Shower for use with solar panel pv heated hot water tank

linedried

Hi all,

Our Solar iBoost sends spare electricity from our solar panels to our hot water tank immersion heater (adjusting the electricity accordingly).  This saves loads of money as it heats up throughout the day.  Unfortunately, we are having trouble finding a shower mixer that is suitable!  The original Mira manual mixer meant little temperature control, so on sunny days, the water became uncomfortably hot.  

So we put in a Triton thermostatic bar mixer instead.  However, this requires minimum 65 degrees hot water (maybe intended for combi boilers) or it gives you mostly cold water (brr!)  It also needs full flow rate, and we want variable (water-saving!)  We need a shower that will give us a decent mix without requiring us to buy electricity to top up the tank temperature for showers when the tank is still heating up to 65 degrees.  

I hope this makes sense.  Any help would be much appreciated!

jennifernil

Are you expecting your panels to generate enough electricity even in winter to heat the water to an acceptable temperature?   

WIAWSNB

AfaIk, most thermo showers require a min ~60oC HW in order to blend properly. 65 seems a tad high.

If you really don't want to top up the hot tank to 65o, then I guess it's back to manual control! But this should work - I wonder why it was hard to control on yours?

Is your system vented or unvented? Are you certain the cold isn't 'mains' whilst the hot is tank-fed, or vicky-verka? 

As for flow control, if you fit thumb-turn isolating valves to the supply pipes, you should be able to tweak the H&C supplies down to your max level - both equally - and let the shower mixer do the rest. But, again, it relies on both supplies being at the same delivery pressure.  

jennifernil

We have solar panels and also a system that can send otherwise unused generation to the HW cylinder to heat the water,  but we can also heat it by gas.

Our system is vented, cold water tank in loft, so all water to bathrooms is at the same pressure.    When we renewed 2 of the bathrooms we fitted Aqualisa thermostatic showers suitable for a low pressure system.  We had Aqualisa before and they were very good, so stayed with the same brand.

In summer there is plenty of excess power to heat the water, but that would not be the case during the rest of the year.   We never had any problems with the water not being hot enough in summer, and in winter there were occasional days when there was enough sun to have an excess, but as we otherwise use gas, it would top up the water heating when required.  Our tank is set to 60 degrees on gas heating, and the immersion heater was set to 70 when we were using it as it is only a short element intended for occasional use.  It did however, when powered all day by the sun, manage to produce a full tank of HW.

These days we can get more for our exported electricity, 15p per kWh, than it costs to heat the tank using gas, so we have turned off the element in the tank.  Things may change in the calculation, so we can always turn it on again!

linedried

Hi, thank you for your replies.  Our system is vented, and we can top up the hot water using our gas system boiler as well.  Maybe Aqualisa showers are worth a look.  

QrizB

We have solar panels, gas boiler and a vented system. Much like you we heat water with surplus electricity in the summer months.

Our shower is a pumped Aqualisa Quartz. Not the cheapest option to buy but works well.

linedried

(It was about hot water generation in the warm months.)

WIAWSNB

linedried said:

Hi, thank you for your replies.  Our system is vented, and we can top up the hot water using our gas system boiler as well.  Maybe Aqualisa showers are worth a look.  

Are you 100% certain the cold is also from the CWS tank?

ComicGeek

I think even the Aqualisa mixer showers need 55 degrees to control effectively. 

But it sounds like you're not controlling the times right on the cylinder, if the cylinder temperature is dropping too low. If you have your showers in the morning, then you use the daylight hours to heat up as much as possible with free solar. You should then top up with your boiler in the evening so that the cylinder is ready for the next shower session.

I doubt that the savings outweigh the cost of replacing shower units, so I would just set the boiler programmer to top up the cylinder before you use the shower.

Say you use 150 litres of hot water each day. 
7 kWh to heat replacement water from 20 degrees to 60 degrees.
Using gas boiler with 90% efficiency = 7.8 kWh of gas per day = circa 51p/day, circa £188/year

So the actual saving from the iBoost system is probably less than £100/year in reality. A lot of the Aqualisa showers are over £500, so really not worth spending lots of money on shower replacements to "save" £100.

jennifernil

We did not go for anything fancy when we replaced our showers, so our Aqualisa ones were around £225.

When we were using the system which sent power to the immersion heater, we were on deemed export, which only paid us about 6p per kWh, our installation is from 2012 so we are on a high FIT payment as well.

Once  we got a smart meter we could see how much we were exporting so changed to metered export and turned off the diverter,  but when we were using it, in summer, our HW was always VERY hot.

As long as gas prices are less than what we are paid for export, that will remain the case.

I would agree with the post above, no point in spending on a new shower mixer if you can top up with gas when required.   Are you sure the Triton needs water at 65 degrees?

linedried

Thank you for your replies.  The shower is broken so we are replacing it quickly and just wondered if anyone had a suggestion.  Going off to talk to plumbers.