Solar electric hot water system

[mrmadmax]

I was wondering if anyone could give me more information regarding using solar electric panels to heat water in my storage tank.

I was considering the following is a system:

I have seen these 12v immersion heaters for sale:

http://cgi.ebay.co.uk/12v-Volt-1"-W...vr_id=&cguid=62cafc7b1260a0e204975477ff518161

There is a connection kit available so they can be retro fitted to an existing water tank, as shown in the next link:

http://www.reuk.co.uk/200W-12V-Immersion-Heater.htm

Then I was hoping it would be possible to link the immersion heater to a solar panel.
I understand the system would need thermostatic control to prevent the boiler overheating.

I have done some calculations for a 200w panel and they are as follows:


That gives 200 * 60 * 60 = 720000 watts hour

It takes 4.186 Joule to heat 1 gram of water 1 °C.

I have 150 L or KG of water in my tank.

So to heat my tank by 1 °C. it should take

4.186w * 150000g = 624000w

So every hour the panel is operating it should raze the temp of the tank by 1 °C

If anyone has any experience with this type of system it would be great if you could offer some advice.

thanks

 

[wotan]

Perhaps if you lived in a land of eternal sunshine, it may just work, but a one degree C increase every hr, there are not enough hours of sunshine in a day.
I very much doubt you would reach the required efficiency, to achieve what your figures suggest.

Wotan

 

[davelx]

If you want to use solar energy to heat your water, it's MUCH more efficient to do it directly - the conversion efficiency of PV cells is not too good.

http://www.vaillant.co.uk/homeowners/renewable-energy/solar_systems/#solar_systems

and many others. You can even build your own, but it won't be as good as you won't be using vacuum insulation.

 

[mrmadmax]

thanks for the replies.

The idea behind this system is to have a low cost system.

Traditional PV systems require inverters and transformers as well as changes to your electrical system to run the meter backwards ect. These extra components add cost and inefficiency to the system. You will also have to get them professionally installed.

Traditional solar hot water systems require expensive installation lots of extra pipe work, pumps and heat exchanges.

I accept a solar hot water panel will heat more water per m2 of panel but the systems are so expensive that the pay back times a very large.

The system I have suggested requires fewer components and should assumable run at a higher efficiency than traditional PV system as there are no transformers or inverters. It should be possible to dump nearly every watt generated into the water. The 200w system should cost around £650-£700 for the components (panel wires hearer etc). And as it is all low voltage and does not link to my supply I should be able to install it my self. (Please correct me if I a wrong regarding the legality of diy installation)

I don’t relay know a lot about solar systems so any advice is appreciated.

Thanks

 

[flameport]

You can install PV systems yourself, but it is notifiable work, regardless of what voltage it uses or if connected to the other circuits in your house.

Paying £700 to obtain a 200 watt water heater is a complete waste of money and time. The heating benefit will barely be noticeable, even if the system operated at 200 watts for the whole day (say 10 hours).
A 200 watt heater for 10 hours would use 2 kWh of electricity, or less than 30p per day. The best part of 7 years before you even recover the initial cost of the system.

In reality, the output will be far below the maximum, since PV panels only produce the maximum output in bright sunlight. They do work in cloudy conditions, but the output is significantly reduced.
Even at 50% average for 10 hours per day, you are looking at 14+ years to recover the initial costs, and a lot longer before any worthwhile savings are made.

If you have £700 to spend on energy saving products, there are far better uses for it than a PV system.

 

[ban-all-sheds]

Based on a system lifetime of 25 years the cost of the PV generated electricity
was found to be between 20.9p/kWh and 184.7p/kWh with an average of
47.5/kWh. If known underperforming systems are removed, the average and
maximum costs are 39.1p/kWh and 77.8p/kWh respectively.

OK - that's based on a study done 5-10 years ago, and I'm sure that technology has improved and got cheaper since then, but I still think that PV is a chimera, and a much better ROI is obtained from solar heating of water and/or spending the PV budget on better insulation and heat recovery.


Also see http://www.ibpsa.org/proceedings/BS2009/BS09_0789_796.pdf

 

[holmslaw]

..

 

[londonboy]

mrmadmax there are all sorts of grants available at the moment, for both solar thermal and solar pv.

Apparently properties with solar systems can be worth 8/10% more than properties without.

Have a look here:
http://www.energysavingtrust.org.uk...ants-and-offers/Grants-and-Discounts-Database

 

[londonboy]

In the UK, PV is a waste of time and money.

The systems I've recently installed have generated 200watts during a fairly average day!

 

[holmslaw]

..

 

[londonboy]

£7500 including £2500 from the government.

Well 200 watts is enough to make the average houses' meter run backwards for the majority of the day.

 

[NamelessRob]

200W, 10 hours / day, 365 days / year = 730 kWh / year

@ 14p / kWh, = £102.20 / year

Which is about 2% annual return on a £5k investment; I'd rather just keep the £5k in the bank.

 

[londonboy]

200W, 10 hours / day, 365 days / year = 730 kWh / year

@ 14p / kWh, = £102.20 / year

Which is about 2% annual return on a £5k investment; I'd rather just keep the £5k in the bank.

+ the 25yr feed in tariff + value added to the property

 

[ban-all-sheds]

The systems I've recently installed have generated 200watts during a fairly average day!

1) That is not a rebuttal to holmslaw's assertion that in the UK PV is a waste of time and money.

2) What do you mean by "average day"? Is 200W the average output of the system, when looked at over an entire year? What are the minimum and maximum outputs in December & January? What are the minimum and maximum outputs when you've got several cm of snow on the panels in the winter?

£7500 including £2500 from the government.

What kWp capacity do you sell for £7500?

Well 200 watts is enough to make the average houses' meter run backwards for the majority of the day.

On average, how many kWh do your £7500 system customers sell back every year, and at what price?

 

[ban-all-sheds]

200W, 10 hours / day, 365 days / year = 730 kWh / year

@ 14p / kWh, = £102.20 / year

Which is about 2% annual return on a £5k investment; I'd rather just keep the £5k in the bank.

And that's assuming that you can use every single watt that your system produces. If you cannot use it then you can do 3 things:

1) Store it for future use - this significantly increases the cost of your PV system and makes your PV electricity cost even more.

2) Sell it back to the grid - they won't pay you anywhere near as much as they charge when you buy, so you don't save anywhere near 14p/kWh, so the PV electricity you do use costs even more.

3) Throw it away, so the PV electricity you do use costs even more.

The effective return on your £5K investment will be nowhere near 2%.