DIY Guide: How To Build Your Own Small Solar System

image outdated electricity system

Why Build A Small Solar System?

Load shedding again or a power failure exactly when you’re working on your PC or watching an episode of your soapy? A small solar system would give you just the perfect remedy, compensating for ESKOM’s every whim.

Currently solar energy generation is usually associated with huge installations. They provide houses or entire complexes with hot water and/or electricity at least partially or intermittently. But solar energy can also be used by small ‘island’-type solar systems, installed in your back yard or even on your balcony. It’s not difficult to assemble those systems by DIY. Size, capacities and performance you can pinpoint in detail according to your practical needs and your budget.

What size (capacity) should it be?

In this article we’re going to deal only with small PV installations (“Photovoltaic” systems producing electricity) which you can compile and manage yourself. The power generating capacity of this type should be big enough to feed

  • a few lights,
  • a PC or laptop,
  • a small TV set,
  • plus some other gadget requiring not too much electricity.

It will not, however, be capable to support a regular fridge or freezer, a washing machine, a dishwasher or electric kettles.

The level of capacity provided by those island-systems also reflects a certain level of investment in terms of components necessary to acquire (see following section). Let’s define this level at a maximum of 7000 Rand in total.

This article aims to show you precisely how such an installation would work in reality, what performance you can expect. You will come to know what components you would need to obtain, and how to set it up and maintain it, doing it yourself (DIY). It will also indicate approximate price ranges for the components. And, finally, it will let you in on various “secrets” to bear in mind when handling your installation. Surely you can find lots of detailed technical instructions elsewhere on the Internet on photovoltaic systems. From my own experience I know for sure however, that some questions or doubts still remain unanswered and give you headaches. In most cases these are issues put by beginners, obviously too banal and self-evident to solicit technical experts’ attention,

How much power take-off will you probably need?

So let’s start with identifying the power requirements of various appliances you might want to run independently some times or when you’re forced to by ESKOM:

3 lights consuming 10 Watt/hour each (of course, only 5 or 10 Watt energy saving bulbs or LED lamps are suitable), switched on for 5 hours = 150 Watt in total;
One PC/laptop, consuming 120 Watt/hour or less, running for 5 hours = 600 Watt in total;
One TV set at 100 Watt/hour switched on for 3 hours = 300 Watt in total

This example should give you an impression of the order of magnitudes involved. You will need to put those figures into line with your own specific situation. Just have a look at the specification labels attached to your gadgets. In many cases however, indicated power ratings are to low and the real power consumption might well be higher than declared. Anyway, the example above results in a total of 1050 Watts you are going to draw from your system during one “session”.

Planning

Batteries, preferably deep-cycle solar batteries, should never get discharged to less than about 60% of their nominal capacity. This means that in order to match the requirements listed above, the size (nominal capacity) of your battery or batteries (connected parallel) should be greater than 150 Ampere Hours (Ah) because 1050 Watt divided by 12 (Volt) as usual (24-Volt systems are also on the market) result in 87.5 Ah, equivalent to about 58% of the battery’s nominal capacities, leaving only about 42% untouched – too little in the long run. So, for 1050 Watt total power requirement you would need a 200Ah solar battery to be on the safe side.

O sole mio – where are you?

Depending on the orientation of the place your system is positioned the sun will shine brightly enough to allow the light sensitive cells to transform light into electricity only for a few hours a day. Let’s say, your PV-panels or “solar panels” (see below) enjoy maximum sunlight for 6 hours during a day. In this case you would need to divide your 1050 Watt requirement (see example) by 6, which, provided 100% perfect exposure all the time, no single tiny cloud passing, would result in a figure of 170 Watt, indicating the theoretical minimum size of the solar panel you need to recharge the battery (compensate for the amount of your usage. In reality, however, this figure must be doubled at least in order to compensate not only for passing clouds but also for the changing of exposure (the sun stands at different heights and changing angles during the day and so changes the amount of light received by the cells, varying their efficiency in transforming light into electricity (‘photovoltaic’). To conclude with a concrete recommendation: In order to cover 1050 Watt I would install at least a 385 Watt panel, which I did myself when building up my system.


2 tips: When it comes to the question how to position the panel the best solution would be a ‘mobile’ approach, enabling you to move the panel twice or thrice during the day in order to optimise it’s orientation towards the ‘moving’ sun. Secondly, as in southern Africa the sun climbs steeply and rather high in the course of the day, your panel should be tilted to about 30° or even 10° (which is nearly flat) in order to ensure that the panel surface remains as perfectly perpendicular to the sun rays as possible most of the day. This will enhance the efficiency of your panel substantially, bringing it to the desired level of about 21 to 23 % overall.

A backyard revolution just round the corner!

It looks like a really revolutionary approach to using photovoltaic cells in small solar systems is on offer now. It promises multiplied efficiency and reducing space simultaneously.
Starting from research done by the MIT (Massachusetts Institute of Technology), a guy in the US developed the original idea further and came up with a well-devised and widely tested installation model. It uses a very different approach: building cubes or towers that extend the solar cells upward in three-dimensional configurations instead of placing them flat or in a fixed angle onto some surface. This structure provides the incredible boost in power-producing efficiency of the solar cells (up to 20 times).


The Components

Take a quick glance!

