Maximising your investment in renewable energy

By Ossie Cartsens, Lightcycle Energy Management

The market for standby and base load electrical solutions has been thrown wide open while Eskom is trying to uphold the grid with standby and emergency solutions. These are not long-term solutions and serious flaws in this strategy are now evident. It is foreseen that this situation will not improve in the short-term, and even if it does, the market is now sensitised to alternative energy solutions that will not only deliver more reliable electricity, but also cheaper electricity in the long term.

The cost of electricity from the national utility has been increasing at an alarming rate of of 15% over the past 12 years. Cumulatively electricity is now 478% more expensive than it was 12 years ago.

Furthermore, the integrity of electricity supply from the national utility and the municipal grid has been deteriorating to such an extent that many end-users have been forced to look at alternate energy sources. These included standby gensets, photovoltaic panels, and batteries. Many of these interventions were so-called “grudge purchases” as most of the end-users were not geared for the sudden debt exposure. In many instances their business model did not allow for major capital investments of this nature.

This has had an immensely negative effect on the productivity of businesses in the country as well as broad economic, social, safety and convenience implications within almost every sector. It has also had a detrimental effect on foreign investors who are increasingly being discouraged by the load-shedding situation. In this highly unstable energy supply situation there is clear business sense in seeking solutions whereby the consumer is assured of a constant, stable energy supply. Another important consideration is that most new buildings or developments could face the possibility of not even being able to be serviced by Eskom as the utility simply does not have the money to connect or supply.

The shortfall in being able to supply the energy needs of the country is vast. Apart from the substantial power needs of commerce and industry and the residential needs of the country, there are also other major imperatives requiring reliable energy supply. It is estimated that approximately 3,000 schools are not yet on the grid. Much of the agricultural sector is off the grid and is currently generator driven at a huge cost. There are many other examples such as residential developments, shopping centres and health care facilities where stable energy supply solutions are essential, but missing.

This is where the gap is in the marketplace. Many of these end-users have excellent credit risk ratings and are in the market to pay for reliable and consistent electricity supply.

Energy from the sun
Generating energy from the sun is a wise investment especially in Southern Africa where the average solar day is about 5.5 hours long and solar irradiance of up to 6.5kWh/m2 per day in some areas is achieved.

A solar day in the photo-voltaic (PV) context is defined as the time when the sun rises to when the sun sets. PV solutions are all about panel selection based on energy consumption and time of use of that energy. The most economical design is where the load profile of the site fits well into the solar day and energy generated from the sun is utilised without any “wastage”.

It is important to analyse the load profile as a great deal of information is hidden and entrenched in it. One needs to move loads into the solar day to maximise the use of free energy. If that cannot happen, then the next move is to store excess energy during the day in a battery for use at the required time, and so on.

It is important to do PV-panel selection after carefully analysing the shape of the energy consumption profile. The shape of the energy profile is the entry point for the process of selecting renewable energy products that form a synergistic solution – hence the importance of measuring and recording energy consumption.

Energy storage is the ultimate answer to maximise the return on your capital investment as one can store the excess energy in batteries for use outside of the solar day.

Who needs a battery to store energy?
The introduction of smart meters opened another avenue to store energy. Smart meters can be programmed to measure the excess energy produced from the PV panels. They can be programmed to allow excess energy to be fed back into the grid to be resold. Reselling can either happen as a credit on your bill or a credit on the meter itself.

If the local municipality allows selling energy back to the grid it becomes a great investment if one has a large roof area. In that case, you can fill your roof with PV panels and have an annuity income for at least the next 25 years.

If the municipality only allows your account to run into credit then it can be used at times when energy from the PV panels is not there or not enough.

Available storage options
The market for a variety of energy storage technologies had been steadily increasing over the past few years. The most common technology is lead acid batteries which have been in use for many years.

Energy density is the amount of energy a battery can store and is measured in Wh per kg. Energy density for lead acid batteries is typically 60Wh/kg, capacitor batteries typically 150Wh/kg, and lithium varieties typically 300Wh/kg. Newer technologies can store up to five times the amount of energy, which means that by inference it requires less space to store energy.

A lead acid battery has two electrodes and is filled with an electrolyte, typically a weak solution of sulphuric acid. It is usually charged using a constant voltage charger, which means that a carefully controlled variable current is used to protect the battery from overcharging. The electrolyte needs periodical replenishment as losses occur during the natural chemical processes. Modern designs have ensured that these losses are minimal.

The lead acid technology is very robust and can withstand a lot of adverse conditions, but its life gets affected when it is exposed to extreme hot and cold temperatures and sub-optimal charging. Its design life is typically about 1500 cycles on average (one charge and discharge per day count as a cycle), but its life can reduce dramatically if the surrounding environment is not ideal. It also needs a good five hours or more to recharge before the next cycle. Newer technologies like lithium batteries and capacitor batteries can be charged and discharged at least five times faster, do not have electrolyte challenges and can store at least 5 times more energy per kg.

Designing around physical constraints like limited sun hours, optimal weight, optimal footprint in limited space means that the choice of the correct battery for the application becomes crucial.

Do you really need a battery when going green?
Grid–tied system or hybrid system? Battery backup or not? The challenge is to choose whether your photo-voltaic (solar) system needs a battery or not and whether one can install a battery at a later stage. The answer lies in the latter part of this statement.

If you are certain that you would only need energy in the solar day then you would decide on what is called a grid-tied system. That means the PV-system will work when the national utility (or a generator set) is providing a reference voltage. A reference voltage or handshake is needed to modify the yield from the invertor to the site’s existing installation parameters. For reference, South Africa typically supplies electricity at 380V/550V/3300V/6600V at 50z, other countries supply it at 60Hz.

The downside to a grid-tied system is that when the national grid is off, your system is off as well – painful!

There are a few ways to solve this challenge, but one way is to install a small standby generator in the same system which starts automatically when the grid is off. Once there is a reference voltage and a reference frequency your invertor will synchronise or handshake with it and your PV system will generate and yield energy appropriately.

Another option is to use a small battery pack and convertor to supply reference voltage and frequency to your system, which will yield energy appropriately.

All these plans can be costly if the wrong invertor is installed. Where possible always choose a hybrid invertor even if you do not think you will use a battery as backup. A hybrid system is geared for any eventuality, even when your solar day becomes compromised during those weeklong rainy day periods and you might need battery back-up.