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Solar hot water: Reducing our reliance on coal

A couple of years ago our government offered rebates to replace electric hot water systems with solar and we used this offer to replace our aging electric hot water system. We wanted a solar hot water system for a while to reduce the amount of fossil fuels that are needlessly used to heat our hot water. Our new system uses just over a quarter of the electricity that our previous electric system used and it saves us some money too. In the right climate this is an easy way to significantly reduce the amount of fossil fuels use.

Here is what we have learned from the experience.

Our family

There are two adults and two children in our house. We have a dishwasher that is connected to the hot water tap to take advantage of the new solar system, but it does heat water using its own internal element if the hot water supply runs low. We have a 5kg front loading washing machine that we have connected to the cold water system and wash with cold water (although we sometimes pour in a bucket of hot water if we think the wash may need it).

The systems

Our old hot system was a gravity fed system with the tank sitting on a platform in the roof space of our house. It worked reasonably well, but it was 30 years old and I have heard these have a usual life span of 25 years, so we decided to look for a replacement rather than risk a failure. Urgently arranging a replacement was not something I wanted to do even. To take advantage of the government rebates we had to replace all the current system with a new one – we couldn’t use the existing tank, which was ok because it was old anyway.

There are a number of different systems, but the type that we decided to go for was a roof mounted system. To be honest I think those with the tank up on the roof are a bit ugly, but there were only two other alternatives that I discovered. The first was to replace the existing systems tank with a new one that used thermosiphoning to circulate water with a couple of panels on the roof. This would keep the system simple, but I could not find an installer that would replace the tank in the roof space.

The other alternative is to have the tank on the ground or indoors and use a pump to circulate water through the panels. I decided against this as it is more complicated, given that there is already piping and power in the roof space. Also it would more expensive and would have ended up with more water pipe between the tank and taps which would mean more wasted water waiting for the hot to come through.

Panels or tubes

Not that long ago the choice was simpler – you just got panels. Now there is a new system on the market based around evacuated tubes. These are a bit like the inside of old thermos flasks, a glass tube inside another with a vacuum in between. Thermal energy can enter the tube, but cannot easily pass back out due to the vacuum. A heat pipe located in the centre of each tube has a partial vacuum and a small amount of evaporative liquid. The top of the heat pipe fits into a fitting at the top. Cold water in the tank is circulated through the fitting and absorbs this heat. The heated water is then returned to the tank. There are a lot of good things about them. The installers I talked to like them because they are lighter and are easier to fit.

I wanted to get a system based on the evacuated tubes, but I couldn’t find a system with a roof mounted hot water tank at the time, but I believe these systems are now available.

Frost

It gets cold here, sometimes below -10°C (14°F), so the system would need some sort of frost protection. The evacuated tube systems that I looked at with the tank on ground use the pump to circulate a small amount of water to the panels when the temperature gets near or below freezing.

In the end we chose a Solarhart 302J system that does not circulate water through the panels. Instead it circulates a mixture of water and propylene glycol which has a low freezing point. The hot water cylinder sits inside a slightly larger cylinder and the glycol circulates through the panel and around in this outer tank with the heated water stored in the inner tank.

Our solar hot water system

Backup heating

The water in the tank can get surprisingly hot from the sun – up to 95°C (203°F). A temperature limiter is used to mix cold water with hot so that it is not dangerously hot at the taps. Of course it is not always sunny and that affects its operation.

If there is sunshine for at least half the day we usually have enough hot water for the day. There is usually plenty of hot water during a cloudy day if there has been a full day of sunshine the previous day, however by the second day of cloudy weather the electric backup element kicks in.

Some people turn off the backup heater and only turn it on when needed. That is probably not a bad plan if the electric element is connected to the normal (rather than off-peak) supply. However, our system is connected to the off-peak supply which usually only supplies power during the night. If we run out of hot water we don’t want to wait until the next day before getting more so we leave it on all the time. This works well with our system as the backup heater only heats the tank to 60°C (140°F), but the sun can heat it up to 95°C. So, it does not heat every night, rather only if the hot water drops below 60°C. It does mean that on extended cloudy weather we have less and cooler hot water. This doesn’t sound great but in practice it works well for us. During these periods we don’t put the dishwasher on until after showers are over because the dishwater will heat water for itself if needed.

How energy and money is saved

If you installed one just to save money you may be disappointed, particularly if you cannot get any government assistance to install it. As mentioned earlier we also wanted to reduce the amount of fossil fuels we use. Before the solar system was installed hot water accounted for around half of our electricity consumption.  However, the hot water was heated by off-peak electricity which is much cheaper than the usual domestic supply ($0.1229 kWh compared to $0.3129 kWh), so hot water was only ever a smaller portion of our electricity bill.

