How to buy a solar system
By August 2, 2017
A Guide on how to buy a quality solar system that suits your needs.
So, you’ve decided to go green and are considering a PV system for your home, factory or office. Great, here are some things you should consider when going and getting quotes for a system. First let’s go over some vocabulary:
Inverter: The device which converts the DC energy created by the panels to AC energy which can be used by most appliances. Inverters generally come in 2 forms: Grid-tie and Island. Grid tie means that the inverter connects only to the panels and will produce electricity as long as the grid is available. Island inverters, are designed to work with batteries, so they can charge the batteries as well as discharge them for power when there is no sun.
Batteries: Batteries come in many different shapes and sizes. You can think of them just like the double AA batteries you find in your remote controller or the lead acid ones you find in your car. They are quite heavy bulky and expensive. They are also quite sensitive and can be the most expensive component that fails the most often, do to misuse. Batteries are rated by voltage and Ah (or kWh) , which will tell you how much energy they can hold. Though, this is not the only component cycle life and depth of discharge play an important role in the lifespan of batteries.
RM: Remote monitoring, this is what is used to monitor a system from afar. It’s an important tool used by installers to diagnose issues and prevent misuse of systems. You can think of it as the dashboard of your solar system.
Panels: Panels are the components that converts the sunlight into electrical energy. You’ll find them generally looking like the dark blue color of silicon. Panels are generally rated by wattage. This tells how much energy the panel will produce in the optimal scenario. The panels have no moving parts, due to thi, they generally last a long time (20 years on average). Though, the energy they produce will be less with time as well. Panels are categorized mostly into 2 types. Monocrystaline and Polycrystaline, you don’t have to think of this too much. Monocrystaline panels are generally more efficient and more expensive allowing them to create more power from a smaller space. If you’re limited on space you might need to use this, though we’ve seen that polycrystalline is generally the option of choice with customers, due to its lower price and our clients having lots of roof space.
Charge Controller: This refers to a component designed to charge the batteries from the panels. Charge controllers can come in 2 forms. MPPT and PWM, these optimize the power coming from the panels to be as efficient as possible when charging the batteries.
Autonomy: This refers to the number of days the solar system can run of the batteries, in case there is little to no sunlight available during the day.
Iridescence: This refers to the amount of electricity a solar system can produce based on the weather and angle of the sun in the sky.
BoS: Balance of system, the idea here is that balance of system all the rest of the bits and bobs around the system that makes it work. These can protection equipment such as breakers, surge arrestors or just other electrical components such as wiring, combiner boxes, bus-bars, etc.
What is your goal by having this solar system?
This questions might seems obvious, however over the years we get approached by people with many different objectives. A large portion of clients approach us indicating that they would like to save money on their electricity bill. We know that in Rwanda the tariffs set by the energy utility can be quite high (0.22 $/kwh August 2017). Though, the problem here, is that solar systems are not cheap. So, to save money, ideally the system would pay for itself after 5-6 years. But, wait a minute! In the US and Europe these systems pay themselves back very quickly, even though the electricity cost is cheaper. What’s the difference here? The problem here, in Rwanda, the utilities don’t allow feed-in tariffs. Which means, any excess energy use produce, will be lost and cannot be sold back to the grid. Which, as a result makes the payback time for the system less economical. This only makes sense when you have a very high daytime energy consumption, like a big factory or a large office.
The other answer we get often is that the grid is too unreliable and you are losing power or the voltage is fluctuating too often. We’ll look at that point next.
We are losing power very often and we don’t want to buy a loud and dirty generator
Generators can be very useful, but they are loud, dirty and they require frequent maintenance. Just like your car. Often we get approached by people who think a solar system is the answer to a generator. Well, this can be true, if you have no grid in your area, a solar system will be comparable in cost to a large generator. With the added bonus of being clean, quiet and requiring much less maintenance.
However, if you do have grid in your area, a solar system will likely be less economical, due to the cost of grid energy being so cheap and batteries being expensive. Here, we recommend using simply a battery backup system. A battery backup system is just like a solar system, but without all the expensive bits around power generation. Think of this as a large UPS similar to the one that might sit underneath your desk at work. Most of the time, if we design a system to be a UPS style system, the cost will be much less compared to one designed to be a solar system.
If you can’t figure out what you want on your own, then just drop us an email, and we’re happy to talk to you to understand your needs and make a recommendation.
We simply don’t have electricity!
In this case, solar makes a lot of sense. Living off-grid isn’t easy, the most important factor that determines cost here will be deciding the amount of the systems autonomy. It’s important to find a sweet spot between practicality and functionality. More autonomy means more batteries and panels, which in return means more cost. In these situations, it’s better to limit the loads and monitor your consumption per weather patterns and size for 90% uptime rather than 100% uptime. We recommend having a small generator that can supply energy for the remainder of the 10%. This can drastically reduce costs. Also, remote monitoring the system, will allow to see the condition of your batteries and plan for bad weather. The engineering company should also have a detailed look at the weather patterns in the area. This is generally available, through online meteorological tools.
Now I know what I need. What next?
Now that you have a basic idea on the solar system you’ve decided to go with, you need to find a supplier that can build the system per your needs. This generally requires some engineering work. The solar engineering firm would ask you about your loads or even better come and install a data logger, that will log your energy consumption (given you have electricity already) for a few days. This will provide them with a clear understanding of how they need to design and size of the system. Here are a few other things to look out for when looking for a supplier.
Component quality
Keep in mind, the brand and make of the systems used is very important. Especially here in Rwanda where finding replacement components can be difficult and costly. Ask about warranties on components and maintenance contracts. Even though, there are no moving parts in most systems, things still do break and having someone on hand that can response when it does is important. European suppliers are generally the best when it comes to quality followed by the USA. Make sure they are well known and supported brands around the main components like the batteries and the inverters. Also, make sure that the balance of system is strong.
Project Experience
PV systems can seem simple and complex at the same time. Specially in an environment like Rwanda where some places can be quite remote. The key here is finding a supplier that works well in this environment. Ask about their project experience and references. Make sure they have a good track record of successful systems and maintenance.
Price
Price can be a bit tricky, generally a steep difference between prices from suppliers can mean two things. One is neglecting certain BoS components and using much lower quality components or they might have sized the systems very differently. The reality is, you want a good price but also a good system that will last 10+ years. Make sure the components and brands are clearly labeled in the quotation you receive. Double check the engineering, as the system could have been undersized for you, which would also cause all sorts of problems. Also, ask about how they sized the system. Which of your loads did they consider?
Communication
This might not be obvious in the beginning, though working with a supplier that is responsive and diligent is important. A lot of times installers will walk away from the system after installation not picking up the phone. There is no clear way to grade this, but make sure you feel comfortable with the clear communication around expectations you have from the system and what the supplier is trying to sell you.