The Ultimate Guide to Solar

 

1. Understanding Solar

Two fundamental concepts you must understand are kilowatts (kW) and kilowatt-hours (kWh).

Kilowatt (kW)

This is a measure of power, or the rate at which electricity is used. Think of it like the power setting on an electric oven. An oven might be rated at 2 kW. A solar system's size is also measured in kW; a 10 kW system can produce 10 kilowatts of power at its peak, under ideal sunny conditions.

Kilowatt-hour (kWh)

This is a measure of energy, or the total amount of electricity used over time. Think of it like the total electricity needed to cook a meal. If you run that 2 kW oven at full power for one hour, you have used 2 kWh of energy. Your utility bill is measured in kWh because it tracks the total amount of energy you consumed all month.

Solar System Parts

  • Solar Panels: Roughly 5.6 feet long and 3.6 feet wide (1.7 by 1.1 meters). Each of these panels has a power rating, measured in watts. Modern, high-quality panels for home installations typically produce between 400 and 450 watts of power under ideal, sunny conditions. It converts the sunlight into Direct Current (DC) electricity.
  • The Inverter: This is the brain of the system. Your home's appliances run on Alternating Current (AC), not DC. The inverter's job is to convert the DC electricity from the panels into usable AC power.
  • The Grid: This is the public utility network that your home is connected to. When your panels produce more electricity than you're using, the excess can be sent to the grid. When you need more power than your panels are producing (like at night), you pull it from the grid.
  • The Battery: A battery is an optional component that stores your excess solar energy for later use. Instead of sending all the extra power to the grid, you can save it to use at night or during a power outage.

2. How to Size Your Solar System

The Importance of Location

The single most important factor determining your solar system's output is the amount of sunlight your home receives. This varies dramatically by location and season. Let's look at three examples for the same hypothetical 5 kW solar system:

  • Uppington, SA: Being a very sunny location, this system could produce approximately 8,000 kWh per year.
  • In a less sunny location, the same system would produce significantly less, around 5,000 kWh per year.
  • In a location known for its cloud cover, the system's output would be lower still, at about 4,200 kWh per year.

This highlights that your system's performance is fundamentally tied to the predictable, year-round sunlight available at your specific location.

Why Your Electricity Bill Is a Bad Starting Point

Many solar installers will propose a system size based on your last 12 months of electricity bills. While this is a starting point, it's a flawed, reactive strategy because it sizes a system for your past, not your future.

Getting solar changes your habits. Suddenly, electricity is an abundant resource you've already paid for, not a costly one to conserve. This encourages "electrifying everything"—switching from fossil fuels to efficient electric alternatives to maximize your solar investment.

  • Electric Vehicles (EVs): Charging an EV can add 2,000-2,400 kWh to your annual electricity usage.
  • Heat Pumps: Switching from a standard household geyser to an electric heat pump for heating water can add another 4,000-6,000 kWh annually.

A system sized only for your old bills will be undersized once you electrify, forcing you to buy expensive power from the grid. The golden rule is to plan for the home you'll have in five years, not the one you have today. One of the most common regrets I hear from new solar owners is, "I wish I had installed more panels."

Finding the Financial Sweet Spot: Sizing for the Year, Not the Winter

While it's crucial not to undersize your system, it's equally important for your return on investment not to oversize it. It might be tempting to build a system large enough to cover 100% of your energy needs even in the cloudy months, but this is a financial trap. To generate those last few kilowatt-hours in overcast months, you would need to add several extra panels. Those same panels would then create a massive, wasteful surplus of energy in sunny months.

The most cost-effective strategy is to find the sweet spot: size your system to cover your total annual energy needs. It is almost always cheaper to buy a small amount of electricity from your utility during the cloudy months than it is to pay for the extra panels and equipment needed to cover that worst-case scenario.

Helpful Sizing Tools

Before you even talk to an installer, you can get a great preliminary estimate of your home's solar potential using free online tools.

