Solar panels

GRØNBID’s Procurement Choices

As part of guaranteeing its customers the best value, GRØNBID takes the responsibility of selecting the best technical solutions for each house while taking advantage of the group purchasing leverage. The purpose of this text is to break down prices of solar panels and basic concepts of solar systems, like inverters and optimizers. With experience from dozens of solar installations, our team uses these specifications in its Request-For-Quotations:

Solar Panels: Minimum requirements are BNEF Tier 1 manufacturer, 10-year product warranty and 20-year performance warranty. GRØNBID estimates the quotations on an individual basis.

Inverters: Solar Edge inverter with P300 optimizers. No other offers are accepted.


Information about the solar panel technical parameters and pricing


People often hear about the efficiency of solar panels. This means how much of the received irradiance the panel can convert to electricity. One important aspect to notice is that the efficiency is calculated as output per area. Therefore, a 300W panel that is identically sized as a 200W panel has higher efficiency, but the per Watt production is the same. This means that 100W capacity produces the same amount of power, whether it is from a panel with 22% efficiency or 18% efficiency, only the area required changes.

In order to maximize the output under strict space limitations it makes sense to increase the nominal power of the system i.e. have as many watts as possible in a certain area. However, the higher efficiency comes with a cost. If you look at the SEK/W cost to compare the exact price that one Watt of power costs, higher efficiency panels are always more expensive.

A typical residential solar installation is sized to maximize the profit, not the electricity output. As a rule of thumb, system output should be no higher than the yearly power consumption of the house. In Skåne one Watt of solar panel nominal power produces 1000 Wh per year. This means that the solar panels produce at their nominal power for 1000 hours during one year.

A house with 15 000 kWh* yearly consumption should not therefore install a system larger than 15 kW or 15 000 W. For comparison, let’s take two panels that are the same physical size, Jinko Eagle HC 60M and HC 60P.


Model Efficiency (W) Price (kr) kr/W Area (m^2) W/m^2 Panel count Total area  (m^2) Total panel price
Jinko Eagle CH60P 280 1765 6.3 1.64 171.1 53 87       93,545
Jinko Eagle CH60M 310 2171 7.0 1.65 187.7 48 79     104,220

Table 1. Price-per-Watt comparison. Prices are from taken on 2018-7-16


These panels are from the same manufacturer and have the same exact properties aside from the efficiency. By using higher efficiency panels, the required quantity of panels for the system is reduced by 5, but at the same time the price of the modules is increased by over 10,000 kr.

This example is to show that maximizing the efficiency or even the maximal output is not often the best solution. This is why GRONBID collects the important information about your house and uses this information to request quotations for a correctly sized system that yields the best profit.

*Note! Energy is measured in Power x time with hour being the unit of time. When you take together all the hours of the year and multiply them with the average power of each hour, you’ll get 15 000 kilowatt-hours. If you have a 10W light-bulb on for one hour, you’ve used 10Wh of electric energy with the average power of 10W.


Inverters and Optimizers

For residential rooftops, an inverter with optimizers is the most suitable solution, thanks to panel-level monitoring and increased production with partial shade. From the brands on the market, Solar Edge is cost competitive and proven technology with good service. Importantly the monitoring portal of Solar Edge is intuitive and logical, which makes it easy to track your production and troubleshoot in case of problems.

In the next article I will explain in detail why Solar Edge Optimizers are such a good solution that we don’t even inquire other products. In short they are the safest to operate while offering the best production and most efficient use of your roof space.

Solar panel installation

Next article explains the details of solar system design going all the way to the basics of electricity.

About the Author : Tuukka

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