device to use unused soler pv export power to run heater or hot water

grahamc2003

Dave_Fowler wrote: »

I can't see how I can not gain from using the higher temperature. I am using electricity which would otherwise be exported. It costs me nothing to run the tank hotter - except perhaps a shorter life expectancy of the immersion heater.

One of the benefits of running the tank at a higher temperature is that with the indifferent weather, when there are rarely two days of reliable sunshine together, I can go two days without having to top up the HW tank using the gas heating.

Dave F

I'm not saying you won't gain, I'm saying it's a possibility you won't - and impossible to tell without knowing lots of data.

Obviously, if your thermostat is set to a higher temperature, then when you use the immersion without solar contributing 100% you'll be paying for the extra heat loss. The only possibility of never having an offest to the gain is if the immersion is never used when not fully covered by solar. While I appreciate it's possible you may try never use the immersion under those circumstances, it's also possible that you (or others) might. I nevertheless think it its useful to point out the possible factors affecting the efficacy of any action. I appreciate I'm probably the only person who thinks that!

John_Pierpoint

I suppose you could always have two thermostats and normally keep the immersion turned off ? Though you soon get into human intervention and heuristic algorithms to control the two sets of kit - that rather defeats trying to create something automatic.

Must dash it is time to make a coffee, the sun has just come out.:D

Dave_Fowler

grahamc2003 wrote: »

I'm not saying you won't gain, I'm saying it's a possibility you won't - and impossible to tell without knowing lots of data.

Obviously, if your thermostat is set to a higher temperature, then when you use the immersion without solar contributing 100% you'll be paying for the extra heat loss. The only possibility of never having an offest to the gain is if the immersion is never used when not fully covered by solar. While I appreciate it's possible you may try never use the immersion under those circumstances, it's also possible that you (or others) might. I nevertheless think it its useful to point out the possible factors affecting the efficacy of any action. I appreciate I'm probably the only person who thinks that!

Hi Graham,

I understand what you are saying and appreciate that if I were to use the immersion heater importing power off the grid that I could lose out because of the extra heat loss due to the higher tank temperature. It is a good point and worthwhile making for those that don't have a set-up like mine. However, as I only supply the immersion through my Immersun copy, it is impossible for me to use power from the grid. My normal HW heating is gas - which as usual has its own separate thermostat.

Dave F

dannyboyroberts

I would like them please

slacky555

Could someone send me the details please.

Pm me or preferred can you send them to

J.slack@hotmail.co.uk

Also why r some people saying this cost over £100 when it shud only be £15ish?

Dave_Fowler

slacky555 wrote: »

Could someone send me the details please.

Pm me or preferred can you send them to

[EMAIL="J.slack@hotmail.co.uk"]J.slack@hotmail.co.uk[/EMAIL]

Also why r some people saying this cost over £100 when it shud only be £15ish?

The Immersun and the lower cost copy I made are quite different from the relatively simple on/off design made by energysavingexp.

The Immersun output is controlled so that it can use up every last Watt of excess power generated by the PV system whereas the simpler system has to be set to turn on only when the excess power is greater than that taken by the immersion heater. As the excess power from the PV system may rarely exceed the 3kW power rating of a standard immersion heater, many people are replacing their original immersion heater (or adding an extra heater) with a 1kW heater.

The Immersun uses what is technically called a phase-angle controlled switch. This can vary the power to the immersion heater from zero to the 3kW maximum. The power tracks precisely the excess power from the PV system.

The one-off retail price of the phase angle controller, through stockists such as RS and Farnell, is over £50. To add to this you need a power filter (to reduce unwanted interference), a clamp-on current detector to measure the excess power and a control circuit to make all the calculations. (and a box and fan to cool the heatsink).

I have gone quite a way on my website to draw up the plans (I can't post the link here, but just check my MSE profile to get the details) If anyone wants the full design details I will make time to place the remainder of the design on the website too.

Dave F

Energetic_2

Dave_Fowler wrote: »

The Immersun and the lower cost copy I made are quite different from the relatively simple on/off design made by energysavingexp.

The Immersun output is controlled so that it can use up every last Watt of excess power generated by the PV system whereas the simpler system has to be set to turn on only when the excess power is greater than that taken by the immersion heater. As the excess power from the PV system may rarely exceed the 3kW power rating of a standard immersion heater, many people are replacing their original immersion heater (or adding an extra heater) with a 1kW heater.

The Immersun uses what is technically called a phase-angle controlled switch. This can vary the power to the immersion heater from zero to the 3kW maximum. The power tracks precisely the excess power from the PV system.

