As the Internet reaches more remote locations and carries an increasing share of everyday mission-critical services, from telephony and messaging to banking and telemedicine, reliable power supply is essential for both end users and network infrastructure operators.
Solar photovoltaics (PV) with battery energy storage has become an attractive alternative to long, precarious grid supply lines and diesel generators, particularly over the last decade. Solar panel prices have plummeted to a fraction of what they were, and with reliable high-capacity lithium iron phosphate batteries also becoming available in quantity at lower prices, solar PV is now generally a worthwhile addition to residential and commercial grid supply, even in urban areas.
For the newbie, however, solar PV can still be bewilderingly complex. This can lead to projects that fail to meet local needs, stall, or are abandoned early, with infrastructure ultimately removed and never replaced. I have seen this happen even in projects run by power utilities in developed urban areas, so if you are in a remote area and you are feeling a little anxious, that’s understandable. But it can be made to work, even for you, so let’s take off the rose-tinted glasses and examine how to put things on the right track.
Step 1: Figuring out what you need
Before you even look at pricing or quotes, the first question to settle is what equipment loads you will need to supply: Servers, routers, switches, uninterruptible power supply (UPS) equipment, air conditioning, lighting, computing equipment on site, link transmitters and receivers, power tools for on-site working parties …? Make a list (a spreadsheet is great).
All of these loads have a power consumption attached. Look for the manufacturer label on the device and find the number that ends in a ‘W’ for watts. If you can’t find a label, try looking up the device or equipment class on the Internet (your favourite Artificial Intelligence (AI) bot can likewise help you estimate power consumption), or spend a few dollars on a plug-in power meter.
Look for hidden loads such as hot water cylinders that might end up in your circuit but live behind a cupboard, especially anything that generates heat. If you cannot exclude them from the PV supply, you need their numbers too.
Put these numbers into your spreadsheet and add them up. The total is the minimum power you need to be able to get out of your system at peak. If some loads will only rarely reach their maximum power consumption (like your kettle, which won’t run 24/7, or computer power supplies), then try to work out how much to expect on average, or measure if you can. That’s your power audit done, and it’ll prevent you from buying a system that’s too small for what you need.
The next step is to decide what type of system you want or need:
A standalone ‘island’ PV system
A standalone ‘island’ PV system that is not connected to any sort of grid is sometimes the only choice if there is no grid.
Advantages: It is the least complex setup, and you don’t really need to ask a utility for permission to connect it to their grid.
Disadvantages: You need to size the system to meet your power needs even during extended periods of bad weather. This requires a larger system that will produce a lot more power than you need. Without the ability to export this power into a local grid, there is no way of making the system pay for itself more quickly. Also, any work on the system that requires you to shut it down means power loss to your loads, although you could bridge that with a mobile generator.
Grid connected
A PV system that is connected to a local power grid but capable of ‘islanding’ itself in the case of a grid outage has distinct pros and cons:
Advantages: You can generally export excess generation into the grid to help offset the system cost. In a small grid, such as on a Pacific island that relies primarily on diesel generators, exporting excess power to the grid can be particularly attractive. It reduces load and therefore wear on these generators, along with diesel consumption. Your system might even help stabilize your island’s grid.
Disadvantages: Setup is somewhat more complicated, with three potential power sources (PV panels, batteries, and grid) and three possible places where power can go (loads, batteries, and grid). Determining whether to charge batteries rather than export to the grid at times when this is attractive is particularly challenging. That said, this challenge can be overcome. Good modern inverter systems manage this well.
Another disadvantage is that you definitely need a UPS for any equipment that must not lose power at any time. Grid-connected systems must synchronize with the Alternating Current (AC) frequency of the grid. When the grid goes away and the system islands itself from the grid supply wiring, it has to generate its own AC frequency, which will most likely not match the AC signal from the grid once the grid returns. This requires a short inverter shutdown at the beginning and end of a grid outage, which the UPS needs to bridge.
Never choose a PV system as a backup-only system. This is the worst of all options. While the grid is there, you will pay for expensive power while your PV system sits idle.
Step 2: Modelling your system
The purpose of this step is to see how much panel generating capacity you need and how much you can accommodate on your site.
Most standard-size PV panels have a peak generating capacity of between 430 and 460Wp (watt peak). They only reach their peak wattage when the sun hits them at the right angle on a clear day, and when the panels are clean and relatively cool. In most real conditions, it’s a lot less, and this is why you model.
To model, you need a tool. Several reputable inverter manufacturers and other organizations have such tools available online and for free, including:
Modelling needs your location, roof pitch and orientation (if that’s where the panels are to go), available roof area, and an idea about how much shading you can expect from nearby trees or buildings.
Pick an average panel. For small systems (loads under 10kW), choose a hybrid inverter capable of handling at least ten times the average power requirement calculated in Step 1. That allows you to charge the battery while also supplying your load, bearing in mind that you will not be able to charge all day.
For larger systems, you need separate inverter capacity for the PV and battery systems accordingly. In terms of battery storage, choose a capacity that allows you to power your loads for five days without any charge going in. Storage is measured in kilowatt-hours (kWh), and dividing available storage by expected load will give you expected backup time. As a general rule, the more panel and inverter capacity you have, the more you can compromise on storage, as you will be able to recharge faster.
Connect panels in series to form strings, adding their nominal Direct Current (DC) voltages to reach a total ideally about 100–200V below the maximum permitted in your location. Then connect these to the inverter’s Maximum Power Point Tracking (MPPT) inputs in the model and see whether this allows you to supply your load in island mode.
Run your model to see what you can expect over the course of a year for your location, then refine your model. If you get a lot of excess minimum power, you can go easier on the panels or inverter. Not enough power to run what you have? Add panels, inverter, or battery capacity and see what difference it makes. Or see what loads do not really need to be supported and could be shed in an outage.
Play with the model until you’re confident that you know what you need.
Considerations
- There is a tradeoff between panel/inverter capacity and battery capacity.
- Any sizeable PV system beyond a few kilowatts should really be a three-phase AC system.
- Adding panels is cheap.
Looking ahead
At this point, you should have a good understanding of your power requirements and a model that indicates the PV, battery, and inverter capacity needed to support them. In Part 2, we’ll look at selecting suppliers and components, evaluating quotes, assessing cybersecurity and support, and ensuring your solar PV system remains reliable over the long term.
Dr Ulrich Speidel is a senior lecturer in Computer Science at the University of Auckland with research interests in fundamental and applied problems in data communications, information theory, signal processing, information measurement and assessment integrity. His work on connectivity research and implementation has been supported by the APNIC Foundation.
The views expressed by the authors of this blog are their own and do not necessarily reflect the views of APNIC. Please note a Code of Conduct applies to this blog.