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Obviously, a solar water heater creates hot water by absorbing energy from the sun. But what happens in the winter when there is less sun, or on overcast days?
Well, to some extent, the heater will still work, but the chances are that you will accumulate less heat, which means that you will probably need an alternative form of heating.

Many hot water cylinders have two independent heat exchangers. One is connected to the solar heater and the other connected to a conventional boiler. Additionally, many cylinders have an aperture for an electric immersion heater.

How you use the hot water that you create from your solar heater is entirely your choice. One idea I had was to create two heating panels supplying different parts of the house (bathroom and kitchen). In the bathroom, we would obviously prefer to have a constant supply of hot water, which means that we would probably need a dual heat exchanger cylinder. For the kitchen, however, it is less critical because we don’t use nearly as much hot water in the kitchen as we do for showers and baths.

The washing machine is not fussy. If it is supplied with hot water, it uses it. If it is supplied with cold water, it heats it up to the required temperature. So if the hot water tank is emptied of hot water, the washing machine will still operate, albeit less efficiently. Today’s modern detergents work in lower temperatures anyway, so they are already saving us energy.

My reasoning behind having two solar heaters is that I have two prime locations for the collectors and they happen to be convenient for the both the bathroom and the kitchen. It also means that if we run the washing machine, it will not affect our ability to have a bath or shower.

If you think this is all a little ad hoc, it doesn’t really matter. The investment in home-made water heaters is little enough that they will pay for themselves in a very short time period.

The solar collector for my solar water heater project is going to consist of an array of copper pipes enclosed in an insulated box of wooden construction. The top of the box will be glass to retain heat – the “greenhouse effect”.

I found an online calculator for determining the size of collector required to provide enough hot water based on the number of family members. There was no criteria specified for the type of collector, the spacing of the copper pipes etc.

The formula they used was about 2 square metres each for the first 2 people in the house, and then 0.8 square metres each for every additional person.
So for a family of 4 people, that would work out at 5.6 square metres. I have seen a lot of commercial units fitted to houses in my neighbourhood and they don’t appear to be of that size, although it is difficult to tell from ground level.

The roof space on which I plan to mount my heater is 1.7m x 2.0m = 3.4 square metres. However, at the latitude of my house I would need to mount the collector at about 39 degrees from the horizontal (it varies throughout the year, but that’s a good average). This would increase the area of my panel to 4 square metres.

Commercial units use parabolic reflectors to direct the sunlight that falls between the pipes back up to the pipes. Personally I think that the system would be more efficient if there were more pipes, mounted closer together, so they are heated directly. A colleague also suggested using a central-heating radiator which has no spaces between. I estimate that with a higher pipe density, a 4 square metre panel will be sufficient for my family.

Another alternative is to use microbore copper pipe which is flexible enough to be spread out in coils throughout the collector box. This would make for rapid construction as a single length of pipe could be used.

However, it is my plan to use 15mm copper pipe with solder joints, mounted on a metal backing plate.

Pipe Arrangement
For best heating efficiency, the cold heating medium will be fed in at the bottom of the pipe array. It will then flow upwards through several parallel, vertically mounted pipes to the outlet at the top of the panel. This is the same configuration as the commercial units and I assume they have done research on the best arrangement. However, I do wonder whether a single pipe that zig-zags its way up the panel would get hotter than a set of parallel pipes.

If you’re reading this because you’re interested in building your own water heater and are not confident enough in your ability to construct the collector, commercial ones are available.

Solar water heaters are very simple devices, which is why their construction is not beyond the average DIY enthusiast. This article briefly describes the various components of a solar water heater.

Solar Collector
This is the part of the system that captures and exploits the heat of the sun. Their construction can vary, but the basic principle is the same. It is a set of pipes containing a liquid (Heating Medium) that is exposed to direct sunlight. When sunlight falls on the pipes, they heat up, heating the liquid inside. This liquid is then pumped to the heat-exchanger coils of a hot water tank.

Commercial units often use copper pipes mounted in evacuated glass tubes which is supposed to increase efficiency. The tubes are then mounted side-by-side on a panel fitted to a roof. The panel often has reflectors that bounce the sunlight/heat that falls between the tubes back up to the tubes.

Evacuated tubes can be bought for DIY projects, but they are expensive and are not entirely necessary. Instead, pipes are usually mounted in a shallow box that has a glass top. However, the commercial units look good and might be a good alternative if your constructional skills are not so good.

You can easily demonstrate the effect of solar heating if you have a garden and a hose-pipe. Simply ensure the hose is full of water and leave the hose lying in the sun for 30 minutes. When you come back, the water in the hose will be warm or even hot.

