How To Select Your Solar Power System

How to Select your Backup Power System

This document details a step-by-step approach to selecting your Solar Power System.

1. Are you trying to be green?
2. Are you trying to save money?
3. Do you have capital up front?
4. Do you need battery storage?
5. Do you need to charge your batteries when the grid is down?
6. How much solar capacity do you need?
7. How much storage capacity do you need?
8. Disadvantages of Solar Power
9. The eternal dilemma!
10. How does a Solar System Work?

1. Are you trying to be green?

   Unfortunately, Solar Power is not green in any sense of the word. There is a more comprehensive discussion here [1]. It is unlikely that it will ever be green. There are three major reasons -

   • The manufacturing process requires rare elements that require a filthy process to produce.

   • The manufacturing process requires an enormous amount of energy which is ignored in the calculations for Green-ness.

   • Solar power is not produced at night or on dark and stormy days. You are still using power. Your batteries will not provide total backup.

     The production of this requires existing fossil plants to continue to operate. In some countries, the fossil-based production may even have to be increased.

2. Are you trying to save money?

   In the past, the math did not add up. The return on capital invested was not good. The good news is that right now, the payback period is not bad. In New Zealand, you can get 20 years without batteries and 8 to 10 years with batteries. Other countries are better at 6 to 10 years.[2]

   It costs more to have battery storage but the savings are so much greater. This is because, without storage, the power you do not use is exported to the grid. The grid payments are abysmal. In Some countries they are starting to charge the user for exporting.

   You should examine the payback period provided to you. See an explanation here [3].

3. Do you have capital up front?

   A decent, comprehensive system will cost you anywhere between $15,000 and $50,000. My rationale is that you pay up front when you are more able to pay it and recoup the benefits when you retire.

   What if you do not have the capital up front? There are companies that will pay for the equipment and charge you for the power you use. There are Pros and Cons [4][5].

   Advantages

   • There is NO up front cost
   • You do get Savings on Power Costs
   • You can pretend to be Green.
   • You get power in the event of a grid outage
   • There is no maintenance cost

   Disadvantages

   • You don't own the equipment
   • Savings on Power Cost are lower
   • If you sell the house, the contract HAS to go to the new owner, who may not want it.

4. Do you need battery storage?

   If your budget is tight then you may opt for a no-battery solution, but be aware that the payback without a battery is very long (see the section on Saving Money). If the grid fails then you have no backup either.

   I would highly recommend that you get battery storage. The advantages are -

   • Shorter payback period (even though the capital cost is higher).
   • A battery smoothes and offsets your grid usage. For example, if a cloud passes over your panels, the energy stored in your battery just a few minutes earlier will supply the power.
   • Grid failure backup.
   • Payback on exports. This is prominently advertised, but in reality, you get a pittance back. In New Zealand is only between 6 and 8 cents a unit and you will still pay for line charges.

5. Do you need to charge your batteries when the grid is down?

   Did you say "Yes Duh!". Well, believe it or not, many suppliers provide a battery that does not charge when the grid is down. This is called an "AC Coupled Battery".These systems are cheaper. If the grid is down during the day, solar will supply the house but the batteries will not charge!. Surprisingly, most suppliers will NOT tell you this.

   If you want a decent system or an off-grid system, or your grid is unreliable, then ask for a DC Coupled Battery. This will charge even when the grid is down.

6. How much solar capacity do you need?

   The more solar capacity you have the better it is. I would suggest that there is no point in going Solar unless it provides 50% of the usage for a small house (2-3 people) or 30% of the power usage for a large house (4+ people). You may want to go off-grid and opt for 100% of the usage.

7. How much storage capacity do you need?

   There is no point in paying for storage if you are not going to use it (See the Dilemma section). If your bill shows (or your provider gives you online access to) hourly power usage, then sum it up for 8 hours of the night. Take a day from each month of the year and average it. I would suggest at least doubling the solar capacity. This will help cover the shady parts of the day.

8. Disadvantages of Solar Power

   • Let's not kid ourselves, Solar Power is not Green and may not ever be Green (see Section 1).
   • It has a limited life. The battery may need replacing in 10 years time. The panels may last as long as 20 years.
   • Solar can not (easily) power high-energy appliances such as induction cook-tops, ovens, and heat pumps. So, you can either go without or use Gas to get some of the convenience back. In our case, we also have a diesel generator to power the heat pumps for the spa and house.

9. The eternal dilemma!

   To recover your investment, you would want to

   • charge the battery fully before sunset
   • discharge the battery fully before sunrise.

   But you may also want to reserve some storage for grid blackouts. The two requirements are not compatible. I have only used the "Tesla" app and it treats you like a baby. The only way to get this to work is to change the settings in the morning and in the evening. Another way is to reserve some storage for blackouts. I would suggest between 30% and 50%. The Tesla app lets you allocate a blackout storage figure. One good thing about the Tesla app is that it has a storm warning feature, where it will attempt to charge up the battery when a storm is forecast.

10. How does a Solar System Work?

    There are many designs, here is a Basic explanation.

    • Many Solar Panels generate electricity from sunshine as DC.
    • An inverter converts this to another voltage suitable for the battery.
    • Another inverter converts the solar electricity to AC for the house.
    • When the grid fails, the DC voltage stored in the battery is converted to AC using another inverter.

    If you want to make your own system, you can. This also has a basic explanation of how things work[6].

A Step-by-Step Process to Select your Solar Power System