The one-off retail price of the phase angle controller, through stockists such as RS and Farnell, is over £50. To add to this you need a power filter (to reduce unwanted interference), a clamp-on current detector to measure the excess power and a control circuit to make all the calculations. (and a box and fan to cool the heatsink).

I have gone quite a way on my website to draw up the plans (I can't post the link here, but just check my MSE profile to get the details) If anyone wants the full design details I will make time to place the remainder of the design on the website too.

Dave F

Hi Dave,

We've fitted a few Immersuns and a few of the Wooldridge Sola Controla. In terms of what's best for the customer the Immersuns extra features (timed boost etc) and tidy design makes it the most consumer friendly of the two but the wooldridge is very good at what it does also.

The Sola controlla is burst fire so just wondering what your thoughts are on Phase Angle vs Burst Fire for this application and does it make a difference?

Dave_Fowler

Energetic wrote: »

Hi Dave,

We've fitted a few Immersuns and a few of the Wooldridge Sola Controla. In terms of what's best for the customer the Immersuns extra features (timed boost etc) and tidy design makes it the most consumer friendly of the two but the wooldridge is very good at what it does also.

The Sola controlla is burst fire so just wondering what your thoughts are on Phase Angle vs Burst Fire for this application and does it make a difference?

From my understanding of what is meant by a 'Burst Fired' switch is that the switch turns on fully for a short time (1 second or so) and then off. During the 'on' period power is imported and during the 'off' period it is exported. In this way the average power can be controlled. - This is very much like a microwave oven on the lower power settings except the 'burst' period is much shorter. I would expect that any normal electricity meter would register the 3kW power taken during the bursts. (I'm not sure if there's a short time constant built into the latest meters).

I rejected trying a burst firing control in my design for this very reason. Perhaps someone can help with just how the latest burst firing controls and modern electric meters may interact.

A phase angle system reduces the power by only turning on the power for a short period during each cycle of the mains and hence would not take 3kW at any time (unless the phase angle were set to turn on at the start of each cycle).

The advantage of burst fired is that the power can be controlled on and off at zero voltage crossing points on the cycle and hence creates no interference whereas the phase angle method inherently produces a lot of interference (RF) as there are quite high current peaks when the switch turns on part way through each cycle - hence the need for a substantial interference filter on the control system.

Dave F

daytona32

energysavingexp wrote: »

hi kernel

if you take a look at my past posts i dont mind discussed publicly
but there a few on here that like to think they are always right
and dont like other people having some thing they cannot have.
if i can help anyone for free i will,
this device is not for everyone only people who have solar pv and are good at diy its not easy to explain thats why i sayed message me so i can tell them where to buy the parts and how to build it
if it can save you money for £15 ish then if they are intrested then ask and ill do my best to help
ive only put it on here after recieving a pm from a member asking me about it and he called me today after buying the parts from a local shop and said i should tell everyone and share the info.
but like i say its not for everyone.
i'll share any money saving ideas i have ive even got a system in place to save £500 of my water bill that has been running now for last 4 years

:jHi Please can you send me a copy of your switch circuit etc. I am having a 3.5 kw solar system fitted tomorrow . Best regards H

John_Pierpoint

grahamc2003 wrote: »

While it's difficult to calculate the actual heat loss from the tank, it's easy to calculate the relative heat loss at different temperatures. For example, the heat loss when sitting at 65C will be about 8% greater than when sitting at 60C (the heat loss is proportional to absolute temp to the power of five).


There are lots of variables (an important one being exactly how many hours each day the tank is at its max temp, among many others). I expect most will have a very well insulated tank, but if not, it may be marginal whether or not there's a benefit by turning the thermostat up.

Hi Graham (and all the other engineers & scientists reading this),

It is over 50 years since I did "O level" physics, but isn't the power of five relationship referring to sources in a vacuum radiating heat (best known example: that round golden thing in the sky we don't see much of these days).

The hot water tank is losing most of its heat by convection and conduction (especially if the copper expansion pipe coming out of the top goes straight up) and for practical purposes the heat loss is proportional to the excess temperature?

eg Normal temperature of the "airing cupboard" 15 Celsius, Tank set at a warm enough for washing, 65.
Now boost the excess temperature by 5 and get 100 / 50 * 55 = 110.
That 10% is much the same as your 8% but a lot more easily understood and acted upon by the average UK citizen, who still has problems doing percentages "I was never any good at maths at school; can you pass me the homoeopathic remedy your highness"

Time to turn down the setting on the thermostat for my immersion I think [Question, will she notice and run off all the hot water in the hope that it will get really hot? ].