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SOLAR DIARY (Click here for day by day diary of results since 30-August 2008 )

The link to this page from Wikipedia has now been removed by the socialist brothers there. You will find little else of any use on Wiki regarding Solar Hot water. The pages on Wikipedia regarding solar hot water are skillfully and stealthily edited to reflect the views of the solar thermal trade ( the green thieves ). Take a look and click on the " view history tab " on the top right of the page. You will see the ongoing edit war that is Wikipedia. The Wiki admins don't allow links to this site because they say its a comercial site, although they do allow links to thousands of porn sites.

At the time of writing this 10/03/08. I would estimate that I am spending about £300 a year on hot water. We use this amount for washing and bathing and about another £100 that we use to run our washing machine and dishwasher. A total of about £400 for our family of four living in a three bedroom semi. With the solar hot water system described here I am hoping to save about a half of this. About £200. This I consider a worthwhile saving that will increase year after year as gas and electricity prices continue to rise.

Have had a few questions on these figures. Some people think that £400 is an exaggerated figure for heating water in a year. While a few others say they spend more than this. I think that before you embark on this sort of project it would be a good idea to try to work out how much you actually spend on hot water. You will need to look back over a years electricity and gas/oil bills and add them up. If you do not keep old bills you will have to study your old bank statements. So I have been told about 30% of this total will be your hot water costs. So for example if your total energy costs for a year come to £1500 then for hot water your costs will be £500. You will probably be able to save about 40% to 50% of this amount £200 to £250.


Important disclaimer

It is possible to hurt your self. You can cut, burn, choke, poison, or scald yourself messing about with this. You could also fall from the roof or fall down the ladder with a cable around your neck on to a wooden stake. You could electrocute your self ( with power tools ). Blow lamps can explode and solder flux can give you dermatitis. You could get tetanus or blood poisoning from a splinter or paper cut. You could have an accident on the way to B&Q in the car. So if you follow these instructions its at your own risk. Wear goggles, steel toe cap boots, thick leather gloves, a face mask and hard hat at all times. Use an RCD and proper scaffolding . Never work outside in a thunder storm. Anything you do is your own fault, it's not my fault. I am not your mum. Good Luck see you in the next life.


It's a great idea to have a solar hot water system , but at what cost. Solar hot water has become very big business these days, with gas and electricity prices just going up and up. Many people who are "just enquiring" end up being sold ( often on credit ) systems that are very unlikely to ever recover their capital costs. I believe I can save about £200 a year with this system. If I were to purchase a professionally made,installed and maintained system for say £6000 it would take me about 30 years to recover this cost. This is without taking into account the on going costs of servicing and repairs to over complicated evacuated tube systems. Buying a system on credit will also have to include the cost of credit ( interest ) that is often overlooked. If I would pay £6000 cash up front for a system there is also the cost of lost interest to be factored in. £6000 in a decent savings account will probably earn more money in interest than you can save by using solar to heat your hot water. As we know from past experiences with double glazing, conservatories etc, very few of these companies that are selling expensive solar hot water systems with long guarantees, will be around in five years time. Its got to be a DIY system or no system.

Flat plate vs Evacuated tube solar collectors/panels.
It is claimed that evacuated tube solar collectors are typically more efficient than flat plate collectors. This does not mean that evacuated tubes can produce more hot water, it's just that the panel area can be reduced. You will need a larger flat plate panel than an evacuated tube array to heat the same size water tank, but with either type you will get about the same amount of hot water each year. You can't make your own evacuated tube array. You have to buy from China. Salesmen like evacuated tubes, they are much more sexy and need a much more complicated system that is considerably more expensive and needs servicing. Money Money Money. An independent study by the DTI compared a number of different types of system and the panel that produced the most hot water was of the flat plate variety. Tubes are for suckers. Most evacuated tube systems require mains electricity for pumps, valves, controllers etc thus negating any gains over flat plate collectors. These complicated systems will almost certainly come with an annual service contract that will be linked to any warranty.

Send us your quotes. We hear that some big name UK companies are quoting up to £12000 for a solar hot water system. If you have such a quote please send it so I can publish it here.

Quote 1: ( Bournmouth ) Two hour high pressure visit. 1 solar panel, 40 gallon hot water cylinder, pump and box of electronics, £11,500 or £6,400 if ordered within 24 hours.

Quote 2: British Gas claim you can save £85-£350 a year with their system, costing £3600.00. Will take from 10.2 to 42 years to pay for it self ( is nothing goes wrong ).

Quote 3: Solartwin. £3,699 installed or £2,699 DIY.

Quote 3: According to the Energy Saving Trust, the average price for a system is £4800.00.