Heating Medium
This is the liquid that is heated by the solar collector and used to heat up your water.

In hot countries, the medium can be water, but anywhere where there is risk of frost, another medium must be used. Typically, this would be a non-toxic anti-freeze, or mineral oil.

Pipework
Temperatures in the solar heater can get very high, so it is usual to use copper pipes. Plastic pipes could melt. This is true even for plastic pipes used for modern central heating systems.

Pump
The pump is used to circulate the heating medium around the system. For even more energy saving, it could be driven from a PV solar cell.

PV Solar Cell
PV or PhotoVoltaic cells create electricity when exposed to light. A small, low-cost panel should be sufficient to power the pump.

Controller
The controller determines when the pump should operate. It measures the temperature of the hot water tank and the temperature of the solar collector. If the collector is hotter, the pump operates so that heat is transferred to the water in the tank. If the water tank is hotter, then the pump will not operate as this will have the effect of cooling the water.

Any electronics enthusiast could construct a controller, however commercial units are available at quite a low cost.

Hot Water Tank
This is a storage tank for your hot water. It is usually cylindrical and made of copper or stainless steel. Most are covered with an insulating foam. Insulation can be improved by the addition of a cylinder jacket.

Inside the water tank there are one or more heat-exchanger coils. The heating medium is pumped through the heat exchanger, thus heating the water in the tank. The heating medium, now cooled, then returns to the solar collector to be re-heated.

The heating medium is totally isolated from the water in the tank by the heat-exchanger coil.

The second heat-exchanger may be connected to an alternative heat source, such as a gas-fired boiler in the case that there is insufficient sunlight to heat the water, such as in the winter or during hours of darkness. Many tanks also have provision for the fitting of an electric immersion heater.

Safety Devices
The heater can get very hot on sunny days, and there is the danger that the water in the tank is heated to or beyond boiling point. The hot water tank will therefore require an expansion tank, and the entire system will need an additional temperature sensor that shuts down the heater’s pump if the water gets too hot.

Similarly, if the the heater has been shut down, the heating medium in the solar collector will start to get very hot. An expansion tank will therefore be needed for the heating circuit. Additionally, the heating circuit should be fitted with a self-bleeding radiator valve to expel any air that builds up in the system, otherwise the heater will fail to operate correctly.

Mounting Brackets
Your solar collector needs to be fitted in a position where it gets good incident sunlight for as long as possible. Most people have them mounted on a sloping roof that faces the sun (ie South-facing if in the northern hemisphere). Special brackets are available that hook over purlins and fit between roof tiles. This allows the collector to be fitted without impairing the integrity of the roof.

This has been an overview of the components of a solar water heater. Further details of each component, along with construction tips, may be found in other articles. Check out the list of articles in my Solar Water heater Project category, listed in the side panel of this site.

For some time, I have taken an interest in solar water heaters. These are simply arrays of pipes containing a liquid that are mounted outside and are heated by the sun. The liquid inside is then passed through a heat-exchanger to heat a tank of hot water. It’s a little like a central-heating radiator used in reverse.

Commercial solar water heaters are very expensive. One designed to supply enough hot water for an average family costs in the region of £7,500, installed, at time of writing.

Anyone with basic DIY skills could build one for considerably less than that. I estimate that I could build one, including a solar array, new hot water cylinder, controller, pump and pipework for under £500.
Fitting it to the roof of most houses might be beyond the capabilities of many DIYers, but I’m fortunate enough to have a flat-roofed porch that gets long exposure to the sun. It’s low enough to access without having to resort to scaffolding towers and I have worked safeley up there before (painting the house).

So the plan is to construct one of these heaters over the winter period (2011/2012). Although solar heaters do work on sunny days in the winter, the main benefit will be during the warmer months.

It’s a long-term project that will be spread over the winter whenever I find the time. This will give me time to locate the parts at the best prices. I shall construct the various components of the system as I acquire the parts.

And the first parts are on their way. A colleague is renovating his house and is disposing of some old secondary double-glazing panels. These are basically large sheets of glass set in aluminium frames. They will be ideal for making the lid of the solar collector boxes.

I’ll post some photos as I acquire the parts, and during construction, so that anyone else interested in building their own solar water heater can see how I do it.

If you have researched alternative energy sources, you will no doubt have come to understand that if you generate your own electricity, it is generally Direct Current (DC) at about 12 or 24 volts. Knowing that the electrical supply in your home is Alternating Current (AC) at 230 volts, you may be wondering how the 12 volt DC can be of use to you.

