Grid-Connected Photovoltaic Solar System

The panels are up and producing. The final step is for the national electricity supplier to install the two-way meter required to credit it us for any surplus we produce, up to a limit.

 



The Background

When Purasol installed our solar-powered hot-water heater, Pierre (founder) described it at an introduction to the world of solar energy. The introduction has been a success - we rarely need to heat water during Costa Rica's dry season and we've enjoyed many hot showers. However, in the wet season our electricity bills have tended to increase, and are increasing - electrical energy purchased from ICE doesn't come cheap and is projected to become progressively more expensive as demand grows and generating it becomes more difficult and dependent on fossil fuels to cope with the peaks and troughs. Although it said to be trying to reduce this dependency (article in Spanish).

The System

So when Purasol said they had a special offer for installing a grid-connected photovoltaic solar system we were immediately interested. They had various offers available for different sized installations and we chose the one that seemed to best match our probable consumption without going over: in ICE's pilot "distributed generation" scheme, which began back in 2010, they will not pay us for monthly solar electricity production that exceeds the amount we consume. The roof-mounted system comprises eight, 200W panels, which when they are functioning at full capacity will produce 1,600W of electricity.
The electricity produce is DC so it first needs to get inverted to create the AC power needed for most domestic appliances. The invertor is a big box, which if I understand right, also contains a big computer that regulates the amount of power drawn / sent back to the grid based on how much is being produced by the photovoltaic solar panels on the roof. But don't take my word for it. Others can explain this much better than I ever will.

The Efficiency - PV in Cloudy Costa Rica?

We had had our doubts - our house is located in a region of Costa Rica that is renowned for its cloudy days, especially afternoons in the six months from May and November, also known as the wet season. Photovoltaic (PV) cells will not work well during periods of cloud cover. However, the technology has improved a lot and on a foggy afternoon in June when our brand new PV panels were first switched on they managed to produce between 100 and 200W, about 10% of their total capacity.

The Maths

The idea is that our average electricity bill going forward will be zero. In practice, this is unlikely. However, given average monthly consumption of about $40, even assuming we produce enough to reduce the amount we need to purchase by $25 we will save $300 per year. With the cost of electricity rising the way it is, this probably equates to nearer $500 per year in the not too distant future. Assuming average savings of $400 per year we will break even on the $4,000 investment in approximately 10 years. I hope this is a conservative estimate.

The Hard Work

From what I saw and was told, mounting the panels up on the roof is the easy part of this process. First of all, a lot of hard work goes into making sure all the ICE paperwork gets filled in correctly so that you get a new two-way meter and can be credited for the energy you produce. Then on the day of the installation the hard part is connecting up all the cables where they need to be without making too many holes in your house.
So if you've not yet started building, it's a great time to think about how you can leave space in the electrical system to make adding things like a grid-connected PV solar system that bit easier.