  • PVWatts Calculator: Developed by the U.S. National Renewable Energy Laboratory (NREL), this tool provides detailed estimates of monthly and annual energy production based on your location and desired system size. You can find it here.
  • European Commission PVGIS: A valuable tool for users all over the world, providing detailed solar radiation and photovoltaic system performance data. You can find it here.

3. Sizing a Battery: Daily Use vs. Full Autonomy

The primary financial benefit of a battery is to store your cheap solar energy from the daytime to use at night, avoiding grid power. A strategically sized battery (e.g., 10-15 kWh) is perfect for this daily cycle and provides backup for essential appliances during short outages.

However, home batteries are still quite expensive. A quality 10 kWh battery can cost between R15,000 and R20,000. Trying to achieve full autonomy for a multi-day power cut is often not worth the investment. For example, to cover a typical household's needs for two full days, you might need 30 kWh of storage. This would require stacking three batteries, costing anywhere from R45,000 to R60,000 for the battery system alone. For most people, this is an extremely high price to pay for insurance against a rare event.

4. The Real Costs of Going Solar

The price of a solar system varies dramatically based on location, equipment quality, and hidden factors.

Product Quality Matters

Inverters

The choice of inverter technology is a critical strategic decision. String inverters are the traditional, cost-effective option. They work by connecting multiple solar panels together in series to form a "string." A single, central inverter (which may have inputs for two or three strings) then converts the power from all the panels in the string at once. This is a great solution for simple, unshaded roofs, but if one panel in the string is shaded, it reduces the output of the entire string.

Microinverters represent a more advanced, and more expensive, approach. A small, individual inverter is attached to every single panel. This means each panel operates independently, maximizing its own production regardless of shading on other panels. This makes microinverters the superior, more efficient choice for complex roofs with multiple angles, intermittent shading, or for homeowners who want to maximize their system's output and have the flexibility to easily add more panels in the future. The decision between the two depends entirely on your specific roof, shading conditions, and budget.

Batteries

The cheapest battery is rarely the best value. When evaluating a battery, look beyond the price tag at these key performance metrics:

  • Power Rating (kW): This measures how fast a battery can deliver electricity. It determines which appliances you can run at the same time. A battery with a low power rating might not be able to start a high-demand appliance like a heat pump or air conditioner, even if it's fully charged. Look for two numbers: continuous power (the steady power it can provide, typically around 5 kW for residential batteries) and peak power (a short burst of higher power to start large motors).
  • Capacity (kWh): This measures how much energy a battery can store. This determines how long you can run your appliances. A higher capacity means longer backup time.
  • Depth of Discharge (DoD): A quality battery should have a DoD of 90-100%, meaning you can use its full rated capacity without damaging it. A higher DoD is better. It means you can use more of the energy that you paid to store.
  • Lifespan/Cycle Life: How many times can it be fully charged and discharged? Look for a warranty of at least 10 years or 6,000 cycles.
  • Chemistry: Lithium Iron Phosphate (LiFePO4 or LFP) is the modern standard, offering better safety and a longer lifespan than older chemistries.

Hidden Costs & Grid Differences

Be prepared for potential upgrades, such as a roof replacement if yours is old.

5. Calculating Your True Return on Investment

When calculating the return on your solar investment, the biggest mistake is to only think about how much you will save on your electricity bill. The true financial power of solar is unlocked when you use it to eliminate other energy bills entirely. Instead of just saving on electricity, think about how much you could save by electrifying everything. How much do you currently spend on natural gas for heating? That cost can be eliminated by switching to a heat pump powered by the free energy from your roof. How much do you spend on fuel for your car? The real return on investment comes from displacing your total energy expenditure, not just a fraction of it.

Ultimately, every home and every person's needs are different, and you should always do your own research for such a big investment. By going solar, you're not just making a smart financial decision; you're contributing to a cleaner planet. To build a zero-carbon future, we need to electrify everything, and that future will require more and more energy. As non-renewable energy sources become scarcer, they will inevitably become more expensive. Generating your own clean power is the ultimate path to energy independence.