Guide to Solar


Guide to Solar

 

Introduction to Solar

The word solar means "related to the sun". However, when most people use the word "solar", they are referring to energy savings. Proven technologies to save energy includes equipment that does not relate directly to the sun such as energy efficient lighting and heat pumps. Then again some technologies rely completely on the sun such as solar water heating. I will cover them all.

 

Solar Systems

If you want to install solar and you know what you are looking for then skip to the relevant tab on the menu bar. If you are looking for more information then read further to get you started.

What is the most cost effective route to going solar?

The standard electrical supply to a residential household in South Africa is 60 Amps which is roughly 12 kW of energy. To install  a 12 kW PV solar system is costly and also unnecessary for most. So the first step is to reduce your electricity consumption where possible. This mostly applies to lighting. Modern LED lights are much more efficient than the old incandescent lamps and somewhat more efficient than CFL. Try replacing those first.

Next step is to look at the biggest consumers, your geysers. If you are able to install solar geysers, then solar geysers are the best place to start before installing a PV solar system. A solar geyser converts sun energy directly into heat. PV solar systems convert sun energy into electricity. This can be converted again into heat, but this double conversion is less efficient. Running your geysers off a water solar panel called a solar collector will pay itself back in 3 years.

You are ready to go PV solar

We have standard kits that we suggest you consider before getting a custom designed PV system. Every solar inverter on the market has its strengths. And each solar inverter requires a specific configuration of panels and also has an optimum configuration. It is possible to change this configuration but the most cost effective route is to comply with the optimum array size for each inverter type.

Most Popular Residential Solar Systems

For residential PV solar systems there are 3 popular sizes that we mostly install. If you are a large electrical user with a pool, air conditioners and other luxuries then we suggest a full 10 kVA solar inverter with a 6 kW solar PV array. This is enough for almost all households. If you are good at managing your power, you should install the 5kVA solar inverter with a 3kW PV array. Just stay within the power limit of the inverter otherwise you may trip your power. Then for the small user such as a holiday home, caravan or site office, a simple 3kVA inverter with 1200 Watts of solar panels may be sufficient.

Commercial Solar Systems

For a shop, business or factory, the requirement would be 3 phase power. We install mostly grid tie systems for commercial users. Because commercial users all have different consumption,  we install off the shelf inverters up to 40 kW in size. Solar inverters larger than 40 kW require custom manufacturing. Typically we would install several smaller inverters to ensure that we can control the amount of energy produced by switching inverters on and off as required. This prevents electricity from feeding back into the grid.

Can I start small and expand

Yes, you can start small. The only consideration is that you would have to choose which circuits you would like to power form your solar PV system. If you overload the solar inverter, the inverter will trip. Although the solar inverters have an automatic bypass switch, the bypass switch is normally rated at the same capacity as the inverter. So you cannot rely on the bypass switch if you overload your inverter. The bypass will also trip.

How much is 5kVA really

Households typically have about 1 kVA of continuously running load. This is made up of many small items such as alarm systems, cell phone chargers, fridges, computers, appliances on standby, internet routers, etc. So now you have 4kVA left from the 5kVA of power available. With 4kVA you cannot run two big loads such as a washing machine and kettle or lawn mower and pool pump or kettle and clothes iron etc at the same time. However it is possible to manage your power by putting less circuits onto your inverter. Or simply add another 5kVA solar inverter in parallel and turn your solar inverters into a single 10kVA output.

Can I go completely off-grid

Of course you can go completely off grid. You would need more batteries to store energy for night time usage. Batteries are a complicated purchase. Even batteries of the same type differ considerably among suppliers. We recommend batteries specifically designed for solar such as lead crystal batteries with a 3000 cycle life at 50% depth of discharge. But the same lead crystal battery can be bought from many different suppliers and cycles range from 1000 to 3000 among the different manufacturers. The difference is 3 years vs 9 years of battery life for the same battery. Our advice is that a solar battery should have a data sheet which will detail the life expectancy of the battery. If there is no data sheet, then it is not a genuine solar battery. However, we do install standard deep cycle batteries in many installations but then we set the solar inverter not to cycle the battery significantly. If you are installing to go off grid, buy the solar batteries. If you are installing solar to save money, install cost effective batteries and set the inverter correctly not to cycle the batteries too deeply.

