#1 Dec. 3, 2017 14:49:03

JGS
Registered: 2012-02-22
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Augmenting the hot water from Robin's PV router

I generate most of our hot water using Robin's PV router. In winter, inevitably, the sunshine isn't sufficient and the hot water has to be ‘topped up’. The difficult question is ‘When does it need extra heating?’ It is too late getting in the shower and realising the water is too cold.

I have found a solution that may appeal to members with the same problem. I purchased an electronic cooking thermometer. This has a steel probe designed to stick in the meat and then the temperature data is fed via an armoured cable out of the oven to a transmitter which sends the temperature to a handy little receiver.

I carefully cut a 15cm ‘V’ shaped groove in the foam insulation of the hot water tank making sure that the bare copper surface was exposed. The steel probe was then placed tight against the copper surface and the ‘V’ shaped piece of foam carefully replaced and held in place with parcel tape.

This arrangement gives me a readout of the temperature at my bedside and I can now tell when the day's PV has not been sufficient to give enough hot water for tomorrow's shower. Furthermore I can heat the water just enough to give me a shower without heating gallons to an absurdly high temperature because I can follow the heating.

I have placed the probe about half-way up the hot water tank but obviously the temperature readout will depend to some extent on where the probe is place (though the copper of the tank is a good conductor.)

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#2 Dec. 4, 2017 13:03:42

bhommels
Registered: 2011-10-03
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Augmenting the hot water from Robin's PV router

Hi JGS, I share your problem with my homebuilt PV router, and thank you for giving me a platform to boast about my solution.
I stuck 2 DS18B20 digital temperature sensors into the thermostat ports of my hot water tank, one at the top and one at the bottom. These are read out every 30 seconds by an Arduino. This device also acts as the hot water thermostat, driving the boiler relay, with the temperature set by a dial. The Arduino microcontroller allows it to be very clever for a thermostat, and two temperature sensors give it all kinds of options to play with (hysteresis etc).

The readings are transmitted wirelessly to another Arduino, that puts the received values on a LCD display near the bathroom. In principle there could be many of these, as it just receives data like a radio. It can also timestamp and log the data to SD card to gain insight in heat losses etc.

There are plans to upgrade this system by moving from Arduino to Raspberry Pi, however since the basics work there is very little sense of urgency…

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#3 Dec. 7, 2017 12:21:06

BackYardSolar
From: Surrey, on Gatwick flight path
Registered: 2015-05-30
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Augmenting the hot water from Robin's PV router

JGS/bhommels

I went a different route and used a tank thermostat which cost as little as £13.

I use this to divert spare solar to night storage heaters once the water is hot. In this way I manage to divert 1.9MWh each year using Robins mini PV router. 9+MWh since mid 2012.

I can normally run from May until October heating the water in this way. However, at this time of year I let the hot water heat up over night and just keep it topped up to max all day if there is any solar.
On a sunny day even now both night storage and water stay at max temperature.



SolarEdge SE4000 inverter, 16 x Romag powerglaz 235W panels. South facing at 30 degree angle in Surrey just East of Gatwick and under the flight path.

ESS AC coupled system using a Victron Multiplus 24V/1600VA Inverter/Charger - 8.16kW Trojan 875 battery bank.

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#4 Jan. 31, 2018 17:32:12

Gary
Registered: 2014-06-29
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Augmenting the hot water from Robin's PV router

I don't have a homemade router but do face the same issue. My solution is easy, turn the boiler hot water feed on for two hours in the evening at a time when the GCH is likely to be on meaning I will not then waste energy warming the pipes between boiler and tank. I then let the tank thermostat do its thing. This works for me and ensures we always have enough hot water. Simples……

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