SOLAR & RENEWABLES

 

Every two minutes the sun gives the earth more energy than is used annually.

 

Building Code Requirements

 

There are no Building Code requirements for solar and renewable energy.

 

Active Solar Design Principles

 

Grid Connected Solar Photo Voltaic (PV)

 

Solar should be an integral part of a Healthy Home design. A Solar PV system should not be an afterthought but be designed to integrate into the building and work in harmony with the other systems incorporated into the design. Why is it a good idea to install solar?

 

● Lower annual energy bills.

 

● Increase of energy independence.

 

● Environmental concerns.

 

● Dislike of Energy Retailers control.

 

● Interest in technology.

 

Design Considerations

 

There are many design considerations when installing a solar array on a building to achieve the most efficient performance, and have the design fit in with the surroundings. Deciding on what your motivation is when it comes to generating your own energy will help determine the end design. Do you want a quick return on investment or long-term resilience and energy freedom?

 

● Roof orientation is crucial and the array location/s must be given the highest priority at the design stage, but we do appreciate there will always be compromises.

 

NZ Standard ASNZ5033 (Installation and safety requirements for photovoltaic (PV) arrays) gives clear indications regarding orientation of the PV array:

 

“For the best year-round performance for grid connected systems, a fixed unshaded PV array should generally be vaunted facing true north (+/- 10°) at inclination equal to latitude(+/- 10°) angle or at an angle that will produce the best annual average performance taking in to consideration: seasonal cloud patterns, local shading and environmental factors.”

 

● Roof Azimuth – While noting the above, it is possible to achieve fantastic results with split arrays (panels located on different roof orientations) such as East/West, North/East and North/West or combinations in between. Depending on load demand factors this may be a better option as the sun moving across the sky better matches the daytime load demand, resulting in greater self-consumption, along with Energy Management. A single North array may be a better option if maximum generation is required and/or a battery is being utilised to store surplus generated energy.

 

● Latitude in NZ – Ideally a fixed roof-mounted solar energy system should be at an angle that is equal to the latitude of the location where it is installed. However, this is not always achievable for a number of reasons. A minimum tilt of 10° is recommended to ensure self-cleaning by rainfall.

 

● Shading issues – Consider trees, power poles, sheds, neighbouring buildings, aerials, ridges from adjacent roofs and surrounding landscape; is the building sited in a valley? Large decorative chimneys are not good, as shading is the enemy of the array. Technology can reduce performance losses due to shading, but it is better to get the roof design right from the start. Poor panel placement isn’t just an upfront cost. It is a cost for the lifetime of the system!

 

● Building Envelope – How good is the buildings thermal envelope? The greater the losses, the more energy needed to be generated in winter to meet heating loads.

 

● Aesthetics vs system performance – Aim to always design for performance but if the solar panels are to be laid on shallow roof pitches 5-10°, a larger array will need to be installed to make up for the substantially lower winter generation.

 

● Provision for Electric Vehicle charging – With the uptake and the future of electric vehicles, it makes sense to consider this as part of the selection process when considering the solar hardware and software/control of the solar power generation; a larger array may be required and/or an Inverter with EV charger built in.

 

● Access – Consider access around the array for future maintenance.

 

● 1 phase vs 3 phase supply – as NZ does not have Net Metering it is always going to cost more to get the efficiency out of a 3 Phase residential installation. Remember, Solar PV works exceptionally well but it is not a perfect science as there is no control over the weather. Realistically, aim for a substantially reduced bill rather than an elimination strategy!

 

Do I add a battery or not?

 

Advantages

 

● Utilised to divert surplus daytime energy to the battery for later use at night.

 

● During the day, draw from the battery to supply appliance demands if there is not enough solar generation eg: the battery can constantly be charged and discharged during the day.

 

● Ideal for larger arrays (where more surplus energy is available) and when there is high night load demands and /or regular energy spikes during the day.

 

● Cycling the battery up to twice a day will help to reduce the systems payback period. This means charging during cheaper, off-peak times with the grid, discharging during the morning peak, and then charging again with the sun so that you have some energy stored for when the evening peak comes around.

 

● If power backup is required, eg: in rural locations likely to experience grid outages there are further complexities to consider.

 

Disadvantages

 

● Battery prices have not come down as quickly as hoped and consequently, they are unlikely to pay for themselves in their warranty period, so the cost of a system with batteries is higher.

 

● A Solar PV system with an energy management system (that allows surplus energy to be diverted to multiple appliances in the home) currently offers better returns and shorter payback periods than solar with a battery.

 

● Remember energy from the grid will still do the exact same job as a solar battery, so if it costs less to supply energy (for small demand loads of an energy efficient home) is the capital investment needed for the battery worth the additional cost?

