ConsumerismEnergy Systems

Solar Power: Is it Convenient for You?

Trying to live more sustainably and save a buck or two….

Sustainability and economics

Almost every time, more sustainable systems are far more expensive than our regular way of doing things. This may be the most difficult obstacle to overcome when converting. However, this observation only takes money and cash flow into consideration. There are other points of view that need to be included in a truly objective discussion of this topic.

We may tend to see things in absolutes, and the easiest ‘absolute’ to monitor is the amount in your bank account. In the case of sustainable systems, however, there is a lot more to evaluate. Even though it may be difficult to assess these benefits, they are as real as cash and you should consider them as tangible as the temperature you’re experiencing.

So, when taking a sustainable photovoltaic system into consideration, you should think of the following issues as well, besides just pure, immediate economics:

  • CO2 emissions saved (global over-heating)
  • System dependability (massive blackouts via natural disasters, system failures, and suchlike)
  • Aesthetics (will it look good on your roof?)

Do you want to buy solar or someone is trying to sell it to you?

Everybody is talking about solar power these days. Companies that sell photovoltaic (PV) panels say that it is the best option for you, nevertheless, you should make your own research and check every detail before embarking on what could be a large investment that can take several years to pay for itself.

Steps prior to buying a PV System

Before going out and buying a system rated to meet your current energy consumption level, you should first take steps to ensure you will not invest more than you need. The best place to start is to first reduce your energy use as much as possible.

Illumination

Although lighting may not be the most energy consuming component in your home’s energy use, it may be the most noticeable. You should try to change your bulbs to LED, if possible. LED lights really make a significant difference.

If not, you could use compact fluorescent lights (CFLs). These may save you up to 75% of your lighting bill, but sadly, when disposed of they can be dangerous. They contain mercury, a highly poisonous metal.

Water heating

Maybe the best option for water heating is a solar water heater, but this necessitates your spending a little more. Solar water heating systems may be efficient and cost effective, but are also dependent on the sun, and there is no ‘grid tie’ option.

You could use a propane gas water heater. This may lower your expense, but in the long run, nothing beats solar for this task.

Cooking

Your cooking habits and the appliances you use for this endeavor may take a large chunk of your energy bill.

In most developed countries, gas ranges are almost impossible to find. Everybody uses electricity. This kind of oven is quite easy to use, but they suck up great quantities of energy. The most efficient system may be propane gas, but it also has its own downsides.

Of course, if you’re turning hardcore on sustainability, you may look into biogas (see ‘biogas’ sub-section near bottom of this article), solar cooking, biomass or gasification. All of these have a very low carbon footprint and can give you the least expensive answer, but, there are still some things to consider. We will discuss these systems in another article.


Solar cooker

Air conditioning – heating, refrigeration

This area may be the most expensive in your home. Notwithstanding that there are new, ‘energy efficient’ appliances, they still take up large chunks of electricity; so you have a few options: operate them at their lowest setting, use them less, downsize or change them for the most energy efficient option available.

There are systems that work with propane gas, solar heating systems, and solar aided air conditioners. The main idea is to lower your consumption. You can check on my article regarding solar heating for homes to get some idea.

Clothes washing and drying

You want your clothes clean, nice smelling and dry. If you want all in just two hours flat, you may need a lot of energy to accomplish your task. If you can wait a bit, you still can use your washer (that does not take up a lot of energy) and dry your clothes in a solar clothes dryer, like the one described in the aforementioned article.

Of course there are other options you could consider, like low energy washers or even manual systems.


Solar Clothes Dryer

The reason for these prior steps

The biggest savings you will experience are those that come from energy not spent. This means that the best you can do is to lower your energy consumption before buying a PV system. Of course, you can buy a system to cover the 1,000Kw/h that you consume every month, but if you pay close attention to reducing your energy usage, you can get away with a significantly smaller outlay.

Stand alone or grid tied?

The first thing you have to be sure about is if you need (or want) a stand alone system or a grid tied one. This can make a great difference in your initial investment.

A stand alone system is one that will produce power only for you. This system may require a battery array in order to store energy for the time of the day where there is no sunlight or not enough to meet your needs. A grid tied system is one that sells power to the grid when there is excess energy production and buys it back when there is need. The initial cost of installation may be higher on the stand alone system.

Photovoltaic systems carry a lot of ‘other things’ besides the PV panel. You should have this in mind before taking any further steps. For stand alone systems, you should buy inverters, chargers, battery arrays, breakers and of course all the wiring, fixtures and panels. On the other hand, the grid tied system may not require the battery array (that sometimes is the most expensive item), but depending on your local laws, there may be some requirements in terms of expensive equipment (certain types of regulators, breakers, automatic power interrupting devices and others).

