25/03/2019
Understand that if you are building a new home here, it is wise to consider the project as a whole before you try to produce energy for a poorly built home. As I always say, the cheapest energy is the energy you don't use. Here is my reply to a recent inquiry:
Question:
What type of system would you recommend for a future cement new construction in the Guanacaste area for a home around 2,300 square foot living with a small pool and hot tub and mini splits.
We were hoping for a type of system that could help offset the higher cost of utilities during peak time and then we could reply on the grid at night when rates are much cheaper.
Looking forward to hearing your requirements.
My reply:
Hi Greg,
First of all get a quality builder that knows how to insulate your home. Use the foam boards with steel mesh applied to get at least R21 in your walls. Insulation in the ceiling is a must. That will cut down on your AC use considerably. If you don't insulate by using regular concrete block or prestressed panel construction, why put down more money on solar to cool the outside forever after. Also the concrete retains the heat and reradiates it into the night when you want to be cool.
As for the pool, same issue. A pool builder that wants you to build the infinity pool doesn't tell you how much water it wastes. Not oversizing your pipes costs you money in line drag. Buying a cheap one speed pump costs you energy from the day you start swimming. And the hot tub should be heated with solar hot water the same as your domestic water heater.
We are in the 21st Century. There is no reason to run systems day and night. You can run your pool and hot tub pumps in the daytime when the solar array is producing the most free energy. That only takes planning with a simple timer or more sophisticated energy management system. ICE, the government owned power company, has put access fees on running your meter backwards. So if you run it backwards in the daytime to run your pumps at night, you pay them $.06 per kWh to do so. Energy is cheaper at night when you are buying from the grid. But solar produces nothing at night. And energy costs here are still higher at night than they are at any time in the US.
There is some of the best sun on earth here on Guanacaste and with proper planning you can make it your friend instead of enemy.
So to get back to your question, you can put in a 5 kW system to cover a properly built home or a 20 kW system for a traditional, poorly built, but cheap home.
If you are trying to budget for this, figure $1,800 for permitting and engineering on the PV and $2 per installed Watt on the solar.
The solar hot water is about $2,500 for your tub and water tank.
I hope that gives you a good idea where to start.
Just one example of architects and builders here, when I inquired about insulation on another client's house during construction, the architect told me, "We use tile roofs so that is our insulation." I went back with my thermal camera after the home was built, and the the tile was 158F and the steel roof below it was 132F. So you see, he was right if you like cooling an oven with $.32 per Watt electricity.
The photo gives you an idea what shading does. Under the panels, the steel roof is 80F the same as the air
The same roof in the sun is 140F. Just another benefit from rooftop solar.
Sincerely,
Jon Harrington
President,
Solar Costa Rica
