Archive for the ‘FAQ’ Category

It is easy to get overwhelmed by the choices. However there are some simple things to consider to find the best solar hot water panels for your situation.

Panel Size

Most panels are about 1×2m. Depending on the tank size, you will need between 1 and 3 solar water panels. Usually a system comes with the right number of panels and any installer will always make sure that they are adequate for your situation.

If you have an existing solar hot water system that does not generate enough hot water, you might want to look into getting an additional panel. It is best to go back to whoever sold you the system, to make sure all the fittings go together.

Technology

There are two major technologies to choose from: flat plate and evacuated tube.

Flat plate technology has been around the longest and is the most widely used. The glass is sturdy and they usually get a slightly higher REC rating than the evacuated tube system.

Evacuated tubes have two advantages: they produce a little more heat when there is no sun and in cooler climates and they are not prone to frost damage. The drawback: tubes break more easily (but can be replaced individually), in summer they might be too efficient, which leads to wasted water and they are more expensive.

We have chosen flat panel technology, because for the hot climate in Queensland they give a better return on investment. In colder areas, the tube technology certainly has its place. See solar water panel system differences.

Casing

Yesterday, we replaced a solar hot water system where the panel casing had rusted away. To prevent that for our clients, our panel casing is aluminium. The corrosive layer that forms has the same silvery look and more importantly prevents all further disintegration.

Many panels are made of zincalume. It is coated steel (the coat is made of zinc and aluminium). As soon as the coat is broken at any point (corrosion or any scratch might do that), it will start to rust.

Frost Tolerance

When water freezes, it expands and thus might crack the panels under heavy frost. There are two ways to prevent that: Frost valves and closed-loop systems.

With a closed-loop system, it is glycol that gets heated up in the panels. It is transferred in a heat exchanger to heat the water. Glycol does not freeze, even in below zero temperatures. These systems are more expensive.

When you only experience the occasional frost, frost valves are a good alternative. As temperatures drop, they open up so that the water drains out of the panels. That way, they damage is averted. Please note that some frost valves include the manufacturer’s warranty against frost damage, whereas others don’t.

How do Solar Water Panels Work?

Here is John, our plumber explaining it.

Conclusion

It is good to know about these things, when you talk to salespeople. It means you can ask the right questions. When you go through the free instant online quoting process, you’ll find that the ideal system is chosen, so that you can be certain to get a high quality long-lasting solar water product that keeps producing you hot water.

Water heated by a solar water heater can reach temperatures of up to 90 degrees Celsius. To prevent accidental scolding, we are putting in a tempering valve.

It automatically mixes the hot water with cold water to reach 50 degrees Celsius. So in effect any hot water tap has 50 degree Water coming out of it. It is hot enough to want to mix it with cold water before having a shower. But it will not burn anyone.

The tempering valve works mechanically. The valve inside expands and contracts depending on how hot the water is that comes through. When it expands, it lets less hot water pass and instead adds cold water. The opposite happens as the hot water flows through loses heat: the valve contracts and therefore opens up more of the hot water stream. Out comes the 50 degree Water.

Every solar hot water system comes with a booster for the times when there is not enough sun. There are two types of booster technology: electric and gas.

Electric Solar Hot Water Booster

This is the most common way to boost your water heating. It is the most economical as it does not have a large upfront cost. When you start using your solar hot water system, it is best to leave your booster off until you run out of hot water.

Once you know how many days of clouds that takes (for us it is 3, but that will be different for every family, depending on how you use your water), you can turn the booster on before the water goes cold. But it is worth testing it out first.

Is it not Automatic?

The electric booster has a thermostat that only lets it start when the water temperature falls under 60 degrees Celsius. So you could just leave it on and forget about it. However, that would result in wasted energy.

Let us assume that your whole family has a shower early in the morning. The temperature in the tank drops to 55 degrees. That would trigger the booster to heat the water. However an hour later, the sun hits the panels and would have heated the water far more efficiently and cheaper.

It is therefore best to leave the booster off and only turn it on when you really need it.

Which Tariff?

The official government suggestion is to connect the electric booster to Tariff 33. That is the off-peak tariff, which means it only runs for 18 hours a day. It is cheaper than normal electricity, but in many situations you use far less electricity than the minimum payments.

(Over 3 years, we had our solar hot water connected to night tariff. In that time, we used a total of 177 kWh for the booster. On Tariff 11, we would have paid about $30. Because of the minimum quarterly payment to have access to the night tariff, we paid $120 in that time.)

The story is different if you have something else connected to the off-peak or night tariff (e.g. a pool pump). Then it might be the best financial choice.

Gas Boosted Solar Hot Water System

The other booster uses gas. Even though the greenhouse gas savings are slightly higher with this type of system, you basically have to purchase two hot water systems (one solar and one instantaneous gas heater) which are coupled together.

As long as the water heated by the sun is hot enough, it just flows through the instantaneous gas system. When the temperature drops below the thermostat setting (usually between 45 and 49 degrees) the gas system starts heating.

In some instances it is possible to use an existing instantaneous gas system.

A solar hot water split system only has the panels on the roof. The tank is on the ground in the same position that the old tank was in. That is the main difference of solar hot water heating systems.

Hot water rises up because it has less density than cold water. That means that a pump is necessary to pump the cold water up into the panels on the roof at the same time drawing the hot water down into the tank.

The pump is located on the tank. It is managed by a computer that measures the temperature in the panels and in the tank. Whenever there is a 6 degree Celsius difference (i.e. the water in the panels is 6 degrees warmer than the water in the tank) the pump starts working.

Two reasons for that:

1. You do not want to circulate the water at night or under clouds when there is no sun to heat the water in the panels
2. You want to use the heat as soon as the sun is hot enough, so even a 6 degree difference can make it difference.

But the water in the panels can get a lot hotter. That’s why the pump also stops working when the water in the tank has reached 75 degrees Celsius. That is much hotter than any electric hot water heater (they heat to around 60 degrees).

Hot water is highly corrosive. Basically there are two ways to combat the corrosion of tanks:

Vitreous Enamel

Vitreous enamel is a glass coating that is chemically bonded to steel at high temperatures around 850 degrees Celsius. It is actually glass powder that is used.

The enamel coating does not rust and thus prevents the water from reaching the steel.

In addition these tanks have a sacrificial anode for additional corrosion protection. It needs to get checked every 5 years and usually replaced after 10. In areas with aggressive or hard water, this might be necessary more often.

Stainless Steel

Marine grade stainless steel includes higher levels of chromium. They create a passive film of chromium oxide which prevents further corrosion.

Tanks made of it do not need any maintenance, but they are $600 to $1,000 more expensive than the vitreous enamel systems. It is possible to recycle the stainless steel, whereas the vitreous enamel tanks are just dumped.

For anyone living close to the Ocean, it might be a worthwhile investment, but for most situations the vitreous enamel work perfectly and give a better return on your investment.

How to Decide

When I started researching, all the stainless steel tank suppliers knocked the vitreous enamel tanks and the ones selling vitreous enamel showed me proof of how stainless steel can corrode as well. In reality both systems have been around for over 50 years and proved their longevity.

If you plan to stay in your home for 20+ years or you are close to the Ocean, the extra investment in a stainless steel tank might be worth it. If you are strapped for cash and want to start savings on your electricity bill, a vitreous enamel tank is a good and durable choice.

We recommend vitreous enamel as a standard, but offer to upgrade to a stainless steel tank.

Tank Casing

One last word on the tank casing. Most tanks come with a colorbond casing. It is a coated zincalume steel base, which is used extensively in roofs, walls, fences, garage doors, etc.