Quote 4: Whilst visiting an energy display in my area I was quoted up to £10,000 for thermal panels.

Quote 5: British Gas latest. Approximate cost for a system £ 5000.00 inc VAT ( At least 30 year payback).

Quote 6: Tesco £ 4,339  ( At least 25 + payback )    Double Clubcard points.


I am not claiming any originality for these systems. I have studied many solar hot water web sites and put together what I consider to be the best plan for my needs.

solar diagram 1

This is about as simple and low cost as you can get. The pump and P/V panel are the only parts liable to give any problems. My money at the moment is on the Charles Austen DL2 pump ( Six weeks delivery unfortunately ), but looks the part, and is what I am using in my system. For this pump you will need a P/V panel rated at about 10 watts. These panels appear to give about half of their rated output. If you buy a panel that is too small like I did, you will then have to buy another one. So get one about 10 watts. If its too small its no good, If its a bit too big you can always damp it down a bit. Put the pump and P/V panel so that you can get to them easily. Important. Pump must be situated where it cant freeze. Also pump must be 150mm to 250mm above the water level in the expansion tank that supplies your boiler. You must make sure that the pump does not pump if the panel is frozen. Switch it off on cold nights/mornings.


solar diagram 2

To get the most heat gain from the available Sunshine it is necessary to use some sort of electronic control board and a minimum of two temperature probes. The Solarfriend#1 controller board uses a PIC 16F676 Microcomputer and needs just an 8 to 15 volts DC power supply. The board has a single pole changeover relay that should easily cope with most small pumps. For larger pumps the on board relay could be used to trigger a larger relay. The temperature probes must be situated one on the solar water panel near to the outlet. And the other on the hot water cylinder. Where about's on the cylinder is subject to quite a bit of experimentation. On my system the cylinder probe is under the insulation about 20cm from the top, But I may move this about when I get Time. To begin with I have set the difference adjuster to about 10 degrees. That is to say that the relay only energizes if the panel temperature is 10 degrees above the cylinder temperature. If the panel temperature goes above the difference value the relay energizes for about 5 seconds ( Adjustable ). This will be the pump on time. Then there is an off time about 15 seconds ( adjustable ). The whole thing repeats continually in a cycle. Should the panel temperature fall below 18C the board just idles, using very little current until the temperature rises above 18C. This does away with the worry that the pump will pump into a frozen panel.

solar panel controller

Picture above shows Solarfriend #3. This panel uses PIC 16F833 Micro controller and has a wide range of adjustment for difference value 0-20 degrees approximate, on time 0-20 seconds and off time 12-32 seconds aprox. There is also an ( AUTO ) setting. This panel is designed to suit most DIY systems.

See it on Youtube here


To begin with I made a wooden frame from some 95mm x 20mm hardwood. This frame is made so that a sheet 2445mm x 1222mm of exterior grade 10mm plywood will sit inside the frame flush with the bottom edge screwed to wooden strips 40mm x 20mm that are screwed on edge inside the frame. The sheet of plywood you buy dictates how big you make the frame. The outside dimensions of my frame are 2490mm long x 1268mm wide x 95mm deep. This panel is about 3 square meters in size.


wood for framecorner



The two sheets of 16 swg aluminium that I purchased were just a bit too big to fit inside the frame so it had to be trimmed with tin snips to a final size of 2435mm x 1200mm that was about 20mm smaller than the inside of the frame so as to give a 10mm clearance all around.

trimming sheetally panel

The idea is that the 15mm ID 3mm wall silicone tube gets squashed in between the two sheets of ally. So that the tube is not completely closed up I put a strip of 25mm x 10mm ally around the edge of the sheet and 45 ally 10mm x 25mm round spacers on the sheet. These spacers that are on the sheet can be made square from the same ally bar that is around the edge of the sheet. The four corner most spacer are approximately 175mm in from each corner edge, then in a grid 9 across the sheet 105 mm apart then 5 along the sheet 522mm apart.

solar panel

The holes are 6mm diameter. I put the two ally sheets together, then put on the 10mm spacers that were already drilled. I held the spacers in place with fast curing silicone sealer and left overnight. Next day I drilled through the spacers and sheets so that all the holes would line up when the bottom sheet became the top sheet. And to my surprise the top sheet fitted perfectly. The screws are 5mm x 30mm nickel plated brass.


** ENDPIPE **** FLAT **

The coil of silicone tube that I purchased was 15mm ID with 3mm wall thickness and was 25 meters long. The panel actually took 24 meters so I had to cut off about 1 meter. I fixed the tube in place with tape so that it would not move and get caught between the spacers and the top panel. Cut outs were made in the top panel for the tube to enter and exit and it was painted matt black with Sperex high temp paint. A 500 ml aerosol can is just about enough to cover this size of sheet.