 

● Even with a battery matched to suit a system, its energy storage is limited and you are still likely to be exporting back to the grid especially in summer.

 

● In Winter and on grey days, the PV system may not generate enough surplus energy (after the house demands have been met) to recharge the battery, meaning the battery is being underutilised.

 

● In Summer (with lower house demands) the battery may sit for long periods fully charged being underutilised.

 

● There is a lot of talk about a 'Smart Grid' The possibility to sell surplus energy back to retailers at peak times to meet wholesale market price spikes and curtail peak demand on the Network. This entails allowing Lines Companies priority control over the battery, but are they ever likely to give the client a true credit that reflects the capital expenditure?

 

● Many clients think a battery can function during grid outages and also perform daytime cycling. This is not the case, as the grid may go down at the same time that the battery has been discharged whilst cycling, meaning no energy is available for emergency loads. What are the end requirements? One system design is not suitable for all situations. There will always be compromise!

 

● In a grid outage situation (where emergency loads are required), people have unrealistic views of how long a standard battery (say 7kWhr) will last and what loads it will run. Forget hot water heat pumps, HWC's, spa pools, electric vehicles, we are talking light loads such as fridge/freezer, lights, cellphones etc.

 

A Future Approach

 

For economies of scale (BESS) Battery Energy Storage Systems installed at community level might be a better option to meet peak demands with a combination of the grid and the clients exported energy utilised to recharge the batteries.

 

Summary

 

Installing a battery on an energy efficient home needs to be assessed on a case by case basis. The energy saved vs the battery cost will, most likely, will not stack up from a return on investment perspective, but may be important for the user, from a resilience point of view, when back up energy is required or when energy demands at night cannot be transferred to the daytime.

 

A Different Approach – Using the Healthy Home as a Battery

 

This is an example of a possible solution; Solar PV + Home + Energy Management System:

 

● Minimum 6kW solar array.

 

● 5 / 6kW Grid connected Inverter.

 

● 300L Dual Element standard HWC.

 

● Hydronic underfloor heating/cooling system. Note: A boiler is not required, further reducing the system cost.

 

● Energy Management System provides power management throughout the home. Even on cloudy days, when there is less solar generation, it can still help avoid using expensive mains power by prioritising the most power-hungry appliances to use the solar generated power first, before drawing from the grid.

 

● Case studies of people who have taken the above approach have summer energy bills are around $30.00 per month credit and Winter $60.00 per month, the energy bills speak for themselves, so spending $10,000-$17,000 on a battery to improve the system efficiency further cannot really be justified on a purely financial basis.

 

● Whether a PV system has a battery or energy management system, it is still going to export a certain amount of energy to the grid, at 7-10 cents per kW/hr. This may change at any time but energy demand in NZ is forecast to increase according to Transpower, so there will always be demand for surplus energy. It could be argued that all surplus energy is helping NZ generate more environmentally friendly energy. We need to change our perspective that exporting surplus energy is a bad thing. We are storing energy in the dwelling, HWC, and the National Grid. Current buy back rates https://www.mysolarquotes.co.nz/about-solar-power/residential/solar-power-buy-back-rates-nz/

 

● The next generation of electric vehicles will be V2H (vehicle to home) and V2G (vehicle to grid) capable meaning the cars battery can be charged from the house solar and discharged to supply the small house loads at night and also be utilised to meet energy spikes during the day if the vehicle is available. With (V2G) your Lines Company may want control of your battery to balance their loads and to save them money.

 

So back to the project... how to get the best results...

 

As houses are nearly always different, the average base load for a house will also be different. This has to be taken into account when sizing any system that you are proposing with energy management. The other factors are the lifestyle and behavioural patterns of the owners. Do they work away or from home? Are they retired? When do they shower and what appliances do they have in their home?

 

When do they use appliances? All of these questions need to be asked and factored into the equation. Start with the whole picture when designing an automated system that will use as much of the solar production as possible whilst controlling loads. This will give the best result to the customer – best design – best performance that sets them up for years to come...

 

Electric Vehicles (EV)

 

Electric Vehicles are becoming more popular, so consideration should be given to allowing for or future proofing your healthy home with the necessary infrastructure to connect an EV. The following document provides advice on electric vehicles and the home.

 

https://www.eeca.govt.nz/assets/EECA-Resources/Research-papers-guides/EV-Charging-NZ.pdf

 

You may need to consult your electrician and the local lines company about connection sizes and costs. Lines companies may be able to provide some insight into whether their pricing would favour smart charging options, or even what times should be prioritised for charging, to save cost long term.