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The Power of Solar

Updated: Jan 14, 2021

Victor Luca & Graeme Weston, 15-Apr-20.

The Beacon 22-Apr-20

Solar energy rains down on the Earth for free. Why not use it?

For decades now scientists have been telling us that as a result of human activity and the Greenhouse gases that these activities generate, the Earth is warming and the climate is changing. As a result it is likely that we can expect a loss of land and sea ice and an increase in global average sea level, destruction of ecosystems, loss of biodiversity and an increase in the frequency of extreme weather events. It is clear that we humans cannot continue on this trajectory if life on this planet is to be sustained.

To respond to this potentially catastrophic situation, on the 13th of November 2019 the Climate Change Response (Zero Carbon) Amendment Actbecame part of the law of our land. The stated purpose of the ‘Zero Carbon’ bill is to provide a framework by which Aotearoa can develop and implement clear and stable policies to avert and adapt to climate change. More specifically the ‘Zero Carbon’ bill has the following objectives:

1) contribute to the global effort under the Paris Agreement to limit the global average temperature increase to 1.5° Celsius above pre-industrial levels in line with IPCC recommendations.

2) allow New Zealand to prepare for, and adapt to, the effects of climate change.

To comply with the first item we must reduce our emissions of greenhouse gas emissions and do it soon. This is the commitment that we have made to the global community.

Although we in Aotearoa make only a small contribution to global emissions (less than 0.2%), our nation is amongst the highest emitters in per capita terms. Even if we were to reduce our emissions to zero tomorrow, we would make virtually no difference to the overall global situation. That begs the question of why we should bother to do anything at all?

The answer to this question is simple. We need to reduce our emissions to set an example to the rest of the major emitters. Since we humans inhabit one finite Earth, we are all in this together. In other words, what the major emitters do will affect us all. We are not making a moral argument because the motivations are purely in our own interests.

So let’s take a closer look at New Zealand’s green-house gas emissions. They are broken down by sector in Figure 1a. The lion’s share, or about 49% of these emissions, result from agricultural production while the energy piece of the pie accounts for about 39%. This 39%, of the emissions pie can be further broken down by sector (Figure 1b) and it can be seen that electricity generation and transport account for about 16% and 44% respectively. Electrification of the transport sector could in principle reduce the transport component by half if all vehicles on NZ roads could be converted to battery electric vehicles (BEV) utilizing clean (zero-carbon) electricity.

Figure 1. (a) New Zealand’s GHG emissions by sector in 2013, (b) breakdown of energy sector emissions (data from [6, 7]). IPPU – Industrial processes and product use. Source: MBIE, Energy Greenhouse Gas Emissions, Wellington, NZ, 2014; MfE, New Zealand's Greenhouse Gas Inventory, 2015.

When one inspects the diagram of Figure 2 it can be seen that most of our electricity comes from hydro and geothermal sources. These are generally considered to be renewable and have a relatively small carbon footprint. Thermal base-load power generation using coal and gas as fuels are inherently ‘dirty’ because of the greenhouse gas emissions. Thermal electricity generation constitutes about 15% of NZ electricity generation. Most of this 15% results from burning Indonesian coal and New Plymouth gas at the Huntly thermal plant located in the Waikato. The electricity that is generated basically supplies Auckland.

Renewables such as solar and wind constitute a relatively minor but increasing portion of our electricity generation. Although our electricity grid is relatively clean, and given that we have good base-load sources (hydro & geothermal), removing the 15% contribution from coal and gas and replacing with renewables such as solar and wind, could be particularly advantageous in reducing emissions associated with electricity generation. Replacement of this 15% could be considered low hanging fruit in our quest to reduce emissions. It would be an easy 15% of dirty energy to eliminate.

Figure 2. Electricity generation in New Zealand by source in 2016.

Whether or not the reader believes the incontrovertible scientific evidence on climate change, it is difficult to deny that the nearby nuclear fusion reactor we call the Sun, sustains life on our planet. Without the Sun, our Earth would not be the place it is today and humans would not exist at all. On a typical summer day the amount of sunlight reaching one square meter of ground is quite significant and it would take only two minutes to boil an average kettle. However, modern photovoltaic (PV) panels are only about 15% efficient in converting this energy, so that the electricity generated by a one square meter PV panel would actually take 13 minutes to boil our electric kettle. Slice it how you want however, our Sun is free and it is eternal.

Solar energy conversion using modern PV panels used to be quite costly (see Figure 3). As shown in the figure it used to cost about $77 USD to generate one watt of electricity in 1977. This cost has been reduced exponentially over time thanks to improvements in PV panel efficiency and manufacturing processes. The cost to generate one watt is now less than 30 cents (50 NZ cents). This is a utility scale price. By the time the costs of importing panels, paying taxes and installing on a Whakatāne rooftop, the cost is about NZ$2.00 per watt.

Figure 3. Price history of silicon photovoltaic cells in US $ per watt. Source: Solar Energy Revolution: A Massive Opportunity.

We are very fortunate to live in a district with the highest average sunshine hours in New Zealand, in the range 1700-2600 hours. This is relatively ideal in terms of harnessing solar energy. Of the renewable energy alternatives, solar PV has a relatively higher energy density (W/m2) than say wind energy and therefore it makes a good deal of sense to install this technology more proactively. We are truly fortunate!

To have a meaningful effect on emissions in our district, one alternative would be to expand solar generation by equipping as many roof tops as possible with solar panels (Figure 4a). Cheap as solar PV panels have become over the years, they are still not free. Esthetics aside, the setup shown in Figure 4a would still be relatively expensive and many of us simply would not be able to afford it. A typical four-person household would require about 4 kW of generation, more if the family owns a battery electric vehicle. In addition, each installation requires fixtures, an inverter, a special (smart) meter and wiring to be done. The total cost of a 4 kW PV system would be about $10,800. That is, $2700 per kW.

An interesting alternative to installing panels on your own roof is the so-called community solar farm as shown in Figure 4b. Such an installation takes advantage of economies of scale and the cost per kW for a decent size solar farm would be about $1500, or nearly half per kW compared to a roof-top installation. The solar farm could be installed on non-productive land owned by the community or private entities. In other words, the panels do not need to be on your roof for you to benefit. You simply buy a share of the farm and your bill is credited for the energy your share generates. Renters, that don’t own the roofs they live under, would also be able to participate. Because of reduced cost per kW generated, and many other reasons, the idea of a community solar farm has really taken off in recent years. Of course, this funding model is only one of many. An alternative would be for a single public or private entity to fund the construction of the solar farm and sell low-cost electricity into the grid benefiting you the consumer.

Figure 4. (a) roof top solar panels and (b) community solar farm.

We have done some simple calculations and concluded that a 10 MW community solar farm in our district could supply sufficient energy to power 2500 two-person households and it would make a big contribution to reducing our emissions and meeting our obligations under the Paris agreement.

Now doesn’t that make a shit load of sense!

Anyone interested in such a project please feel free to get in touch with one of us.

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