There is also the dependability of your system to take into account. Even though it is reassuring to have your own battery bank to give you energy, the idea that you might find yourself without enough sunlight for a few days or that a part of your equipment may not work properly someday is annoying. Therefore, grid tied systems may provide a little more dependability than stand alone ones.

Your level of energy consumption

After lowering your energy consumption to more manageable levels and deciding upon a grid tied system or a stand alone one, you can start to evaluate different options, which might be:

  • Grid tied with over 100% projected energy production
  • Grid tied with 100% projected energy production
  • Grid tied with less than 100% energy production
  • Stand alone system with over 100% energy production
  • Stand alone system with less than 100% energy production

Calculating the size of your array

If you want to calculate the size of the solar array you need, you will first need to make some calculations:

Insolation

To calculate the average insolation you can count on at your site, you have to search for the data regarding daily solar irradiation for your location. Maybe your local meteorological office can help.

With this information, you can have an idea of how many watts the sun pours onto your roof. Remember, this number will be an average, and so has its ups and downs, so a little bit of conservative caution with your calculations may be advisable.

A little math

So, now let’s look at the numbers. Let’s say you currently consume 400Kw/h a month and that your location has a daily insolation average of five hours per day. This means that your expected insolation maybe in the vicinity of 150Kw a month per square meter.

Now, you have to know that there are different types of systems, each one with its own percentage of efficiency. This means that not all sunlight can be converted into electricity. Typical percentages for the different solar PVs available are from 5 — 20%. This means that if the sun emits 5kw a day over one square meter of your roof, then you can only use from 5% to 20% of that amount.

Lets say you buy PVs with an efficiency of 15%. If you want to cover 100% of your electric needs, you will have to buy:

400Kw/30 days: 13.33Kw/day

If you have five hours of insolation per day, you need to produce 2.667Kw each hour of insolation, this means you have to buy in the vicinity of 2,700 watts of installed PV panels, but if you want to cover yourself for rainy days, you should add at least 15% to this number, ending up with about 3,000 installed watts.

Also, you should calculate relative to your battery bank (if your system is stand alone). This is a number that varies a lot, since there are batteries that offer deep cycles and others that cannot be discharged over 50% (lead acid). It is better that you ask a professional about this.

Buying and installing

Having your number in mind, you can call a contractor in order to buy and get your system installed, or you can DIY. You will have to find a suitable vendor, a good warranty, a good electrician and all your materials.

If you want to make it yourself, then search for a handbook that will show you in detail all steps you need to take to make the installation. Remember, mistakes can be very expensive. Meet all requirements and investigate your local laws.

I hope this helps you to decide upon installing a PV system in your home or office. Please, share your results.

5 Comments

  1. This is an excellent article. We have had a small stand alone system for years. People always ask us how much money we save with it and we always tell them that the money invested in the system will never return, that it is a lifestyle choice. The system puts limits on our electricity usage that can only be overcome by using a noisy, smelly generator. We like it like that. There is one aspect of the system that does pay for itself though. Our deep freeze is a SunDanzer by Electrolux. It runs on the same amount of electricity required to keep a 60 watt light bulb lit for about 6 hours. They make a chest refrigerator with the same usage. Truly efficient refrigeration is the step we always tell folks to take first.

  2. Nice article Juan. You need to study up on units a bit – kW are units of power, whereas kWh are units of energy (not kW/h). When your units are correct, the maths makes more sense.

    To elaborate a bit, the sun delivers 1 kW/sqm of power to your roof. If you could capture that for a day at a location with 5 sun-hours/day of insolation, you’ll have 5 kWh of energy (assuming 100% efficiency). Power times time equals energy. That’s the beauty of the “sun-hours/day” unit. Just multiply it by your system power in watts (and efficiency) and you get energy.

    Likewise, if I use a 1 kW heater for 1 hour, I’ve used 1 kWh of energy.
    power (kW) x time (h) = energy (kWh).

    The easy way to remember all of this is that the electric company charges us for kWh’s (quantity of energy consumed), not caring how quickly it was used (power, or kW’s).

    Good job getting the word out!

  3. hola juna pablo
    tu articulo ha sido muy interesante y educativo.
    mi experiencia en la installacion de sistemas fotovoltaicos para uso domestico me ha ensenado que lo primero que tienes que establecer es un criterio de diseño y este puede ser definido por:
    un diseño para contrarrestar usaje de energía eléctrica (anual)
    un diseño para usar el espacio disponible (área)
    un diseño basado en el presupuesto disponible (costo)
    todo lo anterior tiene que ir reforzado con la implementacion de iniciativas de eficiencia en el consumo/uso de la energía eléctrica
    saludos
    carlos

  4. Gracias Carlos. Sin lugar a dudas mientras más instalaciones haces más aprendes. Me encantaría publicar algo de tu trabajo si me lo permites. Saludos y gracias de nuevo. Juan P.

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