Building Materials – Solar Heating and Electrical

This section of the Building A Home In New Zealand discusses the Building Materials topic of Solar Heating and Electrical.  This topic is intended to be read in conjunction with the other Building Materials sections Windows, Thermal and Noise Wall Insulation, Attic Venting and Internal Moisture Control, and Heating as well as Choosing A Builder or Designing a House.


Using the sun to provide your home with free energy can provide a huge benefit over the life of your home.  Though there is some initial expense, the pay back for utilizing solar energy is typically short. The good news is that the cost of implementing solar energy is reducing, and the efficiency of the hardware is constantly improving.

You have two main options for solar: solar electricity and solar hot water.  Both will use the energy of the sun to supplement or replace utility use in your home, but they have different importance in NZ than in the US.


Solar Electricity

The idea of solar electricity is nearly miraculous. Converting renewable solar energy into usable electricity at the point of use is hugely beneficial to the homeowner as well as to the environment. I won’t be touching on the environmental aspects here but will be discussing the advantages and disadvantages of implementing solar electricity in NZ.

In NZ, electricity is very expensive. At the time of writing, our Genesis Classic Plan provides electricity at 32 c/kWh with an additional $10/month ‘Fixed Charge’. Creating your own electricity can have large financial impacts on your utility bills.  Comparatively, energy prices in the US are much lower. I was paying 13 c/kWh in the US with no additional line or fixed charges. Therefore, the demand for solar adoption in NZ should be much higher than we have seen in the US because of the increased energy costs.

When considering solar, you need to weight he cost of solar against current and future energy prices (both supply and buy-back).  You also need to determine how much electricity you use now and in the future to determine how much solar capacity you should install.  Any extra energy that you create will be put back into the electrical grid unless you invest in large banks of storage batteries.  Electrical companies charge you for the energy you use, in addition other things including company profits.  You may never include in your expectations that they will pay their profit margins back to you when you supply electricity back into their grid for them to charge other customers.  Therefore, expect that the energy you use to always be more expensive than the buy-back rates. The current Genesis rate of buy-back is 8 c/kWh, though it used to be higher.  Therefore, you currently have to sell back 4x more energy than you use to break even on your energy charges, and you will still have to pay the fixed fee/line charges.

There are two additional things to consider. The amount that energy companies pay for your surplus electricity you supply to the grid is not set. Some don’t even pay back at all. So, if you plan for large output to oversupply your home, the future may result in no buy-backs and you are supplying energy companies with free energy which they charge to other customers. Some companies, like Unison, are penalizing solar using customers by charging a solar ‘tax’ to discourage others from producing their own electricity and removing their company profits.  Imagine if other companies took up this logic. Your petrol prices could look like this: $2.10 /L for V8 owners, $2.80 /L for a V6, $4.20 /L for a 4-cylinder, and $6.80 /L for hybrid owners.  Until this type of discrimination is outlawed, the possibility of a penalty for reducing company profits is something to consider when installing solar electrical.

The second additional thing to consider is that the price of solar panels and storage batteries is decreasing while the efficiencies of these items is slowly increasing. Regardless of what the current calculations show, it may be very advantageous to ditch your electrical company in the future and be self-sufficient.  Therefore, it may be worth considering planning for future expansion of solar. You may plan to leave a little extra space in the garage for the storage batteries, leave a little extra space in the electrician box for inverters, make sure that north-facing roof space is accessible through the attic for running cables in the future.


Solar Hot Water

Solar hot water has completely different usage characteristics because all the solar energy is easily stored as hot water. The main consideration is ensuring that the size of the hot water cylinder is large enough to accommodate enough hot water to store enough solar energy for a couple of cloudy days. A secondary consideration is that the hot water cylinder should be within accessible distance to the north facing solar panels.

You will have a few options if choosing solar hot water. There are a couple of types of panels, a flat plate panel and evacuated tube panels.  There are systems that directly circulate the water through the panels, and others that indirectly transfer heat through closed loop systems. There are also differences in how a system responds in cold weather to prevent the panels from freezing, whether a drain back system or continuous circulation system. Each type has advantages for different locations and circumstances. It would be best to discuss the different options with your solar hot water expert.

Whichever system is chosen, they can provide some significant energy savings. Utility based hot water costs can be a major portion of a household’s energy bills. We had a gas-powered hot water on demand system that resulted in nearly half of our utility bills in some months.  By switching to solar, we completely remove that demand for nearly 8+ months of the year by using only solar heating and use solar energy to preheat incoming water for the remaining 4 winter months.


Next Steps:

This concludes the section of Building Materials on Solar Heating and Electricity. The next section on Building Materials is Attic Venting and Internal Moisture Control.