Solar power or solar hot water: The Do’s and Don’t’s

New Zealand ‘s high scepticism towards solar energy

The booming demand for solar power in New Zealand is very unusual, given the fact that scepticism towards solar energy has been very high for many years. Government does not promote solar energy as part of the future energy mix and there is a lot of confusion, misleading information and a huge lack of education on solar energy.

Unlike many developed countries worldwide there is no compulsory feed-in tariff in New Zealand for solar power export to the grid. Unfortunately we also see a lot of solar ‘cowboys’ selling solar PV systems for the wrong reasons, promoted as ‘short pay-back times’ and ‘reducing the energy bill’.

In the field of solar hot water systems we also see ongoing issues on quality and performance reported in BRANZ reports creating even more scepticism towards the use of solar energy. The world is booming in solar energy while NZ is not keeping pace.

We think that solar energy deserves a better place in NZ and we hope to debunk the many myths on solar energy by a series of articles that are informative, and will summarise compelling facts on the state-of-the-art solar technology.

NZ households and energy efficiency - the big problem
Many households use electricity for cooking, hot water and heating in a very inefficient way. More than 80% of all NZ buildings use (too much) electricity for these basic needs.

The energy needs for hot water production in an average NZ household are (too) high as well as the yearly electricity needs. This energy problem can be easily fixed with state-of-the-art technology.

Energy efficiency should be a priority before going solar
Electric hot water cylinders heaters have huge losses which are directly reflected in an expensive energy bill. Electricity losses are average around 30-50% in the NZ household due to inefficient appliances. To overcome those expensive standing losses, the direct use of LPG for cooking, hot water and heating will be much more efficient.

The use of an instantaneous gas califont should be promoted more in NZ to help reducing the energy bill without loss of comfort. The use of LPG gas is not only more efficient than electricity but is also much cheaper to run for the same kWh unit. Average in NZ you will pay 16-19 ct/kWh for LPG compared to 30-35 ct/kWh for electricity.

Is solar power (grid connected) more effective than solar hot water production?The short answer is no – not in New Zealand yet. The reason is very simple. The feed-in tariff in NZ is a financial punishment instead of an incentive to promote solar energy. The pay-back times are still large because of the low feed-in tariff at 8 ct/kWh. Many solar ‘cowboys’ though will try to get you to invest in a solar power system in order to reduce your energy bill. In reality this could be very different.

What system produces the most solar energy? Solar power or solar hot water?
The SHW state-of-the-art system will produce much more energy per square metre panel installed. To compensate the electrical needs for hot water only, a household would need a solar power system of more than 33 sqm solar PV array, while a simple and small SHW of 3-4 sqm can easily cover 70% of the yearly hot water needs with a short pay-back.

Economic evaluation in respect of life expectancy?
The main economic factor to evaluate solar systems is not the price only, but the ratio of price on performance (kWh). The question is how many kWh a system will produce per year for which price on a lifespan of 30 years. At the actual low feed-in tariff in NZ, it becomes very hard to demonstrate short pay-back times with solar power systems. SHW systems on the other hand always save a dollar for a dollar whenever the family uses hot water. SHW systems have proven life span of 30 years without dropping efficiency, unlike solar PV panels that lose efficiency every year.

Can a solar power system directly feed the electric element of a hot water cylinder?
Yes, but only in a limited way. Many days of the year, the direct use of solar electricity will be too low to heat all the water properly in a short time, and it will also take many hours to heat a minimum of water. Comfort problems are inevitable if solar power should be maximised.

Solar power pay-back time in perspectiveIn an average household, pay-back times for solar power will be rather long unless all the solar power is used for self-consumption. SHW systems are much more productive than solar power systems and create a guaranteed pay-back time.

Conclusion
Advanced solar hot water systems will create huge savings and more comfort than electric cylinders. Solar power grid connected systems have proven worldwide to be an important part of a total energy mix of a country. But the situation in NZ is very confusing and not very encouraging towards solar energy. Correct information and education are the key words to promote solar energy. We invite you to our workshops in Kaiwaka-Positive Energy House.

* Abbreviations: kWh = Kilowatthour (called ‘unit’ on your energy invoice); PV = Photo Voltaic (defines the process how solar PV panels can produce electricity); SHW = Solar Hot Water.

By Eric Jansseune, Solar Master Engineer

NEW ENERGY: The use of solar energy in NZ is still in its early stages, and largley misunderstood.