PV Panel Quality

The price of solar panels is very competitive. Each installation uses many pv solar panels. If you find panels at a cheaper price, they are usually not the same quality. Where the saving is made is in the aluminum frame. A 250 watt PV solar panel frame thickness should be 40mm and a 300 watt pv solar panel should have a frame thickness of 50mm.

Solar Regulations

Currently if you live around the Cape Town area, you are billed by either City of Cape Town or by eskom. If you are billed by eskom you are not allowed to  feed back into the grid. If you belong to City of Cape Town, you can apply to belong to the feedback scheme.

Is The Electricity Feedback Scheme Worth Considering

Currently there is a daily charge to belong to the scheme. In order to generate enough electricity to cover the daily tariff you would need to generate at least 3kW more than you need. Also you only get a third of the value of the value for the electricity you feed back. The short answer is that it is not worth considering as you will not be able to earn enough money from the energy produced to cover the scheme charges. But of course it is up to everybody to decide for themselves.

So what size PV system should I install

You should try to stretch your budget to install a 5kVA solar inverter with  when purchasing your first PV system. The reason for this is the 5kVA solar inverter is special as it allows a connection to more inverters of the same type. The output of the inverters work together to form one 10kVA, 15kVA or 20kVA inverter. This allows easy expansion in the future by adding more inverters and panels to your system. Inmother words, no wasted money, you add components,  not replace components.

 

 

 

 

 

 

Guide to Solar Geysers

Types of Geysers

There are many different manufacturers of geysers and each manufacturer has many different models to choose from. The most important criteria to consider is the geyser size. General concensus is 50L minimum plus 50L per person.

The next consideration is the warranty period which gives an indication of a geysers quality. Some geyser have a 3 year warranty and some go up to 10 year warranties. 5 years is standard. All come with SABS approval. Many people accept the minimum as the geyser will be covered by insurance as long as it was installed by a qualified plumber.

Geyser sizing

The most popular size of geyser is undoubtedly a 150L geyser. When installing a solar geyser, the geyser needs to store enough water to allow normal usage without having to heat itself up again until the sun is available the next day. This means that they need to be a little larger than a plain electric geyser. Ideal situation would be 150L for 2 persons, 200L for 3 persons . But do not worry, if the geyser is a little smaller, a little more utility power will be needed to keep the water warm when it runs low. You will never have a cold bath.

Converting an existing geyser to solar

Converting a geyser to solar is called a retrofit. Pipes get installed from the geyser inlet, through the collector via a pump and back into the geyser. Each time the water temperature in the collector is 7 degrees hotter than the collector, then the pump will circulate the water pushing the water from the collector into the geyser.

What are the costs

The cost of the installation is related to the long list of components required. Geyserwise controller, pump, non return, drain valves, Tp valves, isolation valves and mixing valves.

How hot will the water get?

The water at your tap will always be the same temperature at 55 degrees as set by the mixing valve. The mixing valve takes the hot water from the geyser and mixes it with enough cold water to make the temperature 55 degrees. This is done to protect the user from the unpredictable temperatures in the geyser.

 Installation

Installation should be done by qualified and certified plumbers.

 Guide to Heat Pumps

Types of Heat Pumps

There are many different manufacturers of heat pumps. As heat pumps do not rely on the sun, they are very reliable in ensuring constant hot water.

Heat Pump sizing

Generally a 3.5 -4 kW heat pump is used for a 150L geyser and a 5.-6 kW heat pump is used for a 200L geyser. When used on pools and other heating applications, a calculation will need to be done to determine the size. Heat pumps controllers have timers and set points to ensure accurate temperature control.

Converting an existing geyser to heat pump

This is easily done. Pipes get installed from the geyser inlet, through the heat pump and back into the geyser. Each time the water temperature below the temperature set on the heat pump controls, the heat pump will startup automatically and maintain the exact temperature.

What are the costs

The cost of the installation is mostly related to the cost of the heat pump.