During 2008 before we got the new system we used 3545 kWh for hot water and in 2010 with the solar this dropped to 961 kWh. At current prices that is $435.68 in 2008 and $118.10 in 2010. A saving of $317.58 for a year.

Things to keep in mind if you are considering solar hot water

  • You need a good spot that gets a reasonable number of hours of sunshine on the panels per day
  • Connecting the backup heater to off-peak instead of the regular supply will help keep running costs down to a minimum but you may run low on hot water after days of cloudy weather
  • Check how the system will run with your hot water usage patterns. If you have showers at night you may find that the whole of the tank is heated during the night using the regular supply and is hot before morning giving little advantage for having the solar panels.
  • Get a reputable installer. We didn’t and it was not fastened to the roof properly.

Would we do it again?

Definitely. There are more systems to choose from now and I would consider an evacuated tube one, however the Solarhart does the job and we are happy with it.

After getting the solar hot water system we also got a grid connect solar electric system which will be the topic for a later post

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Drying clothes using a thermonuclear powered clothes dryer

To create heat from electricity you need a lot of electricity – if you try to generate it yourself it seems like a colossal amount. I analysed our electricity bill and a large portion was going to produce heat; about half our electricity consumption went on hot water heating and more goes on cooking, drying clothes and heating our home. To make better use of the Earth’s resources, finding better ways of obtaining the heat we need is a worthy goal.

There is one way of reducing our consumption of electricity that we use in the Piffle house that I’m sure is used by many and that is by air drying clothes. The sun is a massive nuclear fusion reactor showering us with energy which is just the thing for drying clothes. We have never owned an electric clothes dryer despite living in a cool climate. There are four people in our family and we usually do at least one load of washing in our 5kg front loading washing machine each day. We get our share of cold and damp weather and yet we have managed to get by. We use a few different methods.

Outside

During the warmer months of the year we use a rotary clothes line of the type that is common throughout Australia. It is simple and efficient. The biggest downside is that coloured clothes, particularly black ones fade in the sun. We usually turn them inside out. It doesn’t stop the fading but it does limit to the inside instead and sometimes the edges. We have to use the clothes line for sheets as they are too big to hang inside. In winter we have to check the weather forecast before washing the sheets to make sure they have a good chance of drying.

Clothes hanging outside on a clothes line

Clothes hanging outside on a rotary clothes line. Water vapour can be see rising in the cold morning air.

Wood heater

Our lounge room has a wood heater and a small bay window. A curtain rod runs across the bay window creating a convenient place to hang coat hangers. In cooler parts of the year when the wood heater is in use, clothes left hanging there dry overnight and we now use this when the weather is cloudy. We deliberately chose a heavy duty curtain rod for the purpose and I reinforced the fittings to take the extra weight because wet clothes do get quite heavy.

Clothes hanging in the lounge room drying from the warmth from the wood heater

Clothes hanging in the lounge room drying from the warmth from the wood heater

Sunroom

Our house has a sunroom and it gets quite warm inside. During sunny winter days the sun sits at a lower angle in the sky and shines directly in. It’s not uncommon for the temperature to rise to 28°C (82°F) by mid afternoon.

I contemplated making a portable timber clothes “horse” that I could hang coat hangers on, but in the end I decided to go with a more permanent fixture as it is often used daily. It consists of a couple of strong hooks screwed into the timber above the ceiling that was previously used to hold hanging pot plants. We simply suspended a timber rod using string salvaged from an old curtain rod.

On a cold frosty morning it is much nicer hanging them inside than out in the cold. Clothes that are hung in the morning are usually dry when I come home from work in the evening.

Clothes hanging in the sunroom

Clothes hanging from a rod in our sunroom. The rod is a semi-permanent fixture.

Cons

Other than fading that can occur when hanging clothes in the sun the clothes end up less fluffy. Tumble dryers seem to fluff up the clothes. Hanging them to dry in still air can result in them being a bit stiff. Some clothes are affected more than others and we don’t find it a big problem.

Tips

Wet clothes are heavy. If you are going to hang them on a curtain rod or from the ceiling make sure it can withstand the weight. If it is screwed into plasterboard it will probably rip out and “tumble” in a different sort of way.

Use coat hangers that are clean and made from plastic or are plastic coated – you don’t want to end up with rust stains or other marks on your clothes.

Other related articles

Building a sunroom: Our temple to the sun god

Experimenting with solar: Using waste heat from the roof to warm our house

Building a sunroom: Our temple to the sun god

Our house, like many old houses in this part of Australia was not designed well for the local climate. In an area that is quite cool, the house was built with minimal windows facing the northern sun. Australian’s have a love affair with verandas and generally that’s ok because most of them live where it is usually hot. What is needed here is passive solar design.

Frosty morning

This is the sort of cold we get here. It can drop below freezing before we go to bed, but it is often followed with a sunny day.

