible to feed hot water into the eco cute instead of cold and then on to your house, simpler and less piping as well. You'd need to speak with MMC and your eco cute maker or a professional installer to be sure but that would save you on electricity heating water in the eco cute.

@Ian

Superb job Sir

Looks really good mounted on top of the framework and should get plenty of sun there. Ours is in shadow from about 4pm yet it still gets plenty hot enough during the day so think yours will also be fine, a seriously professional job and will look very nice once the kiwi's have grown over the framework. Did you use flexible polypipe from the heater into your existing piping or uPVC ?

Your insulation work is a lot neater than mine , I think I'll have to revisit ours this autumn as some of the binding looks very untidy and is slipping already. Mrs N says your MMC sticker looks much happier than ours, we got the old style sticker.

It does seem like they skimped unnecessarily on the frame doesn't it ? Surely would have cost that much extra to include something a bit more sturdy or as you say a stainless frame given that the life expectancy of these things is 25+ years.

[Ian]

Thanks ZN.

I used flexible polyethylene pipe from MMC. Can’t see it in the above pics though, runs along the wall behind the water storage tanks. Wasn’t a straight run to the gas water heater at the house, so had to get extra 90 degree push fit metal elbows from Konan Pro. Would prefer not to, the less joints the better.

Well, now you have a choice for Mrs. N, a yunbo or a sticker.

[Zasso Nouka]

Maybe I could get away with a sunny sticker on the tractor But probably not

I hear what you are saying about the joints and elbows, all straight runs and smooth gentle curves the better but not always possible. Not sure about Hyogo but we're into our second day of rain here in Chiba so the tank is staying in the mid 30's but looks like next week should be sunny.

Do you find yourself checking the temp panel often ? I can't resist looking every time I go past it

[Ian]

Yes, very interesting to check the temp panel ZN.
Clear sky all day yesterday and we were up at 86C in the tank at 1 p.m. Went out, came back about two hours later and the water temperature was at 28C i.e. so we know the automatic relief valve works when the water boils and it drained the hot water okay, refilling with cold water. As we aren't there every day of the week I think we'll have to cover some of the tubes to avoid that situation, as in the MMC manual. At some stage in the future we will live there so it won't be much of an issue. Also in the MMC manual were pics of very deformed tanks that were left to heat up with no water inside, not a pretty sight. The power of the sun!

[Zasso Nouka]

That is something I'm currently looking into, it would be nice if the pressure relief valve would just let out enough water so that the incoming cold would take the temp down a bit and then stop. Obviously the current arrangement is vastly better than the whole tank going bang and spraying shrapnel all over the place but it would be nice if it didn't empty the whole thing and then start all over again.

It is quite surprising how much heat those evacuated tubes can harvest, to look at them you wouldn't think it could be enough to soften the metal on the tank but obviously they do. Our current work around is to drain off enough water when the tank hits around 90C through the house taps to drop the temperature back down to 85C or so. It's all a bit manual but at least it retains most of the hot water or having a bath every evening drops the tank temperature back to around 30 - 35C which will generally only be back to around 80C by the following evening.

[BrettRas]

Nice post Zasso, and Ian.

Looked into these MMC setups a couple years ago when deciding on the solar water system to go with. Seems like a nice unit, particularly if you are looking to mount it somewhere other than the roof.

I'm surprised to hear that the relief valve allows so much of the hot water to escape. It seems to me that it should only vent until the temp/pressure falls back to safe levels, rather than starting you over from scratch.

In the end decided on the more common panel type. Found a good price online for a 225L unit at somewhere around 10man including shipping it out to the island (which can be quite pricy). Doesn't seem like they are nearly that cheap at the moment.

Efficiency seems quite good, though I can't compare it to the MMC units, as I haven't used one. It certainly doesn't take much sunshine to get the water to a nice scalding temp!

No frills setup here, as cold water is piped directly up to the tank on the roof, and the hot is piped directly in to the faucet in the bath (with shutoff valves of course). The bath is wood fired so the tub just gets filled up and some wood is burned if necessary. Honestly the wood isn't needed most of the year. Just a little assistance in the winter if it has been cloudy, or if it has been cold and rainy for a couple days. It's actually almost unfortunate some times, as the wood fired bath water feels so good!

All in all solar hot water, whichever system you use, is spectacular! Such an efficient, simple use of solar energy. Can't encourage folks enough to do it!