Next I fitted the top panel and gradually tightened the 100 or so nuts so that the silicone tube was squashed oval between the two ally sheets. Then I fitted the two 15mm to 6mm brass reducers that will connect to the small bore 6mm ID 3mm wall tubing that will run to the hot water tank.

** FINAL **** OUTPUT **

** SPACER **** SPACIN **

The gap between the plywood base and the bottom aluminium sheet is about 50mm and this is filled with this space blanket insulation that is half price at B&Q at the moment. For this size panel you need about 1.5 rolls leaving the usual annoying bit over. I made three long pillows that just about fitted perfect and were stapled to the wooden frame. If you cut this carefully to size and staple the ends its just about possible to have no contact with the itchy stuff inside at all.


** BOLTS **** HOLE **

** ROOF1 **** ROOFTWO **

The panel mounting brackets were made from 40mm by 40mm by 5mm mild steel angle about 1200mm long with two 150mm pieces welded (could be bolted) on the back. I took the trouble to drill and file two slots 10mm by 60mm in these smaller pieces to make it easier for the holes to end up over a over a joist. You can measure how far apart your joists are from inside the loft and make your bracket to suit. From outside you will have to lift up the tiles and find the joists, so that you can mark the tiles with chalk for drilling. I used a 10mm diamond coated hole saw to drill the holes so as to not break the tiles. You are drilling through two tiles and these hole saws only do about two holes before they go blunt so buy two. You can always take one back if your tiles are easy to drill. Make sure that you hold the drill 90 degrees to the roof slope and not to the tile you are drilling. Next drill a 5 mm pilot hole through the hole in the tile and into the joist so that the bolt does not split the joist. Squirt plenty of silicone into and around the hole and screw in the stainless steel fixing bolt until about 60mm is left sticking out of the roof. Drill the second hole and fit the bracket. Put plenty of silicone all around the holes. I painted the bracket with metal primer then Hammerite.


Above is the finished panel. The poly carbonate sheet was bought cut to size and can be pushed in or out from the lower edge of the panel. The brown fixing strips came from B&Q very low cost and are fixed to the wooden frame with silicone and galvanized nails. So that the sheet pushed in OK I smeared the edges with Vaseline. To hold the sheet in place I used the plastic buttons also stuck with silicone. To use these buttons you need to make 12mm holes in the sheet. If you try to drill these holes you will get lots of swarf inside the sheet and the holes can be jagged. The best way is to heat up a piece of 15mm copper tube with a blow lamp, Holding the tube with pliers and carefully push it through the sheet to melt a neat hole with no swarf. Try this with an off cut first.



The wooden tray with insulation and other bits and pieces came to about 45 Kilo's and had to be pulled from the back garden by rope as well as pushed up the ladder. I cut a piece of plywood that bolted to the lower roof bracket and to this I secured the top of the ladder with several thick cable ties. Next I pulled up the inner solar panel ( 30 Kilo's ) and screwed it down on top of the insulation with ten woodscrews. Then I drilled the holes in the roof and ran the 6mm ID pipes into the Tray top and bottom and connected them via the reducers to the panel. The panel temperature sensor is inside a 15mm copper tube that is screwed to the top of the panel with a copper pipe clip close to the outlet. The wire from the sensor goes through a 6mm hole in the side of the tray and through another hole into the loft along with the wire from the P/V panel that is fitted to the top roof bracket.


I had to make two tee-in connections to my hot water system as shown in the left hand picture here. The red plastic is the insulation jacket on the hot water tank. At the top you can just about see the compression tee fitting close to the hot water outlet going into an isolating valve. Just to the right is another valve that connects to the cold inlet pipe. In the right hand picture you can see these pipes from above the work surface. Both have homemade 22mm to 6mm reducers that connect to the small bore 6mm silicone tube that runs up through the ceiling, across the loft space, out through the roof, and into the hot water panel.


Frozen copper pipes

Quite a few people still insist that they will get away with using copper pipe in their panel. The pictures above show what will happen if you use copper. The 15mm pipe has split and the compression fitting has pushed almost off the end of the pipe after being frozen and thawed a few times.

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The Solar Thermal Trade ( the green thieves ) are pretty much bankrupt. The big problem for them is that domestic fuel at current prices is way far too cheap. Most commercially made and installed solar hot water systems will take 20 or 30 years to pay for themselves. The situation with solar P/V in many times worse. A recent survey by the Consumers Association ( Which ) found that nearly all the companies involved in the solar thermal trade were using dishonest and dubious selling methods to sell solar thermal systems.




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