The image on the right shows examples of the essential components of a small photovoltaic system and how they are connected to each other.

For details, definitions and explanations please see the sections below.

Image of all components needed

Solar (PV) panels

PV panels (photovoltaic cells mounted on some sort of board), the power station of your system, are available in many capacities. You can get them from 50Watt to 500 Watt and bigger. That’s also a matter of the space available. A 500 Watt panel I have examined, measured 2278 by 1133 millimetre (about 7 foot three by 3 foot nine). You can combine smaller panels of the same capacity to reach the desired overall capacity.

In any case, however, you should opt for “monocrystalline” silicon panels (“Monos”) instead of “polycrystalline” ones (“Poly” panels). They are bit more expensive but also more effective especially in converting diffuse light into power. It goes without saying that prices depend on the size. A concrete guidance: you should not pay much more than 8 Rand per Watt of capacity. A couple of months ago I bought my 385 Watt panel at 2640 Rand.

Solar Charge Controller

The electric energy produced by the panel needs to go to the battery before it can be used directly or transformed. In order to protect your battery from overloading by temporarily very strong voltages on the panel side and/or from discharging below about 10.8 Volt (with 12Volt systems) you need a “Solar Charge Controller”. This thing manages input from the panel and output to the load according to the actual state of your battery. It also provides some real-time information about several parameters necessary to manage/control your system.

Depending on the maximum voltage your panel(s) can deliver, the “size” of the controller should be chosen circumspectly. It is also a matter of cost. Usually an affordable 30Ampere or 40 Ampere device should suffice perfectly. 2 types are on the market: PWM versus MPPT. PWMs are rather cheap and, in most cases, serve their purpose quite well.


Tip: Don’t allow yourself to be fooled into buying a bargain MPPT controller. You could fall for an unpleasant marketing trick ’cause quite frequently those cheap products are misleadingly named “MPPT Charger” or simply “MPPT” instead of “Controller”. You should be able to find a 30A PWM controller for around 500 to 600 Rand, for a MPPT one of similar capacity you would have to fork out at least double that amount.


Batteries

Storage of produced electricity during daytime to be used when there is no sun to provide power is certainly the aim of most solar system users. The question of the size we discussed above already. Lead based batteries are still the standard (preferably Gel ones). A 100Ah battery of this type you should find at approximately 2200 Rand. There are also Lithium batteries (LiFePO4) on the market which provide significant advantages but are also significantly more expensive. One of the same size would set you back by at least 4500 Rand.

Power Inverter

PH panels deliver “direct current” (DC) electricity which you could directly use with 12 Volt electrical camping gear, for example. However, as you surely want to run appliances that categorically require 210 to 230 Volt “alternating current” (AC), you further need to connect a “DC to AC Power Inverter” to your charge controller. These things are available in a wide range of nominal capacities, from 10 Watt to 2000 Watt or even 3000 Watt AC output power. You must calculate what output power you might probably need, meaning how many Watts in total you will be drawing from the battery using one or more devices/appliances with certain wattage requirements simultaneously. Just tote up the relevant figures and make a generous allowance for additional requirements either by you, deciding to enjoy running one more devise at the same time, and/or as a precaution against the very real possibility that the indicated power need of appliances is frequently understated. Also bear in mind that many devices need a significantly higher power input when starting up (a booting PC for instance). So if you want to cover a total need to draw, say, 300 Watt simultaneously, you should opt for an inverter providing at least 500 Watt output.


Tip: Insist that this is the figure for continuous output power (reduced to about 400 Watt due to unavoidable losses) and the maximum output power (covering short-term surges) is 1000 Watt. Finally, the inverter itself needs a certain wattage to run. My 500/1000 Watt inverter, for example swallows 0.3 Ampere for cooling (fan), equivalent to 3.6 Watt. Bigger inverters are much more greedy. Just to give you an impression: Around 1000 Rand will certainly buy you a 500/1000 Watt inverter.


Accessories

Last but not least there is the issue of cables, connections, racking and so on. As for cables you must simply adhere to one major principle: the thicker the better! Solar cables (plus and minus) connecting the panel with the controller are offered in 2 varieties: 4 or 6 mm in core diameter at about 10 Rand and 30 Rand per metre respectively. Opt for the thicker ones (6 mm is approximately equivalent to 28 square millimetre) and choose a similar core thickness (normal cable for inside use) if you decide to connect the inverter directly with the battery instead with the load terminal of the controller. This is usually recommended if one wants to run appliances with relatively high power consumption, let’s say, above 200 Watt simultaneously. What sort of racking you need depends solely on your specific arrangement. Every sort of accessories, including cable end-pieces, lugs and MC4 plugs, other connectors, you can get from TheSunPays or from Sustainable (online shops), even from TakeALot. One warning: When connecting cables (to reach a certain distance), don’t use “chocolate blocks”. They are dangerous and unreliable.

Definitions and specifications

DC: Direct current (12, 24 or 48 Volt, usable for small camping/outdoor gadgets)

AC: Alternating current (210 to 230 Volt), required by most household and digital appliances

Solar panel sizes are measured in Watts:

W: watts

kWh: kilowatt

1000 watts = 1 kilowatt

Battery capacity is measured in Ah or mAh (milli-ampere/hour):

Ah: amp hour

mAh: milliamp hour

1000 mAh = 1 Ah

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