How hot will the water get?

As the heat pump has precise temperature control, the temperature will be consistent with its settings.

 Installation

Installation should be done by qualified and certified plumbers.

Guide to PV Systems

Types of Solar Panels

The different types of panels can be split into the different output voltages. A small 12 volt battery needs an 18v solar panel to charge it. A 24 volt battery requires a 36 volt solar panel to charge it. However larger systems for residential solar and commercial application require a specific voltage from 100v to 1000 volt depending on the charger. On larger systems panels are joined together called a string until the correct voltage is achieved. An example would be a typical axpert inverter or pip inverter system which will have a configuration of 3, 6, 9 or 12 panels.

Solar Array Sizing

If the purpose of installing solar is to save on electricity usage then there is no minimum array size. The amount of panels installed will save energy proportionally to the energy generated. For off-grid the array size will need to be big enough to cover all the electricity used per day plus extra to cover losses. To determine the solar array size the amount of solar radiation in your area would need to be established. In cape town the summer radiation would be almost 9 kWh electricity generated per day from each 1 kWh of PV panels installed on your roof. In winter that figure drops to 4 kWh electricity generated from each 1 kWh of solar panels installed.

Types of Solar Inverters

There are two categories of inverters. One is called a grid tie inverter. This type of inverter synchronizes with the utility supply and feeds energy into the electrical system. If energy generated by the inverter is less than the total load, then the inverter will supply as much power as possible with the rest being supplied by the utility. When the inverter supplies more than the total load, then the excess energy feeds back through the electricity meter to the utility.

Grid tie inverter sizing

Grid tie inverter sizing is not critical. Too small or too big makes the difference between paying in or paying out. When feeding back to the utility, an application is sent to the local council. The meter is then changed to allow feedback into the grid. Careful as some electricity meters will charge you for electricity both ways and you end up paying for the electricity you produce. The solution for this is called a grid tie limiter. Grid tie is a great way to install solar and save money.

Off grid inverter sizing

Size does count. Go too small and you could end up tripping your inverter. Fortunately off grid technology is much more affordable than grid tie. The reason for installing an off-grid inverter would be for its lower initial cost and the battery backup power it provides

Combination inverter sizing

The combination inverters can provide the best of both. Packed with technology they are costly. Care should be taken to make sure that the inverter can do both functions simultaneously and that one function is not lost when the other is chosen. These are the best of the best.

Battery Types

There are many different types of batteries on the markets. Many of which are marketed as solar batteries where in fact there are very few genuine solar batteries. Batteries performance is measured in cycles with some deep cycle batteries producing only 200 full cycles and others producing up to 1500 full cycles.  Lead crystal batteries will provide 3600 cycles at 40% depth of discharge, 10 years. Batteries which do not have a graph showing its cycle life are not meant to be used in solar applications. These are automotive batteries.

Battery sizing

Each inverter will have a minimum amount of batteries required to meet its voltage type. Typical inverter battery voltages are 12, 24 and 48 volts. For a 48 volt solar inverter, batteries have to be added in groups of 4 to make up 48 volts. However you can add as many batteries as required in groups of 4. For a completely off grid system, the battery bank should be sized at least double your daily consumption. This will result in your batteries discharging no more than 50% once a day. Batteries that are cycled too deep have a reduced life span, Batteries that are not used at all will also fail due to insulation build up on the plates. The optimum is cycling at 50% depth of discharge and provides the greatest return on investment.

What are the costs

The costs will be relative to the size. Many systems are completely scaleable. A small basic system can be installed and expanded over time by adding more panels, adding more inverters and adding more batteries to improve power output and increase your savings.

How reliable is the system

With grid tie, the important point to remember is that you are still completely reliant on the utility. Without a utility supply, the inverters cannot synchronize and will remain off until the supply is restored. An off grid inverter can use the batteries and solar for backup. The switching from solar to batteries to utility is extremely fast and happens completely automatically, ensuring that you never run out of power.

Warranties on inverters range from 2 years to 10 years. Some have a warranty extension option up to 25 years.

 Installation

Installation should be done by qualified and certified electricians.