Due to the nature of alternative electricity generation, you might not need all the power that you are generating as it is generated. Similarly, when you most need the power, your generator might not be producing anything. An example of this is at night time when your PhotoVoltaic (PV) cells stop working because it is dark. You need electricity in your home to light it, run the refrigerator, television etc.

So, you need to have some means of storing the energy until you need it. This means using a large array of rechargeable batteries. The most common type of batteries used for this purpose are similar to car batteries, but use a gel instead of a liquid acid solution. They are generally termed “deep-cycle” rechargeable batteries which means that they do not quickly deteriorate as a result of fully charging them and discharging them frequently.

Your PV cells or wind turbine will be designed to generate a 12 volt or 24 volt supply, which will be fed through a suitable charging circuit, to the batteries, where the energy is stored.

If you connect wires directly to the terminals of the batteries, you will then get a 12 volt or 24 volt DC, which is not very useful when you want to power a refrigerator or mains lighting.

Transformers and Regulators
If you have a battery powered item such as a mobile phone, or some electronic equipment such as your internet router or a laptop, you usually plug them into the mains electricity supply via a mains adapter or a charger. These adaptors contain a transformer which changes one voltage to another. For example, your laptop might run on 12 volts, so the power adapter contains a transformer that changes the mains 230 volts AC to 12 volts AC. The adapter also contains a “rectifier” circuit that converts the AC to DC, and a regulator that keeps the voltage at 12 volts DC.

So we can reduce voltages and change them from AC to DC, but can we go the opposite way? Fortunately for us, we can.

Inverters
An inverter is an electronic device that takes a low voltage DC and converts it to a higher voltage AC. So if we obtain a 12 volt mains inverter, we can take the 12 volt supply from our batteries and convert it to 230v AC – just what we need for running our mains supply.

If you live in a place that is “off the grid”, then the output of your inverter is your mains supply. However, if you already have a mains supply, then you will need your inverter to tie in to that same mains supply. So when you have used all the stored energy in your batteries, you will seamlessly switch to the external supply.

For this purpose, you will need what is known as a “Grid-tie Inverter” (GTI) or “Grid Interactive Inverter”, which handles the switch over for you. A further advantage of the GTI is that many countries including the USA and UK have “feed-in” tariffs which mean that you sell any excess electricity to the grid, and in many cases, you get paid more per unit of electricity that you generate than the price of normal units.

Being the owner of a fairly large house (by today’s modern standards), I am all too aware of the rising cost of the energy required by the house. Whether it is for hot water, heating the fairly large rooms, lighting, or just powering the various appliances and gadgets that we seem to be accumulating, it all costs money, and I see no sign of those costs ever going down.

So, I have turned to alternative energy and energy saving, and I am now in a constant mode of improving the energy efficiancy of my house, and looking into cheaper (or free) sources of energy.

To put the whole thing in context, let me briefly describe my house.

The house is a fairly large, Victorian, semi-detached house built in 1882. The walls are cavity walls, which is quite rare for properties built at that time. The cavity is currently filled with air only. Some of the windows on the property have double-glazing, but others do not.

The house has 3 bedrooms, 3 reception rooms, a large hall, kitchen and a bathroom. There are two separate WCs and a utility room housing a washing machine and tumble drier.

Heating
Although the house originally had 3 chimneys, previous owners have removed one, and removed a chimney breast from one of the rooms. None of the fireplaces are useable for solid-fuel fires. Two rooms have gas fires and the others have electric, oil-filled radiators. When I bought the property, the other rooms were fitted with storage-heaters which were powered by a low-tariff, night-time electricity supply. However, the heaters were severely inadequate for the size of the rooms, so by mid-evening, they were cold and had to be switched to Boost, which ran on an expensive electricity tariff. Those heaters have been removed and replaced by the aforementioned oil-filled radiators.

As part of the renovation and modernisation of my house, I am installing radiators which will be connected to a gas-fired or bio-mass-fired boiler. All the radiators have thermostatic controls to help to reduce costs.

Lighting
Lighting is standard 230v mains powered lighting. All bulbs have been replaced by Compact Fluorescent Lights (CFL) of equivalent light output.

Insulation
As previously stated, the cavity walls are not filled (with the exception of the kitchen walls) and some rooms have upvc double-glazed windows.

The roof space has at least 6 inches of fibreglass or Rockwool insulation between the joists, and in parts, this has been doubled to 12 inches.

Future Plans
My plans are to improve all aspects of the energy efficiency of my home, without spending a fortune to do it. For example, if it is going to take 25 years for me to recover the costs of doing something, is it really worth me doing it? I’m trying to save money, after all.

Stay tuned for updates on my home energy improvement project.