We found we did not use the veranda often because it was either too hot, too cold, too windy, too many flies buzzing about, too many vicious mosquitoes or there was just too many other things to do. It was just a waste of space that required regular maintenance. We decided to convert it into a sunroom and become lovers of the sun.

The build

I won’t go into too much detail about the build as I’m not a builder and this post is really about the benefits of passive solar design.

This is what it looked like before we started

The build started with help from my father to replace the floor. Then I ordered a lot of windows and a glass door.

A massive hail storm hit the town before our windows were built. Many windows around town were smashed and repairing those was the top priority for glaziers so our windows were delayed until around the time our first baby was born. This added some extra pressure at a time when we didn’t really need it.

Once the windows and doors were in place I removed an existing window between the kitchen and the new sunroom and converted it into a doorway. Next job was fastening some plasterboard over the old weatherboards and hiring a plasterer to finish it off. We got an electrician to install lights and a power point and then we painted the walls and bought and carpet and had that installed. On the exterior we had to add a row of brickwork around below the windows and a small section of tiling at the front door.

The end result. Notice the removable awning on the western side to prevent overheating in summer

Costs

All up it cost around $10 000. That was 15 years ago, so these prices are out of date. The windows and glass front door were the biggest cost at $7000.  We needed 100 meters of fabric for the curtains and our family helped by sewing these. Even so, with curtain rods the total for that was around $1000. The final $2000 went on flooring, carpet, electrician, plasterer and paint.

How good is it?

Aesthetically it is ok. You won’t read about it in Home Beautiful. It’s not going to win any design awards. From a practical viewpoint it’s great. A lot of projects that I have done have not been successful, but this was more successful than I imagined it would be. It went from the least used area of the house to one of the most used. Visitors gravitate to it and are usually surprised at how warm it is inside.

Inside. The original ghastly pink colour I chose for the internal walls has been replaced with stone finish paint.

Some people are surprised that a sunroom will significantly warm a house although they are not surprised at how hot the interior of a car can get parked in the sun and there really is not that much difference between the two. There is roughly 1KW energy per square metre from the sun, or so I beleive. About 14 square metres of sunshine enters through the front windows at midday in winter, so I think that we are getting about 14KW of energy. It doesn’t all get retained as heat as some is reflected back out, but it’s still substantial.

We have a wood heater that is very good, but it only outputs around 10KW of heat. We have a reverse cycle air conditioner as well and it is ok, but it only outputs around 6KW of heat. The sunroom makes a far bigger contribution to our heating than either of these. It only takes a cloudy day to be reminded of this, although even when it is cloudy there is often some warmth in the sunroom. It is now our main heating source with the wood heater only required on cold nights and the reverse cycle usually only on cool mornings when the wood heater has not been used overnight.

During the day it is often 10 – 15°C warmer inside the sunroom than it is outside. It’s not uncommon for it to get up to 28°C (82°F) inside when it is only 13°C (55°F) outside. We usually wear tee shirts in winter and still feel very warm. Parts of the house further away from the sunroom are not as hot as that, but generally they reach very pleasant temperatures.

28.4 degrees celcius

It is was 11°C (52°F) outside when this picture was taken. This is a measurement of the wall temperature in an area that has not been in direct sunlight (28°C – 82°F)

It has changed our house from a cold old house into a warm, light and pleasant place. If you live in a cool climate and you get the opportunity to visit a house that uses passive solar heating then see what it’s like. Using “alternative” technology does not have to be inferior – it can be superior.

Tips

When you have as many single glazed regular glass windows as we do it doesn’t seem to matter if curtains have thermal backing or not, or even if you draw them closed or not, it is still going to get cold overnight. Maybe the temperature will not drop quite as quick but it seems to be just as cold by morning. We overcame this by shutting the sunroom off from the rest of the house at night.

These doors were added later, They are a important part of the design, preventing heat loss at night and also to keep up heat during hot summer days.

Windows on the northern side (in the southern hemisphere) are good. The sun shines in during winter, but not in summer. Windows on the west or possibly the east are not as good. We place a temporary awning above the western windows during summer to reduce the sunshine entering the house otherwise the house would be unbearably hot.

A concrete floor with a high thermal mass should absorb and store heat during the day and release it during the night. That was too difficult for me to do, so we don’t get that benefit.

The sun is harsh on carpet, paint and furniture. We currently have three chairs. We deliberately use old ones. Only one was purchased new, one is second hand and the other came from our local dump shop. Covering them will lengthen their life, otherwise they will not last many years.

Cleaning the house windows became a big job.

To work well the room needs to receive plenty of sunshine. A cloudy climate of shading from trees and buildings will make a vast difference.

Other articles

This is the second post about solar projects we have tried. I have already covered using waste heat from the roof to warm our house. Still to come is our experience with solar hot water heating and grid